API TR 934-F Part 3

This Technical Report conveys the results of API-sponsored research to: (a) quantitatively characterize the internal hydrogen-assisted cracking (IHAC) resistance of modern 2¼Cr-1Mo-¼V steel, in both base metal and weld metal product forms and including the effect of stressing temperature, (b) scope the hydrogen environment?assisted cracking (HEAC) resistance of 2¼Cr-1Mo-¼V base metal, (c) understand the mechanism(s) for the IHAC and HEAC behaviors of Cr-Mo and Cr-Mo-V steels, centered on H interactions with microstructure-scale trap sites, and (d) assess application of data and understanding of IHAC and HEAC to determine the role of subcritical H-assisted cracking on a minimum pressurization temperature estimate relevant to thick-wall hydro-treating reactor vessels.

This work focuses on slow-stable subcritical H cracking, and did not examine the effect of H on the fracture toughness for unstable cracking. The temperature dependencies of internal hydrogen-assisted cracking (IHAC) of 2¼Cr-1Mo-0.3V base plate and weld metal were characterized using slow-rising displacement loading and elastic-plastic fracture mechanics analysis of crack growth measured through direct current potential difference. This test method provides a conservative measure of susceptibility of alloy steels to hydrogen-assisted cracking.