Liquid Orifice Plate Sizing & Rating

Calculation for Liquid Orifice Plate Sizing & Rating based on ISO 5167 & ASME MFC-14M standards.

US CUSTOMARY METRIC / SI

1. Project Data

Project Name

Tag Number

Engineer

2. Process Data

Calculation Mode:

Sizing (Solve for d)

Rating (Solve for ΔP)

Pipe Diameter ($D$, in)

Mass Flowrate ($q_m$, lb/h)

Inlet Pressure ($P_1$, psia)

Required Press. Drop ($\Delta P$, bar)

3. Fluid Properties

Liquid Library

Operating Temperature (°F)

Density ($\rho$, lb/ft³)

Dynamic Viscosity (cP)

Vapor Pressure ($P_v$, psia)

* Vapor pressure ($P_v$) is dynamically calculated via the Antoine Equation for library liquids based on the operating temperature. For unique fluids, select 'Custom Liquid' to override.

4. Sizing Logic

Active Sizing Standard

Standard Logic:
ISO 5167-2 Standard

Applicable for pipe diameters $D \ge 50$ mm.

Specification Summary

Required Bore ($d$) -

Bore Diameter -

Beta Ratio ($\beta$) -

Applied Standard -

Reynolds ($Re_D$) -

Discharge Coeff ($C$) -

Expansion ($\epsilon$) 1.0000 (Liquid)

Inlet Density -

Pipe Velocity -

Throat Velocity -

Cavitation Index ($\sigma$) -

Cavitation Note: Maintain $\sigma > 1.5$ to prevent cavitation. Cavitation causes severe measurement error and permanent physical damage to the pipe and orifice plate.

Please enter process conditions to generate results.

Engineering Reference & Technical Basis

1. Methodology Overview

The application dynamically selects the appropriate sizing algorithm based on pipe diameter ($D$) and the selected standard extension:

Pipe Diameter Range	Applicable Standard	Model Characteristics
$D \ge 50$ mm	ISO 5167-2:2003	Standard concentric orifice with flange taps. Uses RHG equation.
$12.5 \le D < 50$ mm	ISO/TR 15377	Small bore extension. Includes mandatory diameter correction term.
$6 \le D \le 40$ mm	ASME MFC-14M	Precision honed meter runs. Uses Stolz equation for corner taps.

2. Fundamental Flow Equation

q_m = \frac{C}{\sqrt{1 - \beta^4}} \epsilon \frac{\pi}{4} d^2 \sqrt{2 \Delta P \rho_1}

Iterative numerical convergence is applied to solve for the orifice diameter $d$. For liquid (incompressible) flow, the expansibility factor ($\epsilon$) is strictly equal to $1.00$.

3. Cavitation Index ($\sigma$) & Vena Contracta

Used to predict the onset of flashing or cavitation by comparing the lowest static pressure (at the vena contracta) to the liquid's vapor pressure ($P_v$):

P_{vc} \approx P_1 - \frac{\Delta P}{1 - \beta^4} \quad ; \quad \sigma = \frac{P_1 - P_v}{\Delta P}

4. Discharge Coefficient ($C$) Models

A. Reader-Harris/Gallagher (ISO 5167)

Used for standard flange taps. The equation includes pipe Reynolds number ($Re_D$) and tap location terms:

C = 0.5961 + 0.0261\beta^2 - 0.216\beta^8 + 0.000521\left(\frac{10^6\beta}{Re_D}\right)^{0.7} + (0.0188 + 0.0063 A) \beta^{3.5} \left(\frac{10^6}{Re_D}\right)^{0.3} + \text{Tap Terms}

Small-Bore Correction (ISO/TR 15377): For $D < 71.12$ mm, a mandatory term is added:

\Delta C_{small\_bore} = 0.011(0.75 - \beta)(2.8 - D/25.4)

B. Stolz Equation (ASME MFC-14M)

Optimized for corner taps in precision honed small bore runs:

C = 0.5959 + 0.0312\beta^{2.1} - 0.1840\beta^8 + 0.0029\beta^4(10^6/Re_D)^{0.75} + \frac{0.0390\beta^4}{1-\beta^4} - 0.0158\beta^3

References

ISO 5167-2:2003: Measurement of fluid flow by means of pressure differential devices — Part 2: Orifice plates.
ISO/TR 15377:2007: Guidance for the use of ISO 5167 in pipes of diameter outside the range of ISO 5167.
ASME MFC-14M-2001: Measurement of Fluid Flow Using Small Bore Precision Orifice Meters.
ISA-RP75.23-1995: Considerations for Evaluating Control Valve Cavitation (Reference for $\sigma$ logic).
RW Miller: Flow Measurement Engineering Handbook, McGraw-Hill.