Piping systems are designed by selecting piping systems and materials that are compatible with the flowing media and selecting the pipe size that provides the best overall economy for the application. While a larger pipe size may cost more initially, it provides better operating efficiency, which can represent a quick payback. One of the best ways to optimize a pipe flow investment is to calculate the actual pipe flow rates on the basis of pressure losses that might needlessly inflate operating costs.
Things You'll Need
 Calculator
 Pipe flowpressure loss data for the specific piping system
Schedule 40Steel Pipe Water Pumping

Define the steel pipe application. An industrial well application requires pumping 425 gallons per minute (gpm) of water 575 feet away into an inground reservoir that is 80 feet higher than the pump at the well. If a 60psi (pounds per square inch) pump is available, you can calculate the minimum Schedule 40steel pipe size that would handle the flow and pressure constraints.

Determine the pressure available to provide the 425gpm flow. Because the reservoir is 80 feet higher than the pump, some of the 60psi pumping pressure will be lost pushing the water uphill. Dividing 80 feet/2.31 feet/psi yields a static pressure loss of 34.63 psi, which, when subtracted from the 60psi pump pressure, leaves 25.37 psi to push the 425gpm flow through the 575foot pipe.

Scale the pressure drop per 100 feet of pipe, since this is how published pipe data is presented. Substituting values yields 25.37 psi/575 feet/100 feet = 4.41psi drop per 100 feet at 425 gpm.

Consult published pipe pressure and flow data for Schedule 40steel pipe to select a potential pipe size. The 4inch Schedule 40steel pipe pressureloss to flow chart shows a loss of 5.5 psi for a 476psi flow.

Calculate the flow with a 4.41psi loss based on the 5.5psi loss flow at 476 gpm. Since flow varies proportionately to the square root of pressure loss difference, extract the square root of (4.41 psi/5.5 psi) = square root of 0.8018 = 0.895 and multiply by the 476gpm flow cited to yield 426.23 gpm, which would just work for 425 gpm.
Schedule 40Steel Pipe Steam Flow

Define the steam flow application. Saturated low pressure steam at 12 psi is flowing through 3inch Schedule 40steel pipe. If it loses 1.5 psi pressure at the end of 100 feet of the pipe, you can calculate the flow rate in pounds/hour (lb/hr) of steam.

Consult the Steam Flow Rate and Pressure Drop for Schedule 40 Pipe chart (see Resources) to find the reference points for the 3inch pipe. The 1psi drop flow value reads 1,670 lb/hr and the 2psi value reads 2,400 lb/hr.

Calculate your flow at the 1.5psi drop by taking the square root of (1.5/2.0) = 0.866 and multiplying by the 2,400 lb/hr at the higher pressure drop = 0.866 X 2,400 = 2,078.4 lb/hr with a 1.5psi drop.

Compare against the calculation using the lower 1psi drop value to interpolate the actual flow value. Square root (1.5/1) = 2,045.32 lb/hr. Adding half the difference to the lower value or (2,078.4 minus 2,045.32 = 33.08/2 + 2,045.32 = 2,061.86 lb/hr, which would be a reasonable interpolation result in light of the tabular data.
Tips & Warnings
 Conservative design with flow piping may mean moving up one pipe size to require less energy to move the volume.
 Steam and superheated steam can cause serious injury or death from thirddegree burns. Always have pressurized designs checked by a professional.
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References
 Photo Credit pipe fitting image by Joann Cooper from Fotolia.com Pipes image by Sergei M. Kharitonov from Fotolia.com power plant image by Andrei Merkulov from Fotolia.com Pipes inside energy plant image by Andrei Merkulov from Fotolia.com