AU2020413201B2

AU2020413201B2 - Cargo tank unit and ship

Info

Publication number: AU2020413201B2
Application number: AU2020413201A
Authority: AU
Inventors: Ryusuke TAKADA; Shin Terada; Michihisa WATANABE
Original assignee: Mitsubishi Shipbuilding Co Ltd
Current assignee: Mitsubishi Shipbuilding Co Ltd
Priority date: 2019-12-27
Filing date: 2020-12-22
Publication date: 2024-05-02
Anticipated expiration: 2040-12-22
Also published as: JP2021107171A; KR20220098236A; JP7527107B2; EP4056460B1; CN114829245B; DK4056460T3; AU2020413201A1; CN114829245A; KR102700217B1; EP4056460A4; EP4056460A1; WO2021132277A1

Abstract

A cargo tank unit comprising a cargo tank, a skirt, and a welded section. The cargo tank is an IMO tank type C under the IGC code. The skirt has the upper end thereof connected to the lower half of the cargo tank, across the perimeter direction. As the skirt extends downwards, the skirt extends towards the outside, in the radial direction, of the cargo tank and is fixed to the hull. The welded section fixes the upper end of the skirt to the cargo tank, across the perimeter direction.

Description

DESCRIPTION

Title of Invention

CARGO TANK UNIT AND SHIP

Technical Field

[0001]

The present disclosure relates to a cargo tank unit

and a ship.

The present application claims priority with respect

to Japanese Patent Application No. 2019-238408 filed in

Japan on December 27, 2019, the contents of which are

incorporated herein by reference.

Background Art

[0002]

A ship carrying liquefied gas such as natural gas is

equipped with a cargo tank accommodating the liquefied gas.

For example, Patent Document 1 discloses a configuration in

which a cargo tank is supported by a hull via a cylindrical

skirt. The upper end portion of the skirt described in

Patent Document 1 is disposed at the equatorial position of

the cargo tank. The upper end portion of this skirt is

fixed by welding to the equatorial part of the cargo tank.

[0003]

Such cargo tanks are designed in accordance with the

International Maritime Organization (IMO) Tank Type B

requirements specified in the International Gas Carrier (IGC)

Code, which is the IMO safety rules for liquefied gas ships.

Citation List

Patent Literature

[0004]

[PTL 1] Japanese Patent No. 6342358

Summary of Invention

Technical Problem

[0005]

An IMO Tank Type B cargo tank is one in which the

stress of each part of the structure is precisely grasped

using, for example, a model test and a detailed analysis

method, and fatigue analysis and fracture mechanism analysis

are accurately performed. Accordingly, the welded portion

between the cargo tank and a skirt needs to meet the same

fatigue strength requirements as the tank. For this reason,

a ring-shaped member formed by machining is generally used

for the welded portion between the equatorial part of the

cargo tank and the skirt. This ring-shaped member is joined

between the upper half portion and the lower half portion

of the cargo tank. The upper end of the lower half portion

of the cargo tank and the upper end portion of the skirt

disposed on the radially outer side of the cargo tank are welded to the lower end portion of the ring-shaped member.

Accordingly, the thickness of the lower end portion of the

ring-shaped member is the sum of the wall thickness of the

lower half portion of the cargo tank and the wall thickness

of the upper end portion of the skirt.

[00061

In the IMO Tank Type B cargo tank, the upper limit of

the wall thickness of each part including the ring-shaped

member is 40 mm unless the material is an aluminum alloy.

The wall thickness of the lower half portion of the cargo

tank is the thickness of the welded ring-shaped member (up

to 40 mm) minus the wall thickness of the upper end portion

of the skirt. In other words, at least in the lower half

portion of the cargo tank, an increase in wall thickness is

limited to a certain level. This hinders an increase in

the size of the cargo tank required to have pressure

resistance.

[0007]

Preferred embodiments of the present invention seek to

provide a cargo tank unit and a ship enabling an increase

in the wall thickness of a cargo tank and, by extension, an

increase in the size of the cargo tank.

[00081

In accordance with one aspect of the present

invention, there is provided a cargo tank unit comprising: a cargo tank of IMO IGC Code Tank Type C; a skirt having an upper end connected to a lower half portion of the cargo tank over a circumferential direction and extending downward to be fixed to a hull; and a welded portion fixing the upper end of the skirt to the cargo tank over the circumferential direction, wherein the skirt includes a tubular portion and a tank support portion, the tubular portion has a cylindrical shape extending in-an up-down direction, and the tank support portion is continuously provided on an upper portion of the tubular portion and extends downward and outward in a radial direction of the cargo tank, wherein an angle formed by the tank support portion and a central axis of the tubular portion is formed so as to gradually increase upward.

Advantageous Effects of Invention

[00091

According to the ship of the present disclosure, it is

possible to increase the wall thickness of a cargo tank and,

by extension, increase the size of the cargo tank.

Brief Description of Drawings

[0010]

Fig. 1 is a plan view illustrating an overall

configuration of a ship according to an embodiment of the

present disclosure.

Fig. 2 is a half cross-sectional view in which a cargo

tank provided on the ship according to the embodiment of

the present disclosure is viewed from the ship stern

direction.

Fig. 3 is an enlarged cross-sectional view

illustrating the configuration of a cargo tank-skirt joint

according to the embodiment of the present disclosure.

Description of Embodiments

[0011]

Fig. 1 is a plan view illustrating an overall

configuration of a ship according to an embodiment of the

present disclosure. Fig. 2 is a half cross-sectional view

in which a cargo tank provided on the ship is viewed from

the ship stern direction.

As illustrated in Figs. 1 and 2, a ship 1 of the

embodiment of the present disclosure, for example, stores

and carries liquefied gas such as liquefied natural gas.

The ship 1 includes at least a hull 2, a cargo tank 20, a

skirt 30, and a welded portion 40.

For convenience, the cargo tank 20, the skirt 30, and

the welded portion 40 are collectively referred to as a

cargo tank unit.

[0012]

The hull 2 has a pair of broadsides 3A and 3B, a ship

bottom 4, and an upper deck 5, which form the outer shell of the hull 2. The broadsides 3A and 3B are provided with a pair of broadside skins respectively forming the left and right broadsides. The ship bottom 4 is provided with a ship bottom skin connecting the broadsides 3A and 3B. By the pair of broadsides 3A and 3B and the ship bottom 4, the outer shell of the hull 2 has a U shape in a cross section orthogonal to a ship stern direction Da. The upper deck 5 is a whole deck exposed to the outside. In the hull 2, an upper structure 7 having a living quarter is formed on the upper deck 5 on a stern 2b side.

[0013]

In the hull 2, a cargo loading section (hold) 8 is

formed closer to a bow 2a side than the upper structure 7.

The cargo loading section 8 is recessed toward the ship

bottom 4 below the upper deck 5 and is open upward.

[0014]

A plurality of the cargo tanks 20 are provided in the

cargo loading section 8. The plurality of cargo tanks 20

are disposed side by side in the ship stern direction Da.

An upper portion 20a of each cargo tank 20 protrudes upward

beyond the upper deck 5 of the hull 2. The upper portions

20a of the plurality of cargo tanks 20 are covered with tank

covers 25 provided on the upper deck 5. A heat insulating

material (not illustrated) that suppresses heat input from the outside is provided on the outer surface of each of the plurality of cargo tanks 20.

[0015]

The cargo tank 20 has a spherical shape. Liquefied

gas to be carried is accommodated in the cargo tank 20. In

the embodiment of the present disclosure, the liquefied gas

accommodated in the cargo tank 20 is, for example, a high

pressure low-temperature gas of approximately 9 to 20 (BarG)

The cargo tank 20 is an IMO Tank Type C tank specified in

the IMO IGC Code.

[0016]

Each cargo tank 20 includes a lower half portion 21

and an upper half portion 22.

The lower half portion 21 is hemispherical in the lower

portion of the cargo tank 20. The diameter dimension of

the lower half portion 21 gradually increases upward from

below. The lower half portion 21 may, for example, have a

semi-true sphere shape having a constant radius of curvature

or be formed so as to have a radius of curvature increasing

in stages upward from below in the cross section illustrated

in Fig. 2.

[0017]

The upper half portion 22 is provided above the lower

half portion 21. The upper half portion 22 is hemispherical

in the upper portion of the cargo tank 20. The diameter dimension of the upper half portion 22 gradually decreases upward from below. In the embodiment of the present disclosure, the upper half portion 22 may have a semi-true sphere shape having a constant radius of curvature or be formed so as to have a radius of curvature increasing in stages upward from below.

The cargo tank 20 is not limited to the above shape.

The cargo tank 20 may be configured to include a cylindrical

portion (not illustrated) or the like between the upper half

portion 22 and the lower half portion 21.

[0018]

Each cargo tank 20 is supported on the hull 2 by the

skirt 30. Each cargo tank 20 has a tank structure

independent of the hull 2. The cargo tank 20 has a liquid

tight structure and self-supports the load of the liquefied

gas accommodated in the cargo tank 20.

[0019]

Fig. 3 is an enlarged cross-sectional view

illustrating the configuration of the joint between the

cargo tank and the skirt.

The skirt 30 supports the cargo tank 20. The skirt 30

has a cylindrical shape extending in an up-down direction

Dv as a whole. The lower end portion of the skirt 30 is

fixed on a foundation deck portion 9 provided in the bottom

portion of the cargo loading section 8. An upper end 30t of the skirt 30 is connected to an outer peripheral surface

21f of the lower half portion 21 of the cargo tank 20.

[0020]

The skirt 30 includes a tubular portion 31 and a tank

support portion 32.

The tubular portion 31 has a cylindrical shape

extending in the up-down direction Dv and has a constant

diameter dimension over the up-down direction Dv. The

tubular portion 31 in this embodiment has a cylindrical

shape centered on an axis a passing through the center of

the cargo tank 20 in the ship width direction.

[0021]

The tank support portion 32 is provided in the upper

end portion of the skirt 30. The tank support portion 32

is continuously provided on the upper portion of the tubular

portion 31. The tank support portion 32 extends upward and

toward the inside in a radial direction Dr. In other words,

the tank support portion 32 extends toward the outside in

the radial direction Dr and downward from a tip 32t. In

this embodiment, the tank support portion 32 includes a

curved portion 32w that curves upward and to the inside in

the radial direction Dr. The curved portion 32w is formed

such that the angle formed by the curved portion 32w and

the central axis of the tubular portion 31 gradually

increases upward. In this embodiment, the tip 32t of the curved portion 32w on the inside in the radial direction Dr is the upper end 30t of the skirt 30. The tip 32t of the curved portion 32w abuts against the outer peripheral surface 21f of the lower half portion 21 of the cargo tank

20. Here, the radial direction Dr means the radial

direction centered on the axis a described above. In

addition, the circumferential direction in the following

description means the circumferential direction centered on

the axis a.

[0022]

A crossing angle e of the tip 32t of the curved portion

32w with respect to the outer peripheral surface of the

cargo tank 20 can be, for example, approximately 30 degrees

to 90 degrees. Here, the crossing angle e is the angle that

is formed by the innermost part of an inner surface 30f of

the upper end 30t in the radial direction Dr (that is, the

tip 32t) and a tangent tal of the outer peripheral surface

21f (circular arc shape in Fig. 3) of the cargo tank 20 at

the position intersecting the inner surface 30f in a cross

section including the axis a (see Fig. 3). In this

embodiment, the curved portion 32w is provided and the tip

32t of the inner surface 30f is also curved. Accordingly,

the crossing angle e is the angle that is formed by a tangent

ta2 at the tip 32t of the inner surface 30f (curved in Fig.

3) and the tangent tal on the outer peripheral surface 21f

in a cross-sectional view including the axis a.

[0023]

As illustrated in Fig. 2, an inner diameter Dl of the

upper end 30t of the skirt 30 (the tip 32t of the curved

portion 32w) is smaller than an outer diameter D2 at the

equatorial part of the cargo tank 20. In Fig. 2, the inner

diameter Dl and the outer diameter D2 are illustrated in

half for convenience.

As a result, the cargo tank 20 is supported from below

by the upper end 30t of the skirt 30.

[0024]

As illustrated in Fig. 3, the cargo tank 20 and the

skirt 30 are joined by welding. As a result, the welded

portion 40 is formed at the joint between the cargo tank 20

and the skirt 30. A high-strength welding material such as

9% Ni steel can be used as the welding material that is used

in welding the cargo tank 20 and the skirt 30. By using

such a high-strength welding material, the strength of the

welded portion 40 can be enhanced, and thus the reliability

of the welded portion 40 can be improved.

[0025]

The welded portion 40 fixes the upper end 30t of the

skirt 30 to the cargo tank 20. In the welded portion 40

exemplified in this embodiment, the upper end 30t of the skirt 30 is continuously fixed to the outer peripheral surface 21f of the cargo tank 20 over the entire circumference in the circumferential direction. Although a case where the welded portion 40 is continuously formed over the entire circumference in the circumferential direction has been described, the present disclosure is not limited to this configuration. For example, the welded portion 40 may be formed at a part in the circumferential direction.

In this case, the upper end 30t of the skirt 30 is fixed to

the cargo tank 20 at a part in the circumferential direction.

In this case, the welded portion 40 may be intermittently

provided in the circumferential direction of the cargo tank

20, that is, at a plurality of locations.

[0026]

A joining member 50 is provided between the outer

peripheral surface 21f of the lower half portion 21 of the

cargo tank 20 and the inner surface 30f of the skirt 30

facing the inside in the radial direction Dr. The joining

member 50 is provided at a plurality of locations at

intervals in the circumferential direction of the lower half

portion 21 of the cargo tank 20. The joining member 50

exemplified in this embodiment is formed in a flat plate

shape along a vertical plane orthogonal to the

circumferential direction (that is, a virtual plane

including the axis a). The joining member 50 has an inside edge portion 50a welded along the outer peripheral surface

21f of the lower half portion 21 of the cargo tank 20 on

the inside in the radial direction Dr and an outside edge

portion 50b welded along the inner surface 30f of the skirt

on the outside in the radial direction Dr. Welding may

be performed on only one of the inside edge portion 50a and

the outside edge portion 50b. A lower edge portion 50c of

the joining member 50 exemplified in this embodiment is

formed in a circular arc shape that is recessed upward in

the central portion in radial direction Dr. The shape of

the lower edge portion 50c is not limited to the circular

arc shape in which the central portion in the radial

direction Dr is recessed upward.

[00271

The ship of the above embodiment further includes the

joining member 50 provided at a plurality of locations at

intervals in the circumferential direction of the lower half

portion 21 of the cargo tank 20 and joining the lower half

portion 21 of the cargo tank 20 and the inner surface of

the skirt 30.

Accordingly, the spherical lower half portion 21 and

the inner surface 30f of the skirt 30 can be more firmly

joined by the plurality of joining members 50 provided in

the circumferential direction. As a result, it is possible to further enhance the strength with which the skirt 30 supports the cargo tank 20.

[0028]

In the ship of the above embodiment, the upper end

portion of the skirt 30 extends downward and toward the

outside in the radial direction Dr of the cargo tank 20.

The upper end 30t of the skirt 30 supporting the cargo tank

is connected to the lower half portion 21 of the cargo

tank 20. In addition, the upper end 30t of the skirt 30 is

connected by the welded portion 40 to the outer peripheral

surface 21f of the lower half portion 21 of the cargo tank

so as to abut from the outside in the radial direction

Dr.

Accordingly, the upper end 30t of the skirt 30 and the

outer peripheral surface 21f of the lower half portion 21

of the cargo tank 20 are reliably welded, and the joining

strength of the welded portion 40 can be effectively

enhanced.

[0029]

In the ship of the above embodiment, the upper end

portion of the skirt 30 has the curved portion 32w that

curves upward and to the inside in the radial direction Dr,

and the tip 32t of the curved portion 32w is welded to the

outer peripheral surface 21f of the cargo tank 20.

By forming the curved portion 32w in the upper end

portion of the skirt 30 in this manner, the lower end of

the curved portion 32w and the upper end of the tubular

portion 31 can be formed smoothly and continuously.

Accordingly, in the skirt 30 where the tip 32t of the curved

portion 32w is welded to the outer peripheral surface 21f

of the cargo tank 20, stress attributable to the load of

the cargo tank 20 being locally concentrated is suppressed.

[00301

Although an embodiment of the present disclosure has

been described in detail with reference to the drawings,

the specific configuration is not limited to this embodiment

and also includes, for example, design changes within the

gist of the present disclosure.

Although the curved portion 32w is provided in the

upper end portion of the skirt 30 in the above embodiment,

the present disclosure is not limited thereto. The upper

end portion of the skirt 30 may extend downward and toward

the outside in the radial direction Dr of the cargo tank 20

and may have a conical tube shape as an example. In this

case, a corner portion is formed at the joint part between

the lower end of the conical tube-shaped part and the upper

end of the tubular portion 31 in the upper end portion of

the skirt 30. Accordingly, in a case where stress

attributable to the load of the cargo tank 20 may be locally concentrated on the corner portion between the lower end of the conical tube-shaped part and the tubular portion 31, the corner portion may be reinforced or the like so that sufficient strength is ensured.

[00311

In addition, although the upper end portion of the

skirt 30 in the above embodiment is provided so as to extend

downward and toward the outside in the radial direction Dr

of the cargo tank 20, the present disclosure is not limited

thereto. For example, the upper end portion of the skirt

may have a cylindrical shape having a constant diameter

along the up-down direction Dv.

[0032]

Although the joining member 50 is provided in the above

embodiment, the shape of the joining member 50 is not

limited at all. The joining member 50 may have another

shape as appropriate insofar as the joining member 50 joins

the lower half portion 21 of the cargo tank 20 and the inner

surface 30f of the skirt 30. In addition, the

circumferential installation interval, count, and the like

of the joining member 50 can be appropriately changed.

Further, a configuration without the joining member 50 is

also possible.

[00331

Although the cargo tank 20 and the skirt 30 in the

above embodiment are provided in the cargo loading section

8 formed in the hull 2, the present disclosure is not limited

thereto. For example, the cargo tank 20 and the skirt 30

may be provided on, for example, the upper deck 5.

In addition, although the above embodiment assumes

installation on the hull 2, the present disclosure is not

limited thereto. For example, providing on a floating body

(not illustrated) may be performed instead.

[00341

The ship 1 described in the embodiment is, for example,

grasped as follows.

[00351

(1) A cargo tank unit according to a first aspect

includes: a cargo tank 20 of IMO IGC Code Tank Type C; a

skirt 30 having an upper end 30t connected to a lower half

portion 21 of the cargo tank 20 over a circumferential

direction and extending downward to be fixed to a hull 2;

and a welded portion 40 fixing the upper end 30t of the

skirt 30 to the cargo tank 20 over the circumferential

direction.

[00361

The IMO Tank Type C cargo tank 20 is designed based on

pressure vessel standards to be capable of withstanding the temperature and pressure of the liquefied gas accommodated therein. In the IMO IGC Code Tank Type C, fatigue strength requirements are not required up to the joint with the skirt as in the IMO IGC Code Tank Type B. Accordingly, the cargo tank 20 has excellent strength characteristics because it is spherical, it can be designed to be increased in wall thickness, and an increase in diameter and an increase in capacity can be achieved with strength ensured.

[00371

(2) The cargo tank unit according to a second aspect,

which is the cargo tank unit of (1), further includes a

joining member 50 provided at a plurality of locations of

the lower half portion 21 of the cargo tank 20 at intervals

in the circumferential direction and joining the lower half

portion 21 of the cargo tank 20 and an inner surface 30f of

the skirt 30.

[00381

As a result, the spherical lower half portion 21 and

the inner surface 30f of the skirt 30 can be more firmly

joined by the plurality of joining members 50 provided in

the circumferential direction. As a result, it is possible

to further enhance the strength with which the skirt 30

supports the cargo tank 20.

[00391

(3) In the cargo tank unit according to a third aspect,

which is the cargo tank unit of (1) or (2), the skirt 30

includes a tubular portion 31 and a tank support portion 32,

the tubular portion 31 has a cylindrical shape extending in

an up-down direction, and the tank support portion 32 is

continuously provided on an upper portion of the tubular

portion 31 and extends downward and outward in a radial

direction Dr of the cargo tank 20.

[0040]

As a result, the tank support portion 32 is connected

to the outer peripheral surface 21f of the lower half

portion 21 of the cargo tank 20 so as to abut from the

outside in the radial direction Dr. As a result, the tank

support portion 32 and the outer peripheral surface 21f of

the lower half portion 21 of the cargo tank 20 are reliably

welded, and the joining strength of the welded portion 40

is effectively enhanced.

[0041]

(4) In the cargo tank unit according to a fourth aspect,

which is the cargo tank unit of (3), an angle formed by the

tank support portion 32 and a central axis of the tubular

portion 31 is formed so as to gradually increase upward.

[0042]

In this manner, corner portion formation at the joint

part between the tank support portion 32 and the tubular portion 31 is suppressed. As a result, in the skirt 30 welded to the outer peripheral surface 21f of the cargo tank

20, stress attributable to the load of the cargo tank 20

being locally concentrated is suppressed.

[0043]

(5) A ship according to a fifth aspect includes the

cargo tank unit according to any one of (1) to (4).

[0044]

On condition that the capacity of the cargo tank 20 is

increased, the number of the cargo tanks 20 on the hull 2

can be reduced and the manufacturing cost of the ship 1 can

be reduced.

Industrial Applicability

[0045]

According to the present disclosure, it is possible to

increase the wall thickness of a cargo tank and, by

extension, increase the size of the cargo tank.

Reference Signs List

[0046]

The reference in this specification to any prior

publication (or information derived from it), or to any

matter which is known, is not, and should not be taken as an

acknowledgment or admission or any form of suggestion that

that prior publication (or information derived from it) or

known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[00471

Throughout this specification and the claims which

follow, unless the context requires otherwise, the word

"comprise", and variations such as "comprises" and

"comprising", will be understood to imply the inclusion of

a stated integer or step or group of integers or steps but

not the exclusion of any other integer or step or group of

integers or steps.

[0048]

While various embodiments of the present invention have

been described above, it should be understood that they have

been presented by way of example only, and not by way of

limitation. It will be apparent to a person skilled in the

relevant art that various changes in form and detail can be

made therein without departing from the spirit and scope of

the invention. Thus, the present invention should not be

limited by any of the above described exemplary embodiments.

[0049]

1: ship

2: hull

2a: bow

2b: stern

3A, 3B: broadside

4: ship bottom

5: upper deck

7: upper structure

8: cargo loading section

9: foundation deck portion

20: cargo tank

20a: upper portion

21: lower half portion

21f: outer peripheral surface

22: upper half portion

25: tank cover

30: skirt

30f: inner surface

30t: upper end

31: tubular portion

32: tank support portion

32t: tip

32w: curved portion

40: welded portion

50: joining member

50a: inside edge portion

50b: outside edge portion

50c: lower edge portion

Dl: inner diameter

D2: outer diameter

Da: ship stern direction

Dr: radial direction

Dv: up-down direction

0: crossing angle

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

[Claim 1]

A cargo tank unit comprising:

a cargo tank of IMO IGC Code Tank Type C;

a skirt having an upper end connected to a lower half

portion of the cargo tank over a circumferential direction

and extending downward to be fixed to a hull; and

a welded portion fixing the upper end of the skirt to

the cargo tank over the circumferential direction, wherein

the skirt includes a tubular portion and a tank support

portion,

the tubular portion has a cylindrical shape extending

in an up-down direction, and

the tank support portion is continuously provided on

an upper portion of the tubular portion and extends downward

and outward in a radial direction of the cargo tank,

wherein an angle formed by the tank support portion

and a central axis of the tubular portion is formed so as

to gradually increase upward.
[Claim 2]

The cargo tank unit according to Claim 1, further

comprising joining members provided at a plurality of

locations of the lower half portion of the cargo tank at intervals in the circumferential direction and joining the lower half portion of the cargo tank and an inner surface of the skirt.
[Claim 3]

A ship comprising the cargo tank unit according to

Claim 1 or 2.