The pipe has an outer diameter of 20.5 inches and a wall thickness of 0.25 inches. The ASME code allows for a maximum pressure of 2.2 in pipework. The ASME code prescribes an allowed stress (S) of 16,000 psi for this material throughout a temperature range of -20F to +100F. This means that the average annual strain rate is 1.6 x 10-5 per inch, or 160 microstrain per meter. A microstrain is one ten-millionth of a percent. So the average annual strain rate is 160 microstrain per meter, which means that the maximum permissible stress is: Maximum pressure = (flow rate) x (pipe inner diameter) x (wall thickness) / (annual strain rate) Or Maximum pressure = (120 cubic feet per minute) x (20.5 inches) x (0.25 inches) / (1.6 x 10-5 per inch) Maximum pressure = 60,000 pounds per square inch Or, if you want it in terms of forces: Force = flow rate x pipe inner diameter x wall thickness / annual strain rate Pressure = force / area