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TankRadar on LPG/LNG Tanks Provides Safety and Maintenance-free Operation

By Johan Sandberg and Tomas Akerstrom, Saab Marine Electronics

Section 1: Precision Radar Level Gauging On LPG and LNG storage tanks Johan Sandberg

Radar technology is quickly replacing old level gauging technology. The non-contact microwave technology provides safety, high accuracy, high reliability, superior longevity and low cost of purchasing and ownership.

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Background: Level gauging has in the past been dominated by mechanical systems like floats, servo driven displacer, pressure sensors and capacitance probes. All these technologies require active sensor parts to be inserted in to the storage tanks. Moving parts are in contact with the liquids measured. Typically, mechanical and intrusive systems will require regular maintenance to perform reliably. Cost for spare parts, calibration and tank entry makes these old technologies expensive to maintain. Malfunctions in intrusive gauging systems can lead to incorrect Inventory assessment and over fill situations. Mechanical gauges:

Picture 1. Typical servo displacer gauge on a pressurized tank. Servo driven displacer gauges has been used since the early fifties. The servo gauge is an electromechanical devise. The displacer is suspended in a thin wire. The wire is wound up on a drum with one groove per turn, keeping the diameter constant. An electric motor turns the drum moving the displacer up or down. As the displacer hits the liquid surface the tension in the wire changes. A weighing balance

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detector senses this tension-change. The servo control circuit will maintain a constant wire strain and makes the displacer follow the liquid surface as the level changes. See picture 2. A servo gauge contains many moving parts. When the tank is agitated or the liquid is boiling the servomotor is in frequent movement. Maintenance and calibration is needed to keep the unit in good condition. The servo gauge can be isolated from the tank by a ball valve. A calibration chamber above the ball valve is used to calibrate the unit. When inserted in the tank the displacer is maintained in place by a still pipe.

Picture 2. The main components in a servo level gauge. A complicated mechanical design with many moving parts.

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Picture 3. A servo tank gauge under maintenance.

Since it is difficult to determine if the displacer is fully wound up above the ball valve it is possible to break the wire by closing the valve. If this happens the displacer and the wire will fall down to the bottom of the tank. A new displacer and wire needs to be fitted and calibrated. Capacitance sensors consist of multiple, segmented probes. The probes are connected by wring to the electronics outside. Tank entry is needed if any probe with the probes occur.

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Radar Technology Radar level gauging has been available for industrial applications since the mid 1970 s. The technology has gained a large market share over the existing intrusive gauging methods. A radar level gauge consists of a microwave transceiver and an antenna made for the application. A low power microwave signal (< 0.5 mW) is sent from the antenna towards the liquid surface. The liquid reflects the microwaves back to the antenna. The transmitted and received signals are compared and the distance to the surface can be measured within fractions of a millimeter. The radar gauge has no moving parts and no part of the unit is in contact with the liquid. Basically any liquid can be measured. Radar gauges can with proper design be used for level gauging on any hydrocarbon from Methane to Asphalt at the same high accuracy.

Picture 4. Typical Radar Tank Gauge installation on a fixed roof tank.

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How Radar works Pr - received power Pt - transmitted power G - antenna gain λ - wavelength R - distance to surface Γ - reflection coefficient L - loss

2

Pr 2 λ = G2 ? √ ?Γ ?L 8πR ↵ Pt

Pt

G

RADAR

R

Γ

Pr In decibel notation:

Pr = Pt + 2 ? G + DR + Γ + L All properties expressed in decibels.

G>0 DR < 0 Γ 60 m

In-tank verification

Verification Pin

Custody transfer accuracy

¥ Spheres ¥ Bullets ¥ LPG ¥ Condensate ¥ LNG

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Install & Forget ¥Remote readout ¥Remote diagnostics ¥Local readout

Typical LPG installation ¥ Sphere tank ¥ 20 meter range ¥ Butane ¥ 2 - 5 Bar ¥ Temperature inputs

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TankRadar for LNG

TankRadar installed on in-ground LNG storage tank

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Inside an LNG tank equipped with TankRadar gauge

LNG tank pipe-cluster including still pipe for radar level gauging

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TankRadar on LPG & LNG ¥ High reliability ¥ Long range ¥ High accuracy ¥ No moving parts ¥ No maintenance ¥ Long life ¥ Low cost

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Section 2:

Radar tank gauging for marine CTS in LNG applications

Contents: Brief history of radar tank gauging.................................................................................................................................28 LNG application considerations .....................................................................................................................................28 Field experience from LNG vessels applications...........................................................................................................29 System performance and comparative advantages.........................................................................................................30 Acknowledgements .........................................................................................................................................................32

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Brief history of radar tank gauging Since 1975 more than 40.000 radar level gauges have been delivered to tankers and shore based storage tanks. The shore-based applications cover primarily chemical industries, tank terminals and refineries. Radar gauges for storage tanks are available with an accuracy of < ±1 mm and are approved for custody transfer applications. Over 1500 tankers have radar level gauging systems from Saab Marine Electronics installed and today our market share is 50% for crude -, product - and chemical tanker newbuildings. First LNG tanker installation/testing took place in August 1997 onboard Khannur, which has since been operating on its trade with a Saab TankRadar in tank # 5 certified for CTS. Full ship installations certified for LNG tanker CTS took place October 1999 with Saab retrofitting "Delta" (ex Southern) for Argent Marine Operations and Autronica retrofitting "Century" for Bergesen. Both ships took their first LNG loading at the end of 1999. LNG application considerations Current level gauging systems for gas tankers uses intrusive methods (sensor element in contact with liquid), and so far all installations have been duplicated per tank with these systems, to enable measurements while waiting for repair/replacement, which in most cases involves emptying, heating up and gas freeing. Any competitive marine LNG gauging method (radar) will have to comply to similar installation requirements, i.e. gauging inside the pipe tower (Moss-type tanks) or along the tripod structure (Membrane-type tanks). Using a still pipe for such radar gauging is incidentally very advantageous, since this means no disturbances from tank interiors.

The marine LNG radar gauge is intrinsically safe and has only the stainless steel conical adapter to the still

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pipe in the tank vapor. A permanent microwave transparent pressure seal enables the radar electronics to be fast and safely replaced in case of any failure during operation. Thus, one reliable radar may replace current duplicated sensors. The temperature measurements are done using a sealed inerted thermowell in each tank with insertion of typically five steel mantled cable sensors from outside (on dome top). This design has been used by us for more than fifteen years in about 15,000 ship tanks, and is now also used for the cryogenic application. Thus, the temperature measurement installation requires no in-tank cabling and any sensor can be replaced from top of the tank anytime. Field experience from LNG vessels applications Following successful installations and tests of Saab TankRadar on shore LNG tanks in Japan 1993 to 1996, discussions for marine verification test procedure for CTS acceptance continued with NKKK in 1997. The procedure was used both for the Khannur single tank installation and for the first FATs (factory acceptance tests) and deliveries of the first full ship tank installation of Delta and Galeomma (ex. Arzew) in 1999. For LNG/C Khannur, a "Certificate of Accuracy" and a custody transfer approval were given by NKKK, and the ship has been in trade for Osprey since with the system performing and operating to the full satisfaction of the operator and the crew. The number of cargo transfers using the system as CTS are now more than 40. On Khannur tank # 5, the radar still pipe was lowered and installed into a wider pipe for the existing float. On the first full ship installation, LNG/C Delta, which took place in Sept-Oct 1999, the pipes were installed through the existing 6" tank penetration of the removed nitrogen bubbler system and supported to pump pipes in the tank. Extensive logs and follow-ups of Khannur operation reveal that any "accurate" comparison with the secondary (capacitive) system for that ship has not been feasible. LNG/C Delta, since January 2000 trading regularly between Bonny, Nigeria, to Europe has been followed with great interest. This ship has certificate for primary CTS for both the Saab TankRadar and the Foxboro CT4 upgraded system. The Logs from Delta comparing Saab radar and the capacitive system has revealed no suspicions whatsoever on the excellence of radar performance. A sistership, LNG/C Arzew, now renamed Galeomma has been installed and certified with Saab TankRadar in the same way and was set into operation in July this year on trade from Oman to US and Europe. The trading so far has directed these LNG vessels with Saab TankRadar CTS to the following terminals with full acceptance of the radar gauge CTS reports: Terminal Dampier, Aus Arzew, Alg Everett, Ma, USA Lake Charles, La, USA Zeebrugge, B Ras Laffan, Qatar Pyeong Taek, Korea Montoir, Fr Bonny, Nigeria Huelva, Sp Marmara Ereglisi, Tu Qalhat, Oman

Operator NWS Sonatrach Distrigas Trunkline Distrigas NV QatarGas KoGas Gas de France NLNG EnaGas Tupras Oman LNG

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Ships Khannur Khannur Khannur Khannur, Galeomma Delta Delta, Khannur Delta Delta Delta Delta, Khannur Delta Galeomma

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No of transfers >9 >8 > 13 >4+1 gastrial 1+3 1 1 6 4+2 1 gastrial & 1 loading

System performance and comparative advantages Technical Data: • Gauging speed 4 tanks/sec. • Ullage gauging range 0 - 45 m i.e. from 20 mm above bottom to 100% full • Accuracy (sounding) < –5 mm • Temperature gauging -165¡C to +55¡C • Accuracy (temperature) including sensor: < – 0.2¡C @ -165¡C to -145¡C, < – 0.3¡C @ -145¡C to -80¡C, < – 1.5¡C @ -80¡C to +50¡C • Pressure measurement 0.8 -1.4 bar(abs) • Accuracy (pressure) < 0,5% (2000 MUSD, ~18000 employees

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Radar in LNG/LPG gauging

Vision

Shaping the future in tank gauging

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Saab Marine Electronics AB

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Radar tank gauging in retrospect ¥ ¥ ¥ ¥

1976 1980 1983 1985

¥ 1991 ¥ 1994 ¥ 1996 ¥ 1999

First marine vessel system installed by Saab SUM-21 no 1 level gauge on tankers Shore tank testing began by Saab 1st shore & 2nd marine gauge generations in use, and 1st radar competitor on the market 2nd generation shore tank gauge, TRL/2, also used for LPG tanks & test LNG (1993) 3rd generation marine system, G3, introduced 1st LNG gauge in operation (Tokyo Gas), and the Marine liquefied gas gauge introduced 3rd generation shore tank gauge, Saab Rex, and LNG/C Delta in CTS operation with G3 radar 8 (1)

Saab Marine Electronics AB

Radar in LNG/LPG gauging

Saab TankRadar¤ installations ¥ Installed gauges world-wide  

> 40000

gauges on tankers, all types > 20000 gauges in liquefied gas applications  

shore tanks LNG gauges marine LNG gauges

> 1000 6 13

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Saab Marine Electronics AB

Radar in LNG/LPG gauging

LNG application considerations ¥ Performance

-- best in market

¥ Reliability

-- no service or calibration in years

¥ Non-intrusive

-- no delicate components in the tank

¥ Intrinsically safe --

of course

¥ Verifiable

-- with tanks in operation

¥ Repairable

-- with certified spares

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Radar in LNG/LPG gauging

TankRadar CTS Gauge unit Electronic box

Pressure seal

Pressure sensor

Ball valve

Protective hose for cable Antenna cone Thermowell

Still pipe

Temperature sensors

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Saab Marine Electronics AB

Radar in LNG/LPG gauging

Electronic box Protective hose for cable Antenna cone Tank dome penetration Thermowell Still pipe Temperature sensors Pipe for inerting the thermowell

Ventilation hole(s)

Verification pin

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Radar in LNG/LPG gauging

TankRadar G3 CTS for Gas tankers Work Station Gauge

Printer

Work Station

Level Unit

Radar Tank

Redundancy Box I/O Box Interface to other computer

Still pipe and thermowell

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Saab Marine Electronics AB

Radar in LNG/LPG gauging

Bottom attenuator

Patent pending

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Radar in LNG/LPG gauging

Traded terminals, Khannur: (total so far > 40 transfers) Dampier, Aus. Arzew, Alg. Everett, MA, US Lake Charles, LA, US Ras Laffan, Qatar Huelva, Spain

Traded terminals, Delta & Galeomma : (total so far > 20 transfers) Ras Laffan, Qatar Qalhat, Oman Pyeong Taek, Korea Montoir, Fr Bonny, Nigeria Huelva, Spain Marmara, Turkey 15(1)

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Saab Marine Electronics AB

Radar in LNG/LPG gauging

System performance ¥ ¥ ¥ ¥ ¥

Gauging speed 4 tanks/sec. Types of cargo acc to IMO IGC Accuracy (sounding) –5 mm over gauging range 0 - 45 m Temperature gauging -165¡C to +55¡C Accuracy (temperature) incl. sensor: – 0.2¡C @ -165¡C to145¡C

¥ Pressure measurement ¥ Accuracy (pressure) ¥ Start-up time ¥ Verification pin

– 0.3¡C @ -145¡C to -80¡C – 1.5¡C @ -80¡C to +50¡C 0.8 -1.4 barabs LNG 1.0 - 8 barabs LPG < 0.5% (< 3 mbar LNG) < 10 sec. per tank at ~2 m range (above 100% level) 16(1)

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Radar in LNG/LPG gauging

Advantages of Saab TankRadar¤ for LNG - 1 ¥ ¥ ¥ ¥

Easy retrofit installation using existing pipe/penetrations One common tank penetration for level and temperature Easy installations in Moss & Membrane -type tanks, Measuring very close to bottom, accomplished by planar array attenuator (patent pending) mounted on bottom ¥ Verification/certification at installation easily accomplished ¥ Verification easy during operational conditions 

By means of verification pin (patented)  By means of verifiers (test cable lengths 20% and 80% level)  By means of attenuator echo repeatability at empty tank, ~ bottom

¥ Excellent performance on LNG, no disturbance of boiling

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Radar in LNG/LPG gauging

Advantages of Saab TankRadar¤ for LNG - 2 Feature

Saab

Lowest measurable level

20 mm

Accuracy over total tank height

± 5 mm over 45 m

In-tank verification points Level correction method

Using gas and tank physical data

Calibration

Not needed after installation

In-tank items

Only a → 107 mm pipe

Serviceable during operation

All parts 18(1)

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Radar in LNG/LPG gauging

Installation on LNG/C Delta & Galeomma

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Installation on LNG/C Delta & Galeomma

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Radar in LNG/LPG gauging

Installation on LNG/C Delta & Galeomma

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Alternative temperature sensor installation

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Factory Acceptance Testing ¥ A Saab TankRadar CTS has been ordered for HHI #1295/96 for Shell Nigeria a year ago ¥ The first ship system is completed, assembled and under FAT at Saab in Goteborg this week

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