How Conditioning Orifice Plates Improve Flow Measurement in Tight Spaces ?

Orifice plates are among the most widely used flow monitoring tools in a variety of industrial applications over the years. Their simplicity, affordability, and compatibility with differential pressure-based flow measurement systems have made them a consistent option in the natural gas industry as well as in liquid and steam flow monitoring.

Among these, the conventional orifice plate usually with a single concentric bore at the center has long been the industry standard. Improved substitutes have been created, thus, in spite of installation limitations, flow disruptions, and the need for lengthy, straight pipe lines. The Conditioning Orifice Plate (COP) is one example of this innovation.

Limitations of Standard Orifice Plates

The operation of standard orifice plates is based on Bernoulli’s theory and the differential pressure that is generated across the pipeline restriction. Standards such AGA Report Number 3, ASME MFC 3M, and ISO 5167 control these plates. The quality of the upstream flow profile, therefore, greatly affects the accuracy of conventional orifice plates. Upstream piping components such as elbows, reducers, valves, or tees create flow disturbances that distort the velocity profile and hence compromise measurement accuracy.

Standard orifice plates usually need the following to lessen this:

• Straight pipe runs: There are typically 5 downstream and 10 to 50 upstream pipe diameters.
• Flow conditioners are devices that equalize flow, such as perforated plates or tube bundles.

Compact or retrofit installations may find these criteria unfeasible, particularly in skid-mounted systems, offshore platforms, and small industrial facilities.

Refer to This: Orifice Plate Commissioning Checklist

What is a conditioning orifice plate?

A modernized differential pressure flow element, the Conditioning Orifice Plate, overcomes the drawbacks of the conventional orifice plate. Though it adds important design changes for improved performance in actual applications, it uses the same fundamental concepts of flow monitoring as conventional plates.

Unlike normal plates with one bore, the COP has four equally spaced holes distributed in a circular pattern. By spreading the flow evenly before the differential pressure measurement is recorded, this multi-bore design enables built-in flow conditioning. This means that the COP eliminates the need for external flow conditioners or long straight pipes.

Core Principle and Functionality

The principle of operation of the Conditioning Orifice Plate is still based on the Bernoulli energy equation. The overall area of the four bores is supposed to correspond to the area of the single bore used in a standard orifice plate for the same pipe size.  A constant pressure drop-to-flow relationship is ensured by maintaining the beta ratio (β = d/D), which is the ratio of bore diameter to pipe diameter.

As the fluid travels through the four holes, the design allows it to “self-condition,” hence generating a more symmetric and stable velocity profile downstream. Even with little straight pipe runs, this significantly improves consistency and accuracy of measurements.

Click to Discover: Why Drain and Vent Holes are Essential for Efficient Orifice Plate Operation?

Compliance and Deviations from Standards

Though Conditioning Orifice Plates are made to be generally consistent with industry standards like ISO 5167, ASME MFC 3M, and AGA 3, there are intentional variations in four main areas to enhance performance:

1. Plate Thickness
2. Orifice Configuration / Beta Ratio
3. Straight Pipe Requirements
4. Accuracy and Installation Tolerances
   

Instead of being infractions, these deviations are improvements that offer useful advantages under field conditions.

Click to Learn: Why RTD Temperature Sensors are Installed Downstream of Orifice Plates?

Advantages of Conditioning Orifice Plates

1. Better Performance in Limited Areas: The requirement for just two diameters of straight pipe both upstream and downstream lets COPs be installed when space is extremely constrained.
2. Built-in Flow Conditioning: The four-hole design saves space and money by eliminating the need for extra flow straighteners.
3. Improved Accuracy in Wet Gas Conditions:  By use of condensate drainage via the bores, COPs stop the accumulation or “damming” usually seen with single-bore conventional orifice plates.
4. Lowering Installation Cost: Shorter straight pipe lines result in smaller meter runs, a reduced environmental impact, and cheaper labor and material costs.
5. Consistency in Measurement:  Even when put near flow disturbances, the discharge coefficient for COPs closely matches the typical orifice plate curve..
6. Simplified Specification and Inventory:  Fixed beta ratios of 0.4 and 0.65 make selection and stocking easier, regardless of pipe scheduling.

Key Design Differences and Technical Parameters

Orifice Plate Thickness

Usually, COPs employ thicker plates compared to normal orifice plates. This increases structural durability, reduces plate deflection at high flow rates, and boosts long-term measurement dependability. For example, COPs like as the Rosemount 1595 and 405C offer more resistance to pressure-induced deformation than the AGA 3 thickness standard for 6-inch lines.

Orifice Configuration / Beta Ratio

• Standard Orifice Plate: One center bore; beta ratios usually vary from 0.1 to 0.75.
• Conditioning Orifice Plate: Four bores symmetrically arranged. Two fixed beta ratios are used: 0.4 for low to medium flow and 0.65 for high flow. Pipe schedules show constant maintenance of these values.

Read: Orifice Beta Ratio: Why It Falls Between 0.3 and 0.7 for Optimal Flow Measurement

Straight Pipe Requirements

One of the most transformative aspects of COP technology is its minimal piping requirement:

• Only 2D upstream and 2D downstream: One of the most revolutionary features of COP technology is its low piping requirements: only 2D upstream and 2D downstream, which drastically reduces the 10D to 50D upstream and 5D downstream that ordinary orifice plates typically require.

For instance, the conventional orifice plate per ISO 5167 would require 16D upstream for a 6-inch line with a single upstream 90° elbow. A COP would only need 2D, signifying an 88% decrease of pipe.

Click to Use: Orifice Plate Flow Rate Calculator

Measurement Accuracy

The COP keeps great precision still despite loosened installation criteria. Lab experiments show discharge coefficient (UCd) uncertainty as follows:

These numbers are better than the uncertainties specified in ISO 5167 and ASME MFC specifications for standard orifice plates.

The graph titled “Discharge coefficient uncertainties for 0.4 beta” compares the uncertainty levels of different flow measurement standards across varying Reynolds numbers. It highlights that the 1595 and 405C Conditioning Orifice Plates maintain a low and consistent uncertainty of around ±0.5%, outperforming ASME MFC 3M, AGA Report Number 3, and ISO 5167 standards, especially at lower Reynolds numbers. Notably, ASME MFC 3M shows high uncertainty (~1.0%) at low Reynolds numbers, which drops significantly after 2000. This graph demonstrates the superior performance and stability of conditioning orifice plates across a broad range of flow conditions.

The graph titled “Discharge coefficient uncertainties for 0.65 beta” illustrates how uncertainty varies with Reynolds number for different standards. It shows that the 1595 and 405C Conditioning Orifice Plates initially have a higher uncertainty (~1.25%) at low Reynolds numbers, but stabilize at around ±0.75% once the Reynolds number exceeds 2000. In comparison, ASME MFC 3M, AGA Report Number 3, and ISO 5167 standards also show higher uncertainties at low Reynolds numbers, which drop significantly after 2000. Despite a slightly higher steady-state uncertainty, the conditioning plates still offer acceptable and consistent performance across a wide Reynolds number range.

Refer the below link for the for the calculation of Reynolds Number with free excel tool

Conditioning vs. Standard Orifice Plates

Download and Refer: Orifice Plate Flow and Pressure Drop Calculation Excel Tool

The Conditioning Orifice Plate is a major change in technology for measuring differential pressure flow. It provides a contemporary answer to many of the constraints experienced by conventional orifice plates by including flow conditioning into the plate design and reducing the need for long, straight pipe lengths.

COPs not only provide accuracy and dependability but also design flexibility and cost reductions with proven performance in both laboratory and field settings. Conditioning Orifice Plates are especially better than conventional orifice plates in applications where space, installation limits, or multiphase flow conditions occur.

Test Your Knowledge with Orifice Plate Flow Measurement Quiz

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