Hand Calculation Method for Orifice Design

Hand_Calculation_Method_for_Orifice_Design

Chevron Corporation B-1 July 1999

Abstract

This appendix explains how to perform the calculations for orifice plate design by hand For manual look-up of the orifice coefficient, S (given beta) or the diameter ratio, beta (given S), the following eight figures are provided:

Orifice calculation sheets have been prepared for guidance through the orifice calcu-lation steps Calcucalcu-lation sheets filled in with appropriate examples are attached The four orifice calculation sheets are as follows:

• LIQUID, square-edge orifice, Form ICM-EF-59B (Figure B-9)

• LIQUID, quadrant-edge orifice, Form ICM-EF-59C (Figure B-10)

• GAS, square-edge orifice, Form ICM-EF-59D (Figure B-11)

• VAPOR/STEAM, square-edge orifice, Form ICM-EF-59E (Figure B-12) Note that in these calculation sheets, the term "sharp edge" is used instead of

"square-edge."

Results of the hand calculations agree closely with the computer program ORIFICE The two types of calculations that can be performed are orifice sizing and orifice re-ranging, except for quadrant-edge

Figure B-1 Flange Taps - 6 Inch Pipe Size (6.056 in.); S vs Beta for

Different RD Values (Based on Data from ISO 5167) Figure B-2 Flange Taps; Pipe Size Corrections for S Values (Based on

Data from ISO 5167) Figure B-3 Radius Taps; S vs Beta for Different RD Values (Based on

Data from ISO 5167) Figure B-4 Corner Taps; S vs Beta for Different RD Values (Based on

Data from ISO 5167) Figure B-5 Pipe Taps; S vs Beta for Different RD Values (Based on

Data from ISO 5167) Figure B-6 ASME Small Bore with Flange Taps; S vs Beta for

Different RD Values—1 in to 1-1/2 in Pipe Size (Based

on Data from "Fluid Meters: Their Theory and Applica-tion", 6th ed., 1971 Courtesy of ASME)

Figure B-7 ASME Small Bore with Corner Taps (.546 in.); S vs Beta

for Different RD Values—1/2 in Schedule 80 Pipe Size (Based on Data from "Fluid Meters: Their Theory and Application", 6th ed., 1971 Courtesy of ASME) Figure B-8 Quadrant — Edge Data; S and Thickness Ratio vs Beta

July 1999 B-2 Chevron Corporation

B1.0 Calculation Procedure

1 Fill in the STREAM PROPERTY input blocks

2 Fill in the FLOW RATE input blocks

3 Fill in the ORIFICE DATA input blocks

TEMPERAURE degrees Fahrenheit for liquid and vapor/steam

degrees Rankine = °F + 460 for gas

1.00)

for steam, use steam tables

= M.W gas/M.W dry air

= Zb× Real sp gr

GAS AND VAPOR ABSOLUTE VISCOSITY

use centipoise

UNITS: For liquid use BPD, BPH, GPM, or GPH For vapor use

lbs/hour; for gas use SCFH

FULL SCALE: Flow that creates a dp across the orifice taps equal to the

maximum value of the dp transmitter range

NORMAL: For square-edge and ASME small-bore this should be

the mid-range dp value, which equals 707 × (full-scale flow rate)

1/3 FS: For quadrant-edge, equal to 333 × (full-scale flow rate)

square-edge Flange or corner only for ASME

small-bore Flange for quadrant-edge

calculation

Chevron Corporation B-3 July 1999

4 Fill in the CORRECTIONS FACTORS

5 Calculate Pipe Reynold’s Number

Space is provided for values in equations

See examples on sheets provided

6 Calculate orifice size or dp range for square-edge or ASME small-bore orifice Given h, Find d

Fill in equations and solve for S

Look up beta ratio in table

Interpolation is necessary

Use Table in Figure B-2 to correct for pipe size other than 6-inches (2-12 inches)

Use Reynold’s number column that is closest to value calculated in step 5 Given d, Find h

Calculate beta ratio

Look up S in table

Interpolation is necessary

Use Reynold’s number that is closest to value calculated in Step 5 See examples on sheets provided

7 Calculation for quadrant-edge orifice size

Use 3 decimal places

calcula-tion Standard value = 100 inches of

water

Fa Correction for thermal expansion of orifice meter at

flowing temperature found in ASME MFC-3M Tables or API MPMS Chapter 14.3/AGA-3

Y Gas expansion factor for mid-scale flow

Y1 = correction based on upstream pressure

Y2 = correction based on downstream pressure Look up in table or chart - use mid-range differential pressure (dp)

Fpv Supercompressibility correction factor

Rarely used in refinery calculations (usually set = 1.0) Look up in table or chart when used

Zb Compressibility factor at 60°F, 1 Atm

Rarely used in refinery calculations (usually set = 1.0) Look up in table or chart when used

July 1999 B-4 Chevron Corporation

Select a plate thickness, look up values from Figure B-8, and calculate the differential pressure h

If h is too large, make plate thicker; if too small, make plate thinner, and repeat calculation h should equal about 100 inches of water

The permissible range of Reynold’s numbers (at 1/3 full-scale flow) for a quad-rant-edge orifice is a function of the beta ratio:

See example on calculation sheet provided

Chevron Corporation B-5 July 1999

Fig B-1 Flange Taps - 6 Inch Pipe Size (6.056 in.); S vs Beta for Different RD Values (Based on Data from ISO 5167)

July 1999 B-6 Chevron Corporation

Fig B-2 Flange Taps; Pipe Size Corrections for S Values (Based on Data from ISO 5167)

Chevron Corporation B-7 July 1999

Fig B-3 Radius Taps; S vs Beta for Different RD Values (Based on Data from ISO 5167)

July 1999 B-8 Chevron Corporation

Fig B-4 Corner Taps; S vs Beta for Different RD Values (Based on Data from ISO 5167)

Chevron Corporation B-9 July 1999

Fig B-5 Pipe Taps; S vs Beta for Different RD Values (Based on Data from ISO 5167)

July 1999 B-10 Chevron Corporation

Fig B-6 ASME Small Bore with Flange Taps; S vs Beta for Different RD Values—1 in to 1-1/2 in Pipe Size (Based

on Data from "Fluid Meters: Their Theory and Application", 6th ed., 1971 Courtesy of ASME)

Chevron Corporation B-11 July 1999

Fig B-7 ASME Small Bore with Corner Taps (.546 in.); S vs Beta for Different RD Values—1/2 in Schedule 80 Pipe

Size (Based on Data from "Fluid Meters: Their Theory and Application", 6th ed., 1971 Courtesy of ASME)

July 1999 B-12 Chevron Corporation

Fig B-8 Quadrant — Edge Data; S and Thickness Ratio vs Beta

Chevron Corporation B-13 July 1999

Fig B-9 Orifice Calculation Sheet—Liquid, Square-edge Orifice

July 1999 B-14 Chevron Corporation

Fig B-10 Orifice Calculation Sheet—Liquid, Quadrant-edge Orifice

Chevron Corporation B-15 July 1999

Fig B-11 Orifice Calculation Sheet—Gas, Square-Edge Orifice

July 1999 B-16 Chevron Corporation

Fig B-12 Orifice Calculation Sheet—Vapor/Steam, Square-Edge Orifice