Failure Analysis of T91 Finish Superheater Tube in 660 MW Supercritical Thermal Power Plant

In this work, a failure investigation of T91 boiler tube steel from the finish superheater zone of a 660 MW supercritical thermal power plant is carried out. The failure was reported after three years of service in the superheater zone of the PPGCL thermal power plant in Prayagraj, India. The failure occurs at a 90 degrees bend section of the tube where the thickness of the tube reduces significantly at the outer side of the tube. The SEM/EDS analysis revealed the steam side exfoliation of the iron oxides, further reducing the tube's bend section thickness. The crack was initiated due to high stress at the thin wall bend section caused by improper bending and exfoliation from the inner wall of the tube. The XRD analysis shows the precipitation of the coarse chromium carbide phases, which promotes the growth of cracks and leads to the failure of the tube.