Environmental Cracking

Environmental cracking refers to a corrosion cracking caused by a combination of conditions that can specifically result in one of the following form of corrosion damage:

Stresses that cause environmental cracking arise from residual cold work, welding, grinding, thermal treatment, or may be externally applied during service and, to be effective, must be tensile (as opposed to compressive).

The cracks form and propagate approximately at right angles to the direction of the tensile stresses at stress levels much lower than those required to fracture the material in the absence of the corrosive environment. As cracking penetrates further into the material, it eventually reduces the supporting cross section of the material to the point of structural failure from overload. SCC occurs in metals exposed to an environment where, if the stress was not present or was at much lower levels, there would be no damage. If the structure, subject to the same stresses, were in a different environment (noncorrosive for that material), there would be no failure. Examples of SCC in the nuclear industry are cracks in stainless steel piping systems and stainless steel valve stems.

Stress cells can exist in a single piece of metal where a portion of the metal's microstructure possesses more stored strain energy than the rest of the metal. Metal atoms are at their lowest strain energy state when situated in a regular crystal array. Deviations from this lowest-strain state follow (reference):

See also:

Basics of SCC, Causes of SCC, EL AL crash, Environments & SCC, Pipeline SCC,SCC Guide, SCC definition, SCC of aircraft component, SCC Mechanism, Swiss roof collapse, Testing strategy, Williams explosions

Specific materials:

Aluminum alloys, Brass, High strength steel, Passivated steel, Stainless steel

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