Horizontal Fixed Welding of Thick-walled Stainless Steel Pipe

Stainless steel pipe is a kind of hollow long steel, which is used as a pipeline for transporting fluids, such as oil, natural gas, water, gas, steam, etc. Stainless steel tubes are lighter when they have the same bending and torsion strength. They are widely used in the manufacture of mechanical parts and engineering structures. They are also commonly used to produce various conventional weapons, barrels, and shells. For steel pipes subjected to fluid pressure that requires thicker pipe walls, hydraulic tests must be carried out to verify their pressure resistance and that they will not leak, soak, or expand under the specified pressure. Stainless steel pipes are divided into seamless and seam. Seamless stainless steel pipes are also called stainless steel seamless pipes. They are made of steel ingots or solid pipe billets through the perforation and then made by hot rolling, cold rolling, or cold drawing. The specifications of seamless steel pipes are expressed in millimeters of outer diameter × wall thickness. Commonly used 1Cr18Ni9Ti stainless steel pipes, the following takes 1Cr18Ni9Ti stainless steel pipe with a diameter of Ф159mm×12mm as an example to introduce its horizontal fixed welding method.

1. Welding analysis:

   ① Cr18Ni9Ti stainless steel Ф159mm×12mm large pipe horizontal fixed butt joint is 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 not concave. 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 TIG inner and outer wire filling method, and the MAG welding is used to fill and cover the surface layer so that the 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 in all-position welding. 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 stay time of the welding gun are properly coordinated, and the action is coordinated. Adjust the angle of the welding gun at any time to make the weld surface edge fusion neatly and beautifully to ensure filling And cover layer.

   
   

2. Welding method: The material is 1Cr18Ni9Ti, the pipe fitting size is Ф159mm×12mm, using manual tungsten arc welding for bottoming, 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 give 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.