Expansion Joints

According to their physical properties, most metals expand with increasing temperatures and contract with decreasing temperatures.

In pipeline systems, this phenomenon causes a variation in the length of the individual sections of the pipeline.

As pipelines are normally anchored at least on two connection points, any variation in length will result in thermal strain in the material and enhanced forces and moments at these terminal points.

As far as possible, one will utilize the inherent flexibility of a pipeline to compensate the pipe expansion (natural compensation).

Should the expansion, however, exceed the inherent flexibility of the pipe, expansion joints are necessary to compensate these movements.

Additionally, mechanical vibrations of pumps, compressors, turbines and motors should be dampened to avoid any damage to adjoining pipelines, their supports or any installed instruments.

Forces and moments on nozzles of compressors, turbines, vessels and other plant components are limited and must not be exceeded.

In all these cases, expansion joints can be utilized.

The central component of each expansion joint is the metal bellows (*) that, due to its shape and thin wall, acts like a spring. The bellows however has to meet the following basic criteria to qualify for its use as an expansion element.

It must

  • withstand the operating and test conditions (pressure, temperature) of the pipe system,
  • ensure corrosion resistance against internal (flow) and external (atmospheric) conditions,
  • provide sufficient flexibility to compensate thermal expansion and mechanical vibrations with the requested durability (life expectancy)
  • include sufficient squirm stability.

(*) Exceptions are rubber expansion joints.

BOA Group Metal Expansion Joint
BOA Group Rubber Expansion Joint

Expansion joints with stainless steel bellows

The BOA Group offers a wide range of expansion joints, suitable for numerous specific applications.

The BOA expansion joints portfolio basically consists of three main series:

  • Standard series: expansion joints up to DN 150 (6")
  • Industrial series: expansion joints up to DN 1.000 (40")
  • Special series: expansion joints >DN 1.000

The heart of all expansion joints is the metal bellows. Thanks to modern design and manufacturing facilities, all BOA expansion joints offer the following advantages:

  • High flexibility
  • Short build length
  • Large movement capacity
  • Durability and excellent chemical resistance

The BOA Group uses almost every type of bellows forming to offer the best possible solution to its customers: Hydraulic and elastomer forming, punching as well as mechanical rolling.

Axial expansion joints

BOA Axial Expansion Joints

These expansion joints are designed to take up axial movements in a piping system. The advantage of axial expansion joints is the fact that they take up relatively little space and no directional changes in the piping are required. When installing axial expansion joints, proper fix points and guidance are required. Please consult our engineers for more information.

The BOA Group offers two ranges of axial expansion joints:

  • Standard series: (axial) expansion joints up to DN150 (6")
  • Industrial series: expansion joints > DN150 (6")

Depending on the required type, sizes in the industrial series go up to DN1.000 (40").

Besides our standard and industrial program, BOA also manufactures special expansion joints according to customers’ specifications. Diameters of several meters are no exception!

Lateral expansion joints

BOA Lateral Expansion Joints

A lateral expansion joint works in the same way as a hinged expansion joint does. It utilizes the ability of a bellows to rotate in angular direction. The lateral movement capability is the result of the angular rotation of the bellows and their centre to centre distance. The longer the distance between the bellows, the larger is the movement.

A longer centre to centre distance also results in lower displacement forces of the expansion joint. Lateral expansion joints are independent expansion systems in contrast to single hinged expansion joints. They are practically a two pin system. Lateral expansion joints are usually installed with a 50% pre-stressing. This is accomplished by pre-stressing the entire pipe system after the expansion joint is installed.

Angular expansion joints

BOA Angular Expansion Joints

Angular expansion joints are used for large angular movement in one or two planes.

Angular (or hinged) expansion joints are used for large pipe elongations. A system of expansion joints is made of standard elements. This requires two or three expansion joints. The application of angular expansion joints always requires a change in the direction of the piping. Therefore, they are preferably located where a 90° bend has originally been foreseen. The elongation absorption of hinged expansion joint systems is practically unlimited. It is determined by the allowable movement‘s angle of the hinged expansion joints and the length of the pipe section between two angular expansion joints.


  • almost unlimited elongation absorption
  • reduced load on anchor points
  • modular concept application
  • use of normal guides


  • change in pipe direction is always required
  • more space required as compared to axial expansion joints
  • two or three expansion joints required for a system

Expansion Joints Selector

The BOA Constructor, selector for expansion joints, offers the possibility to look for a suitable expansion joint according to your individual requirements.

Expansion Joints Selector

Hydraulic formed expansion joints
Elastomer formed expansion joints

Installation Instructions Expansion Joints

Rubber / PTFE expansion joints

BOA Rubber Expansion Joints

Rubber and PTFE expansion joints are commonly used in industrial and HVAC applications.

Typical examples are:

  • Chemical and petrochemical industry
  • HVAC installations
  • Shipbuilding
  • Piping

The main difference between rubber and PTFE expansion joints is the corrosion resistance and temperature resistance which are significantly higher with PTFE expansion joints.

BOA rubber and PTFE expansion joints are suitable for:

  • Absorption of vibrations
  • Taking up axial or lateral expansion
  • Taking up installation tolerances
  • Noise reduction

Data Sheets Rubber Expansion Joints