Root Cause Analysis of Failure in Superheater Tubes in a Power Plant

Abstract

This paper investigates the failure of superheater tubes, made of AISI 304 stainless steel, after 10 years of service in a power plant. The failure is in the form of fish mouth rupture and is mostly observed at U-bent elbows. Microstructure of the degraded samples was analyzed using optical and scanning electron microscopes. Phases were identified with energy-dispersive x-ray spectroscopy analysis as well. Results show that grain boundaries are heavily oxidized, and this has resulted in the embrittlement of the alloy. The fractography analysis showed that cracks propagated along grain boundaries, resulting in an intercrystalline fracture mode. At the end, some tentative remedial measures are recommended to mitigate similar failure in power plants.