Pipe Fittings – Types and applications

Pipe fittings are used to securely connect pipes, tubes, and hoses. They are used in pneumatics as well as in hydraulics and other fluid-carrying systems. However, suitable fittings and adapters are also available for pipes under vacuum. As an important component of these systems, it is essential that pipe fittings reliably and securely connect the components to be connected. At the same time, they are intended to permanently prevent liquids or gases from entering or exiting. This article introduces different types of pipe fittings and their possible uses, and will help you choose the best pipe fitting for your application.

Pipe connections in general

There are several ways to join pipes. The choice of available joining methods depends greatly on the subsequent accessibility of the connection, the material to be connected, the pressure and type of the medium, as well as any special requirements for the connection or the entire system. Pipe connecting elements are often called fittings. Fittings are just one of the many ways to join pipes.

In general, a distinction is made between releasable and non-releasable connections for pipe connectors. While releasable pipe connections allow for easy assembly and non-destructive disassembly, non-releasable connections can only be released by destroying part of the material. In contrast to releasable connections, non-releasable connections can therefore also not be used in accessible areas.

Releasable connections are typically made with pipe connectors such as threaded connections or screw fittings, compression fittings, flanged connections or pipe couplings. But releasable pipe connections also include sleeve connections, cuff connections and plug-in connections. Releasable connections are often referred to as fittings and couplings. Both are a subset of connectors, but differ as follows: Fittings provide a simple and permanent connection. Couplings, on the other hand, are connections for quickly connecting or disconnecting hoses and pipes. Integrated shut-off valves can be added to automatically stop flow after the pipes are disconnected.

Non-releasable pipe connections are usually somewhat more complex to fabricate than releasable pipe connections: Pipes are welded, adhesive-bonded or soldered to each other or to the appropriate pipe connectors. This type of connection is recommended especially for lines that are under heavy loads or are no longer accessible later. There are also a wide range of fittings and connectors for these purposes. This includes, for example, press fittings and sliding sleeve connections.

What basic forms of pipe connectors are there?

Pipe connectors perform various tasks: They are, for example, designed to connect, reduce or branch pipes in a pipe system. Various pipe connectors and their typical uses are shown in more detail below.

Optimizing pipe connections

There are a few things to keep in mind to ensure that the pipe connection is secure.

Preliminary considerations for pipe connections

There are a few things to consider in order to find the right connector from among the many options. When connecting pipes, problems often occur, for example when two different materials are connected together. Some material combinations react with each other and create a higher risk of corrosion. Even an incorrectly selected pipe connector or excessive force during assembly are common causes of a faulty connection.

The most important points to clarify in advance are therefore:

• Intended use and medium (hydraulic, pneumatic, vacuum, liquid, gas)
• releasable / non-releasable
• Possible chemical reaction of the connector and pipe system materials (non-noble and noble material)
• Temperature
• Is the connector rated for the pressure and medium?
• Are there any regulations to follow (food compatibility, etc.)?
• What is the flow direction? What options and flow direction for manifolds?
• What outlets are required on manifolds (inside/outside and cross-section)?
• Selection of the then still possible system and options for assembly (screws, soldering, flanges, press fits, etc.)
• What tools are needed? Common examples include pipe cutters, pipe wrenches, standard wrenches and a bubble level.

Connection options by pipe material

Different types of pipe connections are available depending on the material and the insert:

• Steel pipes: Preferably connected by welding, otherwise e.g. with flange connections or screw connections (e.g. threaded fittings).
• Copper pipes: Preferably soldering or pressing. Press fittings are for example frequently used in heating applications.
• Plastic pipes: Preferably plug-in connections, clamping connections, also adhesive-bonding and welding. For plug-in connections, the pipe is for example simply inserted into a fitting. Additional tools are not required.
• Stainless steel pipes: Preferably pressing, welding. Press fittings are also a quick and clean method.
• Composite pipes: Preferably pressing or clamping. Clamp fittings secure the pipe with a cap nut.
• Cast pipes: Preferably flanges, socket union. Socket unions have a sealing ring installed, which ensures a particularly tight connection.

Suitable Materials by Application

Choosing the right material depends on the desired application. For example, high corrosion resistance of the pipe connection is essential if water flows permanently through a pipe. Conversely, if high pressure prevails in the pipe, this should also be taken into account when selecting the pipe connection. The following overview outlines some common materials and their application:

• PVC: Suited for water systems because they are resistant to chemicals and corrosion.
• Copper: Copper is lightweight and malleable with relatively good corrosion resistance.
• Brass: In addition to corrosion resistance, brass has a high compressive load capacity.
• Stainless steel: Stainless steel is particularly robust and durable.
• Black steel (carbon steel): low cost, high compressive strength and temperature resistance, but low corrosion resistance
• Galvanized steel: slightly higher cost than black steel, but offers improved corrosion resistance and compatibility with other pipe materials while having approximately the same properties

We recommend our Steel Materials Guide to optimize your choice of steel material.

Cutting and joining pipes

There are straight pipes in standard lengths of e.g. two, three or six meters. For complicated pipe runs, it is therefore often necessary to shorten the pipes to the required length. Pipes with unprepared ends are also sometimes sold, i.e. they are not deburred on the cutting edges. In order to optimize the fit of the pipe connection, it is therefore essential to observe certain things in advance during processing, e.g. when cutting and deburring pipes.

Using a pipe cutter, many metal pipes and plastic pipes can be cut accurately and straight without crushing the pipe. The pipe is then deburred. Especially metal pipes such as copper pipes should be deburred to prevent damaging the fittings, which creates a risk of leakage. But deburring PVC pipes is also recommended. Deburring pipes contributes significantly to the quality and longevity of pipe connections and the entire pipe system. The deburring tool removes sharp edges and burrs. They are available in hand-operated and automatic versions.

Once the pipes are prepared properly, the pipe fitting can be seated. It is important to ensure a tight fit. However, the pipe fitting should not be threaded on excessively tights as this may cause over-threading. Finally, the pipe connection should be checked for leaks. This can be done, e.g., by allowing the medium to flow in. It is of course better to detect leaks beforehand, e.g. with a leak test device or a special leak spray. The leak spray is used to apply a foam or soapy liquid, which then makes bubbles at the leak.

Standardization: Various standards for pipe fittings

Pipe fittings are classified by common threading standards.

The following table summarizes the most important ones:

Please visit our extensive techblog for more information on standard pipe thread dimensions.