Are spring hangers selected for hot design or cold design?

The weight of the pipework doesn’t change when it gets hot, but the pipes move up and down due to thermal expansion. When using simple variable effort supports, the supporting effort necessarily changes as the pipe moves up or down due to the spring rate of the supports. So it is not possible to exactly balance the pipe with the supporting effort from the springs in both the cold and hot conditions. You therefore need to decide in which condition you want to exactly balance the weight of the pipe.

For steam pipes (especially high pressure steam) the material strength is much less at high temperature, so it is usual to have the support loadings exactly matching the weight of the pipe in the hot condition (hot design) and accept the load imbalance and consequent higher terminal point loadings in the cold condition.

For pipes where there is no appreciable reduction in material strength at the design temperature, designers sometimes choose to use the cold design method where the loads balance exactly in the cold condition. This should in theory make the pipework installation easier, as releasing the springs from their locked positions should not result in significant deflection of the pipework since the loads should balance correctly in the cold condition. There will be a load imbalance in the hot condition.

It is good practice to select supports towards the middle of the travel range. Normally one should aim to centralize the cold to hot range rather than just the hot load. Doing this will help to avoid the springs “topping” or “bottoming” out due to any difference between actual and theoretical pipe weight.