Level Measurement Level Measurement andand

Tank Gauging SystemsTank Gauging Systems

Level Measurement Level Measurement andand

Tank Gauging Tank Gauging SystemsSystems

Level Measurement Level Measurement TechniquesTechniques

Manual (Visual):Manual (Visual):

• Visual reading thru’ Visual reading thru’ sight-glasssight-glass

• Dip-tape or dip-rod Dip-tape or dip-rod based manual gaugingbased manual gauging

• Float and counter Float and counter weight on Calibrated weight on Calibrated ScaleScale

Simple Automated Simple Automated measurements:measurements:

• Float with limit-switchesFloat with limit-switches

• Float with potentiometerFloat with potentiometer

• Float & counter weight type Float & counter weight type with potentiometer/encoder with potentiometer/encoder (counting rotation of disk / pulley)(counting rotation of disk / pulley)

Level Measurement Level Measurement TechniquesTechniques

Float & Counter weightFloat & Counter weight

Simple Automated techniques:Simple Automated techniques:

• Capacitance type probesCapacitance type probes

• Vibrating forkVibrating fork

• Displacer methodDisplacer method

• Hydrostatic Pressure sensingHydrostatic Pressure sensing

Level Measurement Level Measurement TechniquesTechniques

Capacitance probesCapacitance probes

Vibrating fork Vibrating fork techniquetechnique

Hydrostatic Pressure Hydrostatic Pressure TransmittersTransmitters

Hydrostatic tank gaugingHydrostatic tank gauging

• Oldest tank Gauging method.Oldest tank Gauging method.

• Uses 1-3 pressure transmittersUses 1-3 pressure transmitters

• Calculates the mass, density and Calculates the mass, density and volumevolume

Advantages:Advantages:• Can be used for corrosive & viscous Can be used for corrosive & viscous

productproduct

• Non-Intrusive with no moving partsNon-Intrusive with no moving parts

Pressure P3

Pressure P1

Pressure P2

HB

HBM

Mass = (P1 - P3) x AreaDensity = (P1 - P2) HBM

Volume = Mass DensityLevel = (P1 - P3) . HB

Density

Limitations:Limitations:• Mounting on the existing tanks, Mounting on the existing tanks,

nozzles, fittingsnozzles, fittings

• Not accurate level measurementNot accurate level measurement

• Generally Not suitable for Custody Generally Not suitable for Custody TransferTransfer

• Density measurement to a limited Density measurement to a limited rangerange

Hydrostatic tank gaugingHydrostatic tank gauging

Advanced automated systems:Advanced automated systems:

• Ultrasonic transducers,Ultrasonic transducers,

• Radar, Radar,

• Guided-wave radar/Impulse,Guided-wave radar/Impulse,

• Servo-gauge,Servo-gauge,

• Gamma-radiation attenuation, Gamma-radiation attenuation, etc…etc…

Level Measurement Level Measurement TechniquesTechniques

Ultrasonic probesUltrasonic probes

RadaRadarr

Radar gaugeRadar gauge

• Developed in the 70’s for gauging in Developed in the 70’s for gauging in

crude-carriers crude-carriers

• Non-intrusive, no moving partsNon-intrusive, no moving parts

• Uses micro-waves (RF) to measure Uses micro-waves (RF) to measure

levellevel

• Accuracy ±1, 3, 10, 25 mm, etc Accuracy ±1, 3, 10, 25 mm, etc

depending on typedepending on type

Limitations:Limitations:

• Less suitable for products with Low Less suitable for products with Low

Dielectric (LPG, LNG, Aromatics, etc.)Dielectric (LPG, LNG, Aromatics, etc.)

• Affected by tank-roof, stilling-pipe, Affected by tank-roof, stilling-pipe,

stirrers, etc.stirrers, etc.

• Affected by vapour density changesAffected by vapour density changes

• Effect of foam?Effect of foam?

Radar gaugeRadar gauge

Impulse probesImpulse probes

Reference pulse

Reference pulse

Servo GaugeServo Gauge

• Measuring ranges: 27m, 37m, etc. upto 150 m total wire lengths

• Wire material: SS-316, Hasteloy C22, Tantalum, Invar, etc

• Mains AC supply: 110/130/220/240 V, (optional) 65 V

• Built-in Density measurement (optional)

Sensing head

Sprocket wheel(houses drive magnets)

Guide wheels

Tape drum

Tape connection

Servo gaugeServo gaugeLimitations:Limitations:• moving partsmoving parts• Viscous products stick to wire Viscous products stick to wire (wire mass-(wire mass-

length compensation will be Erroneous)length compensation will be Erroneous)

• some high viscous products contaminate some high viscous products contaminate wire drum wire drum (length measurement Errors, repeatability errors)(length measurement Errors, repeatability errors)

• Foam Foam (displacer drifting/floating unstabilities)(displacer drifting/floating unstabilities)

• Wire can break if product solidifiesWire can break if product solidifies

• Affected by tank geometricsAffected by tank geometrics

Gamma-radiation techniqueGamma-radiation technique

Tank Gauging SystemTank Gauging System

• A generic name for the static quantity A generic name for the static quantity assessment of liquid products in bulk assessment of liquid products in bulk storage tanksstorage tanks

• Data from Gauging Instrumentation Data from Gauging Instrumentation transmitted to Inventory Management transmitted to Inventory Management System to compute overall state (level, System to compute overall state (level, mass, density, volume) of Product mass, density, volume) of Product inside the tanks.inside the tanks.

Tank GaugingTank Gauging

Purpose of Tank GaugingPurpose of Tank Gauging• Inventory ManagementInventory Management

– Accuracy - How much of which product, in Accuracy - How much of which product, in which tanks at a given instant.which tanks at a given instant.

• Custody transferCustody transfer– Standardized measurement between traders Standardized measurement between traders

for sale/purchase transfers.for sale/purchase transfers.

• SafetySafety– Safe fill and emptying of productSafe fill and emptying of product

• Loss accounting/controlLoss accounting/control– Audit, planning, restructuring operationsAudit, planning, restructuring operations

ActivityActivity UnitUnit AccuracyAccuracy

• Oil Movement & OperationsOil Movement & Operations Level & Vol Level & Vol LowLow

• Stock AccountingStock Accounting Mass or Vol Mass or Vol ModestModest

• Custody TransferCustody Transfer Mass or Vol Mass or Vol HighHigh

• Loss ControlLoss Control Mass or Vol Mass or Vol HighHigh

Purpose of Tank GaugingPurpose of Tank Gauging

Tank Farm ManagementTank Farm Management

Petroleum Products MeasuredPetroleum Products Measured

•Crude oilCrude oil•Lube oil base stockLube oil base stock•Fuel oilFuel oil•Diesel fuelDiesel fuel•KeroseneKerosene•Jet fuelJet fuel•GasolineGasoline•LPGLPG•LNGLNG•Asphalt and bitumenAsphalt and bitumen

Tank Farm ManagementTank Farm Management

Accurate level measurement used in Accurate level measurement used in

conjunction with:conjunction with:

• Water measurement deviceWater measurement device

• Temperature & Density Temperature & Density

measurementmeasurement

• TFM computes mass, vol, density.TFM computes mass, vol, density.

TFM Measurement ParametersTFM Measurement Parameters

•levellevel

•Average or spot temperatureAverage or spot temperature

•PressurePressure

•Average densityAverage density

•Gross observed volume (G.O.V.)Gross observed volume (G.O.V.)

•Volume of water & sediments (S&W)Volume of water & sediments (S&W)

•Mass and net standard volume (N.S.V.)Mass and net standard volume (N.S.V.)

StandardsStandards

API -Manual of Petroleum Measurements API -Manual of Petroleum Measurements

Standards (MPMS)Standards (MPMS)

Chapter 3 – Chapter 3 – Tank GaugingTank Gauging

Section 1B – Section 1B – Standard practice for Level Standard practice for Level

Measurement of liquid hydrocarbons in Measurement of liquid hydrocarbons in

stationary tanks by Automatic Tank Gaugingstationary tanks by Automatic Tank Gauging

Section 3 - Section 3 - Pressurized storage tanksPressurized storage tanks

OIML R85OIML R85

Automatic level gauges for measuring level of Automatic level gauges for measuring level of

liquids in fixed storage tanksliquids in fixed storage tanks

API – MPMS Chapter 3• Section 1A: Standard practices for manual gauging

of Petroleum and petroleum products

• Section 1B: Standard practice for level measurement of liquid Hydrocarbons in Stationary tanks by Automatic tank gauging

• Section 3: Standard practices for level measurement of liquid hydrocarbons in stationary pressurized storage tanks by ATG

• Section 4: Standard practices for level measurement of liquid hydrocarbons on marine vessels by ATG

• Section 5: Standard practices for level measurement of light hydrocarbon liquids onboard marine vessels by ATG

Multiple-Temperature ProbeMultiple-Temperature Probe

Spot RTD ProbesSpot RTD Probes

Interface Level MeasurementsInterface Level Measurements

Common Technologies Used for Common Technologies Used for

Interface Measurements:Interface Measurements:

• Capacitance Capacitance

– Displacers Displacers

– Pressure Pressure

– Guided Wave Radar technologyGuided Wave Radar technology

Capacitance probesCapacitance probes

Density MeasurementDensity Measurement

•Manual sampling and lab analysisManual sampling and lab analysis

•Hydrostatic pressure in conjunction Hydrostatic pressure in conjunction

with level infowith level info

•On-line density measurement devicesOn-line density measurement devices

•Servo-gauge with built-in density Servo-gauge with built-in density

measurementmeasurement

• oscillations sustained at oscillations sustained at

natural frequency against natural frequency against

damping effects.damping effects.

• The resonant frequency is The resonant frequency is

inversely proportional to inversely proportional to

the square root of the the square root of the

mass.mass.

• by calibration, the by calibration, the

frequency of vibration is frequency of vibration is

directly related the density directly related the density

of the fluidof the fluid

Servo Gauge Servo Gauge with built-in with built-in

density density measurementmeasurement

Points to be notedPoints to be noted• Changes in process fluid dielectric? Changes in process fluid dielectric? • changes in vapor space composition?changes in vapor space composition?• probe coating?probe coating?• changes in density?changes in density?• applications with disturbing objects, applications with disturbing objects,

turbulence?turbulence?• low dielectric constant for media?low dielectric constant for media?• dirty, thick, sticky or viscous media?dirty, thick, sticky or viscous media?• Solidifying media (with temperature drops)?Solidifying media (with temperature drops)?• mounting too close to tank walls?mounting too close to tank walls?• Length, small or longer depth of mounting Length, small or longer depth of mounting

chamber, nozzles?chamber, nozzles?

Tank Farm management: SoftwareTank Farm management: Software

• Different Screens / Frames / Windows– For operators– For Engineering

• for monitoring various Tanks in a gist

• for each Tank, showing all parameters

• for groups, eg. different products, zones

• Screens for gauging, inventory, calibration, trending, etc.

Tank Farm management: SoftwareTank Farm management: Software

• Batch transfers

• Alarms

• Event logs

• Reporting

• Operations: Commands for gauging (SG),

valve OPEN/CLOSE, pump ON/OFF, etc.

• Facilitates troubleshooting of Tank

Gauging, interface hardware, etc.

Tank database:

• Tags and Tank Identities, Tank strapping

details, Tank-type, Max. safe fill height, Shell

capacity, Roof weight, Product names,

API/ASTM table code, ref. densities, etc.

• COM-Port definitions, CIU tags & addr., gauge

addr., gauge type, details on installed

instrumentation for temperature, density,

pressure, Engineering Units, scheduling of

water/density dipping, logs, etc.

Tank Farm management: SoftwareTank Farm management: Software

Storage tank DeformationsStorage tank Deformations

• Tank Bottom Movements (Hydrostatic Tank Bottom Movements (Hydrostatic

pressure)pressure)

• Tank Shell Thermal ExpansionTank Shell Thermal Expansion

• Tank Shell Deformation (Hydrostatic press.)Tank Shell Deformation (Hydrostatic press.)

• Roof deformationsRoof deformations

• Tank deformations due to High windsTank deformations due to High winds

• Floor-seismic deformationsFloor-seismic deformations

• Hydraulic pressure effects, dynamics from Hydraulic pressure effects, dynamics from

other tanks, structures in the vicinityother tanks, structures in the vicinity

Storage tank DeformationsStorage tank Deformations

Sl. No. Parameter Description: For Automatic Tank Gauging Method

Uncertainty

1 Level 2 mm

2 Stability of reference points

3 Temperature element (RTD PT100 Class B) 0.5 %

4 Temperature transmitter (SDAU) 0.05 %

5 The uncertainty of the water level probe. 0.3 %

6 Tank Capacity Tables (TCT) 0.2 %

7 Tank hydrostatic deformations

8 Shell expansion

9 ASTM, table 54, Volume Correction Factor tables

0.05 %

10 Density @ 15 deg C is a manual input value obtained from the site Laboratory

0.1 %

11 Field data to computer A/D signal converter 0.025%

Cumulative AccuraciesCumulative AccuraciesTank Gauging Vs Flow-meteringTank Gauging Vs Flow-metering

Tank Gauge (Radar)For parcel size (transfer volume) greater than 5 metre.

•Gross Volume ≈ +/- 0.30 •Gross Std Volume ≈ +/- 0.35•Mass ≈ +/- 0.40

Flowmeter (Turbinemeter)•Gross Volume ≈ +/- 0.25 •Gross Std Volume ≈ +/- 0.28•mass ≈ +/- 0.28

Cryogenic Media? Tank Gauging wins over f lowmeters

Due to difficulties experienced in Due to difficulties experienced in metering of LNG at -160, custody metering of LNG at -160, custody transfer of LNG will still be done by transfer of LNG will still be done by volume measurement by tank gauging volume measurement by tank gauging for time to come till rugged, reliable, for time to come till rugged, reliable, maintenance free and accurate flow maintenance free and accurate flow measurement techniques for measurement techniques for cryogenic liquid like LNG are cryogenic liquid like LNG are developed.developed.

LNG Tanks

Capacity LNG tank : 160,000 m3Diameter: 81 meterMax height: 55 meter

Level in SilosLevel in Silos

Level in SilosLevel in Silos