How do you size a turbine meter for natural gas?

Turbine meter sizing for natural gas involves converting standard flow (MMSCFD) to actual cubic feet per minute (ACFM) at operating pressure and temperature, then selecting a meter size whose capacity range encompasses the minimum and maximum flows. The flow velocity through the meter should be 15-70 ft/s for gas service per AGA Report No. 7.

What is the optimal velocity range for a gas turbine meter?

The optimal velocity range for gas turbine meters is 15-70 ft/s. Below 15 ft/s, the meter may not spin reliably and linearity degrades. Above 70 ft/s, bearing wear accelerates and measurement accuracy decreases. Custody transfer meters should operate in the 20-50 ft/s range for best accuracy.

What is turbine meter rangeability?

Rangeability (turndown ratio) is the ratio of maximum to minimum flow rate at which the meter maintains its specified accuracy. Standard turbine meters achieve 10:1 rangeability, while high-performance meters can achieve 20:1 or better. Higher rangeability means the meter can accurately measure a wider range of flow rates.

How much straight pipe is required upstream of a turbine meter?

AGA Report No. 7 requires minimum 10 pipe diameters (10D) of straight pipe upstream and 5 pipe diameters (5D) downstream of the turbine meter. If fewer than 20D upstream is available, a flow conditioner (tube bundle or plate type) should be installed to remove swirl and velocity profile distortion.

Turbine Meter Sizing Calculator | Gas Custody Transfer Measurement

Fluid & Flow

Fluid Type

Normal Flow Rate

MMSCFD

Minimum Flow Rate

MMSCFD

Maximum Flow Rate

MMSCFD

Operating Conditions

Operating Pressure

psig

Operating Temperature

°F

Gas Properties

Gas Specific Gravity (Air = 1.0)

Typical: 0.55-0.70 (sweet gas), 0.70-0.90 (rich gas)

Compressibility Factor (Z)

Use Z-Factor Calculator for precise values

Liquid Properties

Liquid Density

lb/ft³

Dynamic Viscosity

Meter Requirements

Line Size (NPS)

Rangeability Requirement

Accuracy Class

Understanding Turbine Meter Sizing

How It Works
Turbine meters measure flow by counting rotor revolutions as fluid passes through the meter body. Rotor speed is proportional to volumetric flow rate. Each revolution corresponds to a known volume (K-factor).

Velocity Ranges:
Gas: 15-70 ft/s optimal
Liquid: 3-30 ft/s optimal
Below minimum: poor linearity
Above maximum: bearing wear

Applications:
Custody transfer measurement, allocation metering, pipeline check metering, gas plant inlet/outlet measurement, NGL and refined product metering, gas distribution metering.

📚 Learn the Theory

Understand turbine meter principles, AGA 7 requirements, K-factor linearity, and installation best practices

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Results

Recommended Meter Size

inches

Velocity at Normal Flow -

Velocity at Min Flow -

Velocity at Max Flow -

Pressure Drop -

Reynolds Number -

Rangeability Achieved -

Capacity Utilization -

ACFM at Normal Flow -

ACFM at Min Flow -

ACFM at Max Flow -

Upstream Straight Run -

Downstream Straight Run -

Accuracy at Conditions -

Key Formulas

ACFM = (MMSCFD × 10&sup6; / 1440) × (14.7/P) × (T/520) × (1/Z)

ACFM = Actual cubic feet per minute

P = Operating pressure (psia)

T = Operating temperature (°R)

Z = Gas compressibility factor

v = ACFM / A (flow velocity, ft/s)

ΔP = K × ρ × v² / 2 (pressure drop)

Standards & References

AGA Report No. 7
Measurement of Natural Gas by Turbine Meters
API MPMS Ch. 5.3
Measurement of Liquid Hydrocarbons by Turbine Meters
GPSA Engineering Data Book
Section 3: Measurement
ISO 9951
Measurement of Gas Flow in Closed Conduits — Turbine Meters

Engineering Notes

Gas velocity: Optimal 15-70 ft/s; custody transfer best at 20-50 ft/s
Liquid velocity: Optimal 3-30 ft/s to prevent cavitation and bearing damage
Reynolds number: Must exceed 10,000 for linear response; 50,000+ preferred
Pressure drop: Typically 1-5 psi for gas; 2-10 psi for liquid
Flow conditioner: Required if <20D upstream straight run available
Proving: Custody transfer meters must be proved per AGA 7 / API MPMS Ch. 4

Standard Meter Sizes

2" — 10-250 ACFM (gas)
3" — 25-600 ACFM (gas)
4" — 50-1,200 ACFM (gas)
6" — 100-3,200 ACFM (gas)
8" — 200-6,500 ACFM (gas)
10" — 350-12,000 ACFM (gas)
12" — 500-18,000 ACFM (gas)

Turbine Meter Sizing Calculator

Fluid & Flow

Operating Conditions

Gas Properties

Liquid Properties

Meter Requirements

Understanding Turbine Meter Sizing

📚 Learn the Theory

Results

Key Formulas

Standards & References

Engineering Notes

Standard Meter Sizes

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