Abstract: This paper presents analysis of a SA213 T91 grade reheater tube premature failure occurred in a super critical power plant. Visual inspection showed longitudinal opening on extrados of the bend tube. Microstructural changes such as creep cavity formation, oxide filled voids, grain growth, carbide coarsening were studied in detail with the aid of optical microscope and scanning electron microscope. Microscopic studies were also carried out to analyse the oxide scale formation and exfoliation on steam side of the tube. Observations confirmed that the super heater tube failed under prolonged overheating mechanism. High flue gas temperatures, frequent start-ups and steam side oxide growth/exfoliation lead to higher tube metal temperature which can be identified as root cause of failure.
Authors: Y. Ravi Kumar and Anand Varma
Keywords: T91, Failure analysis, Creep