Technical Note: Microstructure Effects in the Stress Corrosion Cracking of Alloy 28 Under Sour Conditions

Alloy 28 (UNS N08028), an important candidate material for sour gas well service, was investigated for sensitivity to stress corrosion cracking under a sour environment simulating the down-hole service conditions. Three different heat samples were tested, and their microstructure was observed with an optical microscope and scanning electron microscopy (SEM); microchemistry was analyzed using energy-dispersive spectroscopy (EDS). Specimens with precipitates from heat A failed in stress corrosion cracking (SSC) testing, and their specimens without precipitates from heats B and C did not. The precipitated phase was rich in carbon, chromium, and molybdenum, and with high hardness. Some microcracks were observed around the platelet precipitates. The microstructure had a remarkable effect on the SCC of Alloy 28 under sour conditions, so the optimum microstructure was the key to Alloy 28 use in sour service conditions.