NACE Standard TM0198-2004 Item No. 21232
Standard Test Method Slow Strain Rate Test Method for Screening CorrosionResistant Alloys for Stress Corrosion Cracking in Sour Oilfield Service 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 or she 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 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. 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 assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE interpretations issued by NACE in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers. Users of this NACE 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 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 referred to within this standard. Users of this NACE 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 CAUTIONARY NOTICE: NACE standards are subject to periodic review, and may be revised revised or withdrawn at any time in accordance with NACE technical committee procedures. NACE requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication and subsequently from the date of each reaffirmation or revision. The user is cautioned to obtain the latest edition. Purchasers of NACE standards may receive current current information on all standards and other NACE publications by contacting the NACE First Service Service Department, 1440 South Creek Dr., Houston, TX 77084-4906 (telephone +1 281-228-6200).
Revised 2011-10-28 Revised 2004-02-12 Approved 1998-02-23 NACE International 1440 South Creek Drive. Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-051-3 © 2011, NACE International --`,,,``,```,,,,,``,,`,`,`,,,```-`-`,,`,,`,`,,`---
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TM0198-2011
_________________________________________________________________________ Foreword Failures of metals exposed to hydrogen sulfide (H 2S)-containing (sour) oilfield production environments have been reported for more than 50 years and have usually occurred in carbon or 1,2 low-alloy steels. Failures of high-strength steels by brittle cracking (sulfide stress cracking [SSC]) and of lower-strength plate and pipe steels by blistering and hydrogen-induced (stepwise) cracking have also been reported. As a result, engineers and scientists have developed test methods to evaluate steels for resistance to failure by these mechanisms in sour environments. These and other considerations led to the establishment of NACE Task Group (TG) T-1F-9, “Metallic Materials Testing Techniques for Sulfide Corrosion Cracking,” which originally developed 3 NACE Standard TM0177 in 1977. The task group (now TG 085) has continued to revise that standard. An additional interest of the original TG T-1F-9 was the application of corrosion-resistant alloys (CRAs), primarily stainless steels and nickel-based alloys, in oilfield production environments. Some of these CRAs have experienced stress corrosion cracking (SCC) when exposed to H 2S, carbon dioxide (CO2), and brine. Therefore, a standardized method for screening CRAs for use in oilfield production environments is of extreme importance to the entire petroleum industry, and work group TG T-1F-9e (now TG 133) was formed to address this issue. Several screening methods were considered: autoclave tests with statically stressed specimens, fracture mechanics methods, and the slow strain rate (SSR) test methods. Each has advantages and disadvantages that make the selection of a single test method for standardization difficult. However, the SSR test has emerged as a relatively quick, simple method that can be used for the evaluation of CRAs for resistance to a variety of environmental cracking phenomena, including 1,2 SCC, hydrogen embrittlement, and liquid metal cracking. The use of SSR test methods, particularly in screening tests, has become more common in many laboratories for evaluation of CRAs for downhole applications.
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The SSR test incorporates a slow (compared with conventional tensile tests), dynamic strain –9 –7 –7 applied at a constant extension rate. Extension rates of 2.54 x 10 to 2.54 x 10 m/s (1.00 x 10 –5 to 1.00 x 10 in/s) are commonly used. The principal effect of the constant extension rate, in combination with environmental or corrosive attack, is to accelerate the initiation of cracking in susceptible CRAs. By doing so, the SSR acts in much the same way as a notch or precrack in statically stressed environmental cracking tests. Failure is obtained within a few days for commonly used extension rates. Because of its relatively short test duration, the SSR test has been found useful in evaluating CRAs for resistance to SCC in simulated oilfield production environments at elevated 4,5 temperatures. By comparison, it has been observed that it may take thousands of hours of 6,7 exposure time to evaluate CRAs using more conventional statically stressed specimens.
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In a SSR test, the test specimen is pulled to failure. One benefit of this method is that the ultimate failure of the test specimen is a positive result. That is, parameters (includin g reduction in area and plastic elongation) and visual observations can always be quantified. These results are usually further quantified by comparison with the results of similar tests performed in an inert environment. Accelerating the crack initiation by this mechanical technique tends to make the SSR test appear to be a rather severe test by being able to fail CRAs under environmental conditions in which no other test method (at reasonable exposure times) can produce failures. Because the exposure time is short and the strain rate is somewhat arbitrary, the results of SSR testing are not intended to be used directly to infer service performance. It is primarily a screening or ranking method that should be used in combination with a more extensive laboratory evaluation involving complementary testing for corrosion and environmental cracking. Service experience should be reviewed before material selection decisions are made.
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A round-robin testing program was conducted by former TG T-1F-9 during the early d evelopment of this standard to evaluate the variability of SSR test data and the influences of various testingrelated parameters. Draft #5 of the proposed test method was used as the basis for the roundrobin testing program, and a total of seven companies participated. The results of the round-robin testing program indicated that large deviations in the SSR test data were observed for some conditions. However, with the evaluation of the procedures used by the round-robin participants, several recommendations for changes in SSR test procedures were made. Most of the recommended changes were included in this standard to reduce the amount of deviation in the test results. These changes included: (1) Ground surfaces (not turned) and finer surface finish on the test specimen gauge section; (2) Additional specifications regarding testing machine compliance; (3) Improved calculation technique for reduction in area; and (4) References to industry standards containing accepted procedures for autoclave and SSR testing. Based on the above-mentioned considerations, TG T-1F-9 developed this standard test method incorporating the SSR test to be used by laboratory investigators for screening CRAs for SCC in sour oilfield service. This NACE standard was originally developed by TG T-1F-9 in 1998 under the direction of Unit Committee T-1F, “Metallurgy of Oilfield Equipment.” It was revised in 2004 and 2011 by TG 133, “Review and Revise as Necessary NACE Standard TM0198-2004.” TG 133 is administered by Specific Technology Group (STG) 32, “Oil and Gas Production—Metallurgy.” This standard is issued by NACE under the auspices of STG 32.
In NACE standards, the terms shall , must , should , and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual . The terms shall and must are used to state a requirement, and are considered mandatory. The term should is used to state something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional.
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NACE International Standard Test Method Slow Strain Rate Test Method for Screening Corrosion-Resistant Alloys for Stress Corrosion Cracking in Sour Oilfield Service Contents 1. General............................................................................................................................ 1 2. Reagents ......................................................................................................................... 1 3. Test Specimen ................................................................................................................ 1 4. Test Equipment .............................................................................................................. 3 5. Determination of Baseline Material Properties ................................................................ 4 6. Environmental Test Conditions ....................................................................................... 5 7. Mechanical Test Conditions ............................................................................................ 6 8.Test Procedure................................................................................................................. 7 9.Analysis and Reporting of Test Results References ...................................................... 11 Appendix A: Safety Considerations in Handling H 2S (Nonmandatory).............................. 19 Appendix B: Explanatory Notes on Test Method (Nonmandatory).................................... 20 FIGURES: Figures 1: Standard SSR test specimen ............................................................................. 2 Figures 2: Schematic presentation of the possible effects of strain rate on various types of cracking behavior .......................................................................................................... 7 Figure 3: Schematic of typical SSR test system ................................................................. 9 Figure 4: Typical load-versus-time plots for SSR test of a Ni-Fe-Cr-Mo alloy performed at -7 -6 an extension rate of 1x10 m/s (4x10 in/s) in several test environments................. 10 Figure 5: Schematic illustration based on data for a super-13 Cr stainless steel showing basis for determining the failure (E p) based on the total strain to failure (E tot) and the elastic contribution (E el) ............................................................................................... 13 Figure 6: Typical nickel alloy stress-strain curve, where there is no work-hardening ....... 14 Table 1: NACE Uniform Material Testing Report Form (Part 1) Testing in Accordance with NACE SSR Test .......................................................................................................... 17
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TM0198-2011 _________________________________________________________________________ Section 1: General
1.1 This standard establishes a SSR test method for screening CRAs (i.e., stainless steels and nickel-based alloys) for resistance to SCC at elevated temperatures in sour oilfield production environments. The fact that this test method is a screening method implies that further evaluation or additional experience may be required before materials selection decisions can be made. 1.2 This standard specifies reagents, test specimen, test equipment, determination of baseline material properties, environmental and mechanical test conditions, test procedure, and analysis and reporting of test results.
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1.3 The test procedure can be summarized as follows: A SSR test specimen is exposed to a continuously increasing uniaxial tensile stress imposed by a slow and constant extension rate in the presence of an acidic aqueous environment containing H 2S, CO2, and brine at an elevated temperature. The ductility parameters (plastic elongation and reduction in area) obtained from evaluation of the SSR test specimen along with visual observation of its gauge section and fracture surface morphology are used as indicators of the material’s resistance to SCC in the test environment. These results are then compared to the results of a similar test performed in an inert environment to quantify the resistance or susceptibility to SCC in the test environment.
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1.4 Procedures for SSR testing shall be consistent with those provided in ASTM G129. Tests involving high pressure or high 9 temperature, or both, shall be performed using procedures consistent with those provided in ASTM G111. The only deviations from these procedures shall be those specifically stated in this standard. 1.5 Safety Precautions 1.5.1 H2S is an extremely toxic gas that must be handled with extreme care. discussion of safety considerations and toxicity of this gas.)
(See Appendix A [nonmandatory] for a
1.5.2 Precautions must be taken to protect personnel from the hazards of rapid release of hot gases and fluids and explosion when working with the high-pressure, high-temperature test conditions. 1.6 This standard is not intended to include procedures for cyclic SSR testing. However, such procedures are currently under development and are in use in some laboratories.
_________________________________________________________________________ Section 2: Reagents 2.1 Reagent Purity 2.1.1 The gases, sodium chloride (NaCl), and solvents shall be reagent or chemically pure grade chemicals. The reasons for this reagent purity are discussed in Appendix B (nonmandatory). 2.1.2 The water shall be distilled or deionize d and of quality equal to or greater than ASTM Type IV in accordance with 10 ASTM D1193. Tap water shall not be used. 2.2 Inert gas shall be used for removal of oxygen. Inert gas shall mean high-purity nitrogen, argon, or other suitable nonreactive gas.
_________________________________________________________________________ Section 3: Test Specimen 3.1 A uniaxial tensile test specime n shall be used for this test because it provides for a simple stress state and a common basis for comparison of test results. 3.2 The SSR test specimen shall be machined from the CRA to be tested in the most appropriate location and orientation relative to the specific evaluation being performed. The material form of the CRA, however, can often place restrictions on the
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TM0198-2011 SSR test specimen location and orientation. Furthermore, the location and orientation of the SSR test specimen can affect the test results. 3.3 Standard SSR test specimens shall be fabricated in accordance with the criteria and specifications provided in Paragraphs 3.3.1 and 3.3.2. The standard SSR test specimen is illustrated in Figure 1. The length of the SSR test specimen and the threading/gripping details have not been specified to accommodate the use of either of two acceptable test configurations in a range of available test equipment:
Configuration 1—the SSR test specimen is entirely enclosed in the test vessel with metal grips (pull rods) passing through the ends of the test vessel; and
Configuration 2—the SSR test specimen shoulder section is elongated to pass through the ends of the test vessel without the use of metal grips (pull rods) that extend inside the test vessel.
L1 L2 D1 D2 R T Thread
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25.4 NS(A) 3.81 ± 0.05 mm 6.35 ± 0.05 mm 6.35 min. NS NS
1.00 NS 0.150 ± 0.002 in 0.250 ± 0.002 in 0.250 min. NS NS
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Figure 1: Standard SSR test specimen.
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3.3.1 Dimensions
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The standard SSR test specimen shall have the following dimensions: 3.3.1.1 The gauge section diameter (D1) shall be 3.81 ± 0.05 mm (0.150 ± 0.002 in) and the gauge section length (L 1) shall be 25.4 mm (1.00 in). 3.3.1.2 The radius of curvature of the shoulder section (R) at both ends of the gauge section shall be a minimum of 6.35 mm (0.250 in) to minimize stress concentrations and fillet failures. 3.3.1.3
The shoulder section diameter (D2) shall be 6.35 ± 0.05 mm (0.250 ± 0.002 in).
3.3.1.4 The overall length (L2) and thread type and size are at the discretion of the user based on the test configuration and ancillary test equipment used for testing.
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TM0198-2011 3.3.2 Machining 3.3.2.1 The SSR test specimen shall be fabricated in such a way as to avoid overheating and unnecessary cold (2) 11 working of the gauge section. The average surface roughness (as defined by the “Ra value” in ISO 4287 ) of the gauge section shall be 0.25 µm (10 µin) or finer. The preferred method of fabricating the gauge section of the SSR test specimen is by progressive grinding such that at each stage of grinding the deformation induced by the previous grinding step is removed. The method adopted should minimize transverse stress raisers. Alternative methods of fabricating the SSR test specimen gauge section may be used if they have been shown to produce comparable test results. The remainder of the SSR test specimen may be fabricated using conventional methods, though grinding of the shoulder radii may reduce the likelihood of fillet failures. 3.3.2.2 In machining operations, the final two passes should remove no more than a total of 0.05 mm (0.002 in) of material. 3.3.2.3 The gauge section diameter (D1) shall be uniform within the tolerance specified in Paragraph 3.3.1.1. There should be no undercutting of the shoulder radii. 3.4 If material size or shape dictates the use of a SSR test specimen other than the standard SSR test specimen specified in Paragraph 3.3, details of the alternative SSR test specimen geometry must be provided with the test results. CAUTION: The calculations of extension rate, crosshead displacement rate, and nominal strain rate used in this standard are predicated on the standard gauge section length (L1) specified in Paragraph 3.3.1.1. 3.5 Identification Stamping or vibratory stenciling may be used on the ends or shoulder section of the SSR test specimen, but not on the gauge section.
_________________________________________________________________________ Section 4: Test Equipment 4.1 Test Vessels 4.1.1 The test vessels shall be made of corrosion-resistant materials that are effectively inert in the test environment. 4.1.2 Test vessels shall be rated to an adequate working pressure to permit safe operation at the temperature and pressure conditions of the test. ` , , , ` ` , ` ` ` , , , , , ` ` , , ` , ` , ` , , , ` ` ` ` ` , , ` , , ` , ` , , ` -
4.1.3 Test vessels shall be capable of being purged with gases before testing and resistant to leakage during the test. 4.1.4 Test vessels shall be sized to maintain the solution-volume-to-exposed-test-spec imen-surface-area ratio at greater 2 2 than 30 mL/cm (200 mL/in ). 4.1.5 Test vessels and associated fixtures shall be electrically isolated from the SSR test specimens if the vessels and fixtures are made from metals dissimilar to the SSR test specimens. This may be accomplished using nonmetallic (polymeric or ceramic) bushings, coatings, and/or seals. The bushing, coatings, and/or seals shall be made from rigid electrical insulation materials that do not relax or flow under load when the SSR test specimens are stressed at the test temperature. 4.1.6 The test vessels for use with Configuration 1 test specimens shall be designed with pull rods to allow entry into the test vessel for application of load on the SSR test specimen while simultaneously maintaining a seal. The test vessels for use with Configuration 2 test specimens shall be designed to maintain an effective seal on the shoulder portion of the SSR test specimen. Seals with low frictional characteristics shall be used to maintain accurate application of load on the SSR test specimen.
4.2 Test Specimen Grips
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TM0198-2011 4.2.1 The test specimen grips shall be electrically isol ated from the SSR test specimen if the grips are made from metals dissimilar to the SSR test specimens. Alternatively, acceptable nonconductive coatings that can withstand the test environment and mechanical load may be used to electrically isolate the grips from the test environment. 4.2.2 Threaded grips exposed to the test environment shall be vented to allow for removal of entrapped air during the deaeration procedure. Air entrapment in threaded grips has been shown to increase the severity of corrosion and cracking in tests performed in sour environments. 4.3 Testing Machines 4.3.1 SSR testing machines shall be calibrated and maintained to ensure the accuracy of the extension rate. The extension rate shall be within ± 2% of the intended extension rate. 4.3.2 Only those SSR testing machines that have been shown to provide reliable and reproducible application of load at the –9 –7 –7 –5 intended extension rate (typically 2.54 x 10 to 2.54 x 10 m/s [1.00 x 10 to 1.00 x 10 in/s]) shall be used to perform this test. 4.3.3 For the SSR testing machine used, the system compliance (i.e., the slope of the load-versus-time plot) shall be measured using a blank test specimen (i.e., with no gauge section) in a simulated test performed in air in which the crosshead displacement is limited to that of the SSR testing machine and its components. Differences in the system compliance of various SSR testing machines or components can lead to variations in SSR test results. In most cases, these variations are minimized by using the ratios described in Paragraph 9.3.5 and by performing the baseline tests and environment tests on the same SSR testing machine or on different SSR testing machines with similar system compliance. 4.3.4 SSR testing machines that pull a single SSR test specimen are preferred because load frames that test multiple SSR test specimens may impart shock loading to the remaining SSR test specimens when one or more SSR test specimens fail. Load frames that accommodate multiple SSR test specimens may be used only if each SSR test specimen has a separate loading mechanism or if it has been demonstrated that failure of one or more SSR test specimens does not influence the results from other SSR test specimens under test at the same time.
_________________________________________________________________________ Section 5: Determination of Baseline Material Properties 5.1 At least two baseline tests of the CRA under evaluation shall be performed to assess the repeatability of measurement. The average values for the yield strength, ultimate tensile strength, time to failure, elongation, and reduction in area shall be determined and used as the baseline material properties. However, significant variations between the two or more sets of data would suggest material inhomogeneity or problems with the SSR test equipment and should be investigated. 5.1.1 Baseline tests shall be performed in air or other suitably inert environment under the same conditions of temperature and extension rate used for the environment tests, and with the same type of SSR test specimen, the same grips, and the same SSR testing machine used for the environmental tests described in this standard. 5.1.2 The SSR test specimens used for determining baseline material properties shall be machined from adjacent locations in the material and in the same position and orientation as the SSR test specimens used for the environment tests to minimize variation in the properties of the SSR test specimens. 5.1.3 All baseline tests on a particular material shall be performed using the same testing setup and SSR testing machine. 5.1.4 The results of these baseline tests may not produce the same material property values as conventional tensile tests performed with test specimens of different sizes or geometry or at different strain rates. 5.2 Because mechanical properties can vary through the thickness of the material, depending on the material history (e.g., coldworked rod), hardness measurements shall be taken to ensure consistency in the mechanical properties for the different SSR test specimens. These hardness measurements shall be made by performing hardness scans on the base material or by measurement on the blanks prior to SSR test specimen preparation. Hardness measurements shall not be made on the gauge section of the SSR test specimen. ` , , , ` ` , ` ` ` , , , , , ` ` , , ` , ` , ` , , , ` ` ` ` ` , , ` , , ` , ` , , ` -
5.3 A number of material properties may correlate with SCC performance. Consequently, all pertinent data on chemical composition, melting practice, conventional mechanical properties, heat treatment (e.g., aging), and mechanical history (i.e., percent cold reduction or prestrain) shall be included with the SSR test data developed in accordance with this standard.
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TM0198-2011 5.4 Each heat treatment and microstructure of the material of a fixed chemical composition shall be tested as though it were a different material.
_________________________________________________________________________ Section 6: Environmental Test Conditions 6.1 The test environment, including the exact temperature, pressure, and composition of the aqueous and gaseous phases, must be specified by the user and shall be recorded. 6.1.1 Two common approaches are used in SSR testing programs for screening CRAs for petroleum applications. 6.1.1.1 When CRAs are evaluated for a specific service application, the test environment that most closely simulates the corrosive environment found in that specific service application is specified. In this case, a variety of individual alloys representing various types of CRAs are then tested to evaluate their relative performance for that particular service environment to aid in reaching a final materials selection decision. 6.1.1.2 When a number of individual alloys within a specific type of CRA are to be evaluated as part of a general screening exercise, a suitable test environment that provides appropriate discrimination of performance is selected. In this case, the relative performance of individual alloys in a general environment can be evaluated, but the results may not be applicable to a different corrosive service environment. Test conditions for evaluation of CRAs for sour service 12 may be selected from those listed in Table E.1 in NACE MR0175/ISO 15156-3. The test levels provided in this table are not mandatory test environments and are not intended to represent actual service conditions. They are provided to the user of this standard as guidance, particularly if the material or manufacturing/fabrication process being evaluated is to be balloted for inclusion in NACE MR0175/ISO 15156-3.
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6.1.2 Both aqueous and gaseous phases shall be present at the specified test temperature and pressure.
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6.2 Aqueous Phase
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6.2.1 The aqueous phase of the test environment shall consist of a brine solution of specified composition. Distilled or deionized water shall be used to prepare the brine solution. The aqueous phase of the test environment should occupy approximately 80% of the test vessel volume at the intended test conditions. 6.2.2 Sodium bicarbonate is sometimes added to simulate the bicarbonate buffering found in some produced formation water. It generally increases the aqueous phase pH and can decrease the severity of the test environment from the standpoint of SCC. Sodium bicarbonate, added in solid form, is an optional constituent of test environments (see NACE MR0175/ISO 15156-3, Table E.1, row “pH”). 6.2.3 Elemental sulfur is sometimes added to simulate severe sour conditions, especially in conjunction with very high H2S partial pressure. The presence of elemental sulfur generally increases the severity of the test environment from the 13,14 standpoint of localized corrosion and SCC. Elemental sulfur, added in powdered form to the aqueous phase, is an 0 optional constituent of test environments (see NACE MR0175/ISO 15156-3, Table E.1, row “S ”). 6.3 Gaseous Phase 6.3.1 The gaseous phase of the test environment shall consist of a mixture of H2S, CO2, and water vapor and may also contain nitrogen, methane, or inert gas, as required, to reach the intended total pressure. 6.3.2 The gaseous phase shall be characterized in terms of the partial pressure (total absolute pressure times mole fraction) of H 2S and CO2 at the test temperature and pressure. The partial pressure may be expressed also as the multiple of the partial pressure of the species (e.g., H2S) in the test gas and the difference between the total absolute pressure and the vapor pressure above the test solution at test temperature and pressure. 6.3.3 The partial pressures of H 2S and CO2 shall be maintained within ±10% of the specified values. The actual concentration of each gas may be determined by a variety of analytical methods. A common procedure is to use a mass balance as detailed in Appendix B under the heading “Acid Gas Compositions.” 6.4 Test Temperature
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TM0198-2011 The temperature of the test environment in the test vessel shall be maintained within 3 °C (5 °F) of the specified test temperature (the average value during the test) for near-ambient temperature testing and within 5 °C (9 °F) for elevated temperatures (typically, 90 °C [194 °F] and greater). 6.5 Test Pressure 6.5.1 The pressure-measuring device shall have an accuracy of 1% of the maximum system pressure. 6.5.2 If the pressure is measured by a gauge, the maximum system pressure shall be greater than 20% and less than 80% of gauge full scale.
_________________________________________________________________________ Section 7: Mechanical Test Conditions 7.1 Extension Rate 7.1.1 The sensitivity of CRAs to hydrogen embrittlement or SSC is strain-rate dependent, as illustrated schematicall y in 15 Figure 2. Accordingly, the absence of embrittlement in a constant extension rate test at a specific strain rate should not be considered as an indicator that the CRA is fit for service; failure may still occur at a lower strain rate. The method is designed primarily for ranking purposes, and while in-house acceptance criteria exist, there is no general consensus. 7.1.2 For ranking/screening purposes, the strain rate shall be selected to ensure that the test is sufficiently discriminat ing, reasonably rapid, and gives acceptable repeatability and reproducibility. Intrinsically, the optimum strain rate may be CRA dependent. –6 –1
7.1.2.1 Experience has shown that a strain rate of 1 x 10 s gives satisfactory results for many CRAs (e.g., modified 13 Cr steels). –6 –1
7.1.2.2 When more rapid assessment is required, a strain rate of 4 x 10 s may be adopted. The strain rate of 4 x –6 –1 10 s can give satisfactory results for nickel and austenitic alloys, but for other CRAs this may lead to reduced repeatability and reproducibility. Care should be taken to ensure that the SSR test remains sufficiently discriminating for the purpose.
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Case 1 — Stress Corrosion Cracking Case 2 — Hydrogen Embrittlement or Sulfide Stress Cracking
Figure 2: Schematic presentation of the possible effects of strain rate on various types of cracking behavior. _________________________________________________________________________ Section 8: Test Procedure 8.1 Test Specimen/Test Vessel Assembly 8.1.1 The gauge section diameter (D1) of the SSR test specimen shall be measured to the nearest 0.025 mm (0.0010 in) and the value shall be recorded. 8.1.2 The SSR test specimen, grips (if exposed to the test environment), and the internal surfaces of the test vessel shall be cleaned and degreased. Care shall be taken thereafter not to handle or contaminate the gauge section of the SSR test specimen, exposed portion of grips, and internal surfaces of the test vessel. 8.1.3 The test vessel, SSR test specimen, and grips shall be assembled. If the test vessel and the SSR test specimen are dissimilar materials, electrical isolation between the test specimen and the grip assembly or between the SSR test specimen and the test vessel shall be maintained to prevent galvanic effects. The integrity of this electrical isolation shall be checked with an ohmmeter prior to testing and verified again after testing. 8.1.4 The test specimen/grip assembly or SSR test specimen shall be aligned with the test vessel ports (top and bottom) in 16 17 accordance with the alignment procedures and verification techniques for tension tests in ASTM E8 and ASTM E1012. 8.2 Test Environment Make-up 8.2.1 The aqueous phase (brine solution) shall be deaerated with inert gas (nitrogen, argon, etc.) prior to addition to the test vessel. The deaerated aqueous phase shall be prepared in a sealed vessel that is purged with inert gas at a rate of at least 3 100 cm /min for at least 1 h/L of brine solution. 8.2.2 The test vessel shall be deaerated prior to transferring the deaerated aqueous phase.
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TM0198-2011 8.2.2.1 Cyclic application of vacuum (less than –3.9 kPa [29 mmHg]) and inert gas purging (at least two cycles) is the most effective method for deaerating the test vessel. 8.2.2.2
Inert gas purging of the test vessel may also be used.
8.2.2.3 If a rotary oil pump is used to obtain vacuum, an oil mist trap shall be applied between the vacuum pump and the test vessel to prevent oil contamination in the test. 8.2.3 The deaerated aqueous phase shall be transferred into the deaerated test vessel. 8.2.3.1 If the deaerated aqueous phase is transferred into the deaerated test vessel under inert gas, no further deaeration is necessary. However, redundant deaeration procedures should be used to remove any oxygen contamination that may have occurred during the transfer. 8.2.3.2 If the deaerated aqueous phase is transferred into the deaerated test vessel by other means that do not maintain an inert gas blanket, redundant deaeration procedures shall be used to remove any oxygen contamination that may have occurred during the transfer. 8.2.4 Upon completion of the deaerated aqueous phase transfer and any subsequent deaeration procedures, the test vessel shall be pressurized with inert gas to the specified test pressure to check for leakage from tubing, valves, fittings, and seals. A simple procedure for this check is application of a mild soap solution to these areas. Soap bubbles indicate leakage of gas. 8.2.5 After successfully passing the leak check, the inert gas pressure shall be released to ambient pressure from the test vessel. If the test environment will involve a H2S partial pressure less than 100 kPa absolute (15 psia), the test vessel shall be evacuated to remove the inert gas prior to adding the test gas(es). 8.2.6 The test gas(es) shall be added to the test vessel. 8.2.6.1
When adding gases containing H2S, the test vessel shall be pressurized in a ventilated laboratory hood.
8.2.6.2 To obtain H2S partial pressures greater than 100 kPa absolute (15 psia), liquid H2S may be added on a mass basis. A specified number of grams of liquid H2S may be added to the test vessel using a small transfer pressure vessel that is weighed to the nearest 0.1 g before and after filling. This procedure adds the mass of H2S needed to produce the specified partial pressure under the test conditions. 8.2.6.3 The gas in the test vessel must be allowed to equilibrate with the aqueous phase by bubbling of the gas into the aqueous phase or agitating the test vessel. Either procedure should be performed at the starting test pressure. 8.2.6.4 Adjustments to achieve the specified test pressure may be made after heating the test vessel to the specified test temperature for a single-component gas phase; however, such adjustments should not be made for gas mixtures. 8.2.7 After filling the test vessel with the test environment, any excess H2S-containing gas should be released through a suitable scrubbing system to capture the H2S. 8.3 Testing Machine Set-Up 8.3.1 The test vessel containing the SSR test specimen and test environment shall be placed in the SSR testing machine. A schematic drawing of a typical SSR test system is given in Figure 3. 8.3.2 Refer to Appendix A for guidelines on safely performing tests with H2S. 8.3.3 The zero point and calibration of the load-monitoring system shall be checked and set for the required load range. 8.3.4 Precautions shall be taken to prevent compressive loading of the SSR test specimen by thermal expansion during the heating operation. 8.3.4.1 A tensile preload shall be applied to the SSR test specimen prior to heating and should be in the range of 230 to 450 N (50 to 100 lbf). This may be done manually or by using the drive mechanism of the SSR testing machine. 8.3.4.2 During heating, the preload on the SSR test specimen shall be monitored to ensure that it does not decrease to zero or become compressive.
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8.3.5 During heating, the pressure in the test vessel shall be monitored and controlled, if necessary, so that it does not increase beyond the working pressure limits of the test vessel.
8.3.6 Before starting the test, the pressure in the test vessel shall be monitored and controlled, if necessary, to achieve the specified test pressure.
Strip recorder
Signal conditioner
Speed and temperature controller
Load cell
Test vessel Heater bands
Thermocouple
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SSR testing machine
Figure 3: Schematic of typical SSR test system. 8.4 Test Initiation 8.4.1 The test temperature and test pressure shall be recorded immediately before initiating the test. 8.4.2 When the specified test temperature and test pressure have been attained, the SSR testing machine shall be activated to start loading the SSR test specimen at the desired extension rate. 8.5 Test Period 8.5.1 Data shall be recorded continuously throughout the test period with a suitably calibrated strip chart recorder or x-y recorder, or at frequent intervals of time using suitable data acquisition equipment that permits display of the load or stress on the SSR test specimen versus time, displacement, or strain. 8.5.2 Figure 4 shows typical load-versus-time plots for SSR tests.
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Test Environment
H2S
CO2
S
Cl –
Temperature
kPa abs.
psia
kPa abs.
psia
g/L
g/L
°C
°F
A
-
-
-
-
-
-
204
400
B
2,800
400
0
0
0
150
204
400
C
2,800
400
5,500
800
1
150
204
400
Figure 4: Typical load-versus-time plots for SSR test of a Ni-Fe-Cr-Mo alloy performed at an extension –7 –6 rate of 1 x 10 m/s (4 x 10 in/s) in several test environments. (Test Environment A is a reference inert environment.) 8.6 Test Termination 8.6.1 The test shall be considered terminated when fracture of the SSR test specimen is indicated by a decrease in the load on the test specimen to near zero. 8.6.2 Once the SSR test specimen has fractured, care must be taken to restrain the ends of the failed test specimen until the pressure has been bled off from the test vessel. This restraint may be performed either inside the test vessel or by the SSR testing machine load frame. Failure to observe this procedure may result in the failed ends of the SSR test specimen being ejected from the test vessel at high velocity and release of pressure and H2S-containing gas. 8.6.3 Gas pressure in the test vessel shall first be bled off to the brine solution vapor pressure and then the test vessel shall be cooled to 38 to 66 °C (100 to 150 °F). Cooling the test vessel at test pressure can result in sudden unexpected leakage. 8.6.4 All H2S-containing gases and brine solutions shall be captured by a suitable scrubbing system prior to disposal. 8.6.5 The test vessel shall be purged with inert gas to remove any residual H2S to a safe level. 8.6.6 The test vessel shall be opened and the two sections of the failed SSR test specimen removed. This part of the test termination procedure shall be performed in a laboratory hood under proper ventilation to reduce the risk of exposure to any residual H2S. 8.6.7 The SSR test specimen shall be rinsed with distilled water and dried. 8.6.8 The SSR test specimen shall be stored in a desiccator or other suitable noncorrosive environment until further evaluation or analysis is performed.
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TM0198-2011 _________________________________________________________________________ Section 9: Analysis and Reporting of Test Results 9.1 Two basic types of results shall be obtained from this SSR test: (1) Visual examination of the SSR test specimen gauge section for evidence of cracking. (2) Measurements of the ductility parameters of the SSR test specimen and comparison with the baseline material properties determined in air. 9.2 Visual Examination 9.2.1 Both halves of the failed gauge section of the SSR test specimen shall be visually examined under a low-power optical microscope at a magnification of at least 20X. 9.2.2 Based on the visual examination, one of the following classifications shall be assigned: Class 1—Normal ductile behavior (comparable with a SSR test specimen tested in air) with no indication of SCC on the primary fracture surface, and no indication of secondary cracking. Class 2—Ductile behavior with only slight loss (< 20%) of ductility from the baseline value determined in the air tests. Fissures may develop in the necked region of the gauge section immediately adjacent to the primary fracture surface, but no indication of SCC. Class 3—Substantial loss (> 20%) of ductility from the baseline value determined in the air tests. Fissures may develop in the necked region of the gauge section immediately adjacent to the primary fracture surface, but no indication of SCC. Class 4—Evidence of SCC in the gauge section by observation of SCC on the primary fracture surface or secondary cracking in the gauge section, or both. 9.2.3 Metallographic sectioning of the SSR test specimen gauge section and observation at 100X or scanning electron microscopy may be performed, if desired, to more fully characterize the failed SSR test specimens with respect to SCC behavior. These techniques are helpful in identifying Class 2 or Class 3 test specimens as defined in Paragraph 9.2.2. 9.3 Evaluation of Ductility Parameters
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9.3.1 Two ductility parameters shall be used in evaluating the results of the SSR test: (1) elongation and (2) reduction in area. Total time to failure should be measured for comparison purposes. Actual SSR test specimen elongation may be measured based on its physical extension; however, this measurement should not be relied on for quantitative determination.
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9.3.2 The change in cross-sectional area of the SSR test specimen shall be calculated as follows:
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9.3.2.1
For circular fracture surfaces, the change in cross-sectional area shall be calculated as shown in Equation (1):
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RA (%) =
Where:
DI2 - D2F DI2
(1)
x 100
RA = Reduction in area (%)
DI = Initial gauge section diameter in mm (in) DF = Final gauge section diameter at fracture location in mm (in) 9.3.2.2 (2):
For noncircular fracture surfaces, the change in cross-sectional area shall be calculated as shown in Equation
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RA (%) =
Where:
[DI2 - (CFA x CFB )] DI2
(2)
100
CFA = Major axis of fracture surface in mm (in) CFB = Minor axis of fracture surface in mm (in)
9.3.3 The SSR test specimen elongation shall be defined as the total plastic elongation of the test specimen at failure. 9.3.3.1 The plastic strain to failure (EP) shall be determined from the load-versus-time or load-versus-elongation curve by subtracting the elastic strain at failure from the total strain at failure (see Figure 5). NOTE: This parameter has been adopted because, in most testing, the displacement of the gauge section is not measured directly. Rather, the crosshead displacement is measured, and this includes a contribution from the displacement of the shoulders of the SSR test specimen and of the load train. Because these can vary from one test system to another, the calculated strain on the gauge section of the SSR test specimen at any time is sensitive to the test system. The actual strain rate on the gauge section in the elastic loading region also varies from one test system to another, despite similar values of the nominal strain rate. However, once yielding occurs, most of the increase in displacement in the crosshead is associated with the plastic deformation of the gauge section and the differences between test systems should be less significant. Accordingly, for those systems that fail beyond yield, meaningful comparison of data can be made by use of the plastic strain to failure.
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–1,100 mV in 3.5 wt% -1100 mV wt% NaCl NaCl
Test in air
800
) 600 a P M ( s s 400 e r t S
200 Etot 0 0.00
Eel
Ep 0.05
0.10
0.15
0.20
Strain Figure 5: Schematic illustration based on data for a super-13 Cr stainless steel showing basis for determining the plastic strain to failure (Ep) based on the total strain to failure (Etot) and the elastic contribution (Eel).
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9.3.3.2
If a load-versus-time curve is used, EP shall be calculated using Equation (3):
XTF σF XTPL 100 LI σPL LI
EP (%) =
(3)
Where: EP = Plastic strain to failure (%) X = Extension rate in mm/s (in/s) TF = Time to failure in seconds TPL = Time to proportional limit in seconds LI = Initial gauge length, in mm (in) (usually 25.4 mm [1.00 in]; see Paragraph 3.3.1.1) F = Stress at failure PL = Stress at proportional limit NOTE: For the case in which the stress at proportional limit (PL) (i.e., the stress at which the stress-strain curve departs from linearity) and the stress at failure ( F) are equivalent (i.e., no work hardening or necking prior to failure), the term [F/PL] in Equation (3) is equal to one and can be eliminated from the equation. Figure 6 shows a typical stress-strain curve for nickel alloys, which exhibit this type of behavior.
TM0198-2011
9.3.3.2
If a load-versus-time curve is used, EP shall be calculated using Equation (3):
XTF σF XTPL 100 LI σPL LI
EP (%) =
(3)
Where: EP = Plastic strain to failure (%) X = Extension rate in mm/s (in/s) TF = Time to failure in seconds TPL = Time to proportional limit in seconds LI = Initial gauge length, in mm (in) (usually 25.4 mm [1.00 in]; see Paragraph 3.3.1.1) F = Stress at failure PL = Stress at proportional limit NOTE: For the case in which the stress at proportional limit (PL) (i.e., the stress at which the stress-strain curve departs from linearity) and the stress at failure ( F) are equivalent (i.e., no work hardening or necking prior to failure), the term [F/PL] in Equation (3) is equal to one and can be eliminated from the equation. Figure 6 shows a typical stress-strain curve for nickel alloys, which exhibit this type of behavior.
800 ) a P600 M ( s s e r 400 t S
200
0 0.00
0.05
0.10
0.15
Strain Figure 6: Typical nickel alloy stress-strain curve, where there is no work-hardening 9.3.3.3
If a load-versus-elongation curve is used, EP shall be calculated using Equation (4):
EF
σ E F x PL x 100 L I σ PL L I
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(4)
Where: EP = Plastic strain-to-failure (%) EF = Elongation at failure in mm (in) EPL = Elongation at proportional limit in mm (in) NOTE: For the case in which the stress at proportional limit (PL) and the stress at failure (F) are equivalent, (i.e., no work hardening or necking prior to failure) the term [F/PL] in Equation (4) is equal to one and can be eliminated from the equation.
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TM0198-2011 9.3.4 The plastic strain at maximum load (Epmax) shall also be calculated. Using Equation (3), max (maximum stress) may be substituted for F and Tmax (time to maximum load) may be substituted for TF. In Equation (4), max may be substituted for F and Emax (elongation at maximum load) may be substituted for EF. 9.3.5 The comparison of the ductility parameters determined in the test environment with those determined in air shall be performed using the following ratios in Equations (5) and (6):
EpR(%) = Where:
EpA
x 100
(5)
EpR = Plastic strain-to-failure ratio EpA = Plastic strain-to-failure in air EpE = Plastic strain-to-failure in the test environment
RAR(%) = Where:
EpE
RA E RA A
× 100
(6)
RAR = Reduction in area ratio RA A = Reduction in area in air RAE = Reduction in area in test environment
9.3.6 Ductility ratios (i.e., plastic strain-to-failure ratio [EpR] and reduction in area ratio [RAR]) near 100 generally indicate high resistance to environmental cracking, whereas low values generally indicate low resistance to environmental cracking. 9.3.7 Test results shall be reported on a report form similar to that shown in Table 1.
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TM0198-2011 Table 1 NACE Uniform Material Testing Report Form (Part 1)—Testing in Accordance with NACE SSR Test Submitting Company Submitted by Alloy Designation
Chemistry
Submittal Date Telephone No.
Testing Lab General Material Type
Heat Number/Identification
C Mn P S Si Ni Cr Mo V Al Ti Nb N Cu Other
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Material Processing History Melt Practice (OH, BOF, EF, (A) AOD ) Product Form Heat Treatment (Specify time, temperature, and cooling mode for each cycle in process.) Other Mechanical, Thermal, Chemical, or Coating (B) Treatment (A)
Melt Practice: open-hearth (OH), basic oxygen furnace (BOF), electric furnace (EF), argon-oxygen decarburization (AOD). Examples: cold work, plating, nitriding, prestrain
(B)
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TM0198-2011 Table 1 (continued) NACE Uniform Material Testing Report Form (Part 2)—Testing in Accordance with NACE SSR Test Material Specimen Geometry: Length Environment
Standard
I
II
Nonstandard
III
Extension Rate
IV
Specimen mounting configuration (see Paragraph 3.1.2):
V
VI
VII
Other
Gauge Diameter
Gauge
(specify)
Partial pressure H2S (kPa abs. [psia])
Total Pressure
Temperature
Partial pressure CO2 (kPa abs. [psia]) –
Cl (g/L) Sulfur (g/L) Bicarbonate (g/L) Other (A)
Material Location Orientation ) Identification ` , , , ` ` , ` ` ` , , , , , ` ` , , ` , ` , ` , , , ` ` ` ` ` , , ` , , ` , ` , , ` -
(B
Properties in Air
Y.S.
(C)
U.T.S. Ep (%)
RA (%)
Values in Environment
Hardness
max
Ep (%) RA (%) Ep
(D)
SSR Ratio
Visual Rating (E) (Class)
Remarks
(%) EpR (%) RAR (%)
(A)
Location of test specimen taken from test piece may be OD, mid-radius (MR), center (C), or edge (E). Orientation may be longitudinal (L) or transverse (T). (C) Yield strength is assumed to be at 0.2% offset unless otherwise noted. (D) See Paragraph 9.3.5. (E) See Paragraph 9.2.2. (B)
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TM0198-2011 _________________________________________________________________________ References 1. G.M. Ugiansky, J.H. Payer, eds., Stress Corrosion Cracking: The Slow Strain-Rate Technique, ASTM STP 665 (West Conshohocken, PA: ASTM, 1979). 2 R.D. Kane, ed., Slow Strain Rate Testing for the Evaluation of Environmentally Induced Cracking: Research and Engineering Applications, ASTM STP 1210 (West Conshohocken, PA: ASTM, 1993). 3. NACE Standard TM0177 (latest revision), “Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments” (Houston, TX: NACE). 4. D.R. McIntyre, R.D. Kane, S.M. Wilhelm, “Slow Strain Rate Testing for Materials Evaluation in High Temperature H2S Environments,” Corrosion 44, 12 (1988): p. 920. 5. A.I. Asphahani, “Slow Strain Rate Technique and its Application to the Environmental Stress Cracking of Nickel-base and Cobalt-base Alloys,” in ASTM STP 665, Stress Corrosion Cracking: The Slow Strain Rate Technique, eds. G.M. Ugiansky, J.H. Payer (West Conshohocken, PA: ASTM, 1979): pp. 279-293. 6. R.D. Kane, D.F. Jacobs, G.A. Vaughn, H.R. Hanson, J.B. Greer, “Stress Corrosion Cracking of Ni- and Co-Based Alloys in Chloride-Containing Environments,” CORROSION/79, paper no. 174 (Houston, TX: NACE, 1979).
TM0198-2011 _________________________________________________________________________ References 1. G.M. Ugiansky, J.H. Payer, eds., Stress Corrosion Cracking: The Slow Strain-Rate Technique, ASTM STP 665 (West Conshohocken, PA: ASTM, 1979). 2 R.D. Kane, ed., Slow Strain Rate Testing for the Evaluation of Environmentally Induced Cracking: Research and Engineering Applications, ASTM STP 1210 (West Conshohocken, PA: ASTM, 1993). 3. NACE Standard TM0177 (latest revision), “Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments” (Houston, TX: NACE). 4. D.R. McIntyre, R.D. Kane, S.M. Wilhelm, “Slow Strain Rate Testing for Materials Evaluation in High Temperature H2S Environments,” Corrosion 44, 12 (1988): p. 920. 5. A.I. Asphahani, “Slow Strain Rate Technique and its Application to the Environmental Stress Cracking of Nickel-base and Cobalt-base Alloys,” in ASTM STP 665, Stress Corrosion Cracking: The Slow Strain Rate Technique, eds. G.M. Ugiansky, J.H. Payer (West Conshohocken, PA: ASTM, 1979): pp. 279-293. 6. R.D. Kane, D.F. Jacobs, G.A. Vaughn, H.R. Hanson, J.B. Greer, “Stress Corrosion Cracking of Ni- and Co-Based Alloys in Chloride-Containing Environments,” CORROSION/79, paper no. 174 (Houston, TX: NACE, 1979). 7. G.A. Vaughn, J.B. Greer, “High-Strength Nickel Alloy Tubulars for Deep, Sour Gas Well Applications,” 1980 SPE-AIME (3) Annual Meeting, paper no. 9240 (Richardson, TX: Society of Petroleum Engineers [SPE] and New York, NY: American Institute (4) of Mining, Metallurgical, and Petroleum Engineers [AIME], 1980). ` , , , ` ` , ` ` ` , , , , , ` ` , , ` , ` , ` , , , ` ` ` ` ` , , ` , , ` , ` , , ` -
8. ASTM G129 (latest revision), “Standard Practice for Slow Strain Rate Testing to Evaluate the Susceptibility of Metallic Materials to Environmentally Assisted Cracking” (West Conshohocken, PA: ASTM). 9. ASTM G111 (latest revision), “Standard Guide for Corrosion Tests in High Temperature or High Pressure Environment, or Both” (West Conshohocken, PA: ASTM). 10. ASTM D1193 (latest revision), “Standard Specification for Reagent Water” (West Conshohocken, PA: ASTM). 11. ISO 4287 (latest revision), “Geometrical Product Specifications (GPS) – Surface texture: Profile method – Terms, definitions and surface texture parameters” (Geneva, Switzerland: ISO). (5)
12. ANSI /NACE MR0175/ISO 15156-3 (latest revision), “Petroleum and natural gas industries – Materials for use in H2Scontaining environments in oil and gas production – Part 3: Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys” (Houston, TX: NACE and Geneva, Switzerland: ISO). 13. S.M. Wilhelm, “Effects of Elemental Sulfur on the Stress Corrosion Cracking of Nickel-Base Alloys in Deep Sour Gas Well Production,” CORROSION/88, paper no. 77 (Houston, TX: NACE, 1988). 14. A. Miyasaka, K. Denpo, H. Ogawa, “Environmental Aspects of ACC of High-Alloys in Sour Environments,” CORROSION/88, paper no. 70 (Houston, TX: NACE, 1988). 15. C.D. Kim, B.E. Wilde, “A Review of the Constant Extension-Rate Stress Corrosion Cracking Test,” in ASTM STP 665, Stress Corrosion Cracking: The Slow Strain Rate Technique, eds. G.M. Ugiansky, J.H. Payer (West Conshohocken, PA: ASTM, 1979): pp. 97-112. 16. ASTM E8/E8M (latest revision), “Standard Test Methods for Tension Testing of Metallic Materials” (West Conshohocken, PA: ASTM). 17. ASTM E1012 (latest revision), “Standard Practice for Verification of Test Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application” (West Conshohocken, PA: ASTM). (3)
Society of Petroleum Engineers (SPE), PO Box 833836, Richardson, TX 75083-3836. American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME), 8307 Shaffer Parkway, Littleton, CO 80127-4012. (5) American National Standards Institute (ANSI), 25 West 43rd St., 4th Floor, New York, NY 10036. (4)
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18. OSHA Rules and Regulations, 29 CFR 1910.1000 (Washington, DC: OSHA, 1996). 19. Chemical Safety Data Sheet SD-36 (Washington, DC: Manufacturing Chemists Association, 1950). 20. N. Irving Sax, Dangerous Properties of Industrial Materials (New York, NY: Reinhold Book Corp., 1984).
_________________________________________________________________________ Appendix A Safety Considerations in Handling H2S (Nonmandatory)
This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this standard is not required to follow, but may choose to follow, any or all of the provisions herein.
Toxicity H2S is perhaps responsible for more industrial poisoning accidents than is any other single chemical. A number of these accidents have been fatal. H2S must be handled with caution, and any experiments using it must be planned carefully. The OSHA maximum allowable concentration of H2S in the air for an eight-hour work day is 20 parts per million (ppm), well above the 18 level detectable by smell. However, the olfactory nerves can become deadened to the odor after exposure of 2 to 15 minutes, depending on concentration, so that odor is not a completely reliable alarm system. Briefly, the following are some of the human physiological reactions to various concentrations of H2S. Exposure to concentrations in the range of 150 to 200 ppm for prolonged periods may cause edema of the lungs. Nausea, stomach distress, belching, coughing, headache, dizziness, and blistering are symptoms of poisoning in this range of concentration. Pulmonary complications, such as pneumonia, are strong possibiliti es from such subacute exposure. At 500 ppm, unconsciousness may occur in less than 15 minutes and death within 30 minutes. At concentrations above 1,000 ppm, a single inhalation may result in instantaneous unconsciousness, complete respiratory failure, cardiac arrest, and death. 19
Additional information on the toxicity of H2S can be obtained from the Chemical Safety Data Sheet SD-36 and from Dangerous 20 Properties of Industrial Materials. Fire and Explosion Hazards H2S is a flammable gas and yields poisonous sulfur dioxide (SO2) as a combustion product. In addition, its explosive limits range from 4 to 46% in air. Appropriate precautions shall be taken to prevent these hazards from developing. Safety Procedures During Testing All tests shall be performed in a hood with adequate ventilation to exhaust all of the H2S. The H2S flow rates during the test shall be kept low to minimize the quantity exhausted. A 10% caustic absorbent solution for effluent gas can be used to further minimize the quantity of H2S gas exhausted. This caustic solution needs periodic replenishing. Provision shall be made to prevent backflow of the caustic solution into the test vessel if the H2S flow is interrupted. Suitable safety equipment shall be used when working with H2S. Because the downstream pressure frequently rises as corrosion product, debris, etc., accumulate and interfere with regulation at low flow rates, particular attention should be given to the output pressure on the pressure regulators. Gas cylinders shall be securely fastened to prevent tipping and breaking of the cylinder head. Because H2S is in liquid form in the cylinders, the highpressure gauge on the cylinder must be checked frequently, because relatively little time elapses after the last liquid evaporates and the pressure drops from 1.7 MPa (250 psi) to atmospheric pressure. The cylinder shall be replaced by the time it reaches 0.5 to 0.7 MPa (75 to 100 psi) because the regulator control may become erratic . Flow shall not be allowed to stop without closing a valve or disconnecting the tubing at the test vessel because the test solution continues to absorb H2S and move upstream into (6)
Occupational Safety and Health Administration (OSHA), 200 Constitution Ave. NW, Washington, DE 20210.
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TM0198-2011 the flowline, regulator, and even the cylinder. A check valve in the line should prevent the problem if the valve works properly. However, if such an accident occurs, the remaining H2S should be vented as rapidly and safely as possible and the manufacturer notified so that the cylinder can be given special attention.
_________________________________________________________________________ Appendix B Explanatory Notes on Test Method (Nonmandatory)
This appendix is considered nonmandatory, although it may contain mandatory language. It is intended only to provide supplementary information or guidance. The user of this standard is not required to follow, but may choose to follow, any or all of the provisions herein.
Reasons for Reagent Purity Water impurities of major concern are alkaline or acid-buffering constituents that would alter the pH of the brine solution and organic and inorganic compounds and could change the nature of the corrosion reaction. Oxidizing agents could also convert part of the H2S to soluble products such as polysulfides and polythionic acids, which may also affect the corrosion process. Alkaline materials (such as magnesium carbonate and sodium silica aluminate) are often added to (or not removed from) commercial grades of sodium chloride (NaCl) to ensure free-flowing characteristics, and these can greatly affect the pH. Trace oxygen impurities in the purge gas are much more critical if the nitrogen (or other inert gas) is continuously mixed with the H2S to obtain a lower partial pressure of H2S in the gas and hence a lower H2S concentration in the brine solution. Oxidation products could accumulate, resulting in changes in corrosion rate and/or hydrogen entry rate (see the paragraph below on Reasons for Exclusion of Oxygen). Test Specimen Preparation All machining operations should be performed carefully and slowly so that overheating, excessive gouging, cold work, etc., do not alter critical physical properties of the material. Uniform surface condition is critical to consistent SSR test results. Reasons for Exclusion of Oxygen Obtaining and maintaining an environment with minimum dissolved oxygen contamination is considered very important because of significant effects noted in field and laboratory studies. 1. Oxygen contamination in brines containing H2S can result in drastic increases in corrosion rates by as much as two orders of magnitude. Generally, the oxygen can also reduce hydrogen evolution and entry into the metal. Systematic studies of the parameters affecting these phenomena (as they apply to SCC) have not been reported in the literature. 2. Small amounts of oxygen or ammonium polysulfide are sometimes added to aqueous refinery streams in conjunction with careful pH control near 8 to minimize both corrosion and hydrogen blistering. The effectiveness is attributed to an alteration of the corrosion product. In the absence of sufficient data to define and clarify the effects of these phenomena on SCC, all reasonable precautions to exclude oxygen should be taken. The precautions cited in this standard minimize the effects of oxygen with little increase in cost, difficulty, or complexity. Cautionary Notes Cleaning solvents such as 1, 1, 1 trichloroethane, acetone, and other hydrocarbon liquids can be hazardous if the vapors are inhaled or absorbed through the skin. Many chlorinated hydrocarbon compounds are suspected of being carcinogenic and should be used only with the proper safeguards.
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TM0198-2011 Acid Gas Compositions The composition of gases in equilibrium with brine at elevated temperature can be determined by pressure (mass) balance as shown in Equation (B1): PT = PH2O + PH2S + PCO2 Where:
PT = PH2O = PH2S = PCO2 =
(B1)
total absolute pressure at temperature vapor pressure of brine solution at temperature partial pressure of H2S at temperature partial pressure of CO2 at temperature
PT should be determined by using a calibrated pressure gauge to measure the gauge pressure and then adding atmospheric pressure. PH2O should be obtained from data tables. The partial pressures of acid gases should be obtained from their mole fractions, as shown in Equations (B2) and (B3):
Where:
PH2S = (PT – PH2O) xH2S
(B2)
PCO2 = (PT – PH2O) xCO2
(B3)
xH2S = the mole fraction of H2S in the test gas mixture xCO2 = the mole fraction of CO2 in the test gas mixture
Mole fractions should be obtained from calibrated gas mixtures or from analysis of gas samples taken before and/or after testing at ambient temperature when the vapor pressure of H2O can be neglected.
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TM0198-2011
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ISBN 1-57590-051-3
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