Failure analysis of superheater tube

• Non-uniformity at the tube wall thickness far from the failed region was observed.
• Suggested main root cause of failure was fireside corrosion.
• Long-term overheating had worsened the tube condition during the service.
• The formation of sigma-phase particles was revealed after 20 years service.

The failure analysis of a ruptured superheater tube after 20 years service in the oil-fueled boiler, as the typical problems in power plants, was investigated. A thin-lipped rupture at failed region was observed in superheater tube. By measuring the tube’s wall thicknesses far from failed region, non-uniformity was seen. The suggested main root cause of failure was fireside corrosion of the tube during the service. Because of low grade of used fuel, sodium, sulfur, and vanadium elements were observed at the outer surface, which caused continuously scale formation and reduction of wall thickness, by metal consumption. In addition, it seems that it has been worsened by occurrence of long-term overheating. Coagulation of carbides at both outer and inner regions of tube was observed that could prove the occurrence of overheating during the service. In addition, the formation of sigma-phase particles was revealed because of being in the susceptible temperature after 20 years in service. At the end, in order to prevent or decelerate such failure, some recommended remedies were suggested.