Fracture toughness, fatigue crack propagation and creep rupture behaviour in thick section weldments of 3Cr-Mo pressurevessel steels developed for high-temperature/high-pressure hydrogen service

Fracture toughness, fatigue crack propagation and creep rupture properties have been examined in parent plate, weld metal and heat affected zone regions of thick section, commercial size weldments of a 3Cr-11/2Mo-1/2Ni pressure vessel steel, newly developed for improved performance in hydrogen and coal conversion environments. Mechanical tests were performed on the steel, both before and after prolonged (WOO h) exposure to hightemperature/ high-pressure gaseous hydrogen, and results compared to similar data obtained on another 3Cr-lMo 1/4V-Ti-B steel developed by the Japan Steel Works for coal conversion applications. Both plane-strain fracture toughness and creep rupture lives were found to be relatively unchanged in the weldment microstructures compared with parent plate, and they were affected little by environmental damage (hydrogen attack) induced by the prior hydrogen exposure. Creep properties, however, were found to be sensitive to post-weld heat treatment. Similarly, fatigue crack growth properties were only marginally affected by prior hydrogen-attack damage. except for tests on weld metal where, compared to the undamaged microstructures, growth rates below ~10-6 m cycle-1 were accelerated by up to an order of magnitude and fatigue thresholds decreased by around 25%.