Natural gas is transported long distances as liquefied natural gas (LNG) via specialized carriers. Over the past 40 years, the size of LNG carriers has increased significantly to support growing demand. Early carriers held 0-36,000 cubic meters of LNG, while current largest carriers can hold over 220,000 cubic meters. Larger ships allow for more economical transport of LNG between countries without direct pipeline connections. Carrier designs have also evolved, with different containment systems developed to safely store larger volumes of cryogenic LNG cargo over long voyages.

1. Saurabh Agarwal(SPM-PDPU)’16
Why there is need of carrier by countries?
Natural gas is conventionally transferred via pipelines. However, offshore pipelines are less
viable than onshore and are thus generally limited to short to medium distances. Numerous
maritime countries such as Japan, Australia and Indonesia have no direct pipelines connecting
them to their natural gas trading partners. To transport natural gas across water it undergoes a
process known as cryogenic liquefaction. This creates LNG and reduces the volume of gas to one
600th of its original volume, making it feasible to transport the LNG in a specialized LNG
carrier. After the LNG is transported it can be regasified at an on-shore or off-shore
regasification terminal, stored for regasification at a later date.
SHIP DESIGN DEVELOPMENT:
1. Increasing LNG Ship Size:
Over the past 40 years there seen a drastically change in size of LNG ships which is increasing
day by day at an alarming rate.
What were the factors which led to the increase in the carrier sizes and how it
revolutionized the world as per the demanding population?
It doesn’t increased seemingly instead it soars as per the demand of varying countries which
encourage the LNG carrier manufacturer to design ship of larger size to accommodate huge
tonnes of liquified gas to be transported from one place to another. As this jump in size is driven
by project economics and which is enabled by technology improvements.

2. Saurabh Agarwal(SPM-PDPU)’16
As per the source it had been seen that carriers size changed but actually what was the evolution
of the carriers in the world. Henceforth in order to support this statement there are few of the
carriers which were designed by the manufacturer as per the demand arose by the buyers. Some
of them are mentioned below:
Vessel Type Typical Size(Cubic metre) Typical Length(Metre)
Small scale LNG 0-36000 137
Medium scale LNG 36000-90000 260
Lower Conventional LNG 90000-145000 277
Upper Conventional LNG 145000-209000 290
Q-flex LNG 209000-220000 315
Q-max LNG 220000+ 345
From the above figure it shows how significantly carrier sizes changed from the small scale LNG
to Q-max LNG. Below is an additional dimensions of the LNG carrier.
Capacity(cbm) 210000 217000 243000 267000
Length(m) 315 315 335 345
Beam(m) 50 50 51 55
Draft(m) 12 12 12 12
Depth(m) 27 27 27 28
2. Large LNG Design:
As the general arrangements of different size LNG carrier are very similar. Containment system
and propulsion choices results in some of the major differences in designs. For example, a gas
turbine ship requires less engine room space so that the engine room bulkhead can be moved aft
to allow more volume for cargo.
As a result, in the 243,000 cbm Gas Turbine electric propulsion (GT) LNG carrier design each
tank is about 1.5 m longer. This shift in cargo center of gravity prompted designers to explore the
possibility of locating the house forward to offset the shift in weight. Further arrangement
flexibilities are possible since with electrical propulsion systems, gas turbine generators and high
pressure gas can be located above the engine room.
LNG carriers larger than 200,000 cbm generally have 5 cargo tanks instead of 4. A four tank
design in the longer ships, results in longer individual tanks. This creates issues with sloshing in
the membrane tanks. In the Moss spherical tank design, 4 large tanks results in too wide a beam
for shipyard capability and for tank strength requirements Large LNG ships with SPB tanks
fitted with swash bulkheads, both longitudinally and transversely may be an acceptable solution.
Some work has been done on even larger LNG tankers, up to 400,000 cbm capacity, but at this
time these do not appear to fit the evolving trades for a number of reasons. These ships will
either have a very “distorted” hull form, very high beam/draft ratio, which will lead to propulsion

3. Saurabh Agarwal(SPM-PDPU)’16
inefficiencies, if the draft is kept low; or will have very restricted trading opportunities if given a
more normal draft for ships of this size. This work is still ongoing, but based on a high level
review of all factors involved, ship size, terminal requirements, shipbuilding restrictions, market
flexibility,etc. It seems that the next generation of LNG ships may settle down in the 225,000
cbm range.
LNG Vessel Types:
Different types of cargo containment systems:
--_
- _ Self-supporting LNG carrier
(a) Moss tanks (Spherical IMO type B LNG tanks)
(b) IHI (Prismatic IMO type B LNG tanks)
- Membrane tank LNG carrier
(c) TGZ Mark III
(d) GTT 96

4. Saurabh Agarwal(SPM-PDPU)’16
(a) Moss tanks (Spherical IMO type B LNG tanks):
The Norwegian company Moss Maritime designed this type of LNG carrier and due to
which it named it as MOSS Tank. As usual the Spherical IMO type B LNG tanks are
spherical in shape. Most of the Moss type vessels have 4 or 5 tanks.
The outside of the tank has a thick layer of foam insulation that is either fitted in panels
or in more modern designs wound round the tank. Over this insulation is a thin layer of
"tinfoil" which allows the insulation to be kept dry with a nitrogen atmosphere. This
atmosphere is constantly checked for any methane that would indicate a leak of the tank.
Also the outside of the tank is checked at 3 month intervals for any cold spots that would
indicate breakdown in the insulation.
Inside each tank there is a set of spray heads. These heads are mounted around the
equatorial ring and are used to spray Liquid LNG onto the tank walls to reduce the
temperature.
Tanks normally have a working pressure of up to 22 kPa (3.2 psi), but this can be raised
for an emergency discharge. If both main pumps fail then to remove the cargo, the tank's
safety valves are adjusted to lift at 1bar. Then the filling line which goes to the bottom of
the tank is opened along with the filling lines of the other tanks on board. The pressure is
then raised in the tank with the defective pumps which pushes the cargo into the other
tanks where it can be pumped out.

5. Saurabh Agarwal(SPM-PDPU)’16
(b) IHI (Prismatic IMO type B LNG tanks):
It was designed by Ishikawajima-Harima Heavy Industries, the self-supporting prismatic
type B (SPB) tank is currently employed in only two vessels. Type B tanks limit sloshing
problems, an improvement over Membrane LNG carrier tanks which may break due to
sloshing impact, therefore destroying the ship's hull. This is also of prime relevance for
FPSO LNG (or FLNG).
In addition, IMO type B LNG tanks can sustain internal accidental damage due for
example to internal equipment releases. This was incorporated into the design following
several incidents that occurred inside membrane LNG tanks.
(c) TGZ Mark III:
It was first designed by Technigaz,as this type of tank is categorized under membrane
type of carrier. The membrane consists of stainless steel with 'waffles' to absorb the
thermal contraction when the tank is cooled down. The primary barrier, made of
corrugated stainless steel of about 1.2 mm (0.047 in) thickness is the one in direct contact
with the cargo liquid (or vapour in empty tank condition).
From the inside of the tank outwards, the layers are:
∑ LNG
∑ Primary barrier of 1.2 mm thick corrugated/waffled 304L stainless steel
∑ Primary insulation (also called the interbarrier space)
∑ Secondary barrier within triplex membrane
∑ Secondary insulation (also called the insulation space)
∑ Ship's hull structure.

6. Saurabh Agarwal(SPM-PDPU)’16
(d) GT96;
It was first designed by Gaz Transport, the tanks consists of a primary and secondary thin
membrane made of the material Invar which has almost no thermal contraction. The
insulation is made out of plywood boxes filled with perlite and continuously flushed with
nitrogen gas. The integrity of both membranes is permanently monitored by detection of
hydrocarbon in the nitrogen. An evolution is proposed by NG2, with the replacement of
nitrogen by argon as the flushed inert and insulation gas. Argon has a better insulation
power than nitrogen, which could save 10% of boil-off gas.

7. Saurabh Agarwal(SPM-PDPU)’16
Companies which manufactures the LNG carriers:
∑ Shipbuilding & Marine Engineering (DSME)
∑ Hyundai Heavy Industries including Hyundai Samho Heavy Industries
∑ STX Offshore & Shipbuilding Co. Ltd (STX)
∑ Samsung Heavy Industries (SHI)
∑ Hudong Zhonghua Shipbuilding (Group) Co. (HZ)
∑ Kawasaki Heavy Industries (Kawasaki)
∑ Mitsubishi Heavy Industries (Mitsubishi) - Japan – Moss
Companies which operates LNG carrier in the Market:
∑ Royal Dutch Shell plc, (Shell)
∑ Nippon Yusen Kabushiki Kaisha (NYK)
∑ Mitsui O.S.K. Lines, Ltd. (MOL)
∑ Misc Berhad (Misc)
∑ Teekay Corporation
∑ Maran Gas Maritime Inc. (MGM)
∑ Golar LNG Limited (Golar)
∑ BW Group
∑ GasLog Ltd
∑ Kawasaki Kisen Kaisha (K Line)
CONCLUSIONS:
∑ Natural gas is the fuel of choice for many applications and its increasing popularity will keep
the demand for efficient shipping high.
∑ Large LNG ships are here to stay, although the increasing size of LNG ships may have
already reached a natural limit, at least for the time being based on current infrastructure and
markets.
∑ We will continue to see developments in improved LNG containment systems, and
propulsion systems.
∑ New projects with particularly challenging conditions such as shipping LNG from the
Russian and Canadian Arctic will provide exciting challenges for naval architects, marine
engineers and shipbuilders in the years ahead.