[Technical Field]
[0001] The present invention relates to an insulation wall fixing device for liquefied natural
gas storage tanks, and more particularly to an insulation wall fixing device for liquefied
natural gas storage tanks, which couples a primary insulation wall to a secondary
insulation wall disposed for insulation of liquefied natural gas.
[Background Art]
[0002] Natural gas is transported in a gaseous state via onshore or offshore gas pipelines,
or is transported in a liquid state, that is, in the form of liquefied natural gas
(LNG) to a distant destination by an LNG carrier. LNG is obtained by cooling natural
gas to a cryogenic temperature (about -163°C) and has a volume of about 1/600 that
of natural gas in a gaseous state. Thus, LNG is suited to long distance transport
by sea.
[0003] Structures for transporting or storing LNG, such as an LNG carrier designed to carry
LNG by sea to an onshore consumer site, are equipped with a storage tank that can
withstand cryogenic temperatures of LNG (commonly referred to as "cargo hold").
[0004] Such an LNG storage tank is divided into an independent storage tank and a membrane
type storage tank depending on whether a load of cargo is directly applied to an insulator.
Generally, the membrane type storage tank is classified into a GTT NO 96 storage tank
and a MARK III storage tank, and the independent storage tank is classified into a
MOSS storage tank and an IHI-SPB storage tank.
[0005] The NO 96 storage tank comprises primary and secondary sealing walls constituted
of 0.5 mm to 0.7 mm thick Invar (Ni content: 36%) membranes and primary and secondary
insulation walls provided in the form of insulating boxes fabricated by filling a
plywood box with an insulator, such as perlite powder.
[0006] Since the primary and secondary sealing walls of the NO 96 storage tank have almost
the same degree of liquid tightness and strength, it is possible to safely support
cargo for a considerable period of time with only the secondary sealing wall even
upon leakage of the primary sealing wall.
[0007] In addition, since the insulation walls of the NO 96 storage tank are provided in
the form of wood boxes filled with an insulator, the NO 96 storage tank has high compressive
strength and rigidity and thus can secure high levels of weldability and welding automation,
as compared with the MARK III storage tank.
[0008] The MARK III storage tank comprises a primary sealing wall constituted of 1.2 mm
thick stainless steel (SUS) membranes, a secondary sealing wall constituted of triplex
sheets, and primary and secondary insulation walls provided in the form of insulation
panels fabricated by bonding plywood to an upper or lower surface of polyurethane
foam.
[0009] The primary sealing wall of the MARK III storage tank has corrugations to absorb
thermal contraction caused by LNG at cryogenic temperatures. The corrugations can
prevent occurrence of excessive stress on the membranes by absorbing deformation of
the membranes.
[0010] The MARK III storage tank has disadvantages in terms of installation/fabrication
due to a low level of automation of the primary sealing wall, which is constituted
of corrugated membranes. However, since the stainless steel membrane and the triplex
sheet are less expensive and easier to construct than the Invar membrane and the polyurethane
foam has good insulation performance, the MARK III storage tank is widely used.
[0011] The primary insulation wall of the membrane-type storage tank is coupled to a fixing
device disposed on an upper surface of the secondary insulation wall to be securely
mounted on the upper surface of the secondary insulation wall.
[0012] FIG. 1 is a schematic view of a typical insulation wall fixing device for LNG storage
tanks.
[0013] Specifically, FIG. 1(a) shows mechanical coupling between a base socket 10 for coupling
to a primary insulation wall and an upper protective plate 20 of a secondary insulation
wall through rivets, FIG. 1(b) shows coupling between the base socket 10 and the upper
protective plate 20 of the secondary insulation wall through bonding, and FIG. 1(c)
shows coupling between the base socket 10 and the upper protective plate 20 of the
secondary insulation wall through bonding after cutting a portion of a lower surface
of the upper protective plate 20 of the secondary insulation wall. Here, reference
numeral 30 denotes an insulator disposed inside the secondary insulation wall.
[0014] Such a typical insulation wall securing device requires cutting of a substantial
portion of the upper protective plate 20 for securing the base socket 10, thereby
causing reduction in strength of the upper protective plate 20 of the secondary insulation
wall.
[0015] Although not shown in the drawings, welding of a secondary sealing wall is performed
on the base socket 10, thereby causing burn damage of the upper protective plate 20
due to welding heat. Therefore, there is a need for the provision of a solution to
these problems.
WO 2013/004944 A1 and
KR 20150041937 A disclose a thermally-insulating sealed tank.
[Disclosure]
[Technical Problem]
[0016] It is an aspect of the present invention to provide an insulation wall fixing device
for LNG storage tanks, which can improve strength of a coupling region between a primary
insulation wall and a secondary insulation wall by improving a fixing device for coupling
the primary insulation wall and the secondary insulation wall.
[Technical Solution]
[0017] In accordance with one aspect of the present invention, there is provided an insulation
wall fixing device for an LNG storage tank as defined in claim 1.
[0020] The secondary insulator may be formed of polyurethane foam (PUF) and the secondary
upper protective plate may be formed of plywood.
[0021] The base socket may be bonded to the secondary insulator.
[0024] In accordance with another aspect, there is provided an insulation wall fixing device
for securing a primary insulation wall to a secondary insulation wall in an LNG storage
tank, the fixing device comprising: a base socket mounted on a groove formed on an
upper surface of a secondary insulator of the secondary insulation wall, wherein a
lower end of the base socket protrudes in a step shape such that a step portion of
the base socket supports a lower surface of an upper protective plate of the secondary
insulation wall.
[0025] An uppermost surface of the base socket may be flush with an upper surface of the
upper protective plate, a step surface of the step portion protruding from the base
socket may be flush with the upper surface of the secondary insulator, and the base
socket may be formed with a fastening hole through which a stud is coupled to the
primary insulation wall.
[0026] The stud may include a vane protruding therefrom to be coupled to a secondary sealing
wall disposed between the primary insulation wall and the secondary insulation wall,
and the secondary sealing wall may be welded to the vane on the uppermost surface
of the base socket.
[Advantageous Effects]
[0027] In an insulation wall fixing device for LNG storage tanks according to the present
invention, an upper surface of a socket flange supports an upper protective plate
of a secondary insulation wall, whereby the upper protective plate can endure load
applied thereto while maintaining strength thereof, and a cut region of the upper
protective plate can be minimized, whereby the fixing device can have higher strength
than a typical insulation wall fixing device.
[0028] In addition, according to the present invention, welding of the secondary sealing
wall is performed on an upper surface of the base socket, thereby preventing burn
damage to the secondary upper protective plate due to welding heat.
[0029] Furthermore, the insulation wall fixing device according to the present invention
can improve productivity through reduction in on-board labor.
[Description of Drawings]
[0030]
FIG. 1 is a schematic view of a typical insulation wall fixing device for LNG storage
tanks.
FIG. 2 is a schematic view of an insulating structure of an LNG storage tank according
to the present invention.
FIG. 3 is a view of a secondary insulation panel of the LNG storage tank according
to the present invention.
FIG. 4 is a view of a primary insulation panel of the LNG storage tank according to
the present invention.
FIG. 5 is a schematic view of an insulation wall fixing device of the LNG storage
tank according to the present invention.
[Best Mode]
[0031] The above and other aspects, features, and advantages of the present invention will
become apparent from the detailed description of the following embodiments in conjunction
with the accompanying drawings.
[0032] Hereinafter, embodiments of the present invention will be described in detail. Like
components will be denoted by like reference numerals throughout the specification.
[0033] Herein, the terms "primary" and "secondary" are used to distinguish components providing
primary sealing or insulation to an LNG storage tank from components providing secondary
sealing or insulation to the LNG storage tank.
[0034] In addition, as used herein to describe components of a tank, the term "upper" or
"above" refers to an inward direction of the tank, regardless of the direction of
gravity, and the term "lower" or "below" refers to an outward direction of the tank,
regardless of the direction of gravity.
[0035] FIG. 2 is a schematic view of an insulating structure of an LNG storage tank according
to the present invention, FIG. 3 is a view of a secondary insulation panel of the
LNG storage tank according to the present invention, and FIG. 4 is a view of a primary
insulation panel of the LNG storage tank according to the present invention.
[0036] Referring to FIG. 2 to FIG. 4, the LNG storage tank according to the present invention
has a structure in which a secondary insulation wall 200 constituted of multiple secondary
insulation panels 210 and a primary insulation wall 100 constituted of multiple primary
insulation panels 110 are sequentially stacked on an inner wall of a hull.
[0037] A secondary sealing wall 400 may be interposed between the secondary insulation wall
200 and the primary insulation wall 100 and a primary sealing wall (not shown) may
be disposed on an upper side of the primary insulation wall 100. For convenience of
description, the primary sealing wall is not shown.
[0038] The primary and secondary insulation panels 110, 210 may be manufactured as unit
panels each having a hexahedral shape having a width-to-length ratio of about 1:3,
preferably as unit panels having a size of about 1 m x 3 m, without being limited
thereto.
[0039] The primary insulation panel 110 may be a sandwich panel in which plywood sheets
112, 113 are bonded to an upper or lower surface of an insulator 111 formed of polyurethane
foam (PUF) or to both upper and lower surfaces of the insulator 111.
[0040] Likewise, the secondary insulation panel 210 may be a sandwich panel in which plywood
sheets 212, 213 are bonded to an upper or lower surface of an insulator 211 formed
of polyurethane foam (PUF) or to both upper and lower surfaces of the insulator 111.
[0041] Preferably, the primary and secondary insulation panels 110, 210 constituting the
primary and secondary insulation walls 100, 200 are formed of rigid polyurethane foam
(RPUF), which has higher strength than general polyurethane foam, in order to form
the secondary sealing wall 400 with flat Invar membranes, as described below.
[0042] The secondary insulation panels 210 may be secured to an inner wall of the hull by
a bonding agent, such as mastic, or studs, and the secondary insulation panel 110
may be closely coupled to an upper side of the secondary sealing wall 400 by fixing
devices 300 disposed on the upper side thereof, with the secondary sealing wall 400
interposed between the primary insulation panels 110 and the secondary insulation
panels 210.
[0043] The primary sealing wall (not shown) directly contacts LNG to seal the LNG and may
be constituted of multiple stainless steel (SUS) membranes having corrugations formed
towards the interior of the storage tank to absorb contraction due to an extremely
low temperature inside the storage tank.
[0044] The primary sealing wall (not shown) may be constituted of multiple unit membranes
and may be sealed by welding the multiple unit membranes to anchor strips on the primary
insulation panels 110 so as not to generate a gap therebetween.
[0045] The secondary sealing wall 400 may be constituted of Invar membranes.
[0046] The secondary sealing wall 400 may be constituted of multiple Invar strakes and may
be sealed by welding the multiple Invar strakes to tongue members on the secondary
insulation panels 210 so as not to generate a gap therebetween. The Invar strakes
refer to band-shaped metal plates having a narrow width.
[0047] In the LNG storage tank according to the present invention, each of the primary and
secondary insulation walls 100, 200 is realized in the form of an insulation panel
in which plywood sheets are bonded to an upper surface and/or a lower surface of polyurethane
foam, and the secondary sealing wall 400 is constituted of flat invar membranes.
[0048] Typically, since the flat Invar membrane has a low coefficient of thermal contraction,
the flat Invar membrane is not suitable for a panel type insulating system in which
insulation panels are formed of polyurethane foam. In order to allow application of
the flat Invar membranes to the panel type insulating system, the insulation wall
supporting the membranes is required to be constituted of insulating boxes exhibiting
low thermal contraction and having high rigidity, as in a typical NO 96 type storage
tank.
[0049] However, according to the present invention, the LNG storage tank has a structure
for reinforcing the secondary insulation wall 200, whereby the secondary insulation
wall 200 can be constituted of the insulation panels formed of the polyurethane foam
and the secondary sealing wall 400 can be constituted of the flat Invar membranes.
[0050] According to the present invention, in order to reinforce the secondary insulation
wall 200, a corner portion of the storage tank is provided with a transverse connector
(not shown) which supports both ends of the secondary sealing wall 400.
[0051] The transverse connector is a grid structure disposed along an edge of each of front
and rear walls of the storage tank. The transverse connector is welded at one end
thereof to an anchoring bar provided to an inner wall of the hull to be secured to
a corner of the storage tank while supporting both ends of each of the primary and
secondary sealing walls 400 at the other end thereof, thereby enabling transfer of
load to the hull when the load is applied to the transverse connector.
[0052] The transverse connector is preferably formed of an Invar material having high rigidity
and an insulating box having high rigidity may be disposed inside the transverse connector
and between the transverse connector and the hull to support the transverse connector.
The insulating box may be prepared by filling a plywood box with perlite powder.
[0053] According to the present invention, since the transverse connector transfers part
of load applied to the sealing walls to the hull, the secondary insulation wall 200,
which supports the secondary sealing wall 400 constituted of the flat Invar membranes,
can be constituted of insulation panels having lower rigidity than the insulating
boxes.
[0054] As a result, according to the present invention, a welding line can be formed linearly
upon installation of the secondary sealing wall 400 on the secondary insulation wall
200, thereby enabling improvement in productivity through automation of welding.
[0055] Further, according to the present invention, each of the primary and secondary insulation
walls 100, 200 is constituted of the insulation panels formed of the polyurethane
foam, thereby improving insulating performance. The LNG storage tank according to
the present invention can reduce the thickness of the primary insulation wall to about
40% or more and the thickness of the secondary insulation wall to about 20% or more,
as compared with a typical NO 96 type storage tank in which the insulation walls are
provided in the form of insulating boxes, while securing the same insulating effects
as the typical NO 96 type storage tank.
[0056] The LNG storage tank according to the present invention has a structure in which
the secondary insulation panels 210 intersect with the primary insulation panels 110
disposed on the secondary insulation panels 210.
[0057] Referring to FIG. 2, the primary insulation panels 110 may be disposed to intersect
with the secondary insulation panels 210 such that a corner of each of the primary
insulation panels 110 is placed at the center of each of the secondary insulation
panels 210, whereby each primary insulation panel 110 is disposed to straddle upper
surfaces of four secondary insulation panels 210.
[0058] To achieve intersection between the primary insulation panels 110 and the secondary
insulation panels 210, the fixing devices 300 adapted to secure the primary insulation
panels 110 to the secondary insulation panels 210 may be disposed inside edges on
the upper surfaces of the secondary insulation panels 210, for example, at the center
of each of the upper surfaces thereof.
[0059] Referring to FIG. 3, one fixing device 300 may be disposed at the center of the insulation
panel 210 and other fixing devices 300 may be arranged to be separated from the fixing
device 300 at the center of the insulation panel 210 by the same distance in a longitudinal
direction.
[0060] The fixing device 300 is disposed on a central line C on the secondary insulation
panels 210 in a width direction to minimize displacement of the secondary insulation
panels 210 in the width direction due to stress applied to the secondary insulation
panels 210 and slits 214 may be formed at places separated forwards and backwards
from the fixing devices 300 by the same distance to minimize displacement of the fixing
devices 300 in the longitudinal direction.
[0061] Further, each of the primary insulation panels 110 may be provided with securing
portions S for coupling to the fixing device 300 at vertical edges on lateral sides
of the primary insulation panel 110 including four corners of the primary insulation
panel 110. The securing portions S may be arranged at constant intervals in the longitudinal
direction of the primary insulation panels 110.
[0062] Each of the securing portions S may be provided as a groove having a semicircular
or sector-shaped cross-section and may be compressed by fastening a nut to a stud
of the fixing device, with the stud of the fixing device 300 inserted into the securing
portion S so as to pass therethrough, whereby the primary insulation panels 110 can
be brought into close contact with the secondary insulation panels 210. This structure
will be described below in more detail.
[0063] In this embodiment, three fixing devices 300 are disposed on the secondary insulation
panels 210 and eight securing portions S are disposed at vertical edges of the primary
insulation panels 110.
[0064] According to this embodiment, the securing portions S formed on four primary insulation
panels 110 may be coupled together to the fixing device 300 disposed at the center
of the secondary insulation panels 210 and the securing portions S formed on two primary
insulation panels 110 may be coupled together to the fixing devices 300 separated
from the center of each of the secondary insulation panels 210.
[0065] As such, according to this embodiment, adjacent primary insulation panels 110 may
share the fixing devices 300 interposed therebetween and eight points for supporting
the primary insulation panels 110 may be guaranteed merely through three fixing devices
300 provided to one secondary insulation panel 210.
[0066] That is, according to the present invention, the securing portions S for coupling
to the fixing devices 300 are provided to the corners of the primary insulation panels
110, whereby the points for supporting the primary insulation panels 110 can be secured
as many as possible even with a small number of fixing devices 300, thereby improving
stability of the support structure and productivity of the insulation panels.
[0067] Reference numeral 215 indicates insertion grooves formed to receive the tongue members
to which the Invar strakes constituting the secondary sealing wall 400 are welded
and reference numeral 115 indicates insertion grooves formed to receive the tongue
members received in the insertion grooves 215 and edges of the Invar strakes welded
to the tongue members.
[0068] Reference numeral 114 indicates multiple slits formed on the primary insulation panels
110 to distribute stress concentration caused by thermal contraction and reference
numeral 116 indicates anchor strips disposed for welding of the primary sealing wall.
[0069] FIG. 5 is a schematic view of an insulation wall fixing device of the LNG storage
tank according to the present invention. Hereinafter, the structure of the insulation
wall fixing device 300 of the LNG storage tank according to the present invention
will be described.
[0070] As shown in FIG. 5, the primary insulation wall 100 includes a primary insulator
111 and a primary lower protective plate 113, and the secondary insulation wall 200
includes a secondary insulator 211 and a secondary upper protective plate 212. As
described above, both the primary insulator 111 and the secondary insulator 211 may
be formed of polyurethane foam (PUF), and both the primary lower protective plate
113 and the secondary upper protective plate 212 may be formed of plywood sheets.
[0071] The secondary upper protective plate 212 of the secondary insulation wall 200 may
be formed with a hole corresponding to a socket body 311 described below and the primary
insulation wall 100 may be formed with the securing portions S for coupling to the
fixing devices 300. The securing portion S provides a space for receiving an upper
portion of the fixing device 300.
[0072] Referring to FIG. 5, the insulation wall fixing device 300 of the LNG storage tank
according to the present invention includes a base socket 310 disposed on the secondary
insulation wall 200; a stud 320 screwed to the base socket 310 and having an upper
end inserted into the securing portion S formed on the primary insulation wall 100;
and a lock nut 330 coupled to the stud 320 inserted into the securing portion S.
[0073] The base socket 310 includes a socket body 311 which constitutes a body of the base
socket 310, and a socket flange 312 protruding from a lower circumference of the socket
body 311 to be inserted into a space between a groove formed on an upper surface of
the secondary insulator 211 and the secondary upper protective plate 212.
[0074] The base socket 310 may be mounted on the groove formed on the upper surface of the
secondary insulator 211 by bonding a lower surface of the base socket 310 to an upper
surface of the groove.
[0075] An upper surface of the socket body 311 may be flush with an upper surface of the
secondary upper protective plate 212 and an upper surface of the socket flange 312
may be flush with the upper surface of the secondary insulator 211. That is, as shown
in the drawings, the base socket 310 may have a cross-section stepped by the socket
body 311 and the socket flange 312.
[0076] The socket flange 312 is inserted into the space between the groove formed on the
upper surface of the secondary insulator 211 and the secondary upper protective plate
212 such that the upper surface of the socket flange 312 supports an end of the secondary
upper protective plate 212.
[0077] According to the present invention, the socket flange 312 allows the secondary upper
protective plate 212 to endure load applied from the fixing devices 300 by supporting
the secondary upper protective plate 212 and the secondary upper protective plate
212 is not cut in the thickness direction and thus can endure load while maintaining
strength thereof.
[0078] Accordingly, the insulation wall fixing device according to the present invention
can secure higher fastening strength than a typical fastening mechanism (see FIG.
1) and can facilitate strength reinforcement through adjustment of the size or thickness
of the base socket 310, the thickness of the secondary upper protective plate 212,
and the like, as needed.
[0079] The base socket 310 may be formed of stainless steel (SUS).
[0080] The base socket 310 may be secured to an upper side of the secondary insulation wall
200 by placing the base socket 310 on the groove formed on the upper surface of the
secondary insulator 211, followed by bonding the base socket 31 to the secondary upper
protective plate 212 such that the secondary upper protective plate 212 is placed
on the upper surface of the secondary insulator 211 and the upper surface of the socket
flange 312.
[0081] That is, the insulation wall fixing device 300 according to the present invention
may be stored with the base socket 310 disposed on the secondary insulation wall 200,
thereby improving productivity through omission of riveting and bonding operations
in on-board operation.
[0082] According to the present invention, the stud 320 may be a collar stud and may include
a vane 321 protruding from a body of the stud 320 and mounted on an upper surface
of the socket body 311.
[0083] The vane 321 extends from the body of the stud 320 to be slanted downwards therefrom
such that a distal end of the vane 321 is placed on the upper surface of the socket
body 311.
[0084] Here, the secondary sealing wall 400 may be coupled to the distal end of the vane
321 by welding. That is, as shown in the drawings, the secondary sealing wall 400
may be welded to the distal end of the vane 321 to be placed between the secondary
insulation wall 200 and the primary insulation wall 100.
[0085] According to the present invention, a contact region between the secondary sealing
wall 400 and the vane 321 is formed on the upper surface of the socket body 311 and
the secondary sealing wall 400 is welded to the vane 321 in the contact region therebetween.
[0086] Accordingly, according to the present invention, welding of the secondary sealing
wall 400 is performed on the upper surface of the socket body 311, thereby preventing
burn damage on the secondary upper protective plate 212 of the secondary insulation
wall 210.
[0087] In addition, in the structure wherein the stud 320 is provided in the form of the
collar stud including the vane 321 as described above, the vane 321 is welded to the
secondary sealing wall 400 to secure water tightness between the base socket 310 and
the stud 320, whereby a stud fastening hole h of the base socket 310 can be formed
in the form of a through-hole or a blind hole.
[0088] If the stud 320 is a typical stud, water tightness cannot be secured in a gap for
fastening between the base socket 310 and the stud 320. In this case, the stud fastening
hole h of the base socket 310 is preferably formed in a blind hole shape.
[0089] The insulation wall fixing device 300 of the LNG storage tank according to the present
invention may further include a flat washer 340 inserted into the stud 320 through
an upper portion of the stud 320 and supported by the primary lower protective plate
113 in a region of the securing portion S; and a spring washer 350 disposed on an
upper surface of the flat washer 340 and supporting the lock nut 330.
[0090] Although some embodiments have been described herein, it should be understood that
these embodiments are provided for illustration only and are not to be construed in
any way as limiting the present invention, and that various modifications, changes,
alterations, and equivalent embodiments can be made by those skilled in the art.
[0091] Therefore, the scope of the present invention should be defined by the appended claims