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Hazard: Welding stresses increase the stresses acting on a structure during operation, reducing its load-bearing capacity； In the presence of stress corrosion, it will also exacerbate stress corrosion cracking. Welding deformation affects assembly quality; correcting it increases costs and also reduces plasticity. Reason: If a metal material is heated and cooled uniformly as a whole, allowing it to expand and contract freely, no deformation occurs during heating, and no stress is generated ； After cooling, it returns to its original shape and size, with no residual deformation or residual stress, as shown in Figure a below. If it cannot expand or contract at all during heating and cooling, then there are welding residual stresses but no residual deformation. Since welding involves local heating, there are certain rigid constraints during the heating and cooling processes. As shown in figure b, the metal is subjected to compressive stress during heating, resulting in plastic compressive deformation ； During the cooling process, since the metal cannot contract completely freely, tensile stress is generated and remains, which is known as welding residual stress. Measures to reduce and eliminate welding stress: (1) Design measures – Minimize the number and size of welds ； Avoid excessive concentration and intersection of welds ； Use a joint with lower stiffness ； In the tensile stress region, avoid geometric discontinuities. ⑵Process measures: Select the welding sequence and direction appropriately (horizontal first, then vertical) ； Hammer welding method ； Preheating method ； Heat treatment method ； Welding is performed using low wire energy. Measures for controlling and correcting welding deformation ⑴ Control measures: The counter-deformation method is used during pre-welding assembly ； Rigid fixation method ； Use a welding method with energy concentration ； Select a reasonable assembly and welding sequence. Correction Mechanical correction method ； Flame correction method.