Extended Operational and Trade Vocabulary

LNG/LPG Carriers and IGC Code glossary

The gas-carrier vocabulary anchored in the IGC Code: aeration and gas freeing, air locks separating gas-safe and gas-dangerous spaces, ambient-temperature design requirements, the regasification terminals, and the containment and size-class terms. Grounds each term in the IGC Code requirement or the gas-carrier operation it belongs to.

258 defined terms.

Showing 250 on this page (page 1 of 2).

A

Adriatic LNG: Offshore gravity-based-structure regasification terminal in the northern Adriatic Sea off Porto Levante, Italy, commissioned in 2009 and operated by Terminale GNL Adriatico.
Aeration: Forced air movement through cargo to control temperature, gas, or moisture.
Aframax LPG: Informal label occasionally applied to mid-size LPG carriers near 60,000 cubic meters, although the LPG fleet uses VLGC, MGC, and Handygas as the standard size classes.
Air lock: Two-door compartment separating a gas-safe space from a gas-dangerous zone on a gas carrier, required by the IGC Code for entry to electrical equipment rooms.
Ambient temperature design: IGC Code requirement that gas carrier systems be designed for tropical sea and air temperatures, typically 32 degrees Celsius seawater and 45 degrees Celsius air.
Annex I to MARPOL: Pollution prevention regulations covering oil cargoes, generally not applicable to gas carriers whose cargoes fall under the IGC Code rather than MARPOL Annex I.
Anti-rolling tank: Passive or active U-tube for roll damping (Frahm tank).
Articulated tug barge LNG: Small-scale LNG transport configuration used in coastwise trades, employing IMO Type C pressure vessels on a barge coupled to a pusher tug.
Atmospheric pressure cargo: Cargo carried at or close to atmospheric pressure in fully refrigerated tanks, characteristic of LNG and large fully refrigerated LPG shipments.
Avance Gas: Bermuda-based VLGC owner and operator listed in Oslo, with a fleet trading LPG on long-haul export routes from the US Gulf and Middle East.
Avenir Achievement: 7,500 cubic meter small-scale LNG carrier and bunker vessel delivered to Avenir LNG in 2021.
Avenir LNG: Small-scale LNG shipping and supply company majority owned by Stolt-Nielsen and Golar LNG, operating LNG bunker vessels including Avenir Achievement.

B

Ballast voyage: Return voyage of a gas carrier without commercial cargo, typically retaining an LNG heel for tank cooling and fuel.
Bare Boat Charter: Vessel hire without crew; charterer assumes operational control.
Barrier, primary: Inner liquid-tight barrier of a membrane LNG cargo tank in direct contact with the cargo, typically stainless steel or Invar.
Barrier, secondary: Outer liquid-tight barrier of a membrane LNG cargo tank designed to contain leakage from the primary barrier for at least fifteen days under IGC Code requirements.
Bayway: Common shorthand for the Linden, New Jersey area associated with historic LPG and refined product imports, not an active LNG terminal.
BOG: Boil-Off Gas handling at LNG import terminals.
BOG Compressor: Low-temperature centrifugal compressor sending vapor to engine fuel gas system, GCU, recondenser, or reliquefaction unit.
Boil-off rate: Daily percentage of cargo volume lost as vapor, typically 0.10 to 0.15 percent per day on modern membrane LNG carriers.
BOR: Standard abbreviation for boil-off rate used in LNG carrier specifications and charter party terms.
Bow loading: Cable lay operation with the cable departing over a bow chute, used on certain converted vessels.
Bunker delivery note: BDN, document required under MARPOL Annex VI Regulation 18 listing fuel quantity and sulphur content.
BW Gas: Historic LPG arm of BW Group, succeeded by BW LPG as a separately listed company.
BW Group: Singapore-headquartered shipping group with interests across LPG, LNG, product tankers, and offshore LNG infrastructure.
BW LPG: Oslo-listed VLGC owner and operator, one of the largest fleets of Very Large Gas Carriers globally.

C

Calcasieu Pass: Venture Global LNG export terminal in Cameron Parish, Louisiana, commissioned in 2022 using modular mid-scale liquefaction trains.
Cameron LNG: LNG export terminal in Hackberry, Louisiana, operated by Sempra Infrastructure with first cargoes shipped in 2019.
Cargo containment system: Total arrangement of cargo tank, insulation, secondary barrier, and supporting structures used to carry liquefied gas under the IGC Code.
Cargo machinery room: Dedicated compartment housing cargo pumps, compressors, and ancillary equipment on a gas carrier, subject to IGC Code arrangement and ventilation rules.
Cargo Manifold: Crossover piping on tanker deck where shore connections are made.
Cargo Pump Tower: Stainless steel structure inside membrane and SPB tanks carrying discharge pumps, instruments, and emergency pump column.
Cargo segregation: IGC Code requirement that incompatible gas cargoes be carried in separate piping and tank systems to prevent dangerous mixing.
Cargo tank dome: Raised gas-tight structure on top of a cargo tank providing access for piping penetrations and instrumentation.
Cargo tank pressure: Gauge pressure inside a gas cargo tank, maintained within design limits by venting, reliquefaction, or vapor return.
CCS: Cargo Containment System under the IGC and IGF Codes.
CH4: Methane, the primary component of natural gas and LNG, typically 85 to 99 percent by volume depending on source field.
Chapter 1 IGC: Section of the IGC Code covering general application, definitions, equivalents, and survey requirements for ships carrying liquefied gases in bulk.
Chapter 10 IGC: Section of the IGC Code on electrical installations in cargo areas and hazardous zones aboard gas carriers.
Chapter 11 IGC: Section of the IGC Code on fire protection and extinction including water spray, dry chemical, and structural fire protection.
Chapter 12 IGC: Section of the IGC Code on artificial mechanical ventilation of cargo and machinery spaces.
Chapter 13 IGC: Section of the IGC Code on instrumentation including level, pressure, temperature, and gas detection systems.
Chapter 14 IGC: Section of the IGC Code on personnel protection, eyewashes, decontamination showers, breathing apparatus, and protective clothing.
Chapter 15 IGC: Section of the IGC Code on filling limits, defining maximum allowable liquid volume at reference temperature.
Chapter 16 IGC: Section of the IGC Code on the use of cargo as fuel, permitting methane consumption in propulsion and auxiliary machinery under defined conditions.
Chapter 17 IGC: Section of the IGC Code listing special requirements applicable to specific cargoes such as ammonia, chlorine, ethylene, and vinyl chloride monomer.
Chapter 18 IGC: Section of the IGC Code on operating requirements including loading, discharge, watchkeeping, and emergency response on gas carriers.
Chapter 19 IGC: Section of the IGC Code summarizing minimum requirements per cargo in a tabular format used by surveyors and operators.
Chapter 2 IGC: Section of the IGC Code covering ship survival capability and the location of cargo tanks relative to the side and bottom shell.
Chapter 3 IGC: Section of the IGC Code on ship arrangements including segregation of cargo areas, accommodation spaces, and access.
Chapter 4 IGC: Section of the IGC Code defining cargo containment system types A, B, C, membrane, and integral, with associated design and secondary barrier requirements.
Chapter 5 IGC: Section of the IGC Code covering process pressure vessels and cargo piping for liquid, vapor, and pressure service.
Chapter 6 IGC: Section of the IGC Code specifying materials of construction for cargo tanks and piping based on design temperature.
Chapter 7 IGC: Section of the IGC Code addressing cargo pressure and temperature control including reliquefaction and forced vaporization.
Chapter 8 IGC: Section of the IGC Code on cargo tank vent systems, pressure relief, and discharge of vented gas to safe locations.
Chapter 9 IGC: Section of the IGC Code covering cargo containment system atmosphere control, including inerting, drying, and interbarrier monitoring.
Class notation gas carrier: Classification society notation identifying a ship as a gas carrier under the IGC Code, e.g., DNV Tanker for Liquefied Gas.
Cofferdam: Temporary watertight enclosure for construction.
Cold spot: Localized low-temperature area on the hull structure of a gas carrier indicating insulation degradation or cargo containment leakage.
Compressor House: Onshore building housing send-out BOG compressors at receiving terminals.
Conventional LNG carrier: Mainstream class of LNG carrier with capacity in the range of approximately 125,000 to 180,000 cubic meters.
Cool Company: Oslo-listed LNG carrier owner and operator established in 2022, focused on TFDE and modern two-stroke LNG tonnage.
Cooldown: Process of gradually lowering cargo tank temperature with LNG sprays prior to bulk loading to avoid thermal shock.
Coralius: 5,800 cubic meter LNG bunker vessel delivered in 2017 and operated in Northern European waters.
Corpus Christi LNG: Cheniere Energy LNG export terminal near Corpus Christi, Texas, commissioned in 2018.
Cove Point LNG: Bidirectional LNG terminal in Lusby, Maryland, originally an import facility and later converted to export service by Dominion Energy.
CTS: Container Securing Test or Cargo Tank Securing requirements as defined in IACS UR C and CSC.
Custody transfer measurement system: Full term for the CTS used in commercial settlement of LNG cargoes between buyer, seller, and terminal.
Cylindrical pressure vessel: Geometry of IMO Type C cargo tanks, fabricated as cylindrical or bi-lobe pressure vessels with hemispherical heads.

D

Daewoo Shipbuilding and Marine Engineering: South Korean shipbuilder, now Hanwha Ocean, with a long history of LNG and LPG carrier construction including membrane LNG vessels.
DCS: IMO Data Collection System on fuel oil consumption, MARPOL Annex VI, cross-referenced with SOLAS chapter requirements.
Deck tank: Independent IGC Type C tank installed above deck on small-scale LNG and LPG vessels.
Deepwater port: Port capable of receiving large draft vessels.
Density LNG: Liquid density used in CTS calculation, typically near 430 to 470 kilograms per cubic meter depending on cargo composition.
DFDE: Dual-fuel diesel-electric propulsion using four-stroke medium-speed dual-fuel engines driving electric generators.
DFDE LNG carrier: LNG carrier built with DFDE propulsion, common among vessels delivered between approximately 2005 and 2015.
Discharge pressure: High-side refrigerant pressure at compressor outlet.
Discharge rate: Volumetric rate of cargo discharge during unloading, typically 10,000 to 14,000 cubic meters per hour at large LNG import terminals.
Dome cover: Insulated protective cover over the cargo tank dome on a membrane LNG carrier.
Dorian LPG: New York and Oslo-listed VLGC owner and operator headquartered in Stamford, Connecticut.
Dragon LNG: LNG import terminal at Milford Haven, Wales, jointly owned by Shell and Ancala Partners.
Dual-fuel engine: Engine running on both liquid and gaseous fuels (e.g., WinGD X-DF).
Dunkirk LNG: LNG import terminal at Loon-Plage, France, operated by Dunkerque LNG and commissioned in 2017.

E

Earthing system: Bonding and grounding arrangements at the manifold and along cargo piping to dissipate static electricity during cargo operations.
ECDIS gas carrier: Standard electronic chart display and information system installation, with no IGC-specific variation but central to navigation in LNG terminal approaches.
Edison LNG: Italian energy company operating small-scale LNG distribution from Ravenna terminal.
El Paso Paul Kayser: 125,000 cubic meter LNG carrier that ran aground in the Strait of Gibraltar in June 1979 without loss of cargo containment.
Electric propulsion LNG: Propulsion arrangement on DFDE and TFDE LNG carriers where electric motors drive the propeller shaft.
Emergency shutdown: Automatic system that closes manifold valves and stops cargo pumps to halt transfer in the event of unsafe conditions.
Engie Zeebrugge: 5,000 cubic meter LNG bunker vessel delivered in 2017 and based at Zeebrugge, Belgium.
ESD: Emergency Shutdown valve at the ship-shore interface.
ESD link: Hardwired or fiber-optic connection between ship and shore enabling synchronized emergency shutdown during cargo operations.
Ethylene capable carrier: LPG carrier with Type C tanks and materials suitable for carrying ethylene at minus 104 degrees Celsius.
Ethylene Carrier: Smaller IGC Type 2G vessel transporting ethylene at minus 104 degrees C.
Excelerate Energy: Texas-based FSRU pioneer with multiple regasification vessels operating worldwide.
Export terminal: Coastal facility for liquefying natural gas and loading it onto LNG carriers, such as Sabine Pass or Corpus Christi.

F

Filling Limit: IGC maximum loading volume (typically 98.5 percent at reference temperature) preventing overfill.
Fire integrity: SOLAS II-2 standard of resistance for divisions between compartments.
First barrier: Synonym for primary barrier in membrane LNG cargo tanks.
Flag of convenience: Flag of a state with open registration policy.
Flame screen: Mesh in cargo tank vent outlets that arrests flame propagation into the tank.
FLNG: Floating liquefied natural gas facility; liquefaction and storage at sea.
Floating LNG: Offshore LNG production, liquefaction, storage, and offloading facility such as Shell Prelude or Petronas PFLNG Satu.
Floating storage and regasification unit: Full term for FSRU, a vessel converted or built to receive LNG cargoes and regasify them for sendout to shore.
Floating storage unit: Vessel used solely for LNG storage without regasification, often a converted LNG carrier.
Forced vaporization: Use of LNG vaporizers to produce additional gas for engine consumption when natural BOG is insufficient.
Freeport LNG: LNG export terminal on Quintana Island, Texas, operated by Freeport LNG Development with first cargo in 2019.
FSRU: Floating storage and regasification unit for LNG import.
FSU: Floating storage unit; tanker hull used for storage only.
Fully pressurized LPG carrier: Small LPG vessel typically up to 7,500 cubic meters with Type C pressure tanks carrying cargo at ambient temperature and elevated pressure.
Fully refrigerated LPG carrier: Large LPG vessel with prismatic Type A tanks carrying cargo at near atmospheric pressure and design temperature of minus 48 degrees Celsius for propane.

G

Gas as fuel: Use of cargo vapor or forced vaporized cargo as engine fuel under IGC Code Chapter 16, distinct from the more general IGF Code.
Gas combustion unit: Onboard burner that disposes of excess BOG when consumption by main and auxiliary engines is insufficient.
Gas detection: Fixed or portable detectors for hydrocarbons, oxygen, hydrogen sulphide, and CO in machinery and cargo spaces.
Gas free: Condition of a cargo tank verified by measurement to contain less than the permissible flammable and toxic vapor levels for entry.
Gas Trial: Sea trial including first cool-down, gas-up, and cargo machinery testing during newbuild commissioning.
GasLog Ltd: Greek LNG carrier owner formerly listed in New York, operating a fleet of TFDE and two-stroke LNG vessels.
Gassing-up: Replacement of inert gas in cargo tanks with cargo vapor prior to cooldown and loading.
Gate terminal: LNG import and small-scale distribution terminal on the Maasvlakte at Rotterdam, the Netherlands.
Gauging system: Cargo tank level measurement equipment, typically using float, radar, or capacitance technology integrated into the CTS.
Gibraltar LNG: Small-scale LNG storage and regasification facility at Gibraltar serving the power station.
Glycol heater: Heat source used to control hold space humidity and prevent condensation on cold cargo tank surfaces.
Golar LNG: Bermuda-based LNG shipping and FLNG company listed on Nasdaq.
Gravity-based structure terminal: Fixed concrete structure standing on the seabed used for offshore LNG regasification, exemplified by Adriatic LNG.
GTT: Gaztransport and Technigaz, French engineering company that licenses membrane LNG containment systems.
GTT Mark III: GTT membrane LNG containment system using stainless steel primary barrier with corrugations on insulation panels.
GTT Mark III Flex+: Membrane containment with stainless primary.
GTT Mark V: Latest GTT membrane system combining stainless steel primary barrier and Invar secondary barrier.
GTT NO96: GTT membrane LNG containment system using Invar primary and secondary barriers with plywood boxes filled with perlite.
GTT NO96 GW: NO96 variant using reinforced polyurethane foam insulation boxes in place of perlite-filled plywood for improved BOR.
GTT NO96 Max: Further evolution of NO96 with optimized insulation for very low boil-off rate.

H

Handygas: LPG carrier size class of approximately 13,000 to 22,000 cubic meters serving regional fully refrigerated trades.
Heat leak: Heat ingress from environment into cargo tank insulation that drives BOG generation.
Heel: Transverse inclination of the vessel.
Hi-Hi Level Alarm: 98.5 percent or as set by IGC; auto-trip of loading via ESD.
Hoegh LNG: Norwegian LNG shipping and FSRU operator with a fleet of regasification vessels deployed globally.
Hull-cargo interface: Region where cargo tanks transfer loads to hull structure, critical for Moss and SPB tanks.

I

IGC Code: International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk.
IGC Code 2016 edition: Comprehensive revision of the IGC Code applicable to gas carriers built on or after 1 July 2016 with grandfathering provisions for earlier vessels.
IGF Code: International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels.
IHI Corporation: Japanese heavy industries group that developed the SPB self-supporting prismatic IMO Type B containment system.
IMO Type A tank: Independent prismatic cargo tank designed using classical ship structural codes, with a full secondary barrier and design vapor pressure below 0.7 bar, common in fully refrigerated LPG carriers.
IMO Type B tank: Independent cargo tank designed using detailed analysis with crack propagation evaluation, requiring only a partial secondary barrier, exemplified by Moss spheres and SPB tanks.
IMO Type C tank: Independent cargo tank designed as a pressure vessel under pressure vessel codes, with no secondary barrier required, used in semi-refrigerated and pressurized LPG and small-scale LNG service.
Import terminal: Coastal facility for receiving LNG cargoes, storing them in cryogenic tanks, and regasifying for pipeline sendout.
Independent tank: Cargo tank that is structurally separate from the ship hull, transferring loads only at defined support points.
Inerting: Replacing tank atmosphere with inert gas (N2, IG) below 8% O2 for tankers, 5% for chemicals.
Insulation space: Annular space between primary and secondary barriers in membrane LNG tanks, monitored for hydrocarbon leakage.
Interbarrier space: Space between primary and secondary barriers in any independent or membrane gas containment system, monitored under IGC Code Chapter 9.
Invar: 36 percent Ni iron alloy with very low CTE used as primary and secondary membrane in NO96 systems.
Isle of Grain LNG: LNG import terminal on the Isle of Grain in Kent, England, operated by National Grid Grain LNG.

J

Jamnagar: Indian port city in Gujarat with significant LPG import and refining infrastructure, served by VLGCs and MGCs.
JERA: Japanese power generation joint venture between TEPCO and Chubu Electric, one of the largest LNG buyers in the world.

K

K-Line: Kawasaki Kisen Kaisha, major LNG carrier operator with Moss and membrane fleet.
Kairos: 7,500 cubic meter LNG bunker vessel operated by Nauticor for Northern European fueling services.
Kawasaki Heavy Industries: Japanese shipbuilder with a history of constructing Moss-type LNG carriers.
KC-1: Korean Gas/Hyundai/Samsung/DSME Korean membrane CCS introduced on SK Serenity and Spica.
Knutsen OAS Shipping: Norwegian owner of LNG carriers operating predominantly under long-term charters, often referenced as Knutsen LNG.
KOGAS: Korea Gas Corporation, terminal operator and licensor of KC-1 membrane system.

L

Laden voyage: Voyage performed with revenue cargo.
Latent heat of vaporization: Energy required to vaporize a unit mass of LNG, approximately 510 kilojoules per kilogram for methane at atmospheric pressure.
LBV: LNG bunker vessel, a small-scale LNG carrier configured for ship-to-ship LNG fuel delivery.
Liquefied natural gas: Natural gas cooled to approximately minus 162 degrees Celsius at atmospheric pressure, reducing its volume by a factor of approximately 600.
Liquefied petroleum gas: Propane, butane, or mixtures thereof carried at low temperature, elevated pressure, or both, depending on vessel type.
LNG: Liquefied natural gas; ~-162 C, near atmospheric pressure.
LNG bunker vessel: Dedicated LNG bunkering ship.
LNG Carrier: Vessel carrying liquefied natural gas at -162°C.
LNG Carrier Loading Rate: Volumetric rate at which LNG is transferred during loading, typically 10,000 to 14,000 cubic meters per hour at modern export terminals.
LNG Gemini: 125,000 cubic meter LNG carrier involved in the 1979 cargo leak incident at Cove Point, Maryland, where vapor migration into an electrical substation led to a fatal explosion ashore.
LNG Heel: Residual liquid kept on board to maintain tank temperature.
Loading arms: Articulated rigid pipes at the terminal jetty used to connect to the ship manifold for cargo transfer.
Low duty compressor: BOG compressor with relatively low discharge pressure used for forwarding gas to engines or vapor return to shore.
Low pressure dual fuel: Engine category that injects gas at low pressure into the cylinder during the compression stroke, including the Wartsila X-DF series.
LPG carrier: Specialized ship designed to transport liquefied petroleum gas in bulk under the IGC Code.

M

MAN B&W ME-GI: Dual fuel two stroke engine burning LNG with high pressure gas injection.
Manifold: Pipe assembly at the ship side where bunker hoses connect.
Maran Gas Maritime: Greek LNG shipping company part of the Angelicoussis Group, operating a large fleet of LNG carriers.
Materials of construction: IGC Code Chapter 6 requirements specifying low-temperature steels, aluminum alloys, and nickel steels for cargo tanks based on design temperature.
MEGI: MAN ME-GI gas-injection engine, common on Q-Flex retrofits, US-built LNGCs, and many post-2016 newbuilds.
Membrane containment: Cargo containment system in which the cargo load is supported by the inner hull through thin metallic primary and secondary membranes and load-bearing insulation.
Membrane LNG carrier: LNG carrier using a GTT membrane containment system in cargo tanks.
MGC: Mid-size Gas Carrier of approximately 22,000 to 40,000 cubic meters, common in LPG and ammonia trades.
Mid-Scale LNG Carrier: Capacity 18,000 to 100,000 m3, typically Type C IMO tanks; serving regional trade.
Mitsui OSK Lines: Japanese shipping major with a large LNG and LPG fleet, commonly abbreviated MOL.
MOL: Mitsui O.S.K. Lines, now part of Ocean Network Express.
Montoir LNG: LNG import terminal at Montoir-de-Bretagne, France, operated by Elengy.
Moss Maritime: Norwegian designer of the Moss spherical IMO Type B LNG containment system.
Moss sphere: Self-supporting spherical aluminum IMO Type B cargo tank developed by Moss Maritime.
Moss-type LNG carrier: LNG carrier with Moss spherical containment, recognizable by the hemispherical tank covers protruding above the main deck.
Mossmorran: Natural gas liquids fractionation complex in Fife, Scotland, supplying ethylene feedstock by gas carrier from the associated Braefoot Bay marine terminal.
Mostefa Ben Boulaid: LNG carrier named after the Algerian revolutionary; the 2004 Skikda incident was an explosion at the onshore liquefaction plant, not on a vessel.

N

Nakilat: Qatar Gas Transport Company, owner of the Q-Flex and Q-Max LNG carriers serving Qatari LNG exports.
Natural gas: Hydrocarbon gas mixture, primarily methane, that is liquefied for transport as LNG.
Nitrogen generator: Onboard plant producing pressurized nitrogen for inerting and barrier space purging.
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 Max: GTT NO96 evolution providing optimized insulation for very low boil-off performance.
NYK: Nippon Yusen Kaisha, Japanese shipping major with extensive LNG and LPG fleets.

O

Otto cycle dual fuel: Spark-ignited gas-burning combustion cycle used in low-pressure dual-fuel engines such as the Wartsila X-DF series.
Overfill protection: Independent high-level alarm and shutdown system that prevents tank overfilling beyond the IGC Code filling limit.

P

Pantheon Tankers: Greek tanker owner with interests in LPG and gas shipping.
Partial Reliquefaction: LNG reliquefaction unit handling part of BOG, balance burned in engines; common on MEGI carriers.
Pipeline sendout: Regasified LNG discharged from a terminal into the high-pressure natural gas grid.
Plaquemines LNG: Venture Global LNG export terminal in Plaquemines Parish, Louisiana, with first cargoes shipped in 2024.
Pre-Cooling: General term covering tank cool-down with LNG spray nozzles before bulk transfer.
Pressure relief valve: Spring-loaded valve that opens at set tank pressure to vent cargo vapor to the vent mast.
Primary Barrier: Innermost CCS layer in contact with LNG, e.g. 1.2 mm corrugated stainless on Mark III.
Prismatic tank: Non-cylindrical tank with planar faces, used in IMO Type A and SPB Type B containment.
Process pressure vessel: Pressure vessel forming part of the cargo handling system, governed by IGC Code Chapter 5.
Propulsion redundancy: Twin-engine, twin-shaft, or twin-power-train arrangement common on modern LNG carriers to maintain availability.

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.
QatarEnergy LNG: Successor to Qatargas and RasGas, the integrated Qatari LNG producer.
Qatargas: Qatari state-owned LNG marketing entity, now part of QatarEnergy LNG.

R

Reference Temperature: Standard temperature for LNG volume reporting, typically minus 161.5 degrees C per GIIGNL.
Reliquefaction plant: BOG handling unit on LNG carriers.
Rollover LNG: Sudden mixing of stratified LNG layers of different density, causing rapid vapor release.

S

Sabine Pass LNG: Cheniere Energy LNG export terminal in Cameron Parish, Louisiana, the first major US lower-48 LNG export facility with first cargo in 2016.
Safety relief valve: Pressure relief device protecting cargo tanks and pressure piping.
Saturated Vapor Pressure: Equilibrium vapor pressure at a temperature.
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.
Secondary insulation: Layer of insulation between secondary barrier and inner hull in membrane LNG containment.
Self-supporting prismatic tank: SPB tank, an IMO Type B prismatic independent tank developed by IHI Corporation.
Semi-pressurized LPG carrier: LPG carrier with Type C tanks operating at intermediate pressure and temperature, typically 5 to 7 bar.
Semi-refrigerated LPG carrier: Synonym for semi-pressurized LPG carrier emphasizing the intermediate temperature regime.
Semi-refrigerated semi-pressurized: Combined SR/SP designation for LPG carriers operating Type C tanks at moderate pressure and temperature.
Ship-shore link: Communication link between a gas carrier and the terminal supporting voice and ESD signaling during cargo operations.
Shipowner LNG: Generic term covering specialized LNG carrier owners including Maran Gas, GasLog, Nakilat, NYK, MOL, K Line, BW LNG, Cool Company, and Knutsen.
Skikda LNG plant: Algerian onshore liquefaction plant where a January 2004 explosion in a steam boiler destroyed three liquefaction trains, an onshore event distinct from any vessel incident.
Sloshing: Dynamic liquid motion causing impact pressures on membrane; restricts partial fills 10 to 70 percent on many carriers.
Small-scale LNG carrier: LNG carrier in the approximate range of 1,000 to 30,000 cubic meters serving short-sea, bunker, and distribution markets.
South Hook LNG: LNG import terminal at Milford Haven, Wales, jointly owned by QatarEnergy, ExxonMobil, and TotalEnergies.
SPB: Self-supporting Prismatic IMO Type B containment system developed by IHI.
Spherical tank: Moss-type IMO Type B aluminum cargo tank with hemispherical geometry.
Spray Pump: Small deepwell pump in pump tower delivering LNG for cool-down spray and forcing vaporizer.
SS LNG carrier: Steam-ship LNG carrier propelled by steam turbines burning BOG and heavy fuel oil in boilers, dominant in the global LNG fleet from the 1970s to the early 2000s.
Steam turbine LNG carrier: LNG carrier with conventional dual-fuel steam plant comprising boilers and a main turbine.
STS transfer: Ship-to-ship transfer of cargo, used for LNG bunkering and LNG reloading from FSRUs.

T

TFDE: Tri-Fuel Diesel-Electric propulsion using medium-speed engines capable of running on natural gas, marine diesel oil, or heavy fuel oil.
Thermal insulation: Layered insulation system maintaining cryogenic cargo temperature and minimizing BOR.
Total head pump: Cargo pump rated by total developed head used during discharge to the terminal.
Tri-fuel engine: Engine able to consume natural gas, marine diesel oil, and heavy fuel oil; the basis of TFDE propulsion.
Trim: Difference between forward and aft drafts.
Two-stroke dual-fuel: Slow-speed two-stroke engine capable of running on gas or liquid fuel, including MAN B and W ME-GI and Wartsila X-DF series.

U

Ullage: Empty space above liquid cargo in a tank.
Underdeck piping: Cargo piping routed inside a trunk deck or under deck on some LPG vessels for thermal protection.
USCG LOI: US Coast Guard Letter of Intent required for foreign LNG carriers calling at US LNG terminals.

V

Vacuum line: Vapor return line operating below atmospheric pressure used in some LPG cargo systems to manage tank pressure during discharge.
Vapor return line: Cargo gas return between ship and shore on tankers/gas carriers.
Vent mast: Tall structure venting pressure relief valve discharge to a safe height above deck and accommodation.