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How does a toroidal expansion joint work?

December 1, 2010

A toroidal convolution consists of a circular tube (or totus) wrapped around weld ends or pipe ends having a gap at the I.D. to permit axial stroke. A toroidal expansion joint may consist of one convolution, or multiple convolutions. This joint is also known as an Omega bellows expansion joint for it resembles the Greek letter Omega. Most toroidal bellows are hydraulically formed which requires high pressure. Others are free formed, similar to blowing up a balloon. More accurate convolution shapes may be formed into toroidal dye cavities. Since this forming pressure is high, pressure resistance is also high.”U” shaped bellows cause a bending stress due to the pressure load on the convolution side wall. This generally determines the maximum pressure, however the toroid contains only membrane stress thus determining the maximum pressure. Due to the toroidal shape, deflection is limited. With “U” shaped convolutions, more deflection can be achieved but allowable pressures are lower.

Toroidal Bellow Expansion Joint
Toroidal Bellow Expansion Joint
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92″ I.D. Toroidal Bellow Expansion Joint for an ASME “U” Stamp Heat Exchanger Shell

July 2, 2001
92-inch I.D. toroidal bellow expansion joint for an ASME "U" stamp heat exchanger shell
92-inch I.D. toroidal bellow expansion joint for an ASME “U” stamp heat exchanger shell

The toroidal shape gives the bellow the unique ability to carry high pressures; conversely, it also permits modest deflection ability. The expansion joint was designed for 400 PSIG at 500° F and an extension stroke of 5/16″ and the bellow’s element was fabricated from .060″ Inconel® 600 with A-516 gr 70 weld ends. The 92-inch toroidal expansion joint was also designed per ASME Sec. VIII rules as well as the Expansion Joint Manufacturer EJMA Standards. Upon fabrication completion, a hydro test was conducted at 600 PSIG to detect leaks.

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