Major cracking problems have occurred during fabrication of thick wall stainless steel (SS) piping for hydroprocessing units, primarily during heat treatment. This has resulted in costly repairs and schedule delays. These heat treatments are specified for some units to improve sensitization resistance and to reduce residual stresses, which provides the potential benefit of improved resistance to stress corrosion cracking (SCC). However, piping which has not been heat treated has been performing successfully for many years in numerous units. This paper provides some case histories of fabrication cracking and discusses the cracking mechanisms, suggests guidelines for when and when not to heat treat, and gives recommendations for minimizing the risk of cracking when heat treatment is required.
Key Words: Stainless steel, sensitization, stabilization, stress corrosion cracking