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通过对12Cr2MoWVTiB失效泄漏管件焊接接头裂纹产生部位、裂纹形态、金相组织及硬度、SEM断口分析及EMPA微区成分分析,结合锅炉运行实际工况判定,泄漏原因是由于合金管件焊接接头存在脆硬马氏体组织及承受较大的焊接残余拉应力,暴露于氧腐蚀环境下,在晶粒粗大、应力集中的熔合线处产生应力腐蚀裂纹,并由内表面扩展穿透管件壁厚所致。据此改进焊接工艺,增加焊前预热,控制焊接线能量,并提高焊后热处理温度及保温时间,得到了以贝氏体为主的接头组织,焊接残余应力得到大幅度释放,投运后效果良好,未再发生泄漏失效事件。
Based on the actual working conditions of the boiler, the cause of the leakage is the existence of brittle and hard welding joints of 12Cr2MoWVTiB fail-leak welded pipe joints, crack shape, microstructure and hardness, SEM fracture analysis and EMPA micro-zone composition analysis, Martensitic structure and withstand large welding residual tensile stress, exposure to oxygen corrosion environment, in the coarse grain, stress concentration of the weld line to produce stress corrosion cracking, and by the inner surface of the expansion of the thickness of the penetration caused by the pipe. According to this, the welding process is improved, the preheating before welding is increased, the welding wire energy is controlled, the post-weld heat treatment temperature and the holding time are increased, the bainite-based joint structure is obtained, the welding residual stress is greatly released, Good effect, there is no recurrence of leakage failure.