Failure analysis: Sulfur stress corrosion cracking of S30432 stainless steel in the final super-heater

Abstract This paper presents the results of an investigation on the failure of the S30432 stainless steel tube on the final super-heater used in a 1000 megawatt supercritical power plant. To find out the failure causes, residual stress and hardness measurements were investigated by XRD and hardness testing machine, the microstructure of the crack region was investigated by scanning electron microscope equipped with energy dispersive spectroscopy micro-analysis. It revealed that there are large residual stresses in the failed bend area, and sulfur corrosion elements were found. The stresses originated from cold working without solution treatment and the elements originated from coal combustion. Besides, there is no plastic deformation in the crack region, which is characterized by “rock sugar”. In conclusion, the failure was principally owing to sulfur stress corrosion crack. Recommendations are given to minimize such failures.