How to Calculate Pipe Length

Internal volume method

1
Many industrial pipe runs are long and varied.lloyds of london image by Fyerne from Fotolia.com

Define the pipe line in question. In this example, a butt-welded 1-inch Schedule 40 steel water pipeline of unknown length is run throughout an industrial facility. If it takes 9.24-gallons of water to completely fill the pipeline from empty, you can calculate pipe length.
2). Calculate the volume of one foot of 1-inch Schedule 40 steel pipe. Published data shows that the internal diameter is 1.05-inches. Using the volume formula for cylinders, V= (diameter/2)^2 X pi X length X 7.48 gallons/cubic foot. Substituting terms V = (1.05/2) ^squared X 3.1416 X 12 = 0.0449788-gallons/foot of pipe.
3). Calculate the length of the pipe by dividing its 9.24-gallon internal volume by 0.0449788-gallons/foot of pipe to yield 205.43-feet. Since the pipe is butt-welded from the outside, there are no fittings or intrusions to affect this volume, and the pipe can be considered uniformly smooth on the inside, and the 205.43-foot length accurate.

1). Define the pipe line in question. Using the same case as Section 1, a butt-welded 1-inch Schedule 40 steel water pipeline of unknown length is run throughout an industrial facility. When a precise 10-gallon-per-minute (gpm) flow is metered through the pipe, the 60-pound-per-square-inch (psi) entry flow drops by 5.91-psi. You can calculate pipe length from this information.
2
Many pipes in many directions characterize some process plants.Steam Pipes image by Andrei Merkulov from Fotolia.com

Look up the pressure-loss data for 1-inch Schedule 40 steel pipe. The chart shows that at 9.5-gpm, water loses 2.6-psi per 100-feet of pipe.
3). Adjust the published data for your measured example. Since the flow increases as a function of the square root of pressure difference, then (10 gpm/9.5-gpm)^2 (squared) = 1.108, or the proportionally greater pressure loss your length of pipe will see as a result of the greater flow. Multiplying 2.6-psi by 1.108 = 2.881 is the calculated loss for 100-feet of your pipe at 10 gpm.
4). Calculate your actual pipe length by dividing your measured 5.91-psi pressure drop by 2.881-psi/100 feet of pipe = 205.14-feet of pipe, based on pressure drop. This compares reasonably with the 205.43-foot calculated length of Section 1.