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What is a Bellows Expansion Joint?

By B. Turner
Updated May 17, 2024
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A bellows expansion joint is a flexible piece of material used to join two pipes. Typically, installers weld either end of the bellows joint to the end of the adjacent length of pipe. Some installers may also use couplings or other joining methods in temporary or specialty applications. Once the bellows expansion joint is in place, materials can flow freely between the pipes, and even expand or contract without causing damage to the piping.

To understand how a bellows expansion joint works, picture an accordion. Just as the folds of the accordion move laterally or at an angle with ease, so too do the components in a bellows joint. If the pressure or temperature within the pipe changes, or the materials are subject to any unusual forces, these materials can exert extreme force on the pipes. A normal solid-walled pipe could crack or burst under this pressure, but a pipe with a bellows expansion joint offers much more flexibility for this type of scenario.

These joints are commonly found where pipe size transitions from a larger diameter to a smaller one, or in areas where the pipe bends around a corner or obstacle. These applications frequently lead to pressure changes within the pipe that require a bellows expansion joint to maintain the integrity of the system. A bellows joint may also be found in steam pipes, or pipes that carry volatile gases or chemicals. As pressure modulates along the pipe run, one or more bellows expansion joints helps to reduce strain on the walls of the pipe.

Because a bellows joint can move in a number of ways, it's able to absorb a variety of different forces. These joints can expand and contract with ease along an axis, or when subjected to lateral forces. They also move both above and below the elevation of the pipe to absorb angular forces. By moving in a variety of directions, a bellows joint not only absorbs and controls movement, but also reduces the impact of vibration and minor seismic activity. In addition to protecting the piping structure and supports, this also minimizes noise levels within the building.

The walls on a bellows expansion joint must remain fairly thin in order to maintain a high degree of flexibility. To prevent damage to the joint and reduce the risk of leaks, the bellows are often lined with a metal or thermoplastic sleeve. These sleeves not only protect the pipe, but also reduce friction and eliminate material buildup that could impact flow.

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