| Applies To | |||
| Product(s): | AutoPIPE | ||
| Version(s): | 2004, XM, V8i | ||
| Area: | Modeling | ||
| Original Author: | Bentley Technical Support Group | ||
| Date Logged & Current Version |
Jan 2015 09.06.01.10 |
Problem:
How to model a single pipe filled with a mixture of liquid (water) and gas (foam or air) for a Fire Protection piping system in AutoPIPE?
Solution:
AutoPIPE is concerned only with the integrity (Stress) design of the system against specific design codes for various loading conditions and is typical of most Pipe Stress programs. Performing a Static analysis with a single pipe containing two phases would be accomplished by entering the correct pipe property values for the mixed content per linear length.
However, a problem would arise when adding a dynamic (ex. Fluid transient) load case with this mixed content. AutoPIPE's Fluid transient load case is a simplified pessimistic approach and calculates the Joukowski pressure surge for rapidly opening/closing valves and the dynamic effect as the pressure wave travels round through the piping system. It does not account for any complex flow conditions and has no reflected wave or multiphase capability. In order to use AutoPIPE's fluid transient the contents must be either all fluid or all gas (i.e. single phase). This flow condition is something for a CFD problem for a complex fluid flow program like ANSYS, FlowMaster, PipeNet. If these other programs are used and generate specific time history input values, these values can be directly applied in AutoPIPE as a time history load case. AutoPIPE can then be employed to conduct a stress analysis on mixed flow event.
Note, as of Feb 2026, AutoPIPE unable to handle a single pipe containing mixed phases of compressible (air) and incompressible (water) fluids by itself. In addtion, AutoPIPE does not have any NFPA compliance piping codes. User's must select an piping code from the list of available codes. Some companies in the past have used AutoPIPE for designing fire protection ring mains and distribution lines for strength and structural integrity above and below ground.