Effect of H2S Partial Pressure and pH of Test Solution on Hydrogen Induced Cracking of High Strength Low Alloy Steels

Abstract

Hydrogen induced cracking (HIC) is one of the hydrogen degradation phenomena of linepipe steels caused by H2S gas in the crude oil or natural gas. However, NACE TM0284-96 standard HIC test method is hard to satisfy the steel requirements for sour service application since it uses more severe environmental conditions than actual conditions. Therefore, in order to use steels effectively, it is required to evaluate HIC resistance of steels in the practical range of environmental severity. In this study, HIC resistance of two high strength low alloy (HSLA) steels being used as line pipe steels was evaluated in various test solutions with different H2S pressures and pH values. The results showed that the key parameter affecting crack area ratio (CAR) is H2S partial pressure of test solution when the pH value of test solution is not over 4. Hydrogen diffusivity was not a constant value, but it was rather affected by the hydrogen ion concentration (pH value) in the solution.