Extended Operational and Trade Vocabulary

LNG Operations and Custody Transfer glossary

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 250 on this page (page 1 of 2).

A

Aerating: Replacing inert gas in a cargo tank with air to permit safe human entry, after gas freeing reduces hydrocarbon content below LFL.
AGA Report No. 5: Fuel Gas Energy Metering procedures used in conjunction with GC analysis for energy determination.
AGA-8: American Gas Association Report No. 8 detailed characterization equation of state for natural gas density and compressibility, referenced for custody transfer calculation.
Air dryer: Refrigerant or desiccant unit removing moisture from control air to prevent valve sticking.
ALARP: As Low As Reasonably Practicable risk principle applied to LNG carrier and terminal safety case demonstrations.
Ambient Air Vaporizer (AAV): LNG regasification heat exchanger using ambient air as the heat source at receiving terminals.
Annular Space: Insulated void between primary and secondary barriers in membrane containment, monitored for nitrogen purity and pressure.
Anti-rolling tank: Passive or active U-tube for roll damping (Frahm tank).
ASME B31.3: Process Piping code commonly applied to onshore LNG terminal cryogenic piping design.
ASTM D1945: Standard test method for analysis of natural gas by gas chromatography, basis for GIIGNL custody transfer composition.
ASTM D3588: Standard practice for calculating heat value, compressibility factor, and relative density of gaseous fuels.
Atmospheric LNG Tank: Onshore full-containment or single-containment storage operating near atmospheric pressure, typically up to 200,000 m3 gross.
Auto Ignition Temperature: Minimum temperature at which a substance ignites without external flame.
Auxiliary boiler: Oil-fired boiler for steam at sea when waste-heat is insufficient.

B

Ballast Passage: Return leg with cargo tanks empty but cooled by a heel of LNG to maintain readiness for next loading.
Ballast Voyage Boil-Off: Reduced BOG generation during ballast leg, typically 0.04 to 0.06 percent per day of total tank volume.
Barred speed range: Engine speed band of forbidden continuous operation due to torsional resonance, displayed on the tachometer.
Bell-mouth: Flared suction inlet at the bottom of a bunker tank.
Berth Manifold: Onshore manifold at the loading or discharge jetty where hard arms connect to ship manifold.
Berth Productivity Indicator: KPI tracked by LNG terminals expressing average loaded volume per berth hour.
BIRA: Built-In Rotational Allowance, used in tank gauge corrections for hull deformation.
Black start: Restoration of main switchboard from emergency generator after a blackout.
Blow Down: Controlled depressurization of cargo or fuel gas piping to the vent mast or GCU.
BOG Compressor: Low-temperature centrifugal compressor sending vapor to engine fuel gas system, GCU, recondenser, or reliquefaction unit.
BOG Recondenser: Onshore vessel where send-out LNG absorbs BOG before high-pressure pumping to vaporizers.
Boil-off gas (BOG): Vapor from LNG cargo or fuel tanks managed by reliquefaction or use.
Boil-Off Rate (BOR): Daily BOG generation as a percent of tank volume, typically 0.10 to 0.15 percent for modern membrane carriers, around 0.08 percent for latest GTT Mark III Flex+.
Bracket Stay: Internal structural connection in spherical Moss tanks anchoring the equatorial ring to the hull skirt.
British Thermal Unit (Btu): 1055.056 J; LNG cargoes invoiced in MMBtu on energy basis with reference conditions per contract.
Bunker Delivery Note (BDN): Required under MARPOL Annex VI Regulation 18.

C

C6+ Characterization: Method of distributing heavier than n-pentane composition for accurate GHV computation, per GPA 2186 or AGA-8.
C7+ Characterization: Extended grouping used when heavy hydrocarbons are present, applied in GHV and PR EoS density calculations.
Capacitance Gauge: Whessoe Varec or equivalent secondary level gauge using dielectric difference between liquid and vapor.
Capacity Plan: Diagram showing volumes, deadweights and centers for each compartment.
Cargo Compressor Room: Hazardous area containing HD/LD compressors for BOG handling, certified for Zone 1 IIA T1 service.
Cargo Containment System (CCS): Tank and insulation arrangement holding LNG; categorized in IGC Code as independent Types A, B, C and membrane.
Cargo Engineer: Senior officer on LNG carriers responsible for cargo operations, custody transfer, and CCS integrity.
Cargo Heel: LNG retained on board to keep tanks cold for next loading, typically 1.5 to 5 percent of capacity depending on voyage length.
Cargo Machinery Room (CMR): Compartment housing cargo pumps motors, compressors, and heaters with mechanical ventilation.
Cargo Manifold: Crossover piping on tanker deck where shore connections are made.
Cargo Operations Manual: IGC Code mandated document detailing tank handling, cool-down, and emergency procedures.
Cargo Pump (Deepwell): Submerged motor centrifugal pump mounted in the pump tower, typical capacity 1,400 to 1,800 m3/h per tank.
Cargo Pump Tower: Stainless steel structure inside membrane and SPB tanks carrying discharge pumps, instruments, and emergency pump column.
Cargo Tank Cool-Down: Controlled spray of LNG via spray nozzles to lower tank wall temperature before bulk loading; typically reaching minus 130 degrees C.
CCS Provider: GTT (membrane), KOGAS (KC-1), Moss Maritime/Kvaerner (spherical), IHI (SPB) are the principal designers.
Chiksan: SPM-brand marine loading arm, often used generically for any rigid loading arm.
Class Notation: Class society designation reflecting compliance with construction and equipment rules incorporated into SOLAS by reference.
Cofferdam: Temporary watertight enclosure for construction.
Cold Spot Detection: Visual or fiber-optic monitoring of hull steel near barriers for membrane breach indications.
Combustion Chamber GCU: Refractory-lined combustor that disposes of surplus BOG; sized typically for 100 to 150 percent of harbor BOG.
Compatibility Study: Joint analysis between ship and STS or jetty operator covering mooring, manifold, and ESD before transfer.
Compressor Anti-Surge: Recycle control loop preventing centrifugal BOG compressor from operating below stable flow.
Compressor House: Onshore building housing send-out BOG compressors at receiving terminals.
Cool-Down Time: Duration to bring tank metal from ambient to operational temperature, normally 10 to 24 hours for membrane tanks.
CTMS (Custody Transfer Measurement System): Integrated system of radar, temperature, pressure, density, and computer per GIIGNL Custody Transfer Handbook.
CTS Class Approval: Type approval issued by class society for radar/Pt-100 packages used as primary custody instruments.
Cube: Industry shorthand for ship cargo capacity in m3, e.g. "a 174k cube."
Custody Transfer: Quantity measurement event when cargo title passes ship/shore.
Custody Transfer Surveyor: Independent third party (e.g., Inspectorate, Intertek, SGS) witnessing CTMS and certifying delivered quantity.
Cyclic Sloshing Load: Membrane-fatigue loading from partial-fill operation, mitigated by Mark III Flex+ pump tower reinforcement.

D

Daughter Vessel: Smaller craft launched from a salvage mother ship for shallow water work.
Deballasting: Discharging ballast water.
Deepwell Pump: Submerged pump for chemical and product tankers.
Demurrage: Liquidated damages for detention of ship beyond laytime.
Density Calculation: LNG density derived from composition and temperature using Klosek-McKinley revised (KMR) or Peng-Robinson EoS per GIIGNL.
DFDE (Dual-Fuel Diesel Electric): Wartsila 50DF or MAN 51/60DF medium-speed engines burning HFO/MGO and BOG, driving electric propulsion.
Diethylene Glycol Heater: Onshore intermediate fluid loop used in some regas vaporizers (IFV) to transfer ambient or seawater heat.
Dome (Vapor Dome): Top tank dome housing safety valves, gauge nozzles, and vapor line connection.
Drainage Pump (Cofferdam): Submersible pump in inerted cofferdam to remove leaked LNG to spray header collection.
Drip tray: Containment beneath manifold connections to catch spills during bunkering.
Drying (Tank): Removal of moisture using dry air (dew point typically below minus 45 degrees C) before inerting to prevent ice formation.
DSME: Daewoo Shipbuilding & Marine Engineering (now Hanwha Ocean), historical builder of Q-Flex and Q-Max series.
Dual Membrane (NO96): GTT Invar 36 percent Ni primary and secondary barriers with plywood box insulation.
Dust Cap: Protective cap fitted on hard arm couplings between operations to prevent moisture ingress.
DWT: Deadweight tonnage; conventional LNG carriers typically 80,000 to 100,000 DWT.
Dynamic Positioning (DP): Computer-controlled station-keeping via thrusters.

E

Earthing Bond: Insulating flange between ship and shore at hard-arm interface to prevent stray current corrosion.
EEDI: Energy Efficiency Design Index, MARPOL Annex VI Chapter 4.
EEXI: Energy Efficiency Existing Ship Index, MARPOL Annex VI Chapter 4.
Emergency Cargo Pump: Portable submerged pump lowered through emergency pump column for tank discharge if main pumps fail.
Emergency Release Coupling (ERC): Powered, two-valve coupling within hard arms enabling rapid disconnection during ESD-2.
Emergency Shutdown System (ESD): Fail-safe system halting cargo flow; ESD-1 stops pumps and valves, ESD-2 also activates ERS to disconnect arms.
EN 1473: European standard for installation and equipment for LNG onshore facility design.
EN 1474: Standard for LNG transfer systems covering loading arms, hoses, and offshore transfer.
EN 1532: Standard for ship-shore interface requirements at LNG terminals.
Energy Determination: Calculation of MMBtu delivered per GIIGNL Handbook combining volume, density, GHV, and gas displaced.
Engine Fuel Gas System (FGSS): Pipework from BOG/forcing vaporizer through compressors to MEGI (around 300 bar) or X-DF (around 16 bar) engines.
Equatorial Ring: Forged ring forming the structural and thermal interface of a Moss spherical tank to the hull skirt.
Equilibrium Vapor Pressure: Tank pressure setpoint maintained typically 1.06 to 1.25 bar absolute during voyage.
ESD Ship-Shore Link: Hard-wired, fiber-optic, or pneumatic system per SIGTTO ESD Arrangements and Linked Ship/Shore Systems publication.
Ethane Carrier: Type 2G ethane carrier such as VLEC, sometimes converted to ethane fueling.
Ethylene Carrier: Smaller IGC Type 2G vessel transporting ethylene at minus 104 degrees C.
EXC Compressor: Cryogenic centrifugal BOG compressor by Cryostar typically used on Q-Flex and Q-Max units with reliquefaction.

F

Failure Mode and Effect Analysis (FMEA): Required by class for novel CCS, propulsion, and ESD designs.
FERC: Federal Energy Regulatory Commission, US authority for LNG terminal licensing.
Filling Limit: IGC maximum loading volume (typically 98.5 percent at reference temperature) preventing overfill.
Float Gauge: Mechanical level gauge with float on guide wire, retained on some older carriers as secondary device.
Floating LNG (FLNG): Offshore production unit liquefying and storing gas, exemplified by Shell Prelude (3.6 MTPA, 488 m).
Floating Storage and Regasification Unit (FSRU): LNG import unit.
Floating Storage Unit (FSU): Permanent storage tanker.
FMC Hard Arm: Articulated cryogenic loading arm, typical 16-inch liquid line, used at most LNG export and import terminals.
Foam Dam: Annular containment around the spherical tank cover or dome retaining released LNG for water curtain dispersion.
FoamGlas: Cellular borosilicate glass insulation used on cryogenic pipe supports and some tank supports.
Force Vaporizer (LNG): Steam, glycol, or seawater heated unit supplementing fuel gas demand from heel.
Forcing Vaporizer: LNG vaporizer providing supplemental gas to engines when natural BOG is insufficient.
Forward Sloshing: Longitudinal liquid motion in partially filled tanks producing membrane fatigue concerns.
Free Surface Effect: Stability reduction accounted for under SOLAS II-1 stability calculations.
FSRU Send-Out: Continuous regas rate, typically 500 to 1,000 MMscfd peak depending on vaporizer train.
FSRU STS Berth: Side-by-side or tandem berth arrangement for LNGC discharge into FSRU.
Fuel Gas Supply System (FGSS): IGF/IGC compliant skid producing engine-grade gas at required pressure and temperature.
Full Containment Tank: Onshore atmospheric LNG storage with self-supporting concrete outer tank capable of holding the full liquid head.

G

Gas Chromatograph (GC): PVT or Siemens MAXUM analyzer providing online cargo composition for GHV; calibrated to traceable gas standards.
Gas combustion unit (GCU): Thermal oxidizer for excess BOG on LNG carriers.
Gas Dispersion Study: CFD or empirical analysis required for LNG terminal hazard zone definition (e.g., NFPA 59A).
Gas Freeing: Replacement of hydrocarbon vapor with inert gas then air to allow tank entry.
Gas Trial: Sea trial including first cool-down, gas-up, and cargo machinery testing during newbuild commissioning.
Gas-Up: Procedure introducing methane to displace inert nitrogen before loading, monitored by methane concentration sensors.
Generator Cargo Compressor (HD/LD): High-duty and low-duty compressors handling forced and natural BOG respectively.
GHV (Gross Heating Value): Energy released per unit mass or volume on combustion of fuel and condensation of water vapor; reference for sales billing.
GIIGNL: International Group of Liquefied Natural Gas Importers, publisher of the LNG Custody Transfer Handbook (current edition 6.1, 2024).
GIIGNL Custody Transfer Handbook: Industry reference for LNG metering, sampling, GHV, density, and quantity determination.
GPA 2145: Physical properties of hydrocarbon mixtures used in LNG GHV computation.
GPA 2166: Standard for obtaining natural gas samples for analysis by gas chromatography.
GPA 2172: Calculation of GHV, relative density, and compressibility factor for natural gas mixtures.
GPA 2261: GC analysis method for natural gas and similar mixtures up to C10.
GTT (Gaztransport & Technigaz): French licensor of membrane CCS designs NO96 and Mark III families, royalties typically 5 percent of newbuild price.

H

Hard Arm: Articulated steel cryogenic loading arm replacing hose at fixed jetties; OEMs include FMC, KLAW, Niigata Loading Systems.
Hazardous area classification: Zoning of areas containing flammable gases.
Heel: Transverse inclination of the vessel.
Henry Hub: US natural gas price benchmark used in some LNG sales price formulas.
Hi-Hi Level Alarm: 98.5 percent or as set by IGC; auto-trip of loading via ESD.
HiBOG Mode: Operating mode where vaporizer or engine load is increased to consume excess BOG and avoid GCU use.
High-Duty (HD) Compressor: BOG compressor handling large flows during loading vapor return.
High-Pressure Pump (Onshore): Vertical multistage submerged pump (Ebara, Nikkiso) raising LNG to send-out pressure (60 to 100 bar).
HiPAP: Sonar-based position reference on DP FSRUs and shuttle LNGCs.
Hose Saddle: STS handling fixture supporting cryogenic transfer hoses, often Trelleborg or Gutteling supply.
Hull Stress Monitoring (HSM): Strain-gauge system fitted to large LNG carriers monitoring global bending and slamming.
Hydrate: Solid ice-like compound of gas and water; flow assurance hazard.
Hyundai Heavy Industries (HHI): Korean shipbuilder; major LNG carrier yard alongside Samsung and DSME/Hanwha Ocean.

I

IACS: International Association of Classification Societies, 12 members.
ICS Tanker Safety Guide (Liquefied Gas): Industry safety reference jointly with SIGTTO and OCIMF.
IGC Code: International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk.
IGF Code: International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels.
IGS (Inert Gas System): Combustion or nitrogen-based generator producing low O2 inert gas for tank inerting.
IHI: Ishikawajima-Harima Heavy Industries; licensee of MOSS spherical and designer of SPB containment.
IHI SPB: Self-Supporting Prismatic Type B independent tank with internal swash bulkheads and full secondary barrier.
Independent Tank Type A: Prismatic atmospheric tank requiring complete secondary barrier; common on LPG carriers.
Independent Tank Type B: Self-supporting tank with partial secondary barrier; Moss and SPB designs.
Independent Tank Type C: Pressure vessel (typically cylindrical or bilobe) used on small-scale LNG carriers and LNG bunker barges.
Inert gas generator: Combustion based inert gas plant for chemical and product tankers.
Inerting: Replacing tank atmosphere with inert gas (N2, IG) below 8% O2 for tankers, 5% for chemicals.
Initial Cool-Down: First cool-down on a newbuild or after dry-dock, performed slowly to limit thermal stress.
Insulation Box (NO96): Plywood box filled with perlite forming primary and secondary insulation layers in NO96 systems.
Insulation Panel (Mark III): Plywood-faced reinforced polyurethane foam panel (250 to 270 mm) with corrugated stainless primary barrier.
Insulation Space (IS): Outer insulation void between secondary barrier and inner hull, N2 monitored.
Inter-Barrier Space (IBS): Insulation space between primary and secondary barriers in membrane systems, N2 monitored.
Invar: 36 percent Ni iron alloy with very low CTE used as primary and secondary membrane in NO96 systems.
ISO 10976: Refrigerated light hydrocarbon fluids; measurement of cargoes on board LNG carriers.
ISO 13686: Natural gas quality designation, referenced in pipeline gas specifications.
ISO 14532: Natural gas vocabulary used in custody transfer documentation.
ISO 16903: Characteristics of LNG influencing design and operation.
ISO 18132: Refrigerated light hydrocarbon fluids; general requirements for automatic level gauges.
ISO 18683: Guidelines for systems and installations for supply of LNG as fuel to ships.
ISO 20088: Cryogenic spill protection materials test (parts 1 to 3) for terminal structural protection.
ISO 21593: LNG bunkering connections technical requirements for dry-disconnect/connect couplings.
ISO 28460: LNG installations and equipment; ship-to-shore interface and port operations.
ISO 6976: Calculation of calorific values, density, relative density, and Wobbe Index from composition, used in LNG GHV.
ISO 8943: Refrigerated light hydrocarbon fluids; sampling of LNG continuous and intermittent methods.

J

Jetty Boil-Off: BOG generated during cargo transfer at jetty, returned via vapor arm to shore or vented to GCU per terminal design.
Jetty head: enlarged platform at the seaward end of a jetty.
JKM: Japan Korea Marker, Platts LNG spot price benchmark for Northeast Asia.
JT Effect: Joule-Thomson cooling during expansion through control valves on regas trains.

K

K-Line: Kawasaki Kisen Kaisha, major LNG carrier operator with Moss and membrane fleet.
Kawasaki Heavy Industries (KHI): Builder of Moss spherical LNG carriers and supplier of steam turbines for many older LNGCs.
KC-1: Korean Gas/Hyundai/Samsung/DSME Korean membrane CCS introduced on SK Serenity and Spica.
Klosek-McKinley Method: Revised KMR correlation for LNG density from composition and temperature, mandated by GIIGNL.
KOGAS: Korea Gas Corporation, terminal operator and licensor of KC-1 membrane system.
Kongsberg KCM: Cargo Monitoring System integrating tank gauging, ESD, and CTMS on many LNG carriers.

L

Lambda (Insulation Conductivity): Thermal conductivity of CCS insulation; perlite around 0.025 W/m.K, polyurethane foam around 0.022 W/m.K.
Lay Time: Allowed cargo transfer time in charter party; standard 24 to 36 hours for full cargo operations.
LD Compressor: Low-duty compressor handling steady-state BOG to GCU or engines during voyage.
Level Alarms: Hi-Hi (typically 98.5 percent), Hi (95 percent), and Lo (1 percent) per IGC Chapter 13.
Level Sensor: Primary system is microwave radar (Saab Marine TankRadar, Honeywell Enraf, Whessoematic) with float or capacitance backup.
LFL (Lower Flammable Limit): Methane in air 5 percent v/v; trigger for ventilation interlocks in compressor rooms.
Liquefied Gas Carrier: IGC designation for vessel transporting cargoes listed in Chapter 19.
Liquid Header: Common cargo loading and discharge line at deck level connecting tanks and manifolds.
Liquid Manifold: Ship-side liquid presentation connection point per OCIMF MEG standards; typically 16-inch ANSI 150.
List Compensation: Software correction in CTMS converting observed level to true volume given measured list angle.
LNG Ready: Class notation for vessels with structural and arrangement provisions to be converted to LNG dual-fuel.
LNG STS Transfer Guidelines: SIGTTO publication covering ship-to-ship transfer of LNG between carriers and FSU/FSRU.
LNG Terminal Operating Manual: Local procedures aligning IGC, IGF, SIGTTO, and OCIMF/ICS terminal practice.
LNGC: Liquefied Natural Gas Carrier.
Low Temperature Carbon Steel (LT-CS): Fine-grain carbon steel for cargo deck piping and ballast tank steel exposed to LNG spills.

M

MAN ME-GI: Two-stroke high-pressure (around 300 bar) gas-injection diesel engine by MAN Energy Solutions, Diesel cycle.
MAN ME-LGIM: Methanol variant of ME-GI for methanol-fueled ships; not LNG but related dual-fuel platform.
Manifold Drip Tray: See Drip Tray.
Manifold Spool: Removable spacer between ship and shore presentation flanges to align hard arm.
Mark III (GTT): Membrane CCS with corrugated 1.2 mm stainless steel primary barrier and reinforced polyurethane foam insulation.
Mark III Flex: GTT evolution with thicker (400 mm) insulation panels reducing BOR to about 0.085 percent per day.
MARPOL Annex VI: Air pollution and energy-efficiency annex.
Mass Flow Meter (Coriolis): Emerson Micro Motion CMF series used at LNG bunkering and small-scale custody transfer.
Maximum Allowable Working Pressure (MAWP): Container or tank design pressure rating.
MEGI: MAN ME-GI gas-injection engine, common on Q-Flex retrofits, US-built LNGCs, and many post-2016 newbuilds.
Membrane Containment System: Thin metal primary barrier supported continuously by insulation transferring loads to inner hull.
Methane Carrier: Generic term for LNG carrier.
Methane Number: Knock-resistance measure of fuel gas; LNG typically above 70.
Methane Slip: Unburned methane emissions from dual-fuel LNG engines.
Mid-Scale LNG Carrier: Capacity 18,000 to 100,000 m3, typically Type C IMO tanks; serving regional trade.
MMBtu: Million Btu, standard LNG sales energy unit (1 MMBtu = 1.055 GJ).
Mooring analysis: Static and dynamic mooring analysis per OCIMF and PIANC.
Moss Spherical CCS: Self-supporting aluminum sphere on equatorial skirt; designed by Moss Maritime (Norway), built by KHI, MHI, Samsung historically.
Mother vessel: Mainline vessel served by feeders.
MTPA: Million Tonnes Per Annum, capacity unit for LNG liquefaction trains and import terminal throughput.
Multi-Reflection Radar: Saab Tank Radar Rex or Pro using cone antenna and multiple still pipes; selected as primary level gauge.

N

N2 Generator: Onboard membrane PSA nitrogen unit (Air Products, Generon) providing inter-barrier purge gas.
N2 Quality: 97 percent minimum N2 purity for insulation space top-up per CCS designer recommendations.
Natural Boil-Off: BOG produced by heat ingress alone, used as fuel on DFDE/MEGI vessels.
NFPA 59A: Standard for the Production, Storage, and Handling of LNG (US).
Niigata Loading Arm: Japanese OEM of cryogenic loading arms with quick-connect/disconnect couplings.
NO96: GTT membrane CCS using two Invar barriers and plywood boxes filled with perlite.
NO96 GW: GTT variant with glass-wool insulation reducing BOR to about 0.115 percent per day.
NO96 L03 / L03+: Recent GTT enhancements with reinforced plywood boxes and improved insulation reaching about 0.085 percent per day.
NO96 Super+: GTT latest NO96 evolution reaching BOR around 0.07 percent per day on standard 174k cube.
Nominal Capacity (m3): Geometric tank volume at 100 percent filling at reference temperature minus 163 degrees C.
Nor: Notice of readiness to load or discharge.
Nozzle Spray: Cool-down spray nozzles distributing LNG inside tank during cool-down.

O

OCIMF: Oil Companies International Marine Forum, owner of SIRE.
OCIMF/SIGTTO STS Best Practice: Joint guidance on LPG/LNG ship-to-ship transfer operations.
OCS (Open-Loop Cooling System): Seawater intermediate fluid vaporizer in FSRU; environmentally restricted in some jurisdictions.
Off Specification Cargo: Cargo failing GHV, Wobbe, or hydrocarbon limit; subject to claim under sale agreement.
Open Loop / Closed Loop / Combined Cycle Vaporizer: FSRU regasification modes using seawater alone, glycol-water with gas heat, or both.
Operational Filling Limit: 98.5 percent on most LNG tanks at minus 163 degrees C reference per IGC.
OPS (Onshore Power Supply): Shore power connection enabling main and auxiliary engine shutdown at berth.
OPS Manifold: Ship-side connection for shore power, IEC/IEEE 80005-1 compliant on LNGCs.
Outer Hull: Double-hull structure with ballast wing tanks isolating CCS from collision.

P

Partial Reliquefaction: LNG reliquefaction unit handling part of BOG, balance burned in engines; common on MEGI carriers.
PBU (Pressure Building Unit): Atmospheric vaporizer raising tank pressure for discharge on small-scale LNG and bunker barges.
PCS (Process Control System): Cargo and machinery automation, often Kongsberg K-Chief or Wartsila NACOS.
Peak Shaver: LNG storage and regas facility used to meet winter peak gas demand from base-load pipeline networks.
Peng-Robinson EoS: Cubic equation of state used for LNG density and regas calculations.
Performance Test: Charter party speed-and-consumption test verifying BOR, fuel rate, and propulsion margins.
Perlite: Expanded volcanic glass insulation used in inner spaces of NO96 boxes and in onshore storage tanks.
PIBS (Pre-Inspection Boarding Survey): Inspection by terminal representatives before berthing to confirm cargo readiness.
Pipework Pre-Cool: Spraying of liquid header before loading to avoid thermal shock on manifold piping.
Plywood Box (NO96): Birch plywood boxes filled with perlite forming the insulation layer of NO96 CCS.
PMI Compressor: Pressure-Maintaining Inlet on reliquefaction plant balancing suction pressure to BOG generation.
Polyurethane Foam (R-PUF): Glass-fiber reinforced foam used in Mark III insulation panels.
Pop Valve: P/V valve providing safety relief on cargo tanks set at 0.25 barg for membrane tanks.
PORS (Powered Emergency Release System): Loading arm system actuating ERC during ESD-2; see also FERC powered ERC.
Powered Emergency Release Coupling (PERC/FERC): Hydraulic-actuated emergency disconnect coupling within hard arms.