Slow Crack Growth in a High Strength Steel Exposed to H2-H2S Gaseous Mixtures

Crack velocities in heat treated AISI 4335V steel were measured as a function of H2S additions to an H2 gas environment. Tests were conducted at 22 to 27 C and 10 to 100 torr H2 gas pressure. Data are presented showing the relationship between crack velocity and hydrogen pressure, at constant stress intensity. Velocities were then measured for a 0.42 torr H2S gas environment, before and after generous dilution (down to 2.1 Vol%) with H2 gas. It is shown that crack velocities in the gas mixtures are three orders of magnitude higher than those predicted for the pure H2 gas diluent. In addition, the results are shown to agree with those expected for a hydrogen permeation controlled crack growth mechanism.