Pipe sizing calculator & Pressure Drop Calculator
Professional multiphase pipe sizing for oil & gas, chemical plants, and refineries. Darcy-Weisbach, Crane TP-410M, and API RP 14E standards.
Calculate optimal pipe diameter, velocity, and pressure drop for liquid, gas, and two-phase flow. This tool incorporates equivalent length for fittings, flow regime prediction, and erosional velocity checks based on industry standards.
Multiphase Pipe Sizing Calculator
› View Detailed Calculations
› Design Criteria (Velocity & ΔP/L Limits)
| Service Type | Avg ΔP/L | Max ΔP/L | Max Total ΔP | Velocity Range |
|---|
Source: GPSA Engineering Data Book, Section 17; API RP 14E; Perry's Chemical Engineers' Handbook
Calculation Methodologies
Liquid Phase (Darcy-Weisbach):
\[ \Delta P = f \cdot \frac{L_{eq}}{D} \cdot \frac{\rho V^2}{2} \]
Friction factor \(f\) via Swamee-Jain: \[ f = \frac{0.25}{\left[\log_{10}\left(\frac{\varepsilon}{3.7D} + \frac{5.74}{Re^{0.9}}\right)\right]^2} \]
Gas Phase (Crane TP-410M Isothermal):
\[ P_1^2 - P_2^2 = \frac{G^2}{\rho_1} P_1 \left( f \frac{L_{eq}}{D} + 2 \ln \frac{P_1}{P_2} \right) \]
Solved iteratively for \(P_2\). Accounts for compressibility and acceleration.
Two-Phase (Lockhart-Martinelli & API RP 14E):
\[ \Delta P_{TP} = \Delta P_L \cdot \phi_L^2 \quad \text{where} \quad \phi_L^2 = 1 + \frac{20}{X} + \frac{1}{X^2} \]
Erosional velocity limit: \[ V_{max} = \frac{C}{\sqrt{\rho_m}} \]
Understanding Pipe Sizing Criteria
Proper pipe sizing balances capital cost (pipe diameter) against operating cost (pumping/compression energy). Velocities that are too low risk sedimentation or slug flow, while velocities that are too high cause erosion, noise, and excessive pressure drop.
Key Parameters for Multiphase Flow
- Flow regime: Predicted using the Mandhane map based on superficial liquid (\(V_{sl}\)) and gas (\(V_{sg}\)) velocities.
- Equivalent length: Fittings (elbows, valves) are converted to equivalent straight pipe length to accurately calculate total friction loss.
- Erosional velocity: API RP 14E provides a conservative limit to prevent pipe wall thinning due to particle impingement in two-phase flow.
Typical Design Velocities
| Service | Typical Velocity | Max Velocity |
|---|---|---|
| Water Lines (Short) | 0.9 – 2.4 m/s | 3.0 m/s |
| Pump Suction | 0.6 – 1.5 m/s | 1.5 m/s |
| Gas Lines (Inside Battery) | 10 – 30 m/s | 30 m/s |
| Compressor Discharge | 15 – 40 m/s | 40 m/s |
| Two-Phase (General) | 3 – 10 m/s | API 14E Limit |
References & Further Reading
- • API RP 14E (2019). Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems. American Petroleum Institute. (Erosional velocity guidelines)
- • Crane Co. (1988). Flow of Fluids Through Valves, Fittings, and Pipe (Technical Paper No. 410). (Isothermal gas flow method)
- • GPSA Engineering Data Book (13th ed., 2012). Gas Processors Suppliers Association. (Velocity and pressure drop criteria)
- • Lockhart, R.W. & Martinelli, R.C. (1949). "Proposed Correlation of Data for Isothermal Two-Phase, Two-Component Flow in Pipes." Chemical Engineering Progress, 45(1), 39-48.
- • Mandhane, J.M., et al. (1974). "Flow Pattern Map for Two-Phase Flow in Horizontal Pipes." International Journal of Multiphase Flow, 1(4), 537-553.
Frequently Asked Questions
The Darcy-Weisbach equation calculates frictional pressure drop in pipes: \(\Delta P = f \cdot (L/D) \cdot (\rho V^2 / 2)\). It is the most accurate method for liquid pipe sizing and is preferred over empirical formulas for industrial applications.
As gas flows, friction causes pressure to drop. According to the ideal gas law, a drop in pressure causes the gas to expand, increasing its volumetric flow rate and thus its velocity, even though the mass flow rate remains constant.
API RP 14E provides a conservative limit to prevent pipe wall thinning due to particle impingement in two-phase flow: \(V_{max} = C / \sqrt{\rho_m}\), where \(C\) is typically 100 for continuous service and \(\rho_m\) is the mixture density.
Fittings create localized turbulence. This calculator uses the "Equivalent Length" method, where each fitting is assigned a length of straight pipe that would cause the same pressure drop (e.g., a standard 90° elbow ≈ 30 pipe diameters).