Some Case Histories of Failure of Reheater Tubes

Abstract

Failure of reheater tubes in some coal-fired boilers are encountered very frequently. This is in spite of the fact that the operating pressure in reheater is far less than that of superheater. In reheater the pressure is about 30 kg/cm2 whereas in superheater it is 150 kg/cm2. A dominant factor causing premature failure is the overheating and consequently creep or hot corrosion failure. The reheaters begin to receive steam only when the turbine is started up i.e., they are not cooled at all for appreciably long time during boiler start up. The same is true in an emergency shut-down of the boiler. In order to avoid overheating, reheaters are usually of convective type & less frequently of platen type. They are arranged in the zone of moderate heating where the flue gas temperature is around 750°C. In some places reheaters are cooled at a start up and shut down by fresh steam supplied through an attEmperature.