Abstract: The accident of tube cracking in platen superheater of boiler in a power plant was occurred soon after putting into operation, and the chink had features of overtemperature in short time and in long time. Combining the features of the chink, according to the metallographic analysis and hardness test of the cracked tube, some possible reasons were excluded which includes heat deviation of tube platen, misoperation of boiler operator and quality of the tube material. It is defined that there was foreign object in the tube which caused the tube operated in overtemperature at long time, so the oxide coating was created. The oxide coating peeled off during the start up and shutdown and blinded the tube, this caused the tube operated in serious overtemperature, and the tube cracking occurred finally.

Key words: boiler, platen superheater, tube cracking, overtemperature, oxide coating