The Role of Hydrogen in Sulfide Stress Cracking of Low Alloy Steels

It is generally accepted that sulfide stress cracking (SSC) failures are the result of hydrogen embrittlement. However, the evidence heretofore has been mostly circumstantial. The purpose of this paper is to provide the experimental evidence which establishes the causality of hydrogen and the contributory roles of H₂S and anodic dissolution. These experiments show that H₂S is not directly involved in the SSC of low alloy steels, but rather (a) enhances the iron dissolution rate and (b) increases the relative amount of hydrogen absorption. Likewise, iron dissolution only acts to provide the driving force for hydrogen evolution and does not participate directly in the embrittlement process. The data explicitly show that SSC is a manifestation of hydrogen embrittlement.