FLOW - CASE STUDIES and SELECTION

Shiva & Bhaskar
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1
A World of Solutions
General criteria for flow element selection
DP Range selection for DP Flow transmitters
Unit of Measurements for flow
Usage of Diaphragm seal in case of Toxic/Corrosive services
Flow meter for smaller Pipe size
Straight run requirements
Flow meter in Jacketed line for Molten Sulphur
Retractable assemblies for flowmeters
Pressure loss for piping elements
Overheating of electronics
Flow meters in Flare service lines
2
Reynolds Number
 The Reynolds number is the ratio of inertial forces (velocity and density that keep the fluid in
motion) to viscous forces (frictional forces that slow the fluid down).
 Laminar Flow occurs at low Reynolds numbers, where viscous forces are dominant, and is
characterized by smooth, constant fluid motion. Represents max velocity at center and Minimum
towards pipe wall
 Turbulent Flow occurs at high Reynolds numbers and is dominated by inertial forces, producing
random eddies, vortices and other flow fluctuations. Represents uniform velocity Distribution.
Ideal for Flow measurements.
Dvr
Re = m C
D = DIAMETER (FT)
v = VELOCITY (FT/SEC)
r = DENSITY (LB/FT3)
m = VISCOSITY (cp)
C = CONSTANT (6.72X10-4 LB/FT SEC cp)
0 2000 4000
LAMINAR TRANSITION TURBULENT
3
Flow measurement - terms
 Turn down ratio = Process Max flow rate (at specified accuracy/Repeatability)
Process Min flow rate
 Beta Ratio = Differential pressure flow device bore (d)

Internal diameter of pipe (D)
 COMPRESSIBLE FLUID
Fluids (Such As Gasses) where the volume changes with respect to changes in the
pressure & temperature. These fluids experience large changes in density due to
changes in pressure & temperature.
 NON-COMPRESSIBLE FLUID
Fluids (Generally Liquids) which resist changes in volume as the pressure changes.
These fluids experience little change in density due to pressure but changes wrt
temperature.
4
Important points to be considered: Process conditions &
properties
Normally we have to adhere to project specification
The crucial data for designing flow element for various media such as
 Liquid : (Max/Normal/Min cases of Flow/Pressure/Temp/Density, Vapor pressure,

Viscosity, Max allowable pressure drop)
 Gas : (Max/Normal/Min cases of Flow/Pressure/Temp/Density, Viscosity, Max

allowable pressure drop, Compressibility, Cp/Cv & MW)
 Corrosive, Toxic, Solid particles, Buildup tendency
 Unidirectional or Bidirectional.
 Accuracy of measurement of flow for all conditions i.e. min/normal/max flow
5
Units of measurement
 Before sizing we should finalize the unit of measurement because

 Flow turndowns may get changed
 Calibration ranges get effected
 Greater impact on Compressible fluids (gases/Vapours)

 Density
 The engineering unit for a flow given by process means the engineering unit that the operator will
see at his screen in the control room when operating the plant. This does not necessarily mean that
the flow measurement actually measures flow in this engineering unit.
Example: an orifice flow measurement measures pressure difference and not kg/h
 Typically flow compensation is applied in a range of < +/- 5 to 20% of the fixed density. However
process to decide and confirm where they require compensations and what variation of accuracy of
measurement.
 Lesson :
a) Check the flow units and take turndown ratios for volumetric flows (except for mass flow
meters)
b) and check for the requirement of density compensations
6
Commonly used flow devices
 Inferential type – like DP, VAM. These meters infer the flow by some other physical
property such as differential pressure and then experimentally correlate it to flow.
 Orifice Plate - Concentric, Eccentric, Segmental, Quadrant Edge, Integral

 Venturi Tube
 Flow Nozzles
 Pitot Tube, Averaging Pitot Tube (Annubar)
 Variable Area (Rotameter)
 Wedge Meter
 V-Cone
Velocity Type - These meters determine total flow by multiplying the velocity by the
area through which the fluid flows.
 Magnetic
 Ultrasonic - Transit Time, Doppler
 Turbine
 Vortex
Mass Type - measures the mass flow rate directly.

 Coriolis
 Thermal
Other Types
 Positive Displacement (volumetric directly)
7
Flowmeter Selection criteria based on turn down ratio
Typical Turndown ratios
3:1 to 5:1 Orifice Plate, Venturi & Flow nozzle
5:1 to 10:1 Pitot tube
10:1 VAM
10:1 to 20:1 Vortex
20:1 to 40:1 Magnetic
10:1 to 40:1 Doppler ( UFM)
20:1 to 100:1 Transit – time ( UFM )
40:1 TO 100:1 Coriolis
8
FLOW SELECTION GUIDE - CMS
9
10
Points to be noted:
 Always check the reference vendor catalogues for min DP span to be maintained for the
least/minimum flow to be measured accurately and also model code selections. Then accordingly
select the Flowmeter DP range.
 Always keep a note that the calculated pressure loss@ max flow is always be less than the
Maximum allowable pressure loss given by process.
 Differential pressure : Pressure loss : Bore : Beta

Increase Increase Decrease Decrease
Decrease Decrease Increase Increase
A higher Beta ratio means a larger orifice size. A larger orifice plate bore size means greater flow
capacity and a lower permanent pressure loss.
 Minimum Bore & Beta requirement (Orifice)

[>=12.5mm & (0.1 to 0.75) for concentric Orifice plate as per ISO 5167-2]. Re>5000.
[>=15mm & (0.245 to 0.6) for Quadrant Orifice plate as per ISO TR 15377]. Re < 105b.
[>6mm & (0.1 to 0.3) for Conical Orifice plate as per ISO TR 15377]. 80<Re<2 x 105b.
11
DP Flowmeter for turndowns >5:1
There may be cases where orifice plates are shown in P&IDs for turndown > 5:1.
and sizing as Orifice plate may be acceptable.
As per general industrial practice we take two transmitters to meet the higher flow
turndown (i.e. more than 5:1 turndown) in case of DP flow elements(mostly orifice
plate)
It will effect
 No. of Instruments
 Hookup / MTO
 IO count
 Cable lengths
But sometimes single transmitter can also accommodate these turndowns, by

increasing the DP range provided max allowable pressure drop given by process is
met.
12
 For the tag 5100FE-3005: Flow rates are 1197/12724/19087 Kg/hr (TD 16:1). It is in a control
loop with Max allowable pressure loss is 3KPa.
COST: Cost of Installation

and operation? Initial cost of primary and secondary device and
auxiliary equipment?
Installation cost , Including ,Labor and piping?
Initial cost
Energy cost and pumping cost/Pressure loss?
Installation
Reliability Vs Maintenance? Cost
Maintenance
cost Availability of parts and service facilities
Possible use in Future application
13
Cost groups
Group1 Group 2 Group 3

(Low) (Medium) (High)
• Orifice • Vortex • Coriolis
• Wedge • Turbine (D<6 • Magnetic
• Positive in) • Ultrasonic
displacement • Flow nozzle (Time of
(D<2 in (50 • Ultrasonic Flight)
mm) (Doppler) • Positive
displacement
(D>4 in)
14
1) Intially Flow rates for the tags 5100FE-3005 : 1197/12724/19087 Kg/hr (TD 16:1). It is in a control
loop. Considering the 8KPa allowable pressure loss (upon internal discussions with process, from 3KPa).
i)When performed sizing (with Flow Range=0 to 19500 Kg/hr & DP range=0-10 KPa), Min flow that could
be measured accurately is nearly 4500Kg/hr (instead of 1197 Kg/hr).
ii)If a second (additional) transmitter is employed on the Flow element, even then the min flow that can
be measured accurately is at least 2300 Kg/hr (instead of 1197 Kg/hr).
 We requested process to check and confirm the following two points with the LICENSOR for the tag
5100FE-3005 (DP orifice):
a) The requirement of measurement of minimum flow:

i ) Whether Min flow of 1197 Kg/hr is really required to be measured?
ii) If not, whether 4500 Kg/hr least measurable flow is acceptable or not?
[Please be noted that the Low alarm (at 12700 Kg/hr) is much higher than the minimum flow value (1197 or
4500 Kg/hr) and is accurately measured with same single transmitter. If 4500 Kg/hr (low flow value) is
acceptable then second transmitter is not required].
b) If flow has to be less than 4500 Kg/hr, then Second transmitter has to be employed on the same
element. But even in this scenario, the min flow measurable & acceptable is 2300 Kg/hr (instead of 1197
Kg/hr).
15
Earlier
19500
Earlier
19087
16
We again discussed with Licensor and process and licensor agreed to revised the
max flow rate for 5100FE-3005 from (19087 to 14000 kg/hr). (since they want the min.
flow to remain same i.e. 1197 kg/hr and to measure accurately). Also agreed to
increase the pressure drop to 8 kpa at max flow (from 3 Kpa).
So net turndown now became (11.69:1 from 16:1) with flowrates 1197/12724/14000
Kg/hr and to measure all the flow rates accurately Two transmitters 5100FT-3005A
and 5100FT-3005B shall be considered on the same flow element 5100FE-3005.
17
First Transmitter (5100FT-3005A):

(0 to 0.57 KPa) and ( 0-3400 Kg/hr)
Second Transmitter (5100FT-3005B):

(0.5 to 10 KPa) and ( 3200-14200 Kg/hr)
Please make sure there is an overlap between

the high and low DP flow transmitter 5100FT-
3005A/B.
So for example high transmitter 3400-14200
kg/h and low transmitter 0-3200 kg/h OR
anything else as long as there is an overlap in
range it’s ok.
This is to prevent a ‘’bump’’ if we switch from
high to low or from low to high.
18
DP Flow meters on Toxic/Corrosive services
Discussion was to use or not to use diaphragm seal for orifice DP flow
transmitters on corrosive/toxic services. Since P(d)G, P(d)T on the same
services have been shown with diaphragm seal.
19
 As per CBIN, DP flow transmitter with diaphragm seal is not preferred

solution considering its effect on flow measurement accuracy, difficult
installation of diaphragm seal on orifice flange tapping and/or also changing
into radius tapping.
 An alternative is to change measuring principle to either vortex or UFM.
 How corrosive the service is? Is it NACE MR103? Can we still keep normal
DP by selecting proper NACE material for DP TX and Hookup?
 Is medium clogging? Can tracing of impulse lines tubes help any probable
blockage?
 How toxic the service is? Is leakage the only issue here?
 It is decided that diaphragm seal for FT DP can be avoided if proper tracing

and insulation in combination with short impulse lines are applied
Lesson: Check the criteria for seal consideration w.r.t. design basis
/specifications. If not give a proposal and check with LO / client.
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Tags affected:
1) 6100FE-3020: 10” line, Acid Gas : 780/3893/4282 kg/h (T/D 5.489)
Allowed Press. drop 5kPa
2) 6200FE-3022: 12” line, Acid Gas : 2399/7496/8246 kg/h (T/D 3.44)
3) 3000FE-3029: 12” line, Fuel Gas : 3929/13002/14408 kg/h (T/D 3.67)
VORTEX – ORIFICE – VORTEX
FINALLY SELECTED AS VORTEX AS PER LO DECISION
21
Coriolis flow meter recommendation for special service
 The below mentioned tags are of type Integral Orifice assembly (on 12 mm tubing,
UM01 pipe class) as shown in P&IDs but vendor is not able to provide the quote
for Integral Orifice Assemblies. Preliminary calculations indicate that Coriolis is the
only suitable option (other than IOA). We have checked for Coriolis type flow meter
for these tags, with the vendor and vendor is able to provide the same.
 The above selection was confirmed by Chemical Injection Package vendor during
its HAZOP, Because of pump’s pulsating action, a Coriolis flow meter type was
recommended by vendor.
Instrument Tag Flow transmitter as per Latest

S.No. Final Meter to be selected Remarks
Transmitter P&IDs
1 3000FT -3049 Integral Orifice assembly-IOA Coriolis Type flow meter

Supplier couldn’t
provide Integrated
Orifice assembly for
12mm tubing
Lesson: Check for the suitability and availability of the flow meter
for very low line sizes
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 Good Velocity profile; Uniformity in flow
 Straight run is only one method that can be used to effectively eliminate the effects of velocity
profile distortion on the flowmeter such that it can measure accurately.
 Flow conditioners can also be used to develop a good velocity profile when sufficient space for
straight run is not available.
 Typical straight run requirements:

a) 22D : 4D for DP flowmeters (Flow orifice), 20D - 10D for UFM/Magnetic/Coriolis, 10D-5D for
vortex flowmeters
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 Always check in the P&ID about the arrangement and location of the flowmeter (whether
upstream or down stream of the control valve). Avoid considering the flowmeters downstream of
the control valve which requires high straight run length to maintain the flow uniformity. Typically
for such arrangements 50D (at least) is the upstream required.
 Always ensure in the model or check with piping that straight runs that are to be maintained is
available in the actual line in the model or not.
 Instrument interface with Piping document shall always be referred in concurrence.
Lesson: CHECK FOR THE AVAILABILITY OF THE STRAIGHT RUNS
24
Coriolis flow meter in liquid Sulphur service with steam jacketing
The Coriolis flowmeter consists of a vibrating tube with

pick-ups. The complete assembly is housed in a
secondary containment. If LP steam tracing is applied for
this flowmeter the secondary containment will be heated,
but the vibrating tube will not directly be heated, but
indirectly.
25
If an ultrasonic flowmeter with LP steam tracing will be used for this

application the liquid Sulphur will directly be heated by the steam, as the
ultrasonic flowmeter does not have a secondary containment. This will give a
much better result for liquid Sulphur services.
Lesson: Always check selection of flow meter type wrt temperature

suitability of the media before finalizing.
Always ensure the steam jacket heating is direct (on the instrument) i.e.
inline instrument.
26
Retractable assemblies for flow meters
 Retractable assemblies are generally used to take the flowmeter out for maintenance online
without disturbing the actual process.
 Retractable assemblies are available for ULTRASONIC FLOWMETERS / PITOT TUBES /

VORTEX
 Retractable assemblies are not advisable for services with following nature
 High pressure applications
 Toxic services
 Flare services (generally avoided as they are hazardous).
 Cost, space availability, frequently the flowmeter is required to take out for maintence.
Lesson : Check for the need and requirement of Retractable assemblies before placing
the IFQ datasheets.
27
Pressure loss for the piping elements
 We generally perform sizing calculation for the inline flowmeters to check whether there can be any
reduction in its size or not.
 Max allowable pressure loss provided by process is actually the loss (max) to be attributed only
across the flowmeter.
 We should always check with process to confirm whether the loss that is going to be foreseen for
the extra piping elements (reducer+ straight run + expander) are considered in the line or not. This
would ensure Instrumentation to check and consider the correct flowmeter size.
 There would be low pressure systems like NG (in HCU’s case) where process could not provide
any extra pressure drop for the piping components and advised to keep the pressure loss@
flowmeter of reduced size, as low as possible so that the losses due to piping components are
adopted.
 ex;- 10" line size, 10KPa allowable pressure loss, For VORTEX / UFM / MAGNETIC / CORIOLIS if
the meter size resulted is (say) 6" and calculated loss for PROCESS MAX FLOW for 6" meter is 9
Kpa. This implies that the loss calculated is across the 6" meter itself. Process has to check
whether the loss attributed due to the future employment of 10 * 6 reducer / expander (in the line)
can be adopted or not. This can be checked by process by running the PROCESS HYDRAULICS
with 10*6 reducer/expander in the line.
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Flowmeter in flare services
 Please note that for flare service, Ultrasonic flowmeters are preferred.
 LINE SIZED METERS are preferred and not the reduced size meters (like before).
 Since addition of any reducer /expander in the existing line may increase back pressure and
safety valves connected to such flares will have an impact and get effected (i.e. Type of PSV
can get change from CONVENTIONAL to BALANCED BELLOWS/PISTION or even PILOT
OPERATED).
 So consider only line sized meters (any flowmeter) itself in flare lines.
Lesson : Avoid reduced flowmeters in flare lines.
29
Overheating of the electronics
 For very hot applications (typically >300degC), there is usually a tendency that electronics
may get over heated and may cause damage to electronics.
 It is always advisable to recheck with vendors about the overheating and seek his opinion in
mounting the electronics.
 If it is not clear or if vendor is not giving a clear cut answer then better consider the flowmeter
electronics remote mounted.
 When the similar question is raised to GE (ultrasonic Flowmeter vendor), it was advised to
keep the electronics remoted mounted since the maximum process temperature that GE’s
UFMs can withstand is 60degC, if Transmitter electronics is direct mounted.
30
Thank You
31

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Shiva & Bhaskar

Safe Driving in the Fog and Mist

LAMINAR TRANSITION TURBULENT

 Beta Ratio = Differential pressure flow device bore (d)

Normally we have to adhere to project specification

 Liquid : (Max/Normal/Min cases of Flow/Pressure/Temp/Density, Vapor pressure,

 Gas : (Max/Normal/Min cases of Flow/Pressure/Temp/Density, Viscosity, Max

 Corrosive, Toxic, Solid particles, Buildup tendency

 Accuracy of measurement of flow for all conditions i.e. min/normal/max flow

 Before sizing we should finalize the unit of measurement because

 Greater impact on Compressible fluids (gases/Vapours)

 Orifice Plate - Concentric, Eccentric, Segmental, Quadrant Edge, Integral

Mass Type - measures the mass flow rate directly.

Typical Turndown ratios

3:1 to 5:1 Orifice Plate, Venturi & Flow nozzle

5:1 to 10:1 Pitot tube

10:1 to 20:1 Vortex

20:1 to 40:1 Magnetic

10:1 to 40:1 Doppler ( UFM)

20:1 to 100:1 Transit – time ( UFM )

40:1 TO 100:1 Coriolis

 Differential pressure : Pressure loss : Bore : Beta

 Minimum Bore & Beta requirement (Orifice)

But sometimes single transmitter can also accommodate these turndowns, by

COST: Cost of Installation

Installation cost , Including ,Labor and piping?

Possible use in Future application

Group1 Group 2 Group 3

a) The requirement of measurement of minimum flow:

First Transmitter (5100FT-3005A):

Second Transmitter (5100FT-3005B):

Please make sure there is an overlap between

DP Flow meters on Toxic/Corrosive services

 As per CBIN, DP flow transmitter with diaphragm seal is not preferred

 It is decided that diaphragm seal for FT DP can be avoided if proper tracing

VORTEX – ORIFICE – VORTEX

FINALLY SELECTED AS VORTEX AS PER LO DECISION

Instrument Tag Flow transmitter as per Latest

1 3000FT -3049 Integral Orifice assembly-IOA Coriolis Type flow meter

 Good Velocity profile; Uniformity in flow

 Typical straight run requirements:

Lesson: CHECK FOR THE AVAILABILITY OF THE STRAIGHT RUNS

Coriolis flow meter in liquid Sulphur service with steam jacketing

The Coriolis flowmeter consists of a vibrating tube with

If an ultrasonic flowmeter with LP steam tracing will be used for this

Lesson: Always check selection of flow meter type wrt temperature

 Retractable assemblies are available for ULTRASONIC FLOWMETERS / PITOT TUBES /

 High pressure applications

 Flare services (generally avoided as they are hazardous).

Lesson : Avoid reduced flowmeters in flare lines.

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