Publications

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The primary objective of this effort is to identify alloys to replace type 316/316L in hydrogen service for balance of plant (BOP) applications onboard fuel cell electric vehicles (FCEVs). Type 316/316L austenitic stainless steels are used extensively in hydrogen systems for their resistance to hydrogen embrittlement, which is attributed to the relatively high nickel content of type 316/316L alloys. Nickel content, however, drives the cost of austenitic stainless steels, thus type 316/316L alloys impose a cost premium compared to similar alloys with lower nickel content. Since the cost of BOP components is a large fraction of the cost of hydrogen fuel systems (even dominating the cost at low production volumes [1]), alternative materials are desired. In addition, type 316/316L alloys are relatively low strength, thus high-pressure components tend to be heavy to accommodate the stresses associated with the pressure loads. Higher-strength materials will reduce weight of the components (an added benefit for onboard components) and contribute to lower cost since less material is needed. However, engineering data to justify selection of lower cost and higher strength alloys for high-pressure hydrogen service are currently unavailable. Moreover, alloy design could enable low cost solutions to the specific needs of onboard hydrogen storage.

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Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. The reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impeded hydrogen diffusion across the banded pearlite.

This project was intended to enable SNL-CA to produce appropriate specimens of relevant stainless steels for testing and perform baseline testing of weld heat-affected zone and weld fusion zone. One of the key deliverables in this project was to establish a procedure for fracture testing stainless steel weld fusion zone and heat affected zones that were pre-charged with hydrogen. Following the establishment of the procedure, a round robin was planned between SNL-CA and SRNL to ensure testing consistency between laboratories. SNL-CA and SRNL would then develop a comprehensive test plan, which would include tritium exposures of several years at SRNL on samples delivered by SNL-CA. Testing would follow the procedures developed at SNL-CA. SRNL will also purchase tritium charging vessels to perform the tritium exposures. Although comprehensive understanding of isotope-induced fracture in GTS reservoir materials is a several year effort, the FY15 work would enabled us to jump-start the tests and initiate long-term tritium exposures to aid comprehensive future investigations. Development of a procedure and laboratory testing consistency between SNL-CA and SNRL ensures reliability in results as future evaluations are performed on aluminum alloys and potentially additively-manufactured components.

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This project addresses the following technical barriers from the Safety, Codes and Standards section of the 2012 Fuel Cell Technologies Office Multi-Year Research, Development and Demonstration Plan (section 3.8): (A) Safety data and information: limited access and availability (F) Enabling national and international markets requires consistent RCS (G) Insufficient technical data to revise standards.

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