Why An Expansion Joint Works – Part I

Why An Expansion Joint Works – Part I

Why an Expansion Joint Works - Part 1
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On the surface it doesn’t seem to make sense. If the code requires a pipe in a system to have a 3/8” thick wall to contain the internal pressure, how can an expansion joint bellows get by with just a 1/16” thick wall?

Balance the Forces
It’s how the material is arranged. For a pipe, there needs to be a certain amount of metal (in the cross section) per unit length ‘L’ in order to resist the internal pressure force that wants to pull it apart.

More Metal, Please
A single convolute of a bellows is made up of a thin wall of material that is ‘squeezed’ into that same unit length ‘L’. It is the shape of the convolute that causes it to have a cross sectional area that comes close to that of a pipe.

A pipe is typically thicker by design to account for future thinning due to corrosion. A bellows, instead, is always made with a corrosion resistant material.

Form and Function
By a great stroke of fortune, the convolute shape that helps to increase its pressure capacity ALSO makes it flexible in the longitudinal direction.That’s really handy because with several convolutions in a row, the bellows can also angulate and move laterally. The shape of the convolutions increases its pressure capacity along with making it flexible. There are other pressure limitations a bellows has compared to a pipe, but an expansion joint is a useful device for extending the life of piping, nozzle connections, and equipment.


About The Author

Greg Perkins
Greg Perkins
President & General Manager

Greg Perkins has 25 years experience in the expansion joint industry. In his previous employment with Senior Flexonics Pathway, Greg Perkins held the position of CEO and General Manager for 11 years. Prior positions include project engineer, director of engineering, and business unit manager.

In addition Greg, a degreed engineer, served on both the EJMA (expansion joint manufacturers association) technical and management committee tasked with developing/updating bellows and expansion joint performance criteria. Proficient in ASME design codes. Patents include high temperature piping restraint structures for expansion joint applications.

Got questions? Need answers? Call Greg today (830) 626-7773 or send him an email [email protected]!