Piping - Expansion joints

Expansion poses a problem for the design office of any equipment manufacturer or pipe fitter, because it cannot be prevented. In an assembly of elements forming a closed line, any variation in dimension of an element, caused by a difference in temperature and/or expansion coefficient, must be matched in magnitude and direction at the level of this element by the system of deformations resulting from the state of stress exerted on all the assembled elements. Before the arrival of expansion joints on the market, the solutions to this problem were as follows.

This solution can only be envisaged for axial compensation of expansion. Due to the high modulus of elasticity of the materials, compensation exclusively by axial deformation according to Hooke's law is not possible. The solution is to eliminate the mechanical connection by interposing a sliding gland seal. This device allows coaxial displacement of its ends, sealing being obtained by means of a stuffing box. With this solution, the difficulties encountered lie in sealing, guiding and the forces developed by the friction of the gland and by the bottom effect, which will be discussed further below 1.3.1.1 .

In this solution, which only applies to pipelines, the expansion of each element in the line is compensated for by bending and twisting the adjacent elements, which implies a change in their direction. In this way, straight elements and bends, which are more flexible than the latter, are used to create a route that is sufficiently flexible to compensate for expansion without excessive stresses in the bends or excessive stresses in the anchors.

A self-expanding route therefore requires a large footprint and is quickly limited in pipe diameter by the excessive stresses it exerts on civil engineering (at constant pressure, stresses on fixed points vary as the fourth power of the diameter).

Expansion joints have brought advantages to both of the above solutions.

In the first case, the elimination of the cable gland has made it possible to seal the axially compensated device.

In the second case, the very high flexibility of the...