Failure analysis of SS 304 HCu reheater tube of a supercritical power plant

Abstract

The conducive atmosphere for corrosion and simultaneous presence of stress in the material often results in the phenomenon of stress corrosion cracking (SCC). SCC has been reported in both sensitized and un-sensitized austenitic stainless steels widely used in industry. The present investigation is centred around a reheater tube made of stainless-steel SS 304 HCu, which failed in a newly constructed power plant when subjected to hydro test. Optical and electron microscopy was used in the analysis in the vicinity of the attachment weld on the reheater tubes. Even though microstructural investigation showed no sign of sensitization, the presence of chloride (Cl), identified through SEM-EDS scan, and localized strain, identified through EBSD scans near the failed region, confirmed stress corrosion cracking in the material. The results obtained during the investigation have clearly brought out the cause of stress corrosion cracking in reheater tube. Further, it was observed that the weld bead size played an important role in inducing residual stress in the material and the bead size was modified to address the localized stresses at the weld; this helped in solving the problem.