Orifice Plate

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Orifice plate

• aSHVANI Shukla
• CI
• reliance

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• Orifice Plate
• An orifice plate is a device used for measuring
  flow rate, for reducing pressure or for
  restricting flow (in the latter two cases it is
  often called a restriction plate). Either a
  volumetric or mass flow rate may be determined,
  depending on the calculation associated with the
  orifice plate. With an orifice plate, the fluid
  flow is measured through the difference in
  pressure from the upstream side to the downstream
  side of a partially obstructed pipe. The plate
  obstructing the flow offers a precisely measured
  obstruction that narrows the pipe and forces the
  flowing fluid to constrict.

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continuous

• Orifice Plate is the heart of the Orifice Meter.
  It restricts the flow and develops the
  Differential Pressure which is proportional to
  the square of the flow rate. The flow measuring
  accuracy entirely depends upon the quality of
  Orifice plate, its installation and maintains.
• When measuring wet gas or saturated steam a weep
  hole is drilled in a concentrically bored orifice
  plate. This is a small hole drilled on the
  orifice plate such that its location is exactly
  on ID of the main pipe.

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• The Orifice plates are manufactured as per ISA /
  AGA/ API / ANSI standards and in various
  materials
• such as SS304 /SS316 / SS316L /Hestoly C / Monel
  / PTFE coated.
• Various bores are used for various applications.
• Orifice Plate is categories in two types -
  Paddle Type Universal Palate.
• Paddle Type Orifice Plate
• This plate is sandwiched between two Orifice
  Flanges. Tag Plate of orifice plate projects out
  from Orifice flanges and it indicates the
  existence of Orifice plate. Details such as Tag
  NO /Orifice ID / Pipe ID / Plate Material are
  stamped on one side of the tag plate which faces
  upstream side of the pipe line. Outside diameter
  of the orifice plate equals to PCD-1 Bolt Dia.
  This ensures the concentricity with the main pipe
  line. The other method to maintain the
  concentricity is by using sleeves on the bolts or
  by providing dowel pins on the Orifice Flanges.
• Universal Orifice Plate
• This is a circular plate designed to fit in the
  Orifice fittings / Plate holders / carrier rings
  / Ring Type Joints(RTJ).

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Technical Specification
1.Size for Integral Design 15, 20, 25, 40 mm
2.Size for Flanged Design 25, 40, 50, 65, 80,
100, 150 ...250 mm 3.Material- Flanges
Carrier Ring A105 / SS304/ SS316 / SS316L / CS
Other materials on request. 4.Orifice
Plate SS304, SS316, SS316L, Hast C, Monel, PP,
PVC,PTFE, Coated or Clad with PP / HDPE / PTFE.
5.Gasket CAF / SS Spiral Wound CAF / PTFE /
PVC / Rubber, Other materials as per special
request. 6.Stud / Nut ASTM A193 Gr B/ASTM
A194 CI 2H A193 B16/A194 C14 7.Standards
Applicable Design - ISA RP 3.2 / DN 1952 / BS
1042 - 1981-84 8.Bore Calculation ISO 5167 /
BS 1042 / RW Miller / L. K. SPIN / AGE - 3.7
9.Flanges ANSI B-16-36 / or Equivalent
10.Types Square edge concentric, Quadrant
edges, Conical entrance, Eccentric.
11.Pressure Toppings For 1" to 16" - Flange
Taps / Corner Taps. Above 16" - D x D/2
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Type Orifice Plate

• Paddle Type Orifice Plate
• Concentric Beveled Bore
• Application  This Most Common Bore Used In The
  Industries. This Is The Only Type Generally
  Accepted For Use In Custody Transfer Measurement,
  Since Adequate Data Is Not Available For Other
  Bores. Used Primarily For Clean Homogeneous
  Liquids, Gases, Non Viscous Fluids. The Bevel Is
  Matched At 45 Angle To The Desired Throat
  Thickness.

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Application This Type Is Not Used For Flow
Measurement But For Dropping The Pressure
Considerably And Reducing The Flow Accordingly.
The Bore Is Not Beveled But Kept Straight. The
Beta Ratio Has No Limit As Accuracy Is Not The
Goal
Restriction Bore
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Eccentric Bore

• Application  Used For Measurement Of Flow For
  Fluids Containing Solids And Slurries. It Is Also
  Used For Vapors And Gases Where Condensation Is
  Present. The Eccentric Bore Is Offset To Where
  The Bore Edge Is Inscribed In A Circle That Is
  98 The Line Id.

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Segmenta Bore

• Application
• The Segmental Bore Is Located In The Same Way
  That The Eccentric Bore Is. This Type Is Used
  Primarily For Slurries Or Extremely Dirty Gases
  Where The Flow May Contain Impurities Heavier
  Than The Fluid.

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Quadrant Bore

• Application  Used For High Viscous Fluids Such
  As Heavy Crude, Syrups  And Slurries. It Is
  Always Recommended For Flow Where Reynolds Number
  Is Less Than 10,000.The Inlet Is Quarter Of A
  Circle And The Plate Thickness Must Be At Least
  Radius Of The Inlet.

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Ring Type Joint Integral

• Application
• These Are Available In Oval Or Octal Shapes.
  Orifice Plate Is A Part Of RTJ Gasket.

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Ring Type Joint- Separate

• Application  These Are Available In Oval Or
  Octal Shapes. The  Orifice Plate Is Universal
  Type And Snap Fitted On The RTJ Gasket By Screws.

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Universal Orifice Plates
Application  This Is A Circular Plate Designed
To Fit In The Orifice Fittings / Plate Holders /
Carrier Rings / Ring Type Joints(RTJ).
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Various Orifice Assemblies
WNRF - Flange Taps
WNRF - Corner Taps
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Orifice working principle

• Working
• The orifice plate, being fixed at a section of
  the pipe, creates an obstruction to the flow by
  providing an opening in the form of an orifice to
  the flow passage.

When an orifice plate is placed in a pipe
carrying the fluid whose rate of flow is to be
measured, the orifice plate causes a pressure
drop which varies with the flow rate. This
pressure drop is measured using a differential
pressure sensor and when calibrated this pressure
drop becomes a measure flow rate. The flow rate
is given by.
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Where, Qa flow rateCd Discharge
coefficientA1 Cross sectional area of pipeA2
Cross sectional area of orificeP1, P2 Static
Pressures

• The main parts of an orifice flow meter are as
  followsA stainless steel orifice plate which
  is held between flanges of a pipe carrying the
  fluid whose flow rate is being measured.
• It should be noted that for a certain distance
  before and after the orifice plate fitted between
  the flanges, the pipe carrying the fliud should
  be straight in order to maintain laminar flow
  conditions.
• Openings are provided at two places 1 and 2 for
  attaching a differential pressure sensor (U-tube
  manometer, differential pressure gauge etc) as
  shown in the diagram.

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Operation of Orifice Meter

• The detail of the fluid movement inside the pipe
  and orifice plate has to be understood.
• The fluid having uniform cross section of flow
  converges into the orifice plates opening in its
  upstream. When the fluid comes out of the orifice
  plates opening, its cross section is minimum and
  uniform for a particular distance and then the
  cross section of the fluid starts diverging in
  the down stream.
• At the upstream of the orifice, before the
  converging of the fluid takes place, the pressure
  of he fluid (P1) is maximum. As the fluid starts
  converging, to enter the orifice opening its
  pressure drops. When the fluid comes out of the
  orifice opening, its pressure is minimum (p2) and
  this minimum pressure remains constant in the
  minimum cross section area of fluid flow at the
  downstream.
• This minimum cross sectional area of the fluid
  obtained at downstream from the orifice edge is
  called VENA-CONTRACTA.
• The differential pressure sensor attached between
  points 1 and 2 records the pressure difference
  (P1 P2) between these two points which becomes
  an indication of the flow rate of the fluid
  through the pipe when calibrated.

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• Applications of Orifice Meter
• The concentric orifice plate is used to measure
  flow rates of pure fluids and has a wide
  applicability as it has been standardized.
• The eccentric and segmental orifice plates are
  used to measure flow rates of fluids containing
  suspended materials such as solids, oil mixed
  with water and wet steam.
• Advantages of Orifice Meter
• It is very cheap and easy method to measure flow
  rate.
• It has predictable characteristics and occupies
  less space.
• Can be use to measure flow rates in large pipes.
• Limitations of Orifice Meter
• The vena-contracta length depends on the
  roughness of the inner wall of the pipe and
  sharpness of the orifice plate. In certain cases
  it becomes difficult to tap the minimum pressure
  (P2) due to the above factor.
• Pressure recovery at downstream is poor, that is,
  overall loss varies from 40 to 90 of the
  differential pressure.
• In the upstream straightening vanes are a must to
  obtain laminar flow conditions.
• Gets clogged when the suspended fluids flow.
• The orifice plate gets corroded and due to this
  after sometime, inaccuracy occurs. Moreover the
  orifice plate has low physical strength.
• The coefficient of discharge is low.