Hydrogen sulphide resistance of high sulphur microalloyed steels

Abstract

Sulphide stress cracking (SSC) and hydrogen-induced blister cracking (HIBC) studies were conducted on a set of seven microalloyed steels to determine the effects of alloy additions and sulphide shape control on their H2S resistance. Two commercial steels with a sulphur level of 0.025% exhibited poor SSC and HIBC resistance when tested in H2S-containing acidic environments. A laboratory steel with 0.006% S (sulphide shape controlled) gave good SSC and HIBC resistance. High sulphur (0.025%) laboratory steels alloyed with copper, chromium, nickel, aluminium and molybdenum, and rare earth metal (REM) treated for sulphide shape control, gave an H2S resistance equal to or better than the low sulphur steel. Addition of copper, chromium and nickel lowered the corrosion rate and improved both the SSC and HIBC resistance. Further addition of 0.5% Al improved the SSC resistance, while addition of 0.3% Mo improved both the SSC and HIBC properties. The low sulphur steel had the lowest hydrogen concentration after exposure to H2S environments, while alloy additions and REM treatment lowered the amount of hydrogen absorbed by the high sulphur steels. Molybdenum addition seems to be a suitable method to make high sulphur microalloyed steels resistant to H2S environments. © 1990.