Tube Failures in Pulverised Coal Fired Boilers: An Investigation

High temperature corrosion problem in coal based thermal power plants has been matters of concern since the very early days of using the combustion of coals to raise steam to generate electricity. The problems could be separated into water wall corrosion, typically at temperatures in the range 350-450ºC and super-heater and re-heater corrosion, typically at metal temperatures in the range of 500-650ºC. Boiler tubes of coal fired thermal power plant subjected to prolong exposure at elevated temperature loose their load bearing capacity. The corrosion damage at inner and outer surface is responsible for reduction in wall thickness. In service water tubes from FBC boiler after a service life of ten years were collected. Failed tubes from FBC boilers were thoroughly investigated by visual inspection, cross-section and axial measurement, micrography and identification and characteristics of scale by XRD analysis to find the cause of failure. Main cause of failure was found to be corrosion with Fe2O3 as the main corrosion product. Other causes of boiler tube failure were short term overheating, erosion, decomposition of perlite into ferrite.