NorcraftNorCraft Software

We make easy-to-use engineering software for the oil & gas industry. Our software is designed for practical field applications, and the programs have been tested and proven for both onshore and offshore oil and gas installations.  The programs are designed for use right away, easy, clutter-free and fast.

The programs are provided "as is” without warranty of any kind, either expressed or implied, including any warranty of merchantability or fitness for a particular purpose.  In no event shall the author or Norcraft be held liable for any loss of profit, special, incidental, consequential, or other similar claims.

The programs are written as Excel macros and require Microsoft Excel version 2007 or later.  'Macro' must be enabled within Excel to run the programs.  The DEMO-versions received through the direct download link have limited functionality and will only work a few times.  A license fee of $9.95 for each program is required for a full version of the program, which will be e-mailed to you.



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   AGA-3: 1991 Orifice Calculations (ANSI-2130)



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ISO-5167: 2003 Orifice Calculations



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 WatGas - Water-Natural Gas Phase Behavior



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 GOWProp (Gas-Oil-Water PVT Properties)  



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 GOSep (Gas-Oil Separator Flash Calculations) – Freeware



Free Manual

GOWDoc (Documentation File) – Free PDF-file


For more information, please send questions/queries to:

AGA-3 and ISO-5167 Orifice Calculations


Programs AGA3 and ISO5167 will size orifice plates for given design conditions, find pressure drop for a given flow, or flow for a given pressure drop. The standards (AGA-3 ( API-2530: 1991) and ISO-5167: 2003) are originally designed for gas orifices. In these programs they are also used for liquid orifices.

The gas orifices are Natural Gas, Nitrogen and Air.  The fluids for liquid orifices are Crude Oil, Water, Methanol, Mono-ethylene glycol, di-ethylene glycol and tri-ethylene glycol.

For gas-calculations you have to enter specific gas gravity, temperature and pressure. You can also give mole-fractions of N2, CO2 and H2S for sour gas calculations.

The AGA-8 equation is used for calculating Z-factor (compressibility factor) for natural gases, and the Redlich-Kwong equation of state for air and nitrogen.

For oil-calculations you have to enter specific oil gravity, temperature and pressure. It is also recommended to give molecular weight of oil. For water-calculations the input requirements are salinity, temperature, and pressure.

NOTE: It is assumed that all dissolved solids for water are expressed as equivalent sodium chloride concentration.

The results are an orifice specification sheet giving the necessary data for design of an orifice or evaluating an existing orifice.

The results will contain a few factors that you should know:

The velocity of approach factor is defined as:

Ev = 1/(Sqrt(1-Beta^4))

The flow coefficient, Alpha, is defined as:

Alpha = Ev * Cd

and orifice to pipe diameter ratio is given as:

Beta = OD/PID


API/ ANSI-2530 - 1991 (AGA Report No. 3) (AGA)

The basic flow equation is:

Qv = Fn*(Fc+Fsl)*Y1*Fpb*Ftb*Ftf*Fgr*Fpv*Sqrt(Pf1*hw)



Fn = Numeric conversion factor

Cd = Discharge coefficient = (Fc + Fsl)

Fc = Orifice calculation factor

Fsl= Slope factor

Y1 = Expansion factor based on upstream tap

Fpb= Pressure base factor, set to 1.0 (14.73 psia)

Ftb= Temperature base factor, set to 1.0 (60 deg F)

Ftf= Flowing temperature factor

Fgr= Specific gravity factor

Fpv= Super-compressibility factor

Pf1= Absolute flowing pressure based on upstream tap

hw = Orifice differential pressure, in H2O at 60 deg F

The above equation is often simplified to:

Qv = C' * Sqrt(Pf1*hw)

where C' is called the Composite orifice flow factor.

For other factors and the factors for pipe taps you are advised to consult the standard API-2530-1991, Part 3.


ISO-5167-2: 2003 ( ISO)

The basic flow equation is:

Qm = C*E*Eps*Pi/4*OD^2*Sqrt(2*dP*Roh)


Qm = Mass flow rate (kg/s)

C = Discharge coefficient = Alpha/E

E = Velocity of approach factor = 1/(Sqrt(1-Beta^4))

Eps = Expansion factor due to pressure drop

Pi = 3.14159

OD = Orifice diameter at actual flowing conditions

dP = Differential pressure across orifice

Roh = Density of flowing fluid measured at upstream tap

For other factors consult the standard ISO-5167-2: 2003.

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Program  WatGas - Water-Natural Gas Phase Behavior Calculations


Watgas calculates Water-Natural Gas interaction properties, including the following PVT-properties: 

-Hydrate formation calculations

-Water content predictions of natural gases

-Inhibitor quantities (methanol/glycols) to avoid hydrate problems in pipelines

-Solid CO2 formation predictions


The program handles gases with known compositions and non-compositional gases (only gas gravity is needed). Note that the compositional model is more reliable than the non-compositional model, although they give similar results.

Almost all gases contain some water vapor. When leaving the producing formation, gas is saturated with water vapor, which is in equilibrium with reservoir liquid water at temperatures and pressures prevailing there.

Knowing the water content of natural gases is essential to the design and operation of production, dehydration and transmission systems. Water may condense in production and gathering systems. This may result in hydrate formation and plugging of flow systems and damage to internals of production equipment.

Condensed water may form water slugs, which will tend to decrease flow efficiency and increase the pressure drop in a line. Presence of free water in pipeline systems may also cause corrosion. If carbon dioxide and/or hydrogen sulfide are present, the gases may form carbonic acid and sulphurous acid respectively if dissolved in water.

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Program GOWProp (Gas-Oil-Water Physical Properties)

Program GOWProp is a Physical Properties program that calculates PVT properties of gas, oil, and water — with your choice of calculation methods. Pick from a selection of standard        equations for calculating certain properties. More than 12 properties are calculated and the results include a pressure depletion table of the various properties and will plot the output on screen. U.S. and SI Units.


Oil properties are calculated based on a black-oil model. In fluid-property terms the black-oil model employs 2 pseudo-components:

1) "OIL" defined as produced oil at stock tank conditions

2) "GAS" defined as produced separator gas

The basic assumption is that gas may dissolve in the oil phase, but oil will not dissolve in the gas phase. For mixtures of heavy oil and light components this is a reasonable assumption, but is a misleading assumption for mixtures of light and intermediate components.

The following fluids are included:


-Natural gas






-Methanol/Water mixtures

-Monoethylene glycol/Water mixtures

-Diethylene glycol/Water mixtures

-Triethylene glycol/Water mixtures


GOWProp will let you choose between SI-units (metric) or Customary units.

The gas property routine calculates:

-Molecular weight



-Gas formation volume factor

-Z-factor (gas deviation factor)


-Thermal conductivity

-Specific heat

-Ideal isentropic coefficient, Cp/Cv

-Real isentropic coefficient, k

-Pseudo Critical properties

-Pseudo Reduced properties


The liquid property routine calculates:

-API gravity (for oil only)



-Formation volume factor (oil and water only)

-Solution gas-liquid ratio (oil and water only)

-Bubble point pressure (oil only)


-Thermal conductivity

-Surface tension

-Specific heat

-Pseudo Critical properties

-Pseudo Reduced properties


A pressure liberation table of properties (at constant temperature) will also presented from given pressure down to atmospheric conditions (14.696 psia [1.01325 Bara]).

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Program GOSep (Gas-Oil Separtor Flash Calculations)

Program GOSep performs flash calculations for gas/oil separators to optimize liquid recovery.  The program performs vapor-liquid equilibrium calculations for 2 stages of separation and Stock Tank conditions (Standard Conditions), defined in the program as 14.73 psia and 60 °F.

Equilibrium ratios (K-values) are used for calculating compositions of gas and liquid phases at given temperatures and pressures.  Normally an equation of state (EOS) is used for predicting equilibrium ratios, and is a function of composition, pressure and temperature.  Based on the fact that compositional effects on equilibrium ratios are small below about 1000 psia, Standing developed a correlation for calculating equilibrium ratios based on data reported by Katz and Hachmuth.  The correlation gives the following equation for each component:

                   K = (1/P) x 10 (a + c x F)                                                                              


                 F          = b x (1/Tb - 1/T)  

       K          = equilibrium ratio    

                           a, b, c  = correlating parameter  

                 P          = pressure, psia 

                 T         = temperature, deg R    

                 Tb        = boiling point, deg R 

                 X         = mole fraction in liquid phase      

                 y         = mole fraction in vapor phase

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Last Revised: April, 2014