A CONCEPTUAL LNG CONTAINMENT DESIGN

UTILIZING EXPLOSION WELDED TRANSITION

JOINTS

BY CHAD N. FUHRMANN

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1. ABSTRACT

2. INTRODUCTION

a. Short History

b. What is LNG?

c. Future Growth in LNG market

3. DESCRIPTION OF LNG CONTAINMENT AND TRANSPORT

a. Basic Types and Designs of LNG Vessel Containment Systems

i. Containment Design Considerations

ii. Kvaerner-Moss

iii. GTT No 96 Membrane Containment System

iv. GTT Mark III Membrane Containment System

b. Advantages/Disadvantages of Membrane vs. Moss Containment Designs

4. STAINLESS STEEL AND INVAR® VS. ALUMINUM IN LNG

CONTAINMENT

a. Thermal Properties of Each Metal

i. Invar®

1. Coefficient of Thermal Expansion

2. Coefficient of Thermal Conductivity

3. Effect of Thermal Properties on Containment Design

ii. Stainless Steel

1. Coefficient of Thermal Expansion

2. Coefficient of Thermal Conductivity

3. Effect of Thermal Properties on Containment Design

iii. Aluminum

1. Coefficient of Thermal Expansion

2. Coefficient of Thermal Conductivity

3. Effect of Thermal Properties on Containment Design

b. Kvaerner-Moss Design Considerations and Explosion Welded Transition

Joint

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5. INTRODUCTION TO EXPLOSION WELDING OF ALUMINUM AND

STEEL

a. Process and Method

b. Basic Properties of Explosion Welded Aluminum and Steel Transition

Pieces

6. DESCRIPTION OF PROPOSED DESIGN FOR LNG TANKER

CONTAINMENT SYSTEM

a. Containment Cell Design

i. Aluminum Interior Similar to Moss Design

ii. Advantages of Design

1. Aluminum Interior with Cryogenic Advantages

2. Reduced Material Usage

3. Reduced Weight

4. Simplicity/Relative Ease of Installation

b. Explosion Welded Transition Joints/“Floating” Design

i. Description

1. Basic Design

2. Materials Used

ii. Advantages

1. Reliable Structural Support in Lieu of Wood Insulation-

Filled Boxes

2. Collision Safety

c. Piping Considerations

7. FURTHER CALCULATIONS

a. Coefficients of Thermal Expansion and Thermal Conductivity

i. Containment

ii. Transition Joints

iii. Vessel Support Structure

iv. Insulating Foam

b. Shear/Compressive Strength

i. Normal Loading

ii. Collision

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8. LIMITATIONS OF PROPOSED DESIGN

a. Lack of Information Available

i. Current Designs Used in Naval Applications

ii. Design Details are Closely Guarded

b. Possible Design Flaws

i. Rough Estimates For Calculations

ii. Unproven Design

9. CONCLUSIONS

10. WORKS CITED

11. WORKS CONSULTED

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Abstract

This paper introduces a new conceptual design for a liquefied natural gas (LNG)

vessel containment design. This “Floating Containment System,” or FCS, takes

advantage of recent advances in explosion welding, particularly between aluminum alloy

5083 and carbon steel for use as transition joints between the aluminum LNG

containments and the vessel’s hull. The new design will be studied using the coefficients

of thermal expansion for each of the metals used and the advantages and disadvantages of

the design will be described as applicable to cryogenic fluids in general and liquefied

natural gas in particular.

Introduction

Up until the 1970’s, most natural gas was burned off at wells in the oil field.

When it was recognized that this gas could be used for energy production, it was stored

for future use or re-injected back into oil deposits to assist in maintaining pressure within

the well. Today, natural gas is recognized as an extremely efficient, cost effective and

clean-burning fuel. It is being utilized in gas and steam turbines for electrical power

generation, used as an alternative fuel in transportation, heating homes and office

buildings and finding uses in countless other areas of life.

Natural gas is a fossil fuel found, as its name would suggest, in gaseous form and

is the byproduct of the anaerobic decay of organic material. The natural gas is trapped

and then processed for transport and used for energy production is normally found in oil

and natural gas fields but is also produced as biogas in places such as landfills and

swamps. Natural gas is made up of 70-90% methane (CH4), 5-15% ethane (C2H6),

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propane (C3H8) and butane (C4H10), as well as small amounts of carbon dioxide, nitrogen

and other hydrocarbons and sulfur-containing gases.

Before it is transported any great distance, natural gas undergoes extensive

processing. This processing removes acids, moisture, mercury, nitrogen and other

contaminants producing a gas that is roughly 95% methane.

Demand for the fuel is growing, primarily for residential and commercial heating,

power generation and for industrial heat processes. As concerns for the environment

grow, demand for cleaner burning personal and public transportation will also increase

the demand for natural gas.

Description of LNG Containment and Transport

There are five basic sets of conditions for storage and/or transport of liquids or

gases:

1. Liquid at atmospheric pressure and temperature (atmospheric storage);

2. Liquefied gas under pressure and at atmospheric temperature (pressure

storage);

3. Liquefied gas under pressure and at low temperature (refrigerated pressure

storage, semi-refrigerated storage);

4. Liquefied gas at atmospheric pressure and at low temperature (fully

refrigerated storage);

5. Gas under pressure (Mannan pp.4-5).

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For ease of pumping and transport via ship, natural gas is contained as per

conditions 3 or 4, depending on the containment method. For these conditions, the

natural gas must be liquefied. The liquefaction process occurs when the temperature of

the gas is reduced to approximately ( )FC °−°− 260160 . This extensive cooling reduces

the gas to a liquid that is one six hundredth of its initial volume making containment and

transport much more economically feasible. The extremely low temperature, however,

creates a unique set of difficulties that must be addressed.

Any fluid with a boiling temperature of ( )FC °−°− 1309.89 or lower at

atmospheric pressure ( psia7.14 or kPa3.101 absolute) is by definition a cryogenic fluid

(2006 International Fire Code p.279) with inherent dangers and handling/containment

precautions over and above those normally associated with a flammable liquid. At a

temperature of C°−160 , liquefied natural gas falls well within these parameters.

In addition to the precautions that must be taken in regard to safety of personnel

when handling LNG, there are also rules and guidelines that must be followed regarding

its containment and transport on board LNG vessels. Dry cargo or liquid petroleum

vessels are constructed of various types of steel depending on design criteria and the

owner’s preference and budget. However, LNG, due to its cryogenic state must be

treated differently. LNG is transported in vessels specifically designed to carry it. The

fluid is stored on board these vessels in specialized containments that can only be

constructed of specific materials.

There are two basic designs used for LNG vessels today. The general shape and

specific structure of these two containment systems is very different. The first design is

the Kvaerner-Moss spherical containment design. This design was introduced in 1965

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and is the property of the Norwegian Kvaerner Group (www.akerkvaerner.com). The

design consists of a spherical aluminum tank interior covered in steel with a layer of

insulation in between. This design relies on an explosively welded transition joint as a

means of securing the aluminum sphere to the steel structure of the hull. It is this

transition joint that allows the combined advantage of the excellent cryogenic properties

of aluminum and the economic and strength advantage of the vessel’s structural steel.

The second type of LNG vessel containment is the membrane design. Much like

the Kvaerner-Moss design, this design consists of the membrane inner surface that is in

contact with the liquefied natural gas, surrounded by thick layers of insulation. The

entire containment is encased within the protective structural steel shell of the vessel’s

hull. While the spherical Kvaerner-Moss design is a one piece (relatively simple) design

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that can be simply dropped into the hull of the vessel during construction, the membrane

type design is more complicated in its design and construction.

Within the membrane design group are two unique designs designated as the Gaz

Transport & Technigaz No. 96 and Gaz Transport & Technigaz Mark III Membrane

Containment Systems. In both of these containment systems, the liquid cargo membranes

are independent of the vessel’s structure, supported instead by a base of insulation and

plywood that surrounds the containment. Neither of the systems is anchored directly to

the steel hull of the vessel.

Generally, the No. 96 and Mark III Membrane Containment Systems are very

similar in their basic designs. However, each system utilizes different insulation and

membrane materials. The GTT No. 96 Membrane Containment System is built upon a

base of stacked plywood boxes filled with perlite insulation. On top of the stacked boxes

Figure 2--General Membrane Type LNG Vessel Containment Design

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is layered an Invar membrane. Invar® is an iron and nickel alloy known for its uniquely

low coefficient of thermal expansion. The Invar® membrane is anchored in the stacked

layers of plywood boxes.

Secondary Box Level

Primary Box Level

Invar® Membrane

Steel Tank Top

Plywood Base Layers

Foam Insulation

Stainless Steel Membrane Triplex® Liner Sheet

Figure 3--GTT No. 96 Membrane Containment

System Construction (Curt p. 19)

Figure 4--GTT Mark III Membrane Containment System Construction (Curt p. 21)

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The GTT Mark III Membrane Containment System is layered similarly to the No.

96 System. However, the Mark III System consists of layers of insulating foam divided

by layers of plywood and a Triplex®

plastic liner. The Triplex® plastic liner serves to

strengthen the overall membrane and also acts as an additional layer of insulation and as

a moisture guard. On top of the insulation, a baffled stainless steel membrane is installed.

Unlike the Invar® membrane of the GTT No. 96 System, expansion and contraction of

the stainless steel membrane, with its coefficient of thermal expansion of Kmm

mm17 ,

must be considered in its design and construction. The baffles of the stainless steel

membrane thus serve to absorb the thermal movement of the material.

The Kvaerner-Moss spherical containment design and the GTT membrane

containment designs each have advantages and disadvantages in comparison to one

another. The spherical containment has two distinct advantages over the membrane

design. First of all, the spherical tanks are simple in design and construction. They can

be completely fabricated before and during the construction of the vessel and then

installed in one piece on the ship. The aluminum and steel transition joint offers a degree

of structural stability that is not found in the membrane design. However, the spherical

shape of the containment does not fit the generally rectangular design of the vessel.

While the unused cargo space on this type of design serves as an additional safety zone in

the event of collision, it is also serves as dead space within the vessel that can be more

economically used in the better fitting membrane design.

The economic advantage of the membrane design is the primary reason that it is

the preferred design for LNG transport. Because of the better use of space in the

membrane containment system, it can carry more product on a vessel of similar size in

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comparison to the Kvaerner-Moss design. To account for this, vessels using the

Kvaerner-Moss design must be on average 10% longer than the LNG vessels using the

membrane design. Thus, the construction cost is inherently lower for a LNG vessel using

a membrane containment system due to its comparatively smaller size. The size

difference between vessels also accounts for increased shipyard capacities, less difficulty

with canal passage, etc.

The “collision zone” created by the additional space in the Kvaerner-Moss

spherical containment is a safety advantage of this particular design. The same dead

space that makes the design less efficient also serves as an impact zone, protecting the

spherical containments from damage in the event of a collision or grounding.

The membrane containment systems create their own collision safety zone by

virtue of the independent design of the membranes. Again, the membranes are not

directly supported by or connected to the structural members of the vessel. In the event

of a marine casualty, the layers of insulation surrounding the containments creates a

cushioned safety zone around the cargo holds and the unattached design of the membrane

resists the damage from being transferred from structural members to the containment.

Stainless Steel and Invar® vs. Aluminum in LNG Containment

Members of the Workforce should verify that material and equipment that are

used in cryogenic applications are constructed only of materials that do not become

brittle and hazardous at low temperatures (Shrouf, p.7).

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Material Properties Aluminum

Alloy (6061-T6)

Aluminum Alloy (6061-Untempered)

Mild Steel 1010 CREW

304 Stainless Annealed ASTM A269

321 Stainless Annealed

Titanium Cp2

Grade 2 ASTM B

338

Invar®

Tensile Strength MPa (20 C) 310 124 380 590 620 50,000 345 Yield Strength MPa (20 C) 275 55 275 240 245 275 360 Elongation Percent 12 25 20 55 55 20 57.5 Density Kg/m3 2700 2700 7800 8000 8000 4500 8100

Modulus of Elasticity x 103 MPa 0.07 0.07 0.20 0.19 0.19 0.10 0.15 Coefficient of Thermal

Expansion /K (or C) (x 10-6)

(20 C) 23 23 11 17 17 20 1.2

Coefficient of Thermal Conductivity

W/m K (20 C)

225 225 45 20 20-25 15.6 125.7

In addition to construction and design, the major difference between the

Kvaerner-Moss and GTT containment designs is the type of material used that is in

contact with the liquefied natural gas. The above table illustrates the different

characteristics of a selection of different materials. Aluminum, Invar® and stainless steel

are all materials used in the different containment types. The design of the containment

determines the type of the material used in its construction because each of the three

materials reacts differently to temperature extremes. A lower or higher coefficient of

thermal expansion may be incompatible or uneconomical with a given design.

Invar®, as used in the GTT Mark III Membrane Containment system is an alloy

consisting of 64% iron and 36% nickel with additional carbon and chromium. The

coefficient of thermal conductivity of Invar® is approximately Km

W6.125 at C°20 .

This value falls between stainless steel on the low end and aluminum on the high end of

the three materials in question.

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Invar®, however, is especially known for its low coefficient of thermal

expansion. While the average value at low temperatures is Kmm

mm6101 −× , some

formulations of the material have a negative value for the coefficient of thermal

expansion (Incropera, p.537). The lower the value of this coefficient, the less a material

will expand or contract as its temperature varies. As the lining of the Mark III system,

Invar® is therefore an excellent material in that it is largely unaffected by the temperature

of the cryogenic LNG. The minimal contraction of the material at low temperatures

minimizes the risk of fractures due to tension stress in the material. Likewise, when the

membrane is subject to atmospheric conditions when empty, the material will not expand

to the point of buckling with the increase in temperature.

A disadvantage of Invar® is its tendency to creep. As the material is thermally

stressed over a period of time it has a tendency to deform to relieve that stress. This

could lead to weakened areas in the membrane that could eventually lead to leakage or

rupture of the tanks, particularly in the event of a collision.

The coefficient of thermal conductivity of the membrane material will have an

effect the insulation used in the membrane construction. The perlite-filled plywood boxes

used in the construction of the GTT No. 96 Membrane construction help to counteract the

higher thermal conductivity of the Invar®. The perlite insulation has a lower coefficient

of thermal conductivity (approximately Km

W029.0025.0 − at an average temperature

of C°−126 ) as compared to other forms of insulation. Perlite by itself, however, has

little or no compressive strength due to its loose form. Thus, the insulation is used inside

the plywood boxes which assist in adding compressive strength to the insulation layer

along with the Invar® anchors that support the unattached membrane.

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The GTT Mark III Containment System uses a membrane constructed of stainless

steel. Described briefly earlier, this membrane design utilizes a baffle-type design to

prevent stress in the membrane from leading to fractures or buckling over the wide

temperature differential experienced between loading operations. Stainless steel has a

coefficient of thermal expansion of approximately ( )Kmm

mm6100.17 −× at C°20 . This

value is higher than that of Invar®, indicating that there will be more movement in the

material over the expected temperature differential, hence the need for the baffled design.

In comparison to Invar®, the coefficient of thermal conductivity of stainless steel

is low, approximately Km

W45 . In this design a foam insulation product is used. Foam

insulation can have a thermal conductivity in the area of Km

W039.0 at a temperature of

C°0 and lower at cryogenic temperatures (Pittsburgh Corning). This is higher than that

of perlite insulation, but in combination with the lower thermal conductivity of the

stainless steel, is suitable for the application.

The foam has the added benefit of a relatively high compressive strength, about

kPa620 , thus eliminating the need for the plywood boxes and simplifying the overall

construction of the membrane. Plywood sheets are still incorporated as layers of

separation between the foam layers as is a Triplex® sheet which further improves the

thermal conductivity and strength of the insulation layer.

The Kvaerner-Moss spherical containment design uses aluminum as the

construction material for its inner shell. The aluminum sphere is surrounded by foam

insulation. Perlite is not practical in this design for a number of reasons. First, the

insulation-in-box type of structure is not necessary by design as the tank is supported

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directly by the vessel’s steel structure. Secondly, the loose nature of the perlite makes it

impractical for installation around the exterior of the aluminum shell. Foam, though not

necessary for support of the containment, is a solid material that can be pre-formed and

will remain in place around the spherical structure once installed.

Aluminum and its alloys have a thermal expansion coefficient of approximately

( )Kmm

mm61023 −× . In comparison to the other materials, aluminum is therefore subject

to much more expansion and contraction over the anticipated temperature range. For this

reason, the Kvaerner-Moss containment design can use aluminum as its interior material

while it may not be practical for the membrane design. The spherical design of this

containment system allows for the tension and compression forces experienced over the

temperature range to be evenly distributed over the surface of the hold. If aluminum

were to be used in a membrane-type containment system, the forces experienced in the

corners (stress concentrators) of the membrane containment could be excessive and may

very well lead to failure.

The cryogenic nature of liquefied natural gas and the thermal characteristics of

aluminum require that the Kvaerner-Moss containment be designed as it is. Meaning that

the spherical shape of the containment is required to withstand the stresses involved in

the containment. However, this shape requires that the Kvaerner-Moss vessel be larger

than membrane type vessels to be able to carry a comparable amount of LNG.

There are distinct advantages of aluminum in LNG containment and transport.

Despite the higher coefficient of thermal expansion, aluminum has excellent cryogenic

qualities. Unlike other materials, aluminum becomes stronger at cryogenic temperatures

and is not prone to brittle fractures at these low temperatures.

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Unlike the membrane containments described above, the aluminum sphere in the

Kvaerner-Moss design is directly attached to the structural steel portion of the hull. This

is accomplished by the aluminum and steel transition joint located around the circular

base of the spherical tank.

This is the critical area in this type of containment design. Again, because of the

spherical shape of the containment, the forces applied to the structure of the tank are

evenly distributed. Placing the transition joint around the base circumference of the

containment allows the stress of thermal expansion and contraction to be evenly

distributed around the ring’s perimeter, supporting the structure without the risk of

fracture or deformation.

However, having the containment system directly connected with the hull of the

vessel has a disadvantage. In the even of a collision, the joint between the containment

and the structure of the vessel presents a potential danger area. If the support is damaged,

that damage could be transferred to the containment itself.

Introduction to Explosion Welding of Aluminum and Steel

In the Kvaerner-Moss containment design, the aluminum/steel transition joint is

created by a process known as explosion welding. This is a method by which two

dissimilar metals are welded together using tremendous force. The resultant bond is as

strong as any normal welding process but leaves the individual characteristics of the

dissimilar metals intact. In this instance, the aluminum retains its excellent cryogenic

properties, while the strength and toughness of the steel is also preserved.

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Figure 5--Basic Explosion Welding Process (DMC Clad Metal Groupe SNPE p. 1)

As seen in Fig. 5, the explosion welding process begins with preparation of the

two materials to be joined (specifically aluminum and steel in this instance). After

preparation is complete, the two sheets are placed a specified distance apart with the

cladder material (aluminum) over the backer, or base material (steel). A precise amount

of explosive powder is evenly spread across the aluminum and is detonated from a

predetermined starting point. The explosion front travels across the face of the aluminum

at a speed of s

m40002000 − forcing it down upon the steel base metal at pressures

ranging from MPa000,4700 − (Murr p. 186, and High Energy Metals, Inc. p. 1). The

force of collision across the plate surfaces forces out oxides and other impurities

promoting a clean metal-to-metal bond. The metals are forced together at such great

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velocity and with such force as to briefly become viscous fluids. The metals “splash”

together and bond with each other via interlocking waveforms.

Figure 6--Magnified View of Explosion Welded Joint

(Murr p. 188)

Figure 7--X-Ray Photograph of Aluminum/Steel Transition Piece

(Photo Courtesy of Joe Kass Photography, LLC, 2007)

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The end result of the process is a single piece of metal consisting of steel and

aluminum completely fused together across their surface areas each with their original

characteristics still intact. These metal pieces are commonly produced in long strips

approximately cm3801 − wide by cm45.39.1 − thick and can be used in any number of

applications, including transition pieces in LNG containment systems.

Aluminum Plate

Aluminum/Steel Transition Joint

Steel Support Structure

Figure 9--Typical Explosion Welded Transition Joint (Merrem &

laPorte p. 11)

Figure 8--Explosion Welded Stock (Young p. 5)

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The aluminum and steel transition joints manufactured by this process provide

many advantages over traditional fastening methods. The bond between the two different

materials provides a gap-free transition that greatly reduces galvanic corrosion. In

interior compartments, where there is no exposure to seawater or sea air, corrosion is

virtually eliminated. In areas where the transition point is subject to corrosion-inducing

environments, regular painting or coating can inhibit and even prevent corrosion.

Furthermore, the bond created between the metals is permanent and requires no

further maintenance. This is in contrast to other fastening methods between dissimilar

metals, such as nuts and bolts that can loosen or wear over time and exposure to

vibration, thermal expansion, loading, etc.

The explosion bonding process does not affect the original characteristics of the

materials. Contraction and expansion due to temperature changes still affect the

materials according to their thermal characteristics but the continuous joint, as mentioned

earlier, evenly distributes any stress that may occur due to these thermal effects on the

materials as well as any loading on the members they are a part of.

MATERIAL Steel Chemically Pure

Aluminum Aluminum Alloy 5083

Explosively Bonded Metal (Triclad®)

Tensile Strength

( )MPa 380-515

65-95 275-350 80 (min)

181 (typical)

Yield Strength

( )minMPa 205 20 125 ---

% Elongation

min 27 35 17 ---

Shear Strength

( )MPa --- --- ---

70 (min) 94 (typical)

Figure 10--Material Characteristics (Merrem & laPorte, pp. 6-7)

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Proposed Design for LNG Tanker Containment System

The new LNG containment design proposed here attempts to take advantage of

the technological advances made in explosion welding in a new way, offering better

support of the containment cell and higher cargo capacity with less danger of

containment damage in the event of collision or other catastrophic failure.

Like the Kvaerner-Moss LNG containment design, the Floating Containment

System utilizes the excellent cryogenic properties of aluminum for the main component

of the LNG hold. Not only is aluminum excellent for cryogenic applications, it is also

very light (approximately 32700m

kg). This compared to the stainless steel and Invar®

used in the membrane designs, both of which have densities of approximately

38000m

kg. The decreased weight of the construction material allows for more cargo to

be carried on a vessel of a given size, making its use more economical in comparison to

other materials.

Figure 11--Proposed Containment Design Utilizing

"Floating" Supports

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The FCS also utilizes a rounded shape to better withstand the contraction and

expansion of the aluminum with its high coefficient of thermal expansion. The

ellipsoidal containment cell lies within a similar shaped ellipsoidal shell (Fig. 10). While

this creates more dead space within the vessel as compared to the membrane design, the

modified design of the FCS ellipsoidal containment allows for more cargo capacity in

comparison with the Kvaerner-Moss design and, potentially, a slightly lower profile. A

vessel using the ellipsoidal containment allows for a capacity equivalent to a vessel of

equal size using the Kvaerner-Moss design, however, the FCS would only require two

ellipsoidal containments as opposed to the four required by the spherical containments on

an identical vessel.

Figure 12--Ellipsoid

As an example, a large LNG vessel using the spherical containment design can

carry approximately 3000,155 m of liquefied natural gas with four spherical tanks each

measuring approximately 42 meters in diameter. Utilizing two ellipsoid tanks with the

same measurement for width and height and double the length of one sphere, the

volumetric comparison between the two designs is as follows:

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cbaVolume ⋅⋅⋅⋅= π3

4 , where ma 42= , mb 21= and, mc 21=

≈⋅⋅⋅⋅=∴ 2121423

4 πV3600,77 m

=× 2600,76 3m 3200,155 m

While the FCS design will not result in a straightforward increase in cargo

capacity, it will result in cost savings by reducing the amount of materials required to

build two containment cells as opposed to four containments of the traditional Kvaerner-

Moss design.

To further accommodate the expansion and contraction of the aluminum

containment cell and assist in its support, expandable foam insulation would be used in

the void spaces surrounding the aluminum containment. Again, this is similar to the

Kvaerner-Moss design in that the foam insulation can be pre-cut to conform to the

curvature of the containment cell. This foam will be compressed upon installation to

allow for expansion as the containment contracts.

Finally, the FCS also utilizes explosion welded transition joints between the

aluminum of the containment and the steel structure of the vessel. Like the explosion

welded joint of the Kvaerner-Moss design, these joints are integral to the structure of the

containment system. However, unlike the transition joint in the Kvaerner-Moss design,

the FCS design uses “floating” joints (Figs. 12&13) to compensate for the expansion and

contraction of the aluminum containment. These joints surround the containment cell in

broken bands and allow the aluminum to expand and contract freely in all directions

while still securing the containment cell within the vessel’s structure.

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Figure 13--Floating Joint Utilizing Explosion Welded Transition Piece (Cross Sectional View)

Figure 14--Floating Joint (Side View)

Aluminum/Steel Transition

Aluminum Support (To Containment)

Steel Support (To Vessel Structure)

Floating Joint

Explosion Welded Transition

Floating Joint

Structural Steel

Aluminum

To Containment

To Vessel

Hardened Steel

Air Gap

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The joints are constructed of three different materials—the aluminum portion

which is welded to the containment cell, the structural steel member welded to the

vessel’s hull and the hardened steel floating joint. The lower half of the floating joint

(closest to the containment) is bonded to the aluminum via the explosion welded

transition piece.

The hardened steel portion of the joint is designed to allow movement within the

joint without being subject to excessive wear, galling, etc. The surfaces of the joint are

highly polished to have a low coefficient of friction between the surfaces and machined

to be press-fit together at ambient conditions ( )C°20 .

Together, the foam insulation and floating joint system provide a better support

structure for the containment than the Gaz Transport & Technigaz membrane designs.

There is no requirement for plywood structures to assist in the support of the

containment. The foam and floating joint combination provide a lasting, reliable,

maintenance free support structure. The plywood support structures found in the GTT

No. 96 and Mark III membrane containment systems, on the other hand, may fall victim

to problems caused by the effects of moisture and time.

With the dead space surrounding the outer shell of the containment, a safety zone

is built into the design in the event of a collision or grounding. The floating joint support

system adds an additional element of safety. As seen in Figs. 12&13, there are several

stress concentrators present in the floating joint design. Also, the floating joints are not

welded at 90 degree angles to the containment. These two characteristics are safety

features of the FCS design. In normal conditions, the foam insulation and individual

floating joints act as a common system supporting the containment and its contents. In

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the event of a collision, if the vessel’s support structure is damaged to the point of

endangering the containment, these supports are designed to fail at the welded seams

rather than puncture the containment cell.

Further Calculations

Please note that all calculations are rough estimates only. The alloys,

insulating materials, etc. were chosen for the purpose of analyzing this conceptual

design. More accurate analyses must be made for the specific materials chosen.

Before it is filled, the containment is at an ambient temperature of C°20 . As the

cell fills with cryogenic LNG the temperature of the containment and the immediate

surrounding area is reduced to a temperature of approximately C°−160 . Using the

dimensions of the containment cell from the previous example, it can be determined

approximately how much of a decrease in volume will be experienced over the

temperature differential.

Using the equation for the change in volume of a geometric solid, and the

containment dimensions from the previous example, the change in volume of the

ellipsoid containment is as follows:

TVV oellipsoid ∆⋅⋅=∆ α

Where, 3500,66 mV

o≈

Cmm

linearumalu °×=

−6

)(min 1023α

( ) CT °=−−=∆ 18016020

( )( )( ) ≅×=∆∴− 1801023600,77 6V 3320m

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This equates to approximately 3.3 centimeters of joint travel required in the

floating joints around the surface of the ellipsoidal containment cell to compensate for its

contraction over the expected temperature range. This amount will vary, however, as the

contraction around the cell will not be equal in all directions. Specifically, the

contraction will have the greatest effect at the top of the cell with minimal effect at the

bottom.

The materials in the joints themselves will contract as well. Assuming a void

space thickness of 2 meters, the actual floating joint will be approximately 1 meter from

the containment. The explosion welded transition piece in turn will be located 50

centimeters from the containment, half way in between the aluminum containment and

the floating joint. The thermal conductivity of aluminum is very high (approximately

CmW

°225 ) and, since the length of the aluminum portion of the support is relatively

short, the entire segment will be assumed to experience the same temperature differential

as the containment. The approximate contraction of the aluminum portion of the support

is therefore,

( )( )( ) =×=∆⋅⋅=∆− 18010235.0 6TLL

oα m002.0

Likewise, the hardened steel portion of the support, with a coefficient of thermal

expansion of approximately Cm

m°

×−61012 , will be assumed to experience the same

temperature differential as the aluminum portion due to its own thermal conductivity

29

(approximately Cm

W°

35 ), the thermal conductivity of the aluminum and its short

distance from the containment. Thus,

( )( )( ) =×=∆⋅⋅=∆− 18010125.0 6TLL

oα m001.0

Finally, the 1 meter section of hardened and carbon structural steel that makes up

the stationary section of the floating joint and the structural member of the support

system will have a change in length that can be assumed to be negligible in comparison to

the first two sections analyzed. The total joint movement is thus,

=++ 001.0002.0033.0 m036.0

Surrounding the floating joints and the containment cell is the foam insulation.

Again, this insulation is compressed prior to installation to compensate for the increasing

volume seen in the void space as the containment contracts. The material chosen in for

this analysis is Pittsburgh Corning FOAMGLAS® insulation. This insulation provides a

thermal conductivity of only Cm

W°

10.0 , while providing extremely low water

permeability and having a density of 3120m

kg. It also provides a compressive force of

kPa620 . FOAMGLAS® is comparable to the best characteristic of the foam and perlite

insulations used in the GTT No. 96 and Mark III membrane systems (Pittsburgh

Corning).

Insulation Material Perlite Foam FOAMGLAS®

Thermal Conductivity

°CmW 0.14 0.10 0.10

30

Permeability (% absorption by volume) 2-90 0.7 0.2

Density

3mkg

80-208 32 120

Compressive Force ( )kPa 620 310 620

Perhaps the most important characteristic is the compressive strength of the

FOAMGLAS® insulation. In the FCS containment design, the insulation serves an

integral role in the support of the containment. In fact, much like the membrane

containment designs, the insulation is the main source of support for this design. For the

containment cell of the dimensions described above, the surface area is approximately

2300,10 m , the lower half of which ( 2150,5 m ) is supported by the foam. The foam

provides a total vertical supporting force exceeding 300,000 metric tons. Considering

that a full containment of LNG, at a mass of about 3420m

kg, weighs approximately

30,000 tons, the FOAMGLAS® will provide excellent support for the containment.

Perhaps the only drawback to this choice of insulation would be the weight. If the

outside shell of the FCS were 2 meters wider all the way around the containment, the

total volume of space filled by the insulation would be approximately 3500,18 m .

( ) ( ) ( )[ ] ( ) ≈+−−⋅−⋅−⋅⋅=∴ 275500,662182212423

4 πV3500,18 m

This amount of FOAMGLAS® insulation would add about 2,200 metric tons to

each individual containment system. However, if necessary, the top portion of the

containment, which does not require the compressive force of the lower half, could be

insulated using a much lighter foam (polystyrene, for example) at the cost of a small

additional loss of product due to evaporation.

31

( ) ≅

+

32

2

500,18

2

2200 1400 metric tons

The foam and floating joint system together also provide added protection in the

event of a collision or grounding. The floating joints have additional room for movement

due to the contraction of the containment. In addition to its insulating qualities, the

density of the foam provides a cushioning effect that acts against the forces experienced

during a collision or grounding and serves as an additional buoyant layer should the hull

be compromised. The layer of FOAMGLAS® is also another barrier of defense against

puncture of the containment cell.

The supports themselves are installed at angles greater than 90 degrees to the

perpendicular to the containment. Particularly in the areas of the containment where

there would be the greatest likelihood of damage due to collision or grounding. The weld

seams provide stress concentrators in addition to those outlined in the previous

description of the floating joints. Additionally, the welds are weaker than the rest of the

containment cell. The floating joint support structure is purposely designed to break at

the weld seems and/or other stress concentrators rather than puncture the containment

cell.

A number of design considerations and construction materials may be

incorporated in the piping systems required with the Floating Containment System.

Piping may be made of an aluminum alloy similar to the containment cell material. An

explosion welded transition joint can again be used to bond this pipe to a steel or stainless

steel pipe as it penetrates the outer shell of the containment. Another design may utilize

an expanding/contracting bellows of suitable material attaching the containment to the

32

outer shell via a standpipe. Accommodations must also be made for the recovery of gas

vapors for possible use in the vessel’s propulsion engines.

Limitations of Proposed Design

While the FCS design promises advantages over previous design, it has

limitations. For example, while an LNG vessel utilizing the FCS design has greater

capacity than a comparable Kvaerner-Moss vessel, a vessel utilizing either of the GTT

membrane designs still has greater capacity and thus, greater short term economic

benefits.

The FCS design is a new, unproven concept. No design like it has been tested so

its economic and operational feasibility cannot be proven at this time. Likewise, the FCS

floating joint system is a new application of explosion welded transition joints that has

not been used before.

Although LNG containment systems are not new designs, details surrounding

their construction are considered proprietary. The Kvaerner-Moss spherical containment

and the GTT membrane containment systems are exclusive to the respective companies

that designed them. Their construction, particularly the explosion welded transition joint

of the Kvaerner-Moss design is not completely known and the details are kept fairly

guarded.

Likewise, the process of explosion welding is by no means a new technology. It

has been in existence since soldiers first noticed the copper jackets from bullets bonding

to the steel armor of tanks and other armored vehicles. However, the process is still

33

untested in many applications. Many traditional fastening methods on the other hand, are

tried and true in countless industries and functions.

Where explosion welding technology has been tested is in many military

applications. Naval vessels have been constructed with steel hulls and aluminum

interiors that utilize explosion welded joints as transition pieces. For reasons of security,

the details of materials used and results of construction testing such as sea trials are not

public knowledge and are available to very few.

Protected proprietary information and industry secrets make it difficult to

determine whether or not a conceptual design is feasible. As construction details and

results of real world industrial and military applications become a matter of public

knowledge, designs can be determined to be practical or not earlier on in the design

process. Until then designs can be conceived and tested only as far as the technologies

and designs are known to architects, engineers, grad students, etc.

All of the calculations made throughout the design process have been rough

estimates based on certain assumptions. Not all of the assumptions made may be the

correct. Values were used for coefficients of thermal expansion and conductivity based

on general alloy versions of the materials used. They do not take into account certain

factors. For some materials, the coefficient of thermal expansion changes with the

temperature. As a result, further research may show that alternate materials would fare

better in this application. Additionally, the details and characteristics of materials such as

insulation were based off of specifications from manufacturer’s data sheets and given on

their websites. These numbers are more than likely ideal values and may not prove true

in application.

34

Conclusions

The proposed design attempts to use the best aspects of already proven LNG

vessel containment designs. Taking a characteristic from the Kvaerner-Moss

containment design, aluminum is the material of choice in the Floating Containment

System. It is the lightest material of those analyzed allowing for a lighter and therefore

more economical vessel design. Aluminum is also the material with the best cryogenic

properties in comparison to the GTT membrane materials stainless steel and Invar®.

The ellipsoidal containment cell design allows more product to be carried on a

vessel of similar size to one with the Kvaerner-Moss design. The compressed foam

insulation in the support system mimic the support structure of the membrane designs by

holding the containment cell securely, while still protecting it from damage by avoiding a

direct transition joint, unlike the explosion welded transition joint found in the spherical

containment design. The floating joint structure adds an element of support not seen in

the membrane design that increases the strength and safety of the containment system.

While aspects of the Floating Containment System may prove to be impractical or

not economically feasible, it is a new approach that attempts to increase the efficiency of

LNG containment and transport. However, there are many more aspects of the design

and the materials used that must be analyzed.

As demand for cleaner, cheaper fuel sources grows the demand on the LNG

market will grow. The Floating Containment System may prove to be a legitimate

direction for the future of LNG vessel design and construction.

35

Works Cited

2006 International Fire Code. “Cryogenic Fluids”. Chapter 32, pp.279-284. 2006

Aker Kvaerner. History.

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.htm

Curt, Bob. “Marine Transportation of LNG”. QatargasII presentation, Intertanko

Conference. March 29, 2004

DMC Clad Metal Groupe SNPE. “Explosion Clad Plate Manufacturing”. URL

http://www.dynamicmaterials.com/data/brochures/EXWprocess2.pdf

Incropera, Frank P.; DeWitt, David P. Fundamentals of Heat and Mass Transfer, 5th

Edition, Wiley. ISBN 0-471-38650-2. August 9 2001

Mannan, Sam. Editor. Lees' Loss Prevention in the Process Industries (3rd Edition).

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William Andrew Publishing/Noyes. 1988. URL

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http://www.foamglasinsulation.com/mechanicalspecs.asp

Shrouf, Robert. Safe Handling of Cryogenic Fluids. GN470100, Issue B. October 31,

2006. URL http://www-irn.sandia.gov/corpdata/esh-manuals/gn470100/g100.htm

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Young, George A. and Banker, John G. “Explosion Welded, Bi-Metallic Solutions to

Dissimilar Metal Joining”. Society of Naval Architects and Marine Engineers.

Proceedings of the 13th Offshore Symposium. February 24, 2004

37

Works Consulted

2006 International Fire Code. “Cryogenic Fluids”. Chapter 32, pp.279-284. 2006

Aker Kvaerner. History.

http://www.akerkvaerner.com/Internet/AboutUs/AkerKvaernerGroup/History/History

.htm

American Bureau of Shipping. Guide for Building and Classing Membrane Tank Hull

Vessels: Hull Structural Design and Analysis Based on the ABS Safehull Approach.

October 2002

Avallone, Eugene A. and Baumeister, Theodore III. Editors. Mark’s Standard Handbook

for Mechanical Engineers, Tenth Edition. McGraw-Hill Companies, Inc. 1999

Castaneda, Christopher. “Manufactured and Natural Gas Industry”. EH.Net

Encyclopedia, edited by Robert Whaples. September 4, 2001. URL

http://eh.net/encyclopedia/article/castaneda.gas.industry.us

Curt, Bob. “Marine Transportation of LNG”. QatargasII presentation, Intertanko

Conference. March 29, 2004

High Energy Metals, Inc. Explosion Bonding Engineering and Design Basics. March 8,

2000

DMC Clad Metal Groupe SNPE. “Explosion Clad Plate Manufacturing”. URL

http://www.dynamicmaterials.com/data/brochures/EXWprocess2.pdf

Incropera, Frank P.; DeWitt, David P. Fundamentals of Heat and Mass Transfer, 5th

Edition, Wiley. ISBN 0-471-38650-2. August 9 2001

Mannan, Sam. Editor. Lees' Loss Prevention in the Process Industries (3rd Edition).

Chapter 22, pp.1-78. Elsevier Publications. 2005

38

Merrem & laPorte. “Triclad®: Welding Aluminum to Steel”. URL

http://www.triclad.com/pictures/triclad.pdf

Murr, Lawrence E. Shock Waves for Industrial Applications. Chapter 5, pp. 170-215.

William Andrew Publishing/Noyes. 1988. URL

http://www.knovel.com/knovel2/Toc.jsp?BookID=775&VerticalID=0

Pittsburgh Corning. “About FOAMGLAS® Insulation”. URL

http://www.foamglasinsulation.com/mechanicalspecs.asp

Robin Materials Inc. “Invar®”. URL http://www.rmat.com/invar.html

Shrouf, Robert. Safe Handling of Cryogenic Fluids. GN470100, Issue B. October 31,

2006. URL http://www-irn.sandia.gov/corpdata/esh-manuals/gn470100/g100.htm

Triplex GmbH. Basic Information: Triplex Plastic Panels: Extremely Rigid and

Lightweight. 2006. URL http://www.triplex-kunststoffplatten.de/english/basic-

information/plastic-panels.htm

UK P&I Club. “The Carriage of Liquefied Gases”. Issue #8. February 2005. URL

http://www.ukpandi.com/ukpandi/infopool.nsf/HTML/LPCtC8

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Dissimilar Metal Joining”. Society of Naval Architects and Marine Engineers.

Proceedings of the 13th Offshore Symposium. February 24, 2004