How to size high pressure gas piping

Written by brian baer
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How to size high pressure gas piping
High pressure gas pipelines are dangerous and should be designed properly. (Jupiterimages/ Images)

High pressure gas piping must be sized properly to ensure safety. Failure to specify the pressure ratings of the piping and/or the pipe size could lead to pipe rupture, poor performance of the pipeline or an explosion if the gas is flammable. The recommended velocity of high pressure gas piping is 90 to 100 feet per second. This rule-of-thumb is used to calculate the required pipe diameter based on the required gas volumetric flow rate.

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  1. 1

    Determine the required high- pressure gas volumetric flow rate. This will be provided by the application. For instance, assume there is a desired gas flow rate of 120,000 cubic feet per hour at 350 psi (pounds per square inch).

  2. 2

    Determine the optimum pipe diameter based on a recommended gas velocity of 95 feet per second. This velocity must be converted to feet per hour by multiplying the velocity by 3,600 (3,600 seconds equals one hour). This value is 95 x 3,600 or 342,000 feet per hour.

  3. 3

    Divide the volumetric flow rate by the velocity to reveal a cross sectional area of the optimum pipe diameter. This is 120,000 divided by 342,000 which is 0.35 square feet.

  4. 4

    Determine the internal pipe diameter from the cross sectional area. This is done using the formula of A = (d2)∏ / 4 where "A" is the cross sectional area, "d" is the internal diameter in feet and ∏ is Pi which is 3.1416. Since "A" is known, the formula becomes √(A x 4 / ∏) = d. Plugging in the numbers gives a diameter of 0.67 feet or 8 inches. Therefore, for a high pressure gas pipeline flowing 120,000 cubic feet per hour, an 8-inch diameter pipe is required.

Tips and warnings

  • The high pressure piping must be determined by specifying the pipe schedule or pipe wall thickness. This is dependent upon the operating temperature of the pipe and the internal operating pressure. For this example, a schedule 80 pipe would be recommended.

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