螺旋缝焊管成型应力对焊缝力学性能的影响及控制措施

Influence by Forming Stress on Weld Seam Mechanical Properties of Spiral Welded Pipe and Relevant Control Measures

针对螺旋缝焊管焊缝力学性能下降的问题,应用金属焊接及材料力学理论,对焊接熔池形成焊道过程及成型应力进行分析。分析认为:由于焊缝中不可避免地存在少量有害元素,焊接熔池在液固相和固液相相变转变过程中会产生脆性温度区,残余应力传递到脆性温度区,分子间距拉大,形成结晶间隙,使焊缝的力学性能下降。通过选择有害元素含量少的焊接材料和减小成型应力,可改善焊缝的力学性能。

Addressing the problem concerning weakening of weld seam mechanical properties of the spiral weld pipe, analyses of the welding pool-to-weld bead forming process and the forming stress are conducted with the metal welding and material mechanics theories. As a result, the fact as below is identified. Owing to the unavoidable existence of small quantity of harmful chemical elements in the weld, during the process where the welding pool is transforming from the liquid-solid phase into the solid-liquid phase, the brittle temperature zone is developed, and when the residual stress as transmitted into this zone, the intermolecular distance is increased, and this causes form- ing of the granular space, which results in weakening of the weld mechanical properties. Accordingly, it is possible to improve mechanical properties of the weld by means of using welding material containing less harmful chemical elements, and reducing the forming stress.