The ripple-slow strain rate (R-SSR) technique is an alternative screening test to the conventional-SSR (C-SSR) method. Both methods assess susceptibility to environmentally assisted cracking (EAC) of corrosion resistant alloys (CRAs) and involve loading a NACE TM0198-compliant tensile specimen to 100% AYS (0.2% proof stress of actual yield strength) at a slowly applied extension rate. While the C-SSR specimen is monotonically strained to failure, a R-SSR tensile specimen is typically loaded to 100% AYS and subsequently cycled between 80% and 100% AYS until failure or for up to 250 cycles or 1 week of exposure.

This paper will provide a comprehensive review of the current understanding of the R-SSR technique. There are only a limited number of publications discussing the utility of the R-SSR technique, because running a R-SSR test is more complicated than a C-SSR test, and the added phenomenological/ mechanistic value of performing a R-SSR test is unclear. On the one hand, cycling loading may be more representative of certain in-field service conditions. On the other hand, there is evidence to suggest that cyclic loading facilitates film rupture during the tensile loading part of the cycle and repassivation of passive and/or protective film during load reversal, which may influence crack propagation. R-SSR may also be a better approach for martensitic stainless steels than C-SSR where cumulative strain in the conventional test may be detrimental to material performance. Regardless of the motivation, there is not a clearly defined and universally recognized acceptance criteria for assessing EAC resistance/ susceptibility by R-SSR.

A pilot research program was initiated to better understand the value of results generated by R-SSR in comparison to C-SSR. For this study, mod13Cr-110 alloy was used to evaluate and benchmark the two techniques. The overall goal of the project was to provide guidance on when to use R-SSR and how to interpret the test results.

Subject
Environmental cracking, Test methods, Strain rate, Materials, Autoclaves, Sour environments, Mechanical failure, Specimen preparation, Sulfide stress cracking, Fracture, Yield strength, Stress corrosion cracking, Ductility
Keywords:
Slow Strain Rate, Ripple SSR, Cyclic SSR, EAC, Sour Service Qualification, Mod13Cr-110
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2021
Association for Materials Protection and Performance (AMPP)
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