Sustained load cracking

Sustained Load Cracking (SLC) is a type of corrosion that occurs in certain alloys when they are subjected to a constant tensile stress in a corrosive environment. This phenomenon is also known as stress corrosion cracking (SCC).

Overview

Sustained load cracking is a complex process that involves the interaction of mechanical stress and a corrosive environment. The cracking occurs when a susceptible material is exposed to a specific corrosive medium under tensile stress. The stress can be either applied (external) or residual (internal). The cracking is often intergranular, meaning it follows the grain boundaries of the material.

Mechanism

The exact mechanism of sustained load cracking is still a subject of research, but it is generally agreed that it involves a combination of anodic dissolution, hydrogen embrittlement, and microvoid coalescence. Anodic dissolution refers to the removal of material at the anode (or positive electrode) in an electrochemical cell. Hydrogen embrittlement is a process by which various metals become brittle and fracture due to the introduction and subsequent diffusion of hydrogen into the metal. Microvoid coalescence is a mechanism of ductile fracture where small voids or flaws in the material combine to form a crack.

Susceptible Materials

Certain alloys are more susceptible to sustained load cracking than others. These include high-strength aluminum alloys, stainless steel, and nickel-based alloys. The susceptibility of a material to SLC is influenced by its microstructure, the environment, and the level of stress to which it is subjected.

Prevention and Mitigation

Prevention of sustained load cracking involves controlling the environment, the material, and the stress. This can include using materials that are less susceptible to SLC, reducing the level of stress, or altering the environment to make it less corrosive. Mitigation strategies can include regular inspection and maintenance, stress relief treatments, and the use of protective coatings.

See Also

• Corrosion
• Stress corrosion cracking
• Hydrogen embrittlement
• Microvoid coalescence