Steam boiler failure is not only caused by long term overheating but also short term overheating. Short term overheating can occur if temperature of pressure part (tube, drum, pipe and header) increases rapidly in short period exceeding limitation of design temperature. It can occur at the pressure part which has high operating temperature such as superheater, reheater, water wall, roof wall, boiler bank, screen tubes and downcomers and rarely occurs in low operating temperature of pressure part such as air heater and economizer.
When the tube has insufficient cooling from water flow inside and receives excessive heat input from combustion process will lead to short term overheating. To identifying that steam boiler is occurred this condition; operator may identify it with microscopic examination on the failure section tube (see figure 1).
Effort to reduce possibility of short tem overheating should be performed such as ensure feed water before supplied into steam boiler is fulfill the requirement, inspect on area which occur debris accumulation such as U bend-tube, drum and header. Circulation of water, blowdown, corrosion, and all of potential matter which disturb heat transfer should be monitored.