How to control stress corrosion cracking
For stress corrosion cracking to occur, a sensitive material and an environment that causes damage of the material and sufficient of stress. There are hence, several approaches that can be used to prevent SCC, or to offer a suitable lifetime. In a perfect world, a stress corrosion cracking strategy will begin serving at the design level and will aim on the choosing material, the limitation of stress and the control of the environment. The skill of engineer depends on choosing a strategy to offer the desired functionality at the nominal price. For the basic containment pressure vessel in a nuclear reactor we certainly need a nominal damage risk. For the pressed brass decorative trim on a light switch, the occasional stress corrosion crack will not be a severe issue, however regular failures would have an unwanted effect on product returns.
Selection of material
The prime defense line in controlling stress corrosion cracking is to be familiar with the feasibility at the design and production levels. By selecting a material that is not sensitive to stress corrosion cracking in the application media and by correct treatment and production, after stress corrosion cracking problems can be prevented. Unfortunately, it is not always easy. Some conditions like high temperature water are highly rigorous and will result into stress corrosion cracking of many materials.
Mechanical factors like high yield strength, can be very tough to reunite with stress corrosion cracking resistance. Eventually the materials that are resistant to stress corrosion cracking will inevitably be very costly.
Presence of stress on the equipment components is one of the factors of stress corrosion cracking, a method of control is to prevent stress or actually decrease it below to the operation stress, however it may be feasible where the stress causes cracking is a residual stress occurred during welding or developing.
Residual stresses can be eased by stress relief annealing and is commonly used for carbon steels. They have the benefit of comparatively high threshold stress for most conditions, as a result it is very easy to decrease the residual stress to a sufficiently lower level. Oppositely austenitic stainless steels have a nominal threshold stress for chloride SCC. This paired with high annealing temperatures that are essential to prevent other issues like sensitixation and sigma phase embrittlement refers that stress relief is a rarely successful by controlling stress corrosion cracking for this system.
For large scale structures for which complete stress relief annealing is tough or impossible, slight stress relief around welds and other major areas may be significant. Although this should be done in a limited way to prevent the development of new zones of large residual stress and professional advice is recommended to follow an approach.
Stress can be relieved mechanically such as by hydrostatic testing beyond yield will result into even — out the stress and hence decreasing the peak residual stress. In the same way, shot peening introduces surface compressive stress and are advantageous to prevent Stress corrosion cracking.
Practically super alloys such as Inconel 625,alloy Inconel 718 wire and others are used in SCC sensitive conditions.