Publications

Effects of low temperature on hydrogen-assisted cracking in 304L/308L austenitic stainless steel welds were investigated using elastic-plastic fracture mechanics methods. Thermally precharged hydrogen (140. wppm) decreased fracture toughness and altered fracture mechanisms at 293 and 223. K relative to hydrogen-free welds. At 293. K, hydrogen increased planar deformation in austenite, and microcracking of δ-ferrite governed crack paths. At 223. K, low temperature enabled hydrogen to exacerbate localized deformation, and microvoid formation, at austenite deformation band intersections near phase boundaries, dominated damage initiation; microcracking of ferrite did not contribute to crack growth. © 2013 Elsevier Ltd.

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The objective of this work is to enable the safe design of hydrogen pressure vessels by measuring the fatigue crack growth rates of ASME code-qualified steels in high-pressure hydrogen gas. While a design-life calculation framework has recently been established for high-pressure hydrogen vessels, a material property database does not exist to support the analysis. This study addresses such voids in the database by measuring the fatigue crack growth rates for three heats of ASME SA-372 Grade J steel in 100 MPa hydrogen gas at two different load ratios (R). Results show that fatigue crack growth rates are similar for all three steel heats and are only a mild function of R. Hydrogen accelerates the fatigue crack growth rates of the steels by at least an order of magnitude relative to crack growth rates in inert environments. Despite such dramatic effects of hydrogen on the fatigue crack growth rates, measurement of these properties enables reliable definition of the design life of steel hydrogen containment vessels. Copyright © 2013 by ASME.

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This document addresses polymer materials for use in hydrogen service. Section 1 summarizes the applications of polymers in hydrogen infrastructure and vehicle fuel systems and identifies polymers used in these applications. Section 2 reviews the properties of polymer materials exposed to hydrogen and/or high-pressure environments, using information obtained from published, peer-reviewed literature. The effect of high pressure on physical and mechanical properties of polymers is emphasized in this section along with a summary of hydrogen transport through polymers. Section 3 identifies areas in which fuller characterization is needed in order to assess material suitability for hydrogen service.

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Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. Thresholds for crack extension under rising displacement, K THi, for crack extension under constant displacement, KTHi*, and for crack arrest under constant displacement K THa, were identified. These values were not found to be equivalent, i.e. K THi < K THa < K THi*. The hydrogen assisted fracture mechanism was determined to be strain controlled for all of the alloys in this study, and the micromechanics of strain controlled fracture are used to explain the observed disparities between the different threshold measurements. K THa and K THi differ because the strain singularity of a stationary crack is stronger than that of a propagating crack; K THa must be larger than K THi to achieve equivalent crack tip strain at the same distance from the crack tip. Hydrogen interacts with deformation mechanisms, enhancing strain localization and consequently altering both the nucleation and growth stages of strain controlled fracture mechanisms. The timing of load application and hydrogen exposure, i.e., sequential for constant displacement tests and concurrent for rising displacement tests, leads to differences in the strain history relative to the environmental exposure history and promotes the disparity between K THi* and K THi. K THi is the only conservative measurement of fracture threshold among the methods presented here. © 2012 The Minerals, Metals & Materials Society and ASM International.