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

Horizontal fixed welding of thick-walled stainless steel pipes: Stainless steel pipes are hollow long strips of steel that are widely used as pipelines for transporting fluids, such as oil, natural gas, water, coal 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. They are also commonly used to produce various conventional weapons, gun barrels, shells, etc. For steel pipes that require thicker walls to withstand fluid pressure, hydraulic tests must be conducted to check their pressure resistance and that they will not leak, wet, or expand under the specified pressure. Stainless steel pipes are divided into seamless and seamed. Seamless stainless steel pipes are also called stainless steel seamless pipes. They are made of steel ingots or solid tube blanks perforated into capillary tubes and then hot-rolled, rolled, or cold-drawn. The specifications of seamless steel pipes are expressed in terms of outer diameter x wall thickness in millimeters. Commonly used stainless steel pipes are 1Cr18Ni9Ti. The following uses the 1Cr18Ni9Ti stainless steel pipe with a diameter of 159mm×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 pipes that require heat and acid resistance in nuclear power equipment and some chemical equipment. Welding is difficult and requires high welding joints. The inner surface is required to be formed, with moderate convexity and no concavity. 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 both ensure and improve efficiency, the TIG inner and outer filler wire method is used to weld the bottom layer, and MAG welding filler and cover layers are used to ensure both safety and efficiency. 2. The thermal expansion rate and electrical conductivity of 1Cr18Ni9Ti stainless steel are greatly 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 when welding in all positions. In the past, MAG (Ar+1%~2%O2) welding of 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 should be less than 10mm, the swing amplitude, frequency, speed and edge dwell time of the welding gun should be properly coordinated, the movements should be coordinated, and the angle of the welding gun should be adjusted at any time to make the edges of the weld surface fused neatly and the shape beautiful to ensure filling and covering layer.
Second, welding method: The material is 1Cr18Ni9Ti, the pipe specification is Ф159mm×12mm, manual tungsten arc welding is used for the base, mixed gas (CO2+Ar) shielded welding for filling and cover welding, vertical horizontal fixed all-position welding.
Third, 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 lines are smooth, and the equipment and accessories should be in good condition. 3. Assemble according to the size. The tack welding is fixed by ribs (2 o'clock, 7 o'clock, and 11 o'clock are fixed by ribs). In-groove tack welding can also be used, but pay attention to tack welding.

Precautions when using thick-walled steel pipes:
There is some doubt about the wall thickness that can be called a thick-walled steel pipe. In fact, 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 can be considered a thick-walled steel pipe with a diameter of 10 mm. , but for a diameter of 219 mm, 10 mm is only a thin-walled steel pipe. In fact, the basic definition of thick-walled steel pipe lies in the name given to it by customers. Things to note are that when purchasing thick-walled steel pipes, customers must be clear about the material of their steel pipes and the single length of the steel pipes because this involves the number of machined parts and some unnecessary waste.
Then there is the detailed size of the inner and outer diameter of the steel pipe. This must be included in it because the processing volume of some parts must be reserved. As a kind of mechanically processed steel pipe, thick-walled steel pipes are also classified into many categories. Customers must clarify whether they need hot-rolled seamless steel pipes, seamed thick-walled steel pipes, as well as some cast steel thick-walled steel pipes and hot-forged thick steel pipes. Form, explanation that can be replaced, direct emphasis that cannot be replaced.