STP-1491-Engine-Coolant-Technologies.pdf

STP 1491

Engine Coolant Technologies: 5th Volume William N. Matulewicz, editor

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Printed in Columbus, OH April,2008

Foreword This ASTM international publication contains manuscripts from The Fifth International Symposium on Engine Coolant Technology sponsored by ASTM Committee D15 on Engine Coolants. Held in Toronto, Canada, May 2006, this symposium provided a forum for the presentation and exchange of information on advances in engine coolant system components, experimental testing, uses and users experience of both automotive and heavy-duty applications. These papers presented and contained in this publication, focused on areas of 共1兲 international coolant development 共2兲 field testing of coolant additives 共3兲 engine coolant recycling 共4兲 engine component and coolant additive compatibility 共5兲 alternate coolant base technology 共6兲 extended life oxidation and thermal stability 共7兲 new testing methods of cavitation, erosion and localized corrosion. These presentations offered a view of the unique and ongoing research current in engine coolant technology. Much of the work presented is part of continued support offered to ASTM D15 to modify existing and to establish new standards for engine coolants.

Fifth International Symposium on Engine Coolant Technology Opening Comments by William Matulewicz This meeting marks my 20th anniversary in the ASTM D15 Engine Coolant Committee. I now qualify as one of the Old Guards at D15. Certainly not as high a level of Old Guard as Jess Starke and Frank Duffy, who are both at the Master Old Guard level, but certainly I have been in D15 long enough to be at the entry level of Old Guard. When I attended my first D15 meeting I considered myself an expert in engine coolant technology. I was well versed in all of the ASTM D15 standards, which were all of those used in D3306, plus one or two additional standards. I knew how to formulate a high performance engine coolant. Basically, mix ethylene glycol together with phosphate/borate, silicone/silicate, nitrate/ nitrite, tolyltriazole, a little dye 共preferably uranine兲 and a little antifoam. Make sure to add enough caustic to yield the proper pH and RA, balance the DEG and water content and you had a very good engine coolant. Don’t forget the 12 months/12,000 mile rule. I still love the sound of that phrase, 12 months, 12,000 miles. If you turned the TV on and heard that phrase, you knew the air was getting crisp, the leaves were changing color and most importantly, it was time for football. Oh, and change your coolant. That’s right, back then you actually changed your own coolant. Those were good times, all you needed to know was phosphate/borate, silicone/silicate, nitrate/nitrite, tolyltriazole, dye 共yellow兲 and antifoam. Sure, I had heard that there were some exotic formulas in Europe and a TEA/borate fluid in Asia, but we didn’t pay much attention. I walked into my first meeting and soon began my education in engine coolants. Apparently there were two sides to this engine coolant coin, coolants used in trucks and coolants used in cars. I also learned a new acronym, SCA. The truck guys actually added inhibitors to extend the service life of coolants, they did not honor the 12/12 rule. The D15 committee was clearly divided with truck coolant on one side and car coolant on the other. The truck coolant side claimed that there was a problem with phosphate and silicate, something about inhibitor fallout, overheating, pump failures and green goo. What would you expect from a group that does not follow the 12/12 rule? D15 eventually constructed standards for these truck folk and established new definitions, such as, Heavy Duty and Light Duty. Both sides learned to reach across the line, embrace each other and work together to establish D15 standards. Thank goodness for recyclers! OK, I could live with Heavy Duty standards, but I did not see the tempest of new standards to come in the following years. Little did D15 know that events in CT and TX were going to result in numerous new standards, definitions and debates. The Lime, CT area was host to 2 historical events. The first was the disease traced back to a tick bite, hence the name Lymes disease. The second occurred at the same race track where Paul Neuman was known to race. A race team in Lime Rock was experimenting with reversing the coolant flow in an engine and using concentrated propylene glycol. Claims of better heat transfer, better gas mileage, better corrosion control and lower toxicity soon surfaced.

Over a number of years and much debate, D15 established standards and definitions for propylene glycol based coolants. At about the same time down in TX, a man with a star was promoting engine coolants based on an additive that is used to make monofilament fishing line. It was claimed that this new longer, life fluid could last 30, 50 maybe even 100,000 miles. They wanted to totally trash the 12/12 rule! This sebacic acid additive, long life concept grew in popularity, caught root, and landed in D15. Long Life standards and definitions were established and continue to be established today and include the Organic Acid Technology or OAT fluids. By the mid-90s recycling engine coolants became a major issue in D15. Both OEM and the States were demanding performance and chemical standards for recycled coolants. Recycling technology at that time ran the gamut from passing used coolant through a machine with gauges and blinking lights coming out the other end virtually unchanged, to add packs that raised the pH, to reverse osmosis, to distilling and then adding inhibitors and buffers. This recycle technology led to D15 standards for recycled coolants plus a host of new definitions such as; Recycled Coolant, Prediluted Coolant, Recycled Ethylene Glycol and Virgin Ethylene Glycol. Along the development of OAT and long life fluids, not to be confused with extended service fluids, it was found that blending traditional coolant technology with OAT fluids could improve performance. This was the start of Hybrid fluids. I have heard the term HOAT to describe these hybrid organic acid technology fluids. I have heard the term NOAT to describe nitrite containing OAT fluids and MOAT to describe mixed OAT fluids. New research is now investigating developmental organic acid nitate technology, or DONT. More standards, more research, more definitions, more challenges. Compatibility issues, oxidation stability issues, new technology issues. Being an expert in engine coolant technology in 2006 is a little more demanding than the 1986 expertise of phosphate/borate, silicone/silicate, nitrate/nitrite, tolyltriazole, a little dye 共preferably uranine兲 and a little antifoam. But being a new member of the Old Guard at D15 I am entitled to long for days past, meetings with no cell phones or lap tops and breaks with long lines at the pay phone. Days when blackberry was a fruit, blue tooth meant a trip to the dentist and yahoo meant you were really excited. 20 years ago was a simpler time when 12 months and 12,000 miles ruled.

Contents Overview

ix

Coolant Development in Asia—H. EGAWA, Y. MORI, AND M. L. ABEL

1

Heavy Duty Diesel Engine Coolant Technology: Past, Present, and Future— H. J. DEBAUN AND F. C. ALVERSON

8

Field Test for Carboxylate Inhibitor Levels in OAT Coolants—R. J. PELLET, L. S. BARTLEY, JR. AND P. O. FRITZ

17

A Comparison of Membrane Technologies for Engine Coolant Recycling—R. HUDGENS, E. SCHMIDT, AND M. WILLIAMS

26

New Electrochemical Methods for the Evaluation of Localized Corrosion in Engine Coolants—B. YANG, F. J. MARINHO, AND A. V. GERSHUN

45

Compatibility Testing of Multi-Vehicle Coolant Chemistries—A. P. SKROBUL, S. L. BALFE, AND F. C. ALVERSON

59

Investigation of Interaction Between Coolant Formulations and Flux Loading/ Compositions in Controlled Atmosphere Brazed (CAB) Aluminum Surfaces in Heat Exchanger Applications —C. JEFFCOATE, M. RANGER, J. GRAJZL, B. YANG, P. WOYCIESJES, AND A. GERSHUN

69

Effect of Fluoride on Corrosion of Cooling System Metals in Ethylene Glycol-Based Antifreeze/Coolants—B. YANG, A. V. GERSHUN, F. J. MARINHO, AND P. M. WOYCIESJES

77

Heavy-Duty Diesel Engine Cavitation Test —G. DAVIS AND M. SARLO

87

Component Durability and High Mileage Performance of a Full Carboxylate Coolant in Heavy Duty Diesel (HDD) Engines—P. O. FRITZ, L. S. BARTLEY, JR., R. PELLET, V. MOSER, AND C. ULABARRO

96

Cavitation Protection Performance of Nitrite-Free Organic Acid Based Coolant for Heavy-Duty Engines—Y. MORI, M. L. ABEL, AND Y. MIYAKE

109

Accelerated Oxidation and Corrosion Testing of Engine Coolants Using a Rotary Pressure Vessel Oxidation Test—F. C. ALVERSON, S. L. BALFE, AND A. P. SKROBUL

119

Coolants at Elevated Temperatures—S. CLAEYS AND S. LIEVENS

129

Comparison of Bench Test Methods to Elevate Heavy Duty Coolant Thermal Stability—Y. CHEN, R. D. HUDGENS, AND E. R. EATON

139

vii

Overview In May of 2006, the ASTM D15 Committee on Engine Coolants sponsored the Fifth International Symposium on Engine Coolant Technology in Toronto, Canada. The advances in coolant system components and construction continue to impact the modern automotive, heavy-duty, locomotive and free standing engine design and performance. The expanding use of lighter metals, advances in non-metallics, changes in fluid control technologies and coolant filtration in todays engines, plus advancing discoveries in EGR and fuel cell technologies in engines of the future are a few of the challenges facing the experts in engine coolant formulating. Challenges of today include extended service life, liner pitting, the impact of EGR, advances in turbo charging and component compatibility. Research areas must consider state and local regulatory requirements for increasing the use of recycled fluids and efforts for global standardization of test methods. The symposium presented an open forum for the presentation of new research in modern engine coolant formulating addressing the complex issues mentioned above. The symposium was well attended by international technical representatives from OEM and engine coolant producers. The presentations were followed by open comments and questions from the attendees resulting in a robust, professional exchange of ideas. The contents of this STP are the fourteen papers presented at the Fifth International Symposium on Engine Coolant Technology after the completion of a thorough peer review, which included author共s兲/editor共s兲 exchange of comments and suggested revisions, according to the guidelines of the ASTM Editorial Staff. These papers include current overviews of heavy duty coolant technology and coolant development in Asia, new testing methods, both in field and at the bench, designed to help determine localized corrosion by electrochemistry, erosion corrosion, degradation of coolant components at elevated temperatures and under accelerated oxidation, and depletion of corrosion inhibitor additives. Compatibility issues are also presented addressing both multi-fluids mixing and affects of fluid composition on engine components. I want to thank the reviewers that volunteered their valuable time to complete the critique of the papers presented. I also wish to thank the ASTM Editorial staff for providing the guidance and expertise that enabled the successful completion of the Fifth International Symposium on Engine Coolant Technology and the construction of this STP. William N. Matulewicz Wincom, Inc. Blue Ash, Ohio Symposium co-chairman and STP editor

ix

Journal of ASTM International, Vol. 4, No. 6 Paper ID JAI100368 Available online at www.astm.org

Hiroshi Egawa,1 Yasuaki Mori,1 and Michael L. Abel2

Coolant Development in Asia ABSTRACT: Historically speaking, there have always been three major regions, North America, Europe, and Asia, where antifreeze/coolant developments take place independently. These developments were based on the perceived needs of the engine manufacturers, influenced by governmental/regulatory authorities, and heavily influenced by the requirements geography placed upon automobile manufacturers 关1–3兴. In the early days of ethylene glycol based engine coolants, simple inhibitor systems based on borates, phosphates, etc., and utilizing a soft metal inhibitor were sufficient to satisfy the needs of a cast iron engine and copper brass radiator. With the advent of aluminum engines and their rapid usage growth throughout the 1980s and 1990s, engine manufacturers of the regions began to place more stringent requirements on the anticorrosion performance of the OEM coolants. Based on the specific strategies utilized by the cooling system component manufacturers, divergent requirements began to be placed upon the coolant makeup. This paper will speak generally to the regional history of coolant trends and specifically on the activity for coolant development in Asia. KEYWORDS: coolant, automobile, engine, Asia, Japan, anticorrosion, inhibitor, technology, aluminum

Technical Direction of Engine Coolant in Asia Japan In the 1960s European/North American regions used ethylene glycol based coolants and borate was the main anticorrosion inhibitor for the antifreeze/coolant as cast iron engines and iron-containing components were used. On the other hand, in Japan, representing the Asian region, usage of borate inhibited coolant was recorded; however, the main antifreeze/coolant became ethylene glycol based with ethanolamine, and phosphate inhibitor system coolant was adopted due to the BS3150 standard existence and the believed superiority of aluminum metals corrosion protection by amine and phosphate versus borate as a main reason 关4兴. The engine antifreeze/coolant chart for each region since the 1970s is shown in Fig. 1. Silicates were being increasingly used as an inhibitor in the 1970s to protect aluminum metals in European/North American regions. The usage of silicates was avoided in Japan due to silicates having a negative effect on the mechanical seal material of the water pump at that time and the stability performance related to gelling was an issue 关5,6兴. Then the engine antifreeze/coolant trend became amine phosphate based to protect aluminum, and borate usage was discontinued. This is the point when differences in the direction of inhibitor technology developed between European/North American regions and the Asian/Japanese region. In the late 1970s, Japanese automotive manufacturers avoided nitrite antifreeze/ coolants due to Northern Europe’s 共Sweden兲 countermeasure towards nitrosamine. The movement to nonamine antifreeze/coolant was due to Norway’s 1987 regulations on triethanolamine, thus phosphate and organic acid salt antifreeze/coolant 共P-OAT兲 were developed. The phosphate and organic acid salt antifreeze/coolants resulted in increased durability and a five year change interval for antifreeze/coolants by certain car manufacturers and heavy duty truck company recommendations converting from a semiannual antifreeze/antirust change interval to long life coolant being used 关7–10兴. The organic acid technology 共OAT兲 movement began in European/North American regions in the 1990s to take advantage of the increased durability of the antifreeze/coolant. Development of organic acid Manuscript received January 27, 2006; accepted for publication November 7, 2006; published online July 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 CCI Corporation, 12 Shin-hazama, Seki City, Gifu, Japan. 2 CCI Manufacturing IL Corporation, P.O. Box 339, Lemont, IL60439. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

1

2 ENGINE COOLANT TECHNOLOGY

FIG. 1—Current status of engine coolant. technology antifreeze/coolant occurred in Japan as well; however, due to insufficient aluminum corrosion protection under severe operating conditions, the OAT technology was not widely applied. Since 2000 in Japan, the main-stream antifreeze/coolant developed and utilized is organic acid salt, low phosphate, long-life coolant 共LP-OAT兲关11,12兴. Korea The market is composed of Japanese type phosphate and organic acid salt antifreeze/coolant and European/ North American type silicate/borate type coolants due to the Korean automotive industry receiving technological assistance from auto manufacturers in all of the European/American/Japanese regions. Southeast Asia Countries Throughout the 1980s and into the early 1990s, water-based antirusts were mainly used due to the region’s warm climate as the antifreeze function was not necessary. Then came the issue of cooling system corrosion problems apparent in the marketplace because antirust is inferior to antifreeze/coolant in the area of anticorrosion performance. In the late 1990s, the number of aluminum radiators increased and antirust usage was converted to antifreeze/coolant which was determined to be important to maintain aluminum anticorrosion performance. As for antifreeze/coolant types, European/American/Japanese formulas are mixed in this region. Also, in order to maintain proper dilution ratio instructed by automotive manufacturers, as well as quality assurance of dilution water, an increased usage of prediluted antifreeze/coolant in the marketplace is apparent. China The Chinese antifreeze/coolant market is a mixture of European/American/Japanese formulations, the same situation as in Korea and Southeast Asian, due to technical assistance from parent and cooperative companies from the various worldwide regions and the historically newness of the industry in China compared to European/North American/Japanese regional companies. However, the recent automotive industry growth in China is rapid and well documented and it will be interesting to see what the technological growth pattern will eventually be.

EGAWA ET AL. ON COOLANT DEVELOPMENT IN ASIA 3 TABLE 1—Corrosion test in glassware. Item Test Solution Concentration Specific Value Appearance of After Test Specimen Weight Change, mg/ cm2 Copper Solder Brass Steel Cast iron Cast aluminum Weight Loss, mg/specimen Copper Solder Brass Steel Cast iron Cast aluminum

JIS K2234 LLC 30 vol %

ASTM D 3306 33 vol %

No Corrosion

…

±0.15 ±0.30 ±0.15 ±0.15 ±0.15 ±0.30

共−0.37兲共−1.12兲共−0.37兲共−0.37兲共−0.34兲共−1.04兲

共±4兲共±9兲共±4兲共±4兲共±4兲共±9兲

10 30 10 10 10 30

Note: 共兲 data have been converted.

Direction of Japanese Coolant Specifications The Japanese antifreeze/coolant specification was established in 1965, as the Japanese Industrial Specification 共JIS兲 JIS K2234 关13兴 Engine Antifreeze Coolant. The current specification is a modified version of ASTM D 3306 关14兴, and has typical performance as well as the glassware corrosion test, simulated service testing, and cast aluminum heat exchange corrosion testing. Several characteristics of the specification, per Table 1, are more strict when compared to ASTM D 3306 for glassware corrosion test and simulated service test, as the test solution is at 30 % volume and the test specimen appearance 共no corrosion兲 is added and the weight change of the test specimens is more narrow. However, it does not contain sections on cavitation durability performance and compatibility with nonmetallic parts, thus these issues will be future topics. Current Japanese Coolant Technology Antifreeze/coolant development in Japan is derived from the close relationship between the automotive manufacturer, parts supplier, and the antifreeze/coolant supplier. The antifreeze/coolant performance has been improved consistent with the objectives of the automobile company vehicle advancement, resulting in vehicle weight reduction, faster warm-up to optimum engine operating temperature, less fuel consumption, and a contribution to lower emissions. The first major change was the nonamine antifreeze/coolant 共P-OAT兲 movement of the 1990s and, especially important, the movement of the heavy duty truck manufacturer to the usage of long-life antifreeze/coolant technology 关8–10兴. The addition of phosphate and organic acid salt inhibitors as main components allowed for the increased durability of nonamine coolants. Since then, modified phosphate antifreeze/coolant for the protection towards aluminum corrosion under very high temperature operating conditions have improved due to new anticorrosion inhibitor formulation selections and have been necessitated by the engine components and heat exchanger becoming more aluminum alloy intensive. The second major recent change was that since about the year 2000 the new antifreeze/coolant technology has changed from phosphates being the dominant inhibitor component to organic acid salts being the predominant component with phosphate acting as one of the supporting components resulting in this technology increasing the durability of antifreeze/coolant 共LP-OAT兲. Such long-life engine coolants 共LP-OAT兲 are being used worldwide, Japan, Europe and the Americas, and have over five years of actual usage in the marketplace. Not only meeting the general specifications of ASTM D 3306, per Tables 2–4, it has yielded good results in the European FVV testing method test as well.

4 ENGINE COOLANT TECHNOLOGY TABLE 2—Vibration test results.

Property Weight loss mg/h AlCuMg2 New state 20 v / v % 40 v / v % Aged for 120 h 40 v / v % GG 25 New state 20 v / v % 40 v / v % Aged for 120 h 40 v / v %

FVV R476 Specific Values

LP-OAT A

OAT LLC

10.08 max 10.08 max

8.3 7.2

7.3 8.0

12.60 max

10.2

8.5

5.30 max 5.30 max

4.1 4.9

3.2 3.6

7.95 max

4.0

4.0

TABLE 3—Heat test results.

Property Weight loss mg G-AlSi10Mg New State/Deionized Water 40 v / v % New State/10°dGH 20 v / v % 40 v / v % Aged for 120 h 40 v / v % GG 25 New State/Deionized Water 40 v / v % New State/10°dGH 20 v / v % 40 v / v % Aged for 120 h 40 v / v %


LP-OAT A

OAT LLC

50 max

3.3

19.9

50 max 50 max 100 max

1.4 2.1 5.8

28.3 36.3 70.9

20 max

9.1

6.0

20 max 20 max

7.8 9.1

6.2 6.8

40 max

13.0

9.4

Characteristics of Coolant Technology in Japan Main components of coolant in each area are shown in Table 5. In European/North American regions, OAT LLC which contains organic acids as the main inhibitor but does not contain borate, silicate, or phosphate, TABLE 4—Corrosion test results.

Property Weight loss g / m2 G-AlSi10Mg AlMn AlCuMg2 GG 25 Steel 共RRSt 14.05兲 E-Cu CuZn Solder 共L-PbSn 40 Sb兲


LP-OAT A

OAT LLC

10 max 8 max 8 max 2 max 2 max 3 max 3 max 6 max

1.17/1.27 1.03/0.77 1.59/1.62 +1.07/ + 0.17 0.55/0.28 0.24/0.20 0.87/0.83 1.50/1.77

2.28/2.48 3.18/3.52 2.95/2.91 0.71/1.22 0.47/0.39 0.67/0.67 0.79/0.83 2.00/2.00

Note: After final cleaning Pack 1/Pack 2.

EGAWA ET AL. ON COOLANT DEVELOPMENT IN ASIA 5

FIG. 2—Aging tendency of LLCs. TABLE 5—Main components of currently used coolants. Japan

Component Organic acid Phosphate Borate Silicate Triazole Nitrate Nitrite

LP-OAT OO O … … O 共O兲 …

USA

P-OAT O OO … … O 共O兲 …

OAT OO … … … O 共O兲 …

Europe B,SiOAT O … O O O O 共O兲

B,Si-AF … O O O O 共O兲共O兲

OAT OO … … … O 共O兲 …

B,SiOAT O … O O O O 共O兲

Note: OO⫽Contained as a Main Component; O⫽Contained;…; Not Used.

and B,Si-OAT which contains organic acids, borate, and silicate are used most prevalently by the OEM. On the other hand, in Japan, P-OAT and LP-OAT which contain organic acids and phosphate but do not contain borate and silicate are typically used, as it is a characteristic for coolants in Japan to contain phosphate. LP-OAT have not only superior durability 共see Fig. 2兲 but also excellent anticorrosive property against aluminum due to suitable selection and quantity of organic acids and phosphate. Test results of the European evaluation method CEC C-23 Dynamic Corrosion Test are shown in Figs. 3 and 4. LP-OAT has excellent anticorrosive property against aluminum when compared to P-OAT and OAT LLC. Also, the latest generation of Japanese antifreeze/coolant technology, even while containing a low level stabilized phosphate inhibitor, gives excellent results in the GFC L-106-A-90 hard water stability test 共see Fig. 5兲. Therefore, LP-OAT that was developed utilizing the latest Japanese coolant technology is a global coolant that is being used, without reservation, all over the world.

Technical Direction of Next Generation Coolant The world automotive manufacturers are consolidating engines and platforms and utilizing architecture developed in one region throughout their globalized distribution system and the next generation of antifreeze/coolant will be an antifreeze/coolant that possesses performance that any automotive manufacturer can use. Such antifreeze/coolant will be influenced by local/regional regulations as well as automotive manufacturers’ specification. Last but not least, automotive manufacturers will be influenced by LOHAS 共Lifestyles of Health and Sustainability兲 consumers; such consumers will be more demanding and not settle for current technology, as concern for the environment has increased. As a result, automotive manufacturers will bring new technology vehicles for the new world and new long-life coolant must be developed with new technology.


FIG. 3—Dynamic corrosion test results.

FIG. 4—Appearance of test specimen (cast aluminum) after chemical treatment.

FIG. 5—Appearance of after hard water compatibility test. References 关1兴关2兴关3兴关4兴关5兴关6兴关7兴关8兴

Liebold, G. A., Meszaros, L. L., and Schmidt, H. H., “European Automotive Coolant Technology,” SAE Tech. Pap. Ser., No. 900430, 1990. Duffey, F. R., “The Status of U.S. Coolant Standards,” SAE Tech. Pap. Ser., No. 900431, 1990. Shiotani, E., “Overseas present conditions of coolants and brake fluids and the trend of metal corrosion tests.” Bosei Kanri, Vol. 35, No. 10, 1991, pp. 357–366. Kawamoto, S., and Suzuki, H., “The Problems of Using Anti-Freeze and Anti-Rust in Aluminum Engines,” Bosei Kanri, No. 3, 1974, pp. 21–27. Kiryu, K., Tsuchiya, K., Shimomura, T., Yanai, T., Okada, K., and Hirabayashi, H., “The Effect of Coolant Additives and Seal Composition on Performance of Water Pump Seals of Automotive Engines,” SAE Tech. Pap. Ser., No. 890609, 1989. Hercamp, R. D., “Silicate Galation in Heavy-Duty Diesel Engine Cooling Systems,” SAE Tech. Pap. Ser., No. 852327, 1985. Kikuchi, M., and Tajima, H., “Development of Coolant for Heavy Duty Vehicle,” Jidosha Gijutsu, Vol. 42, No. 4, 1988, pp. 471–477. Hara, H., Kishi, Y., and Miyamoto, T., “Development of Non-Amine-Type Long Life Coolant for Truck and Bus,” Mitsubishi Motors Corporation Technical Review, Vol. 1, 1988, pp. 110–119.

EGAWA ET AL. ON COOLANT DEVELOPMENT IN ASIA 7

关9兴

关10兴关11兴关12兴关13兴关14兴

Hashimoto, T., Nishizawa, Y., Kuwamura, I., Taniai, M., and Koide, H., “Development of Long Life Coolant for Heavy-Duty Commercial Vehicles,” Jidosha Gijutsu Kai Gakujutsu Kouen Kai Maezuri Syu, Vol. 10, No. 902136, 1990, pp. 1149–1152. Tange, K., Ishiura, T., and Ashikawa, R., “Durability Evaluation of Coolant for Automobile,” Jidosha Gijutsu, Vol. 45, No. 6, 1991, pp. 86–91. Osawa, M., Morita, Y., and Nagashima, T., “A Study of Extension of Engine Coolant Life Using Low Phosphate Organic Acid Inhibitors,” SAE Tech. Pap. Ser., No. 2003-01-2023, 2003. Nishii, M., Arai, H., Nakada, T., and Tami, H., “A Study of Anticorrosive Technology in Super Long Life Coolant,” SAE Tech. Pap. Ser., No. 2004-01-0055, 2004. JIS K2234-1994, LLC. ASTM, D 3306, “Standard Specification for Glycol Base Engine Coolant for Automobile and Light-Duty Service,” Vol. 15.05, ASTM International, West Conshohocken, PA.


Heather J. DeBaun1 and Fred C. Alverson2

Heavy Duty Diesel Engine Coolant Technology: Past, Present, and Future ABSTRACT: Significant advances have been made in heavy duty diesel engine technology to meet increasingly stringent environmental regulations for emissions. Today’s heavy duty diesel engines are being designed with lighter and softer metals, greater turbocharging, increased combustion controls, and new emission reduction equipment. The cooling systems contained in these vehicles are similarly being impacted by smaller designs, new cooling system configurations, and increased usage of lighter, softer metals. Vehicle thermal loads have significantly increased due to increased power densities, higher engine temperatures, and greater metal-coolant fluxes which places greater emphasis on oxidation/thermal stability, and high temperature corrosion protection performance of the coolant. Other operating conditions 共coolant flow rates, turbulence, pressure drops, deaeration兲 are also becoming more severe calling for improved erosion-corrosion protection, cavitation protection, and elastomer, seal, hose compatibility. This paper reviews the changes in heavy duty diesel engine technology and provides information on coolant performance in 2002-4 emission compliant engines. Predictions are also made on future engine technology and next generation engine coolants. KEYWORDS: heavy duty engine coolants, cooling system trends, oxidation stability, erosion corrosion, cavitation, elastomer compatibility, traditional fully-formulated coolants, extended service coolants, extended life coolants, supplemental coolant additives

Introduction Diesel engines continue to be the work horse engines of industry. Advances in diesel engine technology are being driven by needs for increased power, emission reductions, improved fuel economy, and longer reliability. Today’s modern diesel engines include turbochargers with intercoolers, electronic timed fuel injection, computerized combustion controls, and emission reduction equipment which are all placing greater thermal loads on the coolant. Recent advances in engine cooling and the cooling system have not been as significant. The cooling system still utilizes an engine-driven water pump and fan controlled by engine speed r/min and a mechanical thermostat controlled by radiator bulk coolant temperature. This paper will review some of the changes in heavy duty diesel engine technology and the impacts on the cooling system and coolant along with future trends in the cooling system and coolant technology. Modern Diesel Engines Emission Compliant Equipment In 2002, heavy duty diesel engine manufacturers were faced to meet lower emissions standards for nitrous oxides 共NOx兲 and hydrocarbons. The NOx regulation lowered from 4 to 2 g / bhp-h 共Fig. 1兲. In order to meet these regulations, most engine manufacturers have employed the use of cooled exhaust gas recirculation 共EGR兲 because it offers better fuel economy than retarded timing 关1兴. The exhaust gas is cooled and the turbocharger boost pressures must increase to increase the air into the cylinder. In meeting the lower NOx requirements, the recirculated exhaust gas is cooled. Stainless steel EGR coolers are used to cool the exhaust gas with engine coolant. The use of EGR involves diluting the air/fuel Manuscript received June 8, 2006; accepted for publication October 19, 2006; published online November 2006. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Senior Project Engineer, International Truck and Engine Corporation, 10400 West North Avenue, Melrose Park, IL 60160. 2 Coolant Advisor, Shell Global Solutions, 3333 Highway 6 South, Houston, TX 77082. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

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DEBAUN AND ALVERSON ON HEAVY DUTY DIESEL TECHNOLOGY

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FIG. 1—U.S. emissions regulations. mixture entering the engine with a small amount of exhaust gas 共⬃5 – 15 % 兲. The addition of the exhaust gas lowers the oxygen content and lowers the combustion temperature which reduces the high temperature formation of NOx. The EGR cooler uses the engine coolant to cool the exhaust gas down from ⬃1300 to 325° F which results in significant heat rejection to the coolant. Heat rejection of the coolant increases by 25– 35 % 关2兴 due to the cooling of exhaust gas. In some cases, bulk coolant temperatures increase if radiator size cannot be increased in order to make up for increased coolant heat rejection. The high temperatures in the EGR cooler led to localized boiling, increased degradation of the coolant, and reduced coolant life. Cooling System Changes The OEMs and cooling system component suppliers are using multiple approaches to handle the increased heat loads on the coolant including increasing the boiling point of the coolant by raising the pressure limit on the radiator cap 共⬃7 to 10 psi and higher in some applications兲, using higher performance fans and fan clutches, increasing water pump size or speeds, or both 共i.e., coolant flow rates兲, and using larger and more efficient heat exchangers. With regard to heat exchangers, the trend is toward the use of lighter, softer metals with narrower clearances/tolerances that improve heat transfer efficiency. The use of the lighter, softer metals often have maximum flow rate limitations which must be considered during system design. Overall bulk coolant temperatures have risen to meet the 2004 emission requirements and are expected to further increase to meet 2007–2010 emission regulations 共Fig. 2兲. Along with the overall bulk coolant temperature rise, the coolant is exposed to significantly high metal-coolant heat fluxes in regions around the cylinder heads and liners, and exhaust gas recirculation 共if equipped兲. In some of these regions, heat transfer is accomplished by nucleate boiling which places additional stress and demands on the coolant. In addition to the increased thermal loads on the coolant, the newer engine designs, under the hood configurations, and severe operating conditions of higher water pump speeds/coolant flow rates are making it more difficult to achieve satisfactory deaeration of the coolant. Residual air bubbles in the cooling

FIG. 2—Heat rejection history [3].


system contribute to oxidation and thermal degradation of the coolant. Vehicle and engine deaeration systems and characteristics must also be taken into consideration during cooling system design. Charge Air Coolers Diesel engine OEMs are achieving higher power through the use of turbochargers 共or superchargers兲. The use of a turbocharger allows more air to be forced into the engine which allows more fuel to be burned resulting in increased power. To achieve even more power, the air may be cooled through an air-to-air or air-to-liquid charge air intercooler which increases the density and makes more oxygen available for combustion. For air-to-liquid charge air intercoolers, the intercooler adds an additional thermal load on the coolant. For air-to-air charge air intercoolers, the challenge is locating and achieving sufficient air flow under the hood without adversely affecting air flow for the radiator 关4兴. Direct Fuel Injection and Combustion Control Today’s diesel engines inject the fuel directly into the cylinders using engine control modules 共ECMs兲 that deliver precisely the right amount of fuel when needed. The ECM communicates with an elaborate array of sensors placed at strategic locations to monitor engine speed to coolant and oil temperatures. The electronic controls mean that the fuel burns more thoroughly, delivers more power, greater fuel economy, and fewer emissions 关5兴. With regards to engine cooling, the increase in power output for given cylinder volume during combustion results in increased heat rejection to the coolant. Auxiliary Equipment The addition of auxiliary equipment 共air conditioning, transmissions, oil coolers, etc.兲 is also increasing heat loads on the engine coolant. The air conditioning compressor adds an additional thermal load on engine cooling, particularly under heavy load and idle conditions. Transmissions are operating at higher temperatures resulting in additional heat rejection to the coolant through the transmission fluid cooler. Automatic transmissions with torque converters used in bus applications and package van service place additional heat rejection requirements on the coolant due to significant energy loss 共heat generation兲 during operation. In addition, these vehicles may operate with numerous starts and stops, often resulting in hot soaking of the coolant which raises the coolant temperature and can cause boiling. In some cases, engine coolant service intervals for extended life and extended service coolants used in these vehicles are being lowered to automotive service intervals. Elastomers, Seals, and Hoses Elastomers, seals, and hoses are extremely important since they are widely used throughout the engine and cooling system. Common elastomer materials used in the engine and cooling system include nitrile rubber 共NBR兲, hydrogenated nitrile rubber 共HNBR兲, ethylene propylene terpolymer 共EPDM兲, tetrafluoroethylenepropylene copolymer 共FEPM兲, and silicone. Previous studies have been conducted on comparing the performance of these materials in laboratory aging studies 关6兴. In one study on ethylene glycol and propylene glycol-based coolants containing silicates, it was shown that significant amounts of precipitate may form which may represent leached hose components or destabilization of the silicate from hose and coolant interactions, or both 关7兴. A recent study conducted on a hybrid OAT coolant containing borate, nitrite, nitrate, and silicate with three different EPDM sulfur-cured hose materials in a plugged hosecoolant compatibility test at 168 h at 104° C 共220° F兲 showed similar test results 共Table 1兲. The more severe operating conditions 共higher coolant temperatures, higher under the hood temperatures, greater amount of hot regions in the engine兲 may be having effects on both elastomer/hose and coolant life. In some cases where coolant passages are extremely narrow 共almost filter size兲 such as oil cooler or water pump seal faces, or both, hose-coolant interaction products or other contaminants, or both, can plug the passages resulting in reduced heat transfer, severe oxidation of the coolant, or equipment failure, or a combination thereof. There also have been some problems in the field with certain engines containing silicone seals in high temperature regions using OAT-based coolants which resulted in loss of compression set and leakage. The field problems were corrected by the addition of a silicate field fix or change in elastomer seal material, or


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TABLE 1—Plugged hose-coolant compatibility results. Coolant Result Sediment, vol % pH Silicon, ppm Sulfate, ppm Oxidation, ppm Zinc, ppm

New Nil 8.1 130 Nil Nil Nil

Hose 1 1.6 7.8 51 325 170 15

Hose 2 1.6 7.8 48 335 120 55

Hose 3 2.0 8.0 51 370 130 13

both. Additional cooperative work is required between the OEM, elastomer supplier, and coolant supplier to extend the temperature limitations of elastomers and to improve coolant and elastomer compatibility. Impacts on the Engine Coolant The more severe operating conditions and environments in which heavy duty diesel engines operate have an impact on coolant formulations and performance. Ethylene glycol-based engine coolants are still the predominantly used heat transfer fluid for heavy duty applications. Several different types of engine coolants are used in heavy duty applications, which may be classified by the type of corrosion inhibitors contained in the formulation. In the United States, conventional coolants with the addition of supplemental coolant additives 共SCAs兲, traditional “fully formulated” coolants, extended service interval coolants, and extended life coolants are all used in heavy duty applications. In Europe, Asia Pacific, and other parts of the world, conventional, hybrid, and extended life coolants are used in heavy duty applications. However, there is less distinction between light duty and heavy duty coolants and less usage of SCAs outside the United States. A description of the various types of heavy duty 共HD兲 coolants is provided in Table 2. Engine coolants used in heavy duty applications must provide satisfactory performance in the areas of oxidation-thermal stability, high temperature corrosion protection, cavitation corrosion protection, erosionTABLE 2—Type of HD engine coolants. Conventional coolant

HD Extended life coolant

HD Extended service interval coolant Hybrid coolant

Organic Additive Technology 共OAT兲 Supplemental Coolant Additive 共SCA兲

Traditional fully formulated coolant

Contains inorganic corrosion inhibitors such as borate, molybdate, nitrate, nitrite, phosphate, silicate. In Europe, phosphate is generally not used due to potential hard water compatibility problems. In Asia, silicates are generally not used due to gel and water pump seal abrasion concerns. An engine coolant containing OAT providing long service life. These products may contain nitrites or molybdate, or both, and may be refortified with an “extender” at typical service intervals of 300 000 miles or longer. An engine coolant also providing extended service life. SCAs are typically added at 100 000– 150 000 mile intervals. An engine coolant containing a combination of inorganic and organic corrosion inhibitors. Europe hybrids are phosphate free. Asia hybrids are silicate free. Any group of carboxylic acids including aliphatic mono and diacids and aromatic acids applicable as corrosion inhibitors in coolants. A chemical additive that is periodically added to the coolant to maintain protection against general corrosion, cylinder liner pitting, and scaling in heavy duty engines. A conventional coolant containing an initial dosage of SCA. These coolants require periodic addition of SCAs typically at 20 000 mile 共⬃32 000 km兲 intervals.


FIG. 3—Engine coolant nitrite results. corrosion protection, elastomer compatibility, hard water stability, anti-scaling properties, and preferably nondepleting coolant chemistry. As discussed in the preceding paragraphs, the advances in heavy duty engine technology are placing greater demands on the coolant in all of these performance areas. Oxidation-thermal Stability Since engine coolants are hydrocarbon based, the ethylene glycol-based fluid is susceptible to oxidation which involves reaction of ethylene glycol with oxygen to form glycol degradation acids 共glycolic acid: HO-CH2-COOH, formic acid: HCOOH, oxalic acid: HOOCCOOH, etc.兲. Certain additives in coolants such as nitrites, which are used to protect cast iron/cylinder liners from corrosion, may also undergo oxidation to form nitrates. The increased thermal loading and more severe operating conditions 共higher temperatures, aeration, pressure, and any cooling system contaminants/corrosion metals兲 occurring in today’s engines are factors that can accelerate oxidation and shorten coolant life. A significant amount of test data has been generated on engine coolant performance in 2002–2004 emission compliant engines. In the case of EGR equipped engines, the used coolant data show slightly more rapid pH decline, more rapid nitrite reduction, and increased glycolate formation rates compared to used coolant data obtained from similar non-EGR engines 共Figs. 3 and 4兲. The overall test results indicate that traditional fully formulated, extended service interval and extended life coolants overall are performing satisfactorily with only minimal impacts on oxidation and coolant life. It is anticipated that 2007–2010 engines will require increased oxidation and thermal stability. With regards to oxidation stability, there also have been some sporadic incidents in the field involving black coolant and engine failures. Reports indicate that the incidents have occurred in both older and newer vehicles/engines with and without emission compliant technologies using a variety of coolants. Used coolant and failure analyses have often indicated that the failure mechanism includes severe thermal stressing and oxidation of the coolant. Additional investigation into root causes has indicated a variety of potential contributing factors may be involved including poor maintenance 共coolant concentrations/ corrosion inhibitor levels/SCA dosages兲, mechanical problems, or abnormal operating conditions, or both 共high temperatures, hot spots, aeration, etc.兲.

FIG. 4—Engine coolant pH results.


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TABLE 3—Metal flow rate limits [10]. Metal Iron component General soft metal alloy Aluminum heat exchange tube

Flow Rate Limit 33 ft/ s 15 ft/ s 7 – 9 ft/ s

Cavitation Protection of wet cylinder liners against cavitation corrosion 共liner pitting兲 continues to be of paramount importance with diesel engines. Liner pitting is the result of cavitation and erosion processes that occur on the coolant side of the cylinder liner. Cylinder liners vibrate from the motion of the piston within the cylinder which can cause low pressure regions of the fluid causing vapor bubbles to form and collapse on the surface of the liner. The repetitive formation and collapsing of the bubbles 共generally on the thrust or anti-thrust side, or both, of the cylinder兲 impinge on the metal surface, removing protective films and eroding the metal. Previously published work provides an extensive overview of cavitation corrosion of cylinder liners and its prevention which can be reduced by good coolant maintenance practices, engine and design materials to minimize vibration, and cooling system design 关8兴. A heavy duty engine cavitation test based upon an internal John Deere cavitation test is being considered for adoption as a standard ASTM engine coolant cavitation test. The test has been shown to discriminate between satisfactory and unsatisfactory coolants with regard to cavitation erosion-corrosion protection. Engine coolants 共conventional, traditional fully-formulated, extended service interval, and extended life coolants along with SCAs兲 have commonly used nitrites or a combination of nitrites and molybdate corrosion inhibitors, or both, for cylinder liner corrosion protection. In view of the more severe operating conditions which can contribute to more rapid nitrite depletion, it is anticipated that extended life or extended service nitrite free coolants, or both, will be used to a greater extent in diesel engines. Extended life OAT coolants that are nitrite free have shown satisfactory performance in the heavy duty engine cavitation test 共formerly the John Deere cavitation test兲 and have been used satisfactorily in almost all engine applications in the field. Anti-scaling Performance Scale resulting from the use of hard water, cooling system contaminants, and corrosion inhibiting film agents can block the ability to transfer heat resulting in overheating and metal fatigue failures. Previous studies reported that scale layers in the range of 0.01 to 0.05 in. 共0.254 to 0.127 cm兲 on the metal surface can significantly retard heat transfer and increase metal surface temperatures 共⬃100– 200° F / 38– 93° C兲 around the head or upper part of the cylinder liner depending on conditions of heat flux and coolant flow兲关9兴. Scale tends to form in specific areas of the hot side of the engine resulting in localized hot spots, which also accelerate oxidation degradation of the coolant. The hot scale and deposits 关9兴 test is currently being considered for establishment as a formal ASTM method for engine coolants. The use of good quality water and properly inhibited coolants minimizes these deposits. Erosion-Corrosion Erosion-corrosion protection is becoming more important in view of the increased use of soft metals 共aluminum, copper, and lead兲 in various engine and cooling system components and the more severe operating conditions of higher coolant flow rates. Erosion-corrosion is typically caused or accelerated by excessive flow conditions which generate shear forces sufficient to remove corrosion passivating films or naturally protective oxides, or both. Erosion-corrosion is most prevalent with soft metals which have critical or limiting flow velocities 共Table 3 provides several examples兲 which above the critical flow velocity, corrosion rapidly accelerates. Other factors including turbulence, cavitation, impingement, galvanic effects, and abrasive contaminants 共casting sand, machining debris兲 can add to the severity of the attack. Erosion-corrosion problems have been observed in the field with brass fuel injector cups, aluminum alloy oil coolers, and aluminum heater cores with several different types of coolants. The problems have been resolved by changes in metallurgy, addition of flow restrictors, or cooling system design changes, or a combination thereof.


FIG. 5—Erosion-corrosion study—pH effects. Engine coolant chemistry can also influence erosion-corrosion protection. A recent erosion-corrosion study was conducted on two different commercially available coolants containing nitrite and molybdate in an aluminum alloy oil cooler module at elevated flow conditions 共30 gpm兲. The results 共Figs. 5–7兲 show that at the elevated flow conditions, the aluminum surface may become unpassivated resulting in conversion of nitrite to ammonia which increases the coolant pH and further accelerates the corrosion of aluminum to form aluminate corrosion metals which are soluble in the coolant. Future Trends Diesel engine OEMs are conducting extensive research on various technologies to reduce emissions to meet more stringent 2007 and 2010 environmental regulations for NOx and particulate matter 共PM兲. The engine manufacturers anticipate meeting these limits through a combination of changes in engine technology and additional emission reduction equipment, particularly heavy EGR to reduce NOx and diesel particulate filters to reduce PM. The 2007 emissions regulations will require the use of lower sulfur fuels which may require OEMs to utilize more sophisticated fuel systems. Some engines will be utilizing dual turbochargers for better efficiencies. Larger EGR coolers or dual EGR coolers will be required to lower combustion temperatures to achieve lower NOx. EGR levels are expected to significantly increase from the levels used to meet the 2002 emissions, possibly increasing heat rejection by an additional 25 %. The higher levels of EGR may

FIG. 6—Erosion-corrosion study—nitrite conversion.


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FIG. 7—Erosion-corrosion study—aluminum corrosion metals. cause an increase in coolant temperatures, localized boiling, and high skin temperatures. All of these will increase the stress on the coolant and decrease the life of the coolant. The use of higher EGR is expected to require improvements in coolant oxidation/thermal stability and nondepleting corrosion inhibitor chemistries. Diesel particulate filters will be used to lower the PM emissions. The filter itself will not impact the coolant, but may cause additional stress by modifying the way the engine runs. If the burning of the soot from the diesel particulate filter is through the cylinder post injection of fuel, cylinder temperatures will increase and coolant stresses will increase. The use of selective catalytic reduction technology to reduce NOx emissions may reduce the load on EGR which will lessen the thermal load to the coolant. The emission reduction technologies will impact coolants and cooling systems. Larger water pumps will be used to supply higher coolant flow due to higher power requirements. Larger radiators will be used to reject higher heat loads. Crankcase water jackets may be changed to handle higher pressures. Larger or double EGR coolers will be needed due to higher EGR rates. Lighter, softer metals are being used in cooling systems, and specifically, aluminum is being used more widely for cooling systems. It is also anticipated that advanced modular thermal systems 共electric water pumps, valves, fans兲 will be incorporated into vehicles. The use of electric water pumps in place of conventional pumps will provide benefits in delivering the correct amount of coolant from cold start-up to high operating temperatures. The electric pump will also eliminate hot soak after shutdown by circulating coolant through the engine. Electric valves may be used to provide more precise temperature control of coolant and engine temperatures than conventional thermostats. The use of a single electrical fan may not currently be practical due to the high power consumption required for operation. However, small auxiliary electric fans may be added to the cooling system to achieve more efficient cooling over a single mechanical fan. The cooling system will also include computer controls to accurately control the temperatures for the primary engine cooling, emission equipment, transmission, engine oil, and charge air cooler. Laboratory and field data indicate that extended life coolants or extended service interval coolants, or both, provide performance benefits in terms of oxidation-thermal stability which translates to longer coolant and reduced usage of SCAs. It is anticipated that the usage of extended life and extended service interval coolants will displace conventional and traditional fully-formulated coolants. In addition, coolant suppliers will develop truly next generation coolant technology that provides greater high temperature capabilities, is effective under high flow conditions, and possesses improved compatibility with elastomers. Regarding base fluids, propylene glycol 共1,2-Propanediol兲 may be used to a greater extent for the biodegradability and toxicogical benefits. 1,3-Propanediol 共PDO兲 is currently receiving significant interest for its improved oxidation and thermal stability. Engine coolants in the far future are expected to provide significantly greater heat transfer properties. Current engine coolants rely primarily on the water concentration/dilution for heat transfer. The use of nanotechnology 共particles of ⬃5 nm size dispersed in aqueous medium兲 exhibits significantly greater


thermal conductivities allowing more rapid heat transfer. Ionic fluids are a new class of fluids that are emerging to replace organic solvents commonly used in chemical processing, cleaning, electrolyte, and heat transfer fluid applications. Ionic fluids are organic salts with melting points of less than 100° C. Ionic fluids may be used to reduce or replace glycol, or both, which would also improve heat transfer properties. The use of nanotechnology or ionic fluids, or both, may require or allow significant changes in cooling system design, components, and materials.

Acknowledgments The authors wish to thank Mr. Stede Granger and Mr. James Roberts, with Shell Oil Products U.S., and Mr. Joseph Hill and Ms. Andrea McCoy, with International Truck and Engine Corporation, for their assistance and insight on coolant performance in today’s heavy duty diesel engines.

References 关1兴关2兴关3兴关4兴关5兴关6兴

关7兴

关8兴

关9兴

关10兴

Needham, J. R., Doyle, D. M., and Nicol, A. J., “The Low NOx Truck Engine,” SAE paper 910731, 1991. McGeehan, J. A., “API: CI-4: The First Oil Category for Diesel Engines Using Cooled Exhaust Gas Recirculation,” SAE paper 2002-01-1673. Olson, G. D., “Vehicle Integration/Thermal Management as Result of 2007 Diesel Emissions Regulations,” Society of Automotive Engineers Panel. Challen, B. and Baranescu, R., “Diesel Engine Reference Book–Second Edition; Chapter 15 Auxiliaries, Thermal Loading,” Society of Automotive Engineers, Warrendale, PA, 1999, 408pp. “Just the Basics: Diesel Engine,” U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Bussem, H., Farinella, A. C., and Hertz, D. L., Jr., “Long-Term Serviceability of Elastomers in Modern Engine Coolants,” Engine Coolant Testing: Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 142–180. Greaney, J. P. and Smith, R. A., “Engine Coolant Compatibility with the Nonmetals Found in Automotive Cooling Systems” Engine Coolant Testing: Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 168–181. Hercamp, R. D., “An Overview of Cavitation Corrosion of Diesel Cylinder Liners,” Engine Coolant Testing: Third Volume, ASTM STP 1192, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1993, pp. 107–127. Chen, Y. S., Kershisnik, E. I., Hudgens, R. D., Corbeels, C. L., and Zehr, R. L., “Scale and Deposits in High-Heat Rejection Engines,” Engine Coolant Testing: Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 210–228. Technology Transfer Systems, Inc., “Impingement Corrosion,” Engine Coolants, ISBN 0-97209270-6, Technology Transfer Systems, Inc., Livonia, MI, 2002, 55 pp.


Regis J. Pellet,1 Leonard S. Bartley, Jr.,2 and Paul O. Fritz2

Field Test for Carboxylate Inhibitor Levels in OAT Coolants ABSTRACT: Wet chemistry test methods have been developed to determine the level of alkyl carboxylate inhibition remaining in used OAT coolants. The test strategy of these methods depends on the known alkyl carboxylate ability to protect cooling system metals such as aluminum by forming insoluble metal soaps. Various test configurations make this test strategy suitable for the rapid analysis of used coolants in the field. This paper will document the initial test strategies and the development efforts that led to the first field test for alkyl carboxylate-based coolants. Test kit performance with laboratory and field samples is also discussed. KEYWORDS: coolant, field test, organic additive technology, carboxylate, inhibitor

Introduction In typical operation, a heavy duty diesel engine can generate sufficient heat to warm five single family homes in winter. Only about 33 % of this heat is converted into crankshaft horsepower. In the past, it was estimated that 30 % of the heat generated was expelled through exhaust and 7 % was radiated directly into the atmosphere. This left about 30 % to be carried away by the cooling system. The amount of heat dissipated by the coolant has risen significantly since exhaust gas recirculation 共EGR兲 was introduced by several engine manufacturers in 2002 in order to control emissions. In addition to removing heat generated by fuel combustion, the cooling system must also remove heat generated by other components such as the transmission and turbo charger. Because of the severity of diesel engine operation and the stress that it places on the cooling system, it is especially important that coolant properties are routinely monitored to assure proper protection of cooling system components and the engine itself. Moreover, rapid testing in the field is essential if needed corrections are to be made before damage occurs. At present there is an array of tests available to determine if coolant freeze and boil protection are adequate and if the coolant’s corrosion inhibition is sufficient to protect the engine components from damage. In addition there are tests to detect thermal degradation and contamination with aggressive agents. Freeze point is easily measured using a refractometer. Freeze point test strips are also available but can be somewhat less reliable than the refractometer due to interferences caused by the coolant’s color. Another less reliable method for freeze point determination is the hydrometer which is significantly influenced by coolant temperature and by the possible mixing of ethylene glycol and propylene glycol based coolants 关1兴. Coolant degradation can be followed to some extent by monitoring the coolant pH. pH test strips are available covering the pH range from 6–12. These strips use multiple acid-base indicators to cover this broad range of interest 关2,3兴. Coolant degradation and specifically glycol breakdown create acid decomposition products such as formic, glycolic, and oxalic acids which cause the coolant’s pH to drop. If the coolant is allowed to become acidic, inhibition becomes ineffective and corrosion damage will occur. Monitoring coolant pH is a quick way to detect the possibility of thermal degradation in the field. A rapid pH drop may also be caused by exhaust gas entry into the cooling system. Exhaust gas can enter the cooling system through leaking head gaskets, for example. In addition to a rapid pH drop, exhaust gas in the coolant may also be indicated by the presence of elevated levels of sulfate. There are test Manuscript received February 24, 2006; accepted for publication December 13, 2006; published online February 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Senior Staff Chemist, Chevron Corporation, New Windsor, NY 12553. 2 Chevron Corporation, New Windsor, NY 12553. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

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strips available to rapidly determine sulfate levels. The test method uses a test pad, impregnated with a soluble barium salt and colored chelating agent. Sulfates in the coolant solutions will react with barium irreversibly, removing it from the chelating agent and changing the pad color. Sulfate level is determined by comparing pad color to a standard set of colors provided for that purpose 关3兴. Tests for corrosion inhibition focus on coolant nitrite or molybdate levels, or both. These two corrosion inhibitors are present in most heavy duty coolants to protect the engine’s cylinder liners against damage caused by liner cavitation. Nitrite, and to a lesser extent molybdate, are consumed as they provide protection; supplemental coolant additives 共SCAs兲 are routinely added to the coolant to maintain adequate liner protection. Routine testing is necessary to assure that effective refortification 共SCAs兲 is occurring. Initially, nitrite levels were determined using a wet-chemistry test, where cerous sulfate was added dropwise to a test coolant until a color change from red to blue occurred; the number of drops needed to produce the color change was related to the coolant’s nitrite level 关4兴. The presence of organic components was found to interfere with this test and a test strip method for both nitrite and molybdate was subsequently introduced in 1988 关5兴. With the strip, nitrite levels were estimated colorimetrically by reacting nitrite with sulfonamide in the test pad to produce a diazo compound which was reacted with an aromatic amine also present in the pad to produce an azo dye 关5兴. Pad color is related to nitrite level. With the advent of organic additive technology 共OAT兲 in the U.S. in 1994, an alternate way to protect cooling system components, including cylinder liners became available. Organic additive coolants rely on carboxylate corrosion inhibitors to provide protection; nitrites may also be present for added liner protection but the primary line of defense is provided by carboxylic salts 关6兴. OAT corrosion inhibition, provided by alkyl carboxylate salts, depletes quite slowly and so does not require frequent refortification by SCAs to assure on-going corrosion protection. Unlike conventional coolant technology, frequent testing, performed in the field is not necessary in order to determine compliance with an SCA refortification regimen. Nonetheless, inadvertent top-off with water or with conventional, silicated coolants will ultimately result in dilution of the OAT inhibition and reduce the OAT coolant’s extended life properties. When over-dilution is suspected, a quick test suitable for use in the field would help the end-user determine the condition of his engine’s coolant and take appropriate action if warranted. As discussed above, conventional coolant technologies rely on nitrite and molybdate test strips to determine if the coolant is providing adequate cylinder liner protection. Nitrite test strips can also be used with OAT coolants. However, options were limited if rapid field testing for carboxylates were required. Shortly after the introduction of OAT coolants, a wet chemistry test method was developed to determine the level of carboxylate inhibition remaining in used coolants. The test was highly accurate with field samples, indicating a pass or fail condition based on carboxylate level. While the test was intended for rapid analysis in the field, the initial configuration did involve several steps and coolant manipulation. It has subsequently been replaced with a test strip method that employed the same test strategy but greatly simplified analysis. The following sections document the initial test strategies and the development effort for the early field test. Test kit performance with laboratory and field samples is also discussed. Experimental Details The organic additive coolants used in this study for the development of a carboxylate field test were based on the alkyl carboxylate, ethylhexanoate. These coolants were available commercially from Texaco, Inc., in a nitrite free version, as Havoline® Extended Life Anti-Freeze/Coolant as well as in a heavy duty version containing nitrite, as Texaco Extended Life Coolant/Antifreeze. Metal Ion/Carboxylate Ion Solubility Studies Solubility data were generated by adding 2.0 milli normal 共mN兲 stock solutions of soluble metal salts of aluminum, iron, and copper to 2.0 mN stock solutions of carboxylic acids. All components were dissolved in 50/50 water-glycol; the carboxylate solutions’ pH values were adjusted to 10 to assure that all acids were present in the conjugate base form. 共Also, many commercial coolants have pH values in this region.兲 After mixing, all solutions were heated in closed containers to 80° C and then held at 80° C overnight and then cooled, filtered to remove insoluble matter and analyzed for metal ion content by induction coupled plasma 共ICP兲.

PELLET ET AL. ON CARBOXYLATE LEVELS IN OAT COOLANTS 19

Aluminum/Ethylhexanoate Titration The following experiments were conducted to demonstrate the stoichiometric reaction of aluminum with ethylhexanoate corrosion inhibitor. Six solutions were prepared by adding Havoline® Extended Life AntiFreeze/Coolant in amounts varying from 0 to 10 to 20 mL aliquots of a 0.021 molar aqueous aluminum stock solution. Havoline® Extended Life Anti-Freeze/Coolant is a nitrite free, automotive coolant containing ethylhexanoate anion, 共EHA兲, as a key corrosion inhibitor. The mixtures were further diluted to obtain a constant volume of 50 mL for each resulting solution using deionized water. A precipitate was observed in all mixtures to which coolant was added. Solutions were filtered to remove the aluminumethylhexanoate reaction product and then analyzed by ICP to determine the amount of aluminum cation remaining and by ion chromatography to determine the amount of ethylhexanoate remaining after reaction. Colorimetric EHA Test Development The following experiments were conducted to demonstrate the feasibility of an EHA test method based on reactions with aluminum cation and aluminum detection using hematoxylin. Five solutions were prepared mixing 20 g of aqueous aluminum stock solution 共0.021 N兲 with 0 to 24 g Havoline® Extended Life Anti-Freeze/Coolant. The solutions were prepared to yield EHA to Al molar ratios of 0, 1.0, 1.6, 2.0 and 3.0. Total mixture weight was brought to 50 g by adding additional deionized water to keep the total reaction volume constant. In all but the 0 ratio mixture, an aluminum-EHA soap was formed. The resultant mixtures were filtered to remove this precipitate and then tested for the presence of aluminum using the hematoxylin test method 关7兴. Specifically, the pH of each solution was raised to ⬎8 by the addition of 1.0 g of saturated ammonium carbonate buffer; next 1.0 g of hematoxylin indicator 共0.1 g in 100 g of deionized water兲 were added to each mixture; finally each solution was acidified by the addition of 1.0 g of 30 % acetic acid. Field Coolant Evaluation Prototype kit performance was evaluated using coolant samples from an over-the-road, heavy duty diesel fleet. The fleet employed Texaco Extended Life Coolant/AnitFreeze 共TELC兲, an EHA based coolant containing nitrite. Vehicles in this fleet had been converted to TELC by flush-and-fill procedures, which involved draining of conventional coolant, flushing with water and then filling with TELC. Additional vehicles had been converted using Texaco Extended Life Corrosion Inhibitor Concentrate, a superconcentrated inhibitor package based on EHA. The super-concentrate was, on occasion, used to convert a vehicle to extended life technology by addition to the conventional coolant already in place in the engine without recourse to the drain, flush, and fill procedure. Because of the high EHA content of the superconcentrate as well as variability of diesel engine cooling system volumes, EHA levels significantly above those found in fresh TELC were possible. For the purposes of test kit evaluation, 39 samples were obtained and tested by laboratory methods. Coolant samples were also evaluated using two different prototype versions of the field test. Carboxylate Field Test Development Texaco Extended Life Coolant was the first OAT marketed in the U.S.; it was based on the alkyl carboxylate, ethylhexanoate. At the time of its introduction, there were no rapid and accurate tests for carboxylate ion concentration in coolants. A clue to potential test methodology came from early field experience that revealed excellent corrosion protection for cooling system metals, especially for aluminum 关8兴. Primary evidence came from engine disassembly following extended field testing 共⬎300 000 miles兲 which revealed aluminum components in “like-new” condition. Consistent with these observations was the fact that aluminum ion was almost never detected in used coolant samples, even applications where significant aluminum componentry was present throughout the cooling system. Metal ion/carboxylate ion solubility studies provide insight to help understand the carboxylate protection mechanism. As one might expect, solubility of the metal carboxylate “soap” depends not only on the metal ion but also on the chain length of the carboxylate. This can be seen in solubility data presented in Fig. 1. The figure presents the amount of soluble metal cation in the presence of various alkyl carboxylate anions. Data are presented for aluminum, copper, and iron ions. The graph shows that as the molecular


FIG. 1—Metal carboxylate solubility.

weight or chain length of the carboxylate increases, the amount of soluble metal decreases; the effect is greatest for aluminum cation which is insoluble in the presence of carboxylates with more than two carbons. The effect is least pronounced for copper cation which remains partially soluble in the presence of carboxylates up to ten carbons in length. Thus with Texaco Extended Life Coolant, 共used in the initial test development兲 based on C8 and C10 carboxylates, aluminum cation is virtually insoluble. It is interesting to speculate that the effective corrosion protection, observed with this coolant, may be provided by this insoluble soap formation at the sight of incipient corrosion; soap formation would terminate the corrosion process before damage was done while consuming a minimal amount of inhibitor. For the purpose of field test development, the quantitative reaction of aluminum with C8 and C10 alkyl carboxylates to form an insoluble soap can be related to the amount of carboxylate present in the starting solution 共coolant.兲 This is demonstrated in Fig. 2, where the amount of aluminum cation remaining after reaction with added ethylhexanoate anion 共EHA兲 is plotted as a function of the amount of ethylhexanoate ion added to the solution. From the graph, it can be seen that there is a linear, inverse relation between the amount of aluminum remaining in solution and the amount of ethylhexanoate added to the mixture. From the graph, all aluminum is removed from the stock solution when sufficient ethylhexanoate is added to achieve a ratio of EHA to Al of approximately 1.75 to 1. This suggests that the aluminum ethylhexanoate precipitate formed has an empirical formula approaching Al 共EHA兲2. Importantly, the fact that the graph of aluminum remaining versus ethylhexanoate added is a straight line suggests that this stoichiometry remains constant over the range of aluminum and EHA concentrations examined. This may be more apparent from the data in Table 1. Here, the amounts of aluminum and ethylhexanoate ion present in the initial solutions are compared with the amount of ions present after reaction and filtration. The ratio of EHA and aluminum disappearing from solution remains constant over the concentrations studied.

FIG. 2—Al⫹3 titration with ethylhexanoate anion.

PELLET ET AL. ON CARBOXYLATE LEVELS IN OAT COOLANTS 21 TABLE 1—Aluminum and ethylhexanoate concentrations (moles/litre) before and after reaction and filtration. Initial Al 0.0213 0.0213 0.0213 0.0213 0.0213

Initial EH 0.0428 0.0341 0.0298 0.0256 0.0213

Final Al 0 0.00204 0.00407 0.00641 0.00930

Final EH ⬍0.007 0 0 0 0

Change in Al 0.0213 0.01926 0.01723 0.01489 0.012

Change in EH ⬎0.0358 0.0341 0.0298 0.0256 0.0213

Change Ratio EH/ Al ⬎1.67 1.771 1.73 1.72 1.775

This observation suggests that aluminum can be used to titrate or determine EHA levels in used coolants. To render this method useful for rapid field analysis, a method of soluble aluminum detection in required. Conceptually, a field test might be as simple as: Al+3 + Ethylhexanoate → Al共EHA兲2 + excess Al+3 Excess Al+3 + Indicator → Al共Indicator兲 colored complex In this conceptual test, a premeasured solution containing a predetermined amount of aluminum is added to a measured aliquot of coolant sample from the field. The coolant sample contains an unknown amount of EHA inhibitor. The amount of aluminum in the aliquot can be preselected to be equivalent to the minimum amount of EHA needed for good corrosion protection 共this EHA target value can be varied simply by varying the amount of aluminum cation in the test兲. The two solutions are mixed; a colorimetric aluminum indicator is added to the solution portion of the mixture. The presence of aluminum in the mixture indicates there is insufficient EHA to precipitate all the aluminum and thus there is insufficient EHA inhibition. The colorimetric detection of aluminum indicates a failing coolant that would need to be refortified to provide adequate corrosion protection. There are several colorimetric tests for aluminum reported in the literature; a sampling of possible techniques is provided in Table 2. All of these tests permit the visual detection of aluminum at ppm levels by the formation of colored complexes. Conceptually all could be used in the test described above. However, testing is complicated by the fact that all heavy duty coolants are dyed to help to distinguish them from other engine fluids. Initially heavy duty extended life coolants were dyed red to distinguish them from conventional coolants which were purple or blue. The red color of extended life coolant has since become an industry standard as proposed by the Technology and Maintenance Council’s Recommended Practice 351. Because of coolant color, aluminum indicators that turn red in the presence of aluminum may be of limited use. From Table 2, it can be seen that tests based on hematoxylin should not suffer from this limitation as it develops a violet color in the presence of aluminum. Initial efforts to develop a field test for EHA focused on the use of hematoxylin test which was first reported in 1924. According to the hematoxylin procedure, a test solution containing aluminum must be buffered to within a pH range of 6.5 to 8.5 using a saturated solution of ammonium carbonate in order to form the aluminum indicator complex. The purple colored complex will not form at pH values below 6.5. Above 8.5 the complex forms but decomposes 共fades兲 rapidly. In addition to being an aluminum indicator, hematoxylin’s color is also sensitive to pH. At the pH of solutions made alkaline with ammonium carbonate, uncomplexed hematoxylin is red or purple, masking the violet color produced by the aluminum complex. However, when pH is lowered by the addition of acetic acid, uncomplexed hematoxylin’s color changes to yellow while the aluminum hematoxylin color is unaffected. Thus, lowering the mixture pH after forming the aluminum complex removes the interference and allows aluminum detection if present. TABLE 2—Colorimetric aluminum indicators.

Aluminum Indicator Hematoxylin 8-Hydroxyquinoline 共Oxine兲 Quinizarin Aluminon

Aluminum complex Color violet red red red

Reference 关7兴关9兴关10兴关11兴


FIG. 3—Al⫹3 titration with ethylhexanoate using hematoxylin indicator. To demonstrate feasibility of this test method, solutions were prepared mixing aqueous aluminum stock solution with an EHA containing coolant to yield EHA to Al ratios ranging from 0 to 3. The resultant mixtures were filtered and then tested for the presence of aluminum by raising the pH with saturated ammonium carbonate buffer, adding hematoxylin indicator and then lowering the pH with acetic acid solution. The resulting solutions ranged in color from yellow to deep purple or violet; all solutions at EHA/ Al ratios above 2.0 were yellow; solutions with EHA/ Al ratios below 2.0 were violet. The dramatic color change can be seen in Fig. 3. Note that the color change occurs precisely and sharply at the end-point previously determined using laboratory methods of ion chromatography and ion-coupled plasma. Thus a potential field test should be in excellent agreement with the more time consuming laboratory analysis requiring ion chromatography. Again, by selecting the amount of aluminum added to the field coolant, it is possible to determine if adequate corrosion inhibition is present as indicated by the coolants ability to precipitate all added aluminum. It is also important to note that the dramatic color change is obvious even in black and white photography and so utility of this colorimetric test would not be limited for a color blind observer. Obviously, despite its potential accuracy, this multistep test would be too cumbersome for field use unless carefully designed to minimize coolant and solutions handling and manipulation. With simplification as a goal, a commercial field test kit was designed and ultimately made commercially available. The contents of the commercial kit are shown in Fig. 4. The initial commercial kit consisted of three components: a white-capped test tube contains a premeasured amount of aluminum stock solution. A measured amount of coolant was added to this tube and an aluminum EHA precipitate was formed. The resulting mixture was filtered using the filter syringe provided and the filtered solution was added to the red-capped plastic test tube. There were three ampoules in this tube containing ammonium carbonate, hematoxylin indicator, and acetic acid. The ammonium carbonate ampoule was broken first releasing the buffer and raising the mixture pH to 8; the second ampoule was

FIG. 4—Test kit for alkyl carboxylates.

PELLET ET AL. ON CARBOXYLATE LEVELS IN OAT COOLANTS 23 TABLE 3—Laboratory analysis of used coolant samples.

% Carboxylatea 0 12 15 19 30 32 34 37 38 43 45 48 49 52 52 53 54 56 64 69 69 99 99 99 101 101 101 102 106 113 119 120 122 125 127 154 160 185 262

pH 8.3 7.06 7.87 8 8.37 8.75 8.18 8.5 7.83 8.22 7.6 7.66 8.31 8.7 8.3 7.83 8.13 8.1 7.85 8.73 8.76 8.48 8.73 8.11 8.13 8.54 8.51 8.65 8.31 8.78 8.49 8.05 8.12 8.02 8.54 9.03 8.97 8.49 8.8

% Water 52.2 39.8 54.7 47.4 49.5 45.1 51.5 55.0 50.6 42.4 44.0 54.3 54.7 49.2 41.5 49.4 50.7 51.7 43.5 59.2 55.0 46.5 54.8 52.4 53.0 48.4 47.7 37.5 51.7 58.1 36.9 31.2 58.7 43.8 45.5 47.9 48.6 43.9 33.8

B ppm 212 246 122 256 527 206 586 140 123 314 460 199 389 542 118 109 71 431 1117 155 514 58 320 7.2 454 10 7.6 349 203 17 291 29 189 427 276 384 200 637 206

Si ppm 79 81 80 82 86 79 129 72 53 57 87 39 201 55 62 80 52 40 108 21 57 43 33 40 88 4.9 4.7 75 66 56 83 52 56 89 62 29 47 94 60

Mo ppm 276 37 116 130 154 176 270 2.7 222 156 46 110 151 23 127 22 131 53 66 ⬍1 5.6 28 2.1 ⬍1 48 12 9.2 140 79 6.2 159 2.8 ⬍1 81 38 2.3 18 64 78

NO2 ppm 1160 11.6 660 1140 2300 866 2610 362 761 695 1330 273 1870 250 47.7 490 582 624 1250 242 533 108 580 2110 564 2370 2460 301 71 20.5 381 ⬍7 18.9 559 611 995 422 990 276

NO3 ppm 307 2020 955 1500 1800 520 2230 599 538 996 2020 486 1680 875 1160 458 660 1770 2730 305 830 275 680 55.7 1580 70 61 940 620 251 1560 139 243 2450 548 1200 381 1540 515

PO4 ppm 4680 12.2 2600 2580 2300 4280 3080 1520 2800 2970 562 1650 2250 1120 2800 79.7 1410 1930 532 664 1270 677 1250 8 261 118 84 2270 1290 1080 1860 220 205 1500 569 2300 249 2020 772

TTZ ppm 380 110 280 100 470 1060 300 410 300 740 200 400 600 800 600 460 550 500 210 770 520 1070 770 800 2450 1100 1100 1200 1200 1120 700 1000 1100 720 1000 1380 1460 1700 2300

a

Percentage of ethylhexanoate, relative to fresh TELC.

then broken releasing the indicator and forming the purple aluminum-hematoxylin complex. The third ampoule was broken lowering the pH, removing uncomplexed hematoxylin interference. The resulting color would be yellow if all aluminum had been precipitated by reaction with the coolant’s EHA in the white-capped vial. The resultant color would be purple or violet if there was insufficient EHA to completely remove the soluble aluminum that was initially present. Thus, a final yellow 共or red/orange兲 color indicated a pass; conversely, a final violet color indicates insufficient carboxylate inhibition, a fail. As initially configured, the test took less than five minutes to complete and exhibited high accuracy with laboratory samples. However, a more important indicator was performance with real world, used coolant samples from the field. To this end, prototype test kits were used to evaluate 39 coolants obtained from the field. The results of laboratory analysis of these field samples are provided in Table 3. Nominally, all samples were obtained from a fleet that was using Texaco Extended Life Coolant 共TELC兲, an EHA based heavy duty coolant containing nitrite. However, from the table it can be seen that all coolant samples had varying degrees of contamination with competitive coolant products indicated by the presence of


FIG. 5—Field performance with initial test kit. phosphate, borate, silicate, molybdate, and nitrate. These conventional corrosion inhibitors were absent in fresh TELC. Analysis also revealed varying degrees of dilution with water. In the table, coolants are arranged in order of increasing EHA content which is expressed as a percent EHA relative to fresh coolant. Thus a fresh coolant would have 100 % EHA. It can be seen that in real world use, coolant contamination with conventional inhibitors is quite common. Water contents and coolant pH values also vary significantly. All coolants were tested using the prototype test kit described above. The results of this evaluation are presented graphically in Fig. 5. In this figure, results are tabulated as “pass” or “fail” depending on whether a yellow or purple color resulted from the prototype test kit. Results are presented in order of increasing carboxylate content 共% EHA兲. A number of observations can be made. First, in the initial configuration, coolants with less than fresh 共100 %兲 EHA routinely failed the test; there is only one false pass among the 22 coolant samples with EHA levels less than 100 %. Secondly, for coolants with greater than 100 % EHA, it can be seen that there are several false fails; specifically of the 17 samples evaluated, seven yield a failing indication. Finally, it would appear that any coolant with less than 100 % EHA would fail the test as it had been initially configured. This high end-point and the several false fails observed needed to be corrected. Based on these results and a close examination of the chemical analysis of the coolant samples, it was discovered that molybdate interfered with the test by yielding a near black complex with hematoxylin. Its presence in many of the samples with high EHA, resulted in the false fails observed. In a second test kit which was ultimately commercially released, the amount of aluminum present in the white tube was lowered so that failing results would only be obtained when EHA levels fell to below 75 % of fresh. In addition, an ampoule was added to the white tube containing a lead acetate; lead acetate will precipitate molybdate, allowing it to be removed upon filtration and prior to hematoxylin addition in the red tube. The modified prototype was used to evaluate the same 39 coolant samples from the original test. Results of that evaluation are presented in Fig. 6. Use of the lead acetate ampoule in the white vial has almost eliminated the occurrence of false fail results and accuracy has risen to nearly 90 %. Furthermore,

FIG. 6—Field performance with improved test kit.

PELLET ET AL. ON CARBOXYLATE LEVELS IN OAT COOLANTS 25

by reducing the amount of aluminum cation present in the white vial it was possible to lower the fail point to about 70 %, i.e., coolants with EHA levels less than 70 % of fresh would now yield the violet fail indicator.

Conclusions The first kit for EHA field analysis was commercially introduced in 1998 and exhibited excellent performance in evaluating extended life, alkyl carboxylate coolants even with highly contaminated samples. This test strategy, relying on aluminum solubility should work with any alkyl-based carboxylate coolant. However, aluminum cation is significantly more soluble in the presence of some aromatic carboxylates and so this strategy may not be effective for coolants based on these inhibitors. While most of the field data, presented in this study, were obtained with heavy duty extended life coolant 共containing nitrite and molybdate兲, the strategy is also effective for automotive coolants containing alkyl carboxylates. Ultimately, the hematoxylin method for detecting soluble aluminum was replaced with a two strip test kits. The new kit still relies on the reaction of EHA in carboxylate base coolants with a stock aluminum solution but has been significantly simplified by replacing the hematoxylin wet chemistry test with a test strip method for aluminum detection. Accuracy for the test strip method has remained high while the test procedure takes about a minute to execute.

References 关1兴关2兴

关3兴

关4兴关5兴

关6兴关7兴关8兴关9兴

关10兴

关11兴

Hudgens, R. D. and Bugelski, W. G., “Analysis of Coolants from Diesel Engines,” SAE Technical Paper 900435, 1990. Kreiser, T. H., Makowski, E., Martin, H. R., and Hudgens, R. D., “Evaluation of Test Strips for On-Side Monitoring of Coolants in Heavy-Duty Diesel Engines,” SAE Technical Paper 960645, 1996. Kreiser, T. H., Dandashli, E., Makowski, E., and Martin, H. R., “Development and Evaluation of a Test Strip for Estimating the pH, Chloride and Sulfate Levels in Engine Coolants,” SAE Technical Paper 1999-01-0133, 1999. Kolthoff, I. M., Quantitative Chemical Analysis, The Macmillan Company, London, 4th ed., 1969, pp. 816–839. Hemmes, P. R., Kreiser, T. H., Valle, S., and Hercamp, R. D., “Test Strips for Rapid On-Site Analysis of Engine Coolants,” Engine Coolant Testing, 3rd Volume, ASTM STP 1192, R. Beal, Ed., ASTM International, West Conshohocken, PA, 1993, pp. 165–179. Pellet, R. J., Bartley, L. S., and Hunsicker, D. P., “The Role of Carboxylate-Based Coolants in Cast Iron Corrosion Protection,” SAE Technical Paper 2001-01-1184, 2001. Hattfield, W. D., “Soluble Aluminum and the Hematoxylin Test in Filtered Waters,” Ind. Eng. Chem., Vol. 16, March 1924, pp. 233–234. Mowlem, J. K. and Van de Ven, P., “Comparison of Surface Coating Formed from Carboxylic Acid-Based and Conventional Coolants in a Field-Test Study,” SAE Technical Paper 960640, 1996. Liang, P., Yand, L., Hu, B., and Jiang, Z., “ICP-AES Detection of Ultratrace Aluminum III and Chromium III Ions with Microcolumn Preconcentration System Using Dynamically Immobilized 8-Hydroguinioline on TiO2 Nanoparticles,” Anal. Sci., Vol. 19, 2003, pp. 1167–1171. Kdriss, K. A., Hashem, E. Yl, Abdel-Aziz, M. S., and Ahmed, H. M., “Direct Spectrophotometric Determination of Aluminum Oxide in Portland Cement and Cement Clinker,” J. Cem., Concr., Aggregates (ASTM), Vol. 23, No. 1, June 2001, pp. 57–65. Bertsch, P. M., Allely, M. M., and Ellmore, T. L., “Automated Aluminum Analysis with the Aluminon Methods,” Soil Sci. Soc. Am. J., Vol. 45, 1981, pp. 666–667.


R. Hudgens,1 E. Schmidt,2 and M. Williams2

A Comparison of Membrane Technologies for Engine Coolant Recycling ABSTRACT: Recycling of used engine coolants containing ethylene glycol and other glycols would appear to be well established, particularly for reverse osmosis and nanofiltration membrane, electrodialysis, and distillation-based processes. Both literature and recycling facilities indicate success in employing these techniques. However, many recyclers, particularly those employing a single treatment technology, are not capable of producing recycled product meeting original equipment manufacturer 共OEM兲 requirements for coolant, and these typically fall far short of approaching virgin 共nonrecycled兲 coolant quality. In addition, some recycling facilities have produced and marketed product that led to coolant system damage and engine failure, either as a result of not sufficiently removing contaminants or inadequately reformulating with corrosion inhibitors and other additives. The danger of process upsets resulting in inadequate product is particularly high for those facilities that receive feeds with varying contaminant levels and coolants containing a range of corrosion inhibitors and additives 共silicates, organic acids, etc.兲. However, no study to date has focused on a fundamental assessment of the separation characteristics and interactions of the various classes of coolant technologies with the commercially available reverse osmosis, nanofiltration, and electrodialysis ion exchange membranes typically seen in recycling operations. This study presents results of a comprehensive evaluation of the separation characteristics of a wide range of these membranes with a wide range of coolant types. In particular, the study examined production rate characteristics, inhibitor and other additive separation, and contaminant removal for reverse osmosis, nanofiltration, and electrodialysis. Residual inhibitors remaining in the recycled coolant are examined, with guidance provided on how these residuals might affect coolant reformulation and performance. KEYWORDS: used engine coolant, used antifreeze, recycling, electrodialysis, reverse osmosis, nanofilteration

Introduction Engine coolants are used to protect internal combustion engines from temperature extremes. The coolants normally employ ethylene or propylene glycol at concentrations of 30 to 70 % by volume to lower the freeze point and raise the boiling point of water in internal combustion engines. These coolants also commonly employ chemical inhibitors at concentrations of approximately 1 to 5 % by weight to counteract corrosion. The useful life of engine coolants is limited by the degradation over time of the glycol and inhibitor components and introduction of corrosive components such as chlorides 关1兴. Approximately two billion pounds of concentrated antifreeze is produced in North America each year, with about 80 % of this sold to refill leaking cooling systems, an estimated 7 % used for factory fill, and 13 % for coolant change-out. The amount of coolant changed-out in the past has traditionally been discharged to the sanitary sewer. However, as a result of restrictive legislation on disposal and increasing raw materials cost, recycling engine coolant has and continues to become increasingly desirable. For example, the European Union has just recently enacted environmental legislation that requires recycling of used engine coolant 共Council Directive 2000/53/EC兲. While the idea of designing products for recycling is superior to simple disposal, the public perception of recycling is typically that the recycled product is less in quality. Recently this has been coined downcycling, with the term upcycling meaning that the product quality would be as good or better than its nonrecycled counterpart 关2兴. Some antifreeze recycling methods do indeed result in downcycled product compared to virgin coolants; however, other technologies have been successfully employed to yield upManuscript received April 21, 2006; accepted for publication February 12, 2007; published online April 2007. Presented at ASTM Symposium on Engine Coolant Technolgies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Cummins Filtration, Cookeville, TN. 2 EET Corporation, Harriman, TN. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

26

HUDGENS ET AL. ON MEMBRANE TECHNOLOGIES 27 TABLE 1—Candidate used coolant treatment technologies. Technology GRAVITY SEPARATION Open Tank Plate or Tube Centrifuge

Primary Function

Side-Streams

Free Oil and Dirt Removal Free Oil and Dirt Removal Free Oil and Dirt Removal

Oils, Fuels, Sludge Oils, Fuels, Sludge Oils, Fuels, Sludge

CHEMICAL TREATMENT Precipitation Demulsification Coagulation/Flocculation

Alter Solubility of Metals Demulsify Soluble Oil Conglomerate Particles

Precipitants Oil Sludge

Particle Separation, Filtration, Absorption

Filters Media

MEMBRANE Ultrafiltration Nanofiltration Reverse Osmosis

Soluble Oil Removal Multivalent Ion Removal Aqueous Salts

Reject, Cleaner Wastewater and Membranes

ELECTRO-MEMBRANE Electrodialysis Continuous Deionization

Removal of Charged Ions Removal of Charged Ions

Brine, Membranes Brine, Membranes

Water Evaporation, Salt-Out

Wastewater, Still Bottoms

Dissolved Organics, Color Removal of Trace Ions

Carbon Resins

PARTICLE FILTRATION Cartridge/Bag Depth/Media

DISTILLATION POLISHING Carbon adsorption Ion Exchange

cycled coolant. Since recycling engine coolant has become commercially available, the different methods that have been offered include micron filtration, chemically-assisted filtration, centrifugation/filtration, vacuum distillation, nanofiltration/reverse osmosis, and ion exchange/filtration 关3–12兴. There are considerable separation efficiency differences between these various processes. The originally developed recycling method, conventional filtration alone 共⬎1 ␮m兲, is not adequate to provide complete purification of spent coolant, since it cannot remove degradation products and dissolved solids and corrosive species to provide a consistent finished product with a reduced/known inhibitor balance. Dissolved solids and corrosive species include water impurities, such as chlorides, sulfates, residual inhibitors such as borate, phosphate, silicate, carboxylic acids, and degradation products of glycol 共primarily glycolate and formate兲. Removing a large portion of these total dissolved solids 共TDS兲 while achieving high recoveries in a recycling process is key to recycling economics, since nonrecovered coolant represents lost product and also must be subsequently disposed. Consequently, the desalting technology unit operations required to remove TDS and produce on-specification products at high recoveries are the most essential part of any recycling process. However, antifreeze recycling involves not only the combination of physicochemical separations to produce a glycol or glycol/water base stock of sufficient purity to reformulate to antifreeze, but also additive package reformulation to ensure the recycled product performance properties are equivalent to its virgin 共nonrecycled兲 coolant counterparts. Ingredients in these processes that ensure on- or off-site success are good quality control and assurance, a well engineered and responsibly operated process, and OEM approved and proven reinhibition 共glycol additive package兲 technology that should, ideally at least, integrate with the recycling method selected. A number of separation techniques have been proposed and are actually in use for recycling used engine coolant from the vehicular service industry 关3–12兴. The methods predominately employ, alone or in combination, one of the following unit operations: • Vacuum Distillation • Membrane Separation • Ion Exchange These technologies have been under various stages of development for the past 15 to 20 years. The


FIG. 1—Pressure-based and ion exchange-based membrane processes. most predominant candidate treatment technologies, separation function, and side-streams generated are shown in Table 1. In all these technologies, separating a large portion of TDS from the coolant in the recycling process is key. The key desalting 共also called desalination or desalinization兲 technologies that have been developed over the years are both thermal and membrane-based separation techniques. The desalting technologies are essential unit operations required to produce an on-specification concentrate or prediluted recycled product and include any one or a combination of vacuum distillation, membrane separation, or ion exchange. The thermal and membrane-based desalting devices essentially separate a saline solution into two streams: one with a low concentration of dissolved salts and the other containing the remaining dissolved salts often referred to as the concentrate or brine stream. It is important to realize that desalting processes do not produce more pollutant material or mass; they merely redistribute 共concentrate兲 that which is present in the feed stream. For used coolant recycling, these technologies are the same as used in desalting drinking water, with the same inherent advantages and disadvantages, plus problems caused by the presence of high levels of ethylene glycol 共EG兲. While many early antifreeze studies and recyclers touted each of the recycling technologies as suitable for producing acceptable product, practical experiences have shown that a commercially successful recycling operation will use multi-stage processes in order to produce recycled coolant meeting OEM requirements. Indeed, for those facilities using only a single unit operation, the danger of process upsets resulting in inadequate product is particularly great, as waste coolant feeds typically have varying contaminant levels and contain a range of corrosion inhibitors and additives 共silicates, organic acids, etc.兲 that can impact treatment and reinhibition. Some recycling facilities have produced and marketed product that led to cooling system damage and engine failure, either as a result of not sufficiently removing contaminants or inadequately reformulating with corrosion inhibitors and other additives 关13,14兴. A primary cause of these failures and of critical importance in any recycling process, but unfortunately one in which many recyclers fall short, is removal of corrosive inorganic ions. These include chloride and glycol degradation products that can cause coolant system failure. Also unfortunately, these failures have also caused many to skeptically view antifreeze recyclers out of concern that the technologies used cannot consistently produce a product as good as virgin coolant. As shown in Fig. 1, the goal of this study was to examine the separation characteristics of two unit operations commonly used in recycling systems for removing corrosive species, nanofiltration 共NF兲, which is typically misidentified as reverse osmosis 共RO兲, and electrodialysis 共ED兲, in order to determine if these technologies could effectively and consistently produce recycled product meeting OEM and virgin 共nonrecycled兲 coolant specifications for corrosive and other problematic species. Studies were done with a wide variety of virgin coolants to identify problems that the two unit operations could potentially encounter with the various coolant additives. The studies also examined the impact of different types of membranes available for RO/NF and ED on separation of corrosive species and additive components and process productivity. In addition, the separation characteristics’ effects on potential corrosion reinhibition strategies were examined. Finally, studies with actual used coolants were performed to determine if these technologies could produce a product equivalent to virgin coolant, individually or in combination. RO/NF and ED Terminology The RO or NF process is relatively simple in design; a schematic is shown in Fig. 2共a兲, and Fig. 2共b兲 identifies the three streams 共and associated variables兲 that are associated with a pressure-based membrane

HUDGENS ET AL. ON MEMBRANE TECHNOLOGIES 29

FIG. 2—(a) Schematic of a pressure-based membrane system and (b) pressure-based membrane streams and terminology. process 关15兴. The water or solvent 共e.g., EG兲 flow through the membrane is reported in terms of water or solvent flux, Jw, which is volumetric or mass product flow rate through the membrane divided by the membrane area; typical units are gallons per square foot per day 共gfd兲. Water flux can typically be expressed as a function of pressure as Jw = A共⌬P − ⌬␲兲

共1兲

where A is termed the water or solvent permeability constant and is particular to a particular membrane, ⌬P is the applied pressure across the membrane, and ⌬␲ represents the osmotic pressure difference across the membrane. As the equation indicates, higher pressures across the membrane serve to increase flux, while higher osmotic pressure differences across the membrane decrease flux. Degree of separation in pressure-based membranes is reported in terms of rejection, R, defined as R=1−

CP CF

共2兲

where C P is the product 共permeate兲 concentration and CF is the feed concentration, respectively. Finally, recovery is defined as the ratio of final product volume to feed volume. It is important to note the subtle but important difference between RO and NF. Traditional RO membranes typically have high salt rejection for both monovalent and multivalent ions as well as many organics and are typically capable of producing high purity water in a single pass. This contrasts with NF, for which size and ionic charge play major roles in separation characteristics: large organic species 共such as dyes兲 and multivalent charged anions such as sulfate and phosphate are much more highly rejected by NF membranes than monovalent ions such as chloride and nitrate 关15兴. While antifreeze recycling with RO is many times claimed by commercial recyclers, further investigation reveals their actual use of NF membranes. It is important to note the distinction to avoid misperceptions concerning the separation characteristics that can be achieved with NF as opposed to traditional, high rejection RO. While traditional RO has been used for ethylene glycol concentration, typically these applications have been at very low glycol concentrations 关16兴. The ED process is also relatively simple in design 关17兴. A flow diagram identifying the streams of the ED process is shown in Fig. 3共a兲, and a schematic showing the ED cell is shown in Fig. 3共b兲. Cations and


FIG. 3—(a) Schematic of ED process and (b) schematic of ED cell. anions are transported from the feed 共diluate兲 stream compartments through the ion exchange membranes into the concentrate 共brine兲 stream compartments under the influence of the applied electrical potential difference. Antifreeze Terminology and Recycling Specifications The majority of coolants currently on the market are based on EG. The EG-based coolants use three broad classes of inhibitors to control coolant system corrosion: • Conventional additives, such as silicates, borates, nitrates, and nitrites. • Organic acid technology 共OAT兲 based additives, such as 2-ethylhexanoic acid, sebacic acid, and benzoic acid. TABLE 2—Recycled Coolant Specifications.

Parameter Total Glycol Degradation Acids, mg/L 共Glycolate/Formate兲 Chloride, mg/L Sulfate, mg/L Nitrite, mg/L as NaNO2 Nitrate, mg/L as NaNO3 % Glycol

New Coolant Specification ASTM D 4656 ⬍200

U.S. Military 共TACOM兲 Recycled Limits 1200 max

Recycled Coolant Specification ASTM D 6471 N/a

25 max 50 max N/a N/a 50 min

25 max N/a 1200 min N/a 50 min

33 140 N/a N/a 50 min

HUDGENS ET AL. ON MEMBRANE TECHNOLOGIES 31 TABLE 3—RO/NF membrane properties.

Polymer Type Thin-film composite, polyamide

Standard Test Conditions 500 ppm calcium chloride, 70 psi 2000 ppm magnesium sulfate, 70 psi

Standard Water Flux 共gfd兲 37 31

Nanofiltration

Thin-film composite, polyamide

500 ppm calcium chloride, 70 psi 2000 ppm magnesium sulfate, 70 psi

20 17

35–50 ⬎97

NF-C

Nanofiltration


magnesium sulfate, 100 psi

39

98

NF-D

Nanofiltration



22

98

NF-E

Nanofiltration

Cellulose acetate

2000 ppm, sodium sulfate, 220 psi

28

92

NF-F

Nanofiltration


2000 ppm NaCl, 70 psi 2000 ppm magnesium sulfate, 70 psi

19 24

85–95 ⬎97

NF-L

Nanofiltration



31

96

RO-G

Reverse Osmosis


500 ppm sodium chloride, 100 psi

29

98–99

RO-H

Reverse Osmosis


2000 ppm sodium chloride, 225 psi

26

99

RO-I

Reverse Osmosis

Cellulose acetate

sodium chloride, 420 psi

24

97

RO-J

Reverse Osmosis

Polyamide


26

99.5

RO-K

Reverse Osmosis



22

98.9

Membrane No. NF-A

Membrane Class Nanofiltration

NF-B

Standard Rejection 共%兲 40–60 ⬎97

• Hybrid 共also called HOAT兲 additives, which include both conventional components as well as OAT components. Table 2 lists virgin and recycled coolant ASTM specifications, as well as military recycled coolant standards. Experimental Studies were carried out on lab scale NF/RO and ED systems. The General Electric Sepa™ Cross Filtration CF II Med/High Foulant System was used for NF/RO studies. This system had an effective membrane area of 140 cm2. The system was operated at 300 psi 共or 600 psi for selected RO membranes兲 with 1.5 L of feed; temperatures were maintained in the range 20 to 35° C. Feed flow rate was 7 – 8 L / min, sufficient to

32 ENGINE COOLANT TECHNOLOGY TABLE 4—IX membrane properties. Cation Exchange Membrane

IX Membrane Set No. IX_ A

IX_ B IX_ C IX_ D

Membrane Type Homogeneous, Strong Acid Homogeneous, Strong Acid Homogeneous, Strong Acid Heterogeneous, Strong Acid 共Heat Extrusion兲

Thickness Resistance 共mm兲共ohm-cm2兲 0.18 3 0.16

2

0.16

2

0.34

10

Anion Exchange Membrane Exchange Capacity 共meq/g兲 1.7

Exchange Thickness Resistance Capacity 2 共ohm-cm 兲 Membrane Type 共mm兲共meq/g兲 Homogeneous, 0.17 3 1.6 Strong Base 2.3 Homogeneous, 0.18 1 2.8 Strong Base 2.3 Homogeneous, 0.17 1.4 2.0 Strong Base Not Known Heterogeneous, 0.34 7.5 Not Known Strong Base 共Heat Extrusion兲

minimize polarization effects. Initial screening runs were at least 15 min in duration, with test runs at least 30 min 共approximately 20– 50 % recovery兲. The NF/RO membranes studied are listed in Table 3 along with membrane properties. Integrity of the membranes before coolant studies were verified with standard salt solution. EET Corporation’s High Efficiency Electrodialysis 共HEED®兲 Laboratory/Bench-Scale System was used for ED studies with 1 L of feed solution. A total of ten cell pairs 共CPs兲 with an area of 71.1 cm2 per cell was used for each membrane study, with an applied potential of 2 V/CP applied across the ED cell and a feed rate of 5.7 L / min. Temperatures were maintained in the range 20 to 35° C. Table 4 lists properties of the four ion exchange membrane sets studied. Separation characteristics with each membrane were verified with standard salt solutions prior to coolant studies. Both the NF/RO and ED systems were operated in batch mode, with either reject 共NF/RO兲 or diluate 共ED兲 recycled to the feed tank during the course of the run. Feed solutions consisted of virgin coolants spiked with corrosive water and diluted with deionized water to 40 % ethylene glycol content and containing 200 ppm chloride and 1500 ppm sulfate. Table 5 lists properties of the coolants. These included conventional coolants, OAT coolants, and hybrid 共HOAT兲 coolants with a mixture of conventional and organic acid additives. The used coolant represented a typical batch collected at EET Corporation’s antifreeze recycling facility in late 2005. The used coolant was pretreated using filtration and activated carbon. Concentrations of contaminants and other species were determined by ion chromatography and high performance liquid chromatography 共HPLC兲. Ethylene glycol content was determined by diffraction. Results and Discussion The production rate and separation efficiency of RO, NF, and ED processes were found to be dependent both on membrane characteristics and coolant chemistry. Table 6 presents NF/RO screening results with either coolant C1 共a conventional coolant兲, coolant C5 共a hybrid or HOAT coolant兲, or coolant C10 共also TABLE 5—Coolant Properties. Coolant No. C1 C2 C3 C4 C5 C6 C7 C8

C9 C10

Type Conventional 共EG兲 Conventional 共EG兲 HOAT 共EG兲 HOAT 共EG兲 HOAT 共EG兲 HOAT 共EG兲 OAT 共EG兲 OAT 共EG兲

HOAT 共PG兲 HOAT 共EG兲

Major Components Phosphate, Borate, Nitrate, Silicate Nitrite, Borate, Nitrate, Silicate Phosphate, Nitrite, Borate, Molybdate, Sebacic Acid Nitrite, Nitrate, Molybdate, Sebacic Acid Benzoic Acid, Borate, Nitrate, Silicate Sebacic Acid, Nitrate, Tolyltriazole, Phosphate 2-Ethylhexanoic Acid, Tolyltriazole 2-Ethylhexanoic Acid, Tolyltriazole, Molybdate, Sebacic Acid, Nitrite Phosphate, Nitrite, Molybdate, Borate, Sebacic Acid Sebacic Acid, Benzoic Acid, Molybdate, Nitrate

HUDGENS ET AL. ON MEMBRANE TECHNOLOGIES 33 TABLE 6—RO/NF membrane initial screening.

Membrane NF-A NF-C NF-B NF-D NF-E NF-F NF-L RO-G RO-G RO-H RO-H RO-I RO-J RO-K

Coolant 50 % EG Solution C10 共HOAT兲 50 % EG Solution C10 共HOAT兲 50 % EG Solution C10 共HOAT兲 40 % EG Solution C1 共conv.兲 40 % EG Solution C5 共HOAT兲 40 % EG Solution C5 共HOAT兲 40 % EG Solution C5 共HOAT兲 25 % EG Solution C10 共HOAT兲 40 % EG Solution C5 共HOAT兲 25 % EG Solution C10 共HOAT兲 40 % EG Solution C5 共HOAT兲 25 % EG Solution C10 共HOAT兲 25 % EG Solution C10 共HOAT兲 25 % EG Solution C10 共HOAT兲

Feed Pressure 共psi兲 300 300 300 300 300 300 300 300 600 300 600 300 300 300

Flux 共gfd兲 22 20 6 11 3 ⬍1 13 ⬍1 ⬍1 ⬍1 ⬍1 2 ⬍1 ⬍1

Conductivity Rejection 共%兲 78 % 73 % 85 % 74 % 52 % 75 % 44 % a

87 % a a

30 % a a

a

Insufficient product volume to determine rejection.

FIG. 4—Membrane flux for various NF and RO membranes with 40 % EG coolant solution.

FIG. 5—Conductivity rejection for various NF and RO membranes with 40 % EG coolant solution.


FIG. 6—NF membrane fluxes with eight different coolant solutions. a hybrid�. The table confirms that traditional brackish water RO membranes have very low productivities at the lower pressures ��300 psi� typically used in brackish water systems, with some having no productivity at all, even for relatively low recovery rates. In fact, all the RO membrane flux rates are too low to be considered practical. Even at the relatively high pressure �600 psi� studied with two RO membranes, the productivity was very low. Also, coolant chemistry had very little impact on productivity of the traditional RO membranes: production rates of both conventional and hybrid coolants were similar. In contrast, the NF membranes exhibited much better productivities. These are compared to those of the RO membranes in Fig. 4. As would be expected, the more open, lower salt rejecting NF membranes generally had higher production rates. Conductivity rejection for the eight different spiked coolants covered a wide range, from 40 % for an NF membrane to almost 90 % for a traditional RO membrane �although in several traditional RO cases, production rate was too low to obtain enough sample to measure conductivity!�. Figure 5 summarizes conductivity rejection with a hybrid coolant. While conductivity alone does not indicate coolant quality or correlate well with TDS content, it does provide an indication of the membrane separation efficiency. While membrane class �NF versus RO� was critically important, coolant chemistry also impacted separation characteristics, including for the NF membranes. Figure 6 summarizes average production rate and production rate ranges encompassing all eight coolants for the four NF membranes determined in the initial screening to be practical. Conductivity rejections for these are given in Fig. 7. A given coolant type resulted in as much as 38 % increase or decrease in membrane flux and up to 28 % increase/decrease in

FIG. 7—NF membrane conductivity rejections with eight different coolant solutions.

HUDGENS ET AL. ON MEMBRANE TECHNOLOGIES 35 TABLE 7—Comparison of EG and PG-based coolant separation properties with NF Membrane A.

Coolant C5 �HOAT� C9 �PG HOAT�

Initial Feed Conductivity ��S / cm� 6160 4520

Recovery �%� 23.9 15.9

Permeate Conductivity ��S / cm� 3399.9 2801.5

Water Flux �gfd� 20.1 13.3

Conductivity Rejection 48.6 % 38.6 %

conductivity removal. Furthermore, the specific membrane also played a key role, as membranes with similar traditional salt solution production rates and rejections �see Table 3� had substantially different production rates and conductivity rejections with the 40 % EG coolant solutions. For example, “looser” NF membrane NF-A had essentially the same or better conductivity removal as “tighter” membrane NF-C, with NF-A having much higher production rate; with standard salt solutions, these membranes typically have more similar separation properties. This indicates the importance of considering not only standard salt rejection and water flux, but also the differences in interaction of the ethylene glycol and other constituents of the coolant with the specific membrane used. Key differences between the NF membranes that have the potential to impact productivity and separation with EG-based coolants include the specific membrane polymers and membrane charge, membrane structure �i.e., thin-film composite versus asymmetric�, fouling resistance, and relative porosity. In this study, thin-film composite NF membranes based on aromatic polyamide with a more open pore structure performed better overall when considering both flux and removal on all types of coolants compared to both thin-film composite aromatic polyamide membranes with a tighter pore structure and asymmetric cellulose acetate NF membranes. In each case, the NF membrane fluxes with the 40 % EG solutions were lower than would be expected for similar concentration water solutions. This is in part the result of the higher viscosity of EG compared to water: the higher viscosity EG would be less efficiently transported through the membrane than water at the same pressure. In addition, it is expected that EG would be less absorbed by the membrane than water. The combination of these factors would result in a lower flux and a slight decrease of EG concentration �1 to 2 %� in the permeate product, which was observed in these studies. This behavior was also observed with propylene glycol �PG� based coolants, which had lower flux than those of water solutions and EG solutions. The PG coolants have even higher viscosities than EG and PG would be less absorbed by the membrane than EG. Comparison of fluxes for coolant C5 �hybrid, EG-based� and coolant C9 �hybrid, PG-based� is given in Table 7. Figure 8 better illustrates the effect of coolant type on nanofiltration flux. The flux for each membrane was better with the conventional coolant and less productive with the hybrid or OAT-based coolants. Rejection, shown in Fig. 9, was generally better for the OAT coolant and worse for the hybrid. These figures also show the substantial flux and conductivity rejection variability of each membrane with the different types of coolants. This trend was generally followed for all eight of the coolants studied for each

FIG. 8—NF membrane fluxes with three different coolant types.


FIG. 9—NF conductivity rejections with three different coolant types. membrane, as indicated in Figs. 10 and 11 for membranes NF-A and NF-D. These figures also show the flux and conductivity rejection of a typical pretreated used coolant; flux generally falls below that of the spiked coolants, while rejection is higher. Based on ion chromatograph and HPLC analyses, it was determined that the used coolant contained additives typical of a mix of conventional, hybrid, and OAT-based coolants; Table 8 compares the species in the virgin coolants to those in used coolant. It is informative to examine the individual species rejection, as shown in Figs. 12 and 13 for the “looser” membrane NF-A and “tighter” membrane NF-D with the used coolant. As would be expected, multivalent species such as sulfate, phosphate, and molybdate were rejected well by the membranes, while monovalent species such as chloride, nitrite, and nitrate were poorly removed. Glycol degradation acids, which would consist of primarily glycolic and formic acids, were marginally rejected. It is expected the larger, more polar glycolic acid would be better removed than the smaller formic acid. Silicate and borate, expected to be partially in the nonionized form at the feed pH �8� of the used coolant, was poorly removed. The lower rejection of these would be expected since both are relatively small molecular weight compounds and so separation would be based primarily on charge; both nonionized species passed through the membrane. The “tighter” membrane NF-D performed marginally better than membrane NF-A; however, it is important to note that neither membrane NF-A nor membrane NF-D produced a coolant that would meet specifications for reuse without further treatment. In particular, chloride and glycol degradation acids were too high in the permeate products, even at the low recoveries studied. Higher recoveries would result in even lower removal rates for these. For the typical coolant

FIG. 10—NF membrane fluxes with spiked virgin coolants and pretreated used coolants.


FIG. 11—NF conductivity rejections with spiked virgin coolants and pretreated used coolants. organic additive species, shown in Fig. 13, removals of sebacic acid �SA�, 2-ethylhexanoic acid �2-EH�, and benzoic acid were excellent. All of these species would be present predominately in the ionic form and so were rejected well by the charged NF membranes. Conversely, removal of tolytriazole was poor, possibly because of its expected monovalent charge at the feed pH. Examination of Figs. 12 and 13 in conjunction with Figs. 8 and 9 provide some insight into the flux and conductivity rejection behavior for the coolants. In general, the conventional coolants contain substantial amounts of silicate, tetraborate, nitrites and nitrates, and phosphates. While the phosphate is well removed, removal of the other species is only marginal and so overall conductivity rejection is low. Species that are not rejected do not contribute to the osmotic pressure difference and so do not reduce the pressure driving force across the membrane �see Eq 1�. As a result, flux with the conventional coolants is high. Hybrid and OAT coolants contain substantial amounts of organic acids that are very well rejected by the membranes. However, since these are rejected, there is a substantial osmotic pressure drop across the membrane and corresponding drop in pressure driving force according to Eq 1 and decreases in flux relative to those of the conventional coolants. As expected, the hybrid coolants, with a mixture of the conventional components, organic acids, and molybdate, have fluxes that correlate with organic acid TABLE 8—Spiked virgin coolants and pretreated used coolant analyses. Coolant Type ��40 % Solution�

Compound Total Glycol Degradation Acids �mg/L� Chloride �mg/L� Sodium Nitrite �mg/L� Sodium Nitrate �mg/L� Sodium Phosphate �mg/L� Sulfate �mg/L� Sodium Molybdate �mg/L� Sodium Tetraborate �mg/L� Sodium Silicate �mg/L� Tolyltriazole �mg/L� Sebacic Acid �mg/L� 2-Ethylhexanoic Acid �mg/L� Benzoic Acid �mg/L� % EG pH

C1 C2 C3 C4 C5 C6 �Conventional� �Conventional� �HOAT� �HOAT� �HOAT� �HOAT� 7 10 9 33 11 173 848 2988 1404 1178 782 464

180 1731 469 1430 865 455 243

175 1392 452 3311 1382 684 799 441 480 493

179 1661 767 14 1448 628 479 403 161 580

179 491 2601 1420

C7 �OAT� 46

C8 �OAT� 16

170

221

1307 786 1408

234 725 9

1415

1415 829

4710 512 1178 7506

821 11 622

38 9.8

37 9.9

5 37 10.1

37 9.8

9222 39 7.9

39 8.0

39 8.9

17 833 793 12 767 37 8.5

Pretreated Used Coolant 994 73 178 1014 1523 411 293 553 120 22 861 1871 1972 37 8.2


FIG. 12—Inorganic species rejection by NF membranes for pretreated used coolant.

FIG. 13—Organic species rejection by NF membranes for pretreated used coolant.

FIG. 14—Electrodialysis system production rates with eight different coolant solutions.


FIG. 15—Electrodialysis system conductivity removal with eight different coolant solutions. content: those containing higher organic acid concentrations �as well as molybdate, which is highly rejected� have lower fluxes and higher conductivity rejections while those with higher content of conventional coolant species �silicate, borate, nitrite, nitrate� have higher flux and lower conductivity rejections. The lowering of pressure driving force due to high osmotic pressure difference across the membrane also accounts for the low fluxes of traditional RO membranes: these tight membranes reject most species, resulting in a relatively high osmotic pressure difference across the membrane and correspondingly low flux. Similar trends in flux and rejection characteristics for the individual inorganic and organic species for spiked virgin coolant types �traditional, OAT, and hybrid� were observed with the NF membranes, confirming the separation characteristics of the individual species in the pretreated used coolant. As with the NF membranes, both IX membrane types �anion and cation exchange membrane pair� and coolant type had substantial effects on productivity of the ED process. Figure 14 summarizes average production rate and ranges for the four different ion exchange membranes studied with the eight spiked coolant solutions. Conductivity removal is summarized in Fig. 15. Conductivity removals were substantially higher than those of the NF membranes since batchwise ED operation allows the feed solution to be processed until either the target conductivity is achieved or no further reductions in conductivity are possible. In most cases, feed conductivities �100 �S / cm were possible with most coolant/membrane combinations. However, membrane set IX_ D, heterogeneous ion exchange membranes, had a wider range of final conductivities; in particular, conductivity reduction with some of the hybrid coolants was only marginal. For the homogeneous membrane sets IX_ A, IX_ B, and IX_ C, removals were more consistent,

FIG. 16—Electrodialysis system production rates with three different coolant types.


FIG. 17—Electrodialysis system conductivity removal with three different coolant types. with a minimal 96 % removal rate. In all cases, since the contaminants are transported through the IX membranes as opposed to the feed solution as in the NF process, recoveries were high at �98 %, with typically �2 % EG loss into the brine stream. Figures 16 and 17 provide productivity and conductivity removal for the four different IX membrane sets for three coolant types �conventional, hybrid, and OAT�. In general, productivity was higher with the conventional coolants, followed by the hybrid and the OAT coolants. Conductivity removal was essentially the same for each coolant type and for each membrane. In general, the higher the exchange capacity and lower the membrane resistance of the anion exchange membrane �as with IX_ B�, the higher the productivity with the conventional coolant. However, these had no clear impact on the hybrid and OAT-based coolants productivity. Figures 18 and 19 compare separation characteristics of the three coolant types with that of used coolant with membrane set IX_ C, a fouling resistant membrane. Production rate was similar to that of the OAT coolant, with excellent final conductivity removal. Figures 20 and 21 provide percent removal of specific inorganic and organic species from the used coolant with characteristics that were shown in Table 8 with membrane set IX_ C. Glycol degradation acids, chloride, sulfate, nitrite, nitrate, phosphate, and molybdate were essentially completely removed over the course of the run. Tetraborate and silicate, which were only partially ionized at the feed pH of the used coolant �8�, were removed to a lesser extent, as would be expected since nonionic species are not significantly transported through the IX membranes. Tolyltriazole, sebacic acid, and benzoic acid, all

FIG. 18—Electrodialysis system production rates with spiked virgin coolants and pretreated used coolants.


FIG. 19—Electrodialysis system conductivity removal with spiked virgin coolants and pretreated used coolants. mostly in the ionized form, were also almost completely removed. Removal of 2-ethylhexanoic acid was less than the other organic acids, possibly due to the side chain branching of the compound, resulting in a lower transport number in the IX membrane compared to the divalent sebacic acid and the smaller tolyltriazole and benzoic acid. Comparison of Figs. 18 and 19 with Figs. 12 and 13 shows that the ED process is capable of reducing both contaminants and the residual inhibitors/additives to a greater extent than the NF process, even at high recoveries. However, the ED product does have a slight color, usually a visible yellow tint. While many of the dyes are ionic, these tend not to be completely transported across the IX membranes. Also, as with the NF studies, ED removals of individual inorganic and organic species in virgin spiked coolants followed the same trends as the individual species removals in the pretreated used coolant. As discussed above, a single process usually falls short of producing an acceptable recycled product, particularly if the goal is to produce coolant meeting virgin specifications. While the ED process alone can nearly meet all requirements, the product does contain a slight color. Conversely, the NF process is better at removing color. Permeate from the NF process is water white, while monovalent species removal is usually unacceptable. However, an integrated approach combining these two processes utilizes the advantages of each. NF produces a permeate product that is water white with reduced conductivity and contaminants, and the ED process treatment of the permeate product further reduces the conductivity/ contaminants to virgin specifications. Since not all species need to be removed by the NF process, a lower

FIG. 20—Inorganic species removal by electrodialysis system for pretreated used coolant.


FIG. 21—Organic species removal by electrodialysis system for pretreated used coolant. rejecting, higher flux membrane may be used to lower system capital and operating cost. In addition, ED process production rate also increases since part of the species of concern has been removed by NF. Table 9 shows results from a run simulating this process using NF_ A and membrane set IX_ C. The NF subprocess partially reduced the multivalent species and a fraction of the organic acids, and the ED subprocess removed the remaining species to near virgin ethylene glycol specifications. Due to the reduced feed species, ED system productivity increased by 30 %. Figures 12, 13, 20, and 21 and Table 9 show the individual contaminant and additive species removal efficiencies of NF, RO, and an integrated process with the used coolant; as indicated above, the used coolant represents a mix of conventional, OAT, and hybrid coolants. In general, NF removals of chlorides and conventional additive species were low. However, if the chloride levels met specifications, the presence of the conventional additives would not be a great issue if the recycled coolant reinhibition package consisted of compatible conventional additives. Similarly, the presence of residual organic inhibitors in the NF or ED recycled product would not have a great impact on a recycled product reformulated with compatible OAT-based additives. However, some incompatibilities might exist between some conventional and OAT-based additives. For example, high silicate levels may not be desirable in certain formulations of TABLE 9—Integrated process separation characteristics with pretreated used coolant. Integrated Process Test Samples

Compound Total Glycol Degradation Acids �mg/L� Chloride �mg/L� Sodium Nitrite �mg/L� Sodium Nitrate �mg/L� Sodium Phosphate �mg/L� Sulfate �mg/L� Sodium Molybdate �mg/L� Sodium Tetraborate �mg/L� Sodium Silicate �mg/L� Tolyltriazole �mg/L� Sebacic Acid �mg/L� 2-Ethylhexanoic Acid �mg/L� Benzoic Acid �mg/L� % EG by Brix pH

ED Used Coolant Pretreated NF Permeate ED Diluate Concentrate Overall Feed Used Coolant �Product� NF Concentrate �Product� �Brine� Removal �%� 100.0 % 1088 994 1018 1030 1 190 50 190 1171 1678 197 315 631 121 207 2356 2132 2621 37 8.1

73 178 1014 1523 411 293 553 120 22 861 1871 1972 37 8.2

73 184 1088 393 109 61 514 84 17 0 957 1891 37 8.1

12 47 365 10328 2384 1649 699 184 0 7075 6178 2209 41 8.4

1 1 1 1 1 1 142 67 0 0 0 0 36 5.8

56 10 0 134 112 33 96 20 0 0 184 504 �1 8.4

99.0 99.7 100.0 99.9 99.7 99.8 77.5 44.5 100.0 100.0 100.0 100.0

% % % % % % % % % % % %


OAT-based coolants, in which case the silicate levels must be reduced substantially more, with corresponding drop in process productivity. Ideally, each coolant could be characterized and processed to remove corrosive species and degradation acids to meet corrosive species specifications, with further processing limited only to the extent necessary to reduce species incompatible with the planned reformulation additives. However, due to the expense and lag time of the analytical methods, a more practical alternative is to use operating experience with NF, ED, or NF/ED hybrid processes, knowledge of the robustness of the planned reformulation package, and gross measures such as conductivity to guide extent of processing. Establishment of levels 共such as conductivity兲 at which corrosive species meet specifications and inhibitor additives are acceptable for reformulation could greatly improve process productivity and overall recycling economics. Conclusions Both coolant chemistry and membrane type have been found to tremendously impact productivity and extent of separation for both pressure-based membrane 共RO/NF兲 and ion exchange-based membrane systems 共ED兲. Fluxes of traditional, high salt rejection RO membranes have been verified to be impractical, despite claims by many recyclers that they use RO. NF membrane productivities are acceptable, but conductivity and contaminant removal range from only marginal to good, with none of the studied NF membranes capable alone of producing recycled coolant meeting virgin coolant specifications. While the removals of most organic acids and divalent species were excellent, removal of monovalent species such as chlorides and nonionized species such as silicates were poor. The ED process was capable of reducing conductivity to very low levels and well as removing individual contaminants and other ionic components, although some slight color remained. The productivity of the ED was greatly improved and the product solution was water white when it was combined with an NF process, with ED treating the NF permeate. Ideally, the degree of removal of the residual inhibitors could be customized for each individual batch of used coolant based on the planned reinhibition additive and laboratory analyses for each species present in the coolant. Practically, the robustness of the type of reinhibition additive to be used and conductivity can serve to guide the extent of deionization required. References 关1兴关2兴关3兴关4兴关5兴关6兴关7兴关8兴关9兴

Coburn, C. B., Hudgens, R. D., and Mullen, M. D., “Environmental Effects of Engine Coolant Additives,” SAE Technical Papers, Engine Coolants and Cooling Systems, SP-1456, p. 87, International Congress and Exposition, Detroit Michigan, 1–4 March, 1999. Leadership and Innovation—Designing the Future—Newsweek, 16 May, 2005. Frye, D. K., Chan, K., and Pourhassanian, C., “Overview of Used Antifreeze and Industrial Glycol Recycling by Vacuum Distillation,” Engine Coolant Testing: Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, p. 236. Haddock, M. E. and Eaton, E. R., “Recycling Used Engine Coolant Using High-Volume Stationary Equipment,” Engine Cooling Testing, Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 251–260. Kugn, W. and Eaton, E. R., “Development of Mobile, On-Site Engine Coolant Recycling Utilizing Reverse-Osmosis Technology,” Engine Coolant Testing, Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 261–269. Kurio, N., Shirahase, T., and Oda, H., “Development of Coolant Recycling Technology,” JSAE Rev., Vol. 16, 1995, p. 61. Jehle, W., Staneff, T., Steinwandel, J., and Wagner, B., “Work-up of Spent Coolant 共Ethylene Glycol兲 by a Membrane Hybrid Process,” Chem.-Ing.-Tech., Vol. 66, 1994, p. 671. Richardson, R. C., “A Multi-Stage Process for Used Antifreeze/Coolant Purification,” Engine Coolant Testing: Third Volume, ASTM STP 1192, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1993, pp. 258–275. Hercamp, R. D. and Remiasz, R. A., “Coolant Maintenance and Extension of Coolant Life for Light Duty Vehicles,” ASTM Special Technical Publication 1192, ASTM International, West Conshohocken, PA, 1993, p. 248.


关10兴关11兴关12兴


Huff, J. R., “Using Reverse Osmosis to Recycle Engine Coolant,” SAE Technical Paper Series, 921635, SAE, Warrendale, PA, 1992. McCosh, D., “All the Ways to Recycle Antifreeze,” Popular Science, Vol. 241, 36, 1992. Gavaskar, A. R., Olfenbuttel, R. F., Jones, J. A., and Webb, P. R., “Automotive and Heavy-Duty Engine Coolant Recycling by Filtration,” EPA Report, EPA/600/2-91/066 共PB92-126804兲, Oct. 1991. Penray Technical Bulletin 99.001, The Penray Companies, Elk Grove Village, IL, www.penray.com, 1999. Antifreeze Recycling User’s Guide—U.S. Army Tank-automotive and Armaments Command Research, Development, and Engineering Center, Warren, MI 48397-5000, March 2005. Ho, W. S., and Sirkar, K. K., Eds., “Reverse Osmosis,” Membrane Handbook, Van Nostrand Reinhold, NY, 1992. Preliminary Data Summary, Airport Deicing Operations, U.S. EPA, EPA-821-R-00-016 共August 2000兲. Strathmann, H., Ion-Exchange Membrane Separation Processes, Elsevier Science, 2004.


Bo Yang,1 Filipe J. Marinho,1 and Aleksei V. Gershun1

New Electrochemical Methods for the Evaluation of Localized Corrosion in Engine Coolants ABSTRACT: Due to the need of increasing energy efficiency, reducing pollution and lessening dependency on petroleum, vehicles using more advanced propulsion technologies such as fuel cell and hybrid electric 共e.g., gasoline-electric or diesel-electric hybrid兲 power are being developed constantly. At the same time, extensive development efforts are being devoted to research aiming to increase the use of lighter metals such as magnesium alloys in today’s engines. New engine coolants are often required to meet many of these new developments and the associated changes in cooling system requirements. Since corrosion protection is one of the key performance parameters for engine coolants, new and more effective corrosion measurement methods are useful for evaluating old and developing new coolants to meet the needs of new cooling systems or having improved corrosion protection performance, or both. Particularly, new electrochemical methods capable of more reliable, quantitative, and fast 共ideally, real-time兲 measurements of localized corrosion such as pitting, crevice, and under-deposit corrosion, and corrosion under heat rejecting conditions are highly desired. Existing ASTM test methods for engine coolants either rely on inspection of the sample after a relatively long exposure period to determine the extent of localized attack or do not yield results directly related to localized corrosion. In this paper, coupled multi-electrode sensors test and simulated localized corrosion cell technique are compared and discussed to gain new insight for facilitating the development of more effective inhibited coolants. KEYWORDS: antifreeze/coolant, localized, pitting, crevice, galvanic corrosion, aluminum

Introduction To satisfy the customer’s desire for more power, comfort, and safety, and to meet the need of lower fuel consumption and reduced exhaust emission, new vehicle technologies are being developed constantly. Extensive efforts are being devoted to research to develop new and more environmentally friendly propulsion technologies, such as fuel cell and petroleum-hybrid electric power, and new material technologies, and to explore methods to increase the use of lighter metals or materials, or both. Since corrosion protection is one of the key performance parameters for engine coolants, new and more effective corrosion measurement methods are useful for developing new coolants to satisfy the needs of the new cooling systems or to improve corrosion protection performance, or both. It is recognized that the majority of corrosion phenomena that occurs in engineering systems is nonuniform or localized 关1–4兴. In vehicle engine cooling systems pitting, crevice, under-deposit corrosion, galvanic corrosion, and erosion-corrosion 共or cavitation兲 are some of the most commonly observed forms of localized corrosion. Existing industry test methods usually rely on inspection of the sample after a relatively long exposure period to determine the extent of localized attack or used tests which do not yield results directly related to localized corrosion 关5–9兴. One electrochemical method is used by many to determine the repassivation potential of metal as a measure of relative susceptibility to pitting corrosion in engine coolants 关10兴. However, this method is conducted at room temperature and does not provide a quantitative localized corrosion rate. Thus, methods capable of more reliable, quantitative, and fast 共ideally, real-time兲 measurements of localized corrosion such as pitting, crevice, and under-deposit corrosion, and corrosion under heat rejecting conditions are highly desirable for developing new coolants with improved corrosion protection performance. Since the 1990s, significant advancements have been made in developing more effective, reliable and Manuscript received February 22, 2006; accepted for publication October 4, 2006; published online November 2006. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Honeywell, Danbury, CT 06810 Copyright © 2006 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

45


quantitative measurement techniques for localized corrosion. In the last 10 to 15 years, a number of newly developed techniques such as electrochemical noise, scanning vibrating 共or reference兲 electrode, zeroresistance ammeter 共ZRA兲-based occluded cell techniques, differential flow cells, and coupled multielectrode sensors are being used increasingly to measure the rates of localized corrosion 关11–20兴. Particularly, two of the methods, namely the differential flow cell 共or more appropriately the simulated localized corrosion cell兲 and coupled multi-electrode sensors, appear to be most promising for use as real-time, reliable, and quantitative measurements of rates of localized corrosion such as pitting, crevice, underdeposit corrosion, and galvanic corrosion. The coupled multi-electrode sensor, also called the wire-beam electrode method, was developed for measuring localized corrosion and other heterogeneous electrochemical processes by Tan 关12,13兴. The multi-electrode sensor probes are usually fabricated from an array of nominally identical metal wire electrodes 共typically 1 mm in diameter兲 embedded in insulating material 共e.g., an epoxy resin兲. The surface of one end of the wire electrodes is exposed to the test solution. The other end of the wire electrodes are coupled electrically via zero-resistance ammeters or an equivalent sensing instrument. Localized corrosion can be estimated by measuring the coupling current flowing into or out of the selected wire electrode. A further refinement was introduced by Yang and coworkers by incorporating the use of statistical parameters 共i.e., standard deviation and mean values兲 of the measured coupling current distribution of the multielectrode probe to calculate the maximum penetration current as a representation of localized corrosion rate 关14,15兴. The coupled multi-electrode sensors have been used as a real-time localized corrosion monitor for carbon steel, stainless steels, aluminum, copper, and several nickel-based alloys in various environments, including cooling water, simulated sea water, under salt deposits in air, concentrated chloride solutions, and process streams of chemical plants at elevated temperatures 关14兴. However, the localized corrosion rates determined by the coupled multi-electrode sensor probes have not been verified by independent reliable measurements on the same electrodes. In addition, similar to scanning vibrating electrode and ZRA-based occluded cell techniques, the accuracy of the localized corrosion rate obtained depends on the reliability of the assumption that there is only metal dissolution current associated with the anodic reaction on the wire electrode having the highest coupled anodic current 关1–4兴. The differential flow cell 共or more appropriately simulated localized corrosion cell兲 technique was developed recently for the real-time, on-line, and reliable measurement of localized corrosion rates of metals in industrial water systems 关2,16,18兴. In this technique, a unique combination of linear polarization resistance 共LPR兲 and zero resistance ammeter measurements 共ZRA兲 is used to obtain the rate of localized corrosion 共such as pitting, crevice/under-deposit, microbiologically influenced corrosion兲 for metals including carbon steel and admiralty brass in aqueous solutions 关19兴. The measurements are carried out in an electrolytic cell simulating the essential features of the propagating localized corrosion conditions for a given system’s conditions 共e.g., a differential flow cell is used to simulate the localized corrosion conditions in cooling water systems兲. The simulated localized corrosion cell contains one or more anodes 共or preferential attack areas兲 with a small exposed surface area and one cathode 共or nonpreferential attack area兲 with a much larger exposed surface area. The anodes and the cathode of the cell are normally coupled electrically via the ZRA to simulate the localized corrosion conditions. The ZRA measurements are used to provide the component of the localized corrosion current that results from the galvanic cell interaction between the large cathode and the small anodes. The LPR measurements on the anodes provide the component of the localized corrosion current that results from the contributions of cathodic reactions 共e.g., oxygen reduction, hydrogen evolution inside the pits, etc.兲 occurring on the anodes toward their own corrosion. The cell used in this method simulates faithfully the localized corrosion conditions under the studied conditions. Based on this technique, a new localized corrosion monitor 共LCM兲 capable of monitoring both localized and general corrosion rate in real-time was developed. It has been used extensively in laboratory studies and field applications. Good agreement was obtained between the corrosion rates determined by using a calibrated microscope to measure the penetration depth, and the time average corrosion rates determined electrochemically from the LCM on the same electrode samples under various laboratory test conditions 关16兴. Under properly chosen simulation conditions, the corrosion rate results 共both localized and general rates兲 obtained from the LCM in the field applications were also in agreement with independent physical measurement 共i.e., coupons兲 and heat exchanger inspection 共e.g., ultrasonic inspection兲 or operation results 共e.g., service life or leakage frequency兲 obtained under comparable conditions 关1–4兴. The LCM has been used successfully in many industrial cooling water systems, including

YANG ET AL. ON CORROSION IN ENGINE COOLANTS 47

open-recirculating and closed-loop cooling water systems in petroleum refineries, nuclear and fossil fuel power plants, pulp and paper mills, food processing plants, and chemical processing industry plants. The LCM was demonstrated to be very useful for localized corrosion monitoring and for the performancebased optimization and control of chemical treatments 共i.e., corrosion inhibitors, scale inhibitors, and biocides兲 in these systems. In this paper, the coupled multi-electrode sensors and the simulated localized corrosion cell methods, as well as conventional electrochemical and mass loss methods, are used to study corrosion of aluminum and other alloys in engine coolants. Particularly, localized corrosion results related to pitting and galvanic corrosion obtained from the two methods, i.e., coupled multi-electrode sensors and simulated localized corrosion cell techniques, are compared and discussed to gain new insight for facilitating the development of more effective inhibited engine coolants.

Experimental Solutions The base test solutions were prepared by mixing commercially available coolants with deionized water to yield a coolant concentration of either 25 vol. % or 50 vol. %. Aqueous solution of 40 % 共w/v兲 KF from Spectrum Chemical Mfg. Corp. was used as the source of fluoride. Other components of the test solution were sodium chloride 共ACS grade兲 and commercial products supplied by the producers. NanoCorr Coupled Multi-electrode Sensor (CMS) Tests A Corr Instrumnets NanoCorr Coupled Multi-electrode Sensor Analyzer with CorrVisual Software, Version 1.0.3 was used to determine the localized corrosion rates of cast aluminum in the test solution. In this study, a 25-electrode sensor array probe made of either 25 cast aluminum 共SAE 329, UNS A23190兲 square wire having an exposed surface area of 1 mm2 was used. The 25 wire electrodes sealed in epoxy and spaced uniformly in a 1.2 by 1.2 cm matrix array were connected electrically via the NanoCorr Coupled Multi-electrode instrument. The coupled multi-electrode probe simulates the corrosion conditions of a conventional one-piece electrode surface having an exposed surface area of about 1.4 cm2. One can obtain a localized corrosion rate as a function of time from the probe by measuring the coupling current from each individual electrode in the probe and performing statistical analysis of the measured data. The localized corrosion rate 共or maximum penetration rate, hmax兲 is calculated by the data acquisition software according to the following equation: hmax = 共2.5␴ + Imean兲We/共F␳A兲 where ␴ and Imean are the standard deviation and the mean of one set of coupled currents from the multi-electrode probe; We is the equivalent weight of the material of the wire electrodes; F is the Faraday constant; ␳ is the density of the electrode; and A is the surface area of a wire electrode. In this study, a sampling rate of 30 s per set of data was used. A Pyrex glass beaker holding 500 mL test solution was used as the test cell. The coupled multielectrode array sensor probe, a Ag/ AgCl 共3M KCl兲 reference electrode placed in a Lugin probe with the opening close to the multi-electrode sensor probe, and two temperature sensor probes 共i.e., a thermal couple and a resistance temperature detector with stainless steel sheath兲 are mounted on a Teflon cell cover and immersed in the solution in the beaker. The Teflon cover was used to minimize solution loss during the experiment and used to fix the position of the test probes in the cell. A microprocessor control hot plate was used to heat the solution to the desired temperature during the test. A Teflon coated magnetic stirring bar was also used to agitate the solution during the test. The solution was exposed to the air during the test. In the test designed to study galvanic corrosion, the cathode 共i.e., a nickel plated copper, 1.1 cm2 surface area兲 sealed in an EG&G flat electrode Teflon holder by a silicone O-ring was also inserted into the cell via a Teflon cell cover. The cathode was connected to the coupling point of the NanoCorr CMS analyzer to complete the galvanic coupling connection to the electrodes of the multi-electrode sensor probe. The distance between the CMS probe and the cathode surface was about 1 cm.


Simulated Localized Corrosion Cell (SLCC) Tests The aluminum alloy anode and cathode used in the simulated localized corrosion cell tests were sealed in epoxy. The aluminum electrodes were cast aluminum cut from coolant channels of an engine block or a power electronic device case of a gasoline-electric hybrid powered vehicle 共0.45 cm2兲. In some tests, a cathode 共i.e., a nickel plated copper, 1.1 cm2 surface area cut from the heat sink of the power electronic device of the hybrid vehicle兲 sealed in an EG&G flat electrode Teflon holder by a silicone O-ring was used. A Pyrex glass beaker holding 500 mL test solution as the test cell and a platinum wire as the counter electrode were also used in the test. The distance between the anode and cathode surface is about 1 cm. Other test equipment is the same as those used in the CMS test. Electrochemical measurements were conducted using a commercial potentiostat manufactured by Gamry Instrument. The localized corrosion current density 共Ilocalized corrosion兲 of the anode is calculated according to the following equation 关2,16兴. Ilocalized

corrosion = IZRA + ILPR

where IZRA presents the galvanic coupling current density measured between the anode and the cathode from the simulated localized corrosion cell 共SLCC兲; ILPR represents the LPR 共or linear polarization resistance兲 corrosion current density measured from the anode alone when the anode is temporarily disconnected from the cathode. A Stern-Geary constant for aluminum alloys used to convert the polarization resistance to LPR corrosion current density was either calculated based on anodic and cathodic Tafel slopes measured at the end of the tests on the anodes or assumed to be 49.9 mV according to Ref. 关21兴. The localized corrosion rate of the anode is calculated from the localized corrosion current density, Faraday constant, equivalent weight, and density of the anode. ASTM D 1384 and D 4340 Corrosion Tests Tests were conducted in accordance with ASTM Test Method for Corrosion Test for Engine Coolants in Glassware 共D 1384兲 and Standard Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions 共D 4340兲, respectively. A high lead solder alloy L50113 sample containing 97 % lead, 2.5 % tin, and 0.3 % silver was also used in the ASTM D 1384 test. Conventional Electrochemical Tests Tests were conducted either using a modified GM 9066-P Method 关21兴 or in the CMS test cell, using a commercial potentiostat. The working electrodes were aluminum alloy samples cut from an engine block coolant channel. The counter electrode was a platinum wire. An Ag-AgCl 共3M KCl兲 reference electrode placed in a Lugin probe with the opening close to the working electrode was also used in the test. No mechanical stirring of the solution was used in the test. Results and Discussion ASTM D 1384 and D 4340 Test Results Test results obtained according to ASTM Standard Test Methods D 1384 and D 4340 specifications for two organic acid technology 共OAT兲 coolants with and without corrosive ion contamination 共fluoride兲 and a corrosion inhibition additive are shown in Tables 1 and 2. As shown in the tables, the corrosion protection performance of the two OAT coolants were both very good, yielding corrosion mass loss values well below the acceptable limits specified in ASTM Standard D 3306 for the various metal test samples. In the presence of fluoride ions 共a corrosive species that can be introduced into the engine coolant by the dissolution from the excessive amounts of the flux residue accumulated inside the heat exchangers manufactured by the controlled atmosphere brazing process兲, corrosion of cast aluminum specimen was increased substantially in both OAT coolant formulations, yielding average mass loss values obtained under D 1384 conditions approaching the limits specified by ASTM D 3306. The corrosion of Sn30A solder was also increased in OAT coolant B by the presence of 400 mg/ L fluoride, yielding an average mass loss value approaching the limit specified by ASTM D 3306. The corrosion of other metals under D

YANG ET AL. ON CORROSION IN ENGINE COOLANTS 49 TABLE 1—ASTM Standard Method D 1384 test results for OAT coolants—average mass loss, mg/specimen. Organic Acid Technology 共OAT兲 Coolant Concentrate OAT Coolant A OAT Coolant B OAT Coolant A with 400 mg/ L fluoride OAT Coolant B with 400 mg/ L fluoride OAT Coolant A with 400 mg/ L fluoride and inhibitive additive ASTM D 3306 Limits Time Averaged Uniform Corrosion Rates Corresponding to D 3306 Limitsa

High Lead Solder 108 196 91.6 150 13.4

Copper 0.6 1.4 −2.0 −1.1 −1.8

Sn30A Solder 1.3 1.6 1.8 28.5 6.4

Brass 1.2 1.3 −0.9 −1.5 −1.9

Carbon Steel 0.4 0.0 −0.5 −1.6 −1.8

Cast Iron −1.2 0.5 0.3 −2.0 −1.0

Cast Aluminum 3.3 2.8 26.6 27.2 −6.0

Report NA

10 max 10

30 max 29

10 max 11

10 max 12

10 max 12

30 max 95

Note: Negative value indicates the test specimen had weight 共mass兲 gain after the test. NA= Not available. a The unit for corrosion rate is ␮m / year. High lead solder is Alloy L50113, 97 % lead, 2.5 % tin, 0.5 % silver.

1384 test conditions was not affected by the presence of fluoride contamination. Visual inspection of the metal samples after the tests indicated that pitting and crevice corrosion under the washer connections occurred, especially for the cast aluminum samples exposed to the coolants containing fluoride ions. The addition of the coolant inhibitive additive was very effective for the improvement of the corrosion protection performance of OAT coolant formulation in the presence of fluoride contamination, as shown in Table 1, and as a result, the corrosive effect of the fluoride ions towards cast aluminum was eliminated by the addition of very small amounts of the additive to OAT-type coolant formulations. No degradation of corrosion protection performance of other metals used in the D 1384 tests was observed due to the addition of the coolant corrosion inhibition additive. It should be noted that while the ASTM D 1384 and D 4340 standard tests are very useful as a tool for evaluation of corrosion protection performance of coolants, and they are required corrosion tests for qualifying antifreeze for use in vehicles by vehicle manufacturers, the corrosion results are the averaged values for the exposed sample surface area and the test time periods. Thus, the mass loss results do not provide direct information about the extent of localized corrosion attack under the test conditions. One may use visual observation or tools such as a calibrated microscope to obtain information related to the extent of localized corrosion on the test samples. However, obtaining quantitative localized corrosion rate data using these methods is tedious and labor intensive. It should also be noted that the 30 mg mass loss limit for cast aluminum in the D 1384 test corresponds to a calculated time average uniform corrosion rate of only 95 ␮m / year. The cast aluminum corrosion rate limit of 1.0 mg/ cm2 / week in the D 4340 test corresponds to a calculated time average uniform corrosion rate of 193 ␮m / year. Conventional Electrochemical Test Results—Aluminum Engine Block Sections Corrosion test results obtained using conventional electrochemical methods such as polarization resistance measurements and Tafel extrapolation of the anodic polarization curves are shown in Tables 3 and 4. The tests were conducted using aluminum alloy samples cut from sections of an automotive engine block coolant channel surface as electrodes in OAT coolants A and B, without the addition of any corrosive ion. The electrodes used in obtaining the results given in Table 3 were sealed in a high-temperature epoxy except for a small section of the original coolant channel surface were exposed to the test coolants. The engine block coolant channel surface has both rough and smooth areas. To determine if the two different TABLE 2—ASTM Standard Test Method D 4340 results for OAT coolants. Organic Acid Technology 共OAT兲 Coolant Concen- Cast Aluminum 共UNS A03190兲 Average Corrosion trate Mass Loss Rate, mg/ cm2 / week OAT Coolant A −0.18 OAT Coolant B 0.40 ASTM D 3306 Limit 1.0 max Time Averaged Uniform Corrosion Rate 193 Corresponding to D 3306 Limita Note: The negative value indicated that the specimens had mass gain after the tests. a The unit for corrosion rate is ␮m / year.

50 ENGINE COOLANT TECHNOLOGY TABLE 3—Aluminum engine block surface area average corrosion rates in OAT coolants.

50 vol. % OAT Coolant A, Solution Temperature= Electrode Surface Temperature= 88± 1 ° C Smooth Surface Polarization Resistance E-corr Time at 88° C LPR CorrRate CorrRateគTafelគanodic 共hours兲共V / AgAgCl兲共Ohm*cm2兲共␮m / y兲共␮m / y兲 1 −0.610 6272 86.9 2 −0.574 7064 77.2 2.2 −0.573 73.9 Rough Surface Time at 88° C E-corr Polarization Resistance LPR CorrRate CorrRateគTafelគanodic 共hours兲共V / AgAgCl兲共␮m / y兲共␮m / y兲共Ohm*cm2兲 1 −0.811 4390 124 2 −0.679 5624 97.0 2.2 −0.651 88.4 50 vol. % OAT Coolant B, Solution Temperature= Electrode Surface Temperature= 88± 1 ° C Smooth Surface Time at 88° C E-corr Polarization Resistance LPR CorrRate CorrRateគTafelគanodic 共hours兲共V / AgAgCl兲共␮m / y兲共␮m / y兲共Ohm*cm2兲 1 −0.477 12379 44.2 2 −0.454 9389 58.2 2.2 −0.461 48 Rough Surface Time at 88° C E-corr Polarization Resistance LPR CorrRate CorrRateគTafelគanodic 共hours兲共V / AgAgCl兲共␮m / y兲共␮m / y兲共Ohm*cm2兲 1 −0.636 5996 91.2 2 −0.652 6598 82.8 2.2 −0.658 70.4 Note: Stern-Geary Coefficient of 49.90 mV used to convert polarization resistance to LPR corrosion rate.

surface sections would exhibit different corrosion behavior in the test coolants, electrodes cut from both surface sections were used. The electrode used in obtaining the results listed in Table 4 was an aluminum alloy plate section cut from the same engine block. It was polished to 600 grit sand paper and degreased in acetone before installation into a test cell. The results show that good corrosion protection performance for the aluminum samples was obtained in both coolants. The surface area average corrosion rates obtained decrease as immersion time increases. As expected, the corrosion rates also increase when temperature increases. The results in Table 3 also suggest that the corrosion rates obtained from the rough surface sections tend to be slightly higher than those obtained from the smooth surface sections. In general, the corrosion rates obtained from both coolant formulations were largely the same, especially in view of the fact that different sections of the engine block surface were used to make the electrodes. The differences observed are most likely within the experimental errors of the test methods used. Figure 1 shows the anodic polarization curve measurement of the sample of polished aluminum engine block in 50 vol. % OAT coolant B under conditions similar to heat rejecting engine block operating conditions 共e.g., similar to those specified in GM 9066-P兲. The general features of the polarization curve are similar to those obtained on cast aluminum 共UNS A03190兲 TABLE 4—Aluminum engine block surface area average corrosion rates in OAT coolant B.

50 vol. % OAT Coolant B, Electrode Surface Temperature= 137± 4 ° C 600 grit Sand Paper Polished Surface Polarization Resistance LPR CorrRate CorrRateគTafelគanodic Surface T Immersion Time E-corr 共V / AgAgCl兲共Ohm*cm2兲共␮m / y兲共␮m / y兲共hours兲共°C兲 6.0 −0.810 2015 270.5 136.8 22.0 −0.075 17104 3.18 21.0 28.0 −0.762 3160 172.5 133.6 28.2 −0.768 154 133.8 Note: Test conditions similar to those specified in GM 9066-P. Stern-Geary Coefficient of 49.90 mV used to convert polarization resistance to LPR corrosion rate.


FIG. 1—Anodic polarization curve of polished sample of aluminum engine block sample in 50 vol. % OAT coolant B under conditions simulating heat-rejecting surface. under comparable conditions. The anodic current shows a rapid increase with increasing anodic potential around 0.5V / AgAgCl 共3M KCl兲. This potential may be considered as the pitting potential of the aluminum sample under the test conditions. It should be noted that although the conventional electrochemical tests such as polarization resistance and polarization curve measurements may be used to obtain corrosion protection performance of a test coolant much quicker than various mass loss based corrosion evaluation methods, the corrosion rates obtained were averaged over the whole exposed surface area. Information related to localized corrosion, such as pitting potential, obtained from the conventional electrochemical methods, is largely qualitative, and cannot be used to obtain a reliable localized corrosion rate under the test conditions. Galvanic Interaction of Different Aluminum Engine Block Sections—SLCC Results Since the rough surface sections and the smooth surface sections are physically connected in the same engine block, galvanic interactions among these surface sections affecting the corrosion processes are expected. The simulated localized corrosion cell 共SLCC兲 is well suited to quantify the galvanic interactions and their effects on corrosion. Figures 2 and 3 show the results of using the SLCC method to study the galvanic corrosion of the rough surface area section coupled to a smooth surface area section of the aluminum engine block in an OAT coolant formulation at 88 ° C. The surface area ratio of the electrodes used in the test was roughly the same as observed on the real engine block. The results in Figs. 2 and 3 suggest that the galvanic coupling between the rough surface and smooth surface sections led to an increase of about four to five times the corrosion rates of the rough surface section in comparison to the values observed without the presence of the galvanic interactions 共see Table

FIG. 2—SLCC test results—Rough surface in OAT coolant A.


FIG. 3—Comparison of measured couple current versus calculated galvanic corrosion current. 3兲. The galvanic corrosion rate of the rough surface was observed to decrease rapidly with time. The contribution of cathodic reduction on the smooth surface area electrode towards the corrosion of the rough surface electrode was time-dependent and it generally decreased with time. As shown in Fig. 3, the measured galvanic coupling current 共i.e., Iគcouple in Fig. 3兲 accounted for ⬃80 % of the total rough surface corrosion current 共denoted as Roughគgal.corrគslc in Fig. 3兲 at the initial 1 – 2 hours of the test. It decreased to about 15 % after ⬃20 hours of immersion. The results indicate that the OAT coolant A is very effective in controlling corrosion of the different engine block sections under the test conditions. Post-test visual examination of the electrode surfaces indicated that the corrosion attack on the surface was uniform. In addition, the corrosion rate of the rough surface electrode 共or anode兲 determined at the end of the test using Tafel extrapolation of the anodic polarization curve to the couple corrosion potential was 76 ␮m / year. This value was in good agreement with the value 共88 ␮m / year兲 shown in Fig. 3, determined by using the combined ZRA and LPR measurements. These results suggest that the simulated localized corrosion cell method appears to be applicable for the determination of localized corrosion rates of aluminum alloys in coolants. Galvanic Corrosion of Aluminum and Ni-plated Cu—SLCC Method The simulated localized corrosion cell method is also well suited for the quantitative measurement of galvanic corrosion of aluminum alloy and the nickel plated copper material. Figure 4 shows that the aluminum alloy galvanic corrosion rate increases with increasing temperature. Increasing solution temperature from 75 to 88 ° C led to an increase of the galvanic corrosion rate by 100 %. Furthermore, the

FIG. 4—SLCC results—Aluminum alloy 共0.45 cm2兲 and Ni-plated Cu 共1.1 cm2兲 galvanic corrosion in 50 vol. % OAT coolant A.


FIG. 5—Comparison of measured couple current and galvanic corrosion current—same conditions as in Fig. 4. aluminum galvanic corrosion rate decreases rapidly with time. After 150 test hours of cycling between room temperature and 75 ° C 共⬃7 h per day兲, the aluminum galvanic corrosion rate was reduced to roughly 40 % of the value observed during the first day of immersion. Post-test visual examination of the aluminum electrode surfaces indicated that the corrosion attack on the surface was uniform. In addition, the corrosion rate of the aluminum determined at the end of the test using Tafel extrapolation of the anodic polarization curve to the couple corrosion potential was 209 ␮m / year. This value was in good agreement with the value 共197 ␮m / year兲 shown in Fig. 4, determined by using the combined ZRA and LPR measurements. These results suggest that the simulated localized corrosion cell method can provide an accurate and reliable measurement of galvanic corrosion of aluminum alloy under the chosen test conditions. Figure 5 shows the comparison of measured galvanic coupling current 共Iគcouple兲 flowing between the aluminum anode and the Ni-plated Cu cathode and the galvanic corrosion current 共Iគgal.corr兲 of the aluminum anode determined according to the simulated localized cell method. The results indicate that the contribution of cathodic reaction current on the aluminum anode towards aluminum galvanic corrosion was quite substantial under the test conditions. Conventional approach of measuring the coupling current alone to calculate the galvanic corrosion rate would underestimate the true galvanic corrosion rate significantly. The galvanic couple corrosion potential as a function of time is also shown in Fig. 5, and indicates that the corrosion potential tended to move to a more anodic value as the galvanic corrosion rate of the aluminum alloy decreased. Galvanic Corrosion of Aluminum and Ni-plated Cu—NanoCorr CMS Results Figure 6 shows the maximum galvanic localized corrosion of cast aluminum 共UNS A23190兲 and temperature as a function of time obtained from NanoCorr Couple Multi-electrode Sensor 共CMS兲 exposed to 50 vol. % OAT coolant A. The general trend of the CMS localized corrosion rate is similar to those obtained from the simulated localized corrosion cell method, except the corresponding corrosion rate values are about five to six times higher. Similar to the results obtained from the simulated localized corrosion cell method, the CMS localized corrosion rate for the cast aluminum decreased rapidly with time. After four days of cyclic temperature exposure in the solution, the maximum galvanic localized corrosion rate decreased to about 1 / 2 of the values observed during the first day of exposure. Increasing temperature from 75 to 88 ° C led to a 100 % increase in CMS maximum galvanic localized corrosion rate. Results shown in Fig. 6 also suggest that the addition of small amounts of corrosion inhibition additive into the 50 vol. % OAT coolant solution reduced the maximum galvanic localized corrosion rate of the cast aluminum to about 400 from greater than 1000 ␮m / year. Doubling the amount of the corrosion inhibition additive did not lead to further reduction of the localized corrosion rate of the cast aluminum. Use of a lower level of the inhibition additive also had little detectable effect on the localized corrosion rate of cast aluminum. The time of adding the inhibitive additive and the corresponding cast aluminum maximum localized corrosion rate measured by the CMS instrument were as follows: 共1兲 At 10:54 a.m., slugged low


FIG. 6—CMS results—galvanic corrosion of cast Al and Ni-plated Cu in 50 vol. % OAT coolant A. dose of an inhibitive additive. The CMS cast aluminum localized corrosion rate was 944– 956 ␮m / y just before the additive addition. 共2兲 At 11:29 a.m., slugged regular dose of the inhibitive additive. The CMS cast aluminum localized corrosion rate was 1124– 1135 ␮m / y just before the additive addition. 共3兲 At 14:34, slugged dose two times of regular dose of the inhibitive additive. The CMS cast aluminum localized corrosion rate was 419– 430 ␮m / y. 共4兲 One hour after the addition of two times of regular dose of the additive, the CMS cast aluminum localized corrosion rate was 419– 433 ␮m / y. Figure 7 shows the maximum galvanic localized corrosion current 关I គ corrគ cal= 2.5␴ + abs共Imean兲兴, the maximum anodic current from the coupling current from the 25 cast aluminum wires 共Iគmaxគano兲, and the coupling current of the most corroded wire at the end of the test 共i.e., at the end of the test, the wire had the highest value of time averaged anodic current兲 as a function of time. One can see that the three current values are quite close to each other in most cases. Among them, the coupling current of the most corroded wire tended to yield the smallest time average value. Thus, the results indicate that the NanoCorr CMS

FIG. 7—CMS results—comparison of various localized corrosion current values.


FIG. 8—CMS results—mean galvanic coupling current, maximum anodic current, and couple corrosion potential versus time.

Analyzer may tend to yield a localized corrosion rate higher than the actual maximum average corrosion rate measurable on the probe using an independent physical measurement technique. Figure 8 shows the mean coupling current of the 25 wires on the sensor probe 共Imean兲, the maximum anodic current from the coupling current from the 25 wires 共Iគmaxគano兲, and couple corrosion potential as a function of time. One can see that the couple corrosion potential generally increases as corrosion rates decrease, in agreement with the results obtained from the simulated localized corrosion cell method. The mean coupling current is smaller than the corresponding maximum anodic current value. The mean coupling current values were much higher than the corresponding galvanic coupling current shown in Fig. 5, probably due to the fact that the anode/cathode surface area ratio in the NanoCorr CMS test was only about 55.6 % of the one used in the simulated localized corrosion cell test. In addition, the likely difference in aluminum alloy composition used as the anode in the two tests may also contribute to the observed differences. It should be noted that in calculating the maximum localized corrosion rate, NanoCorr CMS Analyzer assumes that cathodic reaction on the anode sites 共or wire兲 of the probe is negligible. Thus, since cathodic reaction on the anode site tends to reduce the observable true anodic current, the true localized corrosion rate may be even much higher than those yielded by the NanoCorr CMS instrument. Based on the results obtained from the simulated localized corrosion cell method, the true maximum localized corrosion rate may be typically 40 to 80 % higher than the values reported by the NanoCorr CMS instrument. Localized Corrosion of Cast Aluminum in OAT Coolants—NanoCorr CMS Test Results Localized corrosion results of cast aluminum 共UNS A23190兲 in 25 or 50 vol. % OAT coolant formulations measured by the NanoCorr CMS probe are shown in Figs. 9–12. The effects of changing temperature, addition of corrosive species such as chloride and fluoride, and addition of corrosion inhibitor additives were studied. One can see from Figs. 9–12 that the NanoCorr CMS probe yielded a localized corrosion rate higher than the surface area average corrosion rates obtained from conventional electrochemical methods and mass loss methods. The localized corrosion rate obtained correlates very well with corrosivity changes in the test solution. For example, the CMS localized corrosion rate increases with increasing temperature and the addition of corrosive ions and it decreases with the addition of known effective aluminum corrosion inhibitors. In addition, the CMS probe also shows that fluoride may be a more corrosive species with regard to cast aluminum localized corrosion than chloride ions and corrosion inhibition additives are very effective localized corrosion inhibitors for cast aluminum in OAT coolants, even in the presence of high concentrations of fluoride and chloride ions. It should be noted that results in


FIG. 9—CMS results—localized corrosion of cast aluminum in 50 vol. % OAT coolant A. (see text for a full explanation) Fig. 11 show that the CMS calculated localized corrosion current 共Iគcorrគcal兲 values were generally significantly higher than the comparable maximum anodic current or the anodic current from the most corroded wire measured by the CMS probe. In Fig. 9, the time of solution heating and additive addition is as follows. At 11:10 a.m., the heater was

FIG. 10—CMS results—localized corrosion of cast aluminum in 25 vol. % OAT coolant B. (see text for a full explanation)

FIG. 11—CMS results—comparison of various localized corrosion current. (see text for a full explanation)


FIG. 12—CMS results—localized corrosion of cast aluminum in 50 vol. % OAT Coolant B. (see text for a full explanation) turned on. At 13:27 and 15:23, inhibitive additive was added. At 16:13, the heater was turned off. The relevant cast aluminum localized corrosion rates determined by CMS instrument as were follows: 2701 ␮m / y at 13:26; 19.9 ␮m / y at 15:20. In Figs. 10–12, the time of addition of corrosive ions and inhibitive additive, and heating of the solution is as follows. At 11:10 a.m., the heater was turned on. At 13:51 and 15:00, 100 mg/ L fluoride was added. At 15:45, inhibitive additive was added. The relevant cast aluminum localized corrosion rates determined by CMS instrument were as follows: 318 ␮m / y at 13:48; 1556 ␮m / y at 14:58; 2199 ␮m / y at 15:44; 28.8 ␮m / y at 17:09. In Fig. 12, the time of addition of corrosive ions and inhibitive additive, and other changes of corrosivity in the solution is as follows. At 9:39 a.m., the heater was turned on. At 10:47 a.m. and 12:12, 100 mg/ L fluoride ions were added. At 10:17 a.m., solution temperature reached 88 ° C. At 11:21 a.m., stirring of the solution was started. At 13:08, 100 mg/ L chloride ions were added. At 13:39 and 14:36, an inhibitive additive was slugged dose into the solution. The relevant cast aluminum localized corrosion rates determined by CMS instrument were as follows: 22 ␮m / y at 9:40 a.m.; 277 ␮m / y at 10:20 a.m.; 255 ␮m / y at 10:46 a.m.; 624 ␮m / y at 11:19 a.m.; 1321 ␮m / y at 12:11; 2217 ␮m / y at 13:04; 2290 ␮m / y at 15:08; and 1818 ␮m / y at 14:35. It should be noted that the trends obtained from the CMS tests with regard to the addition of corrosive ions 共e.g., fluoride兲, and inhibitive additive are in agreement with those observed in ASTM D 1384 tests provided in Table 1. The trends were also consistent with those obtained from conventional electrochemical tests described in separate publication 关22兴. Conclusions • Recent development in localized corrosion monitoring technology has made the task of development of new and more effective engine coolants for controlling localized corrosion of metal easier to accomplish. • The simulated localized corrosion cell method was shown to be well suited for studying aluminum galvanic corrosion in engine coolants and yielded results in good agreement with those determined by an independent reliable method. • The coupled multi-electrode sensor probe method has the advantage of incorporate statistical analysis in obtaining localized corrosion information and yielded a maximum localized corrosion rate that is correlating well with the corrosivity change in test coolant solutions. • The two methods should be very useful for measuring localized corrosion in engine coolant conditions. References 关1兴

Yang, B., “Minimizing Localized Corrosion via New Chemical Treatments and Performance Based


关2兴关3兴关4兴关5兴关6兴关7兴关8兴关9兴关10兴关11兴关12兴关13兴关14兴关15兴关16兴关17兴关18兴关19兴关20兴关21兴关22兴

Treatment Optimization and Control,” NACE Corrosion/99, 1999, Paper no. 307. Yang, B., “Real-Time Localized Corrosion Monitoring in Industrial Cooling Water Systems,” Corrosion, Vol. 56, 2000, pp. 743–756. Yang, B., “Localized Corrosion Monitoring in Cooling Water Systems,” NACE Corrosion/95, 1995, Paper no. 541. Yang, B., “Advances in Localized Corrosion Control in Cooling Water Systems,” Power Plant Chemistry, Vol. 2, 2000, pp. 324–329. ASTM Standard D 2809-94, “Standard Test Method for Cavitation Corrosion and ErosionCorrosion Characteristics of Aluminum Pumps with Engine Coolants,” Annual Book of ASTM Standards, Vol. 15, ASTM International, West Conshohocken, PA, 2002, pp. 76–81. ASTM Standard D 2570-96, “Standard Test Method for Simulated Service Corrosion Testing of Engine Coolants,” Annual Book of ASTM Standards, Vol. 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 61–67. ASTM Standard D 2758-94, “Standard Test Method for Engine Coolants by Engine Dynamometer,” Annual Book of ASTM Standards, Vol. 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 68–75. ASTM Standard D 4340-96, “Standard Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants under Heat-Rejecting Conditions,” Annual Book of ASTM Standards, Vol. 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 164–167. ASTM Standard D 1384-01, “Standard Test Method for Corrosion Test for Engine Coolants in Glassware,” Annual Book of ASTM Standards, Vol. 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 30–36. ASTM Standard D6208-97, “Standard Test Method for Repassivation Potential of Aluminum and Its Alloys by Galvanostatic Measurement,” Annual Book of ASTM Standards, Vol. 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 260–265. NACE Publication 3T199, “Techniques for Monitoring Corrosion and Related Parameters in Field Applications,” 1999, NACE, Houston, TX. Tan, Y., “Monitoring Localized Corrosion Processes and Estimating Localized Corrosion Rates Using a Wire-Beam Electrode,” Corrosion, Vol. 54, 1998, pp. 403–413. Tan, Y. J., Bailey, S., Kinsella, B., and Lowe, A., “Mapping Corrosion Kinetics Using the Wire Beam Electrode in Conjunction with Electrochemical Noise Resistance Measurements,” J. Electrochem. Soc., Vol. 147, 2000, pp. 530–539. Yang, L., Sridhar, N., Pensado, O., and Dunn, D. S., “An In-Situ Galvanically Coupled Multielectrode Array Sensor for Localized Corrosion,” Corrosion, Vol. 58, 2002, pp. 1004–1014. Yang, L., Dunn, D. S., and Cragnolino, G. A., “An Improved Method for Real-Time and Online Corrosion Monitoring Using Coupled Multielectrode Array Sensors,” NACE Corrosion/2005, 2005, Paper no. 05379. Yang, B., “Method for On-Line Determination of Underdeposit Corrosion Rates in Cooling Water Systems,” Corrosion, Vol. 51, 1995, pp. 153–165. Enzien, M. and Yang, B., “Effective Use of Monitoring Techniques for Use in Detecting and Controlling MIC in Cooling Water Systems,” Biofouling, Vol. 17, 2001, pp. 47–57. Fu, S. L., Griffin, A. M., Garcia, J. G., and Yang, B., “A New Localized Corrosion Monitoring Technique for the Evaluation of Oil Field Inhibitors,” NACE Corrosion/96, 1996, Paper no. 346. Yang, B., “Corrosion Control in Industrial Water Systems,” Presented at NACE Central Area Conference, Corpus Christi, TX, 7–10 October 2001. Corrosion Tests and Standards: Application and Interpretation, R. Baboian, Ed., ASTM International, West Conshohocken, PA, 2005. General Motors Engineering Standard GM 9066-P, “Electrochemical Test for Evaluating Ethylene Glycol Engine Coolants for Corrosion Inhibition at Aluminum Heat-Rejecting Surfaces,” November 1981. Yang, B., Gershun, A. V., Marinho, and Woyciesjes, P. M., “Effect of Fluoride on Corrosion of Cooling System Metals in Ethylene Glycol-Based Antifreeze/Coolants,” accepted for publication in J. ASTM International.


Anthony P. Skrobul,1 Steven L. Balfe,1 and Fred C. Alverson1

Compatibility Testing of Multi-Vehicle Coolant Chemistries ABSTRACT: Multi-vehicle or universal coolants, or both, have been introduced into the marketplace to satisfy the wishes of mass merchandisers, automotive garage and repair shops, quick oil change establishments, and the general public for a convenient single coolant for use in the myriad makes and models of vehicles. Universal coolants are recommended for top off, as well as complete drain and fill of the customer’s cooling system, regardless of the color or inhibitor chemistry of coolant already in use. Coolant mixing, and potential compatibility issues, will result for the top-off scenario, but may also be of concern following coolant system flush-and-fill. However, there are currently no standard compatibility tests to define satisfactory compatibility when coolants of different chemistry are mixed. Previous work to establish compatibility of coolant mixtures documents that potential coolant deterioration of the corrosion protection may occur in the ASTM D 4340 关1兴 Aluminum Heat-Rejection Test when mixing coolants with different additive chemistries. Compatibility testing has been conducted on various universal coolants with traditional high silicate, traditional low silicate, hybrid 共phosphate free兲, hybrid 共phosphated兲, and OAT-only technologies. This paper provides results of the coolant compatibility tests and correlation of coolant chemistry with coolant performance in these tests. KEYWORDS: multi-vehicle coolants, universal coolants, compatibility, antifreeze, OAT, hybrid coolant

Introduction It would be an understatement to say that a lot has happened since the introduction of the first formulated ethylene glycol-based antifreeze in the United States in 1927 关2兴. In the early 1960s, all three U.S. car companies—General Motors, Ford Motor Company, and Chrysler—began installing a 50/50 mix of ethylene glycol antifreeze/water in their new cars 关3兴. Engineering accomplishments have led to the introduction of more efficient engines with more rigorous performance requirements, and placed greater demands on the engine coolant. The use of lightweight metals and plastics in engine cooling systems, as well as new elastomer and hose materials has hastened the evolution of traditional antifreeze. Armstrong and Pellet have also pointed out the contribution of a global marketplace 共with import and export of vehicles and parts兲, and how “changing attitudes toward the protection of human health and the environment,” have impacted antifreeze development 关4兴. There is now a plethora of antifreeze/coolants in the marketplace, and this abundance of antifreeze/coolant choices has resulted in some consumer confusion 关5兴. Many antifreeze/coolant products, while based on glycol 共either ethylene glycol or propylene glycol兲, differ in formulation and color. The vehicle manufacturers unique antifreeze/coolant specifications, defining physical/chemical requirements, corrosion protection requirements, and service life, have resulted in a proliferation of antifreeze/coolant formulations. Fortunately the confusion can be attenuated somewhat by classifying antifreeze/coolants into three broad categories. The three basic types of coolants are 关6兴: • IAT or conventional North American “green” antifreeze. IAT stands for Inorganic Additive Technology. The corrosion inhibitors used are sodium or potassium salts of inorganic anions. Phosphate, borate, silicate, nitrite, and nitrate are most commonly used. A given formulation contains varying amounts of two or more of these chemicals. The formulation would usually contain an azole compound 共tolyltriazole, benzotriazole, or mercaptobenzothiazole兲 as a copper corrosion inhibitor. According to Carley 关6兴, “The fast-acting silicate and phosphate corrosion inhibitors provide quick Manuscript received March 3, 2006; accepted for publication September 19, 2006; published online April 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Coolant Advisor, Technology Manager, and Coolant Advisor, respectively, Shell Global Solutions 共US兲 Inc., 3333 Highway 6 South, Houston, Texas 77082. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

59


protection for bare iron and aluminum surfaces, and have a proven track record for providing trouble-free service in virtually any vehicle application 共domestic, Asian, or European兲, assuming the chemistry is correct.” Because the corrosion inhibitors in traditional coolants deplete in service, this type of coolant should be changed every two to three years or at 30 000 miles 共48 280 km兲. • OAT-based coolants. OAT stands for Organic Acid Technology, and includes organic acids such as 2-ethylhexanoic acid, sebacic acid, azelaic acid, and benzoic acid, among others, providing broadspectrum corrosion protection. Sometimes two or more organic acids are used in the same formulation. At typical pH values of about 7.5–9.0, the organic acids in OAT coolants are in the form of their sodium or potassium salts 共depending upon whether the pH is adjusted with sodium hydroxide or potassium hydroxide兲. OAT coolants also contain an azole additive as a copper corrosion inhibitor. OAT coolants generally provide longer service life than inorganic types. The recommended service life is typically five years or 150 000 miles 共241 402 km兲. OAT-based coolants are usually dyed a different color to distinguish them from traditional North American green antifreeze 关6兴. GM’s DEX-COOL® 共dyed orange兲 is an example of an OAT extended-life coolant. • Hybrid OAT coolants, also known as HOAT. Hybrid OAT coolants use an organic anion as the primary corrosion inhibitor. Selected inorganic salts are added to enhance certain properties. HOAT coolants also contain an azole additive as a copper corrosion inhibitor. North American and European hybrid formulations usually contain silicate as a major inorganic anion. Japanese hybrid formulations usually contain phosphate as a major inorganic anion. While it may be desirable to follow the vehicle manufacturer’s recommendations for coolant type when topping-off or changing coolant, practically speaking, mass merchandisers and shops don’t have the shelf space to stock different coolants for each make and model of vehicle. U.S. aftermarket service fill outlets are embracing multi-vehicle coolants in cases where reduced shelf space and stock keeping units are desired. This has given rise to the popularity of coolants described as “universal,” “global,” or “multivehicle.” The successful use of such coolants in all makes and models of automobiles requires at least two considerations, product color and product compatibility. 1. Product color of universal products is neutral, and as such will mix with other engine coolant colors without making coolant color an issue. Product color is easy to deal with, but begs the question of “compatibility.” 2. For the most part, universal coolants are sold as aftermarket products. As such, most of the time the coolant will be added to a cooling system as top-up to the coolant already in the vehicle. If the initial coolant is working properly, then the cooling system is already passivated prior to the addition of the universal coolant for top-up. If there is no chemical instability, and therefore no inhibitor dropout, the consumer would expect little risk of damage associated with the mixing of two different coolants. It remains for the marketer of the coolant to adequately verify compatibility between their universal coolant and the variety of OEM and service-fill coolants in the marketplace. This paper provides test results for a multi-vehicle coolant that provides excellent corrosion protection by itself, and in mixtures with current OEM and service-fill coolants. Experimental Method Test Procedure Tests were conducted on 50/ 50 volume % mixtures of the multi-vehicle coolant candidate with various OEM and service fill coolants, in accordance with ASTM Standard Specification for Glycol Base Engine Coolant for Automobile and Light-Duty Service 共ASTM D 3306-05兲关7兴. We also conducted ASTM Standard Test Method for Corrosion Test for Engine Coolants in Glassware 共ASTM D 1384-05兲关8兴, and ASTM Standard Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under HeatRejecting Conditions 共ASTM D 4340-96 共Reapproved 2001兲兲关1兴 on the following volume ratios of the multi-vehicle coolant with OEM and service fill coolants: 90/10, 75/25, 50/50, 25/75, and 10/90. However, we didn’t necessarily test each of the above ratios for all coolant mixtures. In many cases we focused only on the 50/50 mixture of coolants, since this ratio would intensify possible additive interactions, and historically was most prone to display incompatibility issues. Given the large number of ASTM D 1384 关8兴 and ASTM D 4340 关1兴 tests required with the above coolant ratios, we deviated from the standards in some

SKROBUL ET AL. ON COMPATIBILITY TESTING OF MULTI-VEHICLE COOLANT CHEMISTRIES 61 TABLE 1—Engine coolant inhibitor formulation. Inhibitor Coolant A B C D E F G H I J K L M N O P

B4O2− 7

NO−2

X X X X

X X X

X

X

X X

X X

NO−3 X

X X X X X X X X X X X X

HPO2− 4

MoO2− 4

X X

X

X

X X

X

SiO2− 3 X

X X X X

X

X X

Azole X X X X X X X X X X X X X X X X

Benzoatea X

Mono Acid

Dibasic Acid X

X X X

X X

X X X X X X X X X

a

Benzoate includes the salts of benzoic acid and substituted benzoic acid.

cases with regard to the number of runs. For the ASTM D 1384 关8兴 we made duplicate runs 共with one exception in which we made a single determination at a 50/50 ratio兲 and reported both runs, rather than reporting the average of triplicate runs per the standard. For the ASTM D 4340 关1兴 we typically made two runs 共per the standard兲 but in some cases we made three determinations, and in other cases single determinations. With the exception of the number of test runs 共discussed above兲 for the ASTM D 1384 关8兴 and ASTM D 4340 关1兴 tests, we followed the standard conditions for these tests. ASTM D 1384 关8兴 requires 1 33 3 volume % coolant diluted with corrosive water 共100 ppm of chloride 共Cl−兲, sulfate 共SO=4 兲, and bicarbonate 共HCO−3 兲 introduced as sodium salts兲 at 88° C 共190° F兲 for 336 h 共2 weeks兲. The metals exposed to the aerated engine coolant 共aeration rate of 100 mL/ min兲 solution were copper, Alloy Grade 30A 共SAE 3A兲 solder, brass, steel, cast iron, and cast aluminum. Corrosion was measured by weight changes incurred by the specimens. ASTM D 4340 关1兴 requires 25 volume % coolant diluted with corrosive water 共100 ppm chloride 共Cl−兲 introduced as the sodium salt兲 under a pressure of 193 kPa 共28 psi兲. The cast aluminum test specimen 共heated from underneath while engine coolant sits on its top surface兲 is maintained at 135° C 共275° F兲 throughout the 168-h 共1 week兲 test. Heat-transfer corrosion is evaluated on the basis of the weight change of the test specimen. Test Fluids The multi-vehicle coolant was mixed with various OEM and service coolants conforming to the above definitions for OAT, conventional and hybrid coolants. Table 1 provides an overview of the inhibitor compositions of the tested coolants. Coolant A is the multi-vehicle coolant under investigation. Results and Discussion Commercial OAT Coolants Table 2 provides ASTM D 4340 关1兴 performance compatibility results for two commercially available OAT coolants 共Coolants B and C兲, in combination with either an OAT coolant 共Coolant C兲 or hybrid-type coolants 共Coolants F, L, and G兲. The three hybrid coolants all contain silicate. As expected, the two OAT coolants were completely compatible at all coolant ratios. However, OAT Coolant B was incompatible with Coolants F and L, and Coolant C was incompatible with Coolants L and G when tested at a 50/50 ratio. Coolant mixtures B&F and C&L were also incompatible at a 75/25 ratio. The relatively high corrosion rates of certain coolant mixtures in the ASTM D 4340 关1兴 test are well documented in the literature 关9,10兴. According to Van de Ven and Maes 关9兴, the ASTM D 4340 关1兴 test “discriminates silicate

62 ENGINE COOLANT TECHNOLOGY TABLE 2—ASTM D 4340 compatibility testing. Corrosion Rate 共mg/ cm2 / week兲 Coolant Mix B/C B/F B/L C/L C/G

10/90 0.02, 0.03 ... ... ... ...

25/75 0.04, 0.03 0.06 ... 0.03 ...

50/50 0.14 9.6, 4.9 2.0, 4.3 4.9, 4.4 3.86, 3.69, 3.77

75/25 0.03 3.1 ... 1.76 ...

90/10 0.08, 0.01 ... ... ... ...

Note: The limit by ASTM D 3306 is 1.0 mg/ cm2 / week, max.

containing coolants on the basis of their silicate content: below a threshold level corrosion will occur; above this level the coolants are no longer differentiated.” The test results shown in Table 2 are consistent with this conclusion. The authors quoted above also tested mixtures of an OAT coolant with a silicate-containing coolant in the ASTM D 1384 关8兴 test. Their data showed no incompatibility problem occurs under heat receiving conditions 关9兴. We did not test the coolant mixtures in Table 2 in the ASTM D 1384 关8兴 test. Multi-Vehicle Coolant Candidate ASTM D 1384 Glassware Corrosion Test—This product was designed to be performance compatible with traditional, hybrid, and OAT engine coolant technology, when tested under the static heat-rejecting conditions of the ASTM D 4340 关1兴 test. We also needed to confirm there are no compatibility issues with mixtures of Coolant A and other coolant technologies in the ASTM D 1384 关8兴 test 共Tables 3–5兲, or in any of the performance tests required by ASTM D 3306 关7兴. In this case we see no incompatibility problem under the heat receiving conditions of the ASTM D 1384 关8兴 test. The weight gain for aluminum with the mixture of 75 % Coolant A / 25 % Coolant I 共Table 4兲 was surprising, since no weight gain was observed for 100 % Coolant A. Van de Ven and Maes observed a trend on the aluminum specimen when they tested mixtures of an OAT coolant and a traditional silicate-containing coolant 关9兴. Adding more of the silicatecontaining coolant resulted in a higher weight gain. The authors concluded that the silicates presented in TABLE 3—ASTM D 1384 compatibility testing: Coolants B and A. Max. Allowed

Test Results on the Various Product Mixes Metal Copper Solder Brass Cast Iron Steel Aluminum

90 % B 10 % A 2, 1 2, 1 2, 1 3, 3 1, 0 0, 1

75 % B 25 % A 2, 2 2, 1 2, 2 3, 2 1, 1 −7, −2

50 % B 50 % A 2 1 2 3 0 1

25 % B 75 % A 0, 2 −1, −1 1, 0 0, 0 −1, 0 1, −1

10 % B 90 % A 1, 1 −2, −1 0, −1 0, 1 0, −1 19, 29

共Wt. loss, mg/coupon兲 10 30 10 10 10 30

TABLE 4—ASTM D 1384 compatibility testing: Coolants I and A. Max. Allowed

Test Results on the Various Product Mixes Metal Copper Solder Brass Cast Iron Steel Aluminum

90 % I 10 % A 0, 0 0, −1 0, −1 0, −1 2, 1 −1, 0

75 % I 25 % A 2, 0 1, 0 0, 0 1, 1 3, 2 −6, 3

50 % I 50 % A 0, −1 −1, −1 −1, 1 −1, −2 1, 1 −6, −9

25 % I 75 % A −1, 0 −1, −1 0, 1 0, 0 2, 4 −30, −35

10 % I 90 % A ... ... ... ... ... ...


SKROBUL ET AL. ON COMPATIBILITY TESTING OF MULTI-VEHICLE COOLANT CHEMISTRIES 63 TABLE 5—ASTM D 1384 compatibility testing of 50/50 mixtures. Max. Allowed

Test Results on 50/50 Mixtures Metal Copper Solder Brass Cast Iron Steel Aluminum

50 % D 50 % A −1, −2 −1, −1 −1, −2 −1, 0 1, 0 0, 0

50 % E 50 % A −1, 0 −2, −3 −1, −1 −2, 0 −2, 19 0, −1

50 % K 50 % A 1, 0 0, −2 0, −1 −2, −2 0, 0 1, 0

50 % M 50 % A 0, 0 −4, −2 −1, −2 −2, −1 −1, 1 1, 0

50 % N 50 % A 1, 0 −1, −1 0, 0 −2, −2 0, 1 1, 1

50 % O 50 % A 0, −1 −1, −2 0, −1 −1, −2 0, 0 0, 1


the silicate-containing coolant deposited into the pores of the cast aluminum coupon, and were not removed during the chemical cleaning process. Insufficient cleaning may explain some of the weight gain we observed. Table 5 includes ASTM D 1384 关8兴 data for 50/ 50 volume % mixtures of Coolant A with six commercial coolant technologies. Coolant D is an OAT coolant, Coolant E is a traditional North American automotive coolant, Coolants K, M, and N are Japanese OEM coolants, and Coolant O is a fully formulated heavy-duty coolant. No compatibility issues were observed with these coolant mixtures. Our data show that ASTM D 1384 关8兴 does not discriminate between neat coolants and mixtures. ASTM D 4340 Heat Rejecting Aluminum Corrosion Test—The test results show no deterioration of corrosion protection in the ASTM D 4340 关1兴 test for the mixed coolants in Table 6. The commercial coolants in the table cover the gamut of coolant categories discussed in the Introduction. Coolant B is an OAT coolant, Coolant J is a nonsilicate hybrid coolant, Coolant L is a silicate-containing hybrid, Coolant M is a nonsilicate hybrid coolant with phosphate, and Coolant P is a traditional fully formulated phosphate free coolant. Reference 关10兴 contains a review of previous studies examining the effect of low levels of silicate and other inorganic inhibitors on hot aluminum corrosion protection. Much discussion is devoted to the observation that mixtures of traditional coolants, at low levels, with carboxylate coolants yield high ASTM D 4340 关1兴 corrosion rates. The authors reject the widely held interpretation that the high corrosion rates are due to incompatibility between these technologies, since an abundance of field data with slightly contaminated vehicles does not show aluminum corrosion 关10兴. The authors go on to show that the Dynamic Heat Transfer Test is a better predictor of the performance of mixed coolants under aluminum heat-rejecting conditions 关10兴. The data of Table 6 show it is possible to formulate a coolant that, when contaminated with other coolant technologies, does not cause the usual high ASTM D 4340 关1兴 corrosion rates. TABLE 6—ASTM D 4340 compatibility testing of commercial coolants and coolant A. Product Mix Test Results 共mg/ cm2 / week兲 Commercial Coolant B J L M P

90/10 0.11, 0.39 0.29 −0.44, −0.28 −0.05, −0.02 −0.20, 0.29

75/25 0.02, 0.09 −0.03, −0.05 −0.28, −0.15 ... −0.03, −0.05

50/50 0.05, 0.2 −0.06 −0.26 −0.03 −0.06

25/75 −0.09, −0.11 −0.11, −0.20 −0.10, −0.39 −0.02 −0.11, −0.20

10/90 −0.06, −0.12 −0.12, −0.18 −0.30 0.0, −0.05 −0.12, −0.18

1. The test limit by ASTM D 3306 关7兴 is 1.0 mg/ cm2 / week, max. 2. For each coolant listed, the first number in each mix ratio is that for the commercial coolant. For example, in the case of Coolant B in column two, the mixture is 90-volume % Coolant B and 10volume % Coolant A. 3. Most test results showed a slight weight gain as indicated by the negative sign.

64 ENGINE COOLANT TECHNOLOGY TABLE 7—ASTM D 3306 physical, chemical and performance testing of Coolant A.

Requirements Physical/Chemical Requirements Relative density 15.5/ 15.5° C Freezing point, °C 共 °F兲 50 vol % in DI water Boiling point, °C 共 °F兲 50 vol % in DI water Undiluted Ash content, mass % pH: 50 vol % in DI water Chloride, ppm Water, mass % Reserve alkalinity, mL Effect on automotive finish General Requirements Color Performance Requirements Corrosion in glassware Wt. loss, mg/specimena copper solder brass steel cast iron aluminum Simulated service test Wt. Loss, mg/specimena copper solder brass steel cast iron aluminum Corrosion of Cast Al Alloys at Heat-Rejecting Surfaces, mg/ cm2 / week Foaming Volume, mL Break time, s Cavitation-Erosion, ratingd

ASTM Test Method

D 1122

Specifications

Results

1.110 to 1.145

1.122

D 1177

−37 共−34兲 max

−37 共−34兲

D 1119 D 1287 D 3634 D 1123 D 1121 D 1882

108 共226兲 min 163 共325兲 min 5 max 7.5 to 11 25 max 5 max report no effect

108.4 共227.1兲 173.9 共345.0兲 0.80 8.3 6 2.53 3.0 no effect

...

Distinctive

Light yellow

D 1120

D 1384

10 30 10 10 10 30

max max max max max max

2, 1 1, 1 1, 1 0, 0 0, −1 −1, 2

20 60 20 20 20 60


−2, 4, 2 5,12, 2 −2, 0, 1 −2, 0, 1 −1, 0, 2 3, 17, 0

D 2570

D 4340

1.0 max

−0.1b, 0.1c

150 max 5 max 8 min

30 0.46 10, 9, 9, 9, 9e, 8e, 8e

D 1881

D 2809

a

Each result is an average of three determinations. Average of two determinations. c Average of three determinations. d Each result is a single determination. e Result at 300 hours. b

ASTM D 3306 Tests of Neat Coolant A and Mixtures—Table 7 contains all test results for universal Coolant A required by the ASTM D 3306 关7兴 protocol. All of the Performance Requirements of ASTM D 3306 关7兴共with the exception of Foam兲 were performed at least in duplicate. ASTM Standard Test Method for Simulated Service Corrosion Testing of Engine Coolants 共D 2570兲关11兴 was run in triplicate. We also evaluated 50/50 mixtures of Coolant A with various commercial coolant technologies against the Performance Requirements of ASTM D 3306 关7兴. The commercial coolants tested in mixture with Coolant A are:

SKROBUL ET AL. ON COMPATIBILITY TESTING OF MULTI-VEHICLE COOLANT CHEMISTRIES 65

TABLE 8—50/50 mix of Coolant B and Coolant A: ASTM D 3306 performance data.

Requirements Performance Requirements Corrosion in glassware Wt. loss, mg/specimen copper solder brass steel cast iron aluminum Simulated service test Wt. Loss, mg/specimen copper solder brass steel cast iron aluminum Corrosion of Cast Al Alloys at Heat-Rejecting Surfaces, mg/ cm2/week Foaming Volume, mL Break time, s Cavitation-Erosion, rating

ASTM Test Method

Specifications

Results

D 1384

10 30 10 10 10 30


2 0 2 1 2 −2

20 60 20 20 20 60


13 10 0 −2 −2 −4

D 2570

D 4340 1.0 max

−0.52

150 max 5 max 8 min

60 1.2 9

D 1881

D 2809

TABLE 9—50/50 mix of Coolant D and Coolant A: ASTM D 3306 performance data.


ASTM Test Method

Specifications

Results

D 1384

10 30 10 10 10 30


1 −1 −1 0 1 3

20 60 20 20 20 60


8 0 7 −1 −1 −3

D 2570

D 4340 1.0 max

0.35

150 max 5 max 8 min

43 0.48 10

D 1881

D 2809


TABLE 10—50/50 mix of Coolant E and Coolant A: ASTM D 3306 performance data.


ASTM Test Method

Specifications

Results

D 1384

10 30 10 10 10 30


2 4 2 1 0 3

20 60 20 20 20 60


0 −1 −2 −3 −4 −11

1.0 max

−0.1

150 max 5 max 8 min

27 0.46 10

D 2570

D 4340

D 1881

D 2809

TABLE 11—50/50 mix of Coolant H and Coolant A: ASTM D 3306 performance data.


ASTM Test Method

Specifications

Results

D 1384

10 30 10 10 10 30


2 1 1 1 1 −2

20 60 20 20 20 60


1 3 2 1 1 5

D 2570

D4340 1.0 max

−0.17

150 max 5 max 8 min

110 4.2 8

D 1881

D 2809

SKROBUL ET AL. ON COMPATIBILITY TESTING OF MULTI-VEHICLE COOLANT CHEMISTRIES 67

TABLE 12—50/50 mix of Coolant I and Coolant A: ASTM D 3306 performance data.


ASTM Test Method

Specifications

Results

D 1384

10 30 10 10 10 30


2 0 1 1 1 17

20 60 20 20 20 60


0 3 1 2 1 2

D 2570

D 4340 1.0 max

0.87

150 max 5 max 8 min

50 1.4 8

D 1881

D 2809

TABLE 13—50/50 mix of Coolant K and Coolant A: ASTM D 3306 performance data.


ASTM Test Method

Specifications

Results

D 1384

10 30 10 10 10 30


2 0 1 1 1 −1

20 60 20 20 20 60


2 3 1 2 2 3

D 2570

D4340 1.0 max

−0.10

150 max 5 max 8 min

40 2.8 8

D 1881

D 2809


Coolants, B, D, E, H, I, and K. The test results are given in Tables 8–13, respectively. To date, all mixtures we have tested meet the performance requirements of ASTM D 3306 关7兴. Fleet Testing Fleet testing in New York City taxicabs was initiated in July 2005 to confirm the real world performance of multi-vehicle Coolant A when used as a top-off antifreeze/coolant, or for complete drain-and-fill. We are monitoring three sets of cabs during this field test: 共1兲 a control group with factory-fill coolant, 共2兲 a set of cabs that has been drained and filled with Coolant A, and 共3兲 a set of cabs for which the coolant is 50 volume % original fill and 50 volume % Coolant A. This 150 000 mile test 共241 402 km兲 will take about 1.5– 2 years to complete. Conclusions A multi-vehicle hybrid coolant has been developed that provides excellent corrosion protection by itself, and in mixtures with current OEM and service-fill coolants. Mixtures of the multi-vehicle hybrid coolant with OAT, hybrid, and traditional coolants show no deterioration of corrosion protection in the ASTM D 4340 关1兴 test or in the ASTM D 1384 关8兴 test. Acknowledgments The authors wish to thank Mr. Terry Charles for his blending and testing support. The authors also thank Southwest Research Institute and Amalgatech for coolant evaluations. Finally, the authors acknowledge the help of Mr. Charlie Doiron of Recochem, Inc., for product development and product validation support. References 关1兴关2兴关3兴关4兴关5兴关6兴关7兴关8兴关9兴关10兴关11兴

ASTM D 4340, “Standard Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions,” ASTM Standards on Disc, Vol. 15.05–06, ASTM International, West Conshohocken, PA, pp. 1–4. “Antifreezes and Deicing Fluids,” Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 3, 4th ed., John Wiley & Sons, Inc., 1992, pp. 347–367. Prestone Company Timeline, URL: http://www.prestone.com/company/timeline.php, December 8, 2005. Armstrong, R. and Pellet, R., “Extended Life Coolants,” Lubrication, Vol. 87, No. 2, 2001, p. 1. Weissler, P., “Coolant Confusion: It’s Not Easy Being Green…or Yellow or Orange or…,” http:// www.motor.com/MAGAZINE/Pdf/082004_04.pdf. Carley, L., “Universal Coolants: The Ultimate Answer?,” URL: http://www.aa1car.com/library/ 2004/us120426.htm, December 7, 2005. ASTM D 3306, “Standard Specification for Glycol Base Engine Coolant for Automobile and LightDuty Service,” ASTM Standards on Disc, Vol. 15.05–06, ASTM International, West Conshohocken, PA, pp. 1–5. ASTM D 1384, “Standard Test Method for Corrosion Test for Engine Coolants in Glassware,” ASTM Standards on Disc, Vol. 15.05–06, ASTM International, West Conshohocken, PA, pp. 1–8. Van de Ven, P. and Maes, J.-P., “A Compatibility Study of Mixtures of a Monoacid/Dibasic Acid Coolant and a Traditional Nitrite-Free Coolant,” SAE 940769, Society of Automotive Engineers, Warrendale, PA, 1994. Fritz, P. O., Bartley, L., Maes, J.-P., and Van de Ven, P., “Extended Life Carboxylate Coolant Compatibility with Other Coolant Technologies—Examining the Data,” SAE 2000-01-1977, Society of Automotive Engineers, Warrendale, PA, 2000. ASTM D 2570, “Standard Test Method for Simulated Service Corrosion Testing of Engine Coolants,” ASTM Standards on Disc, Vol. 15.05–06, ASTM International, West Conshohocken, PA, pp. 1–7.


Carol Jeffcoate,1 Mary Ranger,2 Jerry Grajzl,3 Bo Yang,1 Peter Woyciesjes,1 and Aleksei Gershun1

Investigation of Interaction Between Coolant Formulations and Flux Loading/Compositions in Controlled Atmosphere Brazed „CAB… Aluminum Surfaces in Heat Exchanger Applications ABSTRACT: An investigation was made into the effects of flux formulation and after brazing residue on the pitting potential of the aluminum surface in various types of coolants during laboratory evaluations. Samples of CAB brazed radiator header alloy aluminum, with various flux loadings, were supplied by Behr and the Ford Motor Company. The flux is generally in the form of potassium fluoroaluminate, general formula K1⫺3AlF4⫺6.xH2O. The samples in the flux loading study were all passed through the brazing ovens with the following flux loadings: • No flux, • Half the regular amount of flux, • The regular amount of flux, • Double the regular amount of flux, • Regular amount of flux over half of the surface area. The individual coolants used in the flux loading study were 25 % volumes of the following, each with 100 ppm of chloride: • Conventional, • Hybrid 共HOAT兲, • Organic Acid 共OAT兲, • Modified Organic Acid 共MOAT兲. In the flux composition study, different compositions of potassium fluoroaluminate from three different suppliers were evaluated with hybrid type coolant. All the aluminum samples were run according to a Ford Laboratory Test Method 共FLTM兲 BL105-01 “A Rapid Method to Predict the Effectiveness of Inhibited Coolants in Aluminum Heat Exchangers” 关1兴. The samples were heated and boiled in coolant for 1 h. The temperature was lowered to 70°C and the samples were electrochemically tested by either potentiodynamic polarization or modified Ford FLTM BL105-01. Each coolant at the end of the test was submitted for chemical analysis of fluoride content. The electrochemical results of the flux loading study showed that the higher the flux loading on the aluminum header material, the easier it is to initiate corrosion. Chemical analysis showed the presence of significant quantities of fluoride in the end of test fluids. As the only fluoride-containing component of the system is the flux residue, it was concluded that fluoride leached from the flux residue. The second study showed that not all potassium fluoroaluminate brazing flux is alike. Samples of three fluxes from three different suppliers of the same loading on aluminum were tested with hybrid coolant. When subjected to heating and potentiodynamic polarization, significantly different results were obtained from the three different fluxes. KEYWORDS: antifreeze/coolant, aluminum surface, CAB braze process, heat exchangers, potassium fluoroaluminate flux

Introduction The method for producing radiators has changed over the years. The material of choice for light vehicle applications is now predominantly aluminum. As well as the material, construction methods have also changed. Instead of vacuum brazing or mechanically assembling the components, a process known as controlled atmosphere brazing is being used increasingly. Controlled atmosphere brazing 共CAB兲 is brazing in a controlled nitrogen gas atmosphere using a potassium fluoroaluminate flux. Flux is applied to the surfaces to be joined, the assembled unit is heated in a nitrogen atmosphere controlled oven at high temperatures, and joining occurs. The flux used in this process has been developed by several manufacturers, but was originally developed by Alcan as Nocolok® flux and is a mixture of K3AlF6 – KAlF4. The flux is inactive at temperatures below 560° C but at brazing temperature, it turns active and removes the aluminum oxide layer to enable Manuscript received February 7, 2006; accepted for publication October 4, 2006; published online November 2006. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewiez, Guest Editor. 1 Honeywell, Danbury, CT 06810 2 Ford Motor Company, Dearborn, MI 48121 3 BEHR Heat Transfer Systems, Inc., Charleston, SC 29405 Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

69


joining. The residue of the flux left on the surface after brazing has been thought to be insoluble and nonaggressive, hence no removal was necessary, and allowed the elimination of the costly residue removal operations. In the production process prior to fluxing a heat exchanger, it typically goes through a cleaning step to remove residual lubricants and forming oils. The flux is applied after cleaning to individual parts or assembled units as aqueous slurry by flooding, spraying, or dipping. Agitation is required to prevent the flux from settling. The slurry concentration, typically in the range from 5 to 25 %, regulates the flux loading. An air “blow-off” step is typically used to remove excess slurry accumulated at the downside of the fluxed part. The goal is to achieve a uniform coating of the flux without significant accumulation in any one place, especially inside the radiator or heater tubes. After fluxing, the part is dried, usually at about 200° C. Care is taken not to overheat the heat exchanger as excess heat 共250° C兲 may cause high temperature oxides to form on the aluminum surfaces. The aim of the dry off is simply to remove water from the fluxing stage so that the component is completely free of adsorbed water prior to entering the brazing furnace. CAB flux brazing is carried out in an inert atmosphere such as nitrogen in either batch type furnaces or more commonly in continuous tunnel furnaces 关2,3兴. Nitrogen is introduced in the critical brazing section of the furnace and flows towards the entrance and exit. At the critical brazing zone, the furnace atmosphere has a dew point of ⬍−40° C and an O2 concentration less than 100 ppm. These conditions are necessary for optimum brazing results. In the brazing temperature range of 530 to 560° C, traces of flux 共KAlF4兲 evaporate and, in the presence of moisture, can react to form traces of HF. To the authors’ knowledge, there are no previously reported studies of the interaction between flux loading or types and different coolant types. It has always been assumed that the flux was inert. Experimental Two studies were conducted; in the first study, samples of aluminum radiator header material with differing amounts of Nocolok® flux loadings were tested in various coolant formulas. The second study looked at three different flux chemistries from three different suppliers. The main differences between the flux chemistries were the amount of crystalline water and the mole ratio between the major components KAlF4 and K2AlF5. There were other differences that were thought to be significant. One was particle size and particle distribution and the other was the trace metals in the flux. First Study Sheets of AA 3003 aluminum header alloy with one side AA4045 clad 关4兴 were prepared with flux on the braze clad side. Various amounts of flux were applied to the sheets: regular amount, twice the regular amount, half the regular amount, and regular amount of flux on one-half of the sheet. The amount of flux applied was determined by weighing a virgin plate with no flux. Then the sheet was sprayed with flux in the production process and the sheet was weighed again. The weight of flux for that surface area was taken as a regular flux loading. The weight of the other flux loadings required was weighed and the flux applied by hand. The sheets were then brazed and cut into 2 by 2 in. sections. The sample quality was variable in coverage and thickness of flux. Samples used in the experiments were chosen to be as representative as possible. The samples with only half of the surface fluxed had a thin layer of flux residue over the entire surface after the brazing process 共i.e., the flux wetted out兲.

JEFFCOATE ET AL. ON CAB ALUMINUM SURFACES 71 TABLE 1—Approximate composition of flux from three different suppliers Supplier/ Composition A B C

KAlF4 % wt. ⬎90 ⬃80 ⬃84

K2AlF5 . xH2O % wt. 2.4 共no water兲 15 共water present兲 15 共water present兲

K3AlF6 % wt. … 5 1

Second Study For the second study the various flux suppliers provided samples with the specifications outlined in Table 1. The plates were 4 by 4-in. pieces of aluminum AA3003 with one side 4045 clad alloy 关4兴. Twenty percent by weight flux 共the typical regular flux loading兲 was sprayed on the clad side. The flux-coated plates were put on a tray and dried at 150° C. The plates were then put into an inert nitrogen controlled atmosphere furnace. The braze ovens have a −45° C dew point to prevent any moisture in the furnace that would liberate HF or KF, or both. The O2 was approximately 50 ppm. Fluids Tested For the first study with various amounts of flux loading, the following coolant fluids were tested at 25 % coolant concentrate with deionized water and 100 ppm of chloride 共in the form of sodium chloride兲: • Conventional Silicate Coolant • Hybrid Coolant 共i.e., coolant containing both silicate and an organic acid兲 • Organic Acid Coolant • Modified Organic Acid Coolant For the study of the fluxed and brazed samples from various suppliers, only hybrid coolant was used. The solution was 25 % by volume of coolant with 100 ppm of chloride. Electrochemical Testing The samples were placed into an electrochemical cell specified in FLTM BL-105-01 关1,5–7兴, yielding an exposed aluminum surface area of 8.04 cm2. Test coolant fluid was added to the cell and the aluminum heated until the fluid boiled. The fluid was boiled for 1 h, while maintaining the fluid volume by additions of deionized water 共if required兲, and then the temperature of the fluid was reduced to 70° C. Upon reaching this temperature either the modified FLTM BL-105-01 关1兴 or potentiodynamic polarization tests were conducted. At the end of the test, samples of before and after test fluid were submitted for analysis of fluoride ions. Modified Ford FLTM BL 105-01—Galvanostatic Test—The general procedure for the test method FLTM BL 105-01 关1,5–7兴 was followed with the exception that the cell was at elevated temperature. Testing of varying flux loadings in conventional and hybrid coolants was performed. The temperature of the solution in the cell after boiling for 1 h was lowered to 70± 5 ° C. The sample was connected to a Solartron SI 1287 potentiostat as the working electrode. A graphite rod counter electrode and a silver/silver chloride 共3 M KCl兲 reference electrode in a Luggin probe, both connected to the potentiostat, were added to the cell. The open circuit potential 共Eoc兲 was measured for 5 min then an anodic current of 100 ␮A cm−2 was applied to the aluminum. The potential applied to the cell was monitored with time, for 1 h. The lowest potential measured, after the initial spike, was recorded. This value was used as an approximation of the repassivation potential for aluminum. This test will be referred to as the galvanostatic test for the rest of this paper. Potentiodynamic Polarization—The same experimental setup was used as described for galvanostatic testing 共above兲 except for testing with increasing potential and recording the resulting current. The open circuit potential 共Eoc兲 was measured for 5 min and a potentiodynamic polarization scan was started at −20 mV versus Eoc 共i.e., the open circuit potential兲. The potential was scanned at a rate of 2 mV s−1 in the anodic 共positive兲 direction until pitting 共i.e., a substantial and rapid increase of current兲

72 ENGINE COOLANT TECHNOLOGY TABLE 2—Lowest potential measured, after the initial spike, during a galvanostatic test.

Solution Conventional Hybrid

No Flux, V −0.21 −0.01

1 2

Flux, V −0.28 −0.07

Regular Flux, V −0.40 −0.24

Double Flux, V −0.24 −0.15

1

2 Area Fluxed, V −0.14 −0.21

was observed or the potential reached +2 V, whichever happened first. The current was recorded as a function of potential. The pitting potential and the passive current were tabulated. Results and Discussion Corrosion Properties Galvanostatic Test-Flux Loading Study—The lowest potential measured, after the initial spike, for the solutions and flux loading are listed in Table 2. All values are reported as volts versus Ag/ AgCl 共3 M KCl兲 reference electrode 共SCE-35 mV兲. As the current is first applied, the potential rapidly climbs from the open circuit value. For conventional coolants the rapid climb is followed by a rapid fall in the potential as corrosion has been initiated, Fig. 1. The potential generally becomes approximately constant. The lowest potential, after the initial spike is recorded, is an indication of how the system repassivates after corrosion has been initiated. The tests are designated by Ford as pass or fail with a pass defined as a potential above the arbitrarily chosen value of −0.4 V versus SCE. For the conventional coolant, lower potentials are measured with increasing flux loading, up to a regular flux amount. The regular amount of flux caused the sample to have a marginal test result. Interestingly, the double flux loading on the sample had a higher potential measurement. The double fluxed sample was “crusty” in appearance due to a hard crystalline deposit covering the surface. The lower potential is probably associated with the limited surface area of exposed aluminum on the sample, due to the heavy deposits. The hybrid coolant behaved similarly to the conventional coolant in this test. The lowest potential measured decreased with increased flux loading up to the regular amount of flux. In this case, however, the test was a pass. For the double fluxed sample, the potential was slightly higher than in the regular flux sample. This increase was probably due to the heavy deposit on the surface that limited the amount of aluminum surface area exposed to the solution. For both coolants, any amount of the flux on the surface lowers the “pitting” potential as compared to the sample without flux. The lowest potential in both types of coolant was the sample with the regular flux loading. The sample appearances after the test for different coolants were different. The hybrid coolant samples exhibited dark staining 共small pits兲 around the gasket area. The conventional coolant samples exhibited small pits evenly distributed over the surface.

FIG. 1—Schematic of polarization curve from the galvanostatic test, (a) conventional coolant, (b) organic acid coolant.

JEFFCOATE ET AL. ON CAB ALUMINUM SURFACES 73 TABLE 3—Pitting potential, V versus Ag/ AgCl (3M KCl), passive current, ␮A cm⫺2, measured during a potentiodynamic polarization curve, and surface-area average corrosion rate, ␮m / year, determined by the Tafel extrapolation method.

Solution and Test Conventional

Hybrid

Organic Acid

Mod. Organic Acid

Pitting Passive Current Average Corrosion Rate Pitting Passive Current Average Corrosion Rate Pitting Passive Current Average Corrosion Rate Pitting Passive Current Average Corrosion Rate

No Flux 0.27 1.75 0.23 None NA 0.23 1.02 7.4 13.1 ⬎1 3.89 1.79

1 2

Flux −0.1 5.09 3.00 0.053 3.37 2.26 ⬎1 11.79 25.4 ⬎1 7.16 1.96

Regular Flux −0.16 1.03 0.65 −0.25 3.05 1.98 ⬎1 15.6 14.5 0.53 1.1 0.91

Double Flux −0.32 2.66 2.30 −0.18 1.35 2.21 −0.37 2.05 6.2 −0.27 0.35 0.59

1

2 Area Fluxed 0.005 1.96 1.46 0.05 5.59 3.40 ⬎1 16.62 18.0 0.65 4.11 1.45

NA= Not applicable.

Potentiodynamic Polarization-Flux Loading Study—From the polarization curves, three values were reported: the pitting potential, the onset of stable pitting corrosion; the passive current, the current required to maintain the passive film on the aluminum surface; and surface-area average corrosion rate, determined by Tafel extrapolation of the polarization curve to the corrosion potential. Results are shown in Table 3. The onset of stable pitting is indicated by a change of slope where a large increase in current is coupled with a relatively small increase in potential. The potential at which this rapid increase in current occurs is known as the pitting potential, see Fig. 2. The lower the potential, the easier it is to initiate pitting. For the conventional coolant, the pitting potential decreased with increasing flux loading, Fig. 2. The reduction in pitting potential from no flux to double the regular flux load amounted to 590 mV. This indicates a lowering of the pitting potential with increased flux loading. In other words, it indicates that the flux is not passive 共inert兲, as has been previously thought, but is active and is affecting the corrosion potential of the aluminum. In hybrid coolant, no pitting potential could be discerned in the sample with no flux residue because there was no rapid change in slope during polarization, see Fig. 3. The potential increased as the current increased, however, in a nonlogarithmic way, and reached a high potential similar to that measured during active pitting in other samples. The sample with no flux in hybrid solution also had pitting potential approximately 400 mV above the fluxed samples. This is similar to the conventional coolant and indicates

FIG. 2—Potentiodynamic polarization curve of aluminum 3003 with various flux loading in heated 25 % conventional coolant with 100 ppm chloride.


FIG. 3—Potentiodynamic polarization curve of aluminum 3003 with various flux loading in heated 25 % hybrid coolant with 100 ppm chloride. that flux loading affects the corrosion potential of the aluminum. Potentiodynamic polarization curves in organic acid coolants generally behave in the following manner: as the potential of the aluminum is increased a broad region of passivity is measured, with no pitting occurring before the scan is stopped. This was the case for the organic acid coolant samples with no flux loading and half the regular amount of flux loading, where the pitting potential measured over 1 V. In the sample with double the regular amount of flux loading the pitting potential was measured at −0.37 V. The passive current in Table 3 is the amount of current required to maintain the passive film at the metal solution interface. In the passive region no active pitting is taking place, even though a measurable current is recorded. The region is characterized by only a small change in current over a wide change in potential. The passive currents reported in Table 3 were all within a small range of values from 1.03 to 7.16 ␮A cm−2, with the exceptions of the samples tested in organic acid coolant, with passive currents up to 16.62 ␮A cm−2. The lowest passive current was for a double fluxed sample in modified organic acid coolant at 0.35 ␮A cm−2. The hybrid solution with aluminum with no flux residue had no clear region where the current changed little with increasing potential, and is recorded in the table as NA. As shown in Table 3, for both conventional and hybrid coolants, the presence of flux generally leads to an increase in the corrosion rate. The increase in corrosion rate may be as much as more than an order of magnitude, depending on the amount of flux present on the surface. The corrosion rates in the organic acid coolant were generally higher than the rates in other coolants. But organic acid coolant was less affected by the presence of flux on the surface. Modified organic acid coolant yielded substantially lower corrosion rates under the test conditions. The corrosion rates in modified organic acid coolant were similar and in some cases, even lower than the corresponding values obtained in conventional or hybrid coolants, or both, Table 3. It should be noted that the average corrosion rate in all four coolants was very low for the short immersion period of the tests. Potentiodynamic Polarization—Flux Commercial Compound Study—When samples of the three commercially available flux compounds, brazed into aluminum, were tested by potentiodynamic polarization, very different curves were recorded than in the flux loading study, Fig. 4. The pitting potentials, passive currents, and surface-area average corrosion rates are shown in Table 4. The flux sample “A” had the highest pitting potential of the three samples tested. Flux sample “C” evidenced the lowest pitting potential but the highest passive current and the highest average corrosion rate. Sample “B” appears to be the best formulation of those tested, due to having the lowest passive current and lowest average corrosion rate, as long as it could be maintained below its pitting potential. Fluoride Ion Content—Flux Loading Study—The majority of coolants after galvanostatic and potentiodynamic testing were analyzed for fluoride ion content. The results for the fluoride analysis are shown in Table 5. When no flux residue is present on the aluminum surface, no fluoride is measured in the end of the test fluid. However, when flux residue is present on the aluminum surface, fluoride is measurable by ion chromatography in the coolant sample after test. In addition, the more flux residue present, the higher the

JEFFCOATE ET AL. ON CAB ALUMINUM SURFACES 75

FIG. 4—Potentiodynamic polarizations of three different flux compounds on aluminum sheet, 25 % hybrid coolant with 100 ppm chloride. The potential value versus an Ag/ AgCl (3 M KCl) reference electrode. levels of fluoride measured. The galvanostatic test maintains the sample at high temperature longer than the potentiodynamic test, approximately 2 h 20 min versus 1 h 45 min, respectively. This most likely explains the higher levels of fluoride in the galvanostatic test fluids than the potentiodynamic test fluids. Of the fluids tested, the organic acid coolant had the highest levels of fluoride at the end of the test 共50 ␮g / mL for the regular flux sample in the potentiodynamic test兲. The next highest levels were found in the hybrid 共25 ␮g / mL兲 and the conventional coolant 共14 ␮g / mL兲. The lowest levels occurred in the modified organic acid 共⬍5 ␮g / mL兲. To confirm that the electrochemical testing was not causing the presence of fluoride in the end of test fluids, testing was conducted with double fluxed aluminum samples. The samples were immersed in conventional and hybrid coolants and heated in a similar way as the samples prepared for electrochemical testing 共boil for 1 h, reduce temperature to 70° C, maintain at 70° C for 15 min兲 but were not electroTABLE 4—Pitting potential and passive currents for three different fluxes on aluminum in 25 % hybrid coolant solution with 100 ppm chloride. Test/ Flux Supplier Pitting Potential, V Passive Current, ␮A / cm2 Average Corrosion Rate, ␮m / year

A 0.164 7.66 20.4

B −0.203 4.62 12.8

C −0.27 32.5 49.8

TABLE 5—Fluoride content in after test fluid in ␮g / mL. Measured by ion chromatography. Solution and Test Conventional Galvanostatic Potentiodynamic Hybrid Galvanostatic Potentiodynamic Organic Acid Potentiodynamic Mod. Org. Acid Potentiodynamic Conventional No E-Chem Hybrid No E-Chem Note: ND= None detected.

No Flux

1 2

Flux

1

Regular Flux

Double Flux

2 Area Fluxed

⬍1 ⬍1

9 8

19 14

9 7

8 9

⬍1 ⬍1

26 24

33 25

81 16

28 20

⬍1

25

50

100

55

ND

⬍5

⬍5

⬍5

⬍5

…

…

…

11

…

…

…

…

69

…

76 ENGINE COOLANT TECHNOLOGY TABLE 6—Fluoride content in end of test fluid, measured by ion chromatography. Concentration of Fluoride/Flux Supplier Fluoride, ␮g / mL

A 71

B 31

C 168

chemically tested. Significant amounts of fluoride were present in the end of test fluids, as shown in Table 5. This indicates that fluoride freely leaches into the test fluids from the flux residue during the test. The variation in the amount of fluoride measured in the nonelectrochemistry samples versus the electrochemically tested samples could be due to sample to sample variation. Fluoride Ion Content—Flux Commercial Compound Study—Of the three different flux types tested in hybrid solution with 100 ppm chloride, type “B” flux had the lowest amount of fluoride in the end of the test fluid, as shown in Table 6. The flux type “C” has poor corrosion resistance, as well as the highest fluoride content. Conclusions • Test results indicate the flux from the CAB brazing process is not inert on aluminum surfaces in the presence of various types of coolants, from conventional to hybrid to organic acid. The greater the amount of reacted flux on an aluminum surface, the more active the flux. • The electrochemical results showed that the higher the flux loading on the aluminum header material, the lower the pitting potential and the easier it was to initiate corrosion. This was consistent with all fluids tested. • Chemical analysis shows the presence of significant quantities of fluoride in the end of test the fluid for samples with flux. The modified organic acid coolant evidenced negligible fluoride in the end of the test solution. In the case of no flux loading, no fluoride was detected in all coolants. • Since the only fluoride containing component of the system is the flux, it appears fluoride leaches from the flux. • Results indicate brazing flux composition also affects corrosion potential. Samples of three different flux compositions with the same flux loading and tested with hybrid coolant evidenced significantly different electrochemical results and fluoride ion concentrations. In this round of testing for leaching of fluoride, flux type “B” was considered a better formulation for engine coolant applications. References 关1兴关2兴关3兴关4兴关5兴关6兴关7兴

Ford Test Method BL 105-01, “A Rapid Method to Predict the Effectiveness of Inhibited Coolants in Aluminum Heat Exchanger,” Ford Motor Company, 2001, pp. 1–5. Claydon, D. and Sugihara, A., “Brazing Aluminum Automotive Heat Exchange Assemblies Using a Non-Corrosive Flux Process,” SAE 830021, February-March 1983. Ando, Y., Nita, I., Uramoto, M., Ochiai, H., and Fujiyoshi, T., “Development of Aluminum Radiators Using the Nocolok Brazing Process—Corrosion Resistance of New Aluminum Radiators by Applying a Nocolok Brazing Process,” SAE 870180, February 1983. CASTI Metals Red Book—Nonferrous Metals, 4th ed. on CD-ROM, Casti Publication, Inc., Edmonton, Alberta, Canada, 2003. Wiggle, R. R., Hospadaruk, V., and Tibaudo, F. M., “Corrosion of Aluminum Alloys Under Heat Transfer Conditions,” SAE 810038, Society of Automotive Engineers, Warrendale, PA, 1981. Wiggle, R. R., Hospadaruk, V., and Styloglou, E. A., “The Effectiveness of Automotive Engine Coolant Inhibitors for Aluminum,” J. Mater. Eng. Perform., National Association of Corrosion Engineers, Houston, 1981, pp. 13–18. “A Rapid Method to Predict the Effectiveness of Inhibited Engine Coolants in Aluminum Heat Exchangers,” SAE 800800, Society of Automotive Engineers, Warrendale, PA, 1980.


Bo Yang,1 Aleksei V. Gershun,1 Filipe J. Marinho,1 and Peter M. Woyciesjes1

Effect of Fluoride on Corrosion of Cooling System Metals in Ethylene Glycol-Based Antifreeze/Coolants ABSTRACT: Automotive and light-duty vehicle heat exchangers such as radiators are now predominantly made of aluminum alloys. For over 20 years, a brazing technique known as “controlled atmosphere brazing 共CAB兲 with noncorrosive fluxes” has become the preferred process for producing aluminum automotive heat exchangers for original equipment manufacturers and aftermarket suppliers. Fluoride-based fluxes are typically used in the CAB processes to dissolve the aluminum oxide layer on the surface and inhibit reoxidation during the brazing cycle to allow the clad alloy to flow properly. The flux is generally a mixture of potassium fluoroaluminate, 共K3AlF6, K2AlF5, and KAlF4兲. The flux residue left on the internal surface of heat exchangers after brazing is thought to be insoluble and noncorrosive, hence no removal is necessary. Although external corrosion of brazed aluminum heat exchangers has been studied using salt spray tests, a study addressing the effect of interaction between different antifreeze and flux residues on internal corrosion has not been reported. To the authors’ knowledge, few studies on the effect of fluoride in engine coolants on metal corrosion are available. In this paper, laboratory test data are provided to show that flux residue is soluble in commercially available coolants and can generate fluoride ions that enhance cooling system corrosion. Systematic study on the effect of fluoride on metal corrosion in cooling systems and its remedies are also presented and discussed. KEYWORDS: antifreeze/coolant, aluminum corrosion, fluoride, brazed aluminum, heat exchangers, potassium fluoroaluminate flux

Introduction Aluminum alloys are predominantly used as the material of choice for various components in modern light-duty automotive cooling systems to reduce the weight of the vehicles. Specifically, in addition to the engine block, a variety of heat exchangers in the cooling systems, such as radiator, condenser, evaporator, and heater core, are made of aluminum alloys. In the past, mechanical expansion techniques have been used for mass-production of automotive heat exchangers 关1兴. Because of having inferior thermal performance and relatively high weight, heat exchangers assembled mechanically are not widely used. Heat exchangers are now predominantly formed by a brazing operation, wherein the individual components are permanently joined together with a brazing alloy. Recently, one brazing technique known as “controlled atmosphere brazing 共CAB兲” has become accepted by the automotive industry for making brazed aluminum heat exchangers, including radiators, condensers, evaporators, heater cores, air charged coolers and inter-coolers 关2–4兴. CAB brazing has been preferred over a previous brazing method, i.e., vacuum furnace brazing 关2兴, due to improved production yields, lower furnace maintenance requirements, greater braze process robustness, and lower capital cost of the equipment employed. In the CAB process, a fluxing agent is applied to the preassembled component surfaces to be jointed. During brazing at approximately 560– 575° C, the fluxing agent starts to melt and the melted flux reacts, dissolves, and displaces the aluminum oxide layer that naturally formed on aluminum alloy surface and frees up the filler metal 共clad aluminum兲. The filler metal starts to melt at about 575– 590° C and begins to flow toward the joints to be brazed. During the cooling process, the filler metal solidifies and forms braze joints. The flux present on the surface also solidifies and remains on the surface as residue. Additional functions of the fluxing agent are to prevent reformation of an aluminum oxide layer during brazing, and Manuscript received February 22, 2006; accepted for publication September 22, 2006; published online October 2006. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Honeywell, Danbury, CT 06810 Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

77


enhance the flow of the brazing alloy. The fluxing agent is typically a mixture of alkaline metal fluoroaluminates with the general formula K1-3AlF4-6 · xH2O. One widely used flux for brazing aluminum is sold under the trademark Nocolok®, which is essentially a mixture of K3AlF6, K2AlF5, and KAlF4 关5,6兴. Fluoride-based fluxes are preferred over chloride-based fluxes for brazing aluminum or aluminum alloys because they are considered to be inert or noncorrosive to aluminum and its alloys, and substantially water insoluble after brazing. Hence, no removal is necessary after the brazing operation. Due to the noncorrosive nature of the flux together with its tolerance to brazing assembly fit-up and flexible control, Nocolok® flux brazing is one of the lowest cost methods for the joining of aluminum heat exchangers. It is now commonly used by the automotive industry for manufacturing of heat exchangers 关3,7兴. Corrosion of brazed aluminum heat exchangers has been studied using salt spray tests 关7兴. The presence of flux residues on a heat exchanger surfaces is shown to enhance the corrosion resistance. A study by Davies and Prigmore 关8兴 suggested that the presence of 100 ppm sodium fluoride in distilled water containing 100 ppm KC1 at 25± 1 ° C could delay the onset of pitting of a commercially pure aluminum at −0.85 V versus a Hg/ HgSO4 reference electrode due to a probable formation of a surface film made of some form of aluminum oxyfluoride or hydroxyfluoride. However, replacing the distilled water with 50 % ethylene glycol solution showed that no delay of the onset of pitting of the aluminum under similar test conditions was observed 关8兴. It was determined that a much thinner surface film containing fluoride was formed in the 50 % ethylene glycol solution. To the authors’ knowledge, studies conducted under conditions more relevant to engine cooling system operating conditions have not been reported. Research conducted by Prestone R&D Laboratory shows that the flux residue on an aluminum alloy surface will leach out fluoride ions which can lead to localized corrosion on the metal substrate when it is immersed in a number of commercial coolants under engine cooling system operating conditions. Systematic study on the effect of fluoride on metal corrosion in cooling systems and its remedies are also presented and discussed. Experimental Solutions The base test solutions were prepared by mixing commercially available coolants with deionized water to yield a coolant concentration of either 25 vol. % or 50 vol. %. Aqueous solution of 40 % 共w/v兲 KF from Spectrum Chemical Mfg. Corp. was used as the source of fluoride. Other components of the test solution were sodium chloride 共ACS grade兲 and commercial products supplied by the producers. Metal Plate Samples and Test Procedures Brazed Aluminum with Flux Residues—Sheets of aluminum header alloy 共AA 3003兲 were prepared with flux. The sheets were applied with various load concentrations of flux. The flux types were designated as B1 and B2, respectively. The concentrations of the applied flux were either a regular flux load amount 共B1兲 or a double amount of flux 共B2兲 on the surface. The amount of flux applied was determined by weighing a virgin plate with no flux. Then the sheet was sprayed with flux in the production process and the sheet was weighed again. The amount of the flux for that surface area was taken as a regular flux loading. The sheets were then brazed and cut into 2 by 2 in. sections. The sample quality was variable in coverage and thickness of flux. Samples used in the experiments were chosen to be as representative as possible. The samples were used as received. Wrought Aluminum AA 3003 (UNS A93003)—Sheet of AA 3003 共1 / 16-in. thick兲 obtained from McMaster-Carr were cut into 2 by 2 in. sections. The samples without any visible scratches were chosen for use as the electrode. In some tests, 600 grit silicon carbide sand paper polished plates of Al 3003 共1 / 4-in. thick, 2 by 2 in.兲 were also used as the test electrode. The electrode sample was cleaned with acetone and air dried just before immersion in the test solution for electrochemical tests. Cast Aluminum AA 319 (UNS A03190)—Round plate of AA 319 共2-in. diameter by 3 / 8-in. thick兲 obtained from The Metaspec Co. were used as the electrode. The samples were polished by 600 grit silicon carbide sand paper, cleaned with acetone, and air dried before immersion into the test solution.

YANG ET AL. ON EFFECT OF FLUORIDE 79

Test Cells—A Ford Laboratory Test Method 共FLTM兲 BL-105-1 “A Rapid Method to Predict the Effectiveness of Inhibited Coolants in Aluminum Heat Exchangers” test cell was used to conduct the tests for the metal plate sample. The FLTM BL-105-01 test cell would give an exposed aluminum surface area of 8.04 cm2. The volume of solution used in a test was about 45 mL. A graphite rod was used as counter electrode. A silver/silver chloride 共3 M KCl兲 reference electrode placed in a Luggin probe was used as the reference electrode. Test Procedures—Three test conditions were used for the plate metal samples. In one test, the test coolant fluid was added to the cell and the aluminum heated until the fluid boiled. The fluid was boiled for 1 h, while maintaining the fluid volume by additions of deionized water 共if required兲, and then the temperature of the fluid reduced to 70° C. Once the solution in the cell had reached the temperature of 70° C, the sample was connected to a potentiostat as the working electrode. The open circuit potential was measured for 5 min and a potentiodynamic polarization scan started at −20 mV versus the open circuit potential. The potential was scanned at a rate of 2 mVs−1 in the anodic 共positive兲 direction until pitting was observed or the potential reached 2 V more anodic than the open circuit potential, whichever happened first. The current was recorded as a function of potential. At the end of the test, samples of before and after test fluid were submitted for analysis of fluoride ions. In the second test, the test fluid was added to the cell and the flux residues covered brazed aluminum sample was heated until the solution reaching 80° C and maintained at this temperature for 6 h. At the end of the test, the mass loss of the brazed aluminum sample was determined after drying in a 60° C oven overnight. Samples of the test fluid before and after the test were analyzed for fluoride ions. In this test, no electrochemical measurement was conducted on the sample. In the third test, test coolants containing various concentrations of fluoride ions were used. The test solution was added to the cell and the aluminum AA 319 or AA 3003 electrode sample was heated until the solution reaching 85° C and maintained at this temperature for the duration of the test, typically ranging from 4 h to 7 h. Once the solution in the cell had reached the temperature of 85° C, the sample was connected to a potentiostat as the working electrode. The open circuit potential was then measured for at least 30 min. Immediately after the open circuit potential measurement, a polarization resistance measurement of the sample was conducted using a scan rate of 0.1667 mVs−1. Afterwards, a potentiodynamic polarization scan using a scan rate of 2 mVs−1 in the anodic 共positive兲 direction until reaching about 5 V versus Ag/ AgCl 共3 M KCl兲 was conducted. NanoCorr Coupled Multi-electrode Sensors for Measuring Localized Corrosion A Corr Instruments NanoCorr Coupled Multi-electrode Sensor 共CMS兲 Analyzer with Corr Visual Software, Version 1.0.3, was used to determine the localized corrosion rate of cast aluminum in the test solution. The CMS method is a new electrochemical method capable of real-time monitoring of localized corrosion rates of metal in corrosive media 关9兴. A more detailed description of the use of this method for use in coolant research is described in a separate paper 关10兴. In this study, a 25-electrode sensor array probe supplied by Corr Instruments was used. Each electrode of the probe is made of the same cast aluminum 共SAE 329, UNS A23190兲 square wire having an exposed surface area of 1 mm2. The 25 wire electrodes sealed in Epoxy and spaced uniformly in a 1.2 by 1.2 cm matrix array were connected electrically. The coupled multi-electrode probe simulates the corrosion conditions of a conventional one-piece electrode surface having an exposed surface area of about 1.4 cm2. One can obtain a localized corrosion rate as a function of time from the probe by measuring the coupling current from each individual electrode in the probe and performing statistical analysis of the measured data 关9兴. In this study, a sampling rate of 30 s per set of data was used. A Pyrex glass beaker holding 500 mL of test solution was used as the test cell. The coupled multielectrode array sensor probe, a Ag/ AgCl 共3 M KCl兲 reference electrode placed in a Lugin probe with the opening close to the multi-electrode sensor probe, and two temperature sensor probes 共i.e., a thermal couple and a resistance temperature detector with stainless steel sheath兲 are mounted on a Teflon cell cover and immersed in the solution in the beaker. The Teflon cover was used to minimize solution loss during the experiment and also used to fix the position of the test probes in the cell. A microprocessor control

80 ENGINE COOLANT TECHNOLOGY TABLE 1—Fluoride concentration after electrochemical tests on brazed aluminum in various coolants. Solution boiled for 1 hr. Test Solution Volume ⫽ 45 mL. Potentiodynamic scan test done after solution temperature cooled to 70° C. Surface area average corrosion rate determined by Tafel extrapolation of the anodic polarization curve. Coolant ID Fluoride, mg/L 25 % OAT coolant A + 100 ppm Cl 56 25 % OAT coolant A + 100 ppm Cl, No flux or 0 brazed 25 % HOAT coolant+ 100 ppm Cl 113 25 % SIT coolant+ 100 ppm Cl 26 25 % OAT coolant A + Additive 1 + 100 ppm Cl 7 25 % OAT coolant A + Additive 2 + 100 ppm Cl ⬍5

Observation Corrosion Rate, ␮m / y 90 % surface area were attacked 9.02 Surface 共AA3003兲 showed minimal attack 13.1 Surface Surface Surface Surface

attacked intensively showed isolated localized attack showed very minor attack showed no noticeable attack

140 0.85 1.56 3.81

Note: % coolant is by volume.

hot-plate was used to heat the solution to the desired temperature during the test. A Teflon coated magnetic stirring bar was also used to agitate the solution during the test. The solution was exposed to the air during the test. Results and Discussion Brazed Aluminum—Effects of Different Coolant Chemistry and Organic Additives Table 1 shows the results of solution analysis of fluoride concentrations in various coolant formulations after exposing to a potassium fluoroaluminate flux-brazed aluminum sample and after conducting anodic polarization curve measurements on the sample while immersing in the coolants. The results show that while coolants at 25 vol. % dilution containing organic acids 共OAT兲, low silicate organic acid hybrid 共HOAT兲 and conventional 共SIT兲 high silicate-based corrosion inhibitor formulations can provide excellent corrosion protection for aluminum alloys 共without any flux residue兲 in vehicle operation conditions, their corrosion protection for brazed aluminum containing fluoride-based flux residue on the surface have room for improvement. Concentrations of fluoride in the post-test fluids were 26, 56, and 113 mg/ L for SIT, OAT and HOAT, respectively. Addition of a small amount of corrosion inhibition additives to an organic acid-based coolant resulted in substantial improvement in corrosion protection of the brazed aluminum containing flux residue. The amount of fluoride ions being released into the test fluid was also reduced drastically by the addition of the corrosion inhibition additives. Different additives appeared to yield different results under the same dosage conditions. The anodic polarization curve results 共see Fig. 1兲 show similar results as previously described in Table 1. It should be noted that the results shown in Fig. 1 indicate that additive 1 appeared to yield better corrosion protection for the brazed aluminum than additive 2 under comparable conditions. Table 2 shows the results on solution analysis of fluoride concentrations and brazed aluminum sample mass loss under a different set of test conditions using 50 vol. % coolants. No electrochemical measurement was conducted on the samples in this set of tests. The samples were immersed in the test solutions longer than the ones used in Table 1. The results suggest that electrochemical measurements are not the sole cause of fluoride ions being release from the flux residue covered surface. The addition of 100 ppm chloride seemed to result in an increase in the amount of fluoride ions being release into the test solution. The brazed aluminum corrosion protection performance was increased substantially when a small amount of organic corrosion inhibiting additives was added into an organic acid based coolant. The improvement in corrosion protection performance was demonstrated by the reduction in both the mass loss of the test sample and the amount of fluoride being release to the test solution detected at the end of test by ion chromatography. The results in Table 2 show that the corrosion behavior of the brazed aluminum in 50 vol. % coolant solution is similar to the ones observed in 25 vol. % coolant solutions. Effect of Flux Loadings on Corrosion Protection Performance Table 3 show the corrosion test results 共i.e., surface area average corrosion rates and corrosion potentials兲 and fluoride concentrations contained in the 25 vol. % OAT coolant A 共OAT兲 and a modified OAT coolant


FIG. 1—Effect of coolants on corrosion of brazed aluminum covered with flux residue. A 共MOAT兲 end of test solutions for the various brazed aluminum samples having normal flux loading 共e.g., designated as B1兲 and at a double flux loading 共e.g., designated as B2兲. The results indicate the following: 1. The average corrosion rates determined from Tafel extrapolation of the anodic polarization curves on the brazed aluminum surface with double amount of the flux loadings were higher than the corresponding values with regular amount of flux loading. 2. Addition of organic additive 1 共contained in the MOAT solution兲, substantially reduce the average corrosion rates 共by about 77 to 93 %兲 in comparison with the corresponding values for the coolant TABLE 2—Mass loss and fluoride concentration results for brazed aluminum in various coolants. Solution heated to 80° C for 6 h. Sample exposed surface area ⫽ 8.04c sq cm. Solution V ⫽ 45 mL.

50 50 50 50 50 50

% % % % % %

OAT OAT OAT OAT OAT OAT

Coolant ID Coolant A Coolant A + 100 ppm Cl Coolant B + 100 ppm Cl Coolant C + 100 ppm Cl Coolant A + Additive 2 + 100 ppm Cl Coolant A + Additive 3 + 100 ppm Cl

Fluoride, mg/L 37 71 47 30 3 ⬍5

Mass Loss, mg 5.9 6.4 4.9 5.4 0.8 0.6

Note: % coolant is by volume.

TABLE 3—Fluoride concentration in end of test solution and surface area average corrosion rate determined by Tafel extrapolation of the anodic polarization curve, and corrosion potential of various brazed aluminum in OAT coolants. Brazed Aluminum ID

B1

B2

25 vol. % OAT Coolant A Fluoride, mg/L Corrosion Potential, V/AgAgCl Average Corrosion Rate, ␮m / y Fluoride, mg/L Corrosion Potential, V/AgAgCl Average Corrosion Rate, ␮m / y

90 65 −0.61 −0.584 13.8 40.5 25 vol. % Modified OAT Coolant A 5 5 −0.682 −0.765 3.11 2.94


FIG. 2—Effect of coolant chemistry on brazed aluminum corrosion. without the additive. The corrosion rates in the modified OAT coolant A show little variation with regard to the flux loading. 3. Significant amounts of fluoride ions were detected in the end of test solutions by ion chromatography. The amount of fluoride released to the solution may vary to some degree due to a number of variables involved in the brazing operation. 4. In the modified MOAT A, the amount of fluoride ions being released to the solution were substantially reduced. The very low concentrations of fluoride ions being detected at the end of the test showed little variation with regard to the flux loading. The anodic polarization curves determined by potentiodynamic scan measurements corresponding to the conditions given in Table 3 are shown in Fig. 2. The anodic polarization curve of sample B1 in OAT coolant, showed no obvious pitting potential; however, the current density did increase steadily and exceeded 10 ␮A cm−2 when the potential exceeded 0 V versus Ag/ AgCl reference electrode. The same test with a MOAT coolant gave a more positive corrosion potential and lower overall passive currents, Fig. 2. Similar results were obtained on samples with double the flux loading, i.e., B2 sample. The MOAT coolant maintained the current densities at levels seen within the test with the B1 sample, while the corrosion current in OAT coolant was considerably higher with the B2 sample. Effect of Fluoride on Cast Aluminum Corrosion The effect of fluoride ions on corrosion of cast aluminum 共UNS A03190兲 in OAT coolant A is shown in Fig. 3. The corresponding surface area average corrosion rates are given in Table 4. One can see that increasing fluoride concentration in coolants generally lead to an increase in corrosion in aluminum parts not covered with brazed residue, e.g., engine block. The higher the concentration of fluoride, the more aggressive the coolant could become. An increase in the cast aluminum corrosion rate in the 25 vol. % OAT coolant A can be observed at a fluoride concentration as low as 28 mg/ L. As shown in Table 4, fluoride ions appear to be more corrosive than chloride ions under the test conditions. Effect of Fluoride on Corrosion of Wrought Aluminum AA 3003 in OAT Coolant B The effects of fluoride ions on corrosion of wrought aluminum AA 3003 in 25 vol. % of OAT coolant B is shown in Fig. 4. The corresponding surface area average corrosion rates are shown in Table 4. Similar


FIG. 3—Effect of fluoride on corrosion AA 319 in 25 vol. % OAT coolant A. to the results obtained on cast aluminum in 25 vol. % OAT coolants A, one can see that increasing fluoride concentration in coolant B generally led to an increase in corrosion of wrought aluminum parts not TABLE 4—Effect of fluoride on corrosion of aluminum alloys in OAT coolants. Cast Aluminum UNS A03190 in 25 vol. % OAT Coolant A Polarization Resistance LPR CorrRate CorrRateគTafelគanodic Fluoride Concentration Ecorr Ohm* cm2 ␮m / y ␮m / y mg/L V/AgAgCl None −0.833 4300 127 192 None −0.858 5430 100 152 28 −0.871 1660 328 425 55 −0.922 897 608 797 112 −0.998 675 807 1376

100 mg/ L Chloride

Time at 85° C h 1 1 1 1 1

−0.863

1 1610 339 209 Wrought Aluminum AA 3003 in 25 vol. % OAT Coolant B Time at 85° C Fluoride Concentration Ecorr Polarization Resistance LPR CorrRate CorrRateគTafelគanodic ␮m / y ␮m / y h mg/L V/AgAgCl Ohm* cm2 1 None −0.919 7618 71.5 73.8 1 117 −1.037 275 1985 1224 1 228 −1.081 173.6 3139 1945 1 561 −1.125 64.2 8491 2199 Wrought Aluminum AA 3003 in 25 vol. % OAT Coolant A + Org. Additive Time at 85° C Fluoride Concentration Ecorr Polarization Resistance LPR CorrRate CorrRateគTafelគanodic mg/L V/AgAgCl ␮m / y ␮m / y h Ohm* cm2 1 563 −0.9405 8576 63.6 48.9 Wrought Aluminum AA 3003 in 50 vol. % OAT Coolant B Fluoride Concentration Ecorr Polarization Resistance LPR CorrRate CorrRateគTafelគanodic Immersion Time ␮m / y ␮m / y mg/L V/AgAgCl h Ohm* cm2 −0.9035 15650 34.8 20.2 54 h of cycling between None 565 −1.0266 1708 319 217 85° C 共6.5 h兲 and Room T共17.5 h兲 Note: Corrosion rates were surface area averaged values. Polarization resistance measurements were conducted 10 min before anodic scan. Stern-Geary coefficient of 49.9 mV was used to convert the polarization resistance value to the LPR corrosion rate value.


FIG. 4—Effects of fluoride and organic additive on corrosion AA 3003 in 25 vol. % OAT coolants. covered with brazed residuals. The effect increases with increasing fluoride concentration. In the presence of ⬃560 mg/ L fluoride, the surface area average corrosion rate of the AA 3003 sample was increased approximately 30 times in comparison with the values observed in the absence of fluoride in 25 vol. % of coolant B. Addition of a small amount of organic additive is very effective in reducing corrosion rate of AA 3003 even in the presence of approximately 560 mg/ L fluoride. The effect of fluoride on increasing corrosion rate of AA 3003 persisted after 54 h of cyclic immersion between high temperature 共6.5 h per day兲 and room temperature 共rest of the day兲, as shown in Fig. 5. Again, the average corrosion

FIG. 5—Effect of fluoride on corrosion AA 3003 in 50 vol. % OAT coolant B.


FIG. 6—Localized corrosion rate of cast aluminum in 25 vol. % OAT coolant B. rate of AA 3003 in 50 vol. % OAT coolant B in the presence of approximately 560 mg/ L fluoride after 54 h of the cyclic temperature exposure conditions was increased by about ten times in comparison with the values obtained in the absence of the fluoride ions. Effect of Fluoride and Organic Additives on the Localized Corrosion of Cast Aluminum Figure 6 shows the test results obtained from the NanoCorr Coupled Multielectrode Analyzer instrument using a 25-electrode probe immersed in 25 vol. % OAT coolant B. Each electrode of the probe is made of the same cast aluminum 共UNS A23190兲 square wire having an exposed surface area of 1 mm2. As shown in Fig. 6, localized corrosion rate of the cast aluminum was generally much higher than the comparable general 共or surface area average兲 corrosion rate determined from conventional electrochemical methods 共e.g., the ones determined from Tafel extrapolation of the anodic polarization curve given in Table 4兲. There was also substantial fluctuation in the localized corrosion rate measured by the instrument, probably reflecting the nonsteady state nature of the pitting corrosion processes. As solution temperature increases, the cast aluminum localized corrosion rate also increases. As immersion time increases, the localized corrosion rate appears to be decreased slightly. The cast aluminum localized corrosion rate increased by more than 300 % after the addition of approximately 100 mg/ L fluoride into the solution 共from 300± 40 ␮m / y to 1600± 350 ␮m / y兲. The addition of another 100 mg/ L fluoride 共total approximately 200 mg/ L兲 into the solution increased the cast aluminum localized corrosion rate further, e.g., to about 2300± 500 ␮m / y, and simultaneously increasing the fluctuations of the localized corrosion rate. Addition of a small dose of organic additive led to a very rapid reduction of the cast aluminum localized corrosion rate. About 1.5 h after the corrosion inhibition additive was introduced, the cast aluminum localized corrosion rate was reduced to about 29 ␮m / y. After the solution temperature decreased the localized corrosion rate decreased further, reaching to a value of about 1.3 ␮m / y after 3 h of additional testing. Conclusions • Flux residue remaining on the aluminum alloy heat exchanger surface is soluble in commercial coolants and will leach out fluoride ions that enhance the corrosion of metals in the engine cooling system. • The amount of fluoride ions that releases into the coolant depends on the chemical compositions of


the coolant and other variables 共e.g., flux loading, compositions of the flux used, etc.兲 involved in the brazing process. • The corrosive effect of fluoride for aluminum alloys increases with increasing concentration of fluoride ions. • Addition of the small amount of organic additives into the OAT coolants are shown to be very effective in eliminating the damaging corrosive effect of the fluoride ions on aluminum components of engine cooling system.

References 关1兴关2兴关3兴关4兴关5兴关6兴关7兴关8兴

关9兴关10兴

Conn, P. J., and Schrameck, W. J., US Patent No. 5,360,158. Van Evans, T., Zaluzec, M. J., Mehraban, H., Burt, R. P., Uyeda, S. Y., and Eye, J. B., US Patent No. 6,120,848. Liu, J., “NOCOLOK Flux and Aluminum Brazing,” SAE Paper No. 960244, 1996. Field, D. J. and Steward, N. I., “Mechanistic Aspects of the NOCOLOK Flux Brazing Process,” SAE Paper No. 870186, 1987. Wallace, E. R., and Dewing, E. W., US Patent No. 3,951,328. Cooke, W. E., US Patent No. 3,971,501. Rajagopalan, R., Pierre, E., and Ramez, A., “Effect of Post Brazed Flux Residues of CAB Evaporators on the Consistency of Conversion Coating,” SAE Paper No. 2005–01–1773, 2005. Davies, D. E. and Prigmore, R. M., “The Effect of Sodium Fluoride on the Localized Corrosion of Aluminum in Distilled Water and 50 % Ethandiol Solution,” Proceedings of International Congress on Metallic Corrosion, Vol. 4, June 3–7, 1984, Toronto, Canada, pp. 356–351. Yang, L., Sridhar, N., Pensado, O., and Dunn, D. S., Corrosion, NACE, Vol. 58, 2002, p. 1004. Yang, B., Marinho, F., and Gershun, A. V., Proceedings of ASTM 5th International Symposium on Engine Coolant Technologies, May 17–18, 2006, Toronto, Canada.


Glen Davis and Mark Sarlo

Heavy-Duty Diesel Engine Cavitation Test ABSTRACT: The objective of this study was to develop a test procedure to evaluate the ability of a heavy-duty diesel engine coolant to provide protection against damage resulting from a phenomenon known as cylinder liner cavitation corrosion. The engine cavitation test procedure was developed by modifying a production OEM diesel engine to consistently produce the operating conditions that accelerate damage from cylinder liner cavitation. The resulting, 250-h test procedure was able to quantify a coolant’s ability to protect wet-sleeve cylinder liners from cavitation corrosion. Dozens of coolants were evaluated using this test procedure. The ranking of cylinder liner pit area counts from this procedure’s discrimination matrix was in agreement with the ranking of pit area results seen in high-mileage field tests. Conversely, upon investigation, an acceptable correlation could not be established between field test pit area counts and the results from a known bench test. Obtaining results in a few weeks from a short duration procedure such as this can offer a coolant formulator advantages compared to waiting for the completion of a properly conducted field test. This test procedure creates an accelerated, yet realistic level of liner cavitation that ranks protection levels of coolants being evaluated. This ranking or discrimination is often not possible in field testing because the field test is run under mild service conditions or the engine components have little tendency to promote liner pitting. In addition, the difficulty in controlling field tests often yields unusable, inaccurate results. The test procedure was shown to be repeatable within labs and reproducible between labs thus confirming the viability of this test procedure as a useful tool to assess a coolant’s ability to protect against cylinder liner cavitation damage. It is recommended that the presently developed test procedure be considered for adoption as an ASTM test method. KEYWORDS: cavitation, pitting, pitted area, heavy duty engine coolant, cylinder liner, engine coolant

Introduction Heavy-duty 共HD兲 diesel engines with wet sleeve liners are likely to experience cylinder liner cavitation and resulting damage unless a properly formulated, heavy-duty diesel engine coolant is used in the engine cooling system. Heretofore, companies manufacturing engine coolant had no way of testing their coolant as to its performance for suppressing cylinder liner cavitation other than running extensive dynamometer tests or long term fleet tests. John Deere has modified a production engine to be used as a test engine, and developed a 250-h engine test procedure, that will consistently produce cavitation in order to evaluate coolants as to their tendency to suppress cylinder liner cavitation and resulting damage. One of these modified engines and the test procedure have been given to Southwest Research Institute® 共SwRI®兲 to run on a commercial basis. The purpose of this paper is to provide a description of the test engine, the test method, and the supporting data to ASTM for determining the viability of this test becoming a standard for testing the capability of a candidate coolant to suppress cylinder liner cavitation and resulting damage in heavy-duty diesel engines. An engineering test report from Cummins/Fleetguard is included in the Appendix as supporting data and ongoing research. This report is important since it is an application of this test method by an engine coolant manufacture with the test being run by an independent lab 共SwRI®兲. Historical Background This engine test was originally developed at John Deere Product Engineering Center 共1994兲 in order to test the capability of propylene glycol 共PG兲 base coolant to suppress cylinder liner cavitation and resulting damage as compared to ethylene glycol base coolant. 关1兴 After completing that program, the need was Manuscript received June 7, 2006; accepted for publication October 11, 2006; published online September 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

87


evident for a fired engine/dyno test that would discriminate between coolants as to cavitation control and protection from cavitation damage. Contributing factors for developing an in-cell, engine/dynamometer test were 共1兲 the high costs of fleet testing; 共2兲 the difficulty of controlling a fleet test, which sometimes can result in bad data or no usable data; 共3兲 the inability of bench tests to distinguish closely the difference in protecting the cylinder liners from cavitation damage. A test program was started using the same modified engine configuration to compare different coolants as to their ability to suppress cylinder liner cavitation damage. In 1997 a separate test engine was built, tested, and sent to SwRI® to test for reproducibility between labs, repeatability, and ultimately to be used for commercial running of this test procedure. The Appendix is a Cummins/Fleetguard engineering report on the results of a coolant test program using this test engine and test method. In excess of 40 tests have been run using the two test engines. Test Engine Description The test engine is a John Deere, inline six-cylinder, 10.1-l 共6101H兲, intercooled, turbo-charged, heavyduty, direct injected diesel engine. The coolant thermostats were removed in order to control coolant out at the correct temperature. The direct cooling to the top annulus of each cylinder liner was removed. Each set of test liners was machined to give more annular clearance between the piston outside diameter 共OD兲 and liner inside diameter and between the liner OD and the engine block in order to enhance 共liner vibration兲 cavitation in a controlled manner. Summary of Test Method for Diesel Engine Coolant Cavitation Test Scope This test procedure was designed to evaluate an engine coolant’s ability to prevent, inhibit, or suppress cavitation damage to engine cylinder liners exposed to coolant within the cooling system. Background During the power stroke in a diesel, compression ignition engine, the forces exerted on the internal surface of a diesel engine’s cylinder liners can cause the liner wall surface to vibrate. This vibration can result in the exterior surface of the liner, in contact with the coolant, to rapidly vibrate the coolant, resulting in a potentially damaging mechanism known as cavitation. Without proper protection for this exterior liner surface, damage can occur which will result in pitting of the metal surface. This pitting can propagate through the entire thickness of the liner allowing engine coolant to enter the cylinder chamber ultimately resulting in engine failure. It was found that if certain dimensions of an engine’s geometry were configured in a certain way and certain operating conditions were controlled, damage from cavitation could be enhanced. The John Deere, six-cylinder, 10.1-l, 共6101H兲, turbo-charged, intercooled, heavy-duty diesel engine, with several modifications and operational conditions to optimize an environment for cavitation, was found to be a good test tool to discriminate between the coolant’s ability to protect from cavitation damage. Test Engine The test engine is a John Deere, six-cylinder, 10.1-l, 共6101H兲, turbo-charged, intercooled, heavy-duty diesel engine. Rated speed is 2100 RPM; peak torque is at 1500 RPM. Before each test, the engine is rebuilt with specially machined, pre-measured, cylinder liners. Except for gaskets and expendables, the remaining engine components are reused and replaced according to an as-needed basis. Test Cell Fully instrumented test cell equipped with a dynamometer 共or equivalent兲 capable of absorbing up to 300 kW at 2100 RPM and/or 1425 Nm at 1500 RPM. Maximum speed capability for dynamometer should be 2700 RPM. Entire cooling system should be configured for a total volume of about 50⫾ 10 liters and is

DAVIS AND SARLO ON HEAVY-DUTY DIESEL ENGINE CAVITATION TEST 89

run without a pressure cap. Coolant inlet plumbing to the engine’s coolant pump is configured with smooth, large-diameter piping to reduce flow restriction so that the coolant pump does not cavitate. Test Sequence Break-In After Installing Test Liners Step Number 1 2 3 4 5

Step Time, min 1 2 10 5 1

RPM 950 2100 2100 2100 2600

Torque, Nm Min Loada 780 780 1186 Min Loada

Power, kW Record 172 172 261 Record

Coolant Out, C Record Record 70 70 70

Ramp Time, RPM ¯ 30 s 1 min 1 min ¯

Ramp Time, Torque ¯ 30 s 1 min 1 min ¯

a

Min Load indicates no excitation to dynamometer and the magnitude would be the resulting load from drag

The engine oil and filter are changed to remove wear metals resulting from break-in. This is not an oil evaluation test procedure. 20-h, Steady-State, Extended Break-In Step Time, h 20

RPM 2100

Torque, Nm 762

Power, kW 168

Coolant Out, C 70

On Test, Cyclic, 230 h Step Step Time, Throttle Number min Step Name Position, % 1 1.5 Low idle 0 2 1.0 Peak torque 100 3 4.0 Full load 100 4 1.0 FLoad O-spd 100 5 0.5 Fast idle 0

Torque, Power, Coolant RPM Nm kW Out, C Fuel kg/hr Intake Air, C Fuel, C Ambient, C 800 Minb Record 70⫾ 5 ¯ 29⫾ 10 ⬃40 10–45 1500 ⬃1425 ⬃225 70⫾ 5 ¯ 29⫾ 10 ⬃40 10–45 2100 ⬃1200 ⬃260 70⫾ 5 ⬃61 29⫾ 10 ⬃40 10–45 2310 ⬃795 ⬃195 70⫾ 5 ¯ 29⫾ 10 ⬃40 10–45 2625 Minb Record 70⫾ 5 ¯ 29⫾ 10 ⬃40 10–45

b

Min indicates no excitation to dynamometer and the magnitude would be the resulting load from drag

Oil additions are allowed as this is not an oil evaluation test. After the test engine is rebuilt with the modified test liners, new gaskets, and expendables, the engine is charged with ⬃29.3 kg of John Deere Plus 50 15W-40 heavy-duty engine oil 共or equivalent兲. A new oil filter is installed. The engine’s cooling system should be vacuum filled with approximately 50 l of the coolant to be evaluated. The engine is run through the 19-min break-in sequence and allowed to cool down. The engine oil is drained and the oil filter removed. Again, the engine is charged with ⬃29.3 kg of John Deere Plus 50 15W-40 heavy-duty engine oil 共or equivalent兲. A new oil filter is installed. The test time clock is reset to zero hours and the engine is run through the steady-state, 20-h extended break-in sequence followed by 230 h 共approximately 1725 8-min cycles兲 of On Test conditions to accumulate a total test duration of 250 h. Oil and Coolant Sampling and Analysis Collecting oil and coolant samples is required for this test procedure. As good practice, to monitor the overall condition of the engine, 120-ml oil samples may be collected at each 50-h interval. The lab conducting this test procedure may choose to have the oil sample tested for wear metals, total base number, kinematic viscosity, fuel dilution and possibly soot level. Additionally, as good practice, 250-ml coolant samples may be collected and analyzed at 125- and 250-h intervals. Analysis of Results (Pit Area Counting Procedure) Original Method—After completion of each 250-h test, the engine was disassembled and the cylinder liners cleaned for pit counting. A transparent grid 共2.16-mm squares兲 was used to count the pits in the following manner. 1. Visually inspect each liner. With a fine point permanent marker, outline the outside boundary of pitted areas. This could range from a single pit to many pits concentrated in a given area. Histori-


FIG. 1—Accelerated heavy duty engine cavitation coolant testing. The original method of counting pits was used for these data. A1, John Deere Cool-Gard; A1, John Deere Cool-Gard; A2, John Deere CoolGard (slight modification); A2, John Deere Cool-Gard (slight modification); Z1, Universal Low Silicate ASTM D 4985 (no SCA); Z1, Universal Low Silicate ASTM D 4985 (no SCA); Z1, Universal Low Silicate ASTM D 4985 (no SCA); Z2, Traditional Automotive; B1, European Hybrid; B2, European Hybrid (different version); C, European Organic Acid Technology (OAT); D1, Asian OAT; D2, Asian OAT (10 % reduction in additive package); E1, Asian Hybrid; E2, Asian Hybrid; F1, Water ⫹ John Deere Coolant Conditioner @ 6 %; F2, Water ⫹ John Deere Coolant Conditioner @ 3 %. cally, most of the pits were on the major thrust side of the liner, although pits or pitted areas could occur anywhere on a liner’s exterior surface. The major thrust side is the right side looking from the flywheel end to front as the liner is installed in the engine. Determination of pits and the boundary of pit areas followed by counting were done using a lamp with a lighted magnifying glass. 2. Place the transparent grid over the cavitated area. Assign a count of one pit area to each grid square containing a pit or pits. The pit 共or pits兲 does not have to cover the entire square. If any portion of a pit or group of pits is contained in a square, it gets a count of 1. 3. Total all the pit areas on a given liner and then total the pit areas on all six liners. This is the total pit area count for the coolant being tested. However, there were problems with this procedure. 共1兲 It was difficult to determine what a pit was, what was not, and determining where the pits actually stop when looking at large area of pits. 共2兲 Consistency from person to person when counting pits. 共3兲 Counting pit areas only gives an area pit count. It does not take into account the depth of the pits. These problems have been minimized to a certain extent by the following. 共1兲 One person performing the counting and/or training others and verifying counts. 共2兲 Measuring and recording the depth of the deepest pit on each liner. This original method was used in counting the pits in all the data shown in Fig. 1. Second Method—Recognizing the problems of the original method of counting the pit areas on a liner, there has been a constant effort to improve this technique. About the time a test engine was sent to SwRI® for commercial running of the cavitation test, both labs started using a low-magnification, binocular microscope to look at the liner when marking the pitted areas and counting of pits. As in the original method, the transparent grid was placed over the pitted area on the liner. This has now become the standard


FIG. 2—Fleetguard Bench test versus John Deere dyno test. Test temperature: 71C; test duration: 22 h; test frequency: 20 000 Hz; test amplitude: 0.8 mils; test material: Cast iron. method of counting pit areas. Obviously, the inherent accuracy of this method results in a higher pit area count due to being able to see pits in areas that previously were not as obvious. Particularly, pitted areas concentrated at the top and bottom O-ring sealing edges of the liner area exposed to coolant. This total count difference is evident in Fig. 2. Coolants E and F were counted using this second method, whereas the remainder of the table were counted use the original method. A correlation factor will be developed to relate the two methods. Efforts are continuing to improve this process and assure reproducibility and calibration among those who count pit areas. Participating Laboratories The Diesel Engine Cavitation Test was originally used as an “in-house” test at John Deere’s Product Engineering Center. Repeatability at John Deere’s facility is shown in the table below. The 250-h test showed discrimination between coolants in their ability to prevent, inhibit or suppress cavitation damage to engine cylinder liners exposed to coolant within the cooling system. After development at the John Deere facility, another, specially-configured engine was installed at Southwest Research Institute. Test Repeatability at John Deere Product Engineering Center Test Number 1 2 3 Average Standard Deviation

John Deere Cool-Gard 78 77 ¯ 77.5 0.5

John Deere Cool-Gard共slight modification兲 71 71 ¯ 71 0

Universal Low Silicate No SCA 956 699 757 804 110

Precision Matrix To verify the reproducibility of this test method between laboratories, Southwest Research Institute installed an engine according to direction from John Deere personnel and conducted 250-h tests using known coolant formulations.

92 ENGINE COOLANT TECHNOLOGY Test Reproducibility Between John Deere Product Engineering Center and Southwest Research Institute Coolant John Deere Cool-Gard Universal Low Silicate No SCA

Average Pit Count 77.7 812

Standard Deviation 0.47 96

Number of Tests 3 4

Fuel Fuel meeting ASTM D 975, Grade Low Sulfur No. 2-D, is specified. This broad fuel specification is specified since this is not a wear or deposit test, but a mechanical distress test for cavitation damage on the exterior surface of cylinder liners. Results of Tests Figure 1 illustrates the types of coolants tested. All coolants, except F1 and F2, are 50/50 mix. Conclusions 1. The diesel engine coolant cavitation test adequately provides a method of discriminating between testing heavy-duty diesel engine coolants as to their capability of suppressing cylinder liner cavitation and resulting damage. 2. Resulting data from field tests appears to correlate well with this test when run according to the test procedure described in this paper. 3. If done consistently, the cavitation pit counting procedure gives reproducible and repeatable results of cavitation that occurs on cylinder liners in a heavy-duty diesel engine. 4. Southwest Research Institute 共SwRI®兲 has successfully reproduced the test method and results of tests conducted at the John Deere facility and can provide this test method on a commercial basis. Appendix: Use of the John Deere Engine Dyno Test to Determine Liner Pitting Protection Provided by Non-Nitrite Engine Coolants The following is an internal engineering report by Cummins/Fleetguard. This report documents a series of engine coolant cavitation tests, as described in this paper and test procedure, conducted at Southwest Research Institute as part of an actual coolant approval program. This copy has been altered to protect confidential, proprietary information. Our thanks go to Cummins/ Fleetguard for sharing this very important information with ASTM. Introduction There is an increasing customer preference for coolants without nitrite. This is true in some geographical areas, such as Europe and Japan. It is true for some OEMs, such as Komatsu, and also for some end-user fleets. The current heavy-duty coolant specs 共both TMC and ASTM兲 require the use of nitrite or nitrite/ molybdate for liner pitting protection. Some coolants without nitrite are now available that may perform well enough for liner pitting protection to allow their use in heavy-duty diesel wet sleeve engines. The problem is this: How can liner pitting protection of these coolants without nitrite be measured? In the late 1980s, fully formulated coolants for heavy duty 共HD兲 engines became more generally available. Before that time it was common practice to use a not fully formulated coolant 共ASTM D 4985兲 and precharge it with a large dose of supplemental coolant additive 共SCA兲 to achieve liner pitting protection, along with other performance features needed for successful use in HD engines. In the same time frame, propylene glycol 共PG兲 base coolants became generally available. 关2兴 Both these factors highlighted a serious problem with the ultrasonic cavitation bench test, 关3兴 which had been used since the late 1970s to evaluate liner pitting performance of SCAs. 关4兴 When glycol base, fully formulated coolants were tested in the ultrasonic test rather than SCA treated water, lab test results did not correlate well with field performance. 关3兴 When propylene glycol base coolants were compared to


ethylene glycol base coolants in the ultrasonic cavitation test, 关5,6兴 again lab results did not correlate well with field performance. 关7兴 A large part of the problem with the ultrasonic cavitation bench test was that it overstated the effect of glycol compared to the effect of additives. Thus, it showed only a small difference in cavitation performance for glycol coolants with a known large difference in performance in field test. Figure 2 shows this. The “light-duty coolant” is a universal low silicate conventional coolant 共ASTM D 4985兲 with no nitrite or molybdate. This type coolant was used for many years in heavy-duty diesel engines, but it required use of a precharge SCA package which contained nitrite/molybdate for liner pitting protection. The “heavy-duty” coolant is a fully formulated hybrid coolant meeting ASTM D 6210 liner pitting chemistry levels. Note that the ultrasonic cavitation bench test showed only about a 25-mg greater 共2-1/2 times兲 damage for the light-duty coolant compared to the John Deere engine dynamometer test which gave a ratio of 11 and a pit count difference of over 700. This lack of correlation and poor discrimination of the ultrasonic cavitation lab test compared with performance in engines prompted the development of the John Deere engine dynamometer cavitation test. 关1兴 Meanwhile, in 1995 The Maintenance Council 共TMC兲 coolant specs were developed for fully formulated coolants using chemistry 共nitrite and molybdate兲 requirements for liner pitting protection. 关8,9兴 These were followed in 1998 by similar ASTM specs. 关10,11兴共Note that ASTM D 6210 is being modified to incorporate D6211.兲 ASTM D15 Committee on Engine Coolants is now in the process of writing an ASTM Research Report on the John Deere engine dynamometer cavitation test and will then develop an ASTM test method based on the Research Report information. At the urging of coolant and engine manufacturers, in 1997, John Deere provided an engine to Southwest Research Institute 共SwRI兲 to make the test available to the public. ASTM D 6210-98 Standard Specification for Fully-Formulated Ethylene-Glycol-Base Engine Coolant for Heavy-Duty Engines, 关10兴 already states that the John Deere test is acceptable as proof of performance for meeting the cavitation requirement. However, CES 14603, 关11兴 Cummins’ coolant spec, requires a field test if the nitrite and molybdate chemistry does not meet ASTM D 6210 specifications. This creates a dilemma. Current Cummins engines are generally very mild for liner pitting. How can a valid, severe, Cummins engine field test for liner pitting be currently run? At this point, it cannot. Therefore we need to look at some previous field tests in more severe Cummins engines and use that information to calibrate the results from the John Deere engine dynamometer test. Background In 1996/1997, Fleetguard ran field tests at the BTI fleet in Wyoming using three coolants in two engine models. The six engines were all rebuilt with new cylinder kits before the test started. Three engines were 91N14s, which had proven to be severe for liner pitting, and three engines were 94N14s, which had proven to be mild for liner pitting. The test ran about one year, which was approximately 200 000 miles per engine. All six trucks were maintained at one facility and all ran the same route with the same duty cycle. The three coolants were G, E, and D 共see Table 1 for description of coolants兲. In the BTI field test, D did not prevent liner pitting in either the mild or severe engine. E prevented liner pitting in the mild engine but not in the severe engine. G 共containing nitrite兲 prevented pitting in both the mild and severe engines. The results of this test were reported to the ASTM D 15.11, Subcommittee on Coolants for Heavy Duty Engines, on August 27, 1997. 关12兴 After developing the John Deere engine test for liner pitting, John Deere personnel continued to run many tests in their facility for their own use, which data has not been published. However, a portion of their data has been shared with Fleetguard and Cummins to allow better calibration of the test results from SwRI® on a series of tests jointly funded by SwRI/Cummins, Fleetguard, and Old World 共coolant supplier to Fleetguard兲. Results and Discussion John Deere engine dynamometer test results are shown in Table 1. The John Deere engine dynamometer test results show good repeatability and rank coolants for cavitation liner pitting protection in the same order as their performance in the field. OAT and hybrid

94 ENGINE COOLANT TECHNOLOGY TABLE 1—John Deere Liner Pitting dyno test data. Coolant A

Description Hybrid HD-6210 共good Ref fluid兲 LD universal, conventional 共bad Ref fluid兲

B

Deere 71/77/71

SwRI® 78a

Average 74

Std/Dev 3.8

699/757/956

836a

812

111

C

Conventional light duty

688

D

Non-nitrite European hybrid used in some HD engines

305

E

LD US non-nitrite 2 ethyl hex OAT

270a

F

HD Japanese/US non-nitrite OAT

143a

G

E above with nitrite for HD-6210

No data

a

These results were obtained using the second method of counting pits.

coolants without nitrite perform much better than conventional coolants without nitrite. Among hybrid and OAT coolants without nitrite, F gave twice the liner pitting protection, compared to D and E. Although it is not possible to run a meaningful field test for liner pitting in current, mild Cummins engines, the F coolant has been used to factory fill over 800 Cummins C series wet sleeve engines since April 2001, with no liner pitting problems having been reported. Furthermore, F has been approved for their heavy duty engines and is being sold by Detroit Diesel. More recently, F has been approved for the Cat EC-1 coolant spec. References 关1兴关2兴关3兴关4兴

Davis, G. D. and Christ, R. J., “A Comparison of Engine Coolants in an Accelerated Heavy Duty Engine Cavitation Test,” Engine Coolants and Cooling System Components, SP-1162, SAE 960883, 1996, pp. 145–160. Hercamp, R. D., Hudgens, R. D., and Conghenour, G. E., “Aqueous Propylene Glycol Coolant for Heavy Duty Engines,” Worldwide Trends in Engine Coolants, Cooling System Materials and Testing, SP 811, SAE 900434, 1990, pp. 47–77. Hercamp, R. D. and Hudgens, R. D., “Cavitation Corrosion Bench Test for Engine Coolants,” SAE 881269, 1988, pp. 1–17. Hudgens,R. D. et al., “Refinement of the Vibratory Cavitation Erosion Test for the Screening of Diesel Cooling System Corrosion Inhibitors,” Engine Coolant Testing: State of the Art, ASTM STP


关5兴

关6兴

关7兴关8兴关9兴

关10兴

关11兴关12兴

705, W. H. Ailor, Ed., ASTM International, West Conshohocken, PA, 1980, pp. 233–269. Hercamp, R. D., “An Overview of Cavitation Corrosion of Diesel Cylinder Liners,” Engine Coolant Testing: Third Volume, ASTM STP 1192, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1993, p. 121. Scott, L. F. Jr. and Weir, T. W., “Comparing the Performance of Ethylene Glycol and Propylene Glycol Coolants in Heavy Duty Vehicles,” Engine Coolants and Cooling System Components, SP-1162, SAE 961039, 1996, p. 181. “Fleet Purchasing Specification for Nitrite-Containing Ethylene Glycol Base Coolant,” RP 329, TMC, March 1995, pp. 1–4. “Fleet Purchasing Specification for Nitrite-Containing Propylene Glycol Base Coolant,” RP 330, TMC, March, 1995, pp. 1–4. D6210-98a, “Standard Specification for Fully-Formulated Ethylene-Glycol-Base Engine Coolant for Heavy Duty Engines,” Annual Book of ASTM Standards, Volume 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 266–268. D6211-98a, “Standard Specification for Fully-Formulated Propylene Glycol-Base Engine Coolant for Heavy Duty Engines,” Annual Book of ASTM Standards, Volume 15.05, ASTM International, West Conshohocken, PA, 2002, pp. 269–272. CES 14603, “Coolant, Engine,” Cummins Engineering Standards, pp. 11–14. “Minutes ASTM D15.11 Subcommittee Meeting 8/27/97 at J.I. Case, Hinsdale,” Dated September 4, 1997, R. D. Hercamp, Acting Secretary, 8 pp.


Paul O. Fritz,1 Leonard S. Bartley, Jr.,1 Regis Pellet,1 Virginia Moser,2 and Carmen Ulabarro2

Component Durability and High Mileage Performance of a Full Carboxylate Coolant in Heavy Duty Diesel „HDD… Engines ABSTRACT: Performance of a full carboxylate coolant has been demonstrated in engine bench cavitation testing, fleet testing, and post fleet testing coolant corrosion tests. Performance in the proposed ASTM “Heavy Duty Cavitation Test” was established and found to satisfactorily exceed performance limits. Fleet testing of a full carboxylate coolant technology in Class 8 trucks, using Caterpillar C-12 engines demonstrated minimal inhibitor depletion to 400 000 miles under controlled zero coolant top-off conditions with no refortification. In a second fleet, vehicles accumulated high mileages under real world conditions. In this test, Caterpillar 3406E engines were torn down and inspected demonstrating extended corrosion protection and superior component durability to beyond 700 000 miles, without the addition of supplemental coolant additives or extenders. Coolants from these vehicles were removed and tested in the laboratory to verify their extended life properties. KEYWORDS: extended life coolant, field test, fleet testing, organic additive technology, carboxylate, inhibitor

Introduction This paper is based on an SAE paper number 2005-01-3579. The fleet test data from this SAE paper will be discussed here with an additional focus on bench cavitation results as well as data from coolant corrosion testing performed on coolants taken from vehicles after fleet testing. Fleet testing in heavy duty diesel 共HDD兲 vehicles in the U.S. of the aliphatic carboxylate coolants described in this paper started in the late 1980s. The early field trial performance of these coolants in automotive and HDD vehicles was thoroughly documented by Washington et al. 关1,2兴. In 1998, based on over 50 000 000 miles of fleet test experience, coolant life was deemed acceptable for use to 600 000 miles if extender was added at the half-life. Critics of carboxylate-based coolants were quick to point out that conventional coolants can last just as long as extended life carboxylate-based coolants with proper top up and supplemental coolant additives 共SCA兲 addition 关3兴. And while this is a valid point, the purpose of this paper is to establish and document that there are fundamental differences in these technologies that lead to benefits for the end users. While this is not a new concept, the data in this paper further extends the boundaries established in the literature, and combines field data with engine test data and laboratory corrosion testing to complete the story. Since its introduction in the U.S. in 1995, this technology has collected well over 350 000 000 000 miles of field experience in the U.S. alone based on rough estimates. Certainly coolant life can be extended using SCAs. This requires some amount of time, testing, and cost to do it properly. While any cooling system should be examined regularly, the prescribed maintenance for extended life coolants can be done quickly and easily. Recommended maintenance typically includes checking the coolant level regularly 共usually automatic with level sensor, but can be checked to make sure that this is functioning properly兲, topping up with the correct 50/50 extended life coolant, and checking the coolant on a regular basis with a refractometer to determine the glycol/water concentration 共checking the pressure cap to make sure it is holding the proper pressure once in a while is also a good practice兲. Manuscript received April 21, 2006; accepted for publication January 18, 2007; published online February 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Senior Staff Chemist, Chevron Corporation, New Windsor, NY 12553. 2 Marketing Specialists, Chevron Corporation, Houston, TX c兲

Based, with permission, on a previously published SAE paper 2005-01-3579.

Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

96

FRITZ ET AL. ON PERFORMANCE OF FULL CARBOXYLATE COOLANT IN HDD ENGINES 97

Checking with a refractometer not only ensures that the correct freeze and boil protection is maintained, but also that the heat capacity of the coolant is near the “design” limit. As well, this paper will provide further evidence that when using the proper coolant for top-up, checking the glycol level will also be a good measure of your inhibitor level since inhibitor depletion is minimal with this type of extended life coolant. Besides carboxylate inhibitor levels, limiting factors on coolant life include low or high pH 共usually drop due to glycol breakdown兲, and depletion of noncarboxylate inhibitors such as nitrite and tolyltriazole. These three areas will also be addressed in this paper. Field testing of this extended life coolant technology in Class 8 trucks, equipped with Caterpillar C-12 engines, revealed excellent coolant life with negligible inhibitor depletion to 400 000 miles with no refortification and no coolant top-off in most of the vehicles. In separate evaluations in Caterpillar 3406E equipped trucks, extended corrosion protection and component durability were established out to 700 000 miles, again without the need for refortification other than top-off. The used coolant was then subjected to glassware corrosion testing which showed that inhibitors in the coolant were still able to provide similar protection to that of a new coolant, verifying the extended life nature of this technology. Experimental The extended life coolant examined in this work is based on a synergistic combination of aliphatic monoand dicarboxylate corrosion inhibitors. This composition has been described previously 关4兴 and is available commercially. This heavy duty coolant contains the carboxylates described above, as well as tolyltriazole, molybdate, and nitrite, and these components will be examined in more detail during the discussion that follows. All coolants were evaluated as 50/50 mixtures with deionized water. HD Diesel Cavitation Test For many years the coolants industry has been trying to develop a cavitation test that would correlate with field performance. The ultrasonic test has been used by many laboratories for evaluating liner pitting but due to the variability of the test there has not been any successful correlation made from bench to field data 关5兴. However, an accelerated heavy duty engine cavitation was developed by John Deere and presented at SAE 关6兴. This test utilizes a six-cylinder, 10.1 L diesel engine that is turbo-charged, intercooled, direct injected, with specially-modified 共thinned兲 liners. The test utilizes an open cooling system with the thermostats removed. In this test, the thrust side is affected most where typically a large area is scuffed with various degrees of pitting depending on the coolant. To evaluate the coolant performance, a transparent grid 共approximately 2.16 mm by 2.16 mm兲 is placed over the liner and the number of grids that touch the “pits” are counted using a 10-powered microscope. Here “pits” may be actual pits or simply deeply roughened surface. Once all liners are evaluated the individual “pit” counts 共actually grid counts兲 are combined to obtain a total count for the test. This test which had been a Deere proprietary test is now available commercially at an independent testing facility. A research report D15-1023 documenting the setup and referencing of the stand has been filed with ASTM. A test method is being written for consideration by ASTM and currently what constitutes a “passing” amount of pits/grids is under discussion. At the time of this writing, less than 200 total pits is under consideration as acceptable, although one OEM specification requires less than 100 pits. The stand is referenced using a “good” coolant which is a fully formulated conventional coolant that typically gives between 70 and 90 pits and a “bad” reference which is a low-silicate, conventional coolant which gives between 750 and 900 pits. All coolants give rise to “pits” in this test. Fleet Testing Two separate fleet tests are examined in this paper. In the first fleet, top-off was eliminated by using specially designed impermeable hoses with heat shrink hose clamps to greatly repress coolant loss to accurately test the rate of inhibitor depletion. In the second fleet, trucks from a fleet that had operated to high mileages without supplemental coolant additives 共SCAs兲 were torn down and evaluated. A fleet test was started with 32 trucks 共28 trucks finished the test兲 equipped with Caterpillar C-12 engines. These trucks were fitted with specially designed, impermeable hoses which minimized throughhose evaporation. A commercial extended life coolant containing the mono- and dicarboxylate combina-

98 ENGINE COOLANT TECHNOLOGY TABLE 1—Heavy duty cavitation test results. Coolant Type Fully Formulated Conventional Coolants Fully Formulated Synergistic Carboxylate System Nonnitrited Synergistic Carboxylate System Nonnitrited Aromatic Carboxylate System

Label From research report A B C

Total “Pit” Count 78 83 131 144

tion was used in this fleet. Coolant samples were approximately every 50 000 miles from each truck out to about 400 000 miles. The trucks were not refortified with SCAs or with extender and minimal top-off. The coolant samples were analyzed for water content 共Karl Fisher兲, pH, inhibitors 共HPLC, IC兲, and corrosion metals 共ICP兲. In the second test potential candidate trucks for teardown were identified from a large national truck leasing fleet. Vehicles with Caterpillar’s 3406E engines factory-filled with extended life coolant having accrued a minimum of 650 000 miles in long haul service without refortification over this period were sampled. Normal top-off with extended life coolant occurred throughout the life of the vehicle; however, dilution with other coolant technologies would exclude a candidate from consideration. Using these criteria, and coolant analyses, 100 potential trucks were identified. Of these, four trucks were selected based on ease of availability, proximity, and minimal disruption to customer service. After selection, engines were disassembled and the cooling system components were inspected and photographed. Parts examined included all liners, water pumps, thermostat housing and thermostats, radiators, hoses, seals, heads, and oil coolers. Appropriate components were examined by a metallurgist. Coolant Testing The coolant from the Caterpillar engines that were torn down was retained, and this coolant was used to conduct standard ASTM glassware corrosion tests designed to evaluate new coolants. ASTM Standard D-1384 关15兴 and ASTM D-4340 关16兴 were run on the used coolant. These tests were run as specified with the level of corrosive salts adjusted properly to account for the fact that the test was starting with prediluted coolant.

Results and Discussion Heavy Duty Cavitation Test The carboxylate-based coolant system described in this paper has been commercially available in the marketplace for over ten years with excellent cavitation protection performance. The HD cavitation test was run on both the fully formulated 共nitrite and molybdate兲 version and the nonnitrited version of the synergistic two carboxylate system described above. For comparison purposes a commercially available carboxylate coolant system using aromatic carboxylates and no nitrite was included. The three carboxylate coolant samples were sent blind to the test laboratory and the results are reported in Table 1 alongside previously reported results for a fully formulated conventional coolant. The John Deere company, who originally developed this test, has set a pit/grid count of 100 as a pass. Both of the fully formulated coolants performed equally well in this test, passing this stringent limit. The nonnitrited carboxylate coolants are over the John Deere limit but are well within the limit of 200 pits set by Cummins in Engineering Standard Number 14603 and this limit is also being discussed by ASTM as a passing result. Recall that the “bad” reference, which is a low-silicate coolant that meets ASTM D 4985 关17兴, generally gives between 750 and 900 pits. The test results show that although the full carboxylate coolant can provide protection against cavitation in this test, there can be an additional improvement in cavitation protection when nitrite or nitrite/molybdate is used. This may become relevant if one is concerned about engines known to severely cavitate since the presence of the nitrite and molybdate does improve the anti-cavitation performance in this test. As well, as the nitrite depletes, or disappears through


FIG. 1—The #1 Liners for the three carboxylate coolants—close up of thrust side damage. other reactions, it is clear that the aliphatic carboxylates will impart a high level of cavitation protection. Although very likely these results are within experimental error, directionally the aliphatic carboxylate has less total “pits” than the aromatic carboxylate coolant. One of the drawbacks with this test is the way the pits are measured. As described in the Experimental section, currently a grid is laid over a pit area under a microscope and then it is up to the operator to determine the number of grids that are touching a “pit area.” With a well trained operator, this technique may be repeatable but it does not account for pit depth. A “pit” that has just started 共or severely roughened the surface兲 has the same value as one that has almost perforated the liner. Figure 1 shows a close up of the #1 Liners, and Fig. 2 shows a close up of the #6 liners for the three different carboxylate technologies evaluated. Liners #1 and #6 were selected, since according to the test operators and developers, these liners generally show the worst cavitation. The #2 Liners are also shown in Fig. 3 because this was the worst liner for Coolant B as shown in Table 2 and is shown to present a balanced perspective. As well, the results for the #2 Liner seem to illustrate why this test may yield slightly misleading results. Figure 3 shows the results for the #2 Liners and clearly Coolant A yields the best result, in agreement with the pit/grid count data. For the #2 Liner, Coolant C yields a much better pit count result than Coolant B, since the measuring technician counted more grids touching pits for this liner. What is not counted, however, is the fact that although Coolant B had a bigger surface area with pits and roughening that touched the grid lines, the deepest pit was measured to be 1.0 mm for Coolant B. This was the same as for Coolant A, which also had a deepest pit depth of 1.0 mm. Coolant C had several pits exceeding 1.0 mm, with the deepest being 1.2 mm. Since pitting through the liner is the failure mode, it is possible that the manner in which this test currently evaluates coolants does not weigh all the factors appropriately.

FIG. 2—The #6 Liners for the three carboxylate coolants—Close up of thrust side damage.


FIG. 3—The #2 Liners for the three carboxylate coolants—close up of thrust side damage.

There are a few important notes to make. First, notice that the “Pit Count” from this test, which again is really the “grid count” is actually much higher than the real number of pits in the liner for these carboxylate based coolants. This may not be true for conventional coolants, we have not seen enough data to verify. Second, it is clear from the comparative pictures that if pit depth were a factor for consideration, Coolant “B” might be considered much closer to Coolant “A” in performance than to Coolant “C.” Clearly the actual pitting measured for Coolant “C” is much worse 共more pits and deeper pits兲 than both aliphaticbased carboxylates in this test. Finally, in all cases, the pitting occurred essentially exclusively in a small area on the thrust side. Based on these data, while not all carboxylate coolants are equivalent in performance, it is clear that these carboxylate coolants provide much better protection against cavitation than nonnitrited low-silicate universal coolants. Directionally the aliphatic carboxylate provides better cavitation protection than the aromatic based carboxylates. Fleet Testing—Inhibitor Depletion To best measure inhibitor depletion rates, it is essential to minimize coolant top-off. Top-off is required to replace coolant lost due to leaks and evaporation. It has been reported that top-off can replenish an entire cooling system in as little as one year 关3兴. With extended life technologies, such as those based on carboxylates like the ones used in these studies, there are published claims of minimal depletion over the course of several years’ service 关1,2兴. In order to further verify these claims and continue to understand the limitations of these inhibitor systems, the effects of top-off must be accounted for when determining inhibitor depletion rates. A fleet of 32 Freightliner Century Class trucks equipped with Caterpillar C-12 engines was modified to minimize coolant losses. EPDM hose designed to be especially resistant to water loss/evaporation due to water permeation through the hose wall were used in combination with hose connections that were sealed with heat-shrink hose clamps. These clamps work to eliminate leakage by applying uniform pressure around the entire hose fitting. The fleet was filled with the previously described organic additive

TABLE 2—Pit count per Liner. Cylinder Liner “Pit/Grid” Count Coolant A B C

#1 17 31 36

#2 15 38 24

#3 13 18 19

#4 12 16 15

#5 11 19 16

#6 15 9 34

Total 83 131 144

FRITZ ET AL. ON PERFORMANCE OF FULL CARBOXYLATE COOLANT IN HDD ENGINES 103 TABLE 3—Disassembly candidate repair histories.a Engine Number Mileage Coolant Comments Component Coolant Level Sensor Coolant T Indicator Core and Tank Assembly Cylinder Head Heater Core Heater Hose High Temperature Switch Hose Clamps Injectors Low Coolant Probe Radiator Hose Radiator Inlet Repair Block - Cylinder Tank Top, repair Temperature Sensor Thermostat Water Gasket Water Pump

355655 728 635 Good

357809 748 102 Good

357813 660 845 Good

357814 679 577 Good

434 468 435 373

58 041

432 922 435 818 170 310, 434 302

508 247

58 041 46 968 117 537 647 814 156 900

161 030 195 743

693 829 279 822, 411 828

250 171 119 875

202 453

542 440

599 865

共©2005 SAE International, used with permission.兲

a

Figure 7 plots coolant tolyltriazole levels as a function of coolant age. Significant tolyltriazole depletion was observed in this fleet where top-up was carefully eliminated. As coolant age approaches 400 000 miles, tolyltriazole levels were observed to drop as low as 20 % of fresh. Tolyltriazole protects yellow metals, including copper and brass. Although tolyltriazole levels have dropped dramatically, this is not unexpected. Tolyltriazole behaves similarly to layer forming inhibitors; the tolyltriazole interacts with the yellow metal surfaces and forms a protective layer. This mechanism was examined in an earlier study 关12兴 and this protective layer was found to be quite resilient; electrochemical studies were able to demonstrate that a piece of copper radiator removed from a previously used radiator and exposed to a corrosive salt solution behaved similarly to a new piece of copper in solution with a coolant containing tolyltriazole, and then this was compared to fresh copper with no tolyltriazole. Even though the piece had been removed from the radiator, exposed to air, mechanically handled, it still was fully protected by the tolyltriazole. The protective layer that tolyltriazole provides can be quite robust. As well, carboxylates can also provide some level of protection to copper in the absence of TTZ. These facts taken together demonstrate why the yellow metals are completely protected even though the TTZ levels are as low as 20 % of fresh, which is confirmed by the copper levels. Results of this analysis for the presence of copper are presented in Fig. 8. From the plot we can see that in fact the copper content has remained quite constant over the course of the test. Early data found the copper content to be between 0 and 1.5 ppm and as the test progressed the copper continued to hover around 2 ppm or less. The plot shows the upper limit to 30 ppm, this is to be consistent with the proposed TMC RP 1416 which puts the condemning limit for copper at 30 ppm. Metal content is often used as an indicator for active corrosion. All coolant samples were analyzed for the corrosion metals: aluminum, iron, and lead. All values for all metals for all samples were ⬍1 ppm indicating that corrosion is well controlled by the carboxylate inhibition. Fleet Testing—Component Protection Perhaps more important than the actual inhibitor depletion is the corrosion protection imparted by the coolant. Repair histories were obtained for all candidates prior to disassembly and these were reviewed to identify coolant system repairs. A summary of the repairs for each of the trucks is provided in Table 3. Note that all liners, all radiators, blocks and heads are original equipment. Two of the water pumps were original, despite over 700 000 miles of service. Coolant samples were obtained from each candidate and

104 ENGINE COOLANT TECHNOLOGY TABLE 4—Disassembled Engines’ Coolant Compositionsa Vehicle ID Recent Mileage Coolant Water Quality pH Reserve Alkalinity Water Content 共%兲 Calcium 共ppm兲 Magnesium 共ppm兲 Chloride 共ppm兲 Contaminants and Inhibitors Boron 共ppm兲 Silicon 共ppm兲 Nitrite 共ppm兲 Nitrate 共ppm兲 Phosphate 共ppm兲 Molybdenum 共ppm兲 Tolyltriazole 共ppm兲 Diacid 共% full dosage兲 Monoacid 共% full dosage兲 Corrosion Metal Analysis Aluminum 共ppm兲 Copper 共ppm兲 Iron 共ppm兲 Lead 共ppm兲

355655 728 635

357809 748 102

357813 660 845

357814 679 577

7.87 2.61 42 10 6.2 75

7.98 2.17 49.14 1.7 2 79

7.83 2.03 48.42 13 6.7 61

8.2 2.19 50.25 6.7 4.1 90

6.1 80 319 990 27 427 140 146 107

3.5 72 133 632 71 515 181 119 90

7.1 55 192 497 0 575 418 125 95

2.3 33 268 435 0 562 690 126 102

⬍1 9.5 ⬍1 ⬍1

⬍1 4.2 ⬍1 ⬍1

⬍1 3.7 ⬍1 ⬍1

⬍1 1.5 ⬍1 ⬍1

共©2005 SAE International, used with permission.兲

a

analyzed to determine inhibitor content, extent of contamination with other coolant and to determine corrosion metal content if present. Coolant analyses for all trucks are provided in Table 4 and the analysis confirms the presence of the factory fill extended life coolant with minimum contamination. In this fleet there was no controlled effort to limit top-off. All engines were torn-down so that all cooling system components could be inspected for signs of corrosion. As well, all major components were retained and sent for metallurgical analysis. None of the 24 cylinder liners examined 共six per four engines兲 showed signs of any pitting or scuffing. For additional pictures refer to SAE 2005-01-3579. 共Fig. 9兲. The liner seals on the coolant side are fabricated from EPDM. They are subjected to high temperatures as well as mechanical stress due to vibrations. All liner seals were in excellent condition with no signs of leaks. Laboratory examination indicated less than 75 % compression set for all seals with excellent elasticity retention, see Fig. 10. The radiators were examined on-site and they were in excellent condition, with no signs of leaks. Two of the radiators were retained for further inspection. In laboratory testing, it was determined that all radiator tubes were free from plugging. Metallurgical analysis found that the solder joints were free of corrosion; see Fig. 11 for radiator tubes and decks. Thermostat housings are aluminum and subject to high temperature and erosive damage if not properly protected. The thermostat housings were in excellent condition and showed minimal aluminum corrosion and no corrosion was observed at the junction of the dissimilar metals of the housing with the thermostat itself. All thermostats were operational, see Fig. 12. Before the introduction of extended life coolants it would have been very rare for a water pump to last 500 000 miles. In this test every water pump lasted at least 500 000 miles and two were still in service after 700 000 miles or more. The water pump seal, the most common failure point in a water pump, was still functional and not leaking, indicating that dissolved solids 共which typically build up from continuous SCA use兲 were not a problem. The aluminum pump cover showed only minor erosive damage and the impeller was like new 共Fig. 13兲, indicating extended aluminum and cast iron protection. Inspection of the block and head determined that there was no observable corrosion and minimal flash rust in any of the coolant head and block passages.


FIG. 9—Cylinder liners from vehicle 357814; thrust side (Caterpillar 3406E engine) (©2005 SAE International, used with permission.) Coolant Corrosion Testing After 748 102 Miles (with Top-up) Coolant from the vehicles that were torn down for inspection was collected and sent to the lab for full analysis and glassware corrosion testing. The full analysis of the coolants is shown in Table 4. From the analysis we see that there is some level of contamination in all the trucks, but we estimate the contamination to minimal. Since there was no effort made to control top-up, or to monitor top-up, these are real world samples. No extender was added to these vehicles according to their maintenance records and the coolant analysis agrees. ASTM D-4340 关16兴 testing was carried out on the highest mileage coolant and the result agrees with earlier reported findings 共1兲 that this extended life coolant formulation is able to provide excellent results at this test even after 748 102 miles in the vehicle. While the result obtained was slightly above the limit of 1.0 mg/ cm2/week set by ASTM D-3306 关18兴 for new coolants at 1.28 mg/ cm2/week, this is an excellent result for a used coolant. The presence of extra chloride in the sample, copper, and low levels of borate and phosphate which are known to be aggressive in this test 关13,14兴, verify that the carboxylates are working hard to protect the aluminum. This result combined with the appearance of the aluminum parts is proof of performance.

FIG. 10—O-rings on cylinder liner from Vehicle 357814 (Caterpillar 3406E engine).


FIG. 11—Radiator tubes and decks, Vehicle 357809 (Caterpillar 3406E engine).

FIG. 12—Thermostats and housing, Vehicle 357809 (Caterpillar 3406E engine). (©2005 SAE International, used with permission.)

FIG. 13—Water pump impeller and aluminum pump cover, Vehicle 357809 (Caterpillar 3406E engine). (©2005 SAE International, used with permission.)


FIG. 14—ASTM D-1384 data for new carboxylate-based coolant and for used coolant at 748 102 miles. ASTM D-1384 关15兴 testing was also conducted and the data are shown in Fig. 14. As can be seen from the data, the coolant passes this test for all metals. Conclusion This study has examined coolant inhibitor life as well as corrosion protection for an extended life coolant based on mono- and dicarboxylate corrosion inhibitors. The results presented indicate that this coolant technology allows users to take advantage of the extended life corrosion inhibition performance far longer than previously reported for coolants. Testing in the proposed heavy duty cavitation test verifies the excellent performance of the nitritecontaining aliphatic carboxylate-based coolant technology and validates its proven track record. The performance of the nitrite-free version is also good; however, clearly there are advantages to a “belt and suspenders” system that contains multiple solutions to the known issue of cavitation. Relatively speaking, the nitrite-free aliphatic carboxylate formulation outperformed the nitrite-free aromatic carboxylate formulation in this test with slightly fewer pits, and with much “less deep” pits overall. Used coolant analysis conducted on samples taken from a fleet test using Caterpillar C-12 engines demonstrated that the corrosion inhibitor levels remained acceptable to at least 400 000 miles without top-off and without the use of extenders or supplemental coolant additives that would be required by most conventional coolant systems. Analysis also indicated that the coolant’s pH, remained constant and well above 7, far from an acidic regime throughout the test. A separate field test using Caterpillar 3406 equipment, demonstrated excellent corrosion protection to 700 000 miles and beyond through engine disassembly and component inspection. With respect to water pumps, all survived to 500 000 miles and two pumps were still functional after 700 000 miles of service. Protection of aluminum, iron, and copper components; solder joints, and elastomers were excellent. Glassware corrosion testing verified acceptable corrosion prevention performance of the used coolant out to 748 102 miles. Not all carboxylate-based coolants behave similarly; however, these data verify that the aliphatic carboxylate-based coolants evaluated in this study are capable of providing cooling system protection with minimum maintenance out to a half-million miles and beyond in heavy duty diesel applications. References 关1兴关2兴关3兴

Washington, D. A., Miller, D. L., Maes, J.-P., Van de Ven, P., and Orth, J. E., “Long Life Performance of Carboxylic Acid Based Coolants,” SAE 940500, 1994. Washington, D. A., Miller, D. L., Valkovich, P. B., Amrstrong, R. A., McMullen, F. A., Quinn, M. J., Kelly, F. A., McWilliams, E. J., “Performance of Organic Acid Based Coolants in Heavy Duty Applications,” SAE 960644, 1996. Hudgens, R. D., “Comparison of Conventional and Organic Acid Technology 共OAT兲 Coolants in Heavy Duty Diesel Engine Service,” SAE 1999-01-0139, 1999.


关4兴关5兴

关6兴关7兴关8兴关9兴关10兴关11兴

关12兴


关18兴

Miller, D. L., Bade, R. T., and Orth, J. E., “Corrosion Mechanism of High Lead Solder and Correlation to Dissolved Oxygen,” SAE 940497, 1994. Kelley, F. A. and McWilliams, E. J., “A Bench Test Procedure for Evaluating the Cylinder Liner Pitting Protection Performance of Engine Coolant Additives for Heavy Duty Diesel Engine Applications,” SAE960879, 1996. Davis, G. D. and Christ, R. J., “A Comparison of Engine Coolant in an Accelerated Heavy Duty Engine Cavitation Test,” SAE960883, 1996. Darden, J. W., Triebel, C. A., Maes, J. P., and VandNeste, W., “Monoacid/Diacid Combination as Corrosion Inhibitors in Antifreeze Formulations,” SAE 900804, 1990. Pellet, R. J., Bartley, L. S., and Hunsicker, D. P., “The Role of Carboxylate-Based Coolants in Cast Iron Corrosion Protection,” SAE 2001-01-1184, 2001. Pellet, R. J. and Hunsicker, D. P., “Solder Protection with Extended Life, Carboxylate-Based Coolants,” SAE 2000-01-1979, 2000. Hudgens, R. D. and Hercamp, R. D., “A Perspective on Extended Service Intervals and Long Life Coolants for Heavy Duty Engines,” SAE 961818, 1996. Pellet, R. J., Van de Ven, P., Amaez, D., Fritz, P. O., Bartley, L. S., and Hunsicker, D., “The Role of Nitrite and Carboxylate Ions in Repressing Diesel Engine Cylinder Liner Cavitation Corrosion,” Paper No. 545, Corrosion 98, NACE meeting, San Diego, CA, 1998. Bartley, L. S., Fritz, P. O., Pellet, R. J., Taylor, S. A., and Van de Ven, P., Engine Coolant Testing, 4th Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 76–88. Wiggle, R. R., Hospadaruk, V., and Tibaudo, F. M., “Corrosion of Cast Aluminum Alloys Under Heat Transfer Conditions,” SAE 810038, Society of Automotive Engineers, Feb. 1981. Fritz, P. O., Bartley, L. S., Maes, J. P., and Van de Ven, P., “Extended Life Carboxylate Coolant Compatibility with Other Coolant Technologies—Examining the Data,” SAE 2000-01-1977. ASTM D 1384, “Test Method for Corrosion Test for Engine Coolants in Glassware,” Vol. 15.05, ASTM International, West Conshohocken, PA. ASTM D 4340, “Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions,” Vol. 15.05, ASTM International, West Conshohocken, PA. ASTM D 4985, “Standard Specification for Low Silicate Ethylene Glycol Base Engine Coolant for Heavy Duty Engines Requiring a Pre-Charge of Supplemental Coolant Additive 共SCA兲,” Vol. 15.05, ASTM International, West Conshohocken, PA. ASTM D 3306, “Standard Specification for Glycol Base Engine Coolant for Automobile and LightDuty Service,” Vol. 15.05, ASTM International, West Conshohocken, PA.


Yasuaki Mori,1 Michael L. Abel,2 and Yuji Miyake2

Cavitation Protection Performance of Nitrite-Free Organic Acid Based Coolant for Heavy-Duty Engines ABSTRACT: For decades, most all heavy-duty engine coolants contain nitrites in order to protect against cavitation erosion/corrosion. So much so that many industry specifications require nitrites by name as well as minimum concentration quantities as they have been found to be very effective in minimizing cavitation erosion/corrosion of heavy-duty engine cast iron cylinder liners. However, the use of nitrites has become an issue because it is commonly known that nitrites could produce carcinogens when mixed with amine-type coolants. Legislation in some countries recommend not using it. This paper introduces nitrite-free, organic acid based, long-life coolant technology that gives the desired cavitation protection. KEYWORDS: aromatic carboxylate, aliphatic carboxylate, organic acid, cavitation, heavy-duty, ultrasonic cavitation, elastomer compatibility testing, engine dynamometer testing, fleet testing

Introduction In recent years there are increased demands on reducing the impact on the environment and the push to recycling and reusing vehicle parts is increasingly moving forward. Also, end-users are demanding the decrease of maintenance costs and frequency; hence the desire for longer-life products is becoming stronger. There are mainly two categories of heavy-duty truck coolants. The historically dominant type is the conventional coolant based on inorganic salts including nitrite, silicates, borates, phosphates, etc., and the other type coolant is based on organic acid technologies. These days the latter is becoming increasingly more mainstream because the maintenance interval of the former is shorter and costs over the useful life of the engine can be higher. Even though the base inhibitor systems are somewhat different 共borate versus phosphate based兲, all traditional heavy-duty coolants contain nitrites. Nitrite is the low cost alternative in the protection of cylinder liner pitting. SAE paper 共1999-01-0140兲 introduces how nitrites prevent cylinder liner pitting by conducting the fleet testing using organic acid based coolant with nitrite and without nitrite, and it shows that the organic acid based coolant without nitrite does not sufficiently protect cylinder liner pitting 关1兴. Nitrite is quite effective against cylinder liner cavitation corrosion; however, this anticorrosive additive has extremely high toxicity. Also there is the argument that nitrites can react with amines to produce carcinogenic nitrosamine. The toxicity of nitrite is the highest of the generally used anticorrosive additives of coolants as the LD50 for oral toxicity for rats is rated at 85 mg/ Kg, and is similar to the toxicity of arsenic 关2兴. This report introduces a nitrite-free aromatic carboxylate based coolant that has superior cavitation protection performance. Outline of Composition Aromatic carboxylate based coolant introduced in this report is composed of aromatic carboxylate 共benzoate, p-toluate, and p-tert butyl benzoate兲, tolyltriazole, molybdate, and nitrate but does not contain nitrite, silicate, borate, or amine 关3兴. Phosphate is quite effective against the corrosion of aluminum, but some regions restrain the use because diluting with hard water traditionally has produced an insoluble Manuscript received February 1, 2006; accepted for publication January 4, 2007; published online February 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 CCI Corporation, 12 Shin-hazama, Seki City, Gifu 501-3923, Japan. 2 CCI MANUFACTURING IL CORPORATION, P.O. Box 339, Lemont, IL 60439. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

109


phosphate. Because of this reason, this paper introduces coolant without phosphate, but its addition is recommended for corrosion protection of aluminum even in constrained regions, since using premixed coolant or stabilized phosphates removes the concern 关4兴. The phosphate concern is based more on historical perspectives and misconceptions than on factual performance issues. The reason for the use of aromatic carboxylates as the organic acid is that they have better performance against cavitation than aliphatic carboxylate used for the organic acid type coolant that is currently becoming mainstream. It is also known that aliphatic carboxylate based coolant is aggressive towards silicone rubber 关5,6兴, while it is shown in this paper that the aromatic carboxylates used here have good compatibility with silicone rubber materials. Test Results Ultrasonic Cavitation Corrosion Test Ultrasonic cavitation corrosion test results are shown in Fig. 1. Although the weight change of nitrite-free aliphatic carboxylate based coolant is larger than nitrite containing conventional heavy-duty coolant, if nitrite is added, cavitation protection performance becomes better than that of the nitrite containing conventional heavy-duty coolant. While the cavitation protection effect of nitrite is well documented, even when the aromatic carboxylate based coolant does not have the nitrite, its cavitation protection performance is better than nitrite containing aliphatic carboxylate based coolant and nitrite containing conventional heavy-duty coolant.

FIG. 1—Ultrasonic cavitation corrosion test results. Elastomer Compatibility Test These tests were conducted in accordance with test method CES 14603 共Cummins Engineering Standards兲 to evaluate the aromatic carboxylate based coolant elastomer compatibility and are compared against the nitrite containing aliphatic carboxylate based coolant and nitrite containing conventional heavy-duty coolant. Compatibility was checked against five elastomer types 共NBR, H-NBR, Silicone, EPDM and Viton兲. Test conditions are shown in Table 1. Each type of elastomer was tested separately in its own vessel. Each specimen type test pieces 共for tensile/elongation, hardness/volume, and compression set兲 were combined together in one vessel. The aromatic carboxylate based coolant shows good compatibility with all elastomers tested. Especially with respect to the silicone rubber, the aliphatic carboxylate based coolant shows large physical property changes, while the aromatic carboxylate based coolant shows good compatibility basically equivalent to conventional heavy-duty coolant. Also, remarkable cracks were confirmed on the surface of the tensile/elongation specimen after testing in an aliphatic carboxylate based coolant. There was no significant difference between the aromatic carboxylate based coolant and the conventional heavy-duty coolants. Silicone rubber compatibility test results are shown in Figs. 2–8.

MORI ET AL. ON CAVITATION PROTECTION 111 TABLE 1—Elastomer compatibility test condition. Items Vessel material Vessel capacity, L Coolant amount, L Coolant concentration, vol. % Coolant aging terms, hours Coolant aging temperature, °C NBR H-NBR Silicon EPDM Viton Shape of tensile/elongation specimen Size of vulcanized specimen Size of compression set

Conditions Carbon Steel 4.8 1.6 50 168 共not for tensile/elongation兲, 500, 1000 120 150 150 150 150 According to ASTM D 412 die C 0.63 in.⫻ 0.63 in.⫻ 0.08 in. 共more than 0.5 g兲 0.25 in.⫻ 0.25 in.⫻ 0.08 in.

FIG. 2—Appearance of silicone rubber test specimen after compatibility test.

FIG. 3—Elongation change.


FIG. 4—Tensile change.

FIG. 5—Volume change.

FIG. 6—Hardness change.

MORI ET AL. ON CAVITATION PROTECTION 113

FIG. 7—Weight change.

FIG. 8—Thickness change. Engine Dynamometer Testing In order to check the cavitation protection performance of an aromatic carboxylate based coolant, engine dynamometer testing was performed using a Navistar 530E engine in accordance with test conditions shown in Table 2. The appearance of the cylinder liner after the test is shown in Fig. 9. Pitting was not observed on any of the cylinder liners after the test and the appearance of the cylinder liners was essentially the same as new. TABLE 2—Engine dynamometer test conditions. Item Test cycle Step 1 Step 2 Step 3 Step 4 Test duration, hour Coolant concentration, vol. % Coolant volume, G Coolant flow rate, G/min Engine outlet temperature, °C

Condition Low idle: 30 s Rated speed and load: 120 s High idle: 60 s Peak torque: 120 s 2000 50 18 85 93


FIG. 9—Appearance of cylinder liners after engine dynamometer testing.


Fleet Testing Fleet testing was performed using a total of more than 100 vehicles utilizing Detroit Diesel and CAT engines. The highest mileage at time of tear down was nearly 600 000 miles although the fleets continue to accumulate mileage. The coolant was sampled during the test from all vehicles and analyzed for pH, metal ion concentration, inhibitor content, and degradation product generation. For this evaluation ten sets of parts 共four Detroit Diesel engines and six CAT engines兲 were chosen to be removed from the vehicles. Parts taken included the cylinder heads, cylinder liners, radiators, water pumps, thermostats, thermostat housings, and fuel injector sleeves. Fleet performance results were excellent as there were no problems, such as overheating or LLC leakage, reported in any truck during the fleet testing. TABLE 3—Summary of inspected engine.

Engine/Vehicle # DD #31520 #31525 #31433 #31430 CAT 3406 series #226

Test Mileage Mile 372 373 548 577

Test Duration Month

500 006 216 226

38 38 34 34

379 742

34

#231

427 829

32

#233

372 761

34

#236

360 110

44

#237 #238

243 048 372 021

19 26

Contamination

47 %, 53 586⬃ 177 192 miles 55 %, 294 245⬃ 427 829 miles 33 %, 284 862⬃ 348 113 miles 20%, 289 624⬃ 355 263 miles

State of Coolant Although the pH of this type of coolant falls to about 6.5 by 100 000 miles, it is maintained at 6.5 thereafter. Since this coolant inhibitor system is not using an inhibitor that has a buffering effect in weak alkali domains 共i.e., phosphates or borates兲, the pH fall is early; however, this type of technology has sufficient anticorrosion and anticavitation performance at a pH level of 6.5 and performs satisfactorily at this level. By using an organic acid to protect iron that has essentially no depletion rate, even when the pH moves to 6.5 early in its life, there is a minimum conservative protection life of 300 000 or more miles. It is difficult to corrode iron at higher pH ranges. However, for amphoteric metals 共i.e., aluminum兲, when the pH is moderately high, corrosion is accelerated. This coolant exhibits good and compatible protection of metals from iron to aluminum so it can be said to be in a desirable pH range. Tolyltriazole decreases as expected and remains above 10% at 300 000 miles. This quantity is sufficient for copper and brass protection. The State of Cooling System Parts The summary of the vehicles that collected cooling system parts is shown in Table 3. The cooling parts of an engine running with a nitrite-type conventional heavy-duty coolant were also collected at 420 000 miles for comparison. No extender was added during the test even though test parameters allow for its addition. In vehicles #31520 共372 500 miles兲 and #31525 共373 006 miles兲, light pitting was observed on only one cylinder liner, liner No. 3. The maximum depth of #31525 was 6 %, and the maximum depth of #31520 was 10 %. This is considered to be completely satisfactory. In vehicles #31433 共548 216 miles兲 and #31430 共577 226 miles兲, light pitting was observed on all cylinder liners with a maximum depth of 3 to 14 %. However, these trucks were run 500 000 or more miles


FIG. 10—pH change.

FIG. 11—Tolyltriazole concentration change.

FIG. 12—Aromatic carboxylate concentration change. with no extenders used, and it is considered very acceptable and a pitting state of this level is better than


FIG. 13—Molybdate concentration change.

FIG. 14—Appearance of cylinder liners after fleet testing (DD engine). the state of the cylinder liners which out of the vehicle that accumulated 420 000 miles with a nitrite-type conventional heavy-duty coolant. Vehicle #226 共379 742 miles兲 was contaminated to a level of approximately 47 % of the concentrated coolant level with conventional coolant in the period between 53 586– 177 192 miles. Though in best practice this coolant is not intended to be mixed with conventional coolants, this vehicle was chosen to investigate compatibility issues and shows what has been seen in the laboratory; that the aromatic carboxylate based coolant and conventional coolants are compatible as there were no abnormalities found in the collected parts and coolant performance, properties, inhibitor depletion, or metal ion accumulation. Vehicles # 231 共337 039 miles兲, #233 共427 829 miles兲, and #236 共360 110 miles兲 were also contaminated with a conventional coolant after 280 000 miles. Pitting was not observed on any cylinder liners of all vehicles, therefore it is suggested that a nitrite-free aromatic carboxylate based coolant completely inhibits pitting for over 280 000 miles and is not adversely affected by contamination with borated/nitrited coolants.


FIG. 15—Appearance of cylinder liners after fleet testing (CAT engine).

In vehicles #237 共243 048 miles兲 and #238 共351 496 miles兲, pitting was not observed on any cylinder liners and there were no abnormalities found in the collected parts 共cylinder head, cylinder liners, radiator, water pump, thermostat, thermostat housing, and fuel injector sleeves兲. Moreover, there were no abnormalities found in the coolant performance, such as properties, inhibitor depletion, or metal ion accumulation up to the point that the components were collected. 共see Figs. 10–15兲. Conclusions The aromatic carboxylate based coolant presented has good compatibility with elastomers including silicone rubber and has general performance characteristics more than equivalent with nitrited heavy-duty conventional coolant. Although the aromatic carboxylate based coolant presented in this paper does not contain nitrite, it exhibits good cavitation protection performance and the cavitation protection performance is maintained without performing SCA additions during service intervals. References 关1兴关2兴关3兴关4兴关5兴关6兴

Hudgens, R. D., “Composition of Conventional and Organic Acid Technology Coolant in Heavy Duty Diesel Engine Service,” SAE Paper 1999–01–0140, 1999. Hudgens, R. D., and Bustamante, R. B., “Toxicity and Disposal of Engine Coolants,” Engine Coolant Testing: 3rd Volume, ASTM STP 1192, 1993, pp. 149–164. United States Patent 6126851. Osawa, M., Morita, Y., and Nagashima, T., “A Study of Extension of Engine Coolant Life Using Low Phosphate Organic Acid Inhibitors,” SAE Paper 2003-01-2023, 2003. Automotive Cooling Journal, May 1999, pp. 16–20. Radiator Reporter, Vol. 27, No. 7, August 1999, pp. 73–76.


Fred C. Alverson,1 Steven L. Balfe,1 and Anthony P. Skrobul1

Accelerated Oxidation and Corrosion Testing of Engine Coolants Using a Rotary Pressure Vessel Oxidation Test ABSTRACT: Today’s modern engines are exposing engine coolants to more severe operating conditions involving higher coolant temperatures, greater heat rejection requirements, greater metal to coolant heat fluxes, higher coolant flow rates, higher cooling system pressures, and slower deaeration. These conditions will have a tendency to accelerate oxidation/thermal degradation, reduce corrosion protection, and shorten coolant life. In efforts to simulate the increased severity in operating conditions, an accelerated oxidation and corrosion test, using a rotary pressure vessel oxidation test, was developed and evaluated to assess the oxidation/thermal stability and corrosion protection of conventional, hybrid, and extended life coolants. The test involves exposing the coolant to a high temperature oxygen rich environment under pressure with six different metal corrosion coupons. The test allows a quantitative assessment of corrosion protection of the coupons and the effects on coolant chemistry. Test results are provided on conventional, hybrid, and extended life coolants. The test has also been found to be a promising predictive tool to screen satisfactory versus unsatisfactory coolant formulations, including recycled coolants. KEYWORDS: conventional coolants, hybrid coolants, extended life coolants, oxidation, corrosion, inhibitor depletion

Introduction Engine manufacturers are continuously striving to develop new automotive and diesel engine technology that will provide improved performance/productivity, lower emissions, greater fuel economy, and longer service life. Engine coolants used in these engines are generally exposed to more severe operating conditions including higher coolant temperatures, greater heat rejection requirements, smaller cooling systems, higher coolant flow rates, higher cooling system pressures, slower deaeration, tighter tolerances/narrower coolant passages which are thermally stressing the coolant. All of these factors will tend to accelerate oxidation/thermal degradation, reduce corrosion protection, and shorten coolant life. Ethylene glycol-based engine coolants continue to be the most widely used heat transfer fluid for automobile and truck applications. While these coolants provide the basic functions for freeze protection, boil over protection, and heat transfer, these coolants are susceptible to oxidation and thermal degradation under severe operating conditions. The oxidation reaction involves reaction of ethylene glycol 共HO-CH2-CH2-OH兲 with oxygen to form glycolic acid 共HO-CH2-COOH兲, formic acid 共HCOOH兲, and other glycol degradation acids. Certain additives may also undergo oxidation such as nitrites 共NO2兲 may react to form nitrates 共NO3兲. Glycol degradation acids are extremely corrosive and can cause premature failure of engine and cooling system components 关1兴. Oxidation stability of engine coolants is affected by many parameters. Among the most critical are: fluid temperature, aeration rate, pressure, cooling system corrosion metals 共catalysts兲, and the engine coolant corrosion inhibitors. Similar to lubricants, fluid temperature is probably the most critical parameter. The oxidation rate of coolants increases exponentially with temperature. Slight increases in temperature can have significant effects on engine coolant oxidation stability and corrosion protection, especially at higher temperatures. The second most critical parameter is the type and amount of corrosion inhibitors contained in the coolant. As will be shown in this paper, different types of engine coolant corrosion inhibitor technology 共inorganic only, organic only, hybrid inorganic, and organic兲 exhibit different levels of Manuscript received March 7, 2006; accepted for publication March 17, 2007; published online May 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Coolants Advisor, Technology Manager, and Coolants Advisor, respectively, Shell Global Solutions US Inc., 3333 Highway 6 South, Houston, TX 77082. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

119


oxidation stability and corrosion protection performance when exposed to high temperature oxygen rich environments. ASTM D 3306-05 Standard Specification for Glycol Base Engine Coolant for Automobile and Light Duty Service and ASTM D 6210-04 Standard Specification for Fully Formulated Glycol Base Engine Coolant for Heavy Duty Engines define the physical, compositional, and performance requirements for gasoline, diesel, and natural gas engines. With the increase in severity of operating conditions in modern engines, these test protocols do not currently include performance tests that adequately assess the oxidation effects on coolant corrosion protection. Therefore, an accelerated oxidation and corrosion test was developed using a rotary pressure vessel to assess oxidation/thermal stability and corrosion protection of coolants.

Experimental Test Apparatus and Procedure A literature review showed that the ASTM D 2272-02 Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel test has been used to some extent to evaluate coolant antioxidant and anticorrosion properties 关2兴. The Accelerated Oxidation and Corrosion Test uses a combination of the ASTM D 2272-02 and ASTM D 1384-05 Standard Test Method for Corrosion Test for Engine Coolants in Glassware tests. The test procedure involves placing a 55-mL coolant sample 共50/50 by volume in DI water兲 in ASTM D 2272-02 glassware with a six metal coupon bundle 共copper, solder, brass, steel, cast iron, and cast aluminum兲. The coupon bundle is the same as used in ASTM D 1384-05, except that Teflon spacers electrically isolate each coupon in the bundle. The legs on the bundle are also Teflon rather than brass to minimize etching of the glass 共Fig. 1兲. The test solutions are prepared with deionized water, rather than the ASTM D 1384-05 corrosive water. The metal coupons are prepared, cleaned, and weighed before and after the test as specified in ASTM D 1384-05. The glassware is then placed in the pressure vessel, charged with oxygen to a pressure of 620 kPa 共90 psi, 6.2 bar兲 and rotated axially at 100 r / min at a 30° angle from horizontal in a bath at 121– 150° C 共250– 302° F兲 for 168 h 共Fig. 2兲. The volume of fluid 共55 mL兲 was chosen to maximize the amount of fluid in contact with the metal coupons while at the same time preventing overflow of the fluid into the pressure vessel while rotating in the bath. A small upper portion of the metal coupons is exposed to the oxygen-rich environment during the test. The corrosion-inhibitive properties of the test solutions are evaluated on the basis of weight changes incurred by the specimens. The oxidation-inhibitive properties of the test solutions are evaluated on the basis of changes in pH, corrosion inhibitor contents, and the presence of glycol degradation acids–glycolates and formates.

FIG. 1—ASTM D 2272-02 pressure vessel with ASTM D 1384-05 metal coupon bundle.

ALVERSON ET AL. ON OXIDATION AND CORROSION TESTING 121

FIG. 2—ASTM D 2272-02 bath.

Test Temperatures Test temperatures of 121, 135, and 150° C 共250, 275, and 302° F兲 were utilized in the test. A previous Union Carbide study reported that the rate of ethylene glycol degradation doubled for every 15° C increase in temperature under their test conditions 关3–5兴. The results of this study tend to show greater rates of oxidation at higher temperatures for certain coolants, which may be due to the severe test conditions. The results also indicate that the type of corrosion inhibitor technology significantly affects oxidation stability performance of the coolant. Test Fluids The following types of engine coolants were evaluated in the Accelerated Oxidation and Corrosion Test: light duty extended life coolant 共LD ELC兲, light duty hybrid coolant 共LD HC兲, light duty conventional coolant 共LD CC兲, heavy duty extended life coolant 共HD ELC兲, heavy duty extended service interval coolant 共HD ESI兲, heavy duty traditional fully formulated coolant 共HD TFF兲, and recycled conventional coolant 共RCC兲. Table 1 provides compositional information on the inhibitors contained in engine coolants tested. The Appendix provides additional information on engine coolant and inhibitor terminology referenced in this paper. TABLE 1—Engine coolants and corrosion inhibitors. Inorganic Inhibitors Coolant Inhibitors LD ELC LD HC 1 LD HC 2 LD CC HD ELC 1 HD ELC 2 HD ESI HD TFF RCC 1 RCC 2

Borate

Nitrite

Nitrate

X X

X

X X X

X X X

X X X X X X

X X X X

Phosphate

Organic Inhibitors Molybdate

X X X

X

X

Silicate

X X X

OAT X X X X X

X X X

Azole X X X X X X X X X

ALVERSON ET AL. ON OXIDATION AND CORROSION TESTING 127

Acknowledgments The authors wish to thank Mr. Terry Charles for conducting the numerous Accelerated Oxidation and Corrosion Test runs and Amalgatech for conducting the coolant analyses. The authors are also grateful to Shell Global Solutions and Shell Oil Products for permission to publish the paper.

Appendix Tables 4 and 5.

TABLE 4—General engine coolant terminology. Conventional coolant

An engine coolant containing primarily inorganic corrosion inhibitors such as borate, molybdate, nitrate, nitrite, phosphate, silicate. Sometimes also referred to as a traditional coolant. Coolant A fluid typically consisting of water, glycol, and corrosion inhibitors which functions to transfer heat from an engine and to provide corrosion protection of the engine and cooling system components. Extended life coolant An engine coolant with longer recommended change out intervals 共light duty: 100 000 miles, five years/4000 operating hours; heavy duty: 300 000 miles, 6000 h兲. Extended service interval An engine coolant that can go beyond 100 000 miles in on-highway operation between service intervals without the need to replace depleted chemicals. These coolants may contain delayed release Supplemental Coolant Additives 共SCAs—typically through the use of corrodibledissolvable membrane or slow-release pellets in a filter casing兲 or organic additive technology corrosion inhibitors, or both. Fully formulated coolant A conventional coolant containing an initial dosage of SCA. These coolants require periodic addition of SCAs and provide a service life of 200– 250 K miles 共2–3 years兲 with the proper addition of SCAs. Heavy duty Service duty characterized by average speeds, power output, and internal temperatures that are generally close to maximum such as Class 5 to 8 over the road trucks, off-highway equipment, high output stationary engine applications, and locomotive-marine applications. Hybrid coolant An engine coolant containing a combination of inorganic and organic corrosion inhibitors. Light duty Service duty characterized by average speeds, power output, and internal temperatures generally much lower than potential maximum such as automobiles, pick-up trucks, vans, sport utility vehicles, small farm tractors, and lawn maintenance equipment. Organic Additive Technology 共OAT兲 Any group of carboxylic acids including aliphatic mono and diacids and aromatic acids applicable as corrosion inhibitors in coolants. Supplemental Coolant A chemical additive that is periodically added to the coolant Additive 共SCA兲 to maintain protection against general corrosion, cylinder liner pitting, and scaling in heavy duty engines. Traditional coolant An engine coolant containing primarily inorganic corrosion inhibitors such as borate, molybdate, nitrate, nitrite, phosphate, and silicate. Sometimes also referred to as a conventional coolant. TABLE 5—Inhibitors and primary function(s). Azole Borate Phosphate Molybdate OAT Nitrate Nitrite Silicate

Copper and brass protection pH buffer pH buffer and iron protection Cavitation-erosion and cast iron protection General corrosion protection except yellow metals Light alloy and solder protection Cavitation and cast iron protection Aluminum protection


References 关1兴

关2兴关3兴

关4兴关5兴

Eaton, E. R., Boon, W. H., and Smith, C. J., “A Chemical Base for Engine Coolant/Antifreeze with Improved Thermal Stability Properties,” SAE Paper 2001-01-1182, Society of Automotive Engineers, Warrendale, PA, 2001. Karol, T. J., and Donnelly, S. G., “Functional Additive Composition Based on Organic Amine Salts for Coolants,” U.S. Patent 5,637,251, June 10, 1997. Gershun, A. V., and Mercer, W. C., “Predictive Tools for Coolant Development: An Accelerated Aging Procedure for Modeling Fleet Test Results,” Engine Coolant Testing: Fourth Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1999, pp. 113–132. Neddenreip, R. J., Status Report, Ethylene Glycol Oxidation, Technical Report C-133, Linde Company, 1960. Neddenreip, R. J., Status Report, Ethylene Glycol Oxidation, Technical Report C-135, Linde Company, 1961.


Sandra Claeys1 and Serge Lievens1

Coolants at Elevated Temperatures ABSTRACT: Over the years, new performance requirements and environmental regulations have driven engine manufacturers to design new engines. The new engine technologies have resulted in different operating conditions in cooling systems. In general, a trend towards higher coolant temperatures is observed, which is expected to have an implication on the coolant stability and corresponding lifetime. In heavy duty applications, this trend is even more pronounced as engines are running longer and under more severe conditions. In this paper, a selection of different current coolant technologies available in the market have been tested to obtain more information on the influence of the coolant additive package on the thermal stability of the most commonly used coolant base fluid, mono ethylene glycol 共MEG兲. For this reason glycol oxidation products have been measured after subjecting the coolants to high temperature oxidative conditions. In addition the physical/chemical stability of the coolants and corrosion protection level of the additive packages have been evaluated. KEYWORDS: engine coolant, high temperature, glycol oxidation, corrosion inhibitors

Introduction Looking into the evolution of engine developments, it has always been a challenge for engine manufacturers to create more powerful and efficient engines. During the past couple of years, this general trend towards increasing engine power is combined while striving to improve fuel economy and reduce harmful emissions in order to meet environmental regulations 关1兴. These additional requirements have resulted in changing engine designs and operating conditions, increasing demands on the cooling system and the coolant. The following examples illustrate this trend: • increasing the engine power results in a higher heat flux through the cooling system affecting the local coolant temperature; • weight reduction to improve fuel economy demands smaller coolant volumes, resulting in higher coolant temperatures; • introduction of an exhaust gas recirculation 共EGR兲 system to reduce certain emissions results in 25– 35 % increased heat energy to the coolant 关2兴. Under those demanding conditions, proper coolant selection and maintenance are more vital than ever to ensure satisfactory engine life. Long ago the selection of mono ethylene glycol 共MEG兲 as a base fluid for coolants was established because of its balanced performance properties like heat transfer, freezing protection, flammability, aggressive nature, and toxicity 关3兴. Despite the many advantages for coolant applications, glycols are susceptible to degradation at higher temperatures. Under these conditions in the presence of oxygen, a radical oxidation reaction takes place resulting in the formation of glycol decomposition acids, such as formic and glycolic acid 关4,5兴. These changes in the base fluid illustrate the potential risk of high temperatures on coolant properties such as pH, additive stability, and corrosion protection performance. Taking into account the electrophilic character of metallic ions, catalytic action on the oxidation process is expected. The results are inefficient corrosion protection of metallurgies in the cooling system leading to a more rapid degradation of the base fluid. Many people have been focusing on new coolant additive technologies 关6–10兴 to assist engine manufacturers in their selection of new mechanical designs or material selections. At least one study was undertaken to evaluate the performance and potential oxidation degradation of the base fluid under more extreme temperature conditions 关11兴. Manuscript received January 26, 2006; accepted for publication September 22, 2006; published online November 2006. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Chemist and Manager, Global Coolants Technology, respectively, Chevron Technology Ghent, Technologiepark-Zwijnaarde 2, Ghent, Belgium Copyright © 2006 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

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In the following work, a selection of MEG-based engine coolants representing current technologies has been evaluated for high temperature oxidative stability. For that purpose an in house test setup is used to simulate the high temperature areas in the cooling system. Next to the study of the breakdown products, the work also looks to stability and corrosion protection level of coolant additive packages. Measurements of pH during the oxidation test and changes in reserve alkalinity provide more information on the additive stability under the applied conditions. The corrosion protection properties, before and after being subjected to high temperature conditions, were evaluated electrochemically by a cyclic polarization technique and a static corrosion test. The main focus goes to studying the influence of the additive package on the thermal stability of the MEG-based fluid. Electrophoresis was used as an analytical technique to determine the amount of glycol decomposition acids. Experimental Results High Temperature Oxidation Test The high temperature oxidation resistance of the MEG-based coolants was tested by heating the diluted products 共50 vol % in deionized water兲 to a high temperature 共185° C, liquid temperature兲 in a pressure resisting stainless steel container for twelve days. The heat is transmitted to the liquid through a cast iron coupon 共type ASTM A 48, class 40兲, simulating the effects of high temperature areas in an internal combustion engine cooling system. A valve in the test apparatus allowed for samples to be taken 共Fig. 1兲. The coolant dilutions were prepared according to ASTM Test Method for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes 共D 1176-98/reapproved 2002兲.

FIG. 1—High temperature oxidation test. In order to evaluate the influence of the coolant additive packages on the thermal glycol stability, the other testing parameters 共such as coolant temperature, coolant volume, pressure, …兲 were kept constant for each tested coolant. By running the test in a sealed container, the influence of air oxygen on the glycol degradation process was limited. Coolant Physical and Chemical Properties During the high temperature oxidation test, samples were taken at regular time intervals and pH was measured according to ASTM Test Method for pH of Engine Coolants and Antirusts 共D 1287-91/ reapproved 2002兲. Before and after the oxidation test, the reserve alkalinity was determined according ASTM Test Method for Reserve Alkalinity of Engine Coolants and Antirusts 共D 1121-98/reapproved 2003兲. Capillary electrophoresis 共CE兲 was the analytical technique used for the determination of the MEG degradation products, such as formic and glycolic acids. Separations were done with a P/ACETM MDQ Beckman Coulter apparatus. Electrophoresis is a technique used for separation and quantification of charged molecules. The separation is accomplished under the influence of an electric field, which is the result of a potential difference between an anode 共⫹兲 and a cathode 共⫺兲. In capillary electrophoresis, a narrow-bore fused silica capillary is used as the stationary phase. As a liquid phase, and carrier of the

CLAEYS AND LIEVENS ON COOLANTS AT ELEVATED TEMPERATURES 131

analyzing sample, a conductive medium 共a buffer兲 is critical to obtain a good separation. When passing through an electric field in a conductive medium, molecules with a positive charge move to the cathode, while those with a negative charge move to the anode. Separation of the ions is determined by their difference in mobility, which is largely influenced by their charge and radius. Corrosion Protection Performance Electrochemical Test—A potentiokinetic cyclic polarization technique was used to accelerate the electrochemical corrosion process of a metal in a coolant. The details of the test setup 共apparatus and conditions兲 have been described previously 关10兴. The corrosion protection performance of a coolant corrosion inhibitor package was evaluated by increasing the potential difference between a working electrode 共the metal alloy to be tested兲 and an auxiliary electrode 共a platinum electrode兲. For this study, aluminum 共USA AA 6063兲 and carbon steel 共UNS G10180兲 were used as the working electrode. An all-metal silver electrode was used as the reference electrode. The working electrodes were freshly polished on 600 mesh abrasive paper prior to testing in order to obtain reproducible results. The testing solutions were a 50/ 50 vol % coolant/water dilution, to which corrosive salts 共15.70 mg sodium sulfate 共Na2SO4兲, 17.50 mg sodium chloride 共NaCl兲, 14.64 mg sodium bicarbonate 共NaHCO3兲, and 38.61 mg calcium chloride dihydrate 共CaCl2 · H2O兲 to 105 g of 50 vol % coolant兲 were added. The solutions were stirred until all salts dissolved. The electrodes were immersed in the solution and allowed to equilibrate in the test solutions for 1 h at ambient temperature prior to testing. Special care was taken to avoid the formation of air bubbles on the electrode surface. During this stabilization period no potential difference is forced on the system. Under these conditions an equilibrium is established between oxidation of the metal and reduction of the solution. The equilibrium corrosion potential 共Ec兲共Fig. 2兲 is measured relative to the reference electrode. It is the potential at which oxidation and reduction rate are equal. After stabilization, a positive potential is applied, increasing the corrosion rate which is reflected in an increase of the current density. When a good passivation protective layer is formed on the metal, the current density remains constant during a certain potential interval. When the potential difference becomes too high, the protective film will finally rupture. At a current density of 200 mA/ cm2 the potential is reversed. Under the influence of the protective mechanism of the corrosion inhibitors, the corrosive sites are repassivated, resulting in a decrease of the current density. The result of this test is a potentiokinetic cyclic polarization scan, in which several coolant parameters were monitored. They are as follows 共Fig. 2兲: • Passivation current density 共I0兲—the current density at which the passivation protective film is formed. High current densities correspond with high corrosion rates. • Pitting or rupture potential 共Er兲—the potential at which the passivation film breaks down. • Stability passivation potential 共Es兲 values reported 共Tables 3 and 4兲 are calculated by subtracting the potential at start I0 from the rupture potential Er 共see arrow in Fig. 2兲. • Repassivation potential 共Ep兲—the potential at which active regions are repassivated.

FIG. 2—Example of a potentiokinetic cyclic polarization scan. Glassware Corrosion Test—The static corrosion test is run according ASTM Test Method for Corrosion Test for Engine Coolants in Glassware 共D 1384-05兲. The post oxidation test coolants were diluted to


33 vol % 共as required by D 1384兲, to which the corrosive salts were added. This test evaluates the corrosion protection provided by coolants to different metallurgies by measuring the weight changes of the metal test specimen. The test was run in duplicate. Coolant Selection For both heavy duty and automotive engines, MEG-based coolants have been the preferred choice for many years. Driven by changes in engine designs and regional requirements, coolant manufacturers have been developing new additive packages, resulting in a broad range of coolant technologies. For this study, automotive coolants from different regions characterized by a certain corrosion inhibitor technology 共Table 1兲 have been selected. Coolants A and B represent the organic acid technology. These coolants typically contain carboxylic acid corrosion inhibitors providing aluminum and ferrous metal protection in combination with an azole for copper and brass protection. An overview of this type of coolant technology was earlier given by Weir and Van de Ven 关12兴. Coolant A contains aliphatic monocarboxylic acids in combination with dibasic acids. Coolant B is a combination of different dibasic aliphatic acids. By testing both technologies under high temperature oxidative conditions, the thermal stability of various carboxylic acid formulations was studied. Selected silicate containing coolant technologies are coolants C, D, E, and F. Coolant C is a combination of monocarboxylic/aromatic acids with silicates and other inorganic inhibitors usually present in a class of coolants known as hybrid technology. Coolants D, E, and F are conventional silicate-borate technology without any aliphatic acids. E and F can be considered more traditional coolants from Europe containing nitrite in combination with silicate. As coolant E also contains an organic compound 共aromatic acid salt rather than aliphatic兲 in the United States, it is sometimes considered a hybrid coolant. The phosphate-containing coolant technologies are represented by coolants G and H. Coolant G contains a combination of aromatic acid with phosphate. Coolant H is characterized by additional aliphatic dibasic acid.

TABLE 1—Coolant inhibitor formulations. Coolant Organic Acid Based Inhibitor Monoacid Dibasic acid Aromatic acid SiO2− 3 NO−3 B4O2− 7 PO3− 4 Triazole MoO2− 4 NO−2

A ⫻ ⫻

Silicate Based B

C ⫻

E

F

G

H

⫻

⫻ ⫻

⫻

⫻

⫻ ⫻ ⫻

⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻

⫻

D

Phosphate Based

⫻

⫻

⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻ ⫻

⫻ ⫻ ⫻ ⫻ ⫻ ⫻

Note: ⫻ indicates the presence of this inhibitor by analysis

Results and Discussion Determination of MEG Decomposition Products in Selected Coolants During the high temperature oxidation test, coolant samples were taken at six and twelve days 共at the end of the test兲, respectively, in order to follow the breakdown process of the MEG base. Formic and glycolic acid were identified as the main decomposition products. Due to the alkaline nature 共pH ⬎ 7兲 of the coolants, these compounds are present in the coolant samples as formate and glycolate. Electrophoresis

CLAEYS AND LIEVENS ON COOLANTS AT ELEVATED TEMPERATURES 133 TABLE 2—MEG degradation products present in coolant samples after six and twelve days in test apparatus.

Formate, mg/L Coolant A B C D E F G H

6 Days 67 65 81 16 401 1067 72 62

12 Days 63 65 91 28 429 1332 95 81

Glycolate, mg/L

6 Days 122 199 147 1802 454 1372 243 153

12 Days 117 223 166 2037 512 1752 391 232

Total Amount of Degradation Products, mg/L

6 Days 189 264 228 1818 855 2439 315 215

12 Days 180 288 257 2065 941 3084 486 313

FIG. 3—Total amount of MEG degradation acids during high temperature oxidation test.

was used for the separation and quantification of these decomposition products. The analysis results 共Table 2 and Fig. 3兲 provide information on how the additive package affects the thermal stability of the base fluid. When comparing coolants A, B, C, H 共containing aliphatic organic acid corrosion inhibitors兲 with coolants D, E, F, and G 共which do not contain aliphatic organic acid corrosion inhibitors兲, the lowest amount of decomposition products were measured for the coolants containing aliphatic carboxylic acid corrosion inhibitors. The effect was observed for different coolant class technologies, the pure organic acid-based coolants A and B, the hybrid silicate containing coolant C and the hybrid phosphate containing coolant H. It also appears that coolants containing aliphatic acids are more thermally stable over time. From all of the tested coolants, the organic acid-based coolant A, containing a combination of aliphatic monocarboxylic acids and dibasic acids, produced the smallest amount of MEG degradation acids. The high temperature oxidative stability of the base fluid in this type of coolant could be explained by a combination of characteristics linked to this coolant technology. Earlier work has shown that this synergistic aliphatic monoacid/diacid corrosion inhibitor combination found in coolant A provides superior corrosion protection performance in laboratory and field tests, compared with more traditional engine coolant formulations 关13兴. This may be explained by a difference in corrosion protection mechanism for these coolant additives. Study of the metal surface protective film 关13–15兴 has shown that the aliphatic carboxylate inhibitors form a selective 共at anodic sites兲 thin protective layer, where inhibitors interact with the metal surface through a strong chemical bond. Thicker layers of additives, characteristic for the uniform corrosion protection mechanism of traditional inhibitors 共such as silicates兲, can result in higher metal surface temperatures and higher corrosion rates. As the presence of corrosive metallic ions in

CLAEYS AND LIEVENS ON COOLANTS AT ELEVATED TEMPERATURES 135

in the organic acid-based coolants A and B, it can be observed that the pH changes differently. For coolant A, the pH change is very small, while for coolant B, a larger decrease in pH is observed at the beginning of the test, then over time, the pH becomes more constant. The limited change of the reserve alkalinity can be an extra indication for the high stability of this coolant technology. For the silicated coolant C, and the phosphated coolant G, pH variations are small even though larger amounts of degradation acids are formed compared to the OAT coolants. This can be explained by the working mechanism of a buffer 共such as borate and phosphate兲. The larger change in reserve alkalinity for both coolants is an indication of an important change in coolant composition. Influence of High Temperatures on Corrosion Protection Properties of Selected Coolants As the coolant is in contact with many metals in the engine, one of its important functions is to protect the engine materials against corrosion. This is mainly determined by the stability of the additive package and the physical and chemical properties of the coolant. In this work, the effect of high temperatures on the corrosion protection performance of coolants was studied by a potentiokinetic polarization scan, which was run on the coolants before and after high temperature oxidation test. Two metals, aluminum 共Table 3兲 and carbon steel 共Table 4兲 were evaluated for this purpose. For the organic acid-based coolant technology A, high stability passivation potentials 共above 3300 mV兲 were determined on aluminum. This is an indication for low probability of pit formation 关16兴. The exact value of this potential cannot be reported as the passivation layer remains stable under the applied conditions. For the same reason repassivation potentials cannot be determined 共Fig. 6共a兲兲. On carbon steel it is preferable to describe the pitting potential as the potential at which the protective passivation layer is destabilized. No pitting corrosion is observed as no repassivation potential can be measured 共Fig. 6共b兲兲. Although the corrosion protection behavior 共on aluminum and carbon steel兲 for the

FIG. 6—Potentiokinetic polarization scan of coolant A before high temperature oxidation test; (a) on aluminum, (b) on carbon steel. organic-based coolants A and B is different, both remain unaffected under high temperature oxidation conditions. For the silicate-based coolants 共C, D, E, and F兲 significant decreases in stability passivation potential

FIG. 7—Potentiokinetic polarization scan of coolant D on aluminum; (a) before oxidation test, (b) after oxidation test.


on aluminum and/or carbon steel were observed 共e.g., Fig. 7兲 after the oxidation test. This can be explained by changes in the stability of the additive package or by the formation of high amounts of glycol degradation acids, or both. Although high stability passivation potentials were measured for the phosphate-based coolants 共G and H兲 on both metals, strong decreases in pitting protection and repassivation ability on aluminum were found

FIG. 8—Potentiokinetic polarization scan of coolant G on aluminum; (a) before oxidation test, (b) after oxidation test. after aging of the coolant under extreme conditions 共Fig. 8兲. Together with the large variations in reserve alkalinity found for this technology 共Fig. 5兲, the loss of corrosion protection performance could be attributed to additive instability. Next to rupture potential and repassivation potential, the current density at which passivation occurs

TABLE 3—Potentiokinetic polarization scan characteristics of coolants before and after high temperature oxidation test on aluminum. Stability Passivation Potential 共mV兲 Coolant A B C D E F G H

BeforeTest ⬎3300 1070 1710 1680 2240 1185 3040 3230

AfterTest ⬎3300 1070 1640 950 2180 734 720 1880

Repassivation Potential 共mV兲 BeforeTest … −283 −551 −430 1430 −117 1790 168

AfterTest … −224 −492 −430 1420 −329 −350 −52

Passivation Current 共␮A / cm2兲 BeforeTest 11 12 11 11 11 12 9 10

AfterTest 11 12 13 11 11 12 9 10

TABLE 4—Potentiokinetic polarization scan characteristics of coolants before and after high temperature oxidation test on carbon steel. Stability Passivation Potential 共mV兲 Coolant A B C D E F G H

BeforeTest 720 630 1030 728 270 698 1540 1495

AfterTest 720 630 1030 536 156 180 1565 1350

Repassivation Potential 共mV兲 BeforeTest … … … −310 −159 284 … …

AfterTest … … 574 −310 −178 −273 … …

Passivation Current 共␮A / cm2兲 BeforeTest 8 9 9 13 2 8 16 21

AfterTest 8 9 9 14 10 13 19 21


Taking into account that the same base fluid is used for all coolant compositions, it can be shown that the additive package has an effect on the amount of degradation acids formed. Although the exact causes for the results are not always fully understood, it can be concluded that the use of aliphatic acid corrosion inhibitors provides greater protection against thermal breakdown of the base fluid. Coolants containing only aliphatic acid corrosion inhibitors appeared to have the highest resistance to thermal breakdown. When the same class of additives are used 共e.g., organic acid-based coolants or hybrid type coolants兲 differences could be observed for various coolant parameters, emphasizing the fact that coolant performance, as it relates to oxidative stability or corrosion protection, or both, cannot be predicted by coolant class alone. The study has also shown the importance of looking at several different coolant characteristics, such as physical/chemical properties, the formation of glycol breakdown products, as well as corrosion protection properties in order to get a better understanding of the high temperature stability performance of a coolant.

References 关1兴关2兴

关3兴关4兴关5兴关6兴关7兴关8兴关9兴关10兴关11兴关12兴关13兴关14兴关15兴关16兴

EPA, “Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engines and Vehicle Standards and Highway Fuel Sulfur Control Requirements,” Federal Register, Vol. 66, No. 12, January 18, 2001, Rules and Regulations. Mc Geehan, J. A., Wells, J., Kennedy, S., Huang, A., Shank, G., Stehouwer, D., Larkin, D., Mesfin, B., Tharp, D., Bondarowicz, F., Chao, K., Deere, J., Stockwell, R. T., Passut, C., Kleiser, W., Williams, L., Fetterman, P., Zalar, J., Rutherford, J., Scinto, P., and Malandro, D., SAE Report 2002011673, Society of Automotive Engineers, Warrendale, PA, 2002. Maes, J.-P. and Armstrong, R. “Antifreeze and Coolant,” Lubrication, Vol. 78, No. 2, 1992. http://www.penray. com/bulletins/glycol.htm, January 13, 2006. Brown, P. W., Galuk, K. G., and Rossiter, W. J., Sol. Energy Mater. Sol. Cells, Vol. 16, 1987, p. 309. Mercer, A. D., “Corrosion Inhibition of Engine Coolants,” Corrosion, Protection and Finishing Techniques, The Institution of Mechanical Engineers, Automotive Division, International Seminar, 1985. Wiggle, R. R., Hospadaruk, V., and Tibaudo, F. M., “Corrosion of Cast Aluminum Alloys Under Heat-Transfer Conditions,” SAE Report 810038, Society of Automotive Engineers, Warrendale, PA, 1981. Butler, G. and Mercer, A. D., “Inhibitor Formulations for Engine Coolants,” Br. Corros. J., London, Vol. 12, No. 3, 1977, pp. 171–174. Hersch, P., Hare, J. B., and Sutherland, S. M., “An Experimental Survey of Rust Preservatives in Water: II. The Screening of Organic Inhibitors,” J. Appl. Chem., Vol. 11, 1961, pp. 261–271. Darden, J. W., Triebel, C. A., Maes, J.-P., and VanNeste, W., SAE Report 900804, Society of Automotive Engineers, Warrendale, PA, 1990. Eaton, E. R., Boon, W. H., and Smith, C. J., SAE Report 2001011182, Society of Automotive Engineers, Warrendale, PA, 2001. Weir, T. W. and Van de Ven, P., “Review of Organic Acids as Inhibitors in Engine Coolants,” SAE Report 960641, Society of Automotive Engineers, Warrendale, PA, 1996. Maes, J.-P. and Van de Ven, P., “Corrosion Protection of Aluminum Heat Transfer Surfaces in Engine Coolants Using Monoacid/Diacid Inhibitor Technology,” Engine Coolant Testing, Vol. 3, ASTM STP 1192, ASTM International, West Conshohocken, PA, 1993, pp. 11–24. Verpoort, F., Haemers, T., Roose, P., and Maes, J.-P., “Characterization of a Surface Coating Formed from Carboxylic Acid-Based Coolants,” Appl. Spectrosc., Vol. 53, No. 12, 1999, pp. 1528– 1534. Mowlem, J. K., and Van de Ven, P., “Comparison of Surface Coatings Formed from Carboxylic Acid-Based and Conventional Coolants in a Field-Test Study,” SAE Report 960640, Society of Automotive Engineers, Warrendale, PA, 1996. Bond, A. P., “Pitting Corrosion—A Review of Recent Advances in Testing Methods and Interpretation,” Localized Corrosion-Cause of Metal Failure, ASTM STP 516, M. Henthorne, Ed., ASTM International, West Conshohocken, PA, 1971, pp. 250–261.


Yu-Sen Chen,1 R. Doug Hudgens,2 and Edward R. Eaton3

Comparison of Bench Test Methods to Evaluate Heavy Duty Coolant Thermal Stability ABSTRACT: The past 10 to 15 years have seen a dramatic change in heavy duty coolants and cooling system maintenance practices. Controversy exists about the relative merits of newer organic acid 共OAT兲 coolants and more conventional products, especially in the area of thermal stability. Coolant life has been extended from two years/240 K miles to at least five years/600 K miles. It is not uncommon for the same charge of coolant to remain in the cooling system until engine rebuild. Further, there has been an equally significant increase in the coolant service intervals. Reinhibition of the coolant was once tied to the oil change interval at 15 to 25 K miles. Now this additive addition has been extended in many cases to one year/150 K miles to two years/300 K miles. • Along with these dramatic increases in coolant life and service interval, strategies to reduce exhaust emissions such as EGR have increased and will continue to increase coolant temperatures. Sorting out coolant stability issues in the field is both expensive and time consuming. Further, it is very difficult to control a field test so as to obtain reliable data. In this environment, a bench test method that can quickly simulate high temperature, severe field service conditions is of vital importance. This paper compares four bench test methods as far as their ability to sort out thermal stability issues based on results from five coolants representing different additive packages and glycol qualities. KEYWORDS: heavy duty engine coolants, oxidation stability, corrosion, extended service coolants, conventional fully-formulated coolants, supplemental coolant additives, antifreeze, glycol, glycol esters, off-spec glycol, antifreeze grade glycol

Introduction For several decades the producers of ethylene and propylene glycols were also the major blenders and suppliers of automotive antifreeze in North America and other parts of the world. These included companies such as Dow Chemical, Union Carbide, Texaco, and Shell Chemical. In the past 20 years corporate changes that have occurred in the glycol industry have changed the way in which antifreeze/engine coolant products come to market. Many major brands that were previously owned by the glycol producers have been sold to companies that do not produce glycol, resulting in glycol availability and price fluctuations that have opened the door to many alternate avenues of antifreeze/engine coolant base fluid supplies. In some cases, these alternative lines of supply have proved most satisfactory. For example, technologies have been developed to successfully gather and recycle used engine coolants, often resulting in coolants that performed essentially the same as new products 关1兴. More recently, high demand for antifreeze/coolant products has enabled the entry of unsatisfactory base fluids. They have caused many premature failures in new power systems including radiator, water pump, and general corrosion issues. These experiences have resulted in unnecessary warranty costs to OEMs and very irate end-users. Unfortunately, some of these problematic coolants might even pass ASTM coolant performance requirements on two of the commonly employed corrosion screening tests, ASTM D 4340 “Standard Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions” and ASTM D 1384 “Standard Test Method for Corrosion Test for Engine Coolants in Glassware.” While these tests are certainly not adequate to prove the overall capability of the coolants, they give false comfort to users and some marketers who do not look deep enough into the properties of the coolants. Responding to concerns in the marketplace that seriously problematic coolants are being marketed to Manuscript received May 8, 2006; accepted for publication March 17, 2007; published online May 2007. Presented at ASTM Symposium on Engine Coolant Technologies: 5th Volume on 17 May 2006 in Toronto, Canada; W. Matulewicz, Guest Editor. 1 Research Director, Fluid Management Division, Dober Chemical, 333 West 195th St., Glenwood, IL 60425. 2 Chief Chemist, Fleetguard, Inc., 1200 Fleetguard Road, Cookeville, TN 38506. 3 Chief Engineer, Amalgatech, 2965 West Osborn Road, Phoenix, AZ 85017. Copyright © 2007 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

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consumers and bulk users alike, ASTM Committee D-15 minutes record initial tests performed on a number of coolants employing a modified turbine oil test, ASTM D 2272, which evaluates the oxidation resistance of turbine oils 关2兴. The minutes record that the oxidation stability of coolants was demonstrated to be significant as a property that might affect customer satisfaction and protection of the system. Many of the suspect/problematic coolants may be blended with glycols that are described as “virgin” because they have not previously been used as automotive antifreeze/coolant. However, these fluids have either been used for aircraft deicing, some other manufacturing process, or may be recovered from glycol “still bottoms” that have been observed to have undesirable oxidation properties compared to antifreeze grade 共ASTM E 1177兲 virgin ethylene glycol provided by major EG suppliers. Therefore, if a method could be developed that correctly ranks coolants as to their observed field performance it may provide a good indication of prospective coolant service interval or total life, or both. Further, ASTM Subcommittee D15.21 on Long-Life Coolants has been struggling to agree on a definition, test method共s兲, and performance specification that differentiates between serviceable conventional service interval technologies from those capable of significantly longer service intervals. We also hope to better understand the mechanisms of coolant degradation, specifically how the glycol and additive package contribute to overall corrosion protection as the coolant ages, and to develop methods that best model those mechanisms. To that end, as we proceed with the investigation, we will compare the behaviors of the coolants against published 关3兴 information that describes the depletion behavior of fully-formulated conventionally inhibited coolants as well as the authors’ current experience with other technologies. For convenience, principal graphs from the Hudgens-Mitchell paper in ASTM STP 1335 are attached for reference in the Appendix following the main body of this paper. These are useful tools for readers who may not be familiar with the depletion behaviors of the conventional technology components in engine applications. It will be useful to define some terms that will be used in this paper, see Table 1. What we looked for in selecting coolant samples for testing: 1. A cross section of OEM-branded and aftermarket-branded antifreeze coolants, including coolants defined by the authors as true “virgin” coolants, concentrated and prediluted recycled coolants, and at least one example of a coolant marketed by the supplier as a virgin coolant that has characteristics different than true virgin coolants and that has caused severe and widespread damage to engines in actual use. 2. Conventionally-inhibited, “Long Life” also known as “Extended Life” style technologies that incorporate inorganic, carboxylate, and various forms of hybrid philosophies are represented. More than 15 coolants were tested. The authors have selected five coolants for discussion in this paper that best illustrate the strengths and weaknesses of each of the prototype test methods. They are coded and described as follows: FFC—A virgin conventionally-inhibited, fully-formulated OEM-recommended EG coolant with a decades-long track record of satisfactory performance when properly serviced at recommended intervals 共i.e., oil change intervals兲 with SCAs. NOAT—A virgin nitrite-molybdate-carboxylate 共NMOAT兲 inhibited, fully-formulated OEMrecommended EG coolant with a track record of satisfactory performance when properly serviced at recommended intervals 共i.e., 300,000 miles兲 with OAT extender. NVC—A questionably-identified “virgin” conventionally inhibited, claimed to be fully-formulated coolant, apparently blended from off-spec EG with a track record of very unsatisfactory performance and widespread rapid damage to customers’ equipment. This coolant is reported by the supplier to be made with EG recovered from “glycol bottoms.” H-1—A virgin American hybrid, fully-formulated OEM-recommended EG coolant with a good track record of satisfactory performance when properly serviced at recommended intervals. H-2—A virgin European-style hybrid inhibited, fully-formulated OEM-recommended EG coolant with a decades-long track record of satisfactory performance when properly serviced at recommended intervals.

CHEN ET AL. ON COMPARISON OF BENCH TEST METHODS 141 TABLE 1—Terms used. Term Conventional Inhibition

Organic Acid Inhibition

Hybrid Inhibition

Virgin Glycol

“Questionable” Virgin Glycol

Fully-formulated Antifreeze/Coolant

Recycled Glycol or Engine Coolant

Long Life or Extended Life Coolant

Extended Service Interval

Explanation Corrosion inhibition with traditional packages. Such chemicals may include nitrite, nitrate, silicate, borate, phosphate, molybdate, and azoles. Packages that rely primarily on aliphatic carboxylic acids and azoles. Heavy-duty versions may also contain nitrite or molybdate, or both, but they still fall in the OAT family. These are packages that frequently employ benzoate, an aromatic carboxylate, as their primary organic acid and also heavily depend on various inorganic supplements such as silicate, nitrate, phosphate, and molybdate. Heavy-duty versions may contain nitrite. Three substantial subcategories exist: American hybrids may not use benzoate, but a different carboxylate and otherwise look similar to conventional fully-formulated approaches. European styles rarely use phosphate; Asian styles rarely use silicate and may use multiple carboxylates in combination. Glycol produced by an ethylene glycol manufacturer that meets ASTM E 1177 and that has never been used for any purpose whatsoever and not reprocessed from “still bottoms.” A product marketed as nonrecycled but that did not come directly from a traditional glycol supplier. These fluids may be used in some other process, then sold as a byproduct or waste stream fluid, or may be recovered from “glycol bottoms.” ASTM coolant specifications do not include coolants formulated from these sources of glycols, and their use as automotive antifreeze/coolant has been observed to be highly unsatisfactory in some cases. A product that conforms to ASTM D 6210 or TMC RP329 or RP330 heavy-duty coolant specifications, or a combination thereof. These products do not require, and should not receive, a precharge of SCA before initial use. There exists conventional, OAT, and hybrid examples of fullyformulated coolants. Glycol or engine coolant that has usually been recovered from used engine coolant by a capable technology such as distillation, ion exchange, membrane separation, or a combination of these technologies. The base fluid is usually reinhibited with the same type of additive technologies as are used for true virgin antifreeze/coolant. A coolant technology that does require frequent maintenance with supplemental coolant additives, and may generally stay in service well in excess of 300 000 miles. Most now publish change intervals of 600 000 miles. A coolant chemical service interval that is at least twelve months or 150 000 miles and is not tied to the oil drain interval. 共Conventional coolants are generally treated with supplemental coolant additives every 12 000– 20 000 miles in the form of “charged” filters or liquid additives.兲

The Test Methods and Experimental Conditions Reaction Kettle This is a modification of the accelerated aging procedure originally developed by Gershun and Mercer of Honeywell for light-duty conventional and extended life coolant that was designed to predict coolant composition and performance after 100 K or more miles of use 关4兴.


FIG. 1—Reaction kettle used by Dr. Chen. 1. The 2000-mL reaction kettle 共Fig. 1兲 was equipped with a condenser, a gas dispersion tube, and a thermometer. A total of 1800 mL of EG 85/15 premix solution was added into the kettle and mixed with a magnetic stir bar. Aluminum, iron, and copper turnings 共obtained from Metaspec in San Antonio, TX兲, 3.333 g each, was placed in a 316 stainless steel basket. Subsequently, the basket was suspended into the reaction kettle in the test solution using a thin nichrome wire. 2. To start the test, the hot plate was turned on and the test solution was heated at 115° C 共240° F兲. The solution was purged with air at 100 mL/ min. The test lasted for 14 days. Additional water was added to make up the water loss. Samples were collected at 2, 5, 7, 9, 12, and 14 days and measured for pH, RA, EG, inhibitors concentrations, metals, and glycol degradation acids 共formic and glycolic兲. Modified ASTM D 4340 This test method modification was developed by Valvoline and has been used previously to evaluate the stability of silicate in coolant. It has also been used to successfully demonstrate the oxidation stability differences between uninhibited coolant base chemistries 关5兴. 1. This test method uses all of the equipment/apparatus specified in ASTM D 4340. 2. This test method covers a laboratory screening procedure for evaluating the effectiveness of engine coolants in combating corrosion of aluminum casting alloys and coolant degradation under heat-transfer conditions that may be present in aluminum cylinder head engines. 3. In this test method, a heat flux is established through a cast aluminum alloy somewhat higher than typical of that used for engine cylinder heads while exposed to an engine coolant under a pressure of 193 kPa 共28 psi兲. The temperature of the aluminum specimen is maintained at 150° C 共300° F兲 and the test is continued for one week 共168 h兲. The coolant concentration is 50 % and there are 100 ppm each of chloride and sulfate added to the test fluids. The effectiveness of the coolant for preventing corrosion of the aluminum under heat-transfer conditions 共hereafter referred to as heat-transfer corrosion兲 is evaluated on the basis of the weight change of the test specimen and change in coolant chemistry including both glycol and inhibitor package degradation. 4. Post Modified ASTM D 4340 testing: The coupons are cleaned and corrosion rate determined according to D 4340 共see Fig. 2兲. The used coolant sample is tested for physical properties, corrosion inhibitor levels, and coolant degradation/metal corrosion levels. Results are suspect if significant change in water content occurred. PARR Reactor Test Fleetguard and Dober developed this method to model primarily the nitrite stability of heavy-duty coolants in 300 to 400 K miles of actual field service 共see Fig. 3 and Fig. 4兲. 1. A total of 1200 mL EG 50/50 premix solution was added into the Parr reactor cylinder. A 10-ft copper wire was wrapped around the cooling coils so that the copper wire would be in contact with the test solution. The reactor head was placed on top of the reactor cylinder and the reactor split ring collar was tightened. The type J thermocouple was placed into the reactor head’s thermowell.

CHEN ET AL. ON COMPARISON OF BENCH TEST METHODS 143

FIG. 2—ASTM D 4340 test rigs at Amalgatech.

FIG. 3—The PARR reaction vessel used by Dr. Chen.

2. To start the test, the display, motor, and heater were turned on. The motor speed was set to 40 % maximum for good mixing and the temperature set to 129° C 共265° F兲. Air pressure is about 25 psi, generated from the heating of the coolant. The test lasted for 14 days. Samples were collected at 2, 5, 7, 9, 12, and 14 days. They were measured for pH, RA, EG, copper and glycol degradation acids 共formic and glycolic兲. After each sample collection, heat was stopped and the test solution was cooled with cold water to 25° C. Subsequently, the reactor was refilled with air by pumping air through the reactor for 20 min before the heat was turned back on to continue the test.

FIG. 4—Internal view of the PARR reaction vessel.


Rotating Pressure Vessel Oxidation Test (RPVOT) This test method is a modification presented by Alverson of Shell Oil Products, USA. It is being investigated as a possible tool by the authors and is continuing to be developed at Shell simultaneously. 1. The modified RPVOT uses all of the equipment/apparatus specified in ASTM D 2272 with exception of the copper catalyst coil which is replaced with a modified ASTM D 1384 glassware corrosion metal bundle. 2. Modified ASTM D 1384 glassware metal coupon bundle: In place of the copper catalyst coil, a modified ASTM D 1384 metal coupon bundle is used as the catalyst and to assess corrosion protection performance of the coolant. The modified ASTM D 1384 metal coupon holder consists of two Teflon legs 共in place of brass legs兲 with the ASTM D 1384 six metals coupon bundle 共copper, solder, brass, steel, cast iron, and cast aluminum兲. The metal coupon bundle is assembled in the order as specified in ASTM D 1384 using 2 small Teflon spacers between each metal, rather than the brass and steel spacers. Thus, the metals in the coupon bundle are not galvanically coupled with each other. Due to the small ASTM D 2272 glassware size opening. Teflon spacers are not used between the Teflon legs and end metals 共copper and cast aluminum兲. The metal bundle after assembly with the brass screw/bolt and insulating tube will be shorter than the standard ASTM D 1384 bundle and will require snipping the bolt and insulating tube to allow insertion of the metal bundle in the ASTM D 2272 glassware. The objective is to provide Teflon on the all sides and bottom of the metal coupon bundle to minimize etching of the glass. Used coolant test results after RPVOT testing indicates that the holder/metal coupon still removes some silicon from the ANTM D 2272 glassware 共see Fig. 5兲. 3. Test conditions: EG 50/50 coolant dilution is prepared with deionized water rather than corrosive water, 55 mL coolant sample, 90 psi O2 initial charge at room temperature 共77° F兲, 250° F, 168 h, and 100 r / min. The sample size 共55 mL兲 was selected to maximize the amount of coolant in contact with the metal coupon bundle while attempting to minimize leakage from the glassware into the steel pressure vessel while rotating at 100 r / min at a 30° angle. 4. Post RPVOT testing: The coupons were cleaned and weight changes determined according to ASTM D 1384. The used coolant sample was tested for physical properties, corrosion inhibitor levels, and coolant degradation/metal corrosion levels. Results are suspect if significant change in water content occurred.

FIG. 5—RPVOT test rig.


Results Summary of Reaction Kettle Test Data TABLE 2—Reaction Kettle Table of Data FFC Component Total Acids NaNO2 NaNO3 Na2HPO4 Na2MoO4 Na2B4O7 Na2SiO3 NaTT BZT NaMBT Sebacic Acid 2-EH Acid Benzoic Acid Cu PH RA

NVC

First 9 3,471 1,009 0 0 1,764 860 599

Last 1,596 2,055 1,214 0 0 1,555 99 427

564

0

0 10.8 5.6

16 8.2 3.1

First 471 3,780 27 0 0 409 0 698

0 10.0 5.7

H1 Last 3,153 0 1,335 0 0 367 52 363

225 6.7 0.6

H2

First 13 3,045 1,030 7,552 1,450 1,793 1,015 1,278

Last 1,440 2,817 1,101 3,965 1,329 1,653 522 1,132

825

823

0 10.6 12.4

22 8.7 9.3

FIG. 6—Kettle behavior graphs.

First 73 1,498 5,513 0 0 9,822 1,114 0 947

19,960 0 7.0 12.6

NOAT Last 1,035 65 5,481 0 0 8,626 591 0 881

17,650 1 7.4 11.8

First 47 1,564 20 0 2,219 0 0 2,158

Last 2,314 100 175 0 1,825 0 0 1,640

2,009 28,900

2,904 25,530

0 9.1 4.4

7 8.0 1.1


Summary of Modified ASTM D 4340 Test Data

TABLE 3—D4340 (Modified) Table of Data Coolant ID Color pH Glycolate Formate Nitrite Nitrate Phosphate Mo Boron Silicon BZT MBT TTZ Benzoate 2-eh Sebacic Al D4340 R Value

FFC Before Pink 10.67 0 0 1467 445 0 0 189 116 0 290 277 0 0 0 0

FFC After Pink 8.12 165 160 1385 475 0 0 193 129 0 0 266 0 0 0 0 R = 0.07

NVC Before Green 9.89 150 140 1527 13 0 0 56 0 0 0 297 0 0 0 0

NVC After Green 9.18 470 355 1215 110 0 0 55 0 0 0 241 0 0 0 0 R = 0.20

H1 Before Blue 10.90 0 0 1317 485 3085 392 188 139 0 0 574 0 0 468 0.0

H1 After Blue 10.02 220 110 1215 635 2845 358 175 167 0 0 593 0 0 469 0.0 0.03

H2 Before Yellow 7.77 0 0 960 1787 0 0 1100 135 0 0 0 12740 0 0 0

FIG. 7—Modified ASTM D 4340 behaviors.

H2 After Yellow 7.42 208 136 913 1699 0 0 1086 113 0 0 0 12700 0 0 0 R = −0.13

NOAT Before Red 9.01 0 0 577 0 0 637 0 0 0 0 952 0 15810 1353 0

NOAT After Red 8.25 210 0 470 85 0 688 0 0 0 0 973 0 19120 1349 0 R = −0.02


FIG. 8—ASTM D 4340 aluminum corrosion rate (R value).

Summary of Parr Reactor Test Data TABLE 4—PARR Reactor Data Table FFC Component Total Acids NaNO2 NaNO3 Na2HPO4 Na2MoO4 Na2B4O7 Na2SiO3 NaTT NaMBT 2-EH Acid Cu Fe PH Delta pH RA Delta RA

NVC

H1

H2

NOAT

First 1 2,038 579 0 0 1,043 543 356 337

Last 2,419 1,073 1,294 0 0 1,087 460 267 0

First 185 2,246 8 0 0 223 0

Last 2,901 0 246 0 0 239 86

First 45 1,824 580 4,519 798 918 482

Last 1913 1,635 751 3,147 793 896 332

First 51 1,698 2,215 0 0 6,105 668

Last 1,116 1,298 2,414 0 0 6,184 635

0 0 10.0

118 0 6.9 3.1 0.5 2.8

0 1 10.2

96 1 8.1 2.1 1.0 2.7

0 0 10.4

22 13 7.8 2.6 4.3 2.1

0 0 8.0

95 2 7.6 0.4 6.0 1.3

3.3

3.7

6.4

7.3

First 94 3,706 68 0 0 0 0

Last 1,107 3,055 364 0 0 0 0

18,300 0 0 8.5

18,770 0 0 7.4 1.1 1.7 0.6

2.3


FIG. 9—PARR reactor behaviors.


TABLE 5—RPVOT Data Table ID Code Additive Family

Color pH Glycolate Formate Total Acids Nitrite Nitrate Phosphate Mo B Si MBT TTZ Benzoate 2-eh Sebacic Cu Pb Fe Al

FFC FFC FF Conventional Before Pink 10.47 0 0 0 1403 440 0 0 184 113 265 275 0 0 0 0 0 0 0

After Brown 4.88 3835 2750 6585 0 310 0 0 208 69 0 25 0 0 0 411 50 1093 40

NVC-1 NVC-1 FF Conventional Before Green 9.89 150 140 290 1527 12 0 0 55.5 0 0 298 0 0 0 0 0 0 0

After Black 4.94 6750 5400 12150 0 0 0 0 108 60 0 0 0 0 0 437 0.0 4915 54.0

H-1 H-1 NM HOAT Before Clear 10.90 0 0 0 1317 485 3085 392 187 139 0 573 0 0 420 0 0 0 0

After Yellow 6.94 3410 440 3850 915 1080 2380 389 238 161 0 645 0 0 380 0 5 2 0

H-2 H-2 FF HOAT Before Yellow 7.77 0 0 0 960 1787 0 0 1100 135 0 0 12740 0 0 0 0 0 0

After Yellow 7.00 1692 502 2194 526 2323 0 0 1140 108 0 0 13160 0 0 5 16 0 0

NOAT NOAT NMOAT Before Red 8.32 0 0 0 573 4 0 697 0 0 0 1144 0 18420 1712 0 0 0 0

After Orange 6.71 735 0 735 290 325 0 648 0 40 0 923 0 18490 1445 1 0 0 0


Summary of RPVOT Data Discussion and Comparison of the Test Methods How the data from each of the tests compare to user experiences and generally understood degradation mechanisms.

FIG. 10—RPVOT weight and corrosion losses of metal specimens. 1. Reaction Kettle: While the test did deplete nitrite, especially in the most problematic coolant, the mechanism was not that observed in the field. The NOAT and H-2 lost all of their nitrite with no nitrate increase or only very slight nitrate increase. The results were somewhat counter to field experience. Additive packages made significant differences. The other conventional coolants FFC and H-1 lost nitrite with nitrate increase in an expected way. The NVC coolant lost all nitrite after about ten days into the test 共see Table 2兲. Glycol does not degrade faster in NOAT coolants than other virgin coolants. Actual observa-


FIG. 11—RPVOT behaviors. tions suggest that the reverse is true. The copper attack by the NVC coolant was dramatic, which is consistent. The kettle test showed slow loss of 2-EH acid, benzoic acid, borate and molybdate, consistent with field observations, but depleted phosphate far faster than is observed in actual operating coolants 共see Fig. 6兲. Overall, this test was not a good model of the coolant aging process as we observe it in real vehicles. 2. Modified ASTM D 4340: The types of reactions that are occurring are consistent with the aging behaviors observed in the field. Nitrite is usually oxidizing to nitrate; phosphates and molybdate are stable. Slow-depleting carboxylates and azoles also behave normally. Unfortunately, the amount of aging developed in one week is insufficient to serve the purpose of the test and to adequately sort the coolants. The NVC coolant lost only 20 % nitrite and all after-test coolant samples passed the ASTM D 4340 test 共see Table 3兲. This test would need to give more glycol degradation, some silicate depletion and more nitrite oxidation. Extending the term of the test may provide the desired results. Data from the PARR test reflects that the degradation behavior is not linear, there is an induction period after which it begins, and the rate of degradation thereafter increases exponentially 共see Fig. 7 and Fig. 8兲. 3. PARR Reactor Test: The more advanced inhibition packages withstood the test better than the OEM approved conventional coolants and all performed better than the known negative controls. The nitrite → nitrate change was observed, and other aging properties are consistent with realworld experiences. The exposure did not affect the carboxylates, borates, or molybdate concentrations. Glycol was degraded, and formates and glycolates formed but the negative control 共NVC兲 was somewhat differentiated 共see Table 4兲. PARR tests were able to differentiate the quality of coolants and glycols. Results are consistent with field experiences and directionally encouraging, with the potential for improvement. It is the best of the four tests studied in this project 共see Fig. 9兲. 4. Rotating Pressure Vessel Oxidation Test 共RPVOT兲: This test proved to be a “torture chamber” test.


It was so severe that there were reactions being driven that do not occur in typical cooling systems. In particular, in FFC and NVC coolants, the nitrite → nitrate reaction is nitrite → NOx 共we speculate兲 and there is even a nitrate → NOx reaction. Similarly, other reactions are totally depleting phosphate and molybdate; behaviors not observed in the real world 共see Table 5兲. Nevertheless, coolants H-1, H-2, and NMOAT performed well with good corrosion coupon weight loss data, while NVC and FFC performed poorly with much worse coupon weight loss results. This test method does have promise in that with modifications to reduce its severity, it might very well prove to be the most capable in both ranking the various coolant technologies’ oxidation stabilities and might also provide a useful test to predict if a coolant may be considered for extended service interval applications 共see Figs. 10–12兲. Future Directions Modifications to the Test Methods A. Reaction Kettle 1. The data from these tests were the least consistent and encouraging of the four alternatives. It may not be worthwhile to continue work in the development of this method. B. Modified ASTM D 4340 1. Extending the term of the test to at least two weeks. 2. Increase the antifreeze concentration to 70 or 85 %. C. PARR Reactor Test 1. Pressurize the reactor with air. 2. Add an ASTM D 1384 coupon bundle and study corrosion characteristics through weight losses. D. Rotating Pressure Vessel Oxidation Test 共RPVOT兲 1. Run the test under air instead of O2. 2. Reduce the test temperature to 230° F or lower.

Conclusions The modified ASTM D 4340 at one week duration was clearly not long enough to adequately degrade and satisfactorily rank the coolants. Continuing research will investigate if an acceptable longer duration can succeed at ranking the coolants. With this new condition, the modified ASTM D 4340 may turn out to be a very useful test. The PARR reactor generally modeled the field observations quite satisfactorily. The two-week term is convenient, monitoring the chemical changes well. It is degrading and ranking the coolants to an encouraging degree. It is the best of the four tests studied. Future research will include the use of an ASTM D 1384 style coupon bundle in the reactor to see if RPVOT-type data can be generated. The current RPVOT test conditions appear too severe. Future research with re-engineered test conditions hopefully will create aging that more closely models field observations. The reaction kettle test was the least encouraging of the four methods evaluated 共see Table 6兲.

CHEN ET AL. ON COMPARISON OF BENCH TEST METHODS 153 TABLE 6—Summary.

Test Kettle

Modified ASTM D 4340

PARR

RPVOT

Pros Obtained modest depletion of additive such as molybdate, borate, silicate, and organic acids. Monitored chemical changes with time. Simple apparatus and procedure. Depletion reactions consistent with real-world experience. Good correlation to field results. Nitrite converted to nitrate in a manner very similar to the field. Monitored chemical changes with time. Short duration test that also gives information on corrosion protection as well as add package changes. May be able to predict required coolant service interval.

Cons Excessive, unrealistic nitrite depletion in coolants H-2 and NOAT plus excessive phosphate depletion in coolant H-1. The test at one week is too mild with a low depletion rate of most additives. NVC stood up well to the test. Depletion rate or concentration reduction of molybdate, borate, silicate, and organic acids are too low. Too severe as the test crushes FFC that has a history of good field performance. Also reactions such as nitrate destruction are not seen in the field.

Appendix Depletion Behaviors of Conventionally Inhibited Coolants [6] 共see Fig. 12 and 13兲

FIG. 12—Additive depletion in field test.

Changes for Further Research The authors have no current plans for further development of this method.

Extend time to two to four weeks and increase coolant concentration to 70– 85% by volume. Pressurize the reaction vessel with air 共50 psi兲 and include ASTM D 1384 coupon bundles. Reduce test temperature or pressurize with air, or both, instead of pure oxygen.


FIG. 13—Nitrite depletion in various field tests. References 关1兴关2兴关3兴关4兴关5兴关6兴

Haddock, M. E. and Eaton, E. R., “Recycling Used Engine Coolant Using High-Volume Multiple Technology Equipment,” Engine Coolant Testing, 4th Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1997. Eaton, Edward R., “Engine Reliability of Mixed Vehicle Fleets Operating on Engine Coolant Recycled with Reverse Osmosis Technology,” SAE Technical Paper 962239, Society of Automotive Engineers, Warrendale, PA 1996. October 2004 ASTM Committee D-15 minutes. Mitchell, W. A. and Hudgens, R. D., “Development of an Extended-Service Coolant Filter,” Engine Coolant Testing, 4th Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1997, pp. 412–414. Gershun, A. V. and Mercer, W. C., “Predictive Tool for Coolant Development: An Accelerated Aging Procedure for Modeling Fleet Test Results,” Engine Coolant Testing, 4th Volume, ASTM STP 1335, R. E. Beal, Ed., ASTM International, West Conshohocken, PA, 1997. Eaton, E., Boon, W., and Smith, C., “A Chemical Base for Engine Coolant/Antifreeze with Improved Thermal Stability Properties,” SAE Technical Paper Series 2001-01-1182, Society of Automotive Engineers, Warrendale, PA, 1996. Hudgens, R. D., “Comparison of Conventional and Organic Acid Technology 共OAT兲 Coolants in Heavy Duty Diesel Engine Service,” SAE paper 1999-01-0130, p. 3 and Figs. 1 and 2.

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