DESIGN CHANGES ADDRESSING MEASUREMENT LIMITATIONS OF ORIFICE FLOWMETERS

DR. ZAKI HUSAINTECHNICAL CONSULTANT

ZS TECHNOLOGY, LLC

1

ORIFICE METER LIMITATIONS

• Maximum Differential Pressure

• Reattachment Pointo Effects on downstream pressure port

o Closest Sample Collection Point – 5D

• Single Point Measuremento Fully Developed Flow Profile

o Concentricity of Plate Bore

o Flow Conditioner

o Long Upstream/Downstream Meter Tubes

• Large variations in beta ratio

• Single Phase Fluid Flow

• Permanent Pressure Drop

• Stringent Mechanical Toleranceso Edge Sharpness

o Pipe Roughness

o Pipe Circularity

o Upstream Steps and Gaps

o Upstream/Downstream Tap Distance

o Plate Roughness

o Plate Bore Thickness

o Plate Bevel and Plate Land Thickness

2

EXPERIMENTAL SETUP & RESULT

AIR FLOW FACILITY: 0.3, 0.5, AND 0.7 BETA RATIO PLATES

Reynolds Number Range 21,000 to 160,000TOROIDAL SHAPE INLET PROFILE (Ower & Pankhurst, Measurement of Airflow, Pergamon Press, NY, 5th Edition, 1977)

This paper by Dr. Zaki Husain & Dr. Ray Teyssandier was presented at the 1985 ASME Winter Annual Meeting and later archived as GPA

Technical Report 13. This paper is referenced in the ISO, API, AGA, GPA Orifice Meter standards, which is the basis for minimum piping length

requirements for downstream disturbances and tolerances for upstream and downstream pressure tap locations.

3

EFFECT OF CENTER TAP PRESSURE ON UPSTREAM PRESSURE DISTRIBUTION

Differential pressure referenced to Center Tap pressure, normalized by maximum differential pressure between upstream line

pressure referenced to Center Tap pressure.

4

PRESSURE DISTRIBUTION ON FACE OF THE ORIFICE PLATE

5

DOWNSTREAM PRESSURE DISTRIBUTION

Center Tap Pressure demonstrated minimal influence of flow profile disturbances. Differential pressure readings at any location

of the orifice meter pipe and on plate surface, when normalized by the maximum differential pressure between upstream line

pressure and Center Tap pressure influence of piping and plate geometry indicated minimal influence.

6

EFFECT OF ECCENTRICITY ON DIFFERENTIAL PRESSURE MEASUREMENT

This paper on effect of orifice plate eccentricity by Dr. Zaki Husain and Dr. Ray Teyssandier was presented at the 1983 British

Instrument Society Conference and later archived as GPA Technical Publication 13 is also referenced in ISO, A{I, AGA, and GPA

Orifice Meter Standards

7

EFFECT OF PHYSICAL AVERAGING OF TAPS

8

WITHSTAND HIGH DIFFERENTIAL PRESSURES

9

ELIMINATE INFLUENCE OF DOWNSTREAM DISTURBANCES & SINGLE POINT PRESSURE MEASUREMENT ISSUES

• Averaging Pressure Port

• Higher Differential

• Measured at High Velocity Point

• Minimize Effects of Downstream

Flow Disturbances

• Independent of Downstream

Reattachment point

• Bidirectional Flow Measurement

Capability

PC

10

4” METER 0.3 BETA RATIOCEESI AIR CALIBRATION

11

0.712

0.714

0.716

0.718

0.720

0.722

0.724

0.726

0.728

0.730

200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000

6" TorusWedge 0.5356 BETA - CEESI-water

Cd Ave +0.5% 0.5% +1.0% -1.0%

Dis

char

geC

oe

ffci

en

t, C

d

Reynolds Number, Re

6” METER 0.54 BETA RATIOCEESI WATER CALIBRATION

CENTER TAP

12

0.705

0.710

0.715

0.720

0.725

0.730

- 500,000 1,000,000 1,500,000 2,000,000 2,500,000 3,000,000 3,500,000

Discharge Coefficient Vs. Reynolds Number

+1

6” Water & 4” Air Calibration @ CEESI Calibration FacilityInfluence on discharge coefficient due to line size and bore size is minimized by referring to the Center

Tap pressure

13

0.680

0.705

0.730

0.755

0.780

0.805

0.830

0.855

0.880

0.905

0.930

0.955

0.980

750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000

Dis

cha

rge C

oeff

icie

nt, C

d

Flow Rate, gpm

10" meter 0.7 Beta Water CalibrationWith and without 1/2" Probe 1/2-D Downstream

MTR2+Pr

MTR2-Pr

Sample Probe and/or Density Probe installed 0.5D downstream

of the TorusWedge will obtain better representative samples and

will allow more precise density readings of multiphase flows.

14

MODIFIED DESIGN

Aligning

Pins

Aligning Pin is shown on

the upstream side of the

TorusWedge for visual aid.

Aligning Pins are located

downstream face of the

TorusWedge

High Pressure Tap

Low Pressure Tap

15

INSTALLATION OF TORUSWEDGE

16

SELF ALIGNING CENTER PORT

Differential Pressure

Taps can be offered as

parallel ports, to allow

direct mounting of the

Differential Pressure

Transmitter.

17

DUAL CHAMBER CENTER TAP CONFIGURATION

18

OPTIONAL DIAGNOSTIC CAPABILITY

• ADD SECOND DP TO STANDARD FLANGE TAPS.

• COMPARE THE HISTORICAL PRESSURE RATIO OF DP MEASURED BETWEEN UPSTREAM PRESSURE TAP AND

CENTER TAP TO DP MEASURED BETWEEN STANDARD FLANGE TAPS.

• AT A GIVEN FLOW RATE, THAT PRESSURE RATIO IS CONSTANT AND BE MORE THAN 1.

• DEVIATION OF PRESSURE RATIO FROM THE HISTORICAL VALUE BY MORE THAN 5% IS INDICATION OF

POSSIBLE LEAKAGE AROUND THE PLATE SEALS, DAMAGE TO , OR DEPOSIT ON THE TORUSWEDGE.

19

OTHER FLOW RATE MEASUREMENT CAPABILITY

REMOTE SEAL DP TRANSMITTER FOR FLOWS WITH SUSPENDED SOLIDS OF LIQUID DROPLETS

MODIFIED DESIGN MONITORING CENTER TAP PRESSURE BY REMOTE SEAL DP TRANSMITTER IS AVAILABLE. 20

QUESTIONS

21