Minimizing and/or leiminating SCC risks

Due to the complexity involved, the best opportunity to reduce SCC risk is not in the piping process, sealing system or other stainless steel implementation phase of the operation. Ideally, consideration of SCC should begin at the design stage, including material selection, environmental control, and stress reduction and elimination. When the possibility of SCC is high, engineers must carefully design the piping system to minimize stress concentration. They must also consider the effects of using any corrosive solution. Equivalent pitting resistance values (PRENs) or equivalent pitting resistance values (PREVALUES) can be used as a good starting point for assessing the sensitivity of a given metal to stress corrosion cracking. Although the two forms of corrosion are not identical, they usually start in a similar way. This makes PREN also an indicator of SCC resistance. It is even more critical that the total concentration levels during the intended operation, particularly those involving chloride or sulfide, be analysed and estimated to ensure safety. As we emphasize in the Gap Corrosion guide, concentrations in specific areas or enclosed areas of piping processes or industrial environments will often far exceed the concentration levels of individual solutions used in the process. This means that while systems can be rated and designed to resist SCC based on known concentration levels, failures can occur as solutions collect in different areas over time and concentration levels fluctuate beyond the tolerances originally considered. Once a system is up and running, managing risk becomes trickier. Various metal coatings can provide additional protection, but also add another layer of maintenance complexity and worry. Heat treatment can also reduce residual stress, further improve resilience and prevent SCC. However, it is critical to ensure proper heat treatment, as temperature is an important variable in the formation of stress crack corrosion. If used improperly, the treatment can lead to the very conditions it is meant to prevent.