Extended Operational and Trade Vocabulary

LNG Operations and Custody Transfer glossary (page 2)

The cargo and custody-transfer vocabulary of LNG: aerating and gas freeing, the AGA-8 equation of state and energy metering for custody transfer, air drying and inerting, the ALARP risk principle, and the boil-off, rollover, and tank-gauging terms. Grounds each term in the custody-transfer calculation or the gas-handling procedure it belongs to.

355 defined terms.

Showing 105 on this page (page 2 of 2).

P

PR EoS: See Peng-Robinson EoS; alternative to KMR for density per GIIGNL.
Pre-Cooling: General term covering tank cool-down with LNG spray nozzles before bulk transfer.
Pressure Build-Up Coil: External vaporizer on Type C tanks creating tank pressure for discharge.
Primary Barrier: Innermost CCS layer in contact with LNG, e.g. 1.2 mm corrugated stainless on Mark III.
Primary Insulation Space (PIS/IBS): Space between primary and secondary barriers, monitored by N2 pressure and HC content.
Process Safety Information (PSI): Required under terminal PSM programs (US OSHA 29 CFR 1910.119).
Pt-100 RTD: Platinum resistance temperature detector, primary cryogenic temperature sensor; class-approved per GIIGNL.
Pump Tower: Stainless steel truss structure inside membrane and SPB tanks supporting cargo pumps and instruments.
Pump Tower Base Support (PTBS): Reinforced support for the pump tower foot designed for cyclic sloshing loads.
Pump Trip: Automatic stop on low NPSH, motor overcurrent, or ESD activation.
Purging: Sequential N2 displacement of CH4 from inerted piping prior to opening for maintenance.

Q

Q-Flex: 210,000 to 217,000 m3 LNG carriers, 14 in fleet built for Qatargas, propelled by twin slow-speed engines with onboard reliquefaction.
Q-Max: 263,000 to 266,000 m3 LNG carriers, 14 in fleet for Qatargas, dual reliquefaction trains; world's largest LNGCs.
QCDC (Quick Connect/Disconnect Coupling): ISO 21593 type powered coupling used in LNG bunkering.
Quad Fuel: Capability to burn HFO, MGO, BOG, and forced gas; common on TFDE installations.
Quayside power: shore power outlet on the apron.

R

Radar Gauge: Primary level gauge; FMCW microwave inside still pipe, Saab/Honeywell/Endress+Hauser supply.
Rated Loading Rate: Terminal-specified maximum cargo flow, typically 10,000 to 14,000 m3/h on conventional jetties.
Receiving Terminal: Onshore facility unloading, storing, and regasifying LNG for pipeline send-out.
Recondenser: Onshore vessel mixing send-out LNG with BOG to condense vapor before HP pumping.
Reference Temperature: Standard temperature for LNG volume reporting, typically minus 161.5 degrees C per GIIGNL.
Reliquefaction plant: BOG handling unit on LNG carriers.
Repeatability (CTS): Required accuracy of radar gauges typically +/- 5 mm per GIIGNL Handbook.
RGS (Re-Gasification System): Process train on FSRU or onshore terminal converting LNG to send-out gas.
Roll Period: Time for one complete oscillation; approximated by T = 2 pi k / sqrt(g GM).
Rollover: Spontaneous density inversion in LNG storage tanks causing rapid BOG release; mitigated by recirculation and stratification monitoring.
Rotterdam TTF: Title Transfer Facility, European natural gas price benchmark used in LNG indexation.
RV (Relief Valve): Spring or pilot-operated valve on tank vapor dome set per CCS designer.

S

Saab TankRadar: Brand of Emerson Marine radar gauges widely used as CTMS primary; certified per IEC 60079.
Samsung Heavy Industries (SHI): Korean shipbuilder, leading membrane LNGC yard.
SBT (Segregated Ballast Tanks): LNGC double-hull ballast wings independent of cargo system.
Schlumberger Sampling System: Continuous probe sampling for LNG terminal GC.
Secondary Barrier: Liquid-tight barrier capable of containing cargo for 15 days at IGC design conditions in case of primary failure; full on Mark III/NO96, partial on Moss/SPB.
Send-Out Pump: Onshore HP pump delivering 60 to 100 barg LNG to vaporizers.
Settling Period: Time after loading before custody transfer measurements, allowing density and temperature stabilization, typically 30 min to 2 h.
Ship-Shore Compatibility Study: Pre-arrival check covering manifold geometry, mooring, ESD, and gangway per OCIMF/SIGTTO.
Ship-Shore Safety Checklist (SSSCL): Joint document signed at berthing per SIGTTO LNG Shipping Suggested Competency Standards.
Shrinkage: Density reduction of LNG mix during regas/recondensing accounted for in custody transfer.
SIGTTO: Society of International Gas Tanker and Terminal Operators; principal industry safety body for LNG carriers and terminals.
SIGTTO Competency Standards: Suggested LNG officer training and assessment framework adopted by major operators.
SIGTTO ESD Arrangements and Linked Ship/Shore Systems: Reference standard for ESD-1/2 implementation at LNG terminals.
SIGTTO Liquefied Gas Handling Principles: Standard textbook for LNG/LPG cargo officers (4th edition, 2016).
SIGTTO LNG STS Transfer Guidelines: Authoritative guideline for LNG ship-to-ship operations.
Single Containment Tank: Onshore LNG tank with steel inner and earth-bermed or low outer wall; older design.
Skirt: Cylindrical support beneath Moss spherical tank attaching to the inner hull at the equator.
Sloshing: Dynamic liquid motion causing impact pressures on membrane; restricts partial fills 10 to 70 percent on many carriers.
Slow Steaming: Operating below design speed to save fuel and reduce emissions.
Small-Scale LNG: Vessels typically 1,000 to 30,000 m3 using IMO Type C tanks for distribution.
Smit Inert Gas: OEM of inert gas generators commonly fitted to LNGCs.
SNAM Method: Italian method for LNG density (Klosek-McKinley variant).
Soft Yoke Mooring (SYMS): Permanent mooring system used for some FSRUs.
SPB (Self-Supporting Prismatic Type B): IHI independent prismatic tank with internal bulkheads; used on Pacific Pintail, Polar Eagle, and Prelude FLNG.
Spray Header: Distribution line feeding cool-down nozzles in cargo tanks.
Spray Pump: Small deepwell pump in pump tower delivering LNG for cool-down spray and forcing vaporizer.
SSSCL: See Ship-Shore Safety Checklist.
Stabilization Period: GIIGNL-specified waiting time after pump stop before CTMS readings.
Steam Turbine Propulsion: Traditional LNGC propulsion using dual boilers (Mitsubishi, KHI) consuming HFO and BOG.
STM (Subsea Turret Mooring): Permanent mooring for FLNG units (e.g., Prelude).
Stratification: Vertical density layering of the water column resisting mixing.
STS LNG Transfer: Cargo transfer between two LNG vessels using hoses or hard arms with dedicated fenders.
STS Plan: Master-approved STS Operations Plan per MARPOL Annex I/IMO Resolution adapted to LNG.
Sub-Cooler: BOG handling unit cooling forced LNG to absorb BOG before discharge or send-out, partial reliquefaction principle.
Subnet ESD: Local ESD loops on individual valves, integrated into vessel-wide ESD logic.
Surge Pressure: Hydraulic transient during fast valve closure; mitigated by slow ESD valve closing and surge tank in some terminals.

T

Tank Cover: Insulated stainless cover on Moss tank protrusion above deck.
Tank Dome: Top tank penetration housing instrumentation, vapor lines, and safety valves on prismatic tanks.
Tank Gauge Table: Capacity table issued by class society after laser survey, used in CTMS volume calculation.
Tank Pressure: Operating cargo tank pressure typically 1.06 to 1.25 barg.
Tank Test Pressure: 1.25 times MAWP per IGC pneumatic test.
Temperature Sensor (Cargo): Five Pt-100 sensors per tank (top, three liquid levels, bottom) per GIIGNL minimum.
Terminal Compatibility Matrix: Database matching ship size, manifold, and ESD with terminal acceptance window.
TFDE (Tri-Fuel Diesel Electric): Wartsila 50DF or MAN 51/60DF engines burning HFO, MGO, and gas with electric propulsion.
TGE Marine: OEM of small-scale LNG carriers and Type C tank systems with onboard PBU.
Topside Manifold: Ship deck assembly hosting cargo presentation flanges, drip trays, and emergency shutdown valves.
TPS (Total Pressure System): Type C tank vessel pressure control approach.
Trim and List Correction: Software adjustment in CTMS converting measured level to true volume with trim/list angles, drawing on calibrated tables.
Trim Tank: Aft ballast tank used to manage trim during loading and discharge.
Trunk Deck: Raised central walkway atop membrane LNG carriers housing liquid and vapor headers and pump tower trunks.
Type 2G Ship: IGC notation for LNG carriers per chapter 19 hazard categorization.

U

UFL (Upper Flammable Limit): Maximum vapor concentration that will ignite.
UHP Vapor Line: High-pressure vapor return path from BOG compressor to engines or recondenser.
Ullage: Empty space above liquid cargo in a tank.
Unloading Operations Manual: Cargo officer reference detailing discharge sequences and vapor return procedures.

V

Vacuum Pressure: Negative tank gauge limit per IGC, typically minus 1 kPa, monitored to prevent membrane collapse on Moss/membrane.
Vapor Arm: Cryogenic loading arm returning vapor displaced during loading to shore BOG handling.
Vapor Crossover: Header on jetty enabling vapor return without dedicated arm.
Vapor Dome: Top tank dome through which vapor line and safety valves are installed.
Vapor Header: Common deck line connecting tank vapor domes to compressors and manifold.
Vapor Return Blower: Shore blower returning BOG from ship vapor manifold during loading.
Vapor Return Line (VRL): Pipework from ship's vapor manifold to shore during loading or discharge.
Variable Frequency Drive (VFD): Speed control for cargo and send-out pumps reducing electrical consumption.
VHP (Vapor Handling Plant): Onshore equipment set including BOG compressor, recondenser, and HP pump.
Volume at Reference: Cargo volume corrected to minus 161.5 degrees C and 1.01325 bar per GIIGNL.
Volumetric Custody Transfer: Method computing energy from volume, density (KMR or PR EoS), and GHV (ISO 6976/GPA 2172).

W

Wartsila 50DF: Dual fuel medium speed engine for LNG carriers and dual fuel installations.
Water Curtain: Spray system protecting hull steel from cryogenic spills near manifold area on LNG carriers and jetties.
WinGD X-DF: Low-pressure dual-fuel two-stroke engine family.
WinGD X-DF2.0: Evolution of X-DF reducing methane slip via revised combustion timing.
Wobbe Index: GHV divided by square root of relative density; key gas quality parameter regulated by pipeline operators.
Working Pressure: Operating tank pressure typically 0.07 to 0.25 barg on membrane and Moss.

X

X DF: WinGD dual fuel two stroke engine family using low pressure Otto cycle.

Y

Y-Strainer: Inline cryogenic strainer protecting pumps and meters; common on bunker delivery lines.
Yarrow Boiler: Historic marine boiler type fitted on older steam turbine LNGCs.

Z

Zero Boil-Off (ZBO): Operational state achieved on reliquefaction-equipped carriers (Q-Flex, Q-Max) where all BOG is reliquefied.
Zone 0/1/2 (IEC 60079): Hazardous area classification used in IGC chapter 10 cargo zones for electrical equipment selection.