Failure analysis of S13Cr-110 telescopic tube used in an ultra-deep gas well

The failure reason and stress corrosion cracking mechanism of S13Cr-110 telescopic tube used in an ultra-deep gas well are discussed based on physical and chemical properties, operating con-ditions and construction processes. The results show that: stress corrosion cracking occurred in S13Cr-110 telescopic tube during acid fracturing, the crack initiated from the bottom of the corrosion pit in the inner wall of the telescopic tube and the crack propagation mode is inter-granular cracking. The reason for cracking is that S13Cr-110, the telescopic tube material, is exposed to high-chlorine-containing acid environment for a long time in the acid fracturing process, and the corrosion inhibitor used at the temperature of ultra-deep well has poor corrosion inhibition effect, resulting in inter-granular crack originated from the bottom of the corrosion pit on the inner wall of the telescopic tube. During the subsequent acidizing operations, the tele-scopic tube sustained a high circumferential tensile stress, stress corrosion occurs, and the stress corrosion cracks expand rapidly. It is suggested that the S13Cr-110 pipe string used in acidic environments with high chloride concentrations should be selected with appropriate corrosion inhibitor based on well depth and formation temperature.