What Is The Difference Between Pipe Coupling And Union?

Both couplings and unions are used to connect pipes, but they’re built for different situations.

A coupling is for joining pipe to pipe or pipe to a swage, It is simple; it usually uses threaded connections or welding connections, joining two pipes together permanently. Think of it like a sleeve that extends the pipeline. It’s strong, compact, and reliable, but once it’s installed, it’s not meant to come apart easily.

While a union is for joining and disassembling components of a piping system, it is designed to be easy for connecting two pipes or components, but lets you take them apart whenever needed, perfect for maintenance or replacement. It’s a reusable connection with a threaded middle section.

So, which one should you use?

Use a coupling when you’re building a permanent pipeline and don’t expect to take it apart.
Use a union when you future access any parts you may need to replace.

And, building codes generally don’t tell you to use one or the other. The choice depends on the material, pressure rating, and whether you’ll need access later.

1. What is A Pipe Coupling?

A pipe coupling is a short piece of pipe used to connect two pipes, and the pipe coupling connects two steel pipes through a threaded connection. The seal at the connection is threaded. The disassembly should begin at one end, typically used for lengthening the pipeline. They are typically used for lengthening the pipeline when a single pipe isn't long enough to cover the required distance. If you're laying a long stretch of pipe, you'll be using plenty of these! A common size you might encounter in household plumbing is a 1/2 in coupler.

Couplings are designed for strength and permanence, making them ideal for runs of pipe that aren't expected to be frequently altered.

• Materials

Carbon steel, stainless steel, alloy steel, PVC, and plastic, among others.

• Connection methods    

Threaded connections, welding, sockets, and other related components are essential in various mechanical and structural applications. Threaded connections are very common, especially for smaller diameters. Welding provides a strong, permanent joint. Sockets are used with socket-weld fittings.

• Manufacturing standards

ASME B1.20.1, DIN2986, BS10241.

• Manufacturing process

Forging heats steel ingots or bars to shape them and processes threads on a lathe, while casting melts steel ingots and pours the molten metal into a fixed mold to cool.

• Application

Because of their convenient use, pipe couplings are popular in civil construction, industry, agriculture, and other fields.

2. What Is A Pipe Union?

A pipe union is a commonly used pipe connector that stands out because it can be easily installed and disassembled without rotating the pipes themselves. This ease of separation is its superpower! It mainly consists of three parts: nut, cloud head, and flat connection. The pipe union is used at the ends of valves, water meters, and other equipment in the pipeline and is convenient for disassembly and maintenance. Think of a union as a 'disconnect' point in your piping.

When you see a fitting with a large nut in the middle, chances are it's a union, ready to be taken apart. It's a versatile pipe union fitting.

• Material

Threaded unions are in industries that require metals with high-pressure resistance. Materials such as carbon steel, stainless steel, alloy steel, and brass are commonly used, along with plastics like PVC, PE, and others.

• Connection forms

Socket welding and threaded connection. (Socket welding is to insert a steel pipe into a socket for welding. Therefore, it is called a "socket "Or swivel joint"; the threaded connection is to screw the steel pipe into the screw hole for connection. Therefore, it is called a "threaded union"). The threaded form is particularly popular for its ease of use in many applications.

• Manufacturing standards

ASME B16.11, MSS SP 83.

• Definition

Threaded union refers to a pipe connection with a thread, the most common type of pipe fitting in industry and life. The threaded union simplifies pipeline connections, allowing for easier and more cost-effective disassembly and replacement.

• Type

There are equal diameters and different diameters of threaded unions.

3. Pipe Coupling VS Union

Both pipe couplings and pipe unions belong to pipe fittings.

The fundamental difference between a coupling and a union lies in their functions: a coupling connects pipe to pipe or pipe to a swedge, while a union joins and disassembles components of a piping system, such as a steam trap or control valve, for maintenance or replacement. The use of couplings or unions is not a code issue.

Couplings are pipe fittings in the pipeline. Should use coupling when the pipeline exceeds the length of a single pipe (such as 4m, 6m, etc.), which means that the coupling is purely to extend the pipeline; the union as a pipe fitting disassembles that is, and the things connected through the union can be removed and replaced, such as the valve side, the radiator side, etc., for maintenance and disassembly. Pipe unions are generally on threaded pipes and pipes with small pipe diameters. For disassembling easily to larger pipe diameters are connected using flanges, etc.

The pipe coupling has threaded coupling, butt welded coupling, and socket coupling, while the pipe union only has threaded union and socket union. The socket slip knot must have threads to screw down; with a union, there is no need to screw the pipe. If the union unthreads, move the pipe to disconnect the connection.

From a practical application point of view, the union is used on low-pressure occasions, while pipe coupling is suitable for high-pressure occasions. The union is a threaded connection generally used in public engineering placements of less than 10kg.

4. Advantages and Disadvantages

Pipe couplings have higher durability and can be used in severe environments in the long term due to their high-quality steel or more durable materials. With simple design and installation convenience, it can connect two pipes quickly. A good seal in the joint to avoid leakage of fluid or gas. They can connect diverse sizes or types of tubes to make the system more flexible. However, due to the strong connection with the thread, it is hard to disassemble a portion of the couplings, particularly in high-pressure environments.

Unions disassemble easily, making maintenance and part replacement convenient. The connection method can be selected based on your needs, providing greater flexibility. However, it is less robust when subjected to high pressure or strong vibrations than some fixed connection types. With repeated disassemblies over time, it is likely to become worn and less efficient, making it crucial to handle it with care to maintain its performance.

In summary, if you need a simple, strong, and permanent way to extend a pipe, reach for a coupling. If you need a connection point that allows for quick and easy removal of a component for service, a union is your best friend.

5. About us

Hebei Sanvo is one of the quality pipe fittings manufacturers and suppliers in China and exports a variety of threaded steel pipe fittings, including carbon steel pipe nipples, carbon steel pipe coupling, stainless steel pipe nipples, stainless steel pipe coupling, and stainless steel threaded pipe fittings. 

If you are interested in our pipeline products, please do not hesitate to contact us, and we look forward to hearing the good news.