ROOT CAUSE FAILURE ANALYSIS OF FINAL SUPERHEATER TUBE FROM A COAL FIRED POWER STATION
M.M. Rahman*, A.A. Omar and J. Ahmad
AbstractROOT CAUSE FAILURE ANALYSIS OF FINAL SUPERHEATER TUBE FROM A COAL FIRED POWER STATION
M.M. Rahman1*, A.A. Omar and J. Ahmad2
1Centre for Power Plant Technology and Performance Optimization, College of Engineering, Universiti Tenaga Nasional, Putrajaya Campus, 43000 Kajang, Selangor, MALAYSIA.
2 Kapar Energy Ventures Sdn. Bhd., Jalan Tok Muda, Kapar 42200, MALAYSIA
This paper presents the root cause failure investigation of final superheater tube of unit 5 Stesen Janaelektrik Sultan Salahuddin Abdul Aziz (SJSSAA) Kapar or better known as Kapar Energy Venture (KEV). KEV is the largest power plant in Malaysia with a generation capacity of 2420 MW and the only power station in Malaysia with triple fuel firing capability, i.e., gas, oil, and coal. Boiler unit 5 at KEV uses coal to operate in generating 500 MW of electricity. On 25 November 2011, final superheater tube failed at unit 5 plant (u5 FSH P2T5). A fish mouth fracture was visible at the failed surface of the tube. The material type of the tube is ASM213 T91. The failed tube was sent for identification of the root cause failure. The investigation was conducted through (i) visual inspection, (ii) non destructive testing, (iii) hardness measurement, (iv) bending strength measurement, (v) microstructure evaluation, and (vi) Larson Miller Analysis for oxide scale temperature calculation and life assessment of the tube. After the investigation was done, there was no evidence suggesting that this tube ruptured because of overheating. From the oxide scale temperature calculation, the metal temperature of the tube was about 534.32 °C which did not exceed the design temperature. After revisiting the power plant and conducting a thorough investigation, it was revealed that a malfunctioned soot blower was located near the failed tube. The steam from the malfunctioned soot blower was hitting the failed tube continuously causing the surface of the tube to loose its ductility and strength. The internal pressure forced the tube to rupture and burst. Microstructures of the affected area help to identify one of the causes of the failure.
Keywords: Coal fired power plant; root cause failure investigation; mechanical properties; microstructure.