Pipe Welding: Technology

When building a house or repairing a dwelling, you can build a pipeline system yourself. If it is a question of steel communications, then it is possible to use electric welding. As a result, it is possible to obtain a strong connection, which is obtained through the flow of thermochemical processes, while using conductor electrodes.

Whatever the welding work, they require the master the experience and knowledge that are used in the process. If you are still just learning, you can first get acquainted with the theoretical side of the matter. As for the steel, for the polypropylene pipeline, too, appropriate welding equipment is required. However, practice shows that the latest technology is much easier than the one that will be discussed in the article.

Preparation before work

Welding of the pipeline begins with the preparation of the surface. It is important to make sure that it is dry and even. The next step is to select the current source. On this depends the quality of training. These can be compact inverters or heavy transformers. With their help, high voltage can be converted into a low secondary electric circuit.

For domestic work, electrowelding is the most preferred option. The transformer is more simple to operate. It has the advantages expressed in reliability in operation and endurance. Inverter equipment has less impressive dimensions, in addition, allows you to adjust the operating modes.

Varieties of welded joints

At welding of pipeline systems today the following types of connections are used:

• Butt-end;
• Overlapping;
• gusset;
• T-joint.

The seam position can be vertical or horizontal, as well as ceiling or bottom. The most advantageous position is considered to be the bottom, so if it is possible to re-weld it is necessary to give preference to this method. Welding of pipelines during the laying of communications usually involves the use of a butt joint. The edges in this case it is important to conduct the entire thickness. For thick-walled pipes, double seams are made-external and internal. To reduce the build-up of metal from the inside, when performing work, the electrode must be held at an angle of 45 ° to the horizontal plane.

What else is important to remember when preparing

Before starting manual welding, preparation is necessary. It is important to check the conformity of the pipes to the requirements. The products must correspond to the dimensions, they should not be deformed, they should not have defects. You need to make sure there is no difference in the thickness of the walls.

The pipe material must be of a chemical composition. The edges should be cleaned of dirt and rust. The end is measured, as is the angle of the edge opening, as well as the amount of blunting. According to the norms, the amount of blunting can be equal to the limit from 2 to 2.5 mm. As for the angle of the bevel, it can be 70 °. If inconsistencies were identified, then the edges must be machined.

Attachment of hooks

Welding of technological pipelines should assume the installation of tacks. They represent a component part of the seam, and an electrode is used to perform it, which will be used when making the seam. If we are talking about pipes whose diameter does not exceed 300 mm, then 4 stitches are performed, they should be distributed around the circumference as evenly as possible.

When you have to work with a pipe of a more impressive diameter, the potholes are arranged in steps of 250 mm. The recommended length of tack is 50 mm, while its width is 4 mm.

Features of electric welding

Welding of pipelines must be carried out according to a certain algorithm. It is important to pay special attention to the turning joints. If you have to cook in difficult conditions, then you should keep a small mirror handy. If necessary, then the end of the electrode must be bent, performing the work undamaged part.

A fairly common situation is welding at an angle of 30 ° to the surface of the product. The seam is sealed around the circumference. It can be single-layered at the joints of products made of low-alloy steels. Additional strength can be achieved by performing a repeated seam. The more impressive the pipe wall is, the more passes should be made, there must be 2 or more.

On a circle it is necessary to cook pipes of the big diameter. Their connection is carried out up to half of the seam. Then the sections are cleaned of slag and covered with the next seam at a distance of 1.5 cm from the previous one. Completing the work is necessary by joining the weld with a slight overlap. Without cleaning the slag, it is not recommended to carry out any further work, as it will not be possible to achieve a good result.

Quality checking

When welding the pipes, at the final stage you should make sure that the quality of the seams is perfect. Invisible cracks can be detected with a soap solution, which is applied by brush on welded joints. After that, air is supplied to the system. If there are unprocessed seams or places, then you can notice them on the bubbles.

Rotary welding method

Welding of process pipelines usually involves the maximum number of seams made in the lower position. This indicates that you can use the rotary method. If the pipe has a wall thickness of up to 12 mm, then a triple seam can be made. The first layer is welded by an electrode whose rod thickness varies from 2 to 4 mm. All subsequent layers can be welded with electrodes of a more impressive diameter.

Initially, the joint should be divided into 4 parts. Welding is performed in the first and second sectors, which are located at the top of the pipe. Then the pipe turns, and the master will make a joint on the third and fourth sectors. The pipe in the next stage should be turned again and weld 1 and 2 sectors. When the rotation is repeated, the second layer is superimposed in sectors 3 and 4. The last layer should be applied in one direction, with the pipe rotating all the time.

Automatic welding

The process of pipeline welding can be carried out in large-scale production, where high productivity is important. Under these conditions, manual welding will be time-consuming, therefore welding machines are used for work. In this case, all processes will automatically occur.

Welding is carried out by welding wire, which is unwound from the bay and fed into the work area. In the working zone in the automatic mode, protective gases are also supplied. If the work can not be automated, semiautomatic welding is used.

Alternative methods of welding

Welding and installation of pipelines can be carried out by means of gas welding. This method involves heating the edges to the melting point. Simultaneously, the filler rod is melted, as well as the metal used to fill the seam. As a result, it is possible to obtain a sufficiently strong seam, which will have a protruding roller.

Gas welding is carried out with a mixture of oxygen and acetylene. The main tools are the burner and the cutter. In the body of the first there are two channels through which gases are fed into the mixing chamber. The wizard at the same time regulates the supply of gas when welding different materials.

Welding of steel pipelines can also be carried out using an induction method. This technology assumes that the elements are heated by eddy currents. The edges are connected by pressure rollers. This type of welding is used in industries and in machine building.

Recommendations for Electrode Selection

When welding pipes GOST 16037-80 must be observed. In them the features of a choice of electrodes are registered also. The latter are metal rods made of a welding wire. Its thickness can vary from 2 to 5 mm. The surface is covered with a coating, which is applied in a thick or thin layer. In the latter case, the mass of the coating varies from 1 to 2% of the mass of the rod. If it is a thick layer, its mass can vary from 20 to 30%.

As the main task of coating is the formation of slag, which has the appearance of a nonmetallic alloy of lower weight compared with the metal. The slag floats up when welding, creating a protective coating. After joining the pipelines by welding, the slag must be knocked off. Once the crust is fragile, it can be removed quite easily.

Electrodes are produced today with different types of coatings, the latter of which are designed to solve specific problems. For example, a cellulose coating is used to weld pipelines of impressive diameter. With the help of such electrodes, it is possible to create annular and vertical seams.

On sale it is possible to meet electrodes and with rutile coating, which is easily ignited and forms a slag crust of high brittleness. With the help of such electrodes, it is possible to create seams of a marketing kind, corner seams, to establish potholders and to weld root joints. This allows you to get beautiful appearance connections.

The technology of welding pipelines may involve the use of electrodes with a rutile-acid coating. This material is easy to separate the crust, and the consumption of electrodes is small, which saves. Rutile-cellulose coating is suitable for making seams in any positions that can be directed upward, which is the most difficult.

A seam with a high viscosity can be obtained with the main coating of the electrode. As a result, it is possible to form compounds that do not crack. The material is excellent for working with thick-walled pipes and products that will be used in difficult conditions.

Repair by welding method

You can repair the pipelines by welding. To do this, the defective area must be cleaned mechanically. It can be cleaned by sandblasting, abrasive wheels, grinders and disk wire brushes.

Repair by welding involves surfacing in defective areas. Damage can be caused by corrosion, scratches, scoring and risks can form on the surface. In order to clarify the wall thickness, it is necessary to carry out a measurement and visual inspection. Additional physical methods are acceptable, which will not be destructive.

Defects, the depth of which is 0.2 mm, can be eliminated by grinding. Norms of welding pipes in this case involve the use of a manual method with the use of electrodes with the main type of coating. For welding the first filling joint, it is recommended to use electrodes whose diameter reaches 3.2 mm. For lining and filling joints, the electrode diameter can vary from 3 to 4 mm.

The technological process of welding the pipeline involves calcining the electrodes. It is acceptable to use electrodes that have been calcined under stationary conditions. In this case, they must be delivered to the production site in sealed containers. Storage of electrodes according to state standards should be carried out in heated dry rooms, the temperature of which does not fall below +15 ° C.

The defective area must be heated by electric heating devices before the surfacing starts. You can use the induction method, which ensures the uniformity of heating. It is acceptable to use gas burners or heaters. Welding can be performed using an inverter method. Surfacing is performed at a constant current of reverse polarity.

The arc is ignited at the edges of the sample of the defective section. Welding of filling layers of rectilinear or circular shape is carried out by a narrow roller. The scheme used is counter-symmetric. The direction of the movements in each next seam should be opposite. The width of the filling first layers can vary between 4 and 6 mm. All subsequent layers have a width of 8 to 10 mm.

Conclusion

With the appropriate equipment, you can independently weld the pipeline systems. However, it is important to select the electrodes correctly, and the properties of the materials that lie at the base of the pipes should be taken into account. For example, in order to connect pipes made of carbon steel, you should stock up welding materials with a basic or rutile coating.

If the seams are made on a tube made of galvanized steel, then it is necessary to prepare electrodes for welding galvanized pipes. As the main feature of welding when working with galvanized pipes is the boiling point of zinc. It is lower compared to that which is true for steel. This indicates that the zinc coating will evaporate when heated.