Causes of 15CrMoG steel water cooled wall pipe burst

A water cooled wall pipe burst accident occurred in a certain power plant. The causes of water cooled wall pipe bursting were studied using macroscopic observation, chemical composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that there were a large number of transverse transgranular cracks on the fire side of the tube, and the aging level of the tissue on the fire side was higher than that on the back side, but there was no obvious overheating characteristic. The cracks contained corrosive elements such as S. Frequent peak shaving of the unit and unstable operating conditions of the once-through boiler caused thermal fatigue cracking in the evaporation section where the temperature fluctuation of the pipes was large. Corrosive flue gas accelerated the propagation of cracks, ultimately led to pipe bursting accidents in the water cooled wall pipes.