Horizontal fixed welding of thick-walled stainless steel pipes:
Stainless steel pipes are a kind of hollow long steel strips, which are widely used as pipelines for conveying fluids, such as oil, natural gas, water, coal gas, steam, etc. Stainless steel pipes are light in weight when the bending and torsional strengths are the same. They are widely used in the manufacture of mechanical parts and engineering structures and are also often used to produce various conventional weapons, gun barrels, shells, etc. For steel pipes that withstand fluid pressure, thicker pipe walls are required, and hydraulic tests must be carried out to test their pressure resistance and that they do not leak, soak 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 pipe blanks through perforation to form rough pipes, and then hot rolled, cold rolled, or cold drawn. The specifications of seamless steel pipes are expressed in millimeters of outer diameter × wall thickness. Commonly used are 1Cr18Ni9Ti stainless steel pipes. The following takes the 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 joint is mainly used in nuclear power equipment and some chemical equipment that require heat and acid resistance. The welding difficulty is high, and the requirements for the welding joint are very high. The inner surface requires forming, moderate convexity, and no concave. PT and RT inspections are required after welding. In the past, TIG welding or manual arc welding were used. The former is inefficient and costly, and the latter is difficult to guarantee and inefficient. To ensure and improve efficiency, TIG internal and external wire welding is used to weld the bottom layer, and MAG welding is used to fill and cover the surface layer so that efficiency is guaranteed.
2. The thermal expansion rate and 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 full-position welding. In the past, MAG (Ar+1%~2%O2) welding of stainless steel was generally only used for flat welding and flat corner welding. During the MAG welding process, the welding wire extension length is less than 10mm, the welding gun swing amplitude, frequency, speed, and edge dwell time are properly coordinated, the movements are coordinated, and the welding gun angle is adjusted at any time to make the weld surface edge fused neatly and beautifully formed to ensure the filling and cover layer.
Second, welding method: the material is 1Cr18Ni9Ti, the pipe specification is Ф159mm×12mm, manual tungsten inert gas arc welding is used for base, mixed gas (CO2+Ar) shielded welding is used for filling and cover welding, and vertical horizontal fixed full position welding.
Third, preparation before welding:
1. Clean oil and dirt, and grind the groove surface and the surrounding 10mm to produce metallic luster.
2. Check whether the water, electricity, and gas lines are unobstructed, and the equipment and accessories should be in good condition.
3. Assemble according to size, and use rib plate fixation for positioning welding (2 points, 7 points, and 11 points are rib plate fixation). Positioning welding in the groove can also be used, but pay attention to positioning welding.
Precautions for thick-walled steel pipes in use:
How thick the wall is to be called a thick-walled steel pipe? This is a little doubtful. 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 50 mm can be considered a thick-walled steel pipe if it is 10 mm, but for a steel pipe with a diameter of 219 mm, 10 mm is only a thin-walled steel pipe. The basic definition of thick-walled steel pipe is a name given to it by customers. Precautions refer to when purchasing thick-walled steel pipes, customers must clarify the material of their steel pipes and the length of a single steel pipe because this involves the number of mechanically processed parts and some unnecessary waste.
Then there are the detailed dimensions of the inner and outer diameters of the steel pipe, which should be included because some parts processing volume should be reserved. As a kind of mechanically processed steel pipe, thick-walled steel pipes are also classified in many ways. Customers should clarify 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 steel pipes. The alternatives can be explained, and the non-alternatives can be directly emphasized.
Post time: Dec-24-2024