Abstract: The internal-bore girth welds of the inlet/outlet coolant pipes on the ITER First Wall are located at structurally weak fulcrums; welding-induced distortion is therefore amplified, producing misalignment between the as-built pipe ends and the pre-installed stubs, and preventing final closure welding in situ. A thermo-elasto-plastic model incorporating the robotic pose concept was developed in SYSWELD to simulate bore-weld distortion of the outlet pipe and to quantify the six-degree-of-freedom displacement of the bent-pipe interface. The results demonstrate that the arc-strike location decisively influences the post-weld position and orientation of the assembly end, as well as the force and torque required for corrective alignment during installation. This sensitivity is traced to the circumferential dependence of axial shrinkage distribution, which is the direct cause of the observed differences. Comparative analyses indicate that deliberate selection of the arc-start position together with a dimensional allowance equal to the predicted weld distortion effectively reduces both welding-induced deformation and the assembly loads encountered in the field.

Key words: ITER, Welding deformation, First wall, Pipe weld, Numerical simulation

摘要： 国际热核聚变实验堆(ITER)第一壁进、出水管的内孔焊缝处在结构支点薄弱位置，焊接会造成结构整体严重变形，造成现场安装时第一壁水管接口与预留管口错位，无法完成安装焊接。基于热弹塑性理论，借鉴机器人学中的位姿概念，采用 SYSWELD 软件对出水管内孔焊接变形进行模拟，获得弯管安装接口位置的变化，实现了复杂姿态变化的定量比较。计算结果表明，焊接起弧位置显著影响焊后的安装端位置与姿态，以及现场安装时矫正位置与姿态所需的装配力与力矩。而造成这种差异的直接原因是起弧位置影响轴向焊接收缩量的分布。对比不同条件下的计算结果，认为合理选择焊接起弧位置、预留焊接变形尺寸余量，可以减少焊接变形、减少现场安装时所需的装配力与力矩。

关键词: ITER, 焊接变形, 第一壁, 管焊接, 数值模拟