Failure analysis of water wall tube in circulating fluidized bed boiler

In this work, the failure analysis of the water wall tube located in the circulating fluidized bed boiler is analyzed. Based on the data record, in the last 2 years of operation, 2 leak cases on the water wall tube were detected around the secondary air feeding port and the loop seal outlet presented in this paper. The mode and the root cause of the failure analysis were investigated by metallography structure, microhardness test, SEM, EDX, visual inspection, spectrometry, and thickness measurement. The investigation showed that the internal deposit was formed by a mineral element and lead to overheating. Furthermore, fatigue failure was found during investigation mainly due to corrosion followed by internal pressure and thermal fatigue. Further investigation also revealed that increasing the number of microhardness near the defect caused by overheating from the welding effect.