Cracking reason of water wall tube of a supercritical boiler

The cracking and leakage accident of water wall tube of a supercritical boiler occurred during operation. The causes of cracking and leakage of water wall tube were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope and energy spectrum analysis. The results show that the cyclic thermal stress caused the inner and outer walls of the water wall to form a crack source. Under the interaction of corrosive flue gas and thermal fatigue, the outer wall cracks continued to expand to form a penetrating transverse fatigue crack, which led to the leakage of the water wall tube.