This paper presents hydrogen embrittlement data on small scale test specimens machined from a recent production API 5L X65 pipe and tested under high pressure hydrogen gas. Specimens were coated and uncoated to interrogate whether masking may influence hydrogen embrittlement. This could be important for designing test programs that isolate hydrogen exposure to only the pipe ID surface as would be the case in actual hydrogen pipeline service conditions. The early-stage results presented here indicate that masking can significantly reduce hydrogen embrittlement. Further work is needed to assess the viability for pipe qualification programs targeting hydrogen service.
With growing interest to develop high pressure pipeline networks to transport large volumes of hydrogen gas, evaluation of small-scale test methodologies to properly characterize risk of embrittlement in pipeline steels has become a topic of significant research. Numerous variables related to specimen geometry, forms of loading, hydrogen exposure conditions, and gas purity, among others, are being examined.
Conventional laboratory practice typically requires clean, smooth, bare metal test coupons for most mechanical property tests used to quantify strength, ductility, fracture toughness and fatigue under hydrogen gas environments. In addition, when testing under hydrogen, typically all test specimen surfaces are exposed to hydrogen gas whereas in actual pipeline applications only the internal surface has direct hydrogen exposure. As such, current small scale testing practice may be overly conservative in terms of hydrogen absorption as the hydrogen flux that occurs in these small-scale test coupons may not represent the flux rate in actual pipeline service. That raises an important question; should all coupon surfaces except the ID surface be masked to more closely replicate the hydrogen gas exposure that would occur in actual pipeline service? That question is the basis for the research effort discussed in this paper.
This paper presents early-stage results of research performed by EWI to quantify the effect of surface oxides and epoxy coatings on hydrogen embrittlement using slow strain rate tensile (SSRT) and compact tension (C-T) fracture toughness test coupons prepared from a recent production sour grade API 5L X65 pipe and tested under high pressure pure hydrogen gas. The results obtained from as-machined, bare metal test coupons are compared with identical coupons masked with coatings used in sour service tests and specimens containing surface oxides produced by exposure to an oxidizing environment.
