The so-called welding sequence refers to which part of the welding structure is welded first and which part is welded later, or which weld is welded first and which weld is welded last, that is, the welding sequence of each weld.
Improper selection of welding sequence affects the welding quality as follows:
(1) The welding sequence directly affects the stress and deformation of the weldment. If the selection is improper, it will cause excessive deformation or internal stress of the weldment, which not only reduces the quality of the weldment, but also causes the weldment to be scrapped in severe cases.
(2) Improper selection of assembly welding sequence often results in difficulty in welding of welds at certain positions, or even impossible to weld at all. Seriously reduce the strength or air tightness requirements of the welded structure.
(3) If the welding sequence of the stainless steel welding structure is not selected properly, the working weld in contact with the corrosive medium will be subjected to the thermal action of the post-welded weld after welding, resulting in intergranular corrosion, reducing the corrosion resistance of the weldment.
The basic principles for selecting the welding sequence are as follows:
(1) Considering from the perspective of assembly welding: The welding sequence should be considered on the principle of not causing welding difficulties and inability to weld welds.
(2) From the perspective of reducing welding deformation and residual stress:
1) Weld outward from the center of the welded structure;
2) Welding from the direction of the thick plate to the direction of the thin plate;
3) First weld joints with large shrinkage (butt joints), and then weld joints with small shrinkage (lap joints, fillet joints);
4) Weld the vertical welding seam first, then the flat welding seam;
5) Parallel welds should be welded in the same direction at the same time;
6) Weld the staggered short welds first, and then the straight long welds.
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