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By how many millimetres a pipe run grows between installation and operation – the figure with which the design of expansion loops, expansion joints and anchors begins.
Limits of the calculator. The expansion coefficients are guide values and depend on the temperature range; the material standard or data sheet is binding. The calculator gives the free change in length – not the forces and stresses that arise when the line is restrained.
Free thermal growth is the product of the mean expansion coefficient α of the material, the original length L and the temperature difference ΔT between installation and operation: ΔL = α · L · ΔT. For carbon steel that is roughly 1.2 millimetres per metre and 100 kelvin, for austenitic stainless steel about a third more, for plastic pipe seven to fifteen times as much depending on the material.
The change in length itself is harmless as long as the line is free to move. If it is restrained – between two anchors, at a pump nozzle – forces arise that depend not on pressure but on the stiffness of the line. A straight steel pipe that cannot expand builds up stresses beyond the allowable even with moderate heating.
Expansion is therefore accommodated by design: through the routing itself, through expansion loops or through expansion joints. Which solution fits depends on space, pressure, fluid and allowable nozzle loads.
The change in length says nothing yet about the stresses in the system. That requires geometry, supports and connections – the job of a pipe stress analysis. As an estimate, however, the figure answers two questions at once: how much movement a sliding support must allow and what travel an expansion joint or loop has to absorb.
The run between two anchors – or between an anchor and the point whose movement you want to know. Between two anchors the entire change in length of that run has to be absorbed.
Not for the change in length. It matters a great deal for the forces under restrained expansion: a large, thick-walled pipe is stiffer and generates higher forces for the same expansion.
Their expansion coefficient is roughly seven to fifteen times that of steel. They are far less stiff in return, so the forces stay low – the movement still has to be planned for with guides and flexible legs.
Stress analysis, support concepts and resonance studies for piping systems.
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