Pipework systems which are subject to purely static loading are generally supported on single acting vertical supports such as a hanger rod and pipe clamp or sliding base and, if the pipework is subject to change in temperature, some or all of these vertical supports may be spring supports, either variable or constant effort type. A supporting arrangement such as this is generally not suitable for pipework subject to dynamic loading.

Dynamic loading may occur for a number of reasons. Unsteady flow, such as that caused by valve closure, produces dynamic forces and is referred to as water hammer. In an earthquake, a piping system is also subject to dynamic forces.

Where the pipework system is subject to dynamic forces, vibration of the pipework will occur. this may be injurious to the pipework and connected equipment and plant. pipework systems which are supported on single acting vertical restraints and springs with no lateral restraint will have low natural frequencies of vibration and will experience large dynamic deflections when subject to vibration: this will generally be unacceptable. Pipework stress analysis either by response spectrum or time history analysis can be used to show the need for dynamic restraints.

In pipework systems which are subject to dynamic loading. it may be necessary to use rigid struts, which act in both directions, rather than hanger rods, which only support downward acting loads. Rigid struts are also used to provide lateral restraint where this is required. snubbers are used where dynamic restraint is required, but the pipe has to be allowed to move thermally.