Horizontal fixed welding of thick-walled stainless steel pipes and precautions for use

Horizontal fixed welding of thick-walled stainless steel pipes:

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.

First, welding analysis: 1. 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. The inner surface is required to be shaped, moderately convex, not concave, and requires PT and 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. 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 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 the cover layer.

Second, the welding method: the material is 1Cr18Ni9Ti, the pipe fitting specification is Ф159mm×12mm, using manual tungsten argon arc welding for bottoming, mixed gas (CO2+Ar) protection welding for filling and cover welding and vertical upward horizontal fixed all-position welding.

Third, preparation before welding: 1. Clean up oil and dirt, and grind the groove surface and the surrounding 10mm to give a metallic luster. 2. Check whether the water, electricity, and air circuits are unblocked, and the equipment and accessories should be in good condition. 3. Assemble according to the size, the tack welding is fixed by the rib plate (2 points, 7 points, and 11 points are fixed by the rib plate), and the tack welding in the groove can also be used, but pay attention to the tack welding.

Matters needing attention in the use of thick-walled steel pipes:

How much wall thickness can be called thick-walled steel pipe? This is a bit doubtful. It 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 50 mm, and 10 mm can be regarded as a thick-walled steel pipe. Yes, but for a diameter of 219mm, 10mm is just a thin-walled steel pipe. The basic definition of thick-walled steel pipes lies in what customers call him. Points to note mean that when purchasing thick-walled steel pipes, customers should specify the material of their steel pipes and the single length of the steel pipes because this involves the number of mechanically processed parts and some unnecessary waste. Then there is the detailed size of the inner and outer diameters of the steel pipe, which must be included in the calculation because the processing amount of some parts must be reserved. As a kind of mechanically processed steel pipe, thick-walled steel pipes have many classifications. Customers need to know whether they need hot-rolled seamless steel pipes, seamed thick-walled steel pipes, and some cast steel thick-walled steel pipes and hot-forged thick-walled steel pipes. Form, replaceable description, irreplaceable direct emphasis.