ISO-5167 2003 6.5

Programs AGA (AGA-3) and ISO ( ISO-5167) 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 programs let you calculate the following orifice-types:
- Gas Orifice
- Liquid Orifice
- Restriction Orifice - Gas
- Restriction Orifice - Liquid
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)
where
cFn = 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.....