How to Size an Orifice Plate Flow Meter with Software

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Orifice plate sizing is normally done these days with software provided by the manufactures of the device. This tutorial will use the Daniel Orifice Flow Calculator version 3.1.
Before going through this Orifice sizing tutorial please read:
•The Orifice Flow Meter Equation
•A Guide to Sizing Orifice Plate Flow Meters

In these articles, you will familiarise yourself with the Orifice plate flow equation and the various correction factors applied when determining flow from Orifice plate flow meter installations. You will also learn about the parameters that affect Orifice plate sizing the most.

To size an orifice plate with software, you require the following process parameters:

(a) Operating Temperature
(b) Density or Compressibility factor, Z, at flowing condition
(c) Operating pressure
(d) Specific Gravity
(e) Nominal size of pipe
(f) Maximum flow through the Orifice plate
(g) A suitable differential pressure

When all these parameters are imputed into the Daniel Orifice plate flow calculator, the Beta ratio and the Orifice plate size – bore diameter is automatically calculated.

Suppose we want to determine the size of an Orifice plate to be used in a Natural gas metering station with the following parameters:
(1) Operating temperature is 18.58 degree Celsius
(2) Gas stream density of 54.7kg/m3
(3) Operating pressure of 60barg
(4) Specific gravity of 0.701
(5) Nominal pipe size of 30 inches
(6) Maximum flow of 600MMSCFD
(7) Minimum flow of 200MMSCFD
 Also in this installation, the rangeability of the Orifice flow meter is to be improved using two transmitters in parallel across the Orifice plate.

For this scenario, we have chosen a differential pressure of 100 inches of water. The reasons are:
(a) At 200 inches of water and at 60barg, the operating pressure, the deflection forces on the Orifice plate becomes great which will introduce more errors into our measurement and create other operating problems.

(b) We chose 100 inches instead of 200 inches that would have yielded more accuracy at low flow rates because the rangeability of the Orifice plate flow meter for this particular installation is to be improved by two differential pressure transmitters in parallel across the Orifice plate with one measuring flow between 0 -300MMSCFD and the other measuring flow in the range 300 – 600MMSCFD. See Basics of Flow Measurement with the Orifice Flow Meter II for more on how to improve the accuracy and rangeability of the Orifice plate flow meter.

Next impute all the process conditions into the orifice flow calculator, select: air-gas under the flow type box on the bottom right of your screen. Also select: calculate beta ratio from the options box on the bottom left of your screen as shown below:

Daniel Orifice Plate Flow Calculator

As seen above, we get Beta ratio = 0.60514 and Orifice bore diameter = 17.7 inches. These two values are greened out in the Daniel Orifice Flow Calculator shown above.
When imputing values, don’t forget to select the appropriate units for all the parameters you are imputing.