采用压力管道在役焊接烧穿模拟试验装置,对在役焊接烧穿失稳进行了研究.观察了烧穿宏观形貌,测量了烧穿失稳熔池的尺寸,采用扫描电镜对失稳接头的表面和横截面微观形貌进行了观察分析,综合探讨了在役焊接烧穿的失稳机制.研究结果表明,在役焊接的变形为外凸变形,在带压水介质条件下焊接时,在熔池前端的高温区形成烧穿空洞.当焊接热输入逐渐变得较大时,热影响区晶粒变的粗大,晶间被氧化,晶间结构被破坏,产生裂纹,并且裂纹在应力作用下沿晶间扩展,降低了管道热影响区的材料强度,当此处剩余强度不足以承载管道内部压力时,发生烧穿失稳.%In-service welding burn-through instability was studied by using pressure pipeline in-service welding burn-through simulation device. By observing the burn macro-morphology, measuring the size of bum instability pool and, observing and analyzing the surface and cross-section microscopic morphology of instability joint through SEM, the burn instability mechanism was investigated. The result shows that,when conducting in-serv- ice welding under the condition of the outward convex deformation and the pressure water media, burn morphol- ogy is a cavity at the front high tempreture zone of pool. When the heat input is increased, the grain size of HAZ become coarse. The intercrystalline zone was oxidated and the intercrystalline construct was destroyed, which lead to cracks extending along the intercrystalline under the influence of stress and the decrease of strength of pipeline. When the residual strength of the pipeline was not enough to stand the pressure in the in- temal pipeline, the burn-through occurred.
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