Using Expansion Joint Systems

By: Anna Woodward

An expansion joint is a device that contains one or more bellows, which is used to assist with structural changes, such as those produced by the thermal expansion or tightening of a pipe, tube, or vessel.

An expansion joint can be used to allow movement in a pipeline system. The bellows is a flexible part of an expansion joint that normally consists of several folds. The expansion joint is the best solution when making a piping system more elastic. Flexibility is needed when there are different movements in a pipeline such as, frequent vibrations, pulsations and thermal growth.

There are three basic types of movement that can be applied to the bellows and these are: axial, a movement in a direction parallel to the longitudinal axis; lateral, a movement perpendicular to the longitudinal axis; and angular, a rotational movement of the longitudinal axis.

Metal expansion joints are widely used in pipeline systems. They are vital elements for these technologies. The main reason why these flexible expansion joints are used is because they compensate different variations that may appear in length. Changes in a pipeline's length are usually the result of high temperature differences, which the metal joints are designed to withstand. They are designed with consideration for different factors, such as: temperature, pressure movement and environment.

Metal expansion joints are also required when it comes to absorbing different vibrations produced by motors, compressors or turbines; the various axial, angular and lateral movements can be easily stabilized in almost any situation.

The metal bellows is a cylindrical container or vessel that can be stretched or compressed on account of several circular folds. They are flexible and durable when they are properly used, meaning if they are used within the designed specifications.

Metal bellows are used in many different industries mainly because they can perform many distinctive functions from sealing environments to carrying gases, liquids and slurry. They have the following standard dimensions: inside/outside diameter, free length and spring rate (the spring force applied by the bellows).

There are four different ways to manufacture a metal bellows. The first of them is electroforming, which actually means to deposit several layers of metal on a mandrel of aluminum. Secondly, chemical deposition is very similar to electroforming done by electro-depositing different types of metal on a mandrel; mechanical forming, and the forth one is welding.

The common materials used in the construction of metal bellows are usually aluminum, stainless steel, tantalum, titanium or steel. However, the most common available on the market is the stainless steel expansion joint, which can be manufactured with both single and multi-walled bellows. These can be used in different applications such as turbine piping, engine exhausts, shaft propellers and many others. Metal expansion joints have been effectively used in a wide variety of situations since around the year 1940.

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