Fitness for Service of Cracked Valve on High Pressure Steam Line Header

摘要

Cracks were found on 24" valve at steam header line. This header connects high pressure steam header from Module I to Module II, and the valve was installed in 1989. The cracks occurred at valve body and bonnet with total of seven cracks were observed. Due to risk of valve failure; fitness for service needs to be conducted to ensure valve service ability. Alternating current potential drop technique was used for measuring crack depth. The crack dimensions and material properties are used as input for finite element analysis modelling. Fatigue growth analysis and fracture mechanic analysis were conducted also to obtain of valve properties. The assessment shows that the valve is still in safe region based on API 579 Level 3 assessment but need to monitor the valve service temperature.