By equipping a house or making repairs in a home, you can lay the piping system yourself. If we are talking about steel communications, then you can use electric welding. As a result, it is possible to obtain a strong connection, which is obtained due to the flow of thermochemical processes, using conductor electrodes.
Whatever the welding work, they require the master of experience and knowledge that are applied in the process. If you are just studying, then you can first get acquainted with the theoretical side of the issue. Like steel, polypropylene piping also requires appropriate welding equipment. However, practice shows that the latest technology is much easier than the one that will be discussed in the article.
Preparation before work
Pipeline welding begins with surface preparation. It is important to make sure that it is dry and even. The next step is to select a current source. The quality of training depends on this. It can be compact inverters or heavy transformers. With their help, high voltage can be converted to a low secondary circuit.
For homework, the most preferred option will be electric welding. In operation, the transformer is simpler. It has the advantages of reliability and endurance. Inverter equipment has less impressive dimensions, in addition, it allows you to adjust the operating modes.
Varieties of welded joints
When welding piping systems, the following types of joints are used today:
- butt
- overlapping;
- gusset;
- T-joint.
In this case, the position of the seam can be vertical or horizontal, as well as ceiling or bottom. The lowest position is considered the most favorable position, therefore, if re-welding is possible, it is necessary to give preference to this method. Welding pipelines when laying communications usually involves the use of butt joints. It is important to carry out the edges along the entire thickness. For thick-walled pipes, double seams are performed - external and internal. To reduce the influx of metal from the inside during 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 compliance of the pipes with the requirements. Products must be sized, they must not be deformed, and there must be no defects. You need to make sure that there is no difference in wall thickness.
The material of the pipes must be consistent in chemical composition. The edges should be cleaned of dirt and rust. The butt is measured, as well as the angle of the opening of the edge, as well as the amount of blunting. According to the norms, the blunting value can be equal to the limit of 2 to 2.5 mm. As for the bevel angle of the edge, it can be 70 °. If discrepancies have been identified, then it is necessary to carry out machining of the edges.
Installation of tack
Welding of technological pipelines should involve the installation of tacks. They are an integral part of the seam, and an electrode is used for the execution, which will be used when performing the seam. If we are talking about pipes whose diameter does not exceed 300 mm, then 4 tacks 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 tacks are arranged in increments of 250 mm. The recommended tack length is 50 mm, while its width is 4 mm.
Features of electric welding
Pipeline welding should be carried out according to a certain algorithm. It is important to pay particular attention to the rotary joints. If you have to cook in difficult conditions, then you should keep a small mirror on hand. If necessary, the end of the electrode must be bent, doing the work of the undamaged part.
A fairly common situation is welding at an angle of 30 ° to the surface of the product. The seam overlay is carried out around the circumference. It can be single-layer at the joints of low-alloy steel products. Extra strength can be achieved by re-sewing. The more impressive the pipe wall turns out to be, the more passes must be completed, there must be 2 or more.
In a circle, cook large-diameter pipes. Their connection is carried out to half 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. It is necessary to complete the work by combining the brew with a small overlap. It is not recommended to perform further work without cleaning from slag, since it will not work to achieve a good result.
Quality checking
When welding pipelines, at the final stage you must make sure that the quality of the joints is perfect. Invisible cracks can be detected with a soap solution, which is applied with a brush to the welded joints. After that air is supplied to the system. If there are left undigested seams or places, then you can notice them by the bubbles.
Rotary welding method
Welding 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 with an electrode, the core thickness of which 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 in the upper part of the pipe. Then the pipe turns, and the master has to make a joint in the third and fourth sectors. In the next step, turn the pipe again and boil 1 and 2 sectors. When you repeat the rotation, the second layer is superimposed in sectors 3 and 4. The last layer should be applied in one direction, while the pipe should turn all the time.
Automatic welding
The pipeline welding process can be carried out in large-scale production, where high productivity is important. Under such conditions, manual welding will be time-consuming, therefore, welding machines are used for work . All processes will occur automatically.
Welding is carried out by welding wire, which is wound from the bay and fed into the work area. Shielding gases are also automatically fed into the working area. If the work cannot be automated, welding is used semi-automatic.
Alternative welding methods
Welding and installation of pipelines can be carried out using gas welding. This method involves heating the edges to a melting point. At the same time, 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 using a mixture of oxygen and acetylene. The main tools are the torch and the cutter. In the body of the first there are two channels through which gases are supplied to the mixing chamber. The master at the same time regulates the gas supply when welding different materials.
Welding of steel pipelines can also be carried out using the induction method. This technology involves heating elements by eddy currents. Edges are connected by push rollers. This type of welding is used in industries and in mechanical engineering.
Electrode selection guidelines
When welding pipelines, GOST 16037-80 must be observed. They also registered the features of the choice of electrodes. The latter are metal rods made of welding wire. Its thickness can vary from 2 to 5 mm. The surface is coated 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 we are talking about a thick layer, then its mass can vary from 20 to 30%.
The main task of the coating is the formation of slag, which has the form of a non-metallic alloy of lower weight compared to metal. Slag floats up during welding, creating a protective coating. After connecting the pipelines by welding, the slag must be knocked down. Once the crust becomes brittle, it can be removed quite simply.
Electrodes today are available with different types of coatings, the latest of which are designed to solve certain problems. For example, a cellulose coating is used to weld pipelines of impressive diameter. Using these electrodes, you can create circular and vertical seams.
On sale you can find electrodes with a 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 marketable seams, fillet seams, set tacks and weld root seams. This allows you to get a connection with a beautiful appearance.
Pipeline welding technology may involve the use of rutile acid coated electrodes. This material is easy to peel, and the electrode consumption is low, which saves money. Rutile-cellulose coating is suitable for seams in any positions that can be directed upward, which is the most difficult.
A joint with a high viscosity index can be obtained with a basic electrode coating. 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.
Welding repair
You can repair the pipelines by welding. To do this, the defective area must be cleaned mechanically. Cleaning by sandblasting , abrasive wheels, grinders and disk wire brushes is allowed.
Weld repair involves surfacing in defective areas. Damage can be caused by corrosion, scratches, scratches and risks can form on the surface. In order to clarify the wall thickness, it is necessary to carry out measuring and visual control. Acceptable and additional physical methods that will not be destructive.
Defects with a depth of 0.2 mm can be eliminated by grinding. The norms for welding pipelines in this case involve the use of a manual method using electrodes with the main type of coating. For welding the first filling seam, it is recommended to use electrodes with a diameter of 3.2 mm. For facing and filling joints, the diameter of the electrode can vary from 3 to 4 mm.
The pipeline welding process involves calcining the electrodes. Permissible use of electrodes calcined in stationary conditions. At the same time, they must be delivered to the place of production in sealed containers. Storage of electrodes in accordance with 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 preheated by electric heating devices before surfacing. You can use the induction method, which ensures uniform heating. It is acceptable to use gas burners or heaters. Welding can be performed using the inverter method. Surfacing is carried out with direct current of reverse polarity.
Arc ignition is performed at the edges of the sample of the defective area. Welding the filling layers of a straight or round shape is carried out by a narrow roller. The scheme used is counter-symmetrical. The direction of movement in each subsequent seam should be oncoming. The width of the filling first layers can vary from 4 to 6 mm. All subsequent layers have a width of 8 to 10 mm.
Conclusion
With the appropriate equipment, you can weld the piping systems yourself. However, it is important to choose the right electrodes, while taking into account the properties of the materials that underlie the pipes. For example, in order to connect carbon steel pipes, stock welding materials with a basic or rutile coating.
If the seams are made on a galvanized steel pipe, then electrodes should be prepared for welding galvanized pipes. The main feature of welding when working with galvanized pipes is the boiling point of zinc. It is lower than that which is true for steel. This indicates that the zinc coating will evaporate when heated.