根部成形及错边量对不等壁厚环焊接头局部应变集中行为的影响

Effect of Root Forming and Misalignment on Local Strain Concentration Behavior of Girth Weld Joint with Unequal Wall Thickness

目的探究高钢级管道不等壁厚环焊接头的局部应变集中规律,揭示其局部开裂的根本原因。方法采用STT半自动根焊+自保护药芯焊丝半自动焊填充、盖面的方式焊接X80管道不等壁厚环,并利用DIC技术对3种不同错边量及根部成形的不等壁厚环焊接头进行全壁厚拉伸,观察其在拉伸过程中的应变规律。结果不等壁厚环焊接头的应变集中主要发生在薄壁侧根部焊趾与厚壁侧盖面焊趾的连线区域,这是由于不等壁厚环焊接头受拉时会产生附加弯矩,该弯矩与薄壁侧根部焊趾及厚壁侧盖面焊趾处的应力集中相耦合使该区域发生应变集中。另外,错边量的存在会增大附加弯矩并使根部成形变差,因此错边量越大,应变集中区域面积越小、应变集中程度越高。定量分析结果表明,当薄壁侧管体远端应变达到0.5%时,3类成形接头根部最大应变分别为0.83%、9.60%、11.88%,盖面处最大应变分别为1.00%、7.10%、10.60%。结论大的错边量或差的根部成形会使不等壁厚环焊接头局部出现严重的应变集中,若与焊接缺陷相耦合可能会导致接头局部损伤,为裂纹的萌生与扩展提供条件。因此,在焊接过程中应增加接头的组对精度、减小错边量。

The work aims to explore the local strain concentration law of girth weld joints with unequal wall thickness of high grade steel pipes and reveal the root cause of local cracking.STT semi-automatic root welding and self-shielded flux-cored wire semi-automatic welding were adopted to weld the X80 pipe with unequal wall thickness,and the digital image correlation(DIC)technology was used to carry out the full wall thickness tensile process of three different misalignment and root formed girth weld joints with unequal wall thickness,and the strain law in the tensile process was observed.The strain concentration of the joint with unequal wall thickness mainly occurred in the connection area between the root weld toe of the thin wall side and the weld toe of the thick wall side cover,which was due to the additional bending moment generated when the joint of unequal wall thickness was under tension,and the coupling of the bending moment with the stress concentration at the root weld toe of the thin wall side and the weld toe of the thick wall side cover caused the strain concentration in this area.In addition,the misalignment also increased the additional bending moment and made the root forming worse,so the larger the misalignment,the smaller the area of strain concentration area and the higher the level of strain concentration.Quantitative analysis showed that when the remote strain of the pipe body reached 0.5%,the maximum strain at the root of three formed joints was 0.83%,9.60%and 11.88%respectively,and the maximum strain at the cover was 1.00%,7.10%and 10.60%respectively.Large misalignment or poor root forming will cause serious strain concentration in the local part of the joint with unequal wall thickness.If coupled with welding defects,it may lead to local damage of the joint,providing conditions for crack initiation and propagation.Therefore,in the welding process,the assembly accuracy of the joint should be increased and the amount of misalignment should be reduced.