Effect of hydrogen on the stress corrosion cracking behavior of X80 pipeline steel in Ku'erle soil simulated solution

Hydrogen was a key factor resulting in stress corrosion cracking （SCC） of X80 pipeline steel in Ku＇erle soil simulated solution. In this article, the effect of hydrogen on the SCC susceptibility of X80 steel was investigated further by slow strain rate tensile test, the surface fractures were observed using scanning electron microscopy （SEM）, and the fracture mechanism of SCC was discussed. The results indicate that hydrogen increases the SCC susceptibility. The SEM micrographs of hydrogen precharged samples presents a brittle quasi-cleavage feature, and pits facilitate the transgranular crack initiation. In the electrochemical impedance spectroscopy （EIS） measurement, the decreased polarization resistance and the pitting resistance of samples with hydrogen indicate that hydrogen increases the dissolution rate and deteriorates the pitting corrosion resistance. The potentiodynamic polarization curves present that hydrogen also accelerates the dissolution rate of the crack tip.

Environmentally assisted cracking behavior of U-bend specimens of Mg-RE alloys in chloride containing basic solution

Environmentally assisted cracking(EAC)behavior of two Mg-rare earth(RE)alloys such as Mg-Zn-Gd-Nd-Zr(EV31A)and Mg-Y-Nd(WE43C)alloys was investigated by using U-bend specimens.Open circuit potentials(OCP)of the U-bend specimens were monitored during the EAC tests in 0.1 M NaOH solution with different chloride concentrations at room temperature.EV31A(as-received,and peak aged)and WE43C(peak aged)specimens failed by SCC in 80 ppm chloride containing 0.1 M NaOH solution at OCP.When the EAC initiation occurred,the OCP decreased continuously.Irregular fluctuations of the OCP were observed in the absence of EAC.The OCP versus time profile could be used for monitoring EAC failure of the Mg-RE alloy components in real life service.Applied potentials did not cause cracking of the EV31A alloy in 80 ppm Cl-containing 0.1 M NaOH.Accelerated cracking was observed on the WE43C alloy in peak-aged condition under the applied potentials in the transpassive region when compared to that of OCP condition.Overaging decreased the susceptibility to cracking.