Orifice Assembly………let the restriction do measurement

Compiled by

Mr. Harshal Revandkar (harshal.revandkar@chemtrols.com)Engineer (Metering and Measurement)Chemtrols Industries Ltd.

Under the guidance of

Mr. R. C. RamchandranManager (Flow Elements)Chemtrols Samil (I) Pvt Ltd.

Principles of Fluid Flow in Pipes

laminar flow : the fluid travels as parallel layers (known as streamlines)

Turbulent flow: The fluid does not travel in parallel layers, but moves in a haphazard manner

NR < 2000 – laminar flow NR > 4000 – Turbulent flow 2000 < NR < 4000 – transition region

Why to measure flow ????

Control

Billing

Alarm and indication

Techniques used in flow measurement

Variable area

Magnetic

Vortex

Pressure difference

Ultrasonic

Principle of pressure difference method

Pressure difference type flow elements

Orifice plate

Flow nozzle

Venturi tube

Orifice plateThe orifice plate is the simplest and cheapest. It is simply a plate with a hole of specified size and position cut in it, which can then clamped between flanges in a pipeline

The increase that occurs in the velocity of a fluid as it passes through the hole in the plate results in a pressure drop being developed across the plate.

After passing through this restriction, the fluid flow jet continues to contract until a minimum diameter known as the vena contracta is reached.

Principle of working

The whole principle is based on Bernoulli's principleWhich states that, for an flow of a nonconducting fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure.

Types of Orifice plate

Concentric

Eccentric

Segmental

Quadrant Edge

Concentric 

These are most commonly used for flow measurement. This has special features such as simple structures, high accuracy, and ease of installation & replacement.

The orifice plates are correctly finished to the dimensions, surface roughness, and flatness to the applicable standard.

These plates are recommended for clean liquids, gases & steam flow, when the Reynold number 7 ranges from 1000 to 10000

Eccentric

For liquids containing solid particles that are likely to sediment or for vapours likely to deposit water condensate, this orifice plate is used with its eccentric bore bottom flush with the bottom of the piping inside surface so that the sedimentation of such inclusions are avoided.

Likewise, for gases or vapours, it may be installed with its eccentric bore top flush with the ID of the piping to avoid stay of gas or vapour in its vicinity.

For Liquids

For gases

Segmental 

Segmental orifice plates are most useful where there are impurities and also if there are suspension in the fluids.

This avoids build up in front of the orifice plate. The orifice hole is placed at the bottom for gas service and top for liquids.

The inlet edge of the bore of this orifice plate is rounded to a quarter circle.

This orifice plate is usually used for viscous fluids & Reynolds number between 2000 to 10000.

Quadrant Edge

Conical Entrance

These conical entrance orifice plates are used for low Reynolds number in the range of 80 to 2000 and give more constant or predictable discharge coefficient.

At lower Reynolds numbers, the discharge coefficient of square edge orifice plate may change by as much as 30%. These are more usable for viscous service.

Orifice Flanges and support assembly

Two orifice flanges are called an orifice flange union. Each flange comes with two pipe taps for measuring the pressure drop of the flow through an orifice plate

Support assembly consist of

Gasket

Carrier Ring

Stud and bolts

Corner Tap : In this arrangement, openings for the pressure taps are located in the upstream and downstream flanges holding the orifice plate

Flange Tap : This design places one pressure tap hole 1 inch upstream and the other 1 inch down-stream form the orifice plate. Being closely located to the face of the flange, they are accessible for inspection..They should not be used in pipe sizes less than 2 inches where the ratio is high, because the downstream tap is located in a highly unstable pressure region.

Orifice Tapings

D and D/2 taps are located in the pipe wall one pipe diameter upstream of the face of the plate and half pipe diameter downstream from face

These taps are also called as Radius Taps. The pipe line sizes of 10" and above are recommended to have these taps

D and D/2 tapings

Tapings at glance

Design of orifice plate

Design: per ISO 5167-2/ ASME MFC3M

Nominal size: ≥ 1½" (40 mm)

Nominal pressure rating: as per customer requirements

β-ratio: 0.20 ... 0.75

Accuracy: ≤ ±0.5 % of full scale flow rate

Repeatability: 0.1 % of flow rate

Factors need to be consider while design

1. Pipe Internal Diameter2. Coefficient of thermal expansion for pipe and orifice3. Meter range4. Normal flow5. Density (operating , NTP)6. Viscosity7. Differential pressure8. Specific heat ratio9. Operating pressure10. Operating temperature11. Pipe ID at operating temperature12. Distance of tap13. Reynolds number

14. (Ceβ)^2 , Original15. Emperical value of β16. Iterated value of β17. Pressure ratio18. Expansion factor19. Velocity approach factor20. Discharge coefficient21. (Ceβ)^2 , iterated22. Permanent pressure loss23. Orifice diameter at 20 °C24. Vent/Drain hole (if required)25. Corrected orifice diameter (if V/D hole present)26. Radius of location of vent/ drain hole27. Yield stress (for thickness calculation)

What we offer our clients…

Maximum operating temperature up to 800 °C

Maximum operating pressure up to 400 bar

Materials (Stainless steel , Hastelloy C276 , Monel 400,Duplex and Super Duplex, Others on request)

Accuracy ≤ ±0.5 % of actual flow rate

Repeatability of measurement of 0.1 %

Cost Efficient (cheapest as compare to other flow elements)

Advantages of Orifice plateHigh-quality

High accuracy

A wide range

Very reliable

Low cost

low pressure drop across the meter

All mechanical units can be installed in remote locations

Limitations

Bulky, especially in the larger sizes.

The fluid must be clean for measurement accuracy

A sudden change in the flow rate can damage the meter

Only for limited ranges of pressure and temperature

Require a good maintenance schedule and are high repair and maintenance meters

Need to be replaced after specific time

Targeted Customers

Water suppliers

Petrochemical industries

Oil industries

Natural gas industries

LPG suppliers

Refineries

Power industries

We did it….

Client : Indian Oil Corporation Ltd ,BongaigaonProject : Supply of Orifice plates for liquid flow measurementYear : march 2015

Client : Indian Oil Corporation Ltd ,KothariProject : Supply of Orifice plates for liquid/gas flow measurementYear : march 2015

Client : Indian petrochemical corporation ltd, MthuraProject : Supply of Orifice plates for liquid/gas flow measurementYear : april 2015

Our highly reputed clients

And many more…..