Case study: Cracking occurred in a (UNS S32100) type austenitic stainless steel nozzle fitting at a low point in the reactor effluent piping in a Gasoil Hydrotreater unit following start up. Normal preventive measures had been taken. The failed sample was removed for metallurgical analysis and determination of mechanism(s).
This standard practice provides mitigation methods to protect austenitic stainless steels and other austenitic alloys from polythionic acid (PTA) stress corrosion cracking (SCC) that can occur during a shutdown of refinery equipment. A shutdown includes the actual down time period and the contiguous periods required to shut down and start up the equipment.