What Does Chloride Stress Corrosion Cracking (CSCC) Mean?
Chloride stress corrosion cracking (CSCC) is a type of intergranular corrosion. Chloride stress corrosion involves selective attack of a metal along its grain boundaries. It occurs in austenitic stainless steel under tensile stress in the presence of oxygen, chloride ions and high temperature.
This form of corrosion is controlled by maintaining low chloride ion and oxygen content in the environment and use of low-carbon steels.
Corrosionpedia Explains Chloride Stress Corrosion Cracking (CSCC)
Chloride stress corrosion cracking is a localized corrosion mechanism like pitting and crevice corrosion. It requires a susceptible material and, depending on the material, sufficient levels of:
- Tensile residual stresses
- Time of exposure
CSCC can attack highly resistant austenitic stainless steel. In the formation of the steel, a chromium-rich carbide precipitates at the grain boundaries, leaving these areas low in protective chromium, and thereby, susceptible to attack. It has been found that this is closely associated with certain heat treatments resulting from welding. This can be minimized considerably by proper annealing processes.
A stainless steel that has been attacked by CSCC often has a web-like array of tiny surface cracks. In extreme cases, cracking is so pervasive that the metal can be broken off by hand. This pattern of corrosion occurs because the corrosion tends to follow the direction of highest residual tensile stress, but the actual cracking tends to locally relieve that stress.
CSCC can be controlled by maintaining low chloride ion and oxygen content in the environment and the use of low-carbon steels. Environments containing dissolved oxygen and chloride ions can readily be created in auxiliary water systems. Nickel controls susceptibility to chloride stress corrosion cracking. Materials with little or no nickel (duplex stainless steels and ferritic stainless steels) and those with high nickel content (superaustenitics and nickel-base alloys) have significantly better resistance to stress cracking.
Chloride stress corrosion cracking particularly concerns the nuclear industry because of the wide use of austenitic stainless steel, and the inherent presence of high tensile stresses associated with pressurization. It can also attack pipe-wells and tubing bundles.