While exact values depend on the application, the following guidelines are common:
: Each fitting is assigned an (L_e/D) ratio representing the length of straight pipe (in diameters) that would produce the same pressure drop.
Use industry-standard velocity brackets to prevent erosion, noise, and excessive pressure drop. Fluid Type Recommended Velocity Range (m/s) Recommended Velocity Range (ft/s) Water (Pump Suction) 0.5 – 1.2 1.5 – 4.0 Water (Pump Discharge) 1.5 – 3.0 5.0 – 10.0 Steam (Saturated) 30.0 – 40.0 100.0 – 130.0 Steam (Superheated) 40.0 – 60.0 130.0 – 200.0 Gases (Low Pressure) 15.0 – 30.0 50.0 – 100.0 Calculate Preliminary Diameter ( ):
In Module 3, sizing must also account for integrity. For two-phase flow or slurries, velocity limits are governed by erosion. If the fluid is corrosive, the sizing must include a corrosion allowance (extra wall thickness), which slightly reduces the internal diameter and affects hydraulics. While exact values depend on the application, the
Q=Av=πD24vcap Q equals cap A v equals the fraction with numerator pi cap D squared and denominator 4 end-fraction v 2. Head Loss and Pressure Drop Calculations
Process pipes can normally be considered thin cylinders; only high‑pressure pipes, such as high‑pressure steam lines, are likely to be classified as thick cylinders and must be given special consideration.
To prevent erosion or excessive noise, liquids typically flow between 1–3 m/s, while gases can reach much higher velocities. Pressure Drop ( ΔPcap delta cap P For two-phase flow or slurries, velocity limits are
Pipe sizing is not simply selecting a diameter; it is an optimization process. Common Sizing Methodologies
The design of process piping systems requires a balance between fluid dynamics, material science, and mechanical integrity. Choosing the wrong pipe size can lead to high energy costs or fluid erosion, while an incorrect pressure rating risks catastrophic mechanical failure.
: For process engineers, the internal diameter is the most critical parameter for sizing, while the Nominal Pipe Size (NPS) serves as the standard reference for external dimensions. 3. Pressure Ratings and Wall Thickness Head Loss and Pressure Drop Calculations Process pipes
: Higher material and installation costs but lower friction and power consumption. Sizing Factors
Re=ρvDμRe equals the fraction with numerator rho v cap D and denominator mu end-fraction = Fluid density ( kg/m3kg/m cubed = Mean fluid velocity ( = Inside diameter of the pipe ( = Dynamic viscosity ( Laminar Flow (
Once the size is determined, the pipe must be strong enough to withstand the internal pressure and temperature. ASME B31.3 Guidelines
If you are evaluating a PDF, ensure it explicitly defines the . ASME B31.3 requires that the pressure design thickness, after subtracting corrosion allowance and mill tolerance, remains above the calculated minimum at all times.
