How Conditioning Orifice Plates Work ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

How Conditioning Orifice Plates Work

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Over the years, in many industries especially the natural gas industry, the orifice plate has become the de facto flow meter for measuring flow. In many liquid, steam or gas application, the standard orifice plate with a bore at the centre of the plate is being used with considerable operational reliability and accuracy.

However, standard orifice plates performance are affected by flow distorters such as elbows, tees which introduces flow distortions in the flow stream necessitating some flow conditioning to maintain accuracy. Flow conditioning in standard orifice plate applications can either be  by way of a flow conditioner or lengthy straight pipe runs requirement that are often difficult to achieve in practical situations. 

Conditioning Orifice Plates Standards & Technology
Conditioning Orifice Plates are differential producers used to measure flow in a pipe. Conditioning Orifice Plate Technology is based on the same Bernoulli streamline energy equation
as standard orifice plates, resulting in the same Discharge Coefficient versus Reynolds Number relationship. Standard orifice plates are typically specified and installed according to either AGA Report Number 3, ASME MFC 3M or ISO 5167. Conditioning orifice plates are also manufactured according to the same standards but with some deviations.

How Conditioning Orifice Plates Works
As shown above, Conditioning Orifice Plates have four holes that are placed in a circular pattern, leaving a metal section of the plate in the center of the pipe. This causes the flow to condition itself as it is forced through the four holes, thereby removing the requirement for a flow conditioner. Because of this phenomenon, Conditioning Orifice Plates provide superior performance in short straight pipe run and applications where installation space is limited. Note that the sum of the area of the four bores in a conditioning orifice plate is equivalent to the area of a single bore “d” in the standard equation “beta = d/D” for a standard schedule pipe for a standard orifice plate.

Difference Between Conditioning Orifice Plates & Standard Orifice Plates

Property Conditioning Orifice Plates Standard Orifice Plates
Orifice Bore They have four equally space bores or holes on the plate They have one central bore
Beta Ratio Beta ratio is either 0.4 or 0.65 for all pipe sizes.Conditioning Orifice Plates are designed with 2 standard bore sizes, one for high flow rates and one for low flow rates. These standard bore sizes are fixed and do not change with pipe schedule. Standard orifice plates are sized to  beta ratios from 0.1 to 0.75 (beta ratio = d/D, where “d” is the bore size and “D” is the internal diameter of the pipe/meter tube)
Piping Requirements Conditioning Orifice Plates, require 2 diameters of straight pipe upstream and 2 diameters downstream Standard orifice plates require significant straight pipe to assure an accurate flow measurement
Plate Thickness Conditioning Orifice Plates fall within the thickness values provided in all three standards with one exception, the AGA Report Number 3 standard for the 6” line. Where there are deviations from the standards, conditioning orifice plates are thicker than standard orifice plates preventing plate deflection under high flow rates thereby ensuring accuracy in flow measurement. Thickness values are as specified in the standards
Accuracy Comparable Accuracy to Standard Orifice Plates Standard Accuracy

Advantages of Conditioning Orifice Plates
  1. Requires 2 diameters upstream and 2 diameters downstream of a flow disturbance.

  2. Provides flexibility of flow meter placement and design

  3. Reduces installation costs as compared to standard orifice plates.

  4. Provides highly accurate and repeatable flow measurement in liquid, gas and steam applications.

  5. Conditioning Orifice Plates are used with improved performance in wet gas applications by allowing condensate to pass and preventing the “damming” effect suffered by standard orifice plates