Connecting couplings for metal pipes: types, installation features

Couplings for metal pipes have been used in connecting pipe blanks for a long time.They became an alternative to welded joints and made pipelines detachable. When using them, there was no need to use welding, which not everyone can use, meaning doing the work with their own hands.

There are different types of couplings on the market, which differ from each other in the material of manufacture and methods of connecting metal pipes.

What do couplings for metal pipes look like?

Couplings belong to the category of fittings. They are connecting elements. And since pipelines are cylindrical in shape, all couplings offered today are also hollow cylinders. They are all metal.

Previously, they were mainly used with threads cut into their ends, which could be internal or external. Today, the range has expanded with the advent of new technologies for connecting metal pipes.

Types of couplings

Manufacturers offer three types of couplings used to connect metal pipes:

• threaded;
• compression or clamping;
• press couplings.

Since metal pipes are a broad concept, which includes products made of steel, cast iron and copper, accordingly, not all of the above couplings are used to connect all types of pipelines. Cast iron ones are also thick-walled, but their installation is carried out in ways different from threaded ones.

Threaded

They are used only for connecting steel pipes, because the latter have thick walls that can be threaded.Threaded couplings are made from:

• become;
• cast iron;
• brass

The first are thick-walled cylinders, often with identical internal threads. The walls are thick. Raw materials – black or stainless steel. Withstands great pressure.

Minuses:

• to create a tight joint, it is necessary to use additional insulating materials;
• During operation, a space filled with rust is formed between the threads of the coupling and the pipe, which leads to “sticking” of the metals.

The second ones are the same as the first ones. They are made of gray cast iron, to which soft graphite is added. This material composition allows the couplings to withstand temperatures up to +300 ℃ and pressures up to 25 bar. Service life - up to 80 years. Manufacturing technology – shaped casting. Threads are cut on lathes.

These couplings cannot be installed on copper pipes. The reason is a large difference in the speed of electrochemical processes, under the influence of which corrosion quickly occurs.

The third type of threaded couplings, namely brass, has been on the market relatively recently. They can be classified as universal fittings because they are used to connect not only steel but also plastic pipes. Brass products are not sold in their pure form because this metal does not have high corrosion resistance. Therefore, it is treated with chromium or nickel on top.

Compression metal couplings

This type of couplings for metal pipes belongs to the threadless group. They appeared on the market relatively recently and among craftsmen they are called Gebo couplings (after the first manufacturer). More precisely, the German company Gebo Armaturen.

The problem with this fitting is the difficulty of connecting metal pipes with a threaded coupling.That is, in order to carry out this process, it is necessary to weld bends to the ends of the pipes, which is not always possible. Especially when repairing pipelines. You can cut the thread with a tool, but this method cannot always be used.

Compression couplings consist of two main parts - the coupling itself with external threads at the ends and two nuts. The latter includes three elements:

• clamping ring;
• metal washer;
• rubber cuff, also known as a seal.

The big advantage of this type of connectors is that they are detachable. If necessary, they can be disassembled and replaced, or one of the parts can be replaced. This is also convenient when dismantling the pipeline.

Half couplings, which were also developed by Gebo Armaturen, can be included in this category. The fitting consists of two identical parts, which are connected to each other by four bolts and nuts. A sealant in the form of gaskets is placed inside each part, which ensures the tightness of the joint.

They are most often used when it is necessary to eliminate a leak in a metal pipe. They are used less frequently in connections. Although this is precisely why the Germans developed them. In terms of ease of use, half fittings are better than others. Especially when the joint is in an inconvenient place.

Press couplings

The name speaks for itself. To work with them you need a special tool - collet pliers. With their help, a coupling is crimped into which a metal or metal-plastic pipe is inserted. Press fittings, when talking about metal pipes, are used only for connecting copper pipelines.

There are push fittings. They differ from press couplings in that they do not use pliers. Cuffs are placed inside the edges, which ensure the tightness of the joints.

Installation is simple - the end of the pipe is inserted into the fitting to a certain depth. The cuff compresses the pipe surface. This option is used more often for temporary pipeline installation or when repairs are necessary.

Couplings for cast iron pipes

Cast iron pipelines are connected using a socket method. Therefore, in their design, one end of the tube blank is expanded. The second end of the next pipe in the pipeline, which has a straight cross-section, is inserted into it. But manufacturers produce cast iron products without sockets. To connect them together, you need a metal coupling, at the end of which there are these sockets.

The second option is half models made of either cast iron or steel. They also contain rubber or plastic gaskets. The fitting halves themselves are connected to each other with several bolts on each side.

Bell-type couplings cannot be removed without disassembling the pipeline. Half-hearted ones allow you to do this.

Couplings for copper pipes

In copper pipelines, three types of couplings can be used to connect sections:

• compression;
• press fittings;
• for soldering (they are also capillary).

The first two were introduced. There remains a third type, which uses soldering. This is one of the most reliable ways to connect copper pipes with 100% tightness. Plus - high mechanical strength, hence the durability of the joints.

Disadvantages of soldering:

• large financial costs for consumables;
• Soldering cannot be done without experience and knowledge.

Copper couplings must be used to connect copper pipes. This is the only way to ensure long-term operation of pipelines. Fittings made from other materials can be installed, but temporarily.

How to install couplings for metal pipes

Threaded metal fittings are easy to install:

1. FUM tape is wound onto the pipe thread.
2. The coupling is screwed on so that the edge of the pipe reaches the middle of the length of the fitting.
3. From the opposite side, a drive is screwed into the latter, also to the middle. A sealing material is pre-wound onto it.
4. The squeegee is welded to the second pipe.

The second run must be long so that during welding, when the temperature of the metal increases, the latter does not reach the joint, which can cause the sealing tape to burn out.

Cast iron fittings are installed in the same way. But there is also a difference. You need to purchase nuts for them. They support the ends of the coupling, creating increased tightness of the connection.

The process goes like this:

1. The nut is screwed onto the thread until the end.
2. FUM tape is wound.
3. The fitting is screwed on.
4. First the second nut is screwed onto the squeegee, then the FUM tape. It screws into the coupling.
5. Both nuts are tightened to the edges of the fitting.

Now let's talk about how to install a compression coupling for a metal pipe. There are a couple of requirements here:

1. The ends of the pipes are cut strictly perpendicular to the axis. Their surfaces are cleaned of paint, rust and other layers.
2. Installation of the coupling itself is carried out strictly along the axis. Deviations are allowed, but not more than 3º, otherwise 100% tightness of the connection cannot be guaranteed.

The installation itself is carried out as follows:

1. Put on the ends of the pipes in order: a clamping nut, a ring with a chamfer towards the nut, a washer and a collar with a chamfer towards the coupling.
2. The end of the fitting is pressed against the end of the metal pipe. It is put on in order: cuff, washer and clamping ring.
3. Screw the nut until it stops.

The same process is carried out on the other side.No tools required here.

Press fittings for metal pipelines are also easy to install. They are put on the ends of the pipe elements to be connected and clamped with pliers.

Connection of cast iron pipelines

The first option is minting. When connecting pipes using the socket method, a gap is formed between the elements being connected, which becomes an area of ​​leakage. It is filled, creating a tight joint. This is done like this:

1. A rope is placed inside the circumference, which is pre-treated with technical oil or resin. Laying height is ⅔ of the connection length.
2. The laid bundle is compacted using a hammer and a hammer.
3. Cement mortar is being prepared. This is cement grade M300-400 mixed with water. Proportions 9:1.
4. The thick mass is poured into the gap and minted until a dense layer is formed. Pouring is carried out until the cement is level with the end of the socket.

There is another option that uses cement and asbestos fiber. Both materials are mixed in a 2:1 ratio, respectively. Then water is added to the mixture - 10-15% of the total volume of the mass. This solution is used to caulk the joint.

Cast iron It is easier to connect the joints with half fittings. The latter are separated - the bolts are unscrewed and disassembled into two parts. Pipes are laid in the lower half so that their ends touch. The top element is placed on top. Both halves are compressed with bolts. It is important here that when laying metal pipes, the gaskets do not move.

Of all the indicated methods of connecting metal pipes, soldering is the most difficult. The rest of the options are simple. It is not difficult to do the docking yourself using the fittings indicated above. Some require no tools.You will have to tinker with minting, but it is not a difficult process. The main task is to strictly follow the technology and requirements.

Threadless compression connection: video.

I would like to know from our readers if anyone has experience connecting metal pipelines using the methods described above? Share your experience in the comments. Save the article as a bookmark so you can return to it at any time.