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Types of Deflection

PT&P offers all of the types of metal expansion joints. Each type has advantages and limitations, which when applied correctly, can provide the flexibility, load reduction, structural integrity and reliability desired in a piping system.

Expansion joints, besides acting as sections of a pipe, capable of withstanding the design temperatures, pressures, and media, also provide the flexibility that makes them necessary. That flexibility can be either axial, lateral or angular. However, in many installations, some rigidity or structural strength is needed to support piping loads or to control the motion of the bellows and the pipe. Features are then added to the expansion joint to limit the modes or degrees of freedom, or the types of deflections, and to resist shear, or tension, or compression loads and/or bending moments. The most common types are presented in this catalog.

In order to properly apply expansion joints to piping systems, it is necessary that both the piping specialist and the expansion joint designer each understand not only how the piping flexes, but how the various expansion joint types function and what they are capable of doing. It may be relatively easy to visualize that deflections may result from thermal expansion or the movements and vibrations of equipment and structures; however, all expansion joints do not accept the same types of deflection. Many can accept certain loads and moments, while others are incapable of resisting externally applied forces. Understanding the type, magnitude, and direction of these forces and deflections is critical, not only to the safety of the system but to its cost.

With today’s piping flexibility computer programs, determining where stresses are excessive, and therefore that expansion joints may be necessary, is a simple task. The placement of expansion joints, and their proper selection, still depends upon the designer’s experience and understanding of how expansion joints work, and how the piping must be anchored and supported when expansion joints are used. This section describes the different types of expansion joints available, how they function, what types of deflections they can accept, and what types of forces and movements they can and cannot resist.

The sections below contain samples of applications discussions and examples of how various types of expansion joints can be used to solve piping expansion problems.