Gas tankers transport liquefied gases such as LNG, LPG, and chemicals. There are four main types - fully pressurized, semi-pressurized, ethylene carriers, and fully refrigerated ships. LNG carriers are the largest, transporting LNG at -163°C, while smaller pressurized ships carry gases above their boiling points. Regulations like the IGC Code mandate safety systems to contain gases and protect ships from low temperatures, fires, and explosions during transport.

1. GAS TANKERS
GAS CARRIERS IN THE DEEP SEA
Hashan Rahubaddha
University of Moratuwa

2. SUB CATEGORIES
1. LNG Carrier 2. LPG Carrier 3. CNG Carrier
Liquefied Natural Gas
petroleum gas like Methane
Liquefied Petroleum Gas
petroleum gas like propane,
butane, propylene and butylene.
Compressed Natural Gas
transport Compressed Natural Gas

3. EVOLUTION OF GAS CARRIERS
1. Fully pressured gas tankers 2. Semi pressured gas tankers
4. Fully refrigerated ships 3. Ethylene and gas/chemical
carriers

4. All four ship types are still in use in the
industry.
❖The choice between these systems is a trade-off between initial cost,
cargo flexibility and operating cost.
❖Pressured systems are more economic for small ships and
refrigeration for large ones.

5. 1. Fully Pressurized Gas Carrier
• first generation of ships to carry liquefied gases.
• simplest of all gas carriers in terms of containment systems and
cargo-handling equipment
• carry their cargoes at ambient temperature
• smallest type of liquefied gas carrier afloat (up to about 5,000
cubic meters, although some are larger)
• Carry gas in cylindrical or spherical steel pressure vessels designed
to withstand pressures up to 20 bar
• They are not fitted with liquefaction plant and represent a simple
cost- effective means of transporting LPGs and chemical gases to
the smaller gas terminals

6. 2. Semi Pressurized Ships
• Constructed in the size range 1,500 to 30,000 𝑚3
• This type of gas carrier has evolved as the optimum means of
transporting the wide variety of gases, from LPG and VCM to
propylene and butadiene
• Carries gases in a semi-pressurized/semi-refrigerated state
• Due to further development semi- pressurized /fully refrigerated
gas carriers had started providing high flexibility in cargo
handling
• These are found in the busy coastal gas trades around the
Mediterranean and Northern Europe

7. 3. Ethylene and Gas/Chemical Carriers
• Most sophisticated of the semi-pressurized tankers
• Ethylene ships tend to be built for specific trades and have
capacities ranging from 1,000 to 30,000 𝑚3
• Designed to carry most liquefied gas cargoes except LNG
• Have the ability to carry not only most other liquefied gas
cargoes but can also transport ethylene fully-refrigerated at its
atmospheric pressure boiling point of -104°C
• The ships can load or discharge at virtually all pressurized and
refrigerated terminals, making them the most versatile gas
carriers in terms of cargo-handling ability

8. 4. Fully Refrigerated Ships
• Built to carry liquefied gases at low temperature and atmospheric
pressure between terminals equipped with fully refrigerated
storage tanks
• have prismatic-shaped cargo tanks fabricated from 3.5% nickel
steel, allowing the carriage of cargoes at temperatures as low as
48°C, marginally below the boiling point of pure propane
• The ships are typically in the range 15,000𝑚3 – 85,000 𝑚3, with
three common sizes for LPG/Ammonia trades of 30,000 𝑚3,
52,000 𝑚3 and 80,000 𝑚3.

9. 1st LNG CARRIER
Methane Pioneer was the first oceangoing liquefied natural gas tanker in the world. Built in 1945 as a cargo
ship named Marline Hitch, the vessel was renamed Don Aurelio and Nomarti before being rebuilt in 1958 for the
purpose of transporting LNG and operated between 1959 and 1972.

10. L.N.G CARRIERS
• LNG at its atmospheric pressure boiling point of–163 C
• Typically of between 120,000 and 130,000 𝒎 𝟑 capacity
• Has four to six tanks located along the center-line of the vessel
• Surrounding the tanks is a combination of ballast tanks, cofferdams and voids;
in effect, this gives the vessel a double-hull type design
• Normally dedicated to a specific project where they will remain for their entire
contract life
• A characteristic common to all is that they burn the cargo boil-off as fuel

11. C.N.G CARRIERS

12. L.P.G CARRIERS
• An LPG carrier is a gas carrier or a gas tanker ship designed for
transporting Liquefied Petroleum Gas (LPG) in bulk.
• Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also
referred to as simply propane or butane, are flammable mixtures
of hydrocarbon gases used as fuel in heating appliances, cooking
equipment, and vehicles

13. TYPES OF DIFFERENT CARGO
• Butadiene
• Ethylene
• LPG
• LNG
• Propylene
• Chemical gases such as ammonia, vinyl chloride, ethylene oxide, propylene oxide
and chlorine.

14. DIMENTIONS
Segments Capacity (m3) Length
Overall(m)
Breath(m) Draft(m) Speed(knots)
Very large gas
carrier(VLGC)
At least 60,000 226 35 11 16
Large gas
carrier(LGC)
40,000 -59,999 203 31 12 15
Medium gas
carrier(MGC)
20,000– 40,000 167 26 9 16
Small gas
carrier(SGC)
5,000 – 20,000 120 18 7 14
LPG TANKERS

15. L.N.G TANKERS
Cargo
capacity
(m3)
Dimensions
125,000 165,000 200,000
Length Overall(m) 260 273 316
Breath(m) 47.2 50.9 51
Depth(m) 26 28.3 30.2
Draft(m) 11 11.9 12.2
Number of tanks 4 4 5

16. STRUCTURE

17. STRUCTURE(cont.)

18. STRUCTURE(Cont.)

19. Uses of the structure

20. SPECIAL STRUCTURE

21. 1. Thermal Insulation Systems
Minimize heat flow into cargo
Protect tanker structure from the effect of low temperature
To control temperature of cargo
2. Thermal Insulation Systems
Prevent air entering to cargo system
Maintain closed cargo system
Not allowing vapor in to the atmosphere
Develop inflammable atmosphere

22. 3. Containment System of Gas Tankers
Self-supporting
Tank system sits on cradle
which separates it from
hull
Membrane
Tank is molded to hull
Prismatic
Self supporting tanks with
an inner and outer skin,
but tied into the main hull
structure

23. 4. RELIQUEFACTION AND BOIL-OFF
In order to facilitate transport, Natural is cooled down to approximately −163 °C (−261 °F) at atmospheric pressure,
at which point the gas condenses to a liquid.
The tanks on board an LNG carrier effectively function as giant Thermos to keep the liquid gas cold during storage.
No insulation is perfect, however, and so the liquid is constantly boiling during the voyage.

24. International Code for the Construction and
Equipment of Ships Carrying Liquefied Gases in
Bulk (IGC Code)
• The International Code of the Construction and Equipment of Ships
Carrying Liquefied Gases in Bulk (IGC Code), adopted by
resolution MSC.5(48),has been mandatory under SOLAS chapter VII
since 1 July 1986.

25. Extraction from SOLAS
20. Gas carrier is a cargo ship constructed or adapted and used for the
carriage in bulk of any liquefied gas or other products listed in either:
.1. chapter 19 of the International Code for the Construction and Equipment
of Ships Carrying Liquefied Gases in Bulk adopted by the Maritime
Safety Committee by resolution MSC.5(48) hereinafter referred to as "the
International Gas Carrier Code", as may be amended by theOrganization; or
.2. chapter XIX of the Code for the Construction and Equipment of Ships
Carrying Liquefied Gases in Bulk adopted by the Organization byresolution
A.328(IX), hereinafter referred to as "the Gas Carrier Code", as has been or
may be amended by the Organization;

26. “Gas carrier is a cargo ship constructed or adapted
and used for the carriage in bulk of any liquefied
gas or other products of a flammable
nature listed in chapter 19 of the International Gas
Carrier Code, as defined in regulation VII/11.1.”
Definition from SOLAS

27. I.G.C Code(International Gas Carrier Code)
• The purposes of these codes is to provide an international standard
for the safe transport by sea in bulk of liquefied gases and certain
other substances, by prescribing the design and construction
standards of ships involved in such transport and the equipment they
should carry so as to minimize the risk to the ship, its crew and to the
environment, having regard to the nature of the products involved.

28. Summary of I.G.C code (1993 edition)
1. Chapter 1 – General
2. Chapter 2 – Ship survival capability and location of cargo tanks
3. Chapter 3 – Ship arrangements
4. Chapter 4 – Cargo containment
5. Chapter 5 – Process pressure vessels and liquid, vapour and
pressure piping systems
6. Chapter 8 – Cargo tank vent systems
7. Chapter 13 – Instrumentation (gauging, gas detection)

29. Summary of I.G.C code (1993 edition) cont.
8. Chapter 14 – Personnel protection
9. Chapter 16 – Use of cargo as fuel
10. Chapter 17 – Special requirements
11. Chapter 19 – Summary of minimum requirements
For full version of I.G.C code -
http://www.imo.org/en/Publications/Documents/Supplements%20and
%20CDs/English/IGC_2003sup.pdf

30. Hazards on gas carriers
• Toxicity
• Flammability
• Frostbite
• Asphyxia

31. Gas Carrier Types
• Gas carriers are classed in three types based on hazard potential:
i) type 1G, designed to carry the most hazardous cargoes
ii) type 2G and 2PG, designed to carry cargoes having a lesser degree
of hazard
iii) type 3G, designed to carry cargoes of the least hazardous nature.