Research and Application of 350 MW Unit Water Wall Crack Failure

Abstract

A vast number of cracks have appeared at the exit of the boiler vertical water wall, which causes the boiler outage during the 350 MW supercritical unit. To solve this problem, we analyze the characteristics of cracks and boiler-related operating curve is in operation. The study found that the main factor leading to the cracks at the exit of the boiler vertical water wall is thermal stress resulted from large-scale temperature deviations between pipes and rapid changes in pipe temperature. The thermal stress generally emerged under the low-load condition after the boiler turns to dry state. In addition, there is a correspondence between vertical water wall tube temperature fluctuations and changes in boiler feed water. We made the three following recommendations for the causes and characteristics of cracks at the exit of boiler vertical water wall. First, it is to minimize this type of boiler long-term low-load operation in the dry state. Second, the operating personnel shall monitor the vertical water wall outlet temperature under the low-load after the boiler turns to dry state. Finally, we increase the adjustment ability of automatic water supply and automatic coal supply to coal–water ratio.