Effect of Heat Treatment and Microstructure on the Corrosion and SCC of Duplex Stainless Steels in H2S/Cl− Environments

Abstract

A duplex stainless steel was heat treated at 2200 F (1200 C) (1 hour/water quench) and 2400 F (1315 C) (1 hour/water quench) to change the ferrite:austenite ratio from approximately 50:50 to 77:23 and 94:6, respectively. Slow strain rate (SSR) (4 × 10−6 s−1) experiments in brine solution containing H2S were conducted to determine the mechanism of environmentally caused cracking and to determine if these heat treatments affect cracking susceptibility. The experiments indicated that hydrogen is the primary cause of embrittlement at ambient temperature. Anodic stress corrosion cracking is the principal form of degradation at 350 F (177 C) in environments that contain H2S and chloride. Sulfides and chlorides act synergistically to facilitate loss of ductility of SSR tensile specimens at both low [75 F (24 C)] and high [350 F (177 C)] temperature. Heat treatment [600 and 500 F/250 h (316, 260 C)] to simulate downhole service age of cold worked tubes did not produce any deleterious effects with regard to susceptibility to embrittlement.