Review the model - CAESAR II - Reference Data

CAESAR II Applications Guide (2019 Service Pack 1)

Reference Data
11.0 (2019)

The operating moments (X, Y, and Z) on the pump nozzle are greater than the API 610 allowable limits. Because of this, you must modify the piping system to reduce these loads. Return to the static analysis of Tutorial A to determine the causes of these large loads. You can then make the needed changes to the piping system.

In the Tutorial A static results, compare the operating loads on the pump to the installed loads on the pump. If they are vastly different, the thermal effects cause the overload. If they are similar, the sustained effects cause the high loads.

In this case, only the operating loads are high. Therefore, the piping system has a thermal expansion problem. For a given amount of thermal growth, you can reduce the thermal forces and moments by adding flexibility to the system. Because F = KX, you can reduce the thermal growth between the end point forces or moments by reducing K.

If the system was overloading the pump due to sustained effects, the system pressure or dead weight would be causing the problem. Systems with pressure problems usually include untied expansion joints. Dead weight problems can be traced back to improper system support. Typically, this is either spring pre-loads or support locations.

In the following figure, look at the deflected shapes displacement plot of the operating load case to examine the source of the high moments. Most engineers and analysts find it easier to understand system response to loads in terms of system displacements rather than internal forces and moments. The displacement plot can be used to identify pipe runs that generate the thermal strain and pipe runs that turn the thermal strain into large forces and moments on the pump.

The plot shows that the large moment about the Z-axis at the pump is caused by the thermal growth of B working against the stiffness of legs A and C. The large moment about the X-axis is due to the thermal growth of A working against the stiffness of legs B and C. The thermal growth of the steam stripper vessel connection (at the left end of A and node 40 in the piping system model) may also contribute to these high loads.

How can excessive loads at the pump discharge nozzle be reduced? How can additional flexibility be added to the system so that these loads drop? The possible solutions are:

  • Incorporate flexibilities at the vessel/nozzle intersection.

  • Redesign the piping system to reduce stiffness by adding an expansion loop or an expansion joint to the piping.