1. Welding analysis: 1. Cr18Ni9Ti stainless steel Ф159mm×12mm large pipe horizontal fixed butt joints are mainly used in nuclear power equipment and certain chemical equipment that require heat and acid resistance. The welding is difficult and requires high welding joints. The surface is required to be shaped, with moderate protrusions and no recesses. PT and RT inspections are required after welding. In the past, TIG welding or manual arc welding was used. The former has low efficiency and high cost, while the latter is difficult to guarantee and has low efficiency. To ensure and increase the rate, the bottom layer is welded by the TIG inner and outer wire filling method, and the MAG welding is used to fill and cover the surface layer so that efficiency is guaranteed. 2. The thermal expansion rate and electrical conductivity of 1Cr18Ni9Ti stainless steel are quite different from those of carbon steel and low-alloy steel, and the molten pool has poor fluidity and poor forming, especially when welding at all positions. In the past, MAG (Ar+1%～2%O2) welding stainless steel was generally only used for flat welding and flat fillet welding. In the MAG welding process, the length of the welding wire is less than 10mm, the swing amplitude, frequency, speed, and edge dwell time of the welding gun are properly coordinated, and the action is coordinated. Adjust the angle of the welding gun at any time, so that the welding seam surface edge is fused neatly and beautifully formed to ensure filling And cover layer.

2. Welding method: The material is 1Cr18Ni9Ti, the pipe size is Ф159mm×12mm, the base is made by manual argon arc welding, mixed gas (CO2+Ar) shielded welding and cover welding, vertical and horizontal fixed all-position welding.

3. Preparation before welding: 1. Clean the oil and dirt, and grind the groove surface and the surrounding 10mm to get a metallic luster. 2. Check whether the water, electricity, and gas circuits are unblocked, and the equipment and accessories are in good condition. 3. Assemble according to the size. Tack welding is fixed by ribs (2 points, 7 points, and 11 points are fixed by ribs), or in groove positioning welding, but pay attention to tack welding.