What Does Stress Corrosion Cracking (SCC) Mean?
Stress corrosion cracking (SCC) is a slow cracking process induced in metallic alloy pipelines by mechanical stress due to loading and the presence of a corrosive environment. SCC does not occur as a result of stress at pipe surface with flaws caused by corrosion, though concentration of stress does take place at such areas. The stresses that cause SCC are tensile in nature and are usually below macroscopic yield stress and static loading is mostly responsible for SCC.
Pipelines damaged by SCC can be repaired using trenchless rehabilitation methods such as cured-in-place pipe (CIPP), sliplining and pipe bursting.
Trenchlesspedia Explains Stress Corrosion Cracking (SCC)
SCC is generally observed in a combination of alloy and environment that forms a film on the surface of the metal. This film reduces the rate of uniform corrosion of the metal and hence is more potent in alloys that are resistant to corrosion and exposed to very corrosive environment.
In SCC, cracks propagate at a very slow rate until the stresses in the remaining portion exceeds the fracture strength. SCC happens in three stages - crack initiation, steady-state crack propagation and final failure. Environments conducive to SCC are generally aqueous as condensed layers of moisture or in bulk solutions.
Corrosive environment for one alloy may not be corrosive for another. SCC found in pipelines are either caused by high pH (9 to 13) or near-neutral pH (5 to 7).