LIFE ASSESSMENT OF TERTIARY SUPERHEATER TUBE IN A THERMAL POWERPLANT

摘要

Life assessment of tertiary superheater tubes in a thermal powerplant was performed. Data relating to causes of corrosion attack at the tube outer surfaces, operating conditions, materials selection, and fuel usage were collected for life assessment of the superheater tubes. The estimated values of critical remaining life were between 5-41 years. The most critical position for inspection and maintenance of tertiary superheater tubes that showed 5 years of remaining life, was position E. In the area around this position, high content of sodium (Na) and vanadium (V) in fuel may cause oil ash corrosion. Na and V were observed in the scales on the corroded tubes. Observation of the corroded tube microstructures, using metallography revealed an accumulative of carbides at the grain boundaries and cracks at outer surfaces of the tubes. The presence of coarse carbides and cracks would accelerate the corrosion rates.