Stress corrosion cracking (SCC) is a catastrophic form of corrosion that results from a combination of tensile stress and a corrosive environment. The cracking is invisible on the surface and therefore, failure of the affected material — steel, for example — can occur without warning.
Stress corrosion cracking (SCC) refers to crack growth due to a combination of tensile stress and a corrosive environment. It only occurs in specific alloys in a small number of environments (i.e. aluminum alloys in the presence of chlorides). It can be caused by residual stresses induced by cold working, welding, heat treatment, or machining. The material fails through a series of microscopic internal cracks that cripple the material and can lead to sudden failure. Because much of the cracking is invisible from the surface, it is common for SCC to occur with no warning.
SCC is classified as a catastrophic form of corrosion and failure can occur even with very little material lost. It is responsible for one of the most deadly bridge failures in United States history. In 1967, the Silver Bridge in West Virginia failed and fell into the river. Stress in the eyebar joint caused a stress corrosion crack, which resulted in catastrophic failure and the deaths of 46 people.
SCC is highly undesirable, but there are many ways of preventing it. Most forms of pure steel aren’t even at risk, while the ones that are only have to worry about certain corrosive environments. As previously mentioned, both exposure to the corrosive environment and high tensile stresses are needed for SCC to occur.
In order to prevent the possibility of SCC, residual stresses must be reduced. This can be achieved by annealing or other surface treatments. Another method of prevention is removing susceptible metals from the corrosive environments entirely. When applicable, avoiding metals all together and using plastic composites is also effective at preventing SCC because plastic composite materials are not susceptible to corrosion.