Effect of CP on the occurrence of SCC in X80 and X100 pipe steels in a near-neutral pH environment

In this work, stress corrosion cracking (SCC) of X80 and X100 pipe steels under various cathodic protection (CP) levels in near-neutral pH environment was investigated. The results showed that X100 tended to form longer SCC cracks compared to X80 steel. The crack depth exhibited normal/quasi-normal distributions for both materials. Only a small fraction of cracks within the total number of cracks formed would propagate deep into the steel. It was revealed that the effect of CP on the occurrence of SCC in X80 and X100 steels was different. For X80 steel, CP exhibited an inhibiting effect on both SCC crack initiation and propagation by controlling the anodic dissolution process of steel and the inhibiting effect increased with CP level. The mitigating effect of CP on crack initiation was more significant than that on crack propagation. For X100 steel, it was observed that hydrogen evolution and absorption played an important role in crack initiation, while anodic dissolution of steel dominated the crack propagation process. The increase of CP level could cause more cracks to initiate but retard the crack propagation.