Investigation of the Effect of pH on Stress Corrosion Cracking of API 5L X65 Steel by Impedance Spectroscopy and Slow Strain Rate Tensile Test

Abstract

In this study, impedance spectroscopy, slow strain rate tensile test, and scanning electron microscopy were used to investigate the susceptibility of API 5L X65 steel to stress corrosion cracking (SCC) in a sulfide brine solution with different pHs. According to the analysis of SSRT, steel was susceptible to SCC in a brine solution. The reduction area ratio in the air was measured to be 80.3%, which was more significant than the reduction obtained in a brine solution with different pHs. EIS in different strain time in acidic solution exhibited an inductive element, which indicated strong hydrogen penetration effects and sulfide stress cracking (SSC) of steel in this environment. EIS in neutral and basic brine solutions presented constant phase element behavior of the porous electrodes, which indicated SCC behavior of steel in these solutions. Phase angle analysis indicated that cracks grow considerably after 9 h. Additionally, SEM illustrated a ductile type of fracture in the air and brittle type of fracture in all brine solutions. At low pH, internal cracks showing the interaction of hydrogen embrittlement and SSC before fracture were detected. At medium and high pHs, SEM exhibited many secondary cracks perpendicular to the tensile load, indicating the SCC behavior of X65 steel in these media.