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Pressure thrust/end cap loads are self equilibrating loads. This means that for any given piping component, the distribution of pressure load is in equilibrium. The pressure load at the inlets/outlets is commonly referred to as "End-Cap forces" calculated as shown in Figure 1 and follows a sign convention that a positive end-cap force induces tension on the pipe. Note that for the calculation of analysis loads, no material allowances are considered.
Figure 1: Internal and external pressure acting on straight pipe with end caps.
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Figure 4: Poisson effect on pipe length due to internal pressure
For systems that ARE free to deform (no restraintunrestrained), pressure stresses are from the end-cap/pressure thrust forces as the Pressure elongation can occur. Examples of systems that can be considered unrestrained include:
- Straight pipe fixed/line stop at one end, free or guided at the other;
- Straight pipe fixed/line stop at the center and both ends free or guided.
- Non-buried piping with elbows or other components that allow the elongation to occur.
For systems that are NOT free to deform (restrained), pressure stresses are from the restrained Pressure elongationPoisson effects. Examples of systems that can be considered unrestrained include:
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