How to Calculate Relative Carrying Capacity of Pipes

Calculation for Pipes Carrying Gases or Steam

1. Determine the diameters of the pipes. If you're comparing two pipes, call the diameters D1 and D2.

2. Add 3.6 to D2. Then take the square root. Multiply this value by D1 cubed.

3. Add 3.6 to D1. Then take the square root. Multiply this by the cubed value of D2.

4. Divide the answer at step 2 by the answer of step 3. This result is the relative carrying capacity of two pipes carrying steam or atmospheric gases.

Calculation for Pipes Carrying Water

1. Determine the two pipe diameters to be compared. Call them D1 and D2.

2. Divide D2 by D1. This provides the ratio of the diameters of the two pipes.

3. Raise the result to the power of 2.5. This result is the relative carrying capacity of two pipes carrying water.

References

• "Fire Service Hydraulics"; James F. Casey; 1984
• "Handbook of Public Water Systems"; HDR Engineering; 2001
• "Mechanical Engineering Reference Manual for the PE Exam"; Michael R. Lindeburg; 2006

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Resources

• "Water Transmission and Distribution"; American Water Works Association; 2003

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Tips

Relative carrying capacity of standard sized pipes can be determined from reference tables in hydraulic engineering and fluid mechanics books. However, if the tables are not available or the pipe size is not referenced in the table, the calculations for relative carrying capacity for pipes are necessary.

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Warnings

These equations do not take into account turbulent water or airflow, which reduces pipe capacity.

When performing these calculations for air or gas flow, differences in pressure are not taken into account. Higher pressure air flows will carry more gas than lower pressure air flows, even given the same diameter of pipe.

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Photo Credits

abstract red piping image by marilyn barbone from Fotolia.com

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