Building of Advanced Large Sized
Membrane Type LNG Carrier
JUNSHIRO ISHIMARU*1
KIYOKAZU KAWABATA*1
HIDETOSHI MORITA*1
HIDEFUMI IKKAI*1
YOSHIHIRO SUETAKE*1

In the global demand for the environment friendly energy, LNG based trade has been increasing steadily, and demandfor LNG carriers by customers has become more diversified. Under these circumstances, Mitsubishi Heavy Industries,
Ltd. (MHI) has established the building record of Moss type LNG carriers, and also has been carrying out the technicaldevelopments, repair, and maintenance work of membrane LNG carriers first started in the 1970s. Thanks to the customer's
evaluation for those activities, MHI was awarded the contract for six large membrane ships in 1999, which were the firstlarge sized ships to be built in Japan. These ships were built and delivered by 2004 by MHI. Advanced design and building
methods with new technologies were incorporated in the building of these ships which were endorsed by spherical tanktechnique as well. Accordingly, the most advanced and distinguished, largest class membrane type LNG carriers in theworld were completed. Now MHI is continuing work on the development of the next generation LNG carriers to meet thefurther needs of customers.
2.1 Features and comparison of Moss and membranetank systems
The features of each cargo containment system arebriefly described below. As for detail , refer to reference(1).
(1) Independent spherical tank system (Moss system)
An independent spherical tank system is formed insuch a way that a self-supporting spherical tank is fixed
to the hull by a cylindrical support structure (skirt). The
liquid loaded in the tank acts on the self-supportingtank. MHI has thus far built and delivered 23 LNG
carriers using this system, while improving this system.
Recently, the design of Suez Canal tonnage reduction to reduce Suez Canal fees and so-called stretchtank formed by inserting a cylindrical part into thetank's equatorial part to increase volume efficiency havebeen realized.
(2) Membrane tank system
A membrane system is formed by installing thermal
insulating material into the hull of the ship and covering the surface with a metallic membrane. The purposeof the membrane is to maintain liquid-tightness so as
to prevent any leakage of the cargo liquid. The load of
the cargo liquid acts directly from the thermal insulating material to the hull. This system includes Gaz
Transport System, Technigaz System and a systemcalled the CS-1 (Combined System-One), which will be
described later.
The membrane system makes the deck flat and thesmaller size of the ship compared with a Moss system.
In recent years, there has been increasing demand forthe relaxation of filling limits of cargo liquid levels andrelaxation of limits on tank length of membrane system. In order to improve the estimation accuracy ofsloshing loads acting on the tank, GTT (Gaz Transport
and Technigaz), Classification Societies, and shipyards
have investigated the subject to be of practical use.

1. Introduction
The commercial marine transportation of liquefied
natural gas (LNG), which first began in 1964, is increasing year by year. In 2003, it reached approximately 123
million tons in the world. About 150 LNG carriers were
engaged in the sea-borne trade of LNG in 2003. MHI hasdelivered 26 LNG carriers (including 3 membrane typeships) since 1983, and is now building 10 LNG carriers.
MHI has established a track record as the world's largest
supplier of LNG carriers.
With the construction of those membrane type ships,
MHI has become the first yard in the world to build both
Moss and membrane type Large LNG carriers to meet theneeds of customers.
After reviewing the features of each cargo containment
system and MHI's activities, this paper will summarize thefeatures, development, design, and construction record ofJapan's first large membrane type LNG carrier. Future
trends in LNG carriers are also mentioned briefly here.

2. Cargo containment system of LNG carrier and features of membrane type ships
LNG has several unique properties including temperature that reaches as low as approximately -160oC and a
low specific gravity of 0.43 to 0.50 at atmospheric pressure. Various types of cargo containment systems suitableto accommodate these properties have been put into practical use.
At present, independent spherical tank systems andmembrane tank systems have become the mainstream typesystems due to their economic efficiency and reliability.
LNG carriers are uniquely different from other types ofcargo transport ships in the sense that the cargo containment systems are not unified into one system but rather
multiple systems are used instead.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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Primary
insulation box

Secondary
insulation box

Posterior to challenging to the new products, three ofthe world's largest class advanced membrane LNG carries could be built and delivered with a high level ofcompleteness. A brief outline of these LNG carriers ispresented below.
4.1 Basic concept
Basic concepts in the development and design of theships are as follows;.
The volumetric efficiency and propulsion performance (fuel consumption) shall be to the world's
highest level, and economy in operation shall be excellent.
The quality of the cargo containment system shall bewell assured.
Operatability and maintainability after delivery shallbe excellent. Specifically, the specifications and arrangement are so designed that operation andmaintenance could be performed safely, securely, andeasily.
4.2 Features of design (initial design, performance,
structure, and outfittings)(1) Initial design
Figure 2 shows the general arrangement of one ofthese ships, "Puteri Intan Satu", while Table 1 shows
the principal particulars of the ship.
The major dimensions were determined to achieve
excellent propulsion performance with best use of compactness of the membrane ship. The shape of the cargotanks was improved so that the number of non-standard insulation boxes could be minimized. The crosssections of the Nos. 2, 3, and 4 tanks were the same bywhich the cargo containment work efficiently runs.

Primary
membrane (invar)

Inner hull.
.
.

Secondarymembrane (invar)

Fig. 1 Structural drawing of Gaz Transport NO96 insulation system

The large membrane ships designed and built by
MHI adopt the Gaz Transport system. As shown in
Fig. 1
1, this system consists of a double constructionof invar (36% nickel alloy steel) with 0.7 mm thickness as primary and secondary membranes. The
insulation box is also consists of a double layer structure. The total thickness of the insulation system isapproximately 530 mm to ensure a BOR (Boil-Off
Rate) of 0.15% per day.

3. MHI's activities for membrane type LNG carriers
Whilst, MHI has been recognized as a leading Moss
shipyard. MHI's activities for membrane type LNG carriers started earlier than Moss system. MHI introduced
the technologies of the Technigaz system in 1969 and
the Gaz Transport system in 1973, and has continuously
developed various technical improvements on these systems ever since.
In the Iranian Kalingas project in the latter half ofthe 1970s and the Northwest Shelf project in the former
half of the 1980s, though they were not realized, MHI
worked on development of the membrane system at thepractical level. Since 1973, MHI has also concluded longterm maintenance contracts in the field of ship repair
and has continuously performed repair work on membrane ships of both the Gaz Transport and Technigaz
systems.

Table 1 Principal particulars of the "PUTERI INTAN SATU"

4. Building of large membrane type LNG carriers

Principal dimensions
Length, overall(m)Breadth, moulded(m)
Depth, moulded(m)
Summer draught, moulded (m)

276.0
43.40
25.50
12.01

Dead-weight and tonnage
Dead-weight at
designed draught(t)Gross tonnage (International)
Net tonnage (International)

76 11093 03827 911

Cargo tank capacityo(100%, -163 C)

In 1999, MHI was awarded the contract as a leading
shipyard for six large membrane type LNG carriers for
the PETRONAS Tiga project in Malaysia. Despite nobuilding record of large membrane ships at the time,
MHI's long-term activities on membrane ships and thedesign and construction technologies were evaluated forthe receipt of the order. MHI R & D center, a design
department, and a shipbuilding department devoted alltheir power and energy to the development, design, andconstruction of the first large membrane LNG carriers
to be built in Japan.

137 489 m3

Main engine:
Max. output:
Normal output:

Mitsubishi Steam Turbine x 1set
26 800 kW x 89.0 rpm
24 120 kW x 85.9 rpm

Main boiler:
Max. evaporation:

Mitsubishi Water Tube Boiler x 2 sets
60 000 kg/h per set

Generator:
Turbo generators:
Diesel generator:

2 900 kW x 2 sets
2 900 kW x 1 set

Speed and endurance
Service speed:
Endurance:(kt)(s.mile)Abt. 19.5
Abt. 15 000

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ENGINE
ROOM

NO.4 TANK
TANK
NO.4

NO.3 TANK
NO.3
TANK

NO.2
NO.2 TANK
TANK

NO.1
NO.1 TANKTANKPUTERI NILAM SATU

MANIN DECK
& TRUNK DECK

N0.4 TANK
N0.4
TANK

N0.3 TANK

N0.2 TANK

L.N.G TANKVIEW OF BRIDGE FRONT&TANK SECTION

N0.1 TANK

Fig. 2 General arrangement of "PUTERI INTAN SATU"(2) Propulsion performance and fuel consumption
The optimum shape of a hull differs depending on
the type of cargo containment system inside. MHI
developed the optimum for membrane tanks by fulluse of computational fluid dynamics (CFD), in addition to model tests in a model basin. Figure 3 shows
an improved hull form obtained by CFD.
Parallelly, MHI developed the optimum design ofthe propeller so as to be of high efficiency and vibration free. For the turbine plant, a simple two-stage
feed water system was adopted by customer’s preference in consideration of maintenance, and less fuelconsumption was achieved by the improved heat efficient technologies.
(3) Structural design
Strength of hull structure has been verified by thewhole ship FEM model shown in Fig. 44, and it has
been confirmed enough strength in stress and buckling requirements. Analysis using fine mesh FEM
models was also performed to confirm fatigue strength
mainly for the knuckle points of the inner hull, whichwere the most critical points because of the boundary

between the insulation and the ballast tank. Basedon the above analyses, SDA (Structural Design Assessment for stress and buckling) and FDA (Fatigue
Design Assessment for fatigue) notations, which are
the latest notations of Lloyd's Register of Shipping(LR), were obtained.
Separately, an analysis using DISAM (DIScrete
Analysis Method), which is a MHI's in house special
analysis method, was carried out to confirm fatigue
strength with wave data in the ship's specific sea
route.
(4) Design & arrangement of outfittings and automation
The design for the arrangement of the passages on
the upper and under deck and the engine room wascarried out in consideration of traffic and maintenanceonboard. The arrangement of electrical cables andpipes shall be so designed not to expose, as far as practicable, in consideration of future maintenance. And
the selection of materials and determination of coating specifications were also carefully done considering
long-term use. In the design of the cargo piping arrangement, stress calculations of piping was
performed to assure sufficient reliability.

Fig. 3 Development of ship model by CFD(Estimation of self propulsion factors)

Fig. 4 Strength and fatigue analysis by an FEM model of thewhole ship (amount of deformation is exaggerated for clarity)

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Figure 5 shows the arrangement of the piping system on the deck of the ship.
With regard to the tripod mast of the internal structure in the cargo tanks specific to membrane ships,
MHI independently verified that excessive stress did
not occur under all conditions of operation.
As for the automation system, the factors of themembrane system were incorporated into the system
based on the know-how cultivated from the Moss system in order to simplify various operations such as
cargo operations and to increase safety. In addition,
the ship is also furnished with an automated systemfor exchanging ballast water to protect the marine environment.
4.3 Securing of design quality
The cargo containment system of the ship is an extremely large consisting of some 700000 structuralcomponents. In addition, since the inner hull structure
is directly adjacent to the cargo containment system, sufficient quality must be secured for the inner hull andthe surrounding ballast tanks in order to avoid waterleakage into the cargo containment system.
For this purpose, a joint project team formed of thedesign department and the construction department wasorganized and design issues and building method were
examined about two years before the start of actual design work. During the course of this examination, objects
that needed to be carefully verified were narrowed
through the analysis by FMEA (Failure Mode and Effects Analysis).
And verification in particular of the quality of the partcomponents in the cargo containment system, the containment system itself (membrane, insulation box, otherfastening devices), inner hull structures, coating of theballast tanks, and the arrangement of the parts in theballast tanks were surely studied.

Fig. 5 Arrangement of piping on deck

Once the design began, abt. 100 items to be followed
were taken up from the objective items determined during the preliminary verification, after which a follow-up
system was organized, and efforts were made to secure
the quality of the actual design, accordingly.
4.4 Manufacture and procurement of materials forcargo containment system
The key of the building of a Gaz Transport system
LNG carrier is the procurement of insulation boxes
amounting in quantity to 52000 per ship.
(1) Malaysian content and insulation materials
Upon request of the customer, MHI attempted production of insulation boxes using local plywood in
Malaysia in order to promote industry and cultivate
manufacturing technologies there.
Some kinds of wood were selected from the wood
produced in Malaysia, and the plywood of the somecandidate wood types were manufactured and tested.
Finally, a Keruing plywood was approved by GTT. The
insulation box was formed by Malaysian plywood andonly top plate by Finnish plywood which facilitateshandling by vacuum machine.
In order to adopt the plywood, productivity tests
and the strength tests of box were carried out in addition to the strength tests of the plywood itself.
Figure 6 shows a strength test of the insulation box.
(2) Organization for manufacture of insulation boxes
In the Malaysia plant, approximately 2/3 of the total number of insulation boxes were produced. Mostof them were the standard type. For this purpose, local insulation box manufacturing company of joint
venture were established under the lead of MHI.
Figure 7 shows a view of the insulation boxes being produced at the Malaysia plant. The remaining
1/3 of the boxes, mainly of non-standard boxes, were
manufactured at a plant in Japan.

Fig. 6 Strength test of insulation box
Fig. 7 View of side plate stapling
robot in insulation box
manufacturing factory

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Technical Review Vol. 41 No. 6 (Dec. 2004)4

(3) Procurement of invar materials
Invar materials for LNG carrier used to be exclusively handled by Imphy of France. Hence, MHI adopted
the invar materials produced by Imphy in the 1st and2nd ship of the project based on the track record of thatcompany. At the same time, however, MHI also partly
adopted the invar products of two companies in Japan,
and endeavored to improve the workability andweldability of the materials. As a result, in the 3rd andlater ship, MHI has adopted the products of the Japanese manufacturers, which have greater delivery
flexibility.
As the result of efforts to satisfy the needs of thecustomers, MHI could develop and procure materials
for the cargo containment system from new manufacturers while still placing emphasis on past track records.
These materials form the main part of the membrane
ship and successfully met the specified requirementsfor quality and performance.
4.5 Logistic control and quality control in construction
The cargo containment work on the inner surface of thetank of the membrane type LNG carrier is performed on
the scaffolds that are installed in the tank after the hull
Fig. 8structure has been constructed (Fig.
8).
Unlike Moss ships which use aluminum alloy of approximately 40 to 150 mm in thickness, membrane ships are
not only confronted with a number of technical problems,such as the need to master techniques for welding 0.7 mm

thick sheets, but also need to pay close attention to several
points such as establishing effective logistical and quality
controls. These may include such controls as:
Logistic control of a large volume of thermal insulationmaterials exceeding 700 000 items,
Advanced precise control of the mounting of insulation
boxes and membranes, andConfirmation of the integrity of welded points for membrane that may be as long as approximately 108 km.
(1) Logistic and quality control system
The cargo containment system consists of a varietyof parts such as insulation boxes, invar materials, resinrope (resin material used to make sure the flatness of
the insulation boxes), and couplers (insulation box
mounting fittings). The total number of such items exceeds 700 000 items. Given this large number of items,
effective logistical control of all parts becomes a key tothe secure and proper building of the ship.
For effective logistics and quality control of the parts,
MHI has developed the system so-called LOGIQ(LOGIstics and Quality control system). The logistics
system is requested to deliver parts to a proper place at
a proper time. Parts are always collated with the latest
building schedule, and adjusted and controlled, accordingly. The most important thing in the quality control
system is to hold and evaluate the records of the inspection results ranging from production to final installation.
For example, although the secondary insulation boxes
are mounted on the inner hull through a resin rope, theapplicable portions of the rope and related parts must
be re-worked if the resin is not suitably cured. In thistask, traceability is essential to be able to specify a defective part.
For these purposes, data and inspection results are
stored by the LOGIQ so that they can be monitored fortraceability. The recognition of each part is performed
using bar-codes, and the state of the inspection is confirmed by a separate monitor.
Using this system makes it possible for MHI to perform the logistical and quality control functions of thelarge number of parts much more efficiently and effecFig. 9
tively (Fig.
9).

.
.
.

Fig. 8 Section of cargo tank under construction
Scaffolds for construction of insulation installed in the tank.

Fig. 9 Logistics and quality control system: LOGIQ for components of cargo containment system (Reading of bar codes on parts and control of resin ropes)

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Work/task

Quality check points

Installation of insulation box

Accuracy of coupler installation (1.5mm/10m)
Proper application of resin rope
Accuracy of height of box installation (0.7mm)
Straightness of groove of tongue

Installation of corner parts

Flatness and perpendicularity of anchor bar
Accuracy of box installation
Flanging accuracy
Accuracy of alignment of tongue with flange section

Installation of strakes
Control ofeach tank

Shrinkage of welding
Management of bead shape

Manufacture of invar parts

Seam welding

Check of quality of welding by daily performance
testing (macro check)Welding of end strakes

Proper bead shape, periodical qualification test

Repair of welding

Reheat limit, bead shape, qualification test

Fig. 10 Items of quality control in insulation work

(2) Accurate quality control
The base of the membrane must be adjusted as flatas possible for carrying out the welding of the membrane with a high degree of accuracy to prevent any
problems related to strength from occurring in the membrane part, which forms the inner wall of cargo tank.
The range of the quality checks for this work is wideand deep, including checking the flatness of the inner
hull, the mounting accuracy of the coupler, the height
accuracy of each insulation box, the mounting accuracy of the membrane, and welding accuracy, etc. An
example of quality control items generally covered isshown in Fig. 1010.
(3) Leak test
Welding length of membrane extends to approximately 108 km in total. The welded points must be
checked visually and also shall be confirmed the no possibility of leak. For this purpose, after the membrane
installation work is completed, a helium leak test (identification of leaking parts) and a global tightness test
(confirmation of the tightness of the overall tank system) shall be performed to confirm the integrity of thewelded points.
In the helium leak test, shown in Fig
Fig.. 11, helium witha concentration of 20% is filled into the insulation layer
and pressurized. An helium leak detector runs along
all weld points of the membrane to check for any leakage of helium. In the global tightness test, the insulation
layer is brought to a vacuum (-800 mbG) state, and its
pressure is measured for 24 hours to check that any
variations in pressure fall within allowable values.
These tests are performed for each of the tanks and insulation layers. Apart from the GTT’s instruction, MHI
has developed its own eddy current based defect detector which is utilized beforehand prior to leak inspections
to check the integrity of the welded seam, which comprise about 83% of the all welded points. Figure 12
shows the inner surface of a completed cargo tank.

Fig. 11 Detector for helium leak test

Fig. 12 View of interior of completed cargo tankMitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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5. Future trends of membrane LNG carriers

6. Conclusion

Various future trends of LNG carriers can be considered. A brief description is given here of an enlargement insize and a new cargo containment system.
5.1 Enlargement in the size of cargo tank
The merit of enlarging the size of LNG carriers is toraise the economic efficiency due to a reduction in unittransportation cost. The tank size of the LNG carriers now
under construction are gradually increasing from 135 000
m3 to 145 000 m3 class, with further expansion to 150 000m3 class. Further, work is already now under way on thedesign of 200 000 m3 class. Compared with the Moss typeof the same tank capacity, the membrane type can be designed with more compact form, and it is considered to becomparatively suitable for enlargement of cargo tank size.
One of the points to be considered in enlargement ofsize is the ship-shore compatibility with existing LNG terminals. Based on the restriction of LNG terminals, the150 000 m3 class LNG carriers have best compatibility withexisting LNG terminals, which thus have the maximum
flexibility, in general. Although the number of terminals is
limited, 160 000 m3 class LNG carriers are the maximum
size that have the compatibility with existing terminals.
Carrier sizes beyond this class shall be considered for the
newly planned large terminals.
Another points to be considered in enlargement of sizewith membrane ship is the counter-measures for sloshing.
At present, four tanks design can be done in the range of
150 000 to 160 000 m3 class, and five tanks design is said
to be sure in the 200 000 m3 class from the view point ofsloshing. To reduce the number of tanks, it is necessary tocontinue to investigate and evaluate the sloshing in largesized ships in the future.
5.2 New CS-1 cargo containment system
In recent years, a new CS-1 cargo containment system
has been developed by GTT in which the advantages of bothGaz Transport and Technigaz systems have been combined
together into one system. The basic structure of the system
uses invar (Gaz Transport system) for a membrane, reinforced plastic foam (Technigaz system) for insulation, andtriplex (material formed by aluminum sheet reinforced withglass cloth: Technigaz system) for secondary barriers.
At present, MHI have been performing a technical verification of the CS-1 in association with GTT andClassification Societies mainly with respect to those items
that have been changed from the Gaz Transport system(structure of invar tube corners, corrugated strips, invar/
triplex adhesion) and has been verifying the installation of
the system using a mock-up model. Through these works,
we have reached to the level to offer this system in actual
business according to the request of customers, paying attention to the actual ship application in France.

After introducing the basic technologies of Mosstype and membrane type LNG carriers in the period
from 1969 to 1973, MHI has developed various technologies for safety and economic efficiency, and has
applied these to actual ships. Based on the long-term
accumulation of the technologies and expertise, MHI
has now built and delivered the first large membrane
ship of its type to be built in Japan. Now, MHI could
supply both Moss and membrane systems according to
the needs of customers.
In the ever increasing demand for LNG expected in
the future, the circumstances surrounding LNG is changing and the needs for LNG carriers by customers are also
becoming more diversified. By making full use of the experience in building of membrane ships, MHI would liketo make challenge of supplying customers with attractive LNG carriers. Especially, MHI will actively endeavor
to achieve enlargement in size, environmentally friendly
plants and CS-1 from the viewpoint of a CS (Customer
Satisfaction) improving transportation economy.
Now, MHI has received an order for five large membrane LNG carriers (152 300 m3) on August, 2004.
References(1) Ishimaru, J. et al., Key Technologies of Mitsubishi LNG Carriers - Present and Future -, Mitsubishi Heavy Industries,
Ltd. Vol. 38 No.2 (2001)(2) Yuasa, K. et al., Challenges of Mitsubishi GTT Membrane
LNG Carrier, Gastech 2000 (2000)

Junshiro Ishimaru

Kiyokazu Kawabata

Hidefumi Ikkai

Yoshihiro Suetake

Hidetoshi Morita

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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