Abstract: It is observed that cracking occurs in the seal welding seams of the 660-MW supercritical boiler water walls in Xuangang Power Plant. The analysis on the cracking from the aspects of materials, welding process, wall plug welding, ambient temperature and welding structure is performed. It concludes that first, the welding performance of 15CrMoR steel is poor and there is a strong tendency to cold cracking; second, as the impurities at the edge of fin cuts, such as iron and oil are not completely cleaned up, the hydrogen content in the welded seams is over high and the defects in the welded seams are much more than the allowable number required by the standard after welding, thus forming the potential cracking; third, the ambient temperature at the construction field is so low that the temperature of the welded pieces drops too fast and the transformation of the deposited metal tissue is incomplete, leading to the formation of hardened tissue; fourthly, the welding stress is large due to the dense distribution of welded seams in the small-diameter and thick-wall tubes, the high tube stiffness and the high space limit. Therefore, appropriate precautions and repairing processes are developedand applied in the construction of the power plant with good results.

Key words: 15CrMoR steel, boiler seal welding, crack control