Why do NGL and LPG need a different volume correction than crude?

Light hydrocarbons — propane, butane, Y-grade NGL — expand far more with temperature than crude and refined products and fall below the density range of API MPMS Chapter 11.1. GPA Midstream Standard 8217 (also GPA TP-27 / API MPMS Chapter 11.2.4) provides the correct temperature correction factor (CTL) for them using an extended corresponding-states model.

What inputs does the TP-27 CTL calculation need?

The relative density at 60 °F (between 0.3500 and 0.6880) and the observed temperature (between −50.8 °F and 199.4 °F, i.e. 227.15–366.15 K). The method selects two adjacent reference fluids that bracket the density, scales their saturation densities to the fluid's reduced temperature, and computes CTL.

NGL / LPG Volume Correction (CTL)

Fluid & Conditions

Relative Density at 60 °F (γ₆₀)

Valid 0.3500–0.6880. (Propane ≈ 0.507, n-butane ≈ 0.584.)

Observed Temperature

°F

Valid −50.8 to 199.4 °F (227.15–366.15 K).

Volume (optional)

Observed Volume

bbl

Leave blank for the CTL factor only. If entered, V₆₀ = V × CTL.

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Why light hydrocarbons need TP-27, and the two-reference-fluid corresponding-states method behind Table 24E

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Method

CTL = V₆₀ / Vₜ

Two-reference-fluid corresponding states

δ = (γ₆₀−γ₁)/(γ₂−γ₁)

Tc = Tc₁ + δ(Tc₂−Tc₁)

ρ_sat from the saturation-density equation

CTL from interpolated reference densities

Standards & References

GPA Midstream Standard 8217
(= GPA TP-27 = API MPMS Ch. 11.2.4) Temperature correction for light hydrocarbons — Table 24E
API MPMS Ch. 11.1 / ASTM D1250
For crude & products (heavier than NGL/LPG) — see the VCF calculator

Engineering Notes

Use TP-27 for NGL/LPG (γ₆₀ 0.35–0.69); use Ch. 11.1 for crude & products.
Highly temperature-sensitive: light fluids expand a lot — small temperature errors matter.
Supercritical: if reduced temperature > 1 the fluid is not liquid (CTL = −1).
Reference fluids bracket the relative density (ethane → n-heptane).

Frequently Asked Questions

Why do NGL/LPG need a different correction than crude?

Light hydrocarbons expand far more with temperature and are below the density range of API MPMS 11.1. GPA 8217 / TP-27 (API MPMS 11.2.4) handles them with a corresponding-states model.

What inputs are needed?

Relative density at 60 °F (0.3500–0.6880) and observed temperature (−50.8 to 199.4 °F).

What is the Table 24E method?

A two-reference-fluid corresponding-states calculation: two reference fluids bracket the density, their saturation densities are scaled to the fluid's reduced temperature, and CTL = V60/VT results.

NGL / LPG Volume Correction (CTL) Calculator

Fluid & Conditions

Volume (optional)

📚 Learn the Theory

Results

Method

Standards & References

Engineering Notes

Frequently Asked Questions

NGL / LPG Volume Correction (CTL) Calculator

Fluid & Conditions

Volume (optional)

📚 Learn the Theory

Results

Method

Standards & References

Engineering Notes

Frequently Asked Questions

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