The need for more adequate engineering data and a better theoretical understanding of sulfide cracking has led to a more thorough study of several variables involved in the sulfide cracking of carbon steel. Hardness, yield strength, stress and microstructure were the primary metallurgical variables studied; sulfide concentration and pH were the environmental factors considered. Both failure, no-failure and time-to-failure data were used as dependent variable. A number of alloy steels were tested.
In general, it was found that the time to failure increased with decreasing hardness, decreasing stress, decreasing H2S concentration and increasing pH. Failures occurred even down to 0.1 ppm H2S in solution. Useful hardness limits for carbon steel for various stress and H2S concentrations were developed and used in field operations. However, it was found that excessive cold work can render almost any steel susceptible to sulfide cracking. K-Monel was the only alloy tested that remained immune to cracking failure at high load and at yield strength above 100,000 psia. It was postulated that the time to failure may be related to the time required for hydrogen to diffuse into the steel and reduce ductility sufficiently to allow crack propagation. Crack initiation may be due to the reduction in true fracture stress which accompanies hydrogen entry into steel.
