Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.

Abstract

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. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K THi * is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; 3 K THa is the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K JH is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K THi *, and the crack arrest threshold, K THa , were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustainedload cracking tests under constant displacement. In contrast, K JH , which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which subcritical crack extension is driven by internal hydrogen gas pressure.4 ACKNOWLEDGMENTS