DATA OF INTEREST IN THE DESIGN OF AN EXPANSION JOINT
Selecting and purchasing an expansion joint is not just a matter of finding out information about its dimensions and pressure rating, and the movements in the system.
There are other parameters that have a decisive influence on its design and cost, such as: planned cycles; whether movements are concurrent; the need for an inner sleeve or exterior protection; regulations to be complied with; the pipe coupling planned for use; the space available; the layout of the pipe system, supports, anchoring, guides, etc..; the need and justification for the use of braces; the pipe materials; limitation of the activation forces; etc., etc.
An appropriately designed expansion joint offers durable service with no unexpected surprises.
1- WHAT IS AN EXPANSION JOINT?
An expansion joint or compensator is a flexible element made up of one or more convolutions/arches. It is designed to resist the internal pressure of a particular fluid at its working temperature, and must be sufficiently flexible to absorb any movements present.
2- WHY ARE THEY USED?
In a pipe system there are a variety of methods that can be applied to absorb the stresses produced by termal movements (axial, lateral, and/or angular), or by vibrations, earth settling, assembly misalignments, etc. Of the existing methods (a flexible section of pipe, adjusting plates or ties, sliding joints, or expansion joints), the one preferred by most pipe system designers is the expansion joint, since it can perform the same function while requiring less space.
3- HOW SHOULD THEY BE USED?
Depending upon the design of the pipe system, a joint may belong to either the “unrestricted” or “restricted” type.
If “unrestricted”, perfect placement of the anchoring and guides is required for proper functioning, since under the effects of the pressure a longitudinal force is exerted in both directions from the expansion joint, and this force must be resisted by the system.
For “restricted” joints (control rods, articulations, etc.), only some lightweight supports are needed, which in addition to the external loads (weight, wind, etc.), resist the activation forces of the expansion joint and the rotational forces in the support guides.
4- WHAT DOES THE ACTIVATION FORCE OF AN EXPANSION JOINT MEAN?
This is the force that must be applied to an expansion joint in order to move or activate the movement of its waves, which absorb the corresponding movement. This force is measured in N/mm and is a function of the expansión joint’s design (the rigidity of its construction based upon its design, the materials used, number of layers, reinforcements, etc.). On some occasions this may be excessively high, especially when the pipe system is made from materials with low rigidity (plastics, GRP, etc.)
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