Electrochemical potential dependence of SCC initiation in X60 pipeline steel in near-neutral pH environment

Stress corrosion crack (SCC) in pipelines directly affects the long-term safety service and has a major impact on the continuity of oil and gas delivery. The near-neutral pH SCC propagation process has been widely reported in the past decades, while the crack initiation mechanism is rarely studied in-depth. Here, the crack initiation behavior of x60 pipeline steel under different electrochemical potential levels was investigated by interrupted slow strain rate tensile testing (SSRT) and microstructural characterization. The experimental results show that the SCC initiation is dominated by hydrogen-facilitated anodic dissolution (AD) under the open circuit potential (OCP) environment, while it is by the hydrogen embrittlement (HE) under -1.1 and -1.2 VSCE cathodic potentials. All the SCC cracks in x60 pipeline steel show transgranular features, pathing through the grains in different crystallographic orientations, which showed dependence on the electrochemical potential of the steel: initiation via slip-enhanced dissolution of {110}//ND or {112}//ND texture under OCP environment, but mostly by quasi-cleavage cracking of {100}//ND texture under -1.1 and -1.2 VSCE cathodic potentials.