Natural gas exploration can occur in extremely remote locations all over the world. Once a natural gas pocket is located and drilled, the gas is compressed to a high pressure. This process provides the motive force necessary to transport the natural gas through miles of pipelines to a natural gas processing plant. The size of the high pressure natural gas pipelines is determined by the pressure and required flow rate.
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Determine the volumetric flow rate of natural gas in a particular pipeline. High pressure natural gas pipelines typically have high pressure, high flow and a large diameter. For instance, assume the volumetric flow rate is one million cubic feet per hour at a pressure of 750 pounds per square inch (psi). This is 278 cubic feet of gas flow per second (1,000,000 cubic feet per hour/3600 seconds).
Determine the recommended pipeline velocity of the natural gas. The engineering rule of thumb indicates a recommended velocity between 75-100 feet per second. Assume 90 feet per second.
Determine the cross sectional internal area of the pipeline based on the conditions of 278 cubic feet per second at a rate of 90 feet per second. This is calculated by dividing the volumetric flow rate by the velocity, or 278/90. The internal area of the pipe is 3.09 square feet.
Determine the pipeline nominal size by calculating the internal diameter of the pipe using the cross sectional area. This is done with the formula, A = (d^2 x 3.14)/4 where "A" is the cross sectional area in square feet and “d” is the internal diameter in feet. Rearranging the formula yields d = √A x 4 / 3.14 for an answer of 1.98 feet or 23.8 inches. Therefore, the size of the natural gas line in this example should be a 24-inch-diameter pipe.