Sulfide stress cracking resistance of the welded WDL690D HSLA steel in H2S environment

Sulfide stress cracking resistance of welded high strength low alloy (HSLA) steel for high pressure vessel (called “WDL690D” steel) was evaluated in NACE “A” solution at room temperature. Though the failure time increased with the decreasing applied stress for either WDL690D base steel or its welded joint, the welded joint presented the lower threshold stress of about 53% YS compared with the base steel of about 65% YS, because of its inhomogeneous microstructure distribution. The hydrogen trapping efficiency of the WDL690D base steel and its welded joint was also investigated by measuring the permeability J∞L and the apparent diffusivity (Dapp). The results showed that the welded joint had lower trapping efficiency, but was more susceptible to SSC. In addition, the fractography of both the WDL690D base steel and its welded joint all exhibited a mixed ductile-brittle rupture when exposed in H2S environment under constant loading stress.