电站锅炉中末级再热器金属管道焊接接头断裂原因分析

Analysis on the Causes of the Welded Joint Fracture of the Metal Pipes of the Final Reheater in a Power Station Boiler

国内某电站锅炉的末级再热器使用过程中,异种金属管的焊接接头发生断裂情况。对两种合金金属管进行焊接,对其进行宏观形貌观察,分析化学成分后对断裂原因开展深入探究。研究结果显示,焊接的接头位置沿合金金属管侧的熔合线出现了明显的脆性断裂,焊接位置的接头长期处于高温状态下,发生了扩散及迁移现象,由此造成合金管侧的熔合线位置集结大量碳化物,导致产生微观蠕变裂纹,降低了强度及韧性。而两种不同材质的合金金属管的膨胀系数也存在较大的差异,在高温环境下会产生大量热应力,致使异种金属管焊接接头在热应力及高温蒸汽压力作用下发生断裂。

During the use of the final reheater of a domestic power station boiler,the welded joints of dissimilar metal pipes were broken.Two kinds of alloy metal pipes are welded,the macroscopic appearance is observed,the chemical composition is analyzed,and the cause of the fracture is explored in depth.The research results show that the welded joint position has obvious brittle fracture along the fusion line on the side of the alloy metal tube.The joint at the welded position has been exposed to high temperature for a long time,and diffusion and migration have occurred,resulting in the position of the fusion line on the alloy tube side.A large amount of carbides accumulate,resulting in microscopic creep cracks,reducing strength and toughness.The expansion coefficients of the two alloy metal pipes of different materials are also quite different,and a large amount of thermal stress will be generated in a high temperature environment,causing the welded joints of the dissimilar metal pipes to fracture under the action of thermal stress and high-temperature steam pressure.