Today, people are actively using the pipeline system. It connects many different buildings with each other, and then displayed in special places, if it is, for example, a water drain. A high-quality arrangement of such a system requires one very important thing - a reliable connection of the pipeline. Many different connection methods are known. All of them are selected on the basis of various factors, the most important of which is the material used in the production of pipes.
The main types of connections
There are quite a lot of pipeline connections in our time. However, all of them are conditionally divided into two large groups - these are detachable and inseparable.
Naturally, the main advantage of the first category is the ability to disassemble the pipeline if necessary. Most often, such a need is repair. Plug-in connections of the pipeline allow repair and replacement of damaged sections without violating the entire structure as a whole. Flanges and threaded connectors (fittings) belong to this type of connection.
If we talk about the second method, then such a system can be repaired, however, when parsing a whole structure, it will inevitably receive damage. Among the integral types of pipeline connections, welding is the most common today. In addition to this method, there are several more, for example, gluing, pressing, installing a socket using a cement mixture.
All these methods are used quite widely. These connection methods allow you to create a reliable system for transporting a wide variety of environments, it can be water supply, gas networks, heating pipes, sewage, industrial and technical highways.
Use welding
Welded joints of pipelines are currently the most popular, especially in the field of creating technical communications at production facilities. With their help, it is possible to interconnect the individual parts of the pipe together into a complete system.
It is worth adding here that this method is not limited to welded joints of steel pipelines. By welding, you can also connect plastic products. In certain cases, welding is used even for joining glass elements. This method uses two main methods of conducting work, which differ from each other in their effect on the material being processed:
- Melting welding.
- Under pressure.
If we talk about the welded joints of the pipeline made using the first option, then the following welding methods can be used here:
- ordinary electric;
- electric arc apparatus;
- laser;
- gas welding;
- electropathy.
The most common option is the use of electric arc welding to connect steel pipelines. In this case, an electric arc is used for heating and work. In connection with this type of source, there are two ways to conduct welding. The first - using an arc on a direct current, the second - using an arc on an alternating current.
Since in this case a variety of equipment can be used for pipe installation, according to GOST 16037-80, where the rules for joining steel parts by welding are specified, manual, semi-automatic or automatic welding should be used.
The main types of connections
To create highways, several different types of connections of piping elements are used. There are 4 main options: butt, lap, angular, with welding of different elements.
The following three methods of connecting pipelines are considered the most popular and common today:
- Butt longitudinal and transverse fastening. In this case, when welding can be applied additional applied parts - rings. As for the seam, in such places it can be either unilateral or bilateral. The second option is used in cases where the cross section of the pipe is too large - more than 500 mm.
- Angular connection is one-sided and two-sided. This method of welding in different cases is performed in different ways. Sometimes the corner joint is fastened to the bevel of the edge, in other cases without it.
- The last option is a socket lap grip. According to the rules of connecting the pipeline, the bell-shaped method is used in cases where it is required to dock materials having a high ductility coefficient. Most often this is the assembly of non-ferrous metal parts, as well as other plastic components.
It is worth noting here that welding is quite actively used not only for articulating pipelines of round, but also square cross-section. Typically, such elements are often used in construction, in the manufacture of furniture. However, they are not used in the arrangement of technical highways. The main drawback is their form. The square cross section significantly degrades throughput. Round, on the contrary, is one of the best.
Thread Joints
Naturally, in practice there are cases when there is no possibility to carry out welding work. In such cases, other docking methods are used, which are also quite a lot. The most common is a threaded installation. For threading on pipes, either special machines or an ordinary die are used. If the part has very thin walls, then a knurling method is used to apply thread on the surface.
Subject to all the rules, the connection of pipes of this type will turn out to be quite durable and tight. This method has several indisputable advantages: ease of installation, the ability to repair the pipeline connection, all installation work can be carried out without the use of special equipment.
In this case, some parameters of the thread itself will be important, which will determine the scope of its operation. Firstly, the cutting step is important here, secondly, the depth of the thread and, thirdly, the direction. The cutting step will determine the distance between the top of the turn and its base. When carrying out installation work, it is very important to correctly understand and take into account the direction, since it can be right and left.
Other docking methods
Despite the fact that a threaded connection is considered one of the most popular methods in case of impossibility to use welding, there are other methods that are used quite actively. As for the choice of a particular method, usually everything directly depends on the material from which the pipe is made. Today, all pipes are conventionally divided into two categories - these are flexible and rigid. The first subgroup should include pipes made of polymeric materials, for example, polypropylene pipes, polyethylene, metal-plastic. The second category of products does not have such plasticity, and therefore it includes cast iron, steel, copper and others.
Assembly of flexible and rigid pipes without welding
Most often, in the absence of the ability to conduct welding work, pipe fittings are used to connect the pipes. These are special connecting elements. To ensure a reliable and tight joint of flexible elements, fittings with a greater coverage must be used than for rigid ones.
At present, fittings for assembling a pipeline of flexible material are used only in cases of small and medium section of an element, from 20 to 315 mm. If the parts have a cross section of more than 315 mm, then the use of a fitting is considered impractical. The main problem is the low reliability of such a connection.
To join pipes made of low pressure polyethylene or HDPE, a special type of pipe connection part is usually used - a compression fitting. The main advantages in this case are the speed of installation. In addition, it is worth noting that the use of compression fittings is a budget option for connecting flexible pipes. However, there are also limitations. Compression parts can reliably connect only pipes with a small cross section. A coupling is used for the medium section pipe. A pipe coupling is considered the most common among all other fitting options.
Next, pay attention to the joining of rigid pipes. The use of welding and threading are not the only ways. However, there is a certain rule according to GOST 16037-80, which says that all structures with a cross section above 600 mm can only be connected by welding. Usually, if thread and welding are not used, then resort to the connection through the coupling. This method will allow you to fasten pipes of equal diameter, different sections, and also from different materials. The main features of this compound are high strength and good tightness.
Periodically, pipes connected without welding and threading have flanges, with the help of which the joint occurs. In some situations, certain pipe sections require frequent inspections or repairs. To control the welded joints of pipelines is a rather laborious task, and therefore, in such places, if the pipe section allows, it is the flange joint that is installed. This is due to the fact that this type of docking is quite simple to disassemble and assemble back. It consists of the following elements:
- two main elements - connecting flanges;
- for greater tightness, o-rings are used;
- bolts and nuts are used for fastening.
Fancy articulation methods
In addition to the usual joining methods, which are popular, there are non-standard, rarely used, and for pipes made of special material. Among such joining methods, there is a bonding method, a bell-shaped docking, quick disconnect method joints.
Bonding is used when the pipes are made of plastic. In such situations, the bonding method helps to obtain a reliable and tight connection, but at the same time it will be one-piece. As the name implies, a special adhesive base is applied to the assembly, applied to the surface of the pipes.
As for the second option, a bell-shaped connection, it is most often used in cases of arranging a non-pressure type sewage system. Such systems are characterized in that the wastewater in them moves naturally, without the efforts of pumps, that is, the pipes are installed at an angle. The bell-shaped connection can be either detachable or one-piece. The choice will directly depend on the material from which the pipes are made. Plug-in communications of this type can only be made of plastic. If the parts are made of cast iron, then only one-piece joining can be done. In addition, in cast iron pipes, a seal is required, which is made on the basis of a cement mixture or special hermetic compounds.
Quick couplings
There is a small group of individual connections called quick disconnect or quick disconnect. They are usually installed only in those areas where frequent line analysis is required for any reason. There are three main options for such joints:
- the use of clamps with special wedges for fixing;
- cam connection or camlok;
- ISO connection.
All three options are quite simple in terms of their installation, but at the same time they have good strength characteristics. On an industrial scale, an additional three types of docking are often used: nipple, telescopic, articulated. A nipple connection is used in cases of pipe joining between measuring equipment, and a telescopic one - for connecting rigid pipes with flexible elements. Articulated are used only for the arrangement of highways with complex design.
Requirements for connections in accordance with GOST
The regulatory document specifies certain requirements for pipe joints made on the basis of welding. The following points are indicated in the document:
- In some cases, welding of pipes differing in diameter is required. In this case, if the difference does not exceed a certain value, then the work is carried out in the same way as it would be carried out if there was the same section. The structural elements of all prepared edges, the final seam and other details must correspond to a pipe with a large diameter. In addition, in order to ensure a smooth transition from a larger diameter to a smaller one, it is allowed to make an inclined seam. If the diameter of the pipes differs too much, then a bevel must be made on a product with a large cross section. Work is carried out until the diameter decreases to a value equal to a smaller one. In this case, the seam and structural elements must correspond to the details of a smaller diameter.
- There are requirements for surface roughness, which are prepared for welding. The value of this characteristic should not exceed 80 microns.
- All elements remaining on the pipes (couplings, linings) must be made of steel of the same grade as the pipe itself.
Seam quality control
The weld is very durable, but it needs quality control. There are currently only two validation methods. The first method is characterized by the absence of violations in the integrity of the structure, the second is carried out with violation. To evaluate the quality of all welds, the first method is usually used. It is used both during and after work.
Non-destructive verification method is divided into 5 options:
- permeability test;
- control using a radiographic or magnetic method;
- option using ultrasound;
- carrying out measuring work;
- implementation of an external examination.
Destructive testing methods are also carried out, however, already on those pieces of the product that are cut from the main pipe.
Any verification of connection quality begins with an external inspection. It is important to note here that it can be not only visual. This also includes the use of measuring equipment and the use of any other technical means. This check helps to establish the presence of problems in external factors, as well as to verify compliance of the connection with the requirements of the state standard.
There are capillary checks in which special fluids are used. Contrast material covers welds. In the presence of the smallest damage or cracks, these compounds will penetrate inside. When using such substances, defective places will be painted in a certain color. Penetrants - this is the name of these special fluids. They can consist of such bases as transformer oil, turpentine, benzene, kerosene.
The easiest way to verify this method is to use kerosene. This composition has one of the most important properties for this method - high penetration.
There are several points that play a decisive role in choosing a verification method. One of the most important factors is financial savings and technical data, then the features in which this welded structure was manufactured play an important role. You should also pay attention to the condition of the surface being checked, to the thickness and type of the weld. It is important to correctly determine the brand of metal and understand its physical properties.