Failure analysis of boiler water wall-tubes at a power generation plant

The subject boiler is a suspension type provided on its sides with IK boxes as accesses for retractable soot blowers to clean up the inside of the boiler using steam. The working temperature and pressure of the boiler water wall-tubes are 693 degrees F (367 degrees C) and 2935 psi (20.5 MPa). After approximately 91317 hr. of operation, failure of several boiler wall tubes has taken place at IK boxes. Investigation disclosed that the present failure is attributed to thermal fatigue. Thermal fatigue damage was accelerated as a result of repeatedly rapid cooling by exposure of the external surface of the tubes to water droplets during soot blower function. In this regard, elimination of excessive strain caused by thermal cycles due to the rapid cooling cycles is necessary to eliminate this problem.