While literature indicates that the applied loading rate (dK/dt) can affect environmentally assisted cracking (EAC) behavior, the quantification of dK/dt dependencies and mechanistic understanding of why the applied dK/dt influences EAC remain limited. In this study, a slow-rising stress intensity (K) framework was utilized to measure EAC kinetics over dK/dt ranging from 0.2 to 20 MPa√m/hr in Beta-C Ti, AA7075-T651, AA5456-H116, Monel K-500, 304L SS, Pyrowear 675, and Custom 465-H900 stainless steel immersed in 0.6 M NaCl at applied potentials known to promote modest EAC susceptibility. Results demonstrate that the crack growth rate (da/dt) exhibits two characteristics regimes of behavior with increasing dK/dt across multiple alloys. In particular, a ‘plateau’ regime where da/dt is independent of dK/dt was observed for elevated dK/dt, while a ‘linear’ regime where da/dt linearly scales with dK/dt was noted for slow dK/dt. These findings are analysied in the context of stress- and strain-controlled failure criteria and the environmentally modified Ritchie-Knott-Rice criteria for crack advance. The implications of these findings on recent testing standardization efforts for HEAC are then discussed.
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There is a common misperception that exposure to gaseous hydrogen makes construction steels brittle. Reality, however, is more nuanced. Whereas very high-strength steels can display characteristics of brittle fracture, low- to medium-strength steels remain ductile in gaseous hydrogen. Typical pressure vessel steels (e.g., quench and tempered Cr-Mo and Ni-Cr-Mo steels) and line-pipe steels (e.g., low-carbon steels) remain sufficiently ductile that fracture measurements do not satisfy the requirements of standardized linear elastic fracture mechanics. Generally, for steels with tensile strength 1,000 bar. This presentation reviews the requirements of linear elastic and elastic plastic fracture testing in the context of fracture tests in gaseous hydrogen that have been reported in the literature.
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With the ambition to reuse existing pipelines for hydrogen transport and/or storage, the industry is looking for ways to timely and reliably evaluate pipeline steels and welds for their hydrogen embrittlement sensitivity. A L485MB steel and weld are screened in this work, based on ex-situ tensile testing of hydrogen-charged specimens. Additionally, the effect of notches to generate stress triaxiality in tensile specimens is investigated . The paper reveals differences in the hydrogen embrittlement sensitivity of different materials, at different stress triaxiality levels.
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The ISO 11114 standard describes the disc test (method A) for selecting materials resistant to hydrogen embrittlement. However, the disc-shaped specimen geometry specified by this standard usually fails in the clamping area, making the test analysis more difficult. This work suggests two new sample geometries to obtain the disc rupture outside the clamping area.
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Conventional wisdom suggests hydrogen-assisted fracture occurs principally at slow testing rates as hydrogen requires time to diffuse to the region of elevated stress, such as the crack tip. The effects of testing rate were examined on ferritic-based steels by performing fast rate fracture tests in gaseous hydrogen at testing rates spanning four orders of magnitude.
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