LNG Cargo Containment Systems

Background

Two principal containment system architectures dominate the modern LNG fleet: Moss spherical tanks (developed by Moss Maritime, Norway) and GTT membrane systems (developed by Gaztransport & Technigaz, France). Moss tanks are independent self-supporting aluminium spheres mounted on the hull through cylindrical skirts; GTT systems use a thin invar or stainless-steel membrane supported by a layered insulation system that is itself supported by the ship’s inner hull. Each architecture has substantial advantages and tradeoffs covered in the operational sections below. Beyond these two dominant systems, IHI SPB (Self-Supporting Prismatic shape Type B) tanks and several less-common designs occupy specific market niches. The choice of containment system is the most consequential single decision in LNG carrier design, with substantial implications for boil-off rate, cargo flexibility, partial loading, sloshing behaviour, and operational profile.

The growth of the LNG trade since the 2010s has accelerated containment system development. The market growth from approximately 250 LNG carriers in 2010 to more than 700 in active service by 2024, plus the rapid expansion of small-scale LNG trade, FSRUs (Floating Storage and Regasification Units), and FLNG (Floating Liquefied Natural Gas) facilities, has driven substantial investment in containment system improvement. Modern containment systems achieve boil-off rates of 0.07-0.10% per day (compared to 0.15% on earlier vintages), enabling the substantial commercial advantage of LNG-as-fuel propulsion using boil-off gas plus efficient transport of the liquid cargo. The detailed engineering, regulatory framework, and operational practice are covered in the following sections.

Regulatory Framework

The international regulatory framework for LNG cargo containment combines the IMO IGC Code, IACS Unified Requirements, class society rules, and various flag state and port state regulations.

IGC Code (International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk) is the primary international code governing LNG carriers and other gas carriers. The current version, IGC Code 2014 (as amended by Resolution MSC.370(93) and subsequent amendments), is mandatory under SOLAS Chapter VII Part C. The Code covers:

• Ship survival capability and damage stability
• Cargo containment systems (Type A, B, C, and membrane)
• Process pressure relief (MARVS, Maximum Allowable Relief Valve Setting)
• Cargo handling equipment
• Personnel protection
• Fire safety
• Cargo operations safety

The IGC Code tank type categorisation is foundational:

• Type A tanks: prismatic tanks with conventional structural design and a complete secondary barrier, used historically for LPG, less common for LNG.
• Type B tanks: independent tanks with a partial secondary barrier (drip tray under specific portions). Moss spherical and IHI SPB tanks are Type B. Allowed because the highly engineered design and rigorous testing demonstrate very low probability of through-thickness cracking.
• Type C tanks: pressure vessels designed to ASME or equivalent codes. Common for small-scale LNG and for LPG. No secondary barrier required because the pressure-vessel design and material selection limit crack initiation.
• Membrane systems (sometimes called Membrane Type), the GTT designs operate within a separate IGC framework that allows the thin primary membrane to be supported by the hull through an insulation system, with a complete secondary barrier integrated into the insulation.

IACS Unified Requirements specifically applicable to LNG carriers include:

• IACS UR P3, Pressure vessel testing
• IACS UR L3, Loading manual and instrument
• IACS UR R6, Periodical surveys of liquefied gas carriers
• IACS UR Z23, Hull periodical surveys for liquefied gas carriers
• IACS UR Z18, Periodical surveys of equipment for use in dangerous areas

Class society rules (DNV, Lloyd’s Register, ABS, Bureau Veritas, ClassNK, RINA, KR) implement IGC Code requirements with detailed engineering specifications. Each major class society has substantial expertise in LNG containment system approval, with specific notations such as DNV’s GAS notation, Lloyd’s CCS (Cargo Containment System), ABS’s PMA-LNG, and others.

SIGTTO (Society of International Gas Tanker and Terminal Operators) provides industry guidance for LNG operations. Key SIGTTO publications include:

• SIGTTO LNG Operations in Port Areas
• SIGTTO LNG Bunkering Operations
• SIGTTO LNG Custody Transfer Handbook
• Various other operational guidance documents

Flag state and port state regulations add jurisdiction-specific requirements for LNG carriers operating in their waters. Major LNG export terminals (Qatar, Australia, USA, Russia, Malaysia, Algeria) and import terminals (Japan, China, Korea, Europe, India) each have specific approach, navigation, and operations requirements.

ABS-Class LNG carriers operating to US ports also face USCG regulations 33 CFR Part 154 (Facilities Transferring Oil or Hazardous Material in Bulk) and 46 CFR Part 154 (Liquefied Gas Carriers).

Moss Spherical Tanks

Moss tanks are the original modern LNG containment system, developed by Norwegian designers in the 1970s and used on a substantial portion of the world LNG fleet.

Tank construction consists of a self-supporting aluminium alloy sphere (typically 5083 marine-grade aluminium) approximately 35-45 metres in diameter on standard-size carriers. The sphere is mounted on the ship through a cylindrical aluminium skirt that allows the tank to expand and contract thermally without imposing stress on the ship structure. The skirt connects to the ship at a single horizontal ring level, allowing the sphere to “float” thermally.

Tank insulation uses approximately 250-300 millimetres of polyurethane foam panels covering the entire sphere surface. The foam is protected by an outer aluminium foil vapour barrier and a glass-fibre-reinforced plastic (GRP) outer skin that handles thermal cycling and mechanical impacts. The insulation system maintains the cargo space at LNG temperature while preventing condensation on the outer hull structure.

Boil-off rate for modern Moss tanks: typically 0.10-0.15% per day at design conditions (full cargo, calm seas, design ambient). Modern Moss carriers with advanced insulation achieve 0.10% or below; earlier vintages typically 0.12-0.15%.

Key advantages of Moss tanks:

• No partial loading restrictions: Moss tanks tolerate partial loading without sloshing concerns, allowing flexible cargo operations.
• Robust against fatigue: the spherical geometry and aluminium construction provide excellent fatigue resistance.
• Visible inspection: the spherical structure allows comprehensive surface inspection.
• Type B classification: requires only partial secondary barrier (drip tray under specific zones), simplifying construction.
• Independent from hull: tank movement decoupled from hull deflection.

Key disadvantages:

• Higher height profile: spheres typically protrude above the upper deck, creating substantial windage and higher centre of gravity. Distinctive “bumps” of Moss carriers are immediately recognisable.
• Lower volumetric efficiency: spherical tanks pack less LNG volume per ship displacement than prismatic alternatives.
• Higher capital cost historically.
• Additional steel required for cofferdams and supporting structures.

Typical Moss carrier configurations: 4 or 5 spherical tanks, total cargo capacity 125,000-160,000 cubic metres. Major Moss tank shipbuilders include Mitsubishi Heavy Industries, Kawasaki Heavy Industries, IHI (Japan), and Hyundai Heavy Industries (Korea, with Moss licence).

GTT Membrane Systems

GTT (Gaztransport & Technigaz, France) developed the membrane containment systems that have come to dominate modern LNG carrier construction. The two main GTT systems are Mark III and NO96 (with subsequent variants).

Mark III Flex

Mark III Flex is the current generation of GTT’s stainless-steel membrane system. The principal components:

• Primary membrane: 1.2 millimetre stainless steel (304L) corrugated sheet directly contacting the cargo. The corrugations accommodate thermal contraction without buckling. The membrane is welded to form a continuous gas-tight liquid container.
• Primary insulation: 230-300 millimetres of polyurethane foam in plywood boxes, supporting the primary membrane and providing thermal insulation.
• Secondary membrane: 0.7 millimetre triplex (aluminium-glass-aluminium laminate) providing the complete secondary barrier required by IGC Code.
• Secondary insulation: another 100-150 millimetres of polyurethane foam in plywood boxes, between the secondary membrane and the inner hull.

Boil-off rate: 0.10-0.085% per day for current Mark III Flex+ designs.

Key features:

• Volumetric efficiency: the prismatic geometry maximises cargo capacity within the ship’s hull form.
• Lower windage: tanks fit within the hull, no above-deck profile.
• Modular installation: foam-and-plywood boxes are pre-fabricated and installed during construction.
• Continuous secondary barrier: as required by IGC Code for Type B equivalent.
• Lower height profile compared to Moss.

Manufacturing at major shipbuilders (Hyundai Heavy Industries, Daewoo, Samsung Heavy Industries, Hudong-Zhonghua) under GTT licence. Mark III Flex is the dominant new-build LNG carrier containment system as of 2024.

NO96

NO96 is GTT’s earlier and more traditional invar membrane system. The principal components:

• Primary membrane: 0.7 millimetre invar (36% nickel-iron alloy with very low thermal expansion coefficient). The flat invar membrane requires no corrugations because invar’s thermal expansion is so low.
• Primary insulation: perlite-filled plywood boxes, 230-300 millimetres thick.
• Secondary membrane: 0.7 millimetre invar (same material as primary).
• Secondary insulation: perlite-filled plywood boxes.

NO96 was historically the dominant GTT system through the 1990s and early 2000s. Newer variants include NO96 GW (improved insulation), NO96 L03 (L03 boxes), NO96 Super+, and others. The system remains in service on a substantial portion of the existing fleet.

Boil-off rate: typically 0.12-0.15% per day for older NO96 vessels; 0.10% for the current NO96 GW+ variant.

Comparison Mark III vs NO96:

• Mark III Flex: stainless-steel corrugated membrane with foam insulation. Lower boil-off, lower cost, dominant in new construction.
• NO96 GW: invar flat membrane with perlite insulation. Different cost-benefit profile, less common in new orders but extensive existing fleet.

IHI SPB Tanks

IHI SPB (Self-Supporting Prismatic shape Type B) tanks are an alternative independent-tank design developed by IHI Corporation (Japan). The system uses self-supporting prismatic tanks of aluminium alloy construction.

Key features:

• Prismatic shape: similar volumetric efficiency to membrane systems while maintaining Type B classification (independent tank, partial secondary barrier).
• Aluminium construction: similar to Moss tanks but in prismatic shape.
• Internal structural members: required to maintain tank shape under cargo loading.
• Sloshing-resistant: structural members partition the tank, reducing free-surface effects.

SPB tanks are uncommon, fewer than ten LNG carriers use SPB tanks. The system is more common on smaller-scale gas carriers and FLNG units. The principal advantage is partial-loading capability without sloshing damage, useful for variable-cargo operations.

Type C Pressure Vessel Tanks

Type C tanks are pressure-vessel-designed cargo tanks constructed to ASME or equivalent pressure vessel codes. Type C is the dominant containment system for LPG and small-scale LNG.

Key features:

• Pressure vessel design: typically cylindrical or bilobe construction with hemispherical heads.
• Higher design pressure: 4-8 bar typical, allowing pressure-buildup operations during voyage.
• No secondary barrier required: the pressure-vessel design and material selection (e.g., 9% nickel steel for LNG, carbon steel for LPG) provide adequate primary containment.
• Compact design: efficient for small and medium-scale gas carriers.
• Limited capacity: practical limit ~30,000 cubic metres per tank due to weight and stress considerations.

Type C tanks dominate:

• Small-scale LNG carriers (1,000-30,000 cubic metres)
• LPG carriers (most sizes)
• Ethylene carriers
• CO2 transport ships (emerging market)
• Inland waterway LNG bunker barges

Boil-Off Gas (BOG) Management

LNG inevitably warms slightly during transport, with some cargo evaporating to maintain thermodynamic equilibrium at the tank pressure. The resulting boil-off gas (BOG) must be managed.

BOG generation rate is expressed as a percentage of cargo per day:

• Modern membrane (Mark III Flex+): 0.07-0.10% per day at full cargo
• Modern Moss: 0.10-0.15% per day
• Older vintages: 0.15-0.20% per day

For a 170,000 cubic metre cargo, 0.10% per day BOG = 170 cubic metres of liquid LNG per day = approximately 100 tonnes of natural gas vapour per day.

BOG management options:

BOG to engine room (use as fuel)

The most common modern arrangement: BOG flows from cargo tanks through compressors to the main engine and auxiliary engines as fuel. Modern dual-fuel diesel-electric engines (DFDE), dual-fuel slow-speed two-stroke engines (MAN B&W ME-GI, WinGD X-DF), and dual-fuel four-stroke engines (Wartsila DF) all accept BOG as primary fuel.

Advantages: BOG is essentially free fuel, dramatically improving voyage economics.

BOG to gas combustion unit (flaring)

Excess BOG that cannot be consumed by engines is sent to a gas combustion unit (GCU) for safe combustion. GCUs typically have capacity to handle 2-3 times normal BOG generation, providing margin for cargo conditioning operations.

BOG to reliquefaction plant

Some LNG carriers have onboard reliquefaction plants that compress and cool BOG back to liquid for return to cargo tanks. Reliquefaction:

• Eliminates cargo loss
• Adds substantial capital cost (reliquefaction plant several million USD)
• Requires substantial electrical power (megawatts)
• Common on Q-Flex and Q-Max vessels (ships designed for slow-steaming)

The gas carrier BOG reliquefy calculator addresses reliquefaction operations.

Tank pressure management

BOG generation is coupled with tank pressure. Higher tank pressure (allowed up to MARVS, Maximum Allowable Relief Valve Setting per IGC Code) reduces BOG by raising the LNG boiling point. The IGC MARVS check calculator and IGC MARVS example calculator address operational pressure management.

Typical operating pressures:

• Atmospheric tanks (Moss, GTT membrane): MARVS 0.25 bar gauge
• Pressure vessels (Type C): MARVS 4-7 bar gauge

Cargo Loading and Discharge

LNG cargo operations are highly specialised due to cryogenic temperature and safety requirements.

Cooling Down Operations

Before loading, empty cargo tanks must be cooled down to LNG temperature (-162°C). Cooling proceeds through stages:

1. Inerting with nitrogen to displace air (reducing oxygen below 5%)
2. Initial cool-down with LNG vapour to about -120°C
3. Final cool-down with LNG liquid spray to -162°C

Cool-down typically takes 12-24 hours depending on tank size and temperature differential. Improper cool-down can cause thermal shock damage to insulation.

Loading

Loading is performed via dedicated cargo manifolds with insulated cryogenic loading arms. Loading rates typically:

• Small carriers (10,000-30,000 m³): 1,500-3,000 m³/h
• Medium carriers (90,000-160,000 m³): 8,000-12,000 m³/h
• Large carriers (170,000-180,000 m³): 12,000-15,000 m³/h

During loading, BOG is returned to shore via vapour-return arms, maintaining tank pressure. The LNG loading rate calculator addresses LNG bunker rate considerations parallel to cargo loading.

Discharge

Discharge is essentially the reverse of loading, with cargo pumps (submerged in cargo tanks) pumping LNG to shore. Modern submerged cargo pumps:

• Capacity: 1,000-2,000 cubic metres per hour each
• Multiple per tank (typically 2-3) for redundancy
• Submerged motor design for cryogenic operation

Heel Management

Most LNG carriers retain a “heel” (small quantity of LNG) at end of cargo voyage to:

• Maintain tank temperature for next loading
• Provide BOG fuel for return voyage
• Avoid full warm-up that would require extensive cool-down at next port

Heel management is a balance between commercial cargo (sold at destination) and operational utility (fuel for return).

Tank Cleaning and Inspection Operations

Periodic operations require tanks to be warmed and inspected:

Warm-up: progressive heating from LNG to ambient via inert gas circulation. Takes 3-7 days depending on tank size.

Gas-freeing: replacement of inert gas with air, allowing personnel entry. Atmosphere monitoring throughout.

Tank entry and inspection: by qualified personnel for class society survey, modification, or repair.

Re-inerting and cool-down: reverse of warm-up, taking another 3-7 days.

Major class society surveys typically occur every 5 years and require tank entry. The total period of tank-out-of-service for class survey can be 2-4 weeks.

Sloshing Phenomena

Sloshing is the dynamic motion of cargo liquid within partially-filled tanks under ship motion. Sloshing pressures can damage containment systems if not properly managed.

Membrane systems are particularly sensitive to sloshing because the thin membrane has limited ability to absorb impact pressure spikes. GTT-developed sloshing prediction tools and operational restrictions limit partial-loading conditions.

Filling level restrictions for membrane tanks typical:

• Fill level <10% (essentially empty for transport): allowed
• Fill level 10-70% (partial): restricted/prohibited under most conditions
• Fill level >70% (high fill): allowed
• Fill level >97% (full): allowed

These restrictions effectively prevent partial-loaded voyages on membrane LNG carriers, requiring either full or essentially empty cargo conditions.

Moss tanks are less sensitive to sloshing due to spherical geometry that spreads impact pressures. Moss carriers can typically operate at any fill level.

Type C pressure vessels with internal structural members (anti-sloshing baffles) are also relatively insensitive to sloshing.

The sloshing characteristic is one of the most consequential operational differences between containment system types. Cargo flexibility considerations often drive containment system selection.

Cargo Cooling Operations

LNG cargo operations include various cooling-related procedures.

Sub-cooling

LNG can be sub-cooled below its boiling point to reduce BOG generation. Sub-cooling is achieved by:

• Reliquefaction plant operation during voyage
• Spraying cold LNG over warmer LNG
• Reduced tank pressure operation (lowering boiling point temporarily)

Re-condensing

In some operations, BOG can be re-condensed by spraying it through cold liquid LNG, returning the gas to liquid state. This is done in:

• Onboard reliquefaction systems
• Loading operations with vapour return condensing

The tanker cargo cooling LNG calculator addresses cooling calculations specific to LNG.

Heat Leak Management

Tank insulation maintains low heat leak, but external factors affect actual performance:

• Ambient air temperature (tropics vs polar)
• Sea water temperature (affects double bottom heat leak)
• Wind effects (convection cooling on tank surfaces)
• Thermal short-circuits at tank attachments

Modern operational practice monitors tank temperature distribution, BOG generation rate, and heat leak through-put to identify any developing issues.

Cargo Containment System Survey

Class society surveys of cargo containment systems are mandatory at periodic intervals.

Annual surveys: external visual inspection where accessible.

Intermediate surveys: at 2.5-year intervals, with limited internal inspection.

Special periodical surveys: at 5-year intervals, with comprehensive inspection including tank entry. Major activities:

• Visual inspection of primary and secondary barriers
• NDT (non-destructive testing) of welds where indicated
• Insulation condition assessment
• Pump tower inspection
• Cargo handling equipment inspection
• Pressure relief valve testing

Continuous Class Survey schemes allow distributed inspection through the survey cycle, with chief engineer maintaining records and class surveyors verifying.

5-year hydrostatic testing of pressure-relief valves and piping systems.

The substantial scope of LNG carrier surveys reflects the cargo’s hazardous nature and the consequence of containment system failures. LNG carrier operators typically allocate significant time and budget to survey activities.

Operational Considerations

LNG carrier operations have specific considerations beyond general gas carrier operations.

Manning and Training

LNG carrier crews require specific training:

• IMO Model Course 1.04 (Gas Tanker Familiarisation)
• IMO Model Course 1.06 (Advanced Training for Liquefied Gas Tanker Cargo Operations)
• Gas tanker endorsements per STCW Section A-V/1-2

Crew training typically includes:

• Cargo containment system familiarisation
• Cryogenic handling procedures
• Emergency response (release scenarios)
• Cargo gas hazards (flammability, asphyxiation)
• Specific equipment operation

Senior officers (master, chief mate, chief engineer) require substantial gas tanker experience, typically 3-5 years of progressive gas tanker service before command-level appointment.

Emergency Response

LNG release scenarios require specific response:

Cargo tank release: contained by secondary barrier, controlled venting through pressure-relief system, isolation of cargo equipment.

Manifold leak: emergency release coupling (ERC) automatically separates cargo arms, isolating ship from shore facility.

Fire near LNG: water curtains, dry chemical, foam systems all maintained for emergency use.

Cryogenic exposure: medical kit and procedures for cryogenic burns, evacuation routes from cargo areas.

Cargo Documentation

LNG cargo documentation includes:

• Cargo Operational Plan (specific to voyage)
• Cargo Quantity Survey Report (custody transfer)
• Cargo Quality Certificate (composition analysis)
• Boil-off Gas Calculation Sheet
• Bunker Delivery Note (when LNG used as fuel)

LNG custody transfer is technically complex, with cargo quantity calculated from:

• Tank gauge readings (level, temperature)
• LNG composition analysis
• Pressure-temperature corrections
• Standard reference conditions (typically 15°C, 101.325 kPa)

The tanker calibration UTI tape calculator and tanker calibration portable gas meter calculator address calibration and measurement.

Specific LNG Carrier Configurations

Conventional LNG Carriers (130,000-180,000 m³)

The bulk of the LNG fleet is conventional carriers in the 130,000-180,000 cubic metre range. These vessels typically:

• Length 280-300 metres
• Beam 45-50 metres
• Draft 11-12 metres
• Speed 19-20 knots service
• Crew 25-30
• Two-stroke MAN ME-GI or WinGD X-DF dual-fuel main engine

Q-Flex and Q-Max (210,000-265,000 m³)

Qatari-built ships designed for the Qatar-to-major-import-markets trade. Distinguishing features:

• Increased size driven by economies of scale
• Onboard reliquefaction plant (maintaining cargo as liquid for slow-steaming)
• Larger crew accommodation
• Substantial capital cost

FSRU (Floating Storage and Regasification Units)

FSRUs are LNG carriers modified or purpose-built to provide LNG storage and regasification at the import terminal. Features:

• Permanent or semi-permanent moored at import location
• Onboard regasification plant (heat exchangers, etc.)
• Connected to shore gas grid via subsea or surface pipeline
• Provides flexibility avoiding shore-based regasification investment

FLNG (Floating Liquefied Natural Gas)

FLNG units are floating gas processing facilities producing LNG from offshore gas fields. Features:

• Substantial process plant onboard
• Cargo tanks for short-term storage before shuttle tanker offload
• Often very large (>100,000 m³ cargo, with 200,000+ m³ on largest)
• Operating in dynamic positioning or moored

LNG Bunker Barges and Vessels

Smaller LNG carriers (1,000-30,000 m³) provide bunker fuel to LNG-fuelled vessels. Type C pressure vessel containment dominates.

Future Developments

LNG cargo containment continues to evolve.

Larger Carriers

The ULNGC (Ultra Large Natural Gas Carriers) concept of 250,000-300,000 m³ is technically feasible and being explored.

Reduced Boil-Off

Continued improvement of insulation systems aims for 0.05% per day BOG, reducing operational costs.

Composite Materials

Investigation of composite materials for some non-pressure-bearing structural elements and insulation systems.

Carbon Capture from Cargo Vapour

Onboard carbon capture and storage from BOG combustion is being investigated for low-carbon LNG transport.

Alternative Containment Systems

Research continues on novel containment concepts:

• Glass-fibre composite outer skin
• Aerogel-enhanced insulation
• Active heat-pumping refrigeration

Conclusion

LNG cargo containment systems are among the most highly engineered systems in commercial shipping, combining cryogenic temperature handling, structural integrity under ship motion, low boil-off insulation, and operational practicality. The dominant Moss spherical and GTT membrane systems offer different tradeoffs, with membrane systems dominating new construction due to volumetric efficiency and lower height profile while Moss tanks retain advantages for partial-loading flexibility. The combination of comprehensive IGC Code regulation, IACS Unified Requirements, class society approval, and SIGTTO industry guidance produces the framework that LNG transport requires. Crew members and ship managers responsible for LNG carrier operations must understand the engineering principles, operational practices, and emergency response that together produce safe LNG transport. As the LNG trade continues to expand and as LNG-as-fuel adoption accelerates across the broader shipping industry, containment system technology continues to evolve, but the fundamental principle, safe containment of cryogenic LNG cargo, remains the central focus of gas carrier engineering.

Related Calculators

• Gas Carrier BOG Reliquefy Calculator
• IGC MARVS Check Calculator
• IGC MARVS Example Calculator
• Tanker Cargo Cooling LNG Calculator
• Tanker Bunkering LNG Calculator
• Tanker Calibration UTI Tape Calculator
• Tanker Calibration Portable Gas Meter Calculator
• IGC Argon Liquefied Calculator
• IGC Carbon Dioxide Liquefied Calculator
• IGC Hydrogen Liquefied Calculator
• IGC Nitrogen Liquefied Calculator

Related Wiki Articles

• LNG Carrier
• LNG as Marine Fuel
• LNG Fuel System
• Marine Inert Gas Systems
• Marine Cargo Tank Heating Systems
• Marine Cargo Pumps and Piping
• Marine Tank Gauging Systems
• Chemical Tanker
• IMDG Class 2 Gases
• Methane Slip Deep Dive

References

• IMO International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code 2014, Resolution MSC.370(93) and amendments)
• SOLAS Chapter VII Part C (Carriage of Liquefied Gases in Bulk)
• IACS Unified Requirement P3, Pressure vessel testing
• IACS Unified Requirement R6, Periodical surveys of liquefied gas carriers
• IACS Unified Requirement Z23, Hull periodical surveys for liquefied gas carriers
• SIGTTO Liquefied Gas Handling Principles on Ships and in Terminals (4th edition, 2016)
• SIGTTO LNG Operations in Port Areas
• SIGTTO LNG Bunkering Operations
• DNV Rules for Classification of Ships, Pt 5 Ch 7 Liquefied Gas Tankers
• ABS Guide for Building and Classing Liquefied Gas Carriers
• Lloyd’s Register Rules and Regulations for the Classification of Ships, Pt 7 Ships of Special Service
• USCG 33 CFR Part 154 (Facilities Transferring Oil or Hazardous Material in Bulk)
• USCG 46 CFR Part 154 (Liquefied Gas Carriers)