Investigation Into the Likelihood of Thermal Fatigue Damage to Furnace and Superheater Tubes Caused by On-Load Water Deslagging

Abstract

Boilers operating on brown coal from the Morwell Open Cut in Victoria require frequent off-load cleaning outages because of severe ash deposition on heating surfaces. The problem has been alleviated by the use of on-load water deslaggers in the furnace, and consideration has been given to a similar application in superheaters. Water deslagging in superheaters has been studied by: (a) plant tests to determine cleaning effectiveness and metal temperatures during operation, and (b) laboratory tests where tubes and test specimens have been subjected to repeated water quenching to investigate the initiation and propagation of thermal fatigue cracking. A similar study into the effects of water deslagging of furnace tubes is in progress. Results have shown that cracking will occur in superheater tube steels when the metal temperature is above 500 deg C. Tests on plain carbon steel furnace tubes at 450 deg C have produced cracking, but no significant cracking was found after 64,000 cycles of quenching from 325 deg C.