Pipe connections: types of joints, their characteristics and features

Today, there are many options for connecting pipes in pipeline structures. The choice of connection depends on various factors, but the material from which the communication elements are made plays a major role. The second important factor is the type of work environment. It is also worth noting that the operating conditions of the pipeline play a big role.

The connection method is selected depending on the type of pipes, their diameter and the purpose of the future pipeline

Types of connections

All existing pipe connections are divided into two main groups:

• detachable;
• one-piece.

The use of detachable connections allows, if necessary, to disassemble the joint section. Thanks to this property, it is possible to repair and replace the joint without compromising the integrity of the pipes. Detachable joints include threaded connectors (fittings) and flanges.

In the case of permanent joints, it is possible to disassemble the pipeline, however, this will lead to damage to the pipe material. The most popular option for permanently connecting pipelines is welding. In addition, there are a number of other methods: gluing, pressing, installing a socket using cement mortar.

All of the above methods are quite popular and are used to connect pipelines transporting various media: water pipelines, heating communications, gas networks, sewer systems, as well as industrial and technical lines.

Welded joints

Welding is a very popular method of joining individual parts in a pipeline structure. This method is especially in demand when installing technical communications in factories.

The most commonly used method for installing steel pipelines is hot welding.

It is worth noting that not only individual parts in metal structures, but also plastic products can be connected by welding. In some cases, welding is also used to join glass parts.

Depending on the method of exposure to the material, there are two main methods of such connection:

• fusion welding;
• pressure welding.

Fusion welding has many implementation options:

• electric arc;
• simple electric;
• electrobeam;
• laser;
• gas welding.

The most popular among these options is the first one. The use of electric arc welding implies that the heating source is an electric arc. This type of work can be performed in two ways:

• with alternating current;
• with direct current.

Helpful information! Butt welding of the connected pipeline elements allows the work to be carried out at lower financial costs. This is due to the fact that welding equipment is less expensive and also requires less energy consumption during installation.

Metal welding can be done with electric or gas equipment

This type of installation can be carried out using various equipment, so three types of welding can be distinguished:

• manual;
• semi-automatic;
• automatic.

Types of welded joints

There are different methods for welding individual parts in pipeline communications. Let's look at them:

• end-to-end;
• overlap;
• corner;
• with welding of various elements.

The most popular and common are the following welding connections:

1. Butt (longitudinal and transverse). With this welding option, backing elements - rings - can be used. The seam in such joints can be one- or two-sided. The latter is used in cases where the part has a large cross-section - more than 500 mm.
2. Angular (one-sided and two-sided). This option can be done in different ways. In some cases, corner joints are welded with an edge bevel, and in others - without it.
3. Socket-welded overlap clutch. The socket connection is used to join pipeline elements with a high ductility coefficient. These include parts made of non-ferrous metals, as well as plastic elements.

In addition, square pipes, which are used in construction and the production of various furniture, are also connected by welding. They are not suitable for installation of pipelines. This is due to the shape of their cross-section - it worsens the flow characteristics, while round is the best option for pipeline structures.

Butt welding is used for pipes whose diameter exceeds 50 mm

Threaded connections

But what to do in cases where it is not possible to carry out welding work? There are quite a few ways to join pipeline elements without welding. The most popular option is threaded installation. Pipe threading is done using cutting machines or an ordinary die. If it is necessary to apply threads to a product with thin walls, use the rolling method.

If you follow all the rules for installing a threaded joint, you will get a durable and sealed structure. Let's consider the main advantages of using such a connection:

• ease of installation.
• the ability to repair or replace without damaging the pipeline;
• installation is carried out without the use of special equipment.

In addition, there are several thread parameters that determine its operation:

• cutting step;
• depth;
• direction.

The pitch determines the distance between the top of the coil and its base. Depth is a parameter that is determined as follows: the distance between the base of the coil and its top is measured. The direction of the thread is an important point; if you ignore it, you may encounter problems when installing the pipeline structure. The thread has two directions:

• right;
• left.

Many types of pipes are equipped with threads; they are used where it is necessary to create a reliable but detachable connection

Other types of pipe joining without welding

The use of threaded connections is the most popular and widespread method of installing pipeline structures without welding. However, there are other types of pipe connections that are worth paying attention to.

The choice of method, as a rule, depends on the material from which the pipeline is made. All pipes can be divided into two types:

• flexible;
• hard.

The first group includes products that consist of various polymer materials: polypropylene (PP), polyethylene (PE), as well as metal-plastic products. The second group does not have such ductility and includes: steel, cast iron, polyvinyl chloride (PVC), copper, etc.

Important! When installing flexible pipelines, greater coverage of the pipe material is required to ensure a reliable connection than when implementing joints in rigid pipelines.

Tips and tricks

• When working with cast iron pipes, you must remember that they are fragile. For embossing and pressing, use rubber hammers.
• If the installation of a socket joint is carried out outdoors in hot weather , then when the cement is in the gap, it is suggested to lay a damp cloth on it. So that the cement does not crack.
• When gas welding, the flammable gas acetylene is used. If desired, it can be replaced with propane, which is cheaper and safer.
• When constructing a water or gas supply pipe system, try to weld the rotary joints first, and then, when the entire structure is assembled, weld the fixed joint last.
• When tightening the bolts on the flanges, do not overtighten. It is possible to strip the thread, this also applies to threaded connections.

Connecting flexible pipes without welding

Often, in order to install a pipeline without the use of welding equipment, special connecting elements - fittings - are used. Fittings for flexible pipes must have a large reach to make a reliable and airtight joint.

Compression fittings allow you to create a tight connection without welding or threading

As a rule, fittings are used in flexible pipelines that have small or medium cross-sections (from 20 to 315 mm). For parts with a diameter above 315 mm, a fitting joint is not practical. This is due to the fact that the reliability of such a connection is quite low.

For joining low-pressure polyethylene (HDPE) products, special compression fittings are mainly used. The joining of individual elements in a pipeline structure using compression products allows for quick installation, which is also inexpensive and simple.

However, compression products are most often used to connect small diameter pipes. Medium-diameter pipes are connected using couplings. The coupling is perhaps the most common fitting option.

Using clamps

Reliable and practical hose clamps are widely in demand in a wide variety of industries. Due to their ease of installation, they are used for industrial and domestic purposes. When joining pipes, you can first plug them on both sides to ensure greater strength and reliability.

A clamp for connecting pipes is relatively inexpensive

Experts use a variety of types of clamps:

• For hoses;
• With hinge bolt;
• Spring.

A metal clamp can be used in all types of fastening. For fixation, such products are made of galvanized or stainless steel, and bolts or screws are used to tighten them. If they are used for a plastic pipeline, rubberized seals can be used to avoid damage to the shells and reduce vibration and noise.

In case of increased mechanical loads, it is necessary to use power clamps. Their design allows them to withstand very large loads along the clamp while maintaining integrity. Plastic clamps are used for fastening water and sewer pipes. Their design is similar to metal ones, but they are much less expensive.

Pipe connections can be made in a variety of ways, it all depends on your own preferences.

Connecting rigid pipes without welding

As mentioned above, inelastic pipes are often joined using threads. But there are methods that allow you to connect individual elements of rigid pipelines without the use of welding and threading. Docking without welding equipment is permitted on parts with a diameter of up to 600 mm.

If it is not possible to cut a thread on a rigid pipe or use welding for joining, then the pipeline is mounted using couplings

In order to install a rigid structure without the use of welding equipment, couplings are usually used. The coupling joint allows you to connect the following pipe options:

• equal in diameter;
• with different diameters;
• from various materials.

The connection obtained using such a fitting is characterized by high strength characteristics and good tightness. If it is necessary to connect two pipes without welding and threading, as a rule, special devices are used - flanges. They are also widely used for connecting various equipment to pipes.

Flange connections are recommended for use in cases where a specific section of the pipeline requires frequent inspections or periodic repairs. This is due to the fact that such a clutch is easy to disassemble and reassemble. It includes:

• two connecting flange elements;
• sealing ring;
• nuts and bolts.

Repair and installation clip

A universal product that can be used to repair pipe metal products without welding, as well as polyethylene pipes, is a repair and installation clip.

It consists of two cast cages in the form of semi-bushings, having four ears for bolt fastening. The kit includes a rubber seal in the form of a hose cut to length and four bolts.

In essence, it is a clamp that plumbers often use, but it is made very well. Available for pipes of different diameters, making it possible to repair them without welding or threading.

The product is used for repairing damaged pipelines for various purposes. If a through hole appears in the pipe, a split seal is placed on the damaged area, oriented with the cut in the direction opposite to the damage.

Clips are installed on top of the seal and the bolts are tightened. These repairs do not require welding and can sometimes be done under pressure without shutting down the pipeline.

Non-standard methods of connecting pipes

In addition to the traditional methods of joining pipes, which are the most common, there are also some special installation methods. Pipes can also be made of non-standard material, which requires a special connection.

Sockets are most often used to connect sewer systems

Let's consider the following docking methods:

• gluing;
• bell joint;
• quick connectors.

The first option is used if the structure is made of plastic. The gluing method allows you to obtain a strong and hermetically sealed permanent connection. Joining pipes in this way is done by applying a special glue to them.

The socket connection is used, as a rule, when installing non-pressure sewer systems. In such systems, wastewater moves naturally at an angle, without the use of a special pump. Depending on what material such a pipeline is made of, there may be a detachable or permanent socket connection. The detachable version of the socket coupling is used when installing plastic communications, and the one-piece version is used when installing cast iron pipes. The socket is sealed in cast iron structures using a cement composition or special sealants.

Helpful information! Quick-release or quick-release connections are installed if the operational features of the communication require its frequent disassembly.

Let's look at the main options for quick-release connections:

• clamps equipped with a fixing wedge;
• cam (Camlok);
• ISO connection.

Flexible pipes and hoses can be connected using quick connect fittings such as Camlok

These clutch options are easy to install and have good strength characteristics.

It is also worth noting that for joining pipes that are used for industrial purposes, the following joints are used:

• nipple;
• telescopic;
• articulated.

The first option is used in cases where it is necessary to connect pipes with any measuring equipment, and the second - when joining rigid pipes equipped with flexible elements. The hinged type is used in the construction of highways with complex shapes. This connection allows you to compensate for the effect of twisting the pipeline.

Features of connecting profile pipes

Profile pipes have good strength and relatively low weight, so they are often used for the installation of frame structures, as well as for other construction purposes.

The shape of profile pipes can be:

• rectangular (the most common shape);
• square;
• ovoid (oval);
• others (more complex forms).

The most reliable way to create structures from profile pipes is to fasten them by welding

Electric arc welding is usually used to connect square pipes. There are also special connections that are made using bolts and rivets. Square and rectangular pipes are joined using the same methods.

In addition, various parts can be joined to such pipes. This joining is carried out using self-tapping screws. These elements do not require preliminary holes.

Thread

Threaded connections are among the most ancient. They are used only on round pipes. Based on the direction of torsion, a distinction is made between right-handed and left-handed threads. The second is rarely used, only in special cases.

This type of joint is suitable for water, gas, and oil products.

The ends themselves are twisted using additional fitting coupling parts.

Couplings are standard with internal threads on both sides. There are also combined ones, internal on one side and external on the other.

Threaded connection of steel pipes

Connecting profile pipes without welding

Joining of profile pipes can be carried out without the use of welding equipment. How to connect profile pipes without welding:

• use of a crab system;
• fitting connection.

The crab system for pipes consists of connecting brackets and fixing elements. The connection in this case is made using nuts and bolts and ultimately forms an “X”, “G” or “T”-shaped profile structure. With this connection you can connect from 1 to 4 pipes, but only at right angles. They are as strong as welded seams.

A fitting connection is used when it is necessary to make a branch from the main pipe. There are several types of pipe connectors that allow you to mount workpieces in different configurations. The main ones:

• coupling;
• corner;
• tee;
• cross.

Crab systems are most often used when installing simple outdoor structures, such as a greenhouse or shed

Stainless steel

The use of alloy steel makes the pipes almost eternal. They do not gain mass popularity due to the high cost and difficulty of processing.

Corrugated stainless steel products are increasingly being used. 1 m of such pipe costs about 170 rubles. Working pressure – 12 atmospheres at 100°C.

Corrugated Stainless Steel Pipe

Cast iron

High carbon steel, or cast iron, is used for sewerage. Such products are fragile, very heavy, and if they are not covered with a protective layer, they become overgrown with deposits. The service life of cast iron pipes is more than 80 years.

Structure of cast iron pipe

How to connect pipes from different materials?

In some cases, it is necessary to connect products that are not homogeneous in material. There are special options for these purposes.

How to connect a polypropylene (plastic) pipe to a metal one?

Many people ask the question: how to connect polypropylene pipes with metal ones? There are several popular methods for this:

• thread;
• flange pipe connection.

In the first case, the coupling of pipes of heterogeneous material is carried out using couplings. One end of such a coupling is equipped with a thread, and the other has a smooth surface for joining with polypropylene.

The flange method involves the use of flanges. This connection is made using studs and bolts.

Note! Flanges are used in structures that are often disassembled during operation.

How to connect metal-plastic pipes with metal ones?

The most popular options in this case are:

• press fittings;
• compression fittings.

In the first case, the connection between pipes of heterogeneous material can be made in two ways:

• sliding press fitting;
• crimp coupling.

It is important to remember that connecting metal-plastic pipes with metal and other pipes of heterogeneous material is quite a responsible undertaking and should be carried out by specially trained specialists. Incorrect installation of the connecting element will lead to an emergency in the pipeline.

Advantages of crimp fittings

Industrial enterprises produce compression fittings with one or two ferrules, which are used to connect pipes without welding. As a result of the fittings being pressed during installation, if a section of the pipeline breaks, they will need to be cut off and replaced. Although this seems somewhat uneconomical, professionals still prefer to use these types of fittings. This commitment to this method of pipe installation is caused primarily by the fact that the elements of this design can be installed in places where it is impossible to reach either for welding or tightening threads.

In addition, among the main advantages of compression fittings are:

• absolute tightness of the connection without the need for welding or threading;
• high reliability of pipe joining;

• press fittings are able to withstand the vibration load of the pipeline for a long time.

In this regard, connectors of this type are actively used in metrology, gas turbine and compensating equipment, for piping instrumentation and automation devices and in pipelines operating under high pressure.