How accurate is the shipboard
Custody Transfer Measurement system?
An independent research by SGS.
Gerrit Vermeiren, Manager Oil, Gas & Chemicals – Benelux
Sven Lataire, LNG Business Development Manager
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SGS Survey – LNG Measurement System
� SGS and LNG
� International Developments
� International Standards
� Losses due to Measurement ignorance
� Losses due to Measurement errors
� Losses due to wrong Sampling
� Accuracy of Gas analyses
� Overall in-accuracy of the CTM system
� Conclusions & Guidelines
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SGS Survey – LNG Measurement System
� SGS and LNG
� SGS (Societe Generale de Surveillance)
• Head office – Geneva
• 140 countries
• 1300 offices
• 365 laboratories
• 39000 employees
• 150 LNG Inspectors/Measurement engineers
• 120 LNG Chemists
� LNG Competence Center (Belgium-Antwerp)• Training Institute
• Business Development center
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SGS Survey – LNG Measurement System
� Cargo value/Measurement errors
� Cargo value
• 138 000 m3
• 64 000 Tons
• 3 300,000 MMBTU
• 20 mio US$
� Measurement error• 0.2-0.3 % (ideal)
• 40-60 k US$
• 3 mio US$/year
• 100 mio US$ – 20 years
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SGS Survey – LNG Measurement System
� Cargo value/Measurement errors
� Cargo value parameters
• Level
• Pressure
• Temperature
• Volume calibration
• Sampling
• Gas Testing
• Cargo (vapor/liquid) remainders
• Vapors displaced/Boill-off
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SGS Survey – LNG Measurement System
� International Developments
� Long term objective – bilateral contracts• Strategic• Alternative fuel• Political drivers• Same ships/ports-dedicated trades
• Sustainable (low cost) energy source
=> systematic errors - hidden/undiscovered
- time/number balanced
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SGS Survey – LNG Measurement System
� International Developments
� Short term objective – spot contracts
• New/alternative energy supply
• Increase in: number-size ofships/terminals/supply/demand
• Commercial trading-spot/short/mid term
• Sustainable growth and profit driventrading
=> systematic errors - visual/significant
- not balanced out
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SGS Survey – LNG Measurement System
� International Standards
• NBS Measurement study – 1985
• ISO 13398 LNG procedure for Custodytransfer on board ships
• G.I.I.G.N.L. LNG Custody Transfer Handbook
• ISO – GPA – IP – ASTM
• Klosek Mc Kinley – revised
• Costald
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SGS Survey – LNG Measurement System
� Losses due to Measurement ignorance
• Spurious errors
• Systematic errors
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SGS Survey – LNG Measurement System
� Spurious errors
• Different standards/edition years
• Same standards – different constants/roundings
• Same methods/standards – different ref. conditions
• Use of different Measurement Instruments – L/T/P
• Wrong set-up/design Sampling station
• Displaced vapors/gasphase/Boil-off/ROB linesystem
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Losses due to Measurement ignorance
• Spurious errors e.g.
• Full or empty liquid lines on board
(before/after-loading/discharge-average 46 tons) → 15935 US$• Vapour phases accounted
(before/after-discharge/loading –diff 192 tons) → 59370 US$• Gas boil off (vapour return) during loading
Est. average 300 tons → 92765 US$• Gas received by LNG carrier when unloading
Est. average 192 tons → 59370 US$---------------------
→ 227440 US$
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SGS Survey – LNG Measurement System
� Losses due to Measurement (systematic) errors• Correct measurement
– Calibration– comparison (reference/standard/master)
• Normal Bulk Liquids Measurement:– Dynamic + Static measurement– Calibration Shore tanks / meterproving– Shore/Ship comparison – VEF (0.2-0.5%)– Best practice – Shore 0.2% / Ship 0.3%
• LNG Measurement– Only Static measurement– No shoretank calibration– No ship shore comparison– Best practice – 0.3 � ……..%
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SGS Survey – LNG Measurement System
� Calibration tables• Method – ISO 8311/9091 1-2
– Accuracy 0.2%
• Re-calibrations
• SGS calibration tables – ISO 8311/2550 sect.7-8a
– Accuracy 0.05%
� Financial impact on 20 years employment
• 20 mio US$ Loss or Gain
• due to Under or Over–calibration
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SGS Survey – LNG Measurement System
� Level – manual/automatic• Industry = > +/- 7.5 mm (1200 US$)
• SGS study => +/- 1 cm (2 cm) – (1400 – 2700 US$)
� Temperature
• Resistance – Pt 100
• Accuracy =>
– Industry : +/- 0.3 degrees Celc.
– SGS study : +/- 0.75 degrees Celc.
– Value : 76 k US$
� Pressure• Insignificant : +/- 1% error on full scale
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SGS Survey – LNG Measurement System
� Losses due to wrong Sampling
� True sample
• Independant
• Repeatable
• Reproducible
� True sampling system• Fixed sampling conditions/parameters
• Standard procedures
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SGS Survey – LNG Measurement System
� Accuracy of Gas analyses
� GLC methods – ISO6974/GPA2261……
� Total inaccuracy GHV?• +/- 1% - conc. 1-10%
• +/- 10% - conc. 0.1-1%
• Below 0.1% - 30% relative
• Overall inaccuracy =>
– Industry = 0.35%
– SGS study = 0.41%
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SGS Survey – LNG Measurement System
± 0.60 %± 0.49 %TOTAL INACCURACY OBTAINED by QUADRATIC COMBINATION OF MEASUREMENTS
± 0.41 %± 0.35 %Overall GCV inaccuracy
± 0.04 %± 0.04 %GCV of the components (NBS)
± 0.1 %± 0.03 %Calibration gas (NBS) (weighting process)
± 0.3 %± 0.3 %Inaccuracy sampling (NBS)
GROSS CALORIFIC VALUE
± 0.31 %± 0.27 %Overall density inaccuracy
± 0.20 %± 0.15 %Temperature measurement
± 0.09 %± 0.09 %Gas analysis (NBS)
± 0.10 %± 0.10 %NBS estimate of LNG measurement
DENSITY
± 0.30%± 0.21%Liquid + vapour boil-off + vapour displaced
VOLUME
SGS SurveyINDUSTRYperception
Inaccuracy of Measurement
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SGS Survey – LNG Measurement System
78 mio US$64 mio US$Estimated loss over 20 years contract
130 kUS$107 kUS$Energy value in US$
± 0.60 %± 0.49 %Inaccuracy
SGS Survey (*)INDUSTRYOverall inaccuracy
(*) shipments under SGS supervision
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SGS Survey – LNG Measurement System
� Conclusions & Guidelines
� Technical/System upgrading
� Ship calibration tables accuracy
� Technical performance CT Measurement system
• SGS LNG vessel data base
� Sampling stations –installation/procedures/verification/maintenance
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SGS Survey – LNG Measurement System
� Conclusions & Guidelines
� Supervision/Control upgrading
� Independant Inspection
• Monitoring – => brings no value and a wrong expectation of
Independant Inspection
• True Inspection– => true Independant Inspection and corrective
measures
– => Consultancy on total measurement systemaccuracy
We urge the Industry to take drastic measures to increase the overall accuracy of
Shipboard Measurements, to re-define shore based sampling and testing techniques
and to revise the role and importance of Independant Inspection and Certification
SGS and its LNG Competence Center is at your service to achieve this!
So, How accurate is your Shipboard Custody
Transfer Measurement system and Energy Accounting ?