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  Thin-wall Metallic Expansion Joint: Toroidal

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.

Design equation for toroidal bellows are contained in the Standards of the Expansion Joint Manufacturers Association (EJMA).

   Metalic Expansion Joints

	Thin-wall
	Single Hinged Gimbal Universal Elbow Pressure Balanced In-line Pressure Balanced Externally Pressurized Expansion Joint Toroidal
	Thick-wall (flanged & Flued)
	Slip-type
	Rectangular

   Fabric Expansion Joints