A New Test for Evaluation of Susceptibility to Hydrogen Assisted Cracking in Dissimilar Metal Welds

摘要

Dissimilar metal welds (DMWs) in high strength steels with Ni-base filler metals are widely used in the oil and petrochemical industries. Welding followed by post weld heat treatment (PWHT) of such welds can result in the formation of extremely hard and brittle microstructures at the dissimilar fusion boundary which can be highly susceptible to Hydrogen Assisted Cracking (HAC). A new test has been developed for evaluation of the susceptibility to HAC in DMWs. This test consists of accelerated electrolytic charging with hydrogen of unnotched samples that are subjected to a constant tensile load normal to the dissimilar fusion boundary. The time to failure at particular stress is used to rank the susceptibility to HAC. The influence of welding and PWHT procedures on the susceptibility to HAC in DMWs of steel UNS K21590 (F22 steel) and filler metal UNS N06625 (Alloy 625) was assessed with this new test. The test proved to be very sensitive to the effects of PWHT conditions and welding bead sequence and successfully replicated the fracture morphologies of in-service DMWs failures. The new test provides a reliable tool for ranking the susceptibility to HAC in DMWs, for selection of optimal DMW material combinations, and for development and optimization of welding and PWHT procedures.