Sulphide Stress Cracking (SSC) is a form of hydrogen cracking of a metal under the combined action of tensile stress and corrosion in the presence of water and hydrogen sulphide. A SSC is a cracking mechanism in pipelines, facilities piping and any equipment that comes in contact with sour (wet H2S) service conditions. Among the most prone to sulphide stress cracking include valve trim, blowout preventer hard parts and tool joints.

Reference Definition by Wikipedia: Sulphide Stress Cracking (SSC) is a form of hydrogen embrittlement which is a cathodic cracking mechanism. It should not be confused with the term Stress Corrosion Cracking (SCC) which is an anodic cracking mechanism. Susceptible alloys, especially steels, react with hydrogen sulphide, forming metal sulphides and atomic hydrogen as corrosion by-products. Atomic hydrogen either combines to form H2 at the metal surface or diffuses into the metal matrix. Since sulphur is a hydrogen recombination poison, the amount of atomic hydrogen which recombines to form H2 on the surface is greatly reduced, thereby increasing the amount of diffusion of atomic hydrogen into the metal matrix. This aspect is what makes wet H2S environments so severe.

Related Definitions in the Project: The Metallurgy (Corrosion and Cracking)