Most people understand the concept of a common DME bellows expansion joint, consisting of a bellows attached to a variety of possible end fittings. It is simple, and most of the components are visible to anyone. If someone takes a look at a DME externally pressurized expansion joint or expansion compensator, a scratch of the head is the common response.
Externally pressurized expansion joints are an excellent solution for absorbing large amounts of axial movement in piping systems. The common applications include Oil Refineries, Liquefied Natural Gas (LNG), Steam Plants, Flare Stacks, and Industrial Cooling Systems. Due to the design of the expansion joint, squirm of the bellows is not a factor. When a compression force is applied to an externally pressurized expansion joint, the bellows extends, like pulling on the two ends of a piece of rope. Externally pressurized expansion joints, because they incorporate two built-in guides, are rated for minimal lateral movement.
As you can see in Figure left, the externally pressurized expansion joint consists of an external shroud that also acts as a chamber for media to flow around the external side of the bellows convolutions, unlike the conventional internally pressurized bellows expansion joint. The bellows is fixed to the shroud on one end and on the other end to a piece of pipe capable of sliding in and out of one end of the shroud to allow for expansion or contraction, and also acts as an internal liner, protecting the bellows.
Another possible configuration is what is commonly called a dual externally pressurized expansion joint with an anchor base. This configuration consists of two pieces of pipe attached to an internal bellows sliding in and out of both ends of the shroud, allowing for even more axial movement. This configuration must contain an anchor base, and be anchored appropriately. See Figure left. The most common end fittings on an externally pressurized expansion joint are flanged ends, weld ends and male or female pipe threads.
DME stocks a large variety of Externally Pressurized Expansion Joints, and knowledgeable product specialists are available to assist with your application.