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Gas Orifice Meter Flow Rate Calculator (ISO 5167 / AGA-3)

Concentric square-edged orifice meters are the worldwide standard for custody transfer and pipeline monitoring of natural gas and compressed air flows.

Internal bore diameter of the meter run pipeline (e.g. 154 mm for 6" Sch 40).

Diameter of the concentric circular bore through the orifice plate.

Measured pressure drop across flange or corner taps (typically 5 to 50 kPa).

Absolute static pressure upstream of the orifice plate.

Process gas temperature entering the meter run.

Ratio of gas density to dry air density (typically 0.58 to 0.65 for pipeline natural gas).

Calculated Result
10,378 Sm³/h

Standard Gas Volumetric Flow Rate

Standard Gas Flow Rate

10,378 Sm³/h (8,795,880 SCFD)

Mass Throughput Rate

7,627.7 kg/h

Orifice Bore Velocity

42.54 m/s

Beta Ratio (d/D)

0.5

Gas Operating Pressure

15 bar absolute

Calculation Breakdown

  1. Ideal Gas Density at Operating Conditionsρ = P / (R_gas × T) = (15 × 10⁵) / (478.4 × 293.1) = 10.70 kg/m³
  2. AGA-3 / ISO 5167 Orifice Mass Discharge Formulationq_m = C_d × E × A_orifice × √(2 × ρ × ΔP) = 7,627.7 kg/h
  3. Standard Conditions Volume ConversionQ_std = q_m / ρ_std = 10,378 Sm³/h (8,795,880 SCFD)

Gas Orifice Metering Metrics

Interactive visualization based on your current inputs

Value
0.013253850Beta (×100)Mass Flow (kg/s)Std Flow (kSm³/h)Throat Vel (m/s)Density (kg/m³)ParameterValue

What Is the Gas Orifice Meter Flow Rate Calculator (ISO 5167 / AGA-3)?

The Gas Orifice Meter Flow Rate Calculator computes gas mass and standard volumetric flow rates from differential pressure measurements across an orifice plate.

How Does the Gas Orifice Meter Flow Rate Calculator (ISO 5167 / AGA-3) Work?

It computes actual gas density using real-gas law, evaluates AGA/ISO discharge coefficients and velocity of approach factors, and integrates differential pressure.

Gas Orifice Meter Flow Rate Calculator (ISO 5167 / AGA-3) Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

q_m = C_d \frac{1}{\sqrt{1 - \beta^4}} \frac{\pi d^2}{4} \sqrt{2 \rho_1 \Delta P}, \quad \beta = \frac{d}{D}

ISO 5167-2 / AGA Report No. 3 formulation relating Bernoulli pressure drop to compressible gas mass throughput.

How to Use the Gas Orifice Meter Flow Rate Calculator (ISO 5167 / AGA-3)

  1. Enter pipe internal diameter and orifice plate bore.
  2. Specify differential pressure across taps in kPa.
  3. Input upstream static pressure, temperature, and gas specific gravity.

Step-by-Step Example Calculation

6-Inch Natural Gas Meter Run at 15 bar

Input Values:

pipeInsideDiameterMm:154
orificeBoreDiameterMm:77
differentialPressureKPa:25
gasStaticPressureBarA:15
gasTemperatureC:20
gasSpecificGravity:0.6
Worked Steps: With β = 0.50 and 25 kPa ΔP, delivers 7,472 kg/h mass flow (10,378 Sm³/h or 8.80 MMSCFD).

Understanding Your Result

Standard Volumetric Flow: Normalized throughput at standard metering conditions (Sm³/h and SCFD).

Mass Flow Rate: Mass throughput in kg/h and kg/s.

Beta Ratio: Geometric ratio indicating measurement sensitivity.

Factors That Affect the Result

  • Higher differential pressure increases flow rate proportionally with √ΔP.
  • Elevated static pipeline pressure increases gas density, transporting more mass per unit displacement.

When Should You Use This Calculator?

  • Natural gas custody transfer, refinery fuel gas headers, compressor station discharge, and chemical plant biogas metering.

Assumptions & Limitations

  • Assumes subsonic gas flow and fully developed turbulent velocity profile upstream of the orifice plate.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Adheres to ISO 5167-2:2003 and AGA Report No. 3 / API MPMS Chapter 14.3.

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