Multiple Fluid Densities Using the Fluid Density Multiplier - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
13

If a change in fluid density and the total weight is important for a piping system, you can adjust static load cases based on the known operating conditions by using a Fluid Density Multiplier (FDM).

You can specify a single value for Fluid Density in the Classic Piping Input Dialog. However, during piping system operations, the fluid density might change because the value of internal fluid density is directly proportional to the operating pressure and inversely proportional to the operating temperature. In many systems, the opposite effects of pressure and temperature on the fluid density cancel each other out. In other operating conditions, fluid density fluctuation may become significant.

To accommodate the effect of fluid density changes, CAESAR II includes the Fluid Density Multiplier in the Static Analysis - Load Case Editor Dialog (also called the Static Load Case Editor). You still specify the base (ambient) value of fluid density in the Classic Piping Input Dialog. You can also specify a Fluid Density Multiplier for any basic load case such as the OPE, SUS, or HGR Stress Type in the Static Load Case Editor. The software then scales the fluid density value for each load case. Specifying a value of 1.2 increases the fluid density by 20 percent, while a value of 0.9 reduces the fluid density by 10 percent.

Fluid Density Multiplier is not available for combination load cases.

Example

A piping model contains two operating conditions. Fluid Den 1 is 0.0358 lb/cu in for ambient temperature and atmospheric pressure. For Temp 1 of 400°F, the fluid density reduces by 15 percent to 0.0304 lb/cu in For Pressure 2 of 3000 psi the fluid density increases by 10 percent to 0.0394 lb/cu in.

Fluid Density

1 - 0.0358 (Ambient)

2 - 0.0304 (Reduced 15%)

3 - 0.0394 (Increased 10%)

In the Static Load Case Editor, define Fluid Density Multiplier as 0.85 (a 15 percent reduction) for the OPE load case with T1 (Temp 1), and as 1.10 (a 10 percent increase) for OPE and SUS load cases with P2 (Pressure 2). The Alt-SUS cases automatically display the same FDM as the corresponding OPE case. The software analyzes the regular SUS load case at the ambient temperature, and FDM stays at the default value of 1.0.

During analysis, FDM changes the total weight of the system for affected load cases. The software analyzes displacements, restraint reactions, and stresses with the adjusted weights. The effect is the same as if you manually scaled the fluid density in Piping Input and ran the analysis multiple times to correspond with different values of fluid density.

In the Static Output Processor, all Standard Reports are applicable when you use FDM. You can view the FDM factors in the General Computed Results > Load Case Report.

  • If you create a load case combining T1 and P2, FDM for this example is 1.0 because the fluid density multipliers for T1 and P2 have opposing effects and cancel each other out.

  • FDM affects the fluid component of the W load primitive but not the WW or WNC primitives. When you set FDM to zero, the result is similar to WNC.

  • FDM also applies to load cases that use Uniform Load in Gs.