The service life of high-pressure hydrogen storage vessels at fueling stations is dictated by fatigue crack growth. Standards such as the ASME Boiler and Pressure Vessel Code (BPVC) provide a methodology for calculating the fatigue-limited design life of high-pressure hydrogen storage vessels, in which one essential input is the fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationship measured for the material of construction in the service environment, i.e. hydrogen gas. These measurements must also be conducted at sufficiently slow cyclic loading frequency since decreasing the frequency usually results in faster crack growth rates. Generation of complete fatigue crack growth data sets according to standard test methods becomes very time consuming and expensive when these environment and frequency criteria are met. Two modifications to standard test procedures may reduce the time and associated costs related to this testing. One approach is to accelerate the rate at which ΔK changes with respect to crack extension. This can be accomplished by controlling the normalized K-gradient, C, where C = 1/K·dK/da. In addition, by using negative values of C (i.e. decreasing ΔK), multiple da/dN vs ΔK segments can be generated from a single test specimen. This paper summarizes the status of a project designed to identify the limits to which these two strategies may be employed to measure fatigue crack growth relationships for pressure vessel steels in gaseous hydrogen environments. These limits are defined as the bounds where loading history effects begin to alter the measured da/dN vs ΔK relationships.

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