What is SCC?
SCC stands for Stress Corrosion Cracking.
When you combine a susceptible material, corrosive environment and stress/strain you have the conditions for SCC.
Stainless steels are a susceptible material, Saltwater is a corrosive environment that could enable SCC. Typically SCC occurs over 55 Deg C. However it is possible at lower temps if the environment and stress are sufficient.
Now you add tensile stress. This could be stress or stain caused by the parts use or manufacturing stresses like welding, forming etc.
SCC typically starts with stress/strain breaking the passive oxide layer at the crack tip exposing active material to the corrosive environment and corrosion starts. If the stress is above a threshold level then the crack will continue to propagate exposing more active material leading to more corrosion.
Interestingly the SCC occurs well below the yield strength of the material. So parts can fail well below the designers safety margins. What is yield strength you ask? Yeild strength where a material goes from elastic deformation to plastic deformation. IE bend it and it bounces back = elastic deformation, bend it and it stays bent = plastic deformation.
Perhaps my failed stainless widget has failed due to stress corrosion cracking? or a combination of SCC and IGC?