NACE Standard RP0391-91 Item No. 21050
Standard Recommended Practice Materials for the Handling and Storage of Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers. Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International Membership Services Department, P.O. Box 218340, Houston, Texas 77218-8340 (telephone +1 (281)228/6200). Approved August 1991 NACE International P.O. Box 218340 Houston, Texas 77218-8340 281/228-6200 ©1991, NACE International
RP0391-91
___________________________________________ Standard Recommended Practice Materials for the Handling and Storage of Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures
Contents Foreword ........................................................................................................................ 1 1. General ...................................................................................................................... 1 2. Specific Materials ....................................................................................................... 2 3. Specific Equipment .................................................................................................... 4 4. Safety Considerations................................................................................................. 6 Appendix A: Listing of Alloys .......................................................................................... 7 Appendix B: Specific Apparatus ..................................................................................... 9
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___________________________________________ Foreword This recommended practice provides state-of-the-art information for the design and selection of materials used in the handling and storage of commercial concentrated sulfuric acid up to 120ºF (50ºC). This temperature is approximately the maximum that arises from solar heating of piping or vessels in a tropical climate. Because a code or standard for handling sulfuric acid does not exist, this recommended practice provides guidelines. Therefore it is primarily informational in certain sections. In other sections, where there is complete agreement among users, it contains recommendations. This recommended practice is only concerned with prob-
lems that arise during product storage. It does not consider acid strengths above 100% or below 90%. For completeness, this recommended practice includes an appendix describing applicable materials for a storage and dilution system. This recommended practice was prepared by NACE Task Group T-5A-18, a component of Unit Committee T5A on Corrosion in Chemical Processes, and is issued by NACE under the auspices of Group Committee T-5 on Corrosion in Process Industries. These committees are composed of industry representatives from firms producing and using sulfuric acid.
This standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials.
___________________________________________ Section 1: General 1.1 Concentrated sulfuric acid is a colorless, odorless, syrupy liquid whose oily appearance suggested the name oleum (Latin for oil) to early chemists. Specifically, it was called oil of vitriol (from the Latin vitreum for glass) because of the glassy appearance of some metallic sulfates. It does not contain free sulfur trioxide. Today, the term “oleum” is used only for sulfuric acid containing free sulfur trioxide. 1.2 The term “concentrated sulfuric acid” broadly refers to the concentration range of 90 to 100%. Commercial acid is usually stored at 93% concentration because its minimum freezing point is -30ºF (-34ºC). Sulfuric acid is commonly
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transported in the 98 to 99.5% concentration range. The latter limit is imposed by the much greater corrosivity of 100% acid to carbon steel and by its higher freezing point of about 45ºF (7ºC). 1.3 Concentrated sulfuric acid is an oxidizing agent and, because of its affinity for water, it is also a desiccant. The major problems in its handling and storage relate to its hygroscopic nature (absorbing atmospheric humidity), the exothermic reactivity with water on dilution, and velocity effects that tend to accelerate corrosion of iron and lead base alloys.
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___________________________________________ Section 2: Specific Materials(1,2) 2.1 Carbon Steel 2.1.1 Carbon steel is satisfactorily resistant to concentrated sulfuric acid at ambient temperatures under static or low velocity conditions (less than 3 ft/s [approximately 0.9 m/s]); for some restrictions, see Paragraph 2.1.4. The initially high corrosion rate is quickly reduced by the formation of an insoluble sulfate film that is highly protective unless physically disturbed. However, even at nominal flow velocities within the prescribed limits, rapid localized attack may occur. For example, short-radius elbows or excessive internal protrusion of circumferential welds may cause localized downstream turbulence resulting in high corrosion rates. 2.1.2 An important form of localized attack is hydrogen grooving on vertical or inclined walls exposed to the liquid phase in piping or vessels, caused by evolution and movement of hydrogen bubbles resulting in deterioration of the protective film. 2.1.3 Anodic protection is effective in minimizing corrosion and preventing hydrogen grooving.
2.2 Cast Iron 2.2.1 Gray cast iron and ductile cast iron are more corrosion-resistant to concentrated sulfuric acid than is carbon steel. Velocities up to 5 ft/s (1.5 m/s) can be tolerated. Frequently, velocities up to 7 ft/s (approximately 2 m/s) are accepted in large diameter pipe, but accelerated corrosion may occur at joints and bends as a result of flow disturbance. 2.2.2 Gray cast iron has lost favor in recent years because of its brittle nature. Catastrophic ruptures have occurred in piping as well as pressure vessels. Ductile cast iron has been used successfully for thick wall piping. However, see Paragraph 2.1.6 with regard to turbulence-induced accelerated corrosion at threaded joints. 2.2.3 High silicon cast irons (e.g., UNS F47003 with 14.5% Si) are resistant but are seldom used for simple handling and storage because of their brittleness. 2.3 Austenitic Stainless Steel
2.1.4 In the 99.5 to 100% concentration range, increased corrosion rates may limit the application of carbon steel. The actual corrosion rate is strongly affected by temperature, acid concentration, ferrous and ferric ion concentration, flow conditions, and chloride contamination, since these parameters determine the dissolution rate and stability of the protective iron sulfate film. 2.1.5 In all steel fabrication, it is important that weldments be thoroughly inspected to ensure that they do not contain slag, porosity, laps, or other welding defects that may initiate accelerated corrosion. Steel vessels and piping must also be free of mill scale or serious local attack may occur (see also Paragraph 3.1.7). 2.1.6 Because of a lack of internal smoothness resulting in localized turbulence, threaded or socket-welded piping may cause accelerated corrosion. As an alternative, butt-welded and flanged carbon steel piping have been used successfully (see also Paragraph 3.1.7).
2.3.1 The conventional austenitic stainless steels of the Cr-Ni and Cr-Ni-Mo type are generally resistant to ambient temperature concentrated acid since they have a naturally formed passive film. UNS S31600 is suitably resistant within the 90 to 100% concentration range. UNS S30400 should only be used at concentrations of 93% or more. Conventional austenitic stainless steel grades find application in piping where moderately high velocity is a factor or where iron contamination of the acid must be minimized. Although intergranular corrosion of sensitized stainless steel is not a problem in concentrated acid, the low-carbon grades (i.e., UNS S30403 and UNS S31603) are used for welded piping systems to prevent intergranular attack if dilution or contamination can occur. 2.3.2 The molybdenum-bearing grades (e.g., UNS S31600/S31603 or UNS J92900 [CF-8M]/J92800 [CF3M]) are recommended for improved resistance to velocity-enhanced corrosion or impingement in valves in the entire concentration range.
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The statements in this standard are consistent with the NACE Technical Committee Report 5A151 (1985 Revision), "Materials of Construction for Handling Sulfuric Acid," (Houston, TX: NACE, 1985) and with the MTI/NACE Sulfuric Acid Materials Advisor (CHEM-COR1TM)(Houston, TX: NACE). (2) The text refers to UNS numbers (Unified Numbering System for Metals and Alloys, a joint activity of ASTM and SAE, Warrendale, Pennsylvania). See Appendix A for UNS numbers and materials.
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2.3.3 Valves cast from copper-bearing UNS J93370 (CD-4M Cu) have found successful applications in ambient temperature concentrated acid. UNS J93370 (CD-4M Cu) offers improved resistance to occasional dilute acid if compared to UNS J92700 (CF-3) or UNS J92800 (CF-3M). 2.3.4 Any surface contamination by chlorides, as by sea salt from transportation or storage under marine conditions, can cause rapid localized pitting. To a certain degree, molybdenum-bearing grades can cope with these conditions. 2.4 High-Nickel Stainless Steels and Nickel Alloys 2.4.1 Nickel-chromium-iron-copper-molybdenum type alloys such as UNS N08825, UNS N08028, UNS N06985, UNS N06030, UNS N08904, UNS N08020, UNS N08926, UNS N09925, or their cast versions (see Appendix A) perform better than 18Cr-10Ni-Mo stainless steel under increased velocity conditions (as in pumps). 2.4.2 Alloys of the nickel-chromium-molybdenum type such as UNS N10276, UNS N06625, UNS (3) N06022, and UNS N06455 or their cast versions are preferred where ncontrolled dilution might be encountered. The same applies for UNS N06985 and UNS N06059. 2.5 Other Alloys and Metals 2.5.1 Nonferrous metals such as zinc, tin, copper, and nickel are not resistant and therefore have no useful applications in the handling and storage of concentrated sulfuric acid. Aluminum grades 1100, 3003, and 3004 have been used successfully for sulfuric acid in the concentration range of 98% to 100%. 2.5.2 Chemical lead is resistant to sulfuric acid but the protective sulfate film is increasingly solubilized above about 95% concentration and 77ºF (25ºC). The film is easily damaged by velocity accelerated corrosion even at low velocities. It is very useful as a pan material to catch dripping acid, which is diluted upon exposure to moist air. However, since there will always be uptake of lead by the acid, disposal of the acid causes environmental problems. 2.5.3 Of the reactive metals, titanium and zirconium must not be exposed to concentrate acid. Tantalum is resistant to concentrations up to 97% acid and
thus finds some application, especially as an electroplated coating for orifice plates. 2.5.4 Of the noble metals, gold and platinum are resistant but of very limited applicability. Gold is used to condense and cool reagent grade acid. Silver is not resistant. 2.6 Nonmetallic Materials 2.6.1 Organic 2.6.1.1 The fluorinated plastics listed below are resistant to concentrated acid at ambient temperatures: PTFE (polytetrafluoroethylene); PFA (perfluoroalkoxy); ECTFE (ethylene-chlorotrifluoroethylene); FEP (fluorinated ethylene-propylene); and ETFE (ethylene trifluoroethylene). 2.6.1.2 Polyethylene (PE), polypropylene (PP), and polyvinylchloride (PVC) are subject to environmental cracking. High density cross-linked polyethylene is applicable up to 98%. Polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), and polyphenylene sulfide (PPS) are also resistant to acids up to 98%. CAUTION: Because of mechanical weakness of organic materials, lined piping should be used. 2.6.1.3 Chlorosulfonated polyethylene has been successfully used for hoses up to 93% acid. However, see Paragraph 3.7.1 for more information. 2.6.1.4 High-temperature baked phenolic coatings are routinely used in storage tanks and railroad tank cars from 90 to 98% acid where iron contamination must be minimized and/or corrosion protection is required. At higher concentrations, the coating will slowly carbonize. High-temperature baked phenolic coatings have provided approximately ten years of satisfactory service in H2SO4 from 90 to 98% when properly applied and cured. 2.6.1.5 Polyester, vinylester, and epoxy-based materials will be attacked by concentrated sulfuric acid.
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ASTM A 494/A494 M-87A, "Specification for Castings, Nickel, and Nickel Alloys" (Philadelphia, PA: ASTM, 1987).
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RP0391-91 2.6.2 Inorganic 2.6.2.1 Pure carbon is resistant to acids up to 96% as is impervious graphite.
2.6.2.2 Glass and ceramics, including acid brick, have satisfactory resistance to concentrated sulfuric acid.
___________________________________________ Section 3: Specific Equipment 3.1 Tanks 3.1.1 The basic material of construction for concentrated sulfuric acid storage tanks is carbon steel. Tanks should have a minimum corrosion allowance of 1/4 in. (6 mm) over the design thickness. Under critical conditions, as mentioned in Paragraph 2.1.4, corrosion rates may become excessively high. Avoidance of low temperature, brittle fracture of carbon steel must be considered (4,5) by the appropriate design and fabrication code. 3.1.1.1 The carbon steel tank may have an anodic protection system to minimize iron contamination and to control corrosion. 3.1.1.2 High-temperature baked phenolic coatings also have been applied to concentrated sulfuric acid storage tanks for minimizing the iron pick-up and corrosion, but service life of the tank will be limited at acid concentrations of more than 98% (see also Paragraph 2.6.1.4). 3.1.2 Top-entering nozzles and inlet tubes should be located near the tank center and directed straight down or away from the nearest vessel wall to minimize the potential for localized attack by acid turbulence or hydrogen grooving. 3.1.3 For inlet and outlet nozzles, austenitic stainless steel with moderate or high nickel content or nickel alloys are normally used as solid, lined, clad, or weld (6) overlay construction to cope with the local increase in velocity and resulting turbulence. UNS S31600/S31603, high nickel stainless steel or nickel alloys (as listed in Paragraph 2.4) are used in the 90 to 100% concentration range. Above 93% concentration, UNS S30400/S30403 may be used. 3.1.4 Other recommended design features include a (7) high liquid-level alarm for overflow, a desiccation vent against absorption of atmospheric moisture (unless the
climate is arid), and a suitable containment or run-off area in case of release. The vent must be at the tank's highest point to prevent hydrogen entrapment. 3.1.5 Hydrogen evolved by corrosion can cause pressure buildup in blocked piping, scab patches, or closed tanks not adequately vented. 3.1.6 Especially in cases of higher flow velocities, side-entering nozzles should be austenitic stainless steel with moderate or high nickel content, or nickel alloy solid, lined, clad, or weld-overlay construction to prevent corrosion problems encountered with carbon steel construction (see Paragraph 3.1.3). Alternatively, carbon steel nozzles may be used with an additional corrosion allowance of 1/4 in. (6 mm), designed to limit flow velocities at a maximum of 3 ft/s (0.9 m/s). By using internal nozzle extensions, turbulent conditions are kept from causing localized corrosion or hydrogen grooving problems on adjacent vertical tank walls. 3.1.7 With regard to design details, the proposed NACE Recommended Practice, “Design, Fabrication, and Inspection of Carbon Steel Tanks for the Storage of Concentrated Sulfuric Acid and Oleum,'' is being developed and publication is expected in 1992. For lined tanks, NACE Recommended Practice RP017891 “Fabrication Details, Surface Finish Requirements, and Proper Design Considerations for Tanks and Vessels to be Lined for Immersion Service,'' should also be consulted. 3.2 Rail Tank Cars and Cargo Tanks 3.2.1 Rail tank cars are built from a limited number of grades of carbon steel as approved by the Association (8) of American Railroads (AAR). Since the tank cars are designed for a forty-year life, most new cars are supplied with a baked phenolic lining to reduce corrosion or iron contamination of the acid.
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STD 650-88, "Welded Steel Tanks for Oil Storage" (Washington, DC: American Petroleum Institute, 1988). Boiler and Pressure Vessel Codes, Section VIII, Division 1, "Rules for Construction of Pressure Vessels" (New York, NY: American Society of Mechanical Engineers, 1989). (6) So far there have been no reported problems due to galvanic contacts between carbon steel and corrosion resistant alloys in tanks for concentrated sulfuric acid. (7) Since desiccation vents are not easily maintained, relief valve vacuum breakers (RVVB) with a nitrogen blanket on the tank are used successfully. (8) Association of American Railroads, 50 F Street, NW, Washington, DC 20001. (5)
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3.2.2 Cargo tanks are built to Department of (9) Transportation (DOT) regulations MC 306, 307, or 312. Most new units are fabricated from UNS S31603.
3.3.7 Plastic-lined piping with PP, PVDF, or PTFE liner has also been used successfully. However, PP and PVDF shall not be used for acid concentrations above 98%.
3.3 Piping 3.3.1 Materials selection for concentrated sulfuric acid piping depends on factors including size, velocity, and the pumping schedule.
3.3.8 Where solar heating is extreme or where tracing is required, UNS S31603, high-nickel stainless steels, or nickel alloys are favored (see also Paragraph 3.8.1). 3.4 Valves
3.3.2 Carbon steel piping may be used at ambient temperature and low flow velocity (i.e., maximum 3 ft/s [approximately 0.9 m/s]). Flow velocities up to 5 ft/s (1.5 m/s) may be allowed if the pumping schedule is brief (e.g., a few hours per day). Good quality welds are essential and multipass welds with a minimum of three layers are suggested. See Paragraphs 2.1.6, 2.2.1, and 2.2.2 for information on potential problems caused by lack of internal smoothness. Intermittent pumping can result in hydrogen grooving along the top of the pipe. Therefore, piping should be drained or blown free of acid after transfer is complete, using dry air or inert gas. Crevices caused by threaded or socket-welded piping can make draining or blowing out acid difficult. 3.3.3 Ductile cast iron pipe has an increased tolerance for higher velocities if compared to steel. Ductile cast iron is preferred to brittle gray cast iron since it offers better ductility in addition to comparable corrosion and erosion resistance in the acid strengths covered by this recommended practice (see Paragraph 2.2). 3.3.4 Ferrous metal piping holding concentrated sulfuric acid should not be “blocked in'' or have all valves shut without a properly designed pressure relief device in the line. Otherwise, the hydrogen generated by corrosion will develop sufficient pressure to blow gaskets or rupture the pipe.
3.4.1 For simple shut-off valves, molybdenum-bearing stainless steel is recommended. The industry standard is UNS J92900 (CF-8M); UNS J92800 (CF-3M) is an acceptable alternative. Copper-bearing UNS J93370 (CD-4M Cu) valves are sometimes available at little additional cost and offer greater resistance to dilute acid. UNS J95150 (CN-7M) and nonmetallic lined valves have also been successfully used for this type of service. 3.4.2 For throttling valves with higher velocities and turbulence, UNS J95150 (CN-7M) has been used successfully. This alloy is also applicable for stock tank plug valves to protect against inadvertent localized dilution effects. PTFE-lined valves have also been successfully used in this service. 3.5 Pumps 3.5.1 UNS J95150 (CN-7M) pumps are the industry standard, although pumps made from cast Ni-Cr-Mo alloys are also applicable (see ASTM A 494). Glasslined pumps or pumps made from graphite are also suitable, however, they should be protected against mechanical damage. 3.6 Gaskets
3.3.5 For small diameter piping (e.g., less than 3 to 4 in. [75 to 100 mm]), use of austenitic stainless steel is suggested at ambient temperatures and velocities up to 6 ft/s (1.8 m/s). UNS S30400/30403 may be used for 93 to 100% acid and UNS S31600/S31603 for 90 to 100% (see also Paragraph 2.3.1). The acid-contacted surface must be chloride free (preferably rinsed with a low chloride water and dried) before entry of acid is permitted (see Paragraphs 2.1.4 and 2.3.4).
3.6.1 Compressed sheet asbestos gaskets and asbestos-filled spiral-wound gaskets have been used successfully for decades. However, their use has been curtailed because of personnel exposure concerns. There are suitable alternatives to asbestos available and they should be utilized.
3.3.6 UNS N08020 piping has been successfully used for small diameter piping, especially when flow velocities exceed 6 ft/s (1.8 m/s).
3.6.3 Fluoroelastomers are also applicable.
3.6.2 PTFE-, silica-, or alumina silicate-filled PTFE or stainless steel spiral-wound PTFE is applicable.
3.6.4 Envelope gaskets are satisfactory if the elastomeric or other compressible material within is effectively shielded by a fluorinated plastic envelope.
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Department of Transportation, National Highway Traffic Safety Administration, Washington, DC.
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RP0391-91 3.7 Hoses
3.8 Tracing
3.7.1 Only fluorocarbon-lined braided stainless or suitable elastomeric hoses (e.g., chlorosulfonated polyethylene) can be used in concentrated sulfuric acid. CAUTION: Since hoses are subject to damage from misuse, frequent inspection is strongly recommended.
3.8.1 Electrical tracing for cast iron and carbon steel piping and carbon steel tanks should be used only where climatic conditions necessitate but must be instrumented so that metal/acid interface temperatures cannot exceed 120ºF (50ºC). Steam tracing should be avoided with carbon steel, cast iron, and austenitic stainless steel piping.
___________________________________________ Section 4: Safety Considerations NOTE: Never add water to strong acid, as the reaction is violent. Always add acid to water. Even the acid-to-water procedure will generate high temperatures if not done slowly and/or with supplemental cooling. 4.1 Ambient temperature concentrated acid does not pose a serious fume danger. Accumulation of hydrogen in vessels or piping is a potential explosion hazard. All equipment must be thoroughly vented and purged before entering for internal inspection or conducting any repair welding.
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4.2 Concentrated sulfuric acid is a powerful oxidant and desiccant and can cause serious burns on skin contact. Personnel protection (i.e., face shields, safety glasses, protective clothing) is extremely important. In case of skin contact, a doctor shall be contacted immediately. For details, consult a safety expert. 4.3 Because of safety considerations, appropriate materials, techniques, and specifications for fabrication and joining as well as inspection methods should be carefully selected and used to ensure personnel safety and equipment reliability.
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APPENDIX A: LISTING OF ALLOYS (1)
(2)
CHEMICAL COMPOSITIONS
UNS NO
Al J93370 J92600 J92700 J92800 J92900 S30400
S30403 S31600 S31603 N08904 N08028 J95150 (N08007) N08020 N08825
0.2 max
N08926
N09925
0.10 0.50
C 0.04 max 0.08 max 0.03 max 0.03 max 0.08 max 0.08 max
Co
Cr 24.526.5 18.021.0 17.021.0 17.021.0 18.021.0 18.020.0
Cb
Fe rem rem rem rem rem rem
0.03 max 0.08 max 0.030 max 0.020 max 0.03 max 0.07 max
18.020.0 16.018.0 16.018.0 19.023.0 26.028.0 19.022.0
0.07 max 0.05 max 0.020 max
19.021.0 19.523.5 19.021.0
8xC1.0
0.03 max
19.523.5
0.50 max
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Cu 2.753.25
rem rem
Mn 1.0 max 1.50 max 1.50 max 1.50 max 1.50 max 2.0 max 2.0 max 2.0 max 2.0 max 2.0 max 2.50
Mo 1.752.25
2.03.0 2.03.0 2.03.0
1.02.0 0.61.4 3.004.00
rem
rem
1.50 max
2.03.0 2.03.0 4.05.0 3.04.0 2.03.0
3.04.0 1.53.0 0.501.50
rem
2.0 max 1.0 max 1.0 max
2.03.0 2.53.5 6.07.0
1.503.0
22.0 min
1.0 max
2.503.50
rem
rem
rem rem
N
0.100.20
Ni 4.756.0 8.011.0 8.012.0 9.013.0 9.012.0 8.010.5 0 8.012.0 10.014.0 10.014.0 23.028.0 29.532.5 27.530.5
P 0.04 max 0.04 max 0.04 max 0.04 max 0.04 max 0.045 max
S 0.04 max 0.04 max 0.04 max 0.04 max 0.04 max 0.030 max
Si 1.00 max 2.00 max 1.50 max 1.50 max 2.00 max 1.00 max
0.045 max 0.045 max 0.045 max 0.045 max 0.030 max
0.030 max 0.030 max 0.030 max 0.035 max 0.030 max
32.038.0 38.046.0 24.026.0
0.045 max
38.046.0
0.045 max
V
W
Designation
NAME
ACI CD4M Cu
--
ACI CF-8
(Type 304 casting)
ACI CF-3
(Type 304L casting)
ACI 3M
CF-
(Type 316L casting)
ACI 8M
CF-
(Type 316 casting)
Ti
AISI 304
--
1.00 max 1.00 max 1.00 max 1.00 max 1.00 max 1.50 max
AISI 304L
--
AISI 316
--
AISI 316L
--
--
Alloy 904L
Alloy 28
--
ACI 7M
(Type Alloy 20 casting)
0.035 max 0.03 max 0.030 max
1.00 max 0.5 max 0.50 max
--
Alloy Cb-3
0.61.2
--
Alloy 825
--
0.03 max
0.50 max
1.902.40
Alloy 1925 hMo Alloy 925
--
CN-
20
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RP0391-91 (1)
(2)
CHEMICAL COMPOSITIONS
UNS NO
Al N10276 F47003
N06022 N06985 N06030 N06059
0.10.4
N06455 N06625 --
0.40 max
C 0.02 max 0.701.10
Co 2.5 max
0.015 max 0.015 max 0.03 max 0.010 max 0.015 max 0.10 max 0.12 max
2.5 max 5.0 max 0.301.50 0.3 max 2.0 max
Cr 14.516.5 0.50 max
20.022.5 21.023.5 28.031.5 22.024.0 14.018.0 20.023.0 15.517.5
--
0.02 max
15.017.5
--
0.06 max
20.023.0
--
0.07 max
17.020.0
Cb
Cu
0.50 max
0.5 (3) max
3.15(3) 4.15
3.154.50
1.52.5 1.02.4
Fe 4.07.0 rem
Mn 1.0 max 1.50 max
Mo 15.017.0 0.50 max
2.06.0 18.021.0 13.017.0 1.5 max 3.0 max 5.0 max 4.57.5
0.50 max 1.0 max 1.5 max 0.5 max 1.0 max 0.50 max 1.0 max
12.514.5 6.08.0 4.06.0 15.016.5 14.017.0 8.010.0 16.018.0
2.0 max
1.0 max
15.017.5
5.0 max
1.0 max
3.0 max
1.0 max
N
Ni rem
0.02 max 0.04 max 0.04 max 0.015 max 0.04 max 0.015 max 0.04 max
0.02 max 0.03 max 0.02 max 0.005 max 0.03 max 0.015 max 0.03 max
Si 0.08 max 14.2 014.7 5 0.08 max 1.0 max 0.8 max 0.10 max 0.08 max 0.50 max 1.0 max
rem
0.03 max
0.03 max
0.80 max
8.010.0
rem
0.015 max
0.015 max
1.0 max
17.020.0
rem
0.04 max
0.03 max
1.0 max
rem rem rem rem rem rem rem
P 0.030 max
S 0.030 max
V 0.35 max
W 3.04.5
Designation
NAME
--
Alloy C276 (14.5% Si Cast Iron)
Ti
ASTM A518 Gr.1 0.35 max
2.53.5 1.5 max 1.54.0
----
0.70 max 0.40 max 0.200.40
3.755.25
1.0 max
Alloy C-22 Alloy G-3
--
Alloy G30 Alloy 59
--
Alloy C-4
--
Alloy 625
ASTM A494 CW-12 MW ASTM A494 CW-2M ASTM A494 CW-6MC ASTM A494 CW-6M
(Type Alloy C casting) Type Alloy C-4 casting) (Type Alloy 625 casting) (Type Alloy C276 casting)
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Metals and Alloys in the Unified Numbering System, (Warrendale, PA: Society of Automotive Engineers, 1989). The chemical compostions listed are for identification purposes and should not be used in lieu of the cross-referenced specifications. Cb + Ta
NACE International
RP0391-91
APPENDIX B: SPECIFIC APPARATUS B.1 The single most common apparatus involving exposure to concentrated sulfuric acid is a storage system used to introduce acid into a dilution device, from which the weak acid is used for pH or acidity control. Therefore, guidance on applicable materials is considered appropriate within this recommended practice. A very crude apparatus might simply drip concentrated acid into a wooden trough through which copious amounts of water flows (as in pH control for cooling tower cycle water). Precise control, however, demands more sophisticated equipment. B.2 Figure B.1 is a simplified flow diagram of a storage and dilution system suitable for such applications as pH control of feedwater to a cooling tower, reverse osmosis unit, or electrodialysis system for production of demineralized water. It is included to illustrate applicable materials according to Sections 1 through 3, with added features to cope with the heat and corrosivity of acid dilution. It also includes an approach to prevent back-up of weak acid into materials designed to handle only ambient temperature concentrated acid. The concentrated acid entry piping should enter the dilution tee from below since the high specific weight of the acid ensures against the entry of the more dilute stream with lower specific weight. CAUTION: APPENDIX B IS NOT AN ENGINEERING DESIGN.
Figure B.1 Typical Materials for Sulfuric Acid Dilution System (Simplified Flow Diagram with Metrials Recommendation)
NACE International
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