Through our technical support line, we frequently get inquiries about whether PIPE-FLO Professional results are applicable to systems with compressible gases. We've decided to make system evaluation substantially easier with the use of an XLink spreadsheet. PIPE-FLO Professional uses the Darcy-Weisbach method to calculate pipeline pressure loss which assumes a constant density throughout the system however if certain system conditions are met, the Darcy-Weisbach method produces reasonable calculated results, and the compressibility of the fluid does not play a substantial role in the pressure drops or flow rates calculated throughout the system. These conditions as defined in the most recent version of the Crane Technical Paper No. 410 and are outlined below:

1) If the calculated pressure drop in a pipeline (dP) is less than ~10% of the absolute inlet pressure (P’1), reasonable accuracy will be obtained if the specific volume (density) used in the equation is based upon either the upstream or downstream conditions, whichever are known.

2) If the calculated pressure drop (dP) is greater than ~10%, but less than ~40% of the absolute inlet pressure (P’1), the Darcy equation will give reasonable accuracy by using a specific volume (density) based upon the average of the upstream and downstream conditions.

3) For greater pressure drops, such as are often encountered in long pipelines, alternative methods should be used. Our PIPE-FLO Compressible product takes into account the changing density throughout the system and would be an excellent tool for such systems.

4) In addition, some resources indicate that the Mach number must not exceed 0.1 to 0.2 in order for compressibility effects to be assumed negligible.

When we investigate the impact a compressible fluid will have on the calculated results of PIPE-FLO Professional, we use these conditions. A common mistake we see in designing these systems is that the fluid zone picked for a certain section of pipes is too broad and will not be within the restrictions stated in condition #1. The Fluid zone for a pipe must be within the inlet or outlet pressure of a pipe, or close enough that the error is small enough to ignore.

In order to better facilitate our customers with compressible systems, we have utilized the XLink feature of PIPE-FLO Professional to create the attached spreadsheet which imports all the pipes in your system and analyzes them according to conditions #1 and #4. It is then the job of the engineer to interpret this data and make the best decision for modifying the system or using PIPE-FLO Compressible to more accurately model the system.

To use the spreadsheet, simply open your PIPE-FLO Professional system then open the Compressibility Check.xlsx file and follow the instructions at the top to auto fill the pipelines and perform the analysis.