Views: 8 Author: Site Editor Publish Time: 2021-11-03 Origin: Site
Horizontal fixed welding of thick-walled stainless steel pipe:
Stainless steel pipe is a kind of hollow long steel, used as pipelines for conveying 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, as well as the production of various conventional weapons, barrels, and shells. For steel pipes that are subject to fluid pressure and require thicker pipe walls, a hydraulic test must be carried out to verify their pressure resistance and will not leak, immerse or expand under the specified pressure. Stainless steel pipes are divided into seamless pipes and seamed pipes. Stainless steel seamless pipe is also called stainless steel seamless pipe. They are made by perforating steel ingots or solid tube blanks, and then by hot rolling, cold rolling, or cold drawing. The specifications of seamless steel pipes are expressed in millimeters × wall thickness. Stainless steel pipes are commonly used. The following takes a stainless steel pipe with a diameter of Ф159mm×12mm as an example to introduce its horizontal fixed welding method.
First. Welding analysis:
1. The horizontal fixed butt joint of stainless steel Ф159mm×12mm large pipeline is mainly used for nuclear power equipment and some chemical equipment that requires heat resistance and acid resistance. The welding difficulty is relatively high, and the requirements for welding joints are very high. The inner surface is required to be shaped and protruded. Moderate, not concave, PT, RT inspection is 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 low efficiency. In order to ensure and improve the success rate, the bottom layer is welded by the TIG inner and outer wire filling method, and the surface layer is filled by MAG welding to ensure efficiency.
2. The thermal expansion rate and electrical conductivity of stainless steel are quite different from those of carbon steel and low-alloy steel. The molten pool has poor fluidity and poor formability, especially during 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, and the swing amplitude, frequency, speed, and edge stay time of the welding gun are properly coordinated and the actions are coordinated. The angle of the welding torch can be adjusted at any time so that the edges of the weld surface are welded neatly and beautifully, and the filling and covering layer are ensured.
Second. Welding method:
The size of the pipe fittings is Ф159mm×12mm, using manual tungsten argon arc welding for bottoming, mixed gas (CO2+Ar) shielded welding, cover welding, vertical and horizontal fixed all-position welding.
Third. Preparation before welding:
1. Clean up oil stains, and polish the groove surface and the periphery by 10mm to make it have a metallic luster.
2. Check whether the water, electricity, and gas circuits are unblocked and whether the equipment and accessories are in good condition.
3. Assemble according to size. Spot welding is fixed by ribs. Groove spot welding can also be used, but please pay attention to spot welding.
Precautions for the use of thick-walled steel pipes:
The wall thickness is called thick-walled steel pipe. In fact, this depends on the ratio of the outer diameter of the steel pipe to the wall thickness of the steel pipe. For example, a steel pipe with a diameter of 50mm can be regarded as a thick-walled steel pipe. However, for a diameter of 219mm, 10mm is only a thin-walled steel pipe. It should be noted that when buying thick-walled steel pipes, you must know the material of the steel pipe and the length of each steel pipe because this involves the number of machined parts and other parts. Then there are the detailed dimensions of the inner and outer diameters of the steel pipe. This should be counted in because there are still some parts to be processed. Thick-walled steel pipe, as a kind of machined steel pipe, has many classifications.