Failure investigation of secondary super-heater tubes in a power boiler

This study investigates a failure case in El-Kureimat thermal power station unit number 2 which experienced secondary super-heater tube failures. The failed tubes were reportedly found to be weeping during an operating pressure hydrostatic test, performed after a repair of another boiler component. The failure analysis indicated that the 304H tube leakage was due to stress corrosion cracking. The cracked tubes were studied and found to have undergone sensitization due to either welding or heat treatment of bent parts. Both service-exposed and laboratory specimens were studied in the current work.The service exposed samples that exhibited cracking were removed from the foresaid boiler. The laboratory specimens were used to verify proposed failure sequence and to evaluate the susceptibility of this alloy to sensitization. A correlation was made between artificially sensitized samples and stress corrosion cracking mechanism.