Study on the Pitting Corrosion Mechanism of S13Cr Tubing Under Extreme Oilfield Conditions

ABSTRACT This study employed a high‑temperature high‑pressure autoclave to investigate the corrosion behavior of S13Cr steel under the extreme service conditions of a gas well in the Bohai Oilfield. It aims to reveal the mechanisms of pit initiation and propagation under the synergistic effect of multiple factors (stress and corrosive media). Weight‐loss/stress corrosion tests, macroelectrochemical measurements, and SECM analysis were conducted comprehensively. Under an applied stress of 90% σ s , the pitting rate of S13Cr steel increased from 0.0702 mm/a (stress‑free condition) to 0.3064 mm/a, indicating that stress significantly aggravated the pitting susceptibility of S13Cr steel. Electrochemical analysis revealed that applied stress intensified the interfacial separation between inclusions (e.g., β‑(Mo, Cr) 2 C) and the matrix, leading to a progressive loss of repassivation capability. A vicious cycle of “inclusion‑assisted nucleation‐film damage‐pitting propagation” was ultimately established. Material selection and protection designs should therefore pay special attention to the coupling effect of stress and field conditions.