Gas carrier

"Gas tanker" redirects here. For the road vehicle, see tank truck.

A gas carrier, gas tanker, LPG carrier, or LPG tanker is a ship designed to transport LPG, LNG, CNG, or liquefied chemical gases in bulk.^[1] Gases are kept refrigerated onboard the ships to enable safe carriage in liquid and vapour form and for this reason, gas carriers usually have onboard refrigeration systems.^[2] Design and construction of all gas carriers operating internationally is regulated by the International Maritime Organization through the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk.^[3] There are various types of gas carriers, depending on the type of gas carried and the type of containment system, two of the most common being the Moss Type B (spherical) type and the membrane (typically GTT) type.^[4]

The tugboats Reid McAllister and McAllister Responder push the LPG tanker BW Volans into port at Marcus Hook, on the Delaware River.

Types

Fully pressurized gas carrier

Moss type LNG tanker

The seaborne transport of liquefied gases began in 1934 when a major international company put two combined oil/LPG tankers into operation.^[5] The ships, basically oil tankers, had been converted by fitting small, riveted, pressure vessels for the carriage of LPG into cargo tank spaces. This enabled transport over long distances of substantial volumes of an oil refinery by-product that had distinct advantages as a domestic and commercial fuel. LPG is not only odourless and non-toxic, it also has a high calorific value and a low sulphur content, making it very clean and efficient when being burnt.

Today, most fully pressurised oceangoing LPG carriers are fitted with two or three horizontal, cylindrical or spherical cargo tanks and have typical capacities between 20,000 and 90,000 cubic meters and Length overall ranging from 140 m to 229 m . New LPG Carrier ships are designed for dual-fuel propulsion system possessing the ability to utilize LPG or diesel fuel on a selective basis.^[6] Fully pressurized ships are still being built in numbers and represent a cost-effective, simple way of moving LPG to and from smaller gas terminals.

Semi-pressurised ships

Semi-pressurised ship Gaschem Jümme

These ships carried gases in a semi-pressurized/semi-refrigerated state.^[7] This approach provides flexibility, as these carriers are able to load or discharge at both refrigerated and pressurized storage facilities. Semi-pressurized/semi-refrigerated carriers incorporate cylindrical, spherical or bi-lobe shaped tanks carrying propane at a pressure of 8.5 kg/cm² (121 psi), and a temperature of −10 °C (14 °F).

22,000 cbm Semi-Refrigerated LPG Carrier Navigator Centauri transits Porpoise Bay

Ethylene and gas/chemical carriers

LEG carriers are the most sophisticated of the gas tankers and have the ability to carry not only most other liquefied gas cargoes but also ethylene at its atmospheric boiling point of −104 °C (−155 °F).^[8] These ships feature cylindrical, insulated, stainless steel cargo tanks able to accommodate cargoes up to a maximum specific gravity of 1.8 at temperatures ranging from a minimum of −104 °C to a maximum of +80 °C (176 °F) and at a maximum tank pressure of 4 bar.

Fully refrigerated ships

Fully refrigerated ship LPG/C Maersk Houston

They are built to carry liquefied gases at low temperature and atmospheric pressure between terminals equipped with fully refrigerated storage tanks.^[9] However, discharge through a booster pump and cargo heater makes it possible to discharge to pressurized tanks too. The first purpose-built, lpg tanker was the m/t Rasmus Tholstrup from a Swedish shipyard to a Danish design. Prismatic tanks enabled the ship's cargo carrying capacity to be maximised, thus making fully refrigerated ships highly suitable for carrying large volumes of cargo such as LPG, ammonia and vinyl chloride over long distances. Today, fully refrigerated ships range in capacity from 20,000 to 100,000 m³ (710,000 to 3,530,000 cu ft). LPG carriers in the 50,000–80,000 m³ (1,800,000–2,800,000 cu ft) size range are often referred to as VLGCs (Very Large Gas Carriers). Although LNG carriers are often larger in terms of cubic capacity, this term is normally only applied to fully refrigerated LPG carriers.

The main type of cargo containment system utilised on board modern fully refrigerated ships are independent tanks with rigid foam insulation. The insulation used is quite commonly polyurethane foam. Older ships can have independent tanks with loosely filled perlite insulation. In the past, there have been a few fully refrigerated ships built with semi-membrane or integral tanks and internal insulation tanks, but these systems have only maintained minimal interest. The large majority of such ships currently in service have been constructed by shipbuilders in Japan and Korea.

Liquefied natural gas carriers

Main article: LNG carrier

LNG-carrier Galea

The majority of LNG carriers are between 125,000 and 135,000 m³ (4,400,000 and 4,800,000 cu ft) in capacity. In the modern fleet of LNG carriers, there is an interesting exception concerning ship size. This is the introduction of several smaller ships of between 18,000 and 19,000 m³ (640,000 and 670,000 cu ft) having been built in 1994 and later to service the needs of importers of smaller volumes.

Compressed natural gas carriers

Main article: CNG carrier

Jayanti Baruna - CNG Cargo Carrier

Compressed natural gas (CNG) carrier ships are designed for transportation of natural gas under high pressure.^[10] CNG carrier technology relies on high pressure, typically over 250 bar (2900 psi), to increase the density of the gas and maximize the possible commercial payload. CNG carriers are economical for medium distance marine transport ^[11] and rely on the adoption of suitable pressure vessels to store CNG during transport and on the use of suitable loading and unloading compressors to receive the CNG at the loading terminal and to deliver the CNG at the unloading terminal.^[12]

Builders

These vessels are designed to transport liquefied gas. Builders of Liquefied Gas Carriers are:

• Daewoo Shipbuilding & Marine
• Damen Shipyard
• Hyundai Heavy Industries
• Hyundai Mipo
• Hyundai Samho Heavy Industries
• Jiangnan
• Kawasaki Shipbuilding Corporation
• Mitsubishi Heavy Industries
• Imabari Shipbuilding
• Japan Marine United Corporation

South Korea, Japan and China are the main countries where LPG tankers are built, with small numbers built in the Netherlands and Bangladesh.

Cargoes carried on gas carriers

• Butadiene
• Ethylene
• LPG
• LNG
• CNG
• Propylene
• Chemical gases such as ammonia, vinyl chloride, ethylene oxide, propylene oxide and chlorine.

Gas carrier codes

The International Maritime Organization (IMO) has established three principal regulatory frameworks for gas carriers, based on their build dates. These ensure safety, environmental protection, and update with evolving fuel technologies.

Gas carriers built on or after 1 July 1986 (IGC Code)

Gas carriers constructed from this date are governed by the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code), mandated under SOLAS and enforced through the International Certificate of Fitness carried onboard.^[13]

Recent amendments & developments:

• 1993: Major updates effective 1 July 1994.
• 2016: Amendments per IMO Resolution MSC.370(93) effective 1 January 2016.
• 2024–2025: Updates mandating digital tank and pressure monitoring, enhanced insulation standards, and integration for alternative fuels.^[14]
• Resolution MSC.475(102): Introduces updated requirements for welding certifications on tanks and pressure vessels, effective 1 January 2024.^[15]
• Resolution MSC.566(109): Adds new Chapter 16 enabling the use of liquefied ammonia as a bunker fuel on IGC-class vessels. Entry into force: 1 July 2026; voluntary adoption encouraged from adoption date.^[16]
• IMO CCC Sub‑Committee (Sept 2024): Issued interim guidelines for ammonia as fuel and completed IGC Code review. Work continues on hydrogen and low-flashpoint fuel provisions.^[17]

Gas carriers built between 1 July 1976 and 30 June 1986 (GC Code)

These vessels follow the "Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk" (GC Code), adopted in 1975.^[18]

• Voluntary under SOLAS, but often enforced domestically.
• Multiple amendments since 1975, with the last major revision in 1993.
• Compliance is frequently demonstrated via the Certificate of Fitness, even when not legally obligatory.

Gas carriers built before 1 July 1976 (Existing Ship Code)

Earlier vessels adhere to the 1976 Code for Existing Ships Carrying Liquefied Gases in Bulk.^[19]

• Less prescriptive than later codes, reflecting older technology.
• Not mandatory under SOLAS, but enforced through national laws and port state control.
• The Certificate of Fitness is often required by charterers and port authorities.

Overview of IGC Code 2024–2026 Key Updates

Topic	Description
Digital Monitoring & Data	Mandatory remote tank sensors for pressure, temperature, and volume; automated alerting systems.
Welding & Materials	New welding qualifications and testing protocols under MSC.475(102) from 1 Jan 2024.
Fuel Flexibility	Addition of Chapter 16 to permit ammonia use; applies to vessels built ≥2016, effective 1 Jul 2026.
Insulation & Safety	Tougher thermal insulation standards to reduce boil‑off; new venting configurations.
Enclosed Space & Emergency	Enhanced procedures for enclosed space entry, oxygen displacement, and escape routes.
Alternative Fuel Guidelines	Interim IMO guidance for hydrogen and other low-flashpoint fuels; implementation expected in 2025–2026.

Regulatory Path Forward

• Vessels built before 2016: Not required to adopt ammonia as fuel until 1 July 2026, but voluntary compliance encouraged.
• Capacity-building efforts by IMO to assist developing countries with implementation of digital and new safety technologies.^[20]

See also

• Transport portal
• Energy portal

• IGC Code
• IGF Code
• Ammonia as marine fuel
• Certificate of Fitness for the Carriage of Liquefied Gases in Bulk