Stress Corrosion Cracking on an Insulated Austenitic Stainless Steel Pressure Vessel

摘要

Stress corrosion cracking (SCC) is one failure mode that may occurred on hot insulated austenitic stainless steel pressure vessels and piping. In 2007, Badak LNG experienced this problem on its Amine Regenerator pressure vessel where the shell are insulated and made of Austenitic Stainless Steel Grade 304L. The paper will share the fact and findings, failure analysis, improvement to prevent recurrence, repair methods and inspection. During the Train E overhaul in May 2007, cracks were observed on the shell exterior of Amine Regenerator pressure vessel. The cracks mostly occurred above the external vessel stiffening rings. Results of the failure analysis concluded that the pressure vessel failed by chloride induced stress corrosion cracking, due to moisture accumulation and the presence of chlorides at the affected locations in combination with a vessel operating temperature of 99 °C to 125 °C. Repairs were made by a combination of flush patching and weld built up methods. In addition to a 100% non destructive examination (NDE), a pneumatic leak test was conducted to ensure the integrity of the pressure vessel. Some improvements were implemented to prevent problem recurrence, i.e. coating application on shell external wall surface, implement new specification of thermal insulation and modify the stiffener ring. Further thorough inspections to ensure that no more SCC exists on the pressure vessel were performed using precise NDE tools, i.e. AE (Acoustic Emission) and TOFD (Time of Flight Diffraction). The results were no more cracks indication found. Currently, the pressure vessel has been in service for almost 10 years and no operational issues found related with SCC.