LNG Ship Assignment (liquified natural gases)

MUHAMAD IKHWAN MUHAMAD AZIZIE (UNIKL MIMET)

FOR EDUCATION PURPOSES(OR INFO)

SHIPBUILDING TECHNOLOGY FOR ECONOMIC

PRODUCTION

LNG CARRIER

MUHAMAD IKHWAN BIN MUHAMAD AZIZIE

FAIZAL B. ABD. HADI

YUFARIZA BT HAIR ZAKI


CONTENT

NO TITLE PAGE(S)

1. Introduction 1

2. LNG Tanker design 2

3. Explanation

Full Containment Tank

Membrane

3-7

4. Comparison of design and structure of tank 8

5. Most Economical LNG 9

6. Conclusion 10


LNG Carrier

Self Supporting Membrane

Spherical MOSS

Prismatic IHI

SPB

Gaz Transport

1.0 INTRODUCTION

An LNG carrier is a tank ship designed for transporting liquefied natural gas (LNG). As

the LNG market grows rapidly, the fleet of LNG carriers continues to experience tremendous

growth. There are 2 types of LNG carrier covered in this assignment which are Full containment

and membrane tank type of vessel. Today there are four containment systems in use for new

build vessels. Two of the designs are of the self supporting type, while the other two are of the

membrane type. The liquefied natural gas was turn into a liquid form instead of gases in order to

make it feasible to transport over long distances.

Furthermore, liquid takes up less space than the gas does. The LNG tanker purpose is to

transport the LNG from point A to point B. For this assignment we did a research on the LNG

tanker design, explanation of full containment and membrane tank, comparison between design

and structure of full containment and membrane tank and lastly, which one is the most

economical to be used widely.


2.0 LNG TANKER DESIGN

The design of liquified natural gas tank ships look different from regular tank ships

carrying oil and chemicals. Most LNG tank ships have two hulls, so that, if a collision or

grounding punctures the outer hull, the ship will still float and the LNG will not spill out. LNG

tanks are either spherical (and the upper half of the sphere sticks out above the deck), or box-

shaped. The ships tend to ride high in the water, even when loaded. A typical LNG ship is 950

feet long and 150 feet wide, and many new ships being built are even bigger.

Figure 1: LNG with membrane tank sketch

Figure 2: LNG Carrier with different

design and general arrangement


Figure 3: General Arrangement of LNG Carrier with Membrane Tank

Figure 4: General Arrangement of LNG Carrier


Figure 5: Membrane gaz transport

Figure 6: LNG carrier moss tanks

Figure 7: The Futuristic design of Membrane LNG carrier, X-BOW® vessel. The vessel is a

combination of an LNG (Liquid Natural Gas) carrier and PAX (cargo and passenger transport

vessel).


3.0 TANK TYPE OF LIQUIFIED NATURAL GAS (LNG)

3.1 Full Containment Tank

Full-containment tanks typically feature a primary liquid containment open-top inner tank and a

concrete outer tank. The outer tank provides primary vapor containment and secondary liquid

containment. In the unlikely event of a leak, the outer tank contains the liquid and provides

controlled release of the vapor. It is self supporting and independent.

Figure 8: Moss Tank inside an LNG Vessel


3.2 Membrane Tank

Membrane tank is a cargo tank that is not self-supporting and consists of a thin layer

supported through insulation by the adjacent hull structure. Besides that, prismatic membrane

tanks utilize the hull shape more efficiently and thus have less void space between the cargo-

tanks and ballast tanks. Therefore, the design of membrane tank has been used widely in

shipping industry around the world. The concept of the membrane containment system is based

on a very thin primary barrier (membrane – 0.7 to 1.5 mm thick) which is supported through the

insulation. Such tanks are not self-supporting like the independent tanks. An inner hull forms the

load bearing structure. Membrane containment systems must always be provided with a

secondary barrier to ensure the integrity of the total system in the event of primary barrier

leakage.

The membrane is designed in such a way that thermal expansion or contraction is compensated

without over-stressing the membrane itself. There are two principal types of membrane system in

common use – both named after the companies who developed them and both designed primarily

for the carriage of LNG. These two companies have now combined into one.

Figure 9: Membrane Tank


Figure 10: Inside the membrane tank Table 1: Membrane Tank Details


4.0 COMPARISON OF DESIGN AND STRUCTURE

Based on research, pictures, general arrangement and sketches, it can be seen that the

design and structure are different. Thus, we would like to make comparison between full

containment and membrane tank.

4.1 Comparison of Design

Full Containment Membrane

A full containment tank does not require a dike

or bund wall to contain any leakage, resulting

in saving of space.

Have a barrier wall to contain leakage. Usually

there are 2 barriers which are primary and

secondary barrier.

Appropriate parts of the ship’s hull are

constructed of special steel capable of

withstanding low temperatures.

Designed in such a way that thermal expansion

or contraction is compensated without over-

stressing the membrane itself.

The outer tank is capable of both containing

any leakage of LNG and controlled venting of

vapor created from any LNG leakage.

Membrane containment systems must always

be provided with a secondary barrier to ensure

the integrity of the total system in the event of

primary barrier leakage.

4.2 Comparison of Structure

Full Containment Membrane

Self-supporting; do not require inner hull Not self-supporting; require inner hull.

Do not form part of the ship’s hull structure. Form part of the ship hull structure.

Do not contribute to the hull strength of a ship. An inner hull forms the load bearing structure.


5.0 THE MOST ECONOMICAL TANK

The most economical is the membrane tank because it is built directly in the form part of

the ship hull structure, thus reducing the time and cost consuming for construction and financial

in order to build the ship. Furthermore, the internal size of the tank is much larger than the full

containment tank. Thus it is really flexible in terms of moving large quantity of liquid from one

place to another especially when the sailing sets to be in long term. The design is also

economical because of the tank were form as part of the ship hull which is an advantage for

construction times which can be shorten instead of moss tank, which required the tank to be

build outside of the ship and then assemble it together with the ship hull while the membrane

tank were directly made with the hull of the ship itself.


6.0 CONCLUSION

For conclusion, it has been proof that the most economical LNG tank is the membrane tank

for LNG carrier. There are 2 types of LNG carrier covered in this assignment which are Full

containment and membrane tank. From this assignment, we know that prismatic membrane tanks

utilize the hull shape more efficiently and thus have less void space between the cargo-tanks and

ballast tanks. Thus by reducing space, less cost and spending on budget can be reduce which are

important key in shipbuilding industry.

LNG Ship Assignment (liquified natural gases)

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