超临界锅炉炉墙密封焊接裂纹原因分析及防治

Analysis and Prevention of Seal Welding Cracking in Supercritical Boiler Water Walls

轩岗电厂660 MW超临界锅炉炉墙密封焊缝多处出现裂纹。从材质、焊接工艺、塞块点固、环境温度、焊接结构等多方面进行分析,其原因在于:①15CrMoR钢焊接性较差,有较强的冷裂纹倾向;②鳍片切口边缘氧化铁、油污等杂质未得到彻底清理,焊后焊缝内含氢量过多及焊缝内缺陷严重超标,形成隐含的裂纹源;③施工环境温度较低,焊后冷却速度过快,熔敷金属组织转变不完全,有淬硬组织产生;④超临界机组锅炉管径小、管壁厚,管子刚度大、拘束度大,单位面积内的密封焊缝条数多、密度大,焊接应力大。鉴于此,制订了相应的防范措施和修复工艺,并在工程施工中获得了良好的效果。

It is observed that cracking occurs in the seal wehting seams of the 660-MW supercritical boiler water walls in Xuangang Power Plant. The analysis on the eracking from the aspects of materials, welding process, wall plug welding, ambient temperature and welding structure is performed. It cone, ludes that first, the welding performanee 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 ,nore than the allowable number required by the standard after welding, thus forming the potential craeking; third, the ambient temperature at the construction field is so low that the temperature of the wehted 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.