Water wall leakage of a ultral supercritical boiler was occurred in November 2015. In order to find out the causes of this leakage

site inspections and experimental analysis were carefully conducted

together with investigations on the same type boilers in the other thermal power plants. It had been concluded that the design flaws inherent to this type boilers were the main reason for the leakage. Due to difficulties in adjusting and controlling

thermal fatigue occurred at the entrance area of water wall intermediate mixed heads

which then lead cracking and leakage at the weld-fusion line because this area was the weakest site.