Pipe guide

A guide prevents the pipe from moving sideways and lets it slide along its axis. It thus directs thermal expansion in a desired direction instead of blocking it. Depending on its design it restrains laterally only, or additionally holds the pipe down.

That distinguishes it from a sliding support, which only carries, and from an anchor, which restrains everything.

Guides have four functions, and one guide usually fulfils several at once.

At a change of direction one leg absorbs the expansion of the other by bending. To do so it must be able to deflect sideways. A guide placed too close to the elbow prevents exactly that: the leg becomes short and stiff, and stresses and forces rise sharply.

The first guide after an elbow therefore belongs far enough away for the free leg to absorb the expansion. How far is determined by the stress analysis – it is one of the places where moving a single support changes the result completely.

An axial expansion joint makes the line soft at one point. Under pressure thrust the line tends to buckle there. Guides on both sides of the joint are therefore mandatory. The EJMA standards recommend placing the first guide no more than four and the second no more than fourteen pipe diameters from the expansion joint; further spacings depend on pressure and pipe size.

A real guide has a gap – a few millimetres between pipe shoe and guide bar so that the line does not jam. The gap can be included in the analysis model; the line then makes contact only after a small movement. For sensitive connections this makes a difference.

Once the line bears against the guide, axial movement produces friction. It is small compared with friction at the rests but adds up on long lines with many guides.