If the fluid is a mixture of gas and liquid (two-phase), sizing becomes complex.
Step 1: Gather data – fluid properties, flow rate, allowable ΔP, pipe length, fittings.
Step 2: Assume a reasonable velocity (see ranges above).
Step 3: Calculate initial diameter.
Step 4: Select standard pipe size (NPS) and schedule.
Step 5: Compute actual velocity and Reynolds number. If the fluid is a mixture of gas
Step 6: Calculate total ΔP (friction + minor + static).
Step 7: Compare with allowable ΔP. Adjust diameter if needed.
Rule of thumb: For liquids, keep ΔP below 2 – 3 bar/100 m for economic pumping.
The fundamental equation for fluid flow relating pressure, velocity, and elevation. $$P_1 + \frac12\rho v_1^2 + \rho g h_1 = P_2 + \frac12\rho v_2^2 + \rho g h_2 + \textLosses$$
Calculating the friction loss is the core of hydraulic analysis. Step 1: Gather data – fluid properties, flow
Hazen-Williams Equation: Frequently used for water systems (civil engineering contexts) but generally avoided for process hydrocarbons. $$V = 1.318 \cdot C \cdot R_h^0.63 \cdot S^0.54$$
For straight pipe under internal pressure:
[ t = \fracP \cdot D2(SEW + PY) ]
Where:
After calculating ( t ), add:
Then select the nearest schedule number (Sch 10, 40, 80, etc.) such that the nominal wall thickness ≥ calculated.
Mastering module 3 process piping hydraulics sizing and pressure rating transforms you from someone who can draw a line on a P&ID to an engineer who can specify exactly what that line should be made of and how big it must be. The interplay between friction losses (hydraulics) and wall strength (pressure rating) is at the heart of every safe, economical piping system.
Whether you are studying for an exam or designing a real chemical plant, always remember: Hydraulics gives you the diameter; pressure rating gives you the schedule. Run both calculations, iterate, and never trust a pipe size that hasn’t been checked for erosion velocity and code-required thickness.
Save this article, download the referenced standards, and practice with real problems—because theory becomes engineering only when applied.
Further Reading & Resources:
Need a downloadable PDF version of this article for offline study? Click the “Export to PDF” button in your browser or use a print-to-PDF tool.
Here’s a structured, high-quality text that you can use as the basis for a Module 3: Process Piping Hydraulics – Sizing and Pressure Rating PDF. You can copy this directly into a Word/Google Doc, format it, and save as a PDF.
If the fluid is a mixture of gas and liquid (two-phase), sizing becomes complex.
Step 1: Gather data – fluid properties, flow rate, allowable ΔP, pipe length, fittings.
Step 2: Assume a reasonable velocity (see ranges above).
Step 3: Calculate initial diameter.
Step 4: Select standard pipe size (NPS) and schedule.
Step 5: Compute actual velocity and Reynolds number.
Step 6: Calculate total ΔP (friction + minor + static).
Step 7: Compare with allowable ΔP. Adjust diameter if needed.
Rule of thumb: For liquids, keep ΔP below 2 – 3 bar/100 m for economic pumping.
The fundamental equation for fluid flow relating pressure, velocity, and elevation. $$P_1 + \frac12\rho v_1^2 + \rho g h_1 = P_2 + \frac12\rho v_2^2 + \rho g h_2 + \textLosses$$
Calculating the friction loss is the core of hydraulic analysis.
Hazen-Williams Equation: Frequently used for water systems (civil engineering contexts) but generally avoided for process hydrocarbons. $$V = 1.318 \cdot C \cdot R_h^0.63 \cdot S^0.54$$
For straight pipe under internal pressure:
[ t = \fracP \cdot D2(SEW + PY) ]
Where:
After calculating ( t ), add:
Then select the nearest schedule number (Sch 10, 40, 80, etc.) such that the nominal wall thickness ≥ calculated.
Mastering module 3 process piping hydraulics sizing and pressure rating transforms you from someone who can draw a line on a P&ID to an engineer who can specify exactly what that line should be made of and how big it must be. The interplay between friction losses (hydraulics) and wall strength (pressure rating) is at the heart of every safe, economical piping system.
Whether you are studying for an exam or designing a real chemical plant, always remember: Hydraulics gives you the diameter; pressure rating gives you the schedule. Run both calculations, iterate, and never trust a pipe size that hasn’t been checked for erosion velocity and code-required thickness.
Save this article, download the referenced standards, and practice with real problems—because theory becomes engineering only when applied.
Further Reading & Resources:
Need a downloadable PDF version of this article for offline study? Click the “Export to PDF” button in your browser or use a print-to-PDF tool.
Here’s a structured, high-quality text that you can use as the basis for a Module 3: Process Piping Hydraulics – Sizing and Pressure Rating PDF. You can copy this directly into a Word/Google Doc, format it, and save as a PDF.