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Dear Reader,This is for the private circulation.This document will help to design and select the instruments for flow, level, control valve related applications.I hope this will contribute the get some good results.Thanks and Regards,Dattatray NikamInstrument Design Engineer
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(For Private Circulation Only)
SR.NOPROPERTIES ORIFICE PLATE VENTURI ROTAMETER PITOT TUBE MAG. FLOWMETER VORTEX MASS FLOWMETER ULTRASONIC
1 Working
As the flowing fluid passes through
the orifice plate, the restricted cross
section are causes an increase in
velocity & decrease in pressure.
The pressure difference before &
after the orifice plate is used to
calculte the f,ow velocity.
Similar to pitot tubes but with
multiple openings, averaging Pitot
tubes take flow profile into
consideration to provide better
overall accuracy in pipe flows.
Operates on Faraday's low of
Electromagnetic
Induction.Conducting material
passes through the magnetic field
produces avolatge perpendicular to
magnetic field & velocity of fluids.
E=BLV where E = EMF, B=
Magnetic Field, L = Length of
Conductor, V= Velocity of
Conductor . Therefore
E=4.B.L.Q/Pie d²
1.An obstruction (Bluff body or
strut) located in the flow stream.
Low-low : Fluid flow around
obstruction.
High-Flow: Alternating vortices are
formed.(No. of vortices formed are
proportional to fluid velocity.
2.These vibrations senses by
piezoelectric crystals which convert
it into elctric pulses.
3.Vortex meter can not measure
zero since it works on fluid velocity
principle.It required some flow to
work.
Coriolis mass flowmeters measure
the force resulting from the
acceleration caused by mass moving
towards ( oe away from) a center
rotation..This effect can be
experienced when ridinga merry-go-
round,where moving toward the
center will cause aperson to have to "
lean into" the rotation so as to
maintain balance. As related to
flowmeters, the effect can be
demonstrated by flowing water in
aloop of flexible hose that is "swung"
back & forth in front of the body with
both hands.Becasue the water is
flowing toward & away from the
hands oppsite forces are generated
and cause the hose to twist.
Doppler Type : 1. Under no flow
condition, the frenquencies of the
ultrasonic beams and its reflrction
are the same.
2.With the flow in the pipe
difference between the frequencies
of the Ultrasonic beam and its
reflection increses propotional to
flow velocity.
Transit Time : 1.Transit time
ultrasonic flowmeter alternately
transmit ultrasonic energy into the
fluid in the direction and against the
direction of flow.
2.The time difference between
ultrasonic energy moving upstream
to downstream in the fluid is used
to determine the fluid velocity.
3.Undergo flow condition time for
ultrasonic energy to travel upstream
& downstream are same. 4.With
flow in pipe time for ultrasonic
energy to travel upstream will be
greater than the downstream time.
2 Flowrate Medium High Flow Low Flow rate Wide range of flowsElectric conductivity greater than 5
mS/cm.
Measurement with flow velocities
( Re < 4000) not possible.
1.Measures the acceleration caused
by vibration by moving fluids towards
centers. 2.Amount of twist is
proportional to the massflowrate of
fluid passing through tubes.
3 Pressure Drop ChangesPermanent Pressure drop & good
recovery.Constant Pressure drop Negligible pressure drop
Confirm allowable pressure drop
loss while selecting meter size.
4 Application Suitable for most of gases & liquidsNot handles viscous slurries only
solids fluids.Handle almost corrosive services
Utility services where accuracy is
not necessary.
1.Conductive liquids such as
water,acids, caustic and slurriesMuch higher for gases/vapors.
2.Custody transfer application.
5 Characteristics Predictable Accurate over long range. Accurate over small or short range Wide range flows & pipe sizes.Bi-directional flow and large size
available.
Accuracy degraded during low range
flow application.
6 Rangeability 3.5:1 3.5 : 1 10:01 3:01 10:1, 30:1 10:01 20:01
7 Accuracy 2% ~ 4% of full scale 1% of Full scale 2% ±0.5 % to ±1.5 % ±0.5% typically 1% of measurement 0.2 typically 2% typically
1.Low Cost1.Low differential
press.compensation.
1.Relatively low in cost. 2.Can
handles wide variety of corrosives.
1.Available from 1/2 to 150 inches
of pipe size.1.Large pipe sizes & capacities.
1.Low installtion cost & calibration
not required.
1.Direct mass flow measurement of
any liquid flow.1.Wide flow range.
2.Available in wide range of sizes &
construction.
2. Can be used for slurries & dirty
fluids.
3.Especially suited for low flow
metereing. 4.Linear output2.Long term measurement stability.
2.Can handles slurries & greasy
materials
2.Good accuracy of fluids can be as
good as ±0.75% of rate for gases &
±1% of rate for liquids. 3.Wide
range ( 1/2 " to 12" : 18" on request.
2.Wide rangeability.3.Can be used for highly corrosive
fluids.
3.No moving parts 3.Can be welded into pipe lines.
5.Can be easily equipped with
magnetic,electronic,induction or
mercury switch alarms, or
transmitting devices.
3. Can be placed in service under
pressure.
3.Very small erros in flow
measurement.Measurement in both
directions. 4.No pressure drop. 5.No
obstruction in pipe.
4.Wide temp. range (-200 to
400°C).
5.Can be used for steam, gases or
liquids.
3.Because of the mass flow is
measured,hence the measurement is
not affected by fluid-density ,
viscosity, pressurechanges.
4.Immune to liquid chemistry and
physics property.
6.Glass tube version capable of
measuring low flow rates. 7.
Can be installed immediately
downstream of control valve.
4.Negligible permanent pressure
drop.
5.Minimum lengths of straight
piping runs.
6.Good Linearity over widerange.
7.Unaffeceted by fluid properties
such as density,viscosity &
temperature.
6.Linearity is independent of
density, viscosity & pressure.
FLOW INSTRUMENTATION DESIGN GUIDE
Advantages8
SR.NOPROPERTIES ORIFICE PLATE VENTURI ROTAMETER PITOT TUBE MAG. FLOWMETER VORTEX MASS FLOWMETER ULTRASONIC
FLOW INSTRUMENTATION DESIGN GUIDE
1.Square root relationship. 1.high Cost. 1.must be mounted vertically.1.Not applicable for dirty & sticky
services.1.Relatively high cost.
1.Not suitable for dirty arabrasice
fluid as well as for high viscous
liquids.
1.Pressure drop may be high. 1. Susceptible to noise.
2.Low accuracy. 2. Square root v/s flow relationship.
2.Relatively low temperature
limitations.
3.Limited to small pipe sizes and
capacities unless put in bypass. 2.Operating data still limited.
2.Fluid measured must be atleast
slightly conductive.Not Suitable for
gas service.
2.Measurement with low flow
velocities ( Re < 4000) not
possible.Vortex frequency remains
constant & independent of press.,
temp, density in the range of Re>
20,000 that is utilized for measuring
volume flow.
2.cannot measure gas flow with low
pipeline pressure.
2.Straight run upstream piping is
required.
3.Accuracy affected by density &
flow profile.3. Big & heavy in larger pipe size.
4.May be used only with relatively
clean fluids.
3.Pitot tube doesn't work very well
at low velocities because at low
velocity differential press. Is very
low.
3.Complex elctronic circuitary
neede.
3.Confirm allowable pressure drop
loss while selecting meter size.
3.Can be costly & should be taken
into consideration.
3.Integral
linners(Rubber,Cement,Glass etc.)
must be intimately bonded to pipe
material.
4.Viscosity affects the flowmeters.
4.If support not required then tube
strengths calculation & resonance
frequency vibration for all services
including liquids to be checked.
4.Temperature limit may be depend
on insulation materials (usually less
than 200°C)
4.Vortex meter is used for steam
water , light hydrocarbons and any
gases where large turndown is
required.
10Straight Run
Requirement
1.For Reliable measurement fluid
must enter the primary element free
of Turbulence.This can be achieved
by providing suitable lengths of
straight pipe ( Refer Annexure -A).
1.For Reliable measurement fluid
must enter the primary element free
of Turbulence.This can be achieved
by providing suitable lengths of
straight pipe ( Refer Annexure -A).
Really not required. No Straight Run Requirements.
Long staright lengths necessary
depending on the type of fitting
upstreams.
No straight meter run requirement.Straight Run requirement to be
maintained.
1.Liner material - hard Rubber,PTFE
etc.
When flow is obstructed it creates
vortices across shredder bar which
in turn creates vibrations flow.
Dopper Equation: Vf=K*Df where
K = Constant; Vf= Velocity of fluids
where ultrasonic energy is
reflected; Df=Diff. between
transmitted & reflected frequencies.
2.Electrode material -SS
316,Hestalloy c, titanium,Platinum
etc.
Transmit Time Equation:
Vp=K(Tu-Td)/Tu*Td Where Vp=
Average Velocity ib=n fluid
path,K=Constant;Tu=Upstream
Transit Time, Td= Downstream
transit time.grounding : Done by Rings on
eithrside or Times grounding by
electrode in order to go around
spurious voltages.
General
Requirements11
Disadvantages9
Plates : Orifice Tappings
Pitot Tubes
Magnetic Flowmeter Vortex Flowmeter
Transit-Time Doppler Type
FIELD INSTRUMENTATION DESIGN GUIDE
Venturi Meter
Orifice Plate Assembly
Ultrasonic Flowmeter
Mass Flowmeter
Rotameter
Sl.No. Sensor Rangeability1 Accuracy2 Dynamics (s) Advantages Disadvantages Applications / Remarks
-low cost -high pressure loss
-extensive industrial practice -plugging with slurries
-lower pressure loss than orifice -high cost
-slurries do not plug -line under 15 cm
-good for slurry service -higher cost than orifice plate
-intermediate pressure loss -limited pipe sizes
4 elbow meter 3:1 5-10% of full span - -low pressure loss -very poor accuracy
-low pressure loss
-poor performance with dirty or sticky
fluids
-large pipe diameters - straight run requirement
-wide rangeability
-linear output
-bidirectional flow & large size available
-No straight meter run required
-high reangeability -high pressure drop
-good accuracy -damaged by flow surge or solids
-wide rangeability -high cost
-good accuracy -strainer needed, especially for slurries
-wide rangeability
-insensitive to variations in
density, temperature, pressure, and
viscosity
11 Target flowmeter - Typically 2% -
-for high viscous flow such as
tars,asphalt etc -
-wide rangeability
-no straight meter run required
13
Ultrasonic
Flowmeters Typically 2%
These flowmeters are growing exponentially in popularity, mainly due to their effectiveness in use for measuring natural
gasses. They are non-intrusive and have no pressure drop. It is essential that they operate on clean fluids.
Flow Instruments Comparision Sheet
These twisting meters measure mass flow as opposed to volumetric flow. They are known for their accuracy but their size is
limiting. They carry an initial high cost, but a low maintenance cost. They are used for clean liquids and gases flowing at
medium to high velocity, in pipes six inches and under.
A higher-cost flowmeter, used mainly for water applications. They are limited to conductive fluids. They operate on a voltage
generator.
These are used as an alternative to differential pressure flowmeters. They operate best with clean, low-viscosity, medium to
high speed fluids.
orifice 3.5:1 2-4% of full span -
venturi 3.5:1 1% of full span -
flow nozzle 3.5:1 2% full span -
annubar 3:1 0.5-1.5% of full span -
-
Magnetic flowmeter 10:1 0.5% typically -
-temperature limit may depend on
insulation material (usually less than
200°C)
rotameter 10:1 2% -
positive displacement 10:1 or greater
0.5% of
measurement -
turbine 20:1
0.25% of
measurement -
-expensive
Coriolis mass
flomwmete 20:1 0.2% typically - -
vortex shedding 10:1 1% of measurement -
1
2
12
5
6
7
8
9
10
3
Sr No. Instrument Clean Liquid
Dirty Liquid Slurry Viscous
Liquid
Corrosive / Errosive Liquid
Clean Gas
Dirty Gas Steam Viscosity
EffectFull Bore Size
AvailabilityType of
MeasurementAccuracy
( % )Typical
Rangeability
Reynolds Nos. or other limitations
Sensitivity to Installation
effects
Straight Piping Requirements Typical ancillary Equipments Other Considerations Preferred Meter
Orientation Initial Cost Installation Cost maintenance Cost
Operation Cost
Performance Stability Standard or Recommended Practise.
1Concentric Orifice Plate (Square edge)
G L X X L G L G High > 1" >25mm
Square root
Volumetric
± 2 to ± 4 of full scale
( 0.5% to 3% )3:1 to 5:1 >10,000 High 10D to 40D- Up
2D to 6D DownDrain, Vent Blow -off &
S/D Valves
Pressure and/or Temp. Compensation May be required
Pressure Tap orientation Depends on the Pipe orientation & Fluid Being Metered
Low to High
Medium to High
Medium to High
Medium to High
Performance affected by Edge & Tap Wear
* AGA3* ANSI/API 2530 * ANSI/ASME MFC 3M* ISO 5167 ASME Fluid Meters
2 Segmental Wedge G G G G G G G G Low > 1/2">15 mm
Square root
Volumetric
± 0.5 to ± 2 of full scale(0.5% to 5%)
3:1 to 5:1 > 500 Low5D to 10D - Up2D to 5D - Down
None with Remote Seal Version
Same as Orifice Plate
No Limitations on Remote Seal Elements
High Low Low Low to Medium GOOD -
3 Venturi Tube G G L X L G G G High > 2" >50 mm
Square root Volumetric
± 1of full scale(0.5% to 1.5%) 3:1 to 5:1 >10,000 Low
Upsteram Runs shorter than Orifice Plate by Factor 2-9 times
Same as orifice plate,air purge & vent cleanners on Dirty liquids
Same as Orifice Plate
Same as Orifice Plate
Medium to High Medium Low Low GOOD
* AGA3* ANSI/API 2530 * ANSI/ASME MFC 3M* ISO 5167 ASME Fluid Meters
4 Flow Nozzle G L X X L G L G High > 2" >50 mm
Square root Volumetric
± 1 to ± 2 of full scale(1% to 2%)
3:1 to 5:1 > 75,000 Mod Same as Orifice plate Same as Orifice plate Same as
Orifice plateSame as Orifice plate
Medium to High Medium Low Medium GOOD
* AGA3* ANSI/API 2530 * ANSI/ASME MFC 3M* ISO 5167 ASME Fluid Meters
5 V-cone G L L L L G L G1 to 16"( 25mm to 400 mm)
Square root
Volumetric0.5% to 2% 3:1 to 5:1 > 4000 Low 5 to 10D - Up Same as Orifice plate Same as
Orifice plate - Medium Medium to High Medium Medium GOOD -
6 Target G G G G L G G L Medium > 1/2 " > 15 mm
Square root
Volumetric
± 1 to ± 2 of full scale(0.5% to 5%)
3:1 to 20:1 > 1000 High Same as Orifice plate -
Viscosity Affetcs performace below critical Rd
Zero May need adjustment in vertical installtion
Low to High Low Medium to
High Medium
Performance affected by Wear of Target
-
7 Variable Area G L X L L G L L Medium < 3" < 75mm
Linear Volumetric
± 1 to ± 10of full scale
(0.5% to 5%)10:01
Fluids under 3 Cp
None None - -
Cn only beinstalled Vertical pipe with Flow up
Low to Medium Low Low Medium GOOD -
8 Magnetic G G G G G X X X None > 1/16" > 1mm
Linear Volumetric
±0.5 of rate(0.2 to 2%)
30:1 to 100:1 None Low 5 to 10D - Up
3D - Down
Block valve may be required to Isolate Meter for Servicing
AC Design may give better Performance ON some Slurries
Electrodees must be in Horizonatal plane.Flow should be Upwards in vertical installation.
Medium to High
Low to Medium
Low to Medium Low GOOD ISO 6817
9 Vortex G L X X L G L G1/2" to 12"15 to 300mm
Linear Volumetric
± 1 of rate(0.5% to 1.5%)
10:1 to 20:1 > 20,000 High
Same as Orifice plate with 0.70 Beta
Block valve may be required to Isolate Meter for Servicing
Indicates Zero Flow below cut-off
- Medium Low to Medium
Low to Medium Medium GOOD ANSI / ASME MFC 6M
10 Turbine G L X L L G L G > 1/4" > 6 mm
Linear Volumetric
± 0.25% of rate (0.1% to 1%)
10:1 to 50:1
Fluids under 10 CST
High Similar to Orifice Plate
Strainers, Filters, Air Eliminators, steam taps may be required
Viscosity can affects Performance
Some design must be oriented as Calibrated
Low to High
Medium to High
Medium to High Medium
Performance affected by wear of bearing & other parameters
* AGA7* API 2534* ISO 2715 ASME Fluid meter* API Manual for Petroleum Measurement Standards
11 Ultrasonic - Doppler Type X G G L G X X X None > 1/2 "
> 15 mm
Linear Mass Volumetric
± 5 of full scale (1% to 5%) > 10:1
Fluids Must Have Suspensoids
High Similar to Orifice Plate -
May have problems on concentrated slurries
Transducers must bein horizontal plane
Low to High
Low to Medium Low Low GOOD -
12 Ultrasonic - Transit Time G X X L G G X L None > 1/2 "
> 15 mm
Linear Mass Volumetric
± 1 to ± 5 of full scale(1% to 5%)
> 10:1Fluids must be clean
High Similar to Orifice Plate -
May have problems on Dirty Fluids
Transducers must bein horizontal plane
Low to High
Low to Medium Low Low GOOD ANSI / ASME MFC - YY
L = LIMITED APPLICATION
FLOWMETER SELECTION GUIDETERMINOLOGY G = GOOD X = NOT RECOMMENDED
Sr No. Instrument Clean Liquid
Dirty Liquid Slurry Viscous
Liquid
Corrosive / Errosive Liquid
Clean Gas
Dirty Gas Steam Viscosity
EffectFull Bore Size
AvailabilityType of
MeasurementAccuracy
( % )Typical
Rangeability
Reynolds Nos. or other limitations
Sensitivity to Installation
effects
Straight Piping Requirements Typical ancillary Equipments Other Considerations Preferred Meter
Orientation Initial Cost Installation Cost maintenance Cost
Operation Cost
Performance Stability Standard or Recommended Practise.
L = LIMITED APPLICATION
FLOWMETER SELECTION GUIDETERMINOLOGY G = GOOD X = NOT RECOMMENDED
13 Coriolis Type G G G G L L L X None < 6"< 150 mm
Linear Mass Volumetric
± 0.4 of rate(0.15% to 2%)
40:1 to 100:1 None None None Special supports may be
required for meters
Entrained air may cause problem
Specific orientations vary with meter designs
High Low to Medium Low Low to High GOOD
*ANSI / ASME MFC-11M California weights & standards
14 Thermal Dispersion X X X X X G L G < 3" <75 mm
LogirithmicMass 1% to 5% Upto
100:1 None Mod to High 10 to 20D - UP -
May need to provide comensation for wide TEMP. ranges
Some types require same orientation as in calibration
Low to High
Low to Medium Low Low to
Medium
Performance affeccted by severe Build up on sensor for immersion types
-
Displacer LT Float type
The difference in pressures between to points in a vessel
depends on the fluids between these two points. If the
difference in densities between the fluids is significant,
which is certainly true for a vapor and liquid and can be
true for two different liquids, the difference in pressure can
be used to determine the interface level between the
fluids. Usually, a seal liquid is used in the two connecting
pipes (legs) to prevent plugging at the sensing points.
Perhaps the most frequently used device for the
measurement of level is a differential pressure transmitter.
Using DP for level is really an inferential measurement. A
DP is used to transmit the head pressure that the
diaphragm senses due to the height of the material in the
vessel multiplied by a density variable.
2.Displacers work on the Archimedes
Principle, when a body is immersed in a
fluid it loses weight equal to that of the
fluid displaced.
The float of material that is lighter than
the fluid follows the movement of the
liquid level. The position of the float,
perhaps attached to a rod, can be
determined to measure the level.
1.By Archimedes principle, a body immersed in a liquid is buoyed by a
force equal to the weight of the liquid displaced by the body. ( Thus, a body
that is more dense than the liquid can be placed in the vessel, and the amount of
liquid displaced by the body, measured by the weight of the body when in the
liquid, can be used to determine the level. )
1.Ultrasonic transmitters work on the principle of
sending a sound wave from a peizo electric
transducer to the contents of the vessel. The
device measures the length of time it takes for the
reflected sound wave to return to the transducer. A
successful measurement depends on reflection
from the process material in a straight line back to
the transducer.
Also 2.Time of Flight Technilogy.
3. Short ultrasonic impulses emitted from
transducer. 4.Bursts are created from electrical
energy applied to piezo electric crystal inside the
transducer. 5.The
transducer creates sound wave ( mechanical
energy).
6.With longer measuring ranges a lower frequency
and higher amplitude are needed to produce sound
waves that can travel further.
7.The longer the measuring range the larger the
transducer nust be
Radar Technology is a time flight measurement
1. Microwave energy is transmitted by the radar.
2.The Mircowave energy is reflected off the product surface.
3.The Radar Sensor receives the microwave energy.
4.The time from transmitting to receving the microwave
energy is measured. 5.
The time is converted to a distance measurement and then
eventuallly a level Radar Wavelength =
Speed of Light / Frequency
Ultrasonic LT
2 Arrangement
DP Cell
Level Instruments Design Guide
Working1
Guided Wave Radar level measurement
1.Time of Flight , 2.Top Mounted 3.Solids &
liquids applications. 4.Contact Management.
5.GWR is virtually unaffected by
Temperature,Pressure &
vacuum,Conductivity,Dielectric
constant,Specific Gravity,Vapor steam or Dust
air movement, Build ups & Foam.
Principle of Operation:
Radar LT Guided Wave Radar LTSl.No. CharacteristicsDisplacement type
λλλλ = c / f
Frequency 6.3 GHz
wavelength 5 = 47.5 mm
Frequency 26 GHz
wavelength 5 = 11.5 mm
•A microwave pulse (2 GHz) is guided
along a cable or rod in a 20” diameter or
inside a coaxial system.
•The pulse is then reflected from the solid
or liquid, back to the head of the unit.
•The travel time of the pulse is measured
and then converted to distance.
Displacer LT Float typeUltrasonic LTDP Cell
Level Instruments Design Guide
Radar LT Guided Wave Radar LTSl.No. CharacteristicsDisplacement type
3 Accuracy Typical accuray ± 5~ 10 mm.1. Typical Accuracy for High Frequency(26Ghz " K " Band) - ± 3~ 5 mm. 2.Typical Accuracy for Low Frequency ( 6.3 Ghz - "C" Band-
± 10 mm.
1.the transducer does not come into
contact with the process material
2.No Moving Parts in this level
measurement techniques.
2.There are certain measurements such as total level in
separator vessels that due to wide variations in material
composition of the upper phase DP is the only viable if
not ideal option.
3.a single top of vessel entry makes
leaks less probable than fully wetted
techniques
2.radar can be highly accurate, is immune to
most vapours / physical characteristics of the
measured media, other than, in some cases,
dielectric constant.
1.D/P transmitters are subject to errors due to changes in liquid density.
Density variations are caused by temperature changes or change of
product.
1.It’s primary disadvantage is cost.
2.The pressure ratings on radar antenna are
limited and these devices cannot measure
interfaces.
2.These variations must always be compensated for if
accurate measurements are to be made.
3.DP’s are mainly intended for clean liquids and require
two vessel penetrations. One is near the bottom of the
vessel where leak paths are the cause of the majority of
problems. D/P’s should not be used with liquids that
solidify as their concentrations increase. An example is
paper pulp stock.
3.Pulse radar has difficulty making accurate
measurement when the media is in close
proximity to the antenna because the time
difference between send and return signals is
too fast to measure accurately.
5 Application Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1 Refer Annexure - 1
6 Practical Limitation
Fluid density must be stable if readings are to be
accurate. If liquid density is subject to change a second
d/p transmitter is required to measure density and then
used to compensate for any changes. To accommodate
the measurement of light slurries, differential pressure
transmitters are available with extended diaphragms that
fit flush to the side of the vessel. However, if the d/p
transmitter diaphragm becomes coated, it may require
recalibration, which can be impractical and will add to the
"cost of ownership". Frequently, the measuring device is
only one consideration in the total installation of the job.
Although a D/P transmitter is often less expensive than
other types of level sensors, there is usually considerable
additional hardware and labour required to make a
practical installation. The implementation of a stable, low-
pressure leg and 3 / 5 valve manifolds will add
considerable cost to the installation.
Successful measurement depends on
the transmitter being mounted in the
correct position so that the internal
structure of the vessel will not interfere
with the signal path. To ignore
obstructions in the vessel, tank mapping
has been developed. Tank mapping lets
the operator take a "sonic snapshot" of
an empty vessel. The transducer
transmits a sound burst and the echo is
recorded as a signature of the tank. Any
obstructions in the vessel will send an
echo and create a profile. Later on, this
signature or profile is locked into the
ultrasonic unit’s memory so it will not
respond to echoes created by these
obstructions.
In the case of hydrocarbons, an accurate water
bottoms measurement must be made for precise
inventory control. Typically, another technology, such
as RF Admittance is used to make the interface
measurement between water and hydrocarbons. Some
installations, such as floating roof tanks, require the
installation of a stillpipe. Inconsistencies on the internal
surface of the stillpipe can cause erroneous echoes,
these can have an adverse effect on the accuracy of
some vendor's equipment.
Interface Measurement
1.The primary benefit of DP’s is that it can be externally
installed or retrofitted to an existing vessel. It can also be
isolated safely from the process using block valves for
maintenance and testing.
1.This non-contact technology produces highly
accurate measurements in storage tanks and
some process vessels. Radar is an excellent,
but fairly expensive technology (£1k to £5k per
measurement) for continuous level
measurements.
There are various influences that affect
the return signal. Things such as
powders, heavy vapors, surface
turbulence, foam and even ambient
noise can affect the returning signal.
Temperature can also be a limiting factor
in many process applications. Ultrasonic
devices will not operate on vacuum or
high pressure applications.
1. Displacers and floats should only be used for relatively non-viscous, clean
fluids and provide optimal performance in switch applications and over for short
spans. 2 .Spans of up to 12m are possible, but they
become prohibitively expensive.
3.Cost of installation for displacers is high and many refineries are now replacing
them due to the inaccuracies experienced under process density changes
especially on interface duties.
4. High quality float switches still provide reliable and repeatable performance.
Even with todays array of level technologies, if a 100% process seal is required
under fail conditions for a Cryogenic application the only technique available,
other than nucleonic, is a magnetically coupled float switch
Advantages
2.the process fluid measured must maintain its density if repeatability is required,
this is particularly true of displacers
This is especially problematic in interface measurements, where both liquids
increase or decrease density, while the signal is proportional to the density
difference. Because the displacer is emersed in the process fluid it will be
vulnerable to particulate deposition. This will change the displacer mass and the
effective displacement causing a calibration shift.
Disadvantages5
4
1.Both floats and displacers work well with clean liquids and are accurate and
adaptable to wide variations in fluid densities
Displacers are affected by changes in product density since the displacement of
the body (its weight loss) is equal to the weight of the fluid displaced. eg. If the
specific gravity changes, then the weight of the displaced material changes, thus
changing the calibration.
High frequency shorter wavelength
narrower beam angle more
focused signal ability to measure
smaller vesselswith more flexible
mounting
Low frequency longer wavelength
wider beam angle less focused
signal ability to measure smaller
vessels with difficult application
variables.
3 Accuracy
2 Arrangement
Level Instruments Design Guide
Working1
1.Nucleonic level controls are used for point and continuous measurements, typically
where most other technologies are unsuccessful. 2.The
radioisotopes used for level measurement emit energy at a fairly constant rate but in
random bursts. Gamma radiation, the source generally used for nucleonic level
gauging is similar to microwaves or even light (these are also electromagnetic
radiation, but of lower energy and longer wavelength). The short wavelength and higher
energy of gamma radiation penetrates the vessel wall and process media.
3.A detector on the other side of the vessel measures the radiation field strength and
infers the level in the vessel. Different radioisotopes are used, based on the penetrating
power needed to "see" the process within the vessel. With single point gauges the
radiation provides a simple on/off switching function, whereas with continuous level
measurement the percentage of transmission decreases as the level increases.
The theory of operation for an RF Admittance level transmitter is
similar to that of Capacitance transmitters, but with two important
circuit additions. The oscillator buffer and chopper drive circuits
permit separate measurement of resistance and capacitance. Since
the resistance and capacitance of any coating are of equal
magnitude (by physical laws), the error generated by a coating can
be measured and subtracted from the total output. The result is an
accurate measurement regardless of the amount of coating on the
probe.
Nuclear LT Capacitance LT RF AdmittanceSl.No. Characteristics
A capacitance probe can be immersed in the liquid of the tank,
and the capacitance between the probe and the vessel wall
depends on the level. By measuring the capacitance of the
liquid, the level of the tank can be .As the level rise’s and
material begins to cover the sensing element the capacitance
within the circuit between the probe and the media (conductive
applications) or the probe and the vessel wall (insulating
applications) increases. This causes a bridge misbalance, the
signal is demodulated (rectified), amplified and the output is
increased.
Capacitance Type
RF Ad mittance Type
Level Instruments Design Guide
Nuclear LT Capacitance LT RF AdmittanceSl.No. Characteristics
1.As no penetration of the vessel is needed there are a number of situations that cause
nucleonic transmitters to be considered over other technologies.
2.These applications generally involve high temperatures / pressures or where toxic or
corrosive materials are within the vessel. Placing the source and / or detector in wells
within the vessel can reduce source sizes.
3.An extension of this is to use a moving source within the vessel; this facilitates the
unique ability to combine density profiling with accurate tracking of a moving interface.
5 Application
6 Practical Limitation
From a psychological standpoint, the radiation symbol found on these controls is
frequently the cause of unfounded concern with uninitiated plant personnel. Plant
Management is usually required to ensure that appropriate education is given to any
staff likely to be involved with this measurement technology. Source size regulations
can often be met in difficult applications by placing the source and / or detector in wells
within the vessel if necessary.
Most users’ realise the limitations of Capacitance level
measurement, such as the large errors caused by coatings. This
has led to a decrease in the number of these systems in
operation. Other technologies such as FMCW radar and in
particular RF Admittance have now gained acceptance due to
high levels of reliability and accuracy.
Admittance technology and nucleonic measurement provide the
only practical methods for level measurement in coating
applications. For insulating materials with changing dielectric
constants, the measurement can only be made reliably if the
material being measured is homogeneous. A reference sensor is
added to monitor the dielectric constant and then compensate the
calibration based on this information. Smart RF transmitters are
available providing superior levels of stability and accuracy as well
as remote communication. Knowledge of the approximate electrical
character of the process material is key to optimum system
selection and performance.
In other words
Advantages
Disadvantages5
4
RF Admittance is next generation capacitance as such it is by far
the most versatile technology for continuous level measurement. It
can handle a wide range of process conditions anywhere from
cryogenics to approximately 850 o C and from vacuum to 10,000
psi pressure. Aside from the electronic circuit technology, sensing
element design is very important to handle these process
conditions. There are no moving parts to wear, plug, or jam. As with
capacitance systems there is only a single tank penetration, usually
at the top of the tank, above the actual process level.
RF admittance is intrusive. Insulating granular measurements
require special considerations, such as the moisture range and
location of the sensing element to minimize errors caused by probe
movement.
It would appear that nucleonic gauges provide a truly universal "fit and forget" level
measurement technology. Although when the "cost of ownership" is calculated nuclear
level measurement is often more expensive than conventional systems. Hidden costs
include initial licensing and periodic surveying. These services are usually provided by
external authorities or by the equipment supplier, assuming they have appropriately
qualified staff. If no longer required, the nucleonic gauge must be disposed of through
appropriately licensed, external organizations, which again can be a costly exercise.
Capacitance techniques are capable of operation at extremes of
temperature and pressure. They work well for materials that
won’t leave a coating. Usually only a single tank penetration is
required.
Capacitance systems are intrusive. Have problems with varying
dielectric materials and those media’s, that coat the sensing
element. Thus users are normally limited to water-like media.
Even acids and caustics that don’t appear to coat the sensing
element are so conductive that the thin film they leave can
cause serious errors in measurement.
Single Seated Double Seated 3-Way valve Angle Valve Cage guided Butterfly valve Ball Valve Eccentric spherical plug valve
1. Minimum leakage in close position.1.Higher leakage rate than Singale
seated valve
1.Three pipeline connections provide
general converging (flow mixing0 or
diverging(flow-splitting) services.
1.For high pressure
services
1.Leakage rate is like
as Single seat.
1. For High capacity and low
pressure drop services.
1.Suitable for erosive and viscous fluids
or slurries containing entrained solids or
fiber
1.Usually less costly than conventional
globe valves and adaptable to ordinary
control requirements.
2.Require large actuator force,particulrly
large sizes.
2.Required less actuato forces due to
balancing feature of plug.
2.Usually single port type
only.
2.Balanced Plud design
permits operation with
smaller actuators.
2.Conventional discs provide
throttling control for up to 60°disc
rotation.
2.V-Notch produces an equal % flow
characteristicn,and used for control of
above fluids and application where very
high rangeability is required.
3.Most common body atype & simple in
Construction
3.Noise attenuation or
anti-cavitation type trim
available.
3.Typical wafer body design , a lug
wafer design and flanged design.
3.Low torque requirements can permit
ball valves to be used inQuick manual or
automatic operation.
4.Full Ball : 1.A complete sphere as the
flow controlling member.
2.Rotary shaft design and include aflow
passage.
3.Trunion mounted with a Single piece
ball & shaft to reduce torque
requirements & last motion.
V-Port Ball Valve:1. V -Port ball valve
utilizes a partial sphere that has a V-
shaped notch in it. 2.Notch permits wide
range of service & produces an equal %
flow charcteristics. 3.Straight forward
flow design produces very little pressure
drop & the valve is suited to the control
of erosion & viscous fluids.
4.V-port ball reduces the clogging when
it comes in contact with seal which
produces shearing effect.
Applicable Codes
2BEST SUITED
CONTROLLinear and Equal %
Exhibits approximately equal % flow
characterics.
Quick opening,Linear ; offer full flow with
minimum turbulence and can balance or
throttle fluids.Best suited for On-off .
Linear flow characteristics through 90° of
disk rotation.
3DESIGN
INFORMATION
Valve shall be designed to meet the
design pressure and temperature.
Interchangeability o ftrim permits
choice of several flow characteristics
or noise attenuation or anti-cavitation
components.
1.Actuator selection demands careful
consideration,particularly for
construction with unbalanced valve
plug.
1.High performance butterfly valve
should be sized to control within 15
to 75 range of disk opening.
1.Efiicient throttling
1.Reduced unbalance permits
operation of valves with smaller
actuators than those necessary of
single ported valves.
1.Low cost and Maintenance.
2.High Capacity1.Low cost. 2.High Capacity. 1.Erosion resistance.
2.Accurate flow control2.Higher capacity than the Single
ported valves.3.Good flow control. 3.Low leakage and maintenance
3.Available in Multiple ports
3.Many double seated bodies
reverse, so the plug can be installed
either push-down-to -open or push-
down-to-close.
4.Low pressure drop. 4.Tight sealing with low torque.
1.High Pressure drop1.Will not provide same "Shut-off "
as the Single Seated do.1.High torque required for control. 1.Poor throttling characteristics.
2.More expensive than other valve 2.Prone to Caviation at lower flows. 2.Prone to Cavitation.
1.Throttling service/flow regulation
1.Throttling service/flow regulation
but not generally recommended
because of their maintenance cost
and leakage.
1. Can be used for throttling mid-
travel position control either
converging or diverging fluids.
1.Fully open/closed at throttling
services & on-off valve.1.Fully open/closed, limited -throttling
2.Frequent operation
2.Frequent operation. 3.Minimal
fluid trapping inline. 4.Big
lines(Liquid service upto 96").
2.Higher temperature fluids.
ADVANTAGES
Rotary Valves
1
SR.NO PropertiesGlobe Body Valves
WORKING
Control Valve Comparision Sheet for Reference
DISADVANTAGES5
RECOMMENDED
USED6
4
Single Seated Double Seated 3-Way valve Angle Valve Cage guided Butterfly valve Ball Valve Eccentric spherical plug valve
Rotary ValvesSR.NO Properties
Globe Body Valves
Control Valve Comparision Sheet for Reference
1.Liquids,vapors,gases,corrosive
sustances,slurries
1.Typically used in refineries on
highly viscous fluids (
dirt,contaminants, or process
deposits on trim) concern
1.Coking service.
2.Solids carried in
supsension. 3.Severe
flashing services.
4.Cavitaion services.
5.High pressure drops.
1.Lquid,gases ,slurries,liquids with
suspended solids.
1.Most liquids, high temperatures,
slurries.
2.Specified for application stringent shut-
off requirements.
2.Often used for on-off or low
pressure throttling device.
8CONNECTION
RATING(Typical upto ANSI 2500) As per Piping Specifications.(H-103)
Standard end connections
(Flanged,screwed,butt weld etc.)Can
be specified to mate with piping
design specs.
As per Piping
Specifications.(H-103)
As per Piping
Specifications.(H-103)
Std. Raised faced piping
flanges.Typical ANSI 600.
As per Piping Specifications.(H-
103).Typical upto ANSI 900. As per Piping Specifications.(H-103)
9 MATERAIL As per Piping Specifications.(H-103) As per Piping Specifications.(H-103)Variations include trim materials
selected for high temperature service.
As per Piping
Specifications.(H-103)
As per Piping
Specifications.(H-103) As per Piping Specifications.(H-103) As per Piping Specifications.(H-103)
10 PACKING
PTFE( Polytetrafluro ethylene widely
used because of its inert and has low co-
efficient of friction. Can be applied to
400°F.
11 SEAT LEAKAGE
Metal-to- Metal saeting surfaces pr soft
seating with PTFE.Tight shut-off
achievable.
Metal-to-Metal seating usually
provides only Class II shut-off
capability,although Class III
capability is also possible.
Tight-off can be achieved. Tight shut-off achievable.
13 SIZING
The shear Safety factor should be a
minimum 150% at the specied Shut-
off pressure drop condition.
14 Flow Capacity Moderate High High
12
TRIM
CHARACTER-
ISTICS
7 APPLICATION
Equal% is suitable for pressure control application, or on application where highly varying pressure drop can be expected and pressure drop at the control valve is relatively small against the system pressure drop.
Quick Opening:Provides a maximum change in flowrate at lower valve tarvel with fairly linear relationship and lesser flow increase as the plug further opens.(Normally not used for throttling)
Linear: Provides equal increase in CV for equal increment in stem travel.
Linear one often specified for liquid level control and application requiring constant gain (Pressure drop is Constant)
Equal %:Provides equal% increase in CV for equal increament of stem travel.This characteristic provides throttling control valve at valve close position and rapidly increaasing capacity as the plug is near the open position.
Wire Number(Gauge) (Inches) (MM) (Inches) (MM) (MM2)
1 0.3 7.62 0.289 7,348 42.429
2 0.276 7.01 0.258 6,543 33.592
3 0.252 6.401 0.229 5,827 26.694
4 0.232 5.893 0.204 5,189 21.155
5 0.212 5.385 0.182 4,621 16.763
6 0.192 4.877 0.162 4,115 13.267
7 0.176 4.47 0.144 3,665 10.52
8 0.16 4.064 0.128 3,264 8.346
9 0.144 3.658 0.114 2,906 6.605
10 0.128 3.251 0.102 2,588 5.268
11 0.116 2.946 0.091 2,304 4.154
12 0.104 2.642 0.081 2,052 3.3
13 0.092 2.337 0.072 1,829 2.63
14 0.08 2.032 0.064 1,628 2.086
15 0.072 1.829 0.057 1,450 1.651
16 0.064 1.626 0.051 1,291 1.306
17 0.056 1.422 0.045 1,150 1.038
18 0.048 1.219 0.04 1,024 0.817
19 0.04 1.016 0.036 0,9119 0.65
20 0.036 0.9144 0.032 0,8128 0.515
21 0.032 0.8128 0.028 0,7239 0.407
22 0.028 0.7112 0.025 0,6426 0.321
23 0.024 0.6096 0.023 0,5740 0.255
24 0.022 0.55.88 0.02 0,5106 0.204
25 0.02 0.508 0.018 0,4547 0.159
26 0.018 0.4572 0.016 0,4038 0.125
27 0.0164 0.4166 0.014 0,3606 0.101
28 0.0148 0.3759 0.013 0,3200 0.08
29 0.0136 0.3454 0.011 0,2870 0.066
30 0.0124 0.315 0.01 0,2540 0.049
31 0.0116 0.2946 0.009 0,2261 0.041
32 0.0108 0.2743 0.008 0,2032 0.032
33 0.01 0.254 0.007 0,1803 0.024
34 0.0092 0.2337 0.0063 0,1601 0.02
35 0.0084 0.2138 0.0056 0,1422 0.015
36 0.0076 0.193 0.005 0,1270 0.012
37 0.0068 0.1727 0.0044 0,1143 0.009
38 0.006 0.1524 0.004 0,1016 0.008
39 0.0052 0.1321 0.0035 0,0889 0.006
40 0.0048 0.121 0.0031 0,0787 0.005
S.W.G. American Wire Gauges (AWG) MetricWIRE CONVERSION CHART
American Wire Gauge Diameter Diameter Cross Sectional Area
(AWG) (inches) (mm) (mm2)
1 0 0.46 11.68 107.16
2 0 0.4096 10.4 84.97
3 0 0.3648 9.27 67.4
4 0 0.3249 8.25 53.46
5 1 0.2893 7.35 42.39
6 2 0.2576 6.54 33.61
7 3 0.2294 5.83 26.65
8 4 0.2043 5.19 21.14
9 5 0.1819 4.62 16.76
10 6 0.162 4.11 13.29
11 7 0.1443 3.67 10.55
12 8 0.1285 3.26 8.36
13 9 0.1144 2.91 6.63
14 10 0.1019 2.59 5.26
15 11 0.0907 2.3 4.17
16 12 0.0808 2.05 3.31
17 13 0.072 1.83 2.63
18 14 0.0641 1.63 2.08
19 15 0.0571 1.45 1.65
20 16 0.0508 1.29 1.31
21 17 0.0453 1.15 1.04
22 18 0.0403 1.02 0.82
23 19 0.0359 0.91 0.65
24 20 0.032 0.81 0.52
25 21 0.0285 0.72 0.41
26 22 0.0254 0.65 0.33
27 23 0.0226 0.57 0.26
28 24 0.0201 0.51 0.2
29 25 0.0179 0.45 0.16
30 26 0.0159 0.4 0.13
Sl.No. Remarks