Study on Time Dependence of Trenches on SSC Initiation Limits for Low-Alloy Carbon Steels

Abstract In the oil and gas industries, pipelines are exposed to wet H2S environments (sour environments) that cause sulfide stress cracking (SSC) in low-alloy carbon steels in some cases. Recently, a judgment flowchart was proposed to determine the SSC susceptibility based on the corrosion pit morphologies or stress groove geometries on the steel surface observed in the early stages of SSC. However, whether the crack-like corrosion morphologies, called trench or fissure, that are formed in low-alloy carbon steels containing Ni cause failure remains unclear. In this study, the effects of trench on SSC initiation limits in the Ni-containing steel were investigated focusing on stress intensity factors (K). The K at the tips of various trenches were calculated by finite element analysis (FEA) applying the actual trench geometry at each test duration. The results suggest that the K value increases with trench growth in early stages and the K value of multiple trenches decreases due to the interference effects of notches in late stages of SSC test.