Pienjännityskorrosio

Pienjännityskorrosio, known in English as Stress Corrosion Cracking (SCC), is a type of environmental degradation that occurs in metals when they are exposed to a corrosive environment while simultaneously being subjected to tensile stress. This phenomenon can lead to brittle fracture, even in materials that are generally considered ductile. The combination of tensile stress and a specific corrosive environment is crucial; neither stress nor corrosion alone would typically cause such a failure.

The stress can be applied externally, such as from mechanical loads, or it can be residual stress, often introduced during manufacturing processes like welding, machining, or heat treatment. The corrosive environment can vary widely depending on the metal alloy. For instance, certain stainless steels are susceptible to cracking in chloride-containing environments, while brass can experience SCC in ammoniacal solutions.

The mechanism of SCC involves the initiation of micro-cracks at the surface of the metal. These cracks propagate inwards, often at a slow but steady rate, driven by the applied tensile stress and the corrosive attack. The process can be complex and may involve electrochemical reactions and the formation of brittle corrosion products within the crack tip.

Preventing SCC involves several strategies. Reducing tensile stresses through post-weld heat treatments or shot peening can be effective. Modifying the environment to be less corrosive, for example, by controlling pH or removing aggressive species, is another approach. Material selection is also important, choosing alloys that are known to be resistant to SCC in the expected service conditions. Monitoring and inspection are also vital to detect the early stages of SCC before catastrophic failure occurs.