Stainless steel pipe is a hollow long strip of steel, which is widely used as a pipeline for transporting fluids, such as oil, natural gas, water, gas, steam, etc. Stainless steel pipes are lighter in weight when they have the same bending and torsional strength. They are widely used in the manufacture of mechanical parts and engineering structures and are also commonly used in the production of various conventional weapons, barrels, and shells. For steel pipes subject to fluid pressure that require thicker pipe walls, hydraulic tests are required to verify their pressure resistance and that no leakage, wetting, or expansion occurs under a specified pressure. Stainless steel tubes are divided into seamless and seamed. Seamless stainless steel tubes are also called stainless steel seamless tubes. They are made of steel ingots or solid tube blanks through perforation to make capillary tubes 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 are 1Cr18Ni9Ti stainless steel pipes. The following is a 1Cr18Ni9Ti stainless steel pipe with a diameter of Ф159mm×12mm as an example to introduce its horizontal fixed welding method.
1. Welding analysis:
A. Cr18Ni9Ti stainless steel Ф159mm×12mm large pipe horizontal fixed butt joints are mainly used in nuclear power equipment and some chemical equipment that require heat-resistant and acid-resistant pipes. The welding is difficult and requires high requirements for welded joints. Moderate rise, not concave, requires PT, RT inspection 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 guarantee and improve the efficiency, TIG internal and external wire filling method is used to weld the bottom layer, and MAG welding is used to weld the filling and covering layer so that the efficiency and efficiency are guaranteed.
B. 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 fluidity of the molten pool is poor and the forming is poor, 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. During the MAG welding process, the extension length of the welding wire is less than 10mm, the swing amplitude, frequency, speed, and edge residence time of the welding torch are properly matched, and the actions are coordinated. and cover layer.
2. Welding method: the material is 1Cr18Ni9Ti, the pipe fitting specification is Ф159mm×12mm, the bottom is made by manual tungsten argon arc welding, the mixed gas (CO2+Ar) shielded welding is filled and the cover is welded, and the vertical horizontal fixed all-position welding is used.
3. Preparation before welding:
A. Clean up oil and dirt, and grind the groove surface and the surrounding 10mm to give a metallic luster.
B. Check whether the water, electricity, and air circuits are unblocked, and the equipment and accessories should be in good condition.
C. Assemble according to the size. The positioning welding is fixed by the rib plate (2 points, 7 points, and 11 points are fixed by the rib plate), and the positioning welding in the groove can also be used, but pay attention to positioning welding.