Smart DP Flow MeteringA summary of Established Technology and Latest Innovation

Gary Fish

DP Flow Measurement

• Established Technology

• Large range of line sizes, materials, connection interfaces, etc

• Customised solutions

• New innovations and improvements

Square Edged Orifice Plate

• ISO 5167-2

• β range 0.1 to 0.75

• Min ReD 5 x 103

• Max ReD ∞

• Permanent Pressure loss: β dependent between 42% and 98% of ΔP

• Uncalibrated Uncertainty Cd 0.5% (for β between 0.2 & 0.6)

• General Flow metering applications- gas allocation and fiscal standard

Conical Entrance Orifice Plate

• ISO TR 15377

• β range 0.1 to 0.316

• Min ReD 80

• Max ReD 6.3 x 104 (for β 0.316)

• Uncalibrated Uncertainty Cd 2%

• Application – viscous fluids

Quarter-Circle Orifice Plate

• ISO TR 15377

• β range 0.245 to 0.6

• Min ReD 245 (for β 0.245)

• Max ReD 6 x 104 (for β 0.6)

• Uncalibrated Uncertainty Cd 2% to 2.5%

• Application – viscous fluids

Eccentric Orifice Plate

• ISO TR 15377

• β range 0.46 to 0.84

• Min ReD 4.2 x 103

• Max ReD 8.4 x 105

• Uncalibrated Uncertainty Cd 1% to 2% (can be calibrated to improve)

• Application – entrained gas in liquid service, entrained liquid in gas service, sediments, etc

ISA 1932 Nozzle

• ISO 5167-3

• β range 0.3 to 0.8

• Min ReD 2 x 104 (for β 0.44 or greater)

• Max ReD 1 x 107

• Uncalibrated Uncertainty Cd 0.8% to 1.2% (β dependent)

• Permanent Pressure loss: between 25% and 80% of ΔP (typical)

• high velocity, steam flow.

Long Radius Nozzle

• ISO 5167-3

• β range 0.2 to 0.8

• Min ReD 1 x 104

• Max ReD 1 x 107

• Uncalibrated Uncertainty Cd 2%

• Permanent Pressure loss: between 24% and 92% of ΔP (typical)

• high velocity, steam flow.

• ISO 5167-3

• β range 0.316 to 0.775

• Min ReD 1.5 x 105

• Max ReD 2 x 106

• Uncalibrated Uncertainty Cd 1.2% to 1.7%

• Permanent Pressure loss: between 5% and 20% of ΔP (typical)

• high velocity, steam flow. Low permanent pressure loss

Venturi Nozzle

• ISO 5167-4

• β range 0.4 to 0.75

• Min ReD 2 x 105

• Max ReD 1x 106

• Uncalibrated Uncertainty Cd 1% (for ReD limits shown)

• ReD limits increased according to Annex B – with increased uncertainty

• Permanent Pressure loss: between 5% and 20% of ΔP

• General Flow metering applications- gas allocation, high velocity, low maintenance and intervention. Low permanent pressure loss.

Machined Venturi

• ISO 5167-4

• β range 0.4 to 0.7

• Min ReD 2 x 105

• Max ReD 2 x 106

• Uncalibrated Uncertainty Cd 1.5% (for ReD limits shown)

• ReD limits increased according to Annex B – with increased uncertainty

• Permanent Pressure loss: between 5% and 20% of ΔP

• General Flow metering applications- gas allocation, high velocity, low maintenance and intervention. Low permanent pressure loss.

Fabricated Venturi

‘As Cast’ Venturi

• ISO 5167-4

• β range 0.3 to 0.75

• Min ReD 2 x 105

• Max ReD 2 x 106

• Uncalibrated Uncertainty Cd 0.7% (for ReD limits shown)

• ReD limits increased according to Annex B – with increased uncertainty

• Permanent Pressure loss: between 5% and 20% of ΔP

• General Flow metering applications- gas allocation, high velocity, low maintenance and intervention. Low permanent pressure loss.

Cone Meter

• ISO 5167-5

• β range 0.45 to 0.75

• Min ReD 8 x 104

• Max ReD 1.2 x 107

• Uncalibrated Uncertainty Cd 5%

• Permanent Pressure loss: between 48% and 72% of ΔP (typical)

• General Metering applications, allocation, shorter overall installation than Venturi meter

• ISO 5167-6 (not yet published)

• β range 0.377 to 0.791

• Min ReD 1 x 104 note 1

• Max ReD 9 x 106

• Uncalibrated Uncertainty Cd 4%

• Permanent Pressure loss: between 47% and 79% of ΔP (typical)

• Suspended solids, viscous fluids note 1

Note 1 : Standard will be based upon available data – Wedge Meters have been known to operate at

Re =500, but will require calibration- resulting in much lower uncertainty also.

Wedge Meter

Dall Tube

• No International Standard

• β range 0.3 to 0.8

• Min ReD 5 x 104

• Max ReD∞

• Uncalibrated Uncertainty Cd 3%

• Permanent Pressure loss: between 2.5% and 8% of ΔP (typical)

• Clean process fluids, very low pressure loss requirements

Comparison table for DP Devices

Device Standard

Limits of use

Uncertainty Permanent PressureLine Size (mm) β ReD

Min Max Min Max Min Max

Cd

(UNCALIBRATED)

loss (% of ΔP)

SQUARE EDGED ORIFICE PLATE ISO 5167-2 50 1000 0.1 0.75 5 x 103 ∞ 0.5% NOTE 1 42% to 98%

CONICAL ENTRANCE ORIFICE

PLATEISO TR 15377 25 500 0.1 0.316 80 6.3 x 10

4

2% 86% to 98%

QUARTER-CIRCLE ORIFICE PLATE ISO TR 15377 25 500 0.245 0.6 245 6 x 104

2% to 2.5% 53% to 91%

ECCENTRIC ORIFICE PLATE ISO TR 15377 100 1000 0.46 0.84 4.2 x 103

8.4 x 105

1% to 2% 36% to 77%

ISA 1932 NOZZLE IS0 5167-3 50 500 0.3 0.8 2 x 104

1 x 107

0.8% to 1.2% 25% to 83%

LONG RADIUS NOZZLE ISO 5167-3 50 630 0.2 0.8 1 x 104

1 x 107

2% 24% to 92%

VENTURI NOZZLE ISO 5167-3 65 500 0.316 0.775 1.5 x 105

2 x 106

1.2% to 1.7% 5% to 20%

MACHINED VENTURI ISO 5167-4 50 250 0.4 0.75 2 x 105

1 x 106

1% 5% to 20%

FABRICATED VENTURI ISO 5167-4 200 1200 0.4 0.7 2 x 105

2 x 106

1.50% 5% to 20%

AS CAST' VENTURI ISO 5167-4 100 800 0.3 0.75 2 x 105

2 x 106

0.70% 5% to 20%

CONE METER ISO 5167-5 50 500 0.45 0.75 8 x 104

1.2 x 107

5% 48% to 72%

WEDGE METER ISO 5167-6 NOTE 2 50 600 0.377 0.791 1 x 104

9 x 106

4% 47% to 79%

DALL TUBE NO STANDARD 150 3000 0.3 0.8 5 x 104 ∞ 3% 2.5% to 8%

Notes

1 For β between 0.2 and 0.6

2 Not yet published

All Cd Uncertainties can be reduced with flow calibration over entire operating range

Upstream Straight Length requirements – 1off 90o bend

Upsteam lengths may be reduced with Cd

uncertainties increasing

Generic DP Device βlim

L βlim

L

ORIFICE 0.1 6D 0.75 44D

NOZZLE 0.2 10D 0.8 46D

VENTURI 0.3 8D 0.75 16D

CONE METER 0.45 3D 0.75 6D

WEDGE METER 0.377 7D 0.791 7D

DALL TUBE 0.3 3D 0.8 13D

β L

0.5 22D

0.5 14D

0.5 9D

0.5 3D

0.5 7D

0.5 4D

Upstream Straight Length requirements – 1off 90o bend

Generic DP Device Uncalibrated C

dUncertainty β L

ORIFICE (Square edged) 0.50% 0.5 22D

NOZZLE (ISA 1932) 0.80% 0.5 14D

VENTURI (Machined) 1.00% 0.5 9D

CONE METER 5% 0.5 3D

WEDGE METER 4% 0.5 7D

DALL TUBE 3% 0.5 4D

Upstream Straight Length requirements – 1off 90o bend

Generic DP Device Uncalibrated C

dUncertainty β L

ORIFICE (Square edged) 1.0% 0.5 9D

NOZZLE (ISA 1932) 1.3% 0.5 7D

VENTURI (Machined) 1.5% 0.5 3D

CONE METER 5%* 0.5 3D*

WEDGE METER 4%* 0.5 7D*

DALL TUBE 3.5% 0.5 3D

*No data published in ISO regarding shorterlength uncertainty

Differential Pressure Transmitter Technology

• Largest contribution to enhanced DP meter uncertainty in recent years

• Example 1 :

• Yokogawa EJX130A, ref accuracy :+/-0.04% of span (3σ)

• Example 2:

• Rosemount 3051CD (ranges 2-4), ref accuracy :+/-0.04% of span (3σ)

• Full ‘transparent’ uncertainty analysis can be carried out for DP meters

DP Meter Uncertainty Analysis

Myth : The Differential Pressure is limited to 500mbar for an orifice plate

Limits for Orifice Plate DP

• End User/Operator specifications stating for instance DP limited to 500mbar

• Why ?

• There is no need – providing :

• Permanent Pressure loss is acceptable

• Orifice Plate Elastic or Plastic Deformation is considered

• DP is within expansibility limits

Myth : The flow turndown for DP devices is only 3:1

For mass flow uncertainty below 0.8% we need the DP uncertainty <1%.

Turndown/rangeability is the ratio of the largest to smallest flow rate that can be metered to the meter’s stated flow rate prediction uncertainty at a stated confidence level.

Claim / belief: “You only get 3:1 with an orifice”

Turndown / Rangeability

…With 1 DP Transmitter[200 , 2000] = 10:1 on DP~3.2:1 flow range

Example : 30m/s, 25kg/m3, 12” pipe ~260,000 Sm3/hBeta = 0.6, DP = ~2000mbar

DP H: 0-2000mbarDP M: 0-300mbarDP L: 0-50mbar

Turndown / RangeabilityExample, stacked transmitters

30m/s, 25kg/m3, 12” pipe 260,000Sm3/hBeta = 0.6, DP = ~2000mbar

DP H: 0-2000mbarDP M: 0-300mbarDP L: 0-50mbar

min: 30% of max flow -> 3.3:1 min: 11% of max flow -> 9.1:1min: 4.5% of max flow -> 22:1

Turndown / RangeabilityExample, stacked transmitters

Turndown / Rangeability

+/-0.8%

0 m/s

100% of flow rate(30 m/s)

+/-0.8%

0 m/s

100% of flow rate(30 m/s)

4.5% of flow rate(1.35 m/s)

100%/3.3% = 30i.e. ‘turndown = 30:1’

100%/4.5% = 22i.e. ‘turndown = 22:1’

e.g. USM

e.g. Orifice

Claim / belief: “You only get 3:1 with an orifice”

?3.3% of flow rate(1 m/s)

Turndown / Rangeability

+/-0.8%

0 m/s

100% of flow rate(30 m/s)

3.3% of flow rate(1 m/s)

+/-0.8%

0 m/s

100% of flow rate(30 m/s)

4.5% of flow rate(1.35 m/s)

100%/3.3% = 30i.e. ‘turndown = 30:1’

100%/4.5% = 22i.e. ‘turndown = 22:1’

e.g. USM

e.g. Orifice

Difference? 30:1 from 22:1 is an increase in flow range of (1.2/95.5) 1.26%

Claim / belief: “You only get 3:1 with an orifice”

Similar Turndown to USM in practice

Turndown / Rangeability• Later life example. Reduced Pressure and Flow

• E.g. Max flow: 3 m/s, (i.e. 15,500 Sm3/h)

• USM fixed at ≈ 30 m/s > U (m/s) > 1 m/s, (10% of USM full scale flow).

• 0.6β orifice meter produces 12mbar, (8% of orifice meter full scale flow).

• Easy improvement :change the beta

• 0.2β orifice meter produces 1150mbar

1150 ≥ DP mbar ≥ 5 gives 3 ≥ U (m/s) ≥ 0.2 150:1

Myth : The permanent pressure loss is always too high with DP devices

Permanent Pressure Loss

Higher PPL may sometimes be significant, but meter PPL should be seen in context.

Permanent Pressure Loss

12”, sch 40 gas (ordinary) pipe

• 40 Bar, 150C, 31.8 kg/m3, 15 m/s, 140 MMSCFD

Components in pipe:

• Globe valve (3/4 open) for control

• Open butterfly valve (emergency shut off)

• 4 elbows, T-junction, sample probe, 2 thermowells

• A flow conditioner & flow meter

What is the PPL across the system? What relative impact on overall PPL does the meter system have?

Permanent Pressure Loss

2*

2

avlossloss

VKP

Permanent Pressure Loss

2*

2

avlossloss

VKP

Permanent Pressure Loss

2*

2

avlossloss

VKP

• The PPL is dependent on the length of pipe.

• Most pipe systems are long, that’s why it’s convention to call pipe loss the ‘major’ loss!

Permanent Pressure Loss

• Often pipe losses dwarf any meter PPL.

(Gas transmission compressor stations are > 40 miles apart, platform to shore is miles long etc.)

• Other calibrated DP devices can offer the measurement accuracy requirements and low pressure losses – eg Venturi, Dall tube, etc

Myth : DP devices don’t have diagnostic capabilities

Validation / Diagnostics• Combination of advancement in transmitter technology and specialised

innovative developments the following diagnostics are available for DP meters

• Incorrect Metrology Data• Excessive Flow Disturbance• Contamination Build Up• Saturated DP Tx• Drifting DP Tx• Incorrectly Spanned DP Tx• DP Below Tx Range• Two Phase Flow• Electrical Loop Integrity• Plugged Lines• Process Leakage• Improved Overall Safety Integrity• Etc,Etc..

Validation / Diagnostics - Orifice

Excellent diagnostics – No calibration required.

• 3 x Flow Rate Comparisons• 3 x DP Ratio Comparisons• 1 x DP Integrity Check• DP Synchronisation / turbulence checks

Reasonably objective

Thankyou ! : Questions ?