How to model fluid / gas density in AutoPIPE?
Using AutoPIPE V8i 09.06.xx.xx, a user can input the contents density value on the Pipe Properties dialog screen / Input grid:
Note: As mentioned in AutoPIPE help, Specific gravity is relative to density of Water taken at temperature of 40 deg F and atmospheric pressure (14.7 psi).
Also important to consider that fluid density changes with temperature.
AutoPIPE has a feature on the Load> Static Analysis grid where the user can provide a "Fluid Density Factor" per each analysis set. This factor is multiplied by the "Specific gravity of contents" value for all pipe properties in the model for that analysis set.
Define separate analysis sets for each temperature case and modify the fluid density factor as needed.
Note: Can the fluid density be zero (0.00) or blank? Yes, this is OK. One reason to set the density factor = 0 would be to analyze the piping system in a installed but not operating condition. Another words, this would help users to analyze their model with different states of fluid (no fluid [installed], high temperature, high pressure, etc.) at the analysis level without having to change individual content specific gravity. The 0.0 value of fluid density factor is inclusive of 0.0 value and it does not cause any known problems with any AutoPIPE calculations.
Lastly, be sure to confirm each Static Analysis Set load case dialog for the state of the Contents Checkbox (see help for details on this feature).
How do consider the weight of the fluid in the system, If the service is steam?
Yes, even a gas has a molecular weight that can be considered in the analysis. Suggest entering a small value in the "Specific gravity of contents" field on the Pipe Properties dialog screen. Then be sure that the Static Analysis set "Density factor" is 1.00 as needed.
Modeling Approaches in AutoPIPE