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Water Content Calculator

McKetta-Wehe Correlation

Gas Water Content Calculator (GPSA Method)
Calculates saturated water content in natural gas using McKetta-Wehe/Bukacek correlations. Determines dewpoint temperature and specification compliance for dehydration system design.

Operating Conditions

°F
Valid: -60°F to 400°F
psia
Valid: 1-15,000 psia

Gas Properties

-

Sweet natural gas: 0.55-0.70
Rich/wet gas: 0.70-0.85

Industry Specifications

Pipeline ≤ 7 lb/MMscf
Sales gas ≤ 4 lb/MMscf
Cryogenic ≤ 1 lb/MMscf

Correlations Used

W = W14.7 × (14.7/P) × Cg
W = Water content (lb/MMscf)
W14.7 = Sat. water at 14.7 psia (McKetta-Wehe)
P = Operating pressure (psia)
Cg = Gas gravity correction

Gravity correction: Cg = (1 + SG) / 1.6

Standards & References

  • GPSA
    Section 20, Figure 20-3 (McKetta-Wehe)
  • Bukacek Correlation
    IGT Research Bulletin No. 8 (1955)
  • ISO 18453:2004
    Natural Gas - Water Content Correlation
  • GPA 2145
    Physical Constants for Paraffin HC

Engineering Notes

  • Sweet gas only: Acid gases (CO₂, H₂S) increase water solubility 5-15%
  • Correlation accuracy: ±3-5% for 60-200°F, 100-3000 psia range
  • Dehydration methods: TEG achieves 2-7 lb/MMscf; molecular sieve <0.5 lb/MMscf
  • Temperature effect: Water content roughly doubles per 20°F increase
  • Pressure effect: Water content inversely proportional to pressure

Common Errors

  • Using gauge pressure instead of absolute (psig + 14.7 = psia)
  • Applying sweet gas correlation to sour gas
  • Confusing ppmv with lb/MMscf (not 1:1 conversion)

Frequently Asked Questions

How is water content of natural gas calculated?

This calculator uses the McKetta-Wehe correlation and GPSA Section 20 methods to determine the saturated water content of natural gas at a given temperature and pressure. Results are expressed in lb water per MMscf of gas.

What is the McKetta-Wehe chart used for?

The McKetta-Wehe chart provides equilibrium water vapor content of sweet natural gas as a function of temperature and pressure. It is the industry-standard reference published in the GPSA Engineering Data Book, Section 20.

Does gas composition affect water content calculations?

Yes. Sour gases (H₂S and CO₂) increase the water-carrying capacity of natural gas compared to sweet gas. This calculator applies correction factors for sour gas components per GPSA Section 20.

Why is water content important in gas processing?

Knowing the water content is essential for sizing dehydration equipment such as glycol contactors and molecular sieve beds. Excess water causes hydrate formation, corrosion, and failure to meet pipeline sales gas specifications.