EP1732828B1

EP1732828B1 - Metal membrane panel of insulated lng cargo tank

Info

Publication number: EP1732828B1
Application number: EP04808205A
Authority: EP
Inventors: Keh-Sik 11-1303 Hyun-dai apt. MIN; Oi-Hyun Kim; Ick-Hung Choi; Sun-Il 707 ho Woo-sung apt. 2 dong WON; Byong Man 1002 ho Han-a-rum-hyun-dai KIM
Original assignee: Hyundai Heavy Industries Co Ltd
Current assignee: HD Hyundai Heavy Industries Co Ltd
Priority date: 2004-03-30
Filing date: 2004-11-23
Publication date: 2010-02-10
Anticipated expiration: 2024-11-23
Also published as: JP4564051B2; JP2007530892A; EP1732828A4; EP1732828A1; WO2005095234A1; KR100707675B1; KR20050096357A

Description

Technical Field

The present invention relates to a metal membrane panel of an insulated LNG cargo tank, and, more particularly, to a metal membrane panel of an insulated LNG cargo tank, which includes a plurality of rectangular unit corrugations formed thereon, and transverse and longitudinal connecting corrugations which connect the rectangular unit corrugations to each other, so as to alleviate localized stress concentrations, and thus, to improve a functional stability.

Background Art

Document JP-A-55 082898 discloses that a joint structure in low temperature storage tank to ensure absorption of thermal stress by forming folds in crisscross in circumferential direction of ring corrugation between each engaging part in such a way that fluted corrugations are engaged from three directions or more to a ring corrugatation lower than the top part of the ring corrugation. A quasi-octagonal flat plate is encircled by a convex undulate ring corrugation which has somewhat higher top part than fluted corrugations at even angular parts with the fluted corrugations in convex undulate at the section to cross the straight edge part by 90 deg. which is incorporatively formed by unitizing into a desired size, its internal flat plate part is incorporatively formed at the internal rim of the ring corrugation. And folds in crisscross form in circumferential direction between four engaging parts. Thus, absorption of thermal stress can be done positively because respective absorption of the thermal stress, such as the fold parts done for the both fluted and ring corrugations, which is at the flat plate part and in the circumferential direction of the ring corrugation, and at the dorsal parts and fold parts done for the fluted corrugations, which is in their axial directions.
Document JP-A-55 078895 discloses a membrane structure of low temperature liquid tank to absorb thermal distortion of membrane used for a low temperature liquid tank, by joining each flat portion of oval-shaped ring corrugation with straight corrugations, the phase of major and minor axes of adjacent ring corrugations being alternated. When the inner tank membrane reacts against thermal fluctuation, each juncture of straight corrugation with ring corrugation in the direction of minor axis is expendable in the widthwise direction of ring corrugation to absorb the thermal stress. Accordingly the major and minor axes of adjacent ring corrugations are so configurated, with their phase being changed alternately by 90 deg, that the flat portions distorted in the straight corrugations 9 are distorted in the turning direction as shown by arrows, The widthwise distortion in the straight corrugations is absorbed through contraction or expansion in the said direction. Thus the partial thermal stress is elastically absorbed, which prevents distortion caused by contraction or expansion.
Generally, LNG is extremely cold liquid having a boiling point of -162 °C, and is stored in an insulated cargo tank having a multiple wall structure. To safely store LNG having a boiling point of -162 °C, the insulated cargo tank is comprised of an internal tank wall made of a metal membrane panel and an externally insulated wall surrounding the internal tank wall. By such a multiple wall configuration, it is possible to minimize an amount of vaporized gas due to heat infiltrated into the tank from the outside.
Since the metal membrane panel comes into close contact with LNG in an extremely cold state, the metal membrane panel is made of metal material, such as aluminum alloy, Invar, and 9% nickel steel, which are considerably reduced in a low temperature brittleness to resist distortion due to heat shrinkage. Furthermore, the metal membrane panel includes a plurality of linear corrugations such that the metal membrane panel easily expands and contracts according to repetitive temperature variations and load variations of stored liquid.
As shown in FIG. 9, a conventional metal membrane panel is shaped in a rectangular form by a thin metal plate, and is provided throughout area thereof with a plurality of longitudinal and transverse linear corrugations, to allow for the expansion and contraction according to variations in temperature and load. An inner wall of a conventional insulated LNG cargo tank is typically constructed by a plurality of such metal membrane panels. In an operation of coupling the metal membrane panels to each other, respective metal membrane panels are first overlapped at four edges thereof with edges of other adjacent metal membrane panels, and the overlapped edges of the metal membrane panels are welded by lap welding, thereby providing the resulting tank with airtightness.

Disclosure of Invention

Technical Problem

Such a conventional metal membrane panel is constructed in such a way that a plurality of longitudinal linear corrugations and a plurality of transverse linear corrugations are crossed to form a plurality of intersections on the metal membrane panel. Since each of the intersections is provided with curved surfaces which have a radius of curvature smaller than that of curved surfaces of the longitudinal and transverse linear corrugations, the intersections are easily subjected to a stress concentration. Furthermore, since the metal membrane panel has a relatively complicated configuration, an operation of constructing the metal membrane panel requires increased working time and processing stages, thereby causing the production of the metal membrane panel to be costly. Further, when performing an operation of joining adjacent metal membrane panels to each other by lap welding, the large number of curved portions on a welding line of the metal membrane panel causes a welding efficiency to be lowered.

Technical Solution

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a metal membrane panel of an insulated LNG cargo tank, which is improved in a stability in terms of stress by decreasing localized stress concentration areas, and which is also improved in a welding efficiency by reducing the number of corrugations on overlapped welding edges of an adjacent metal membrane panel to reduce the number of curved portions to be welded.
In order to accomplish the above object, the present invention provides a metal membrane panel of an insulated LNG cargo tank, which includes a plurality of rectangular unit corrugations arranged on the panel to be spaced from each other by predetermined intervals, each of the plurality of rectangular unit corrugations being comprised of a pair of transverse bulging portions and a pair of longitudinal bulging portions and being shaped to have gently curved corners, transverse and longitudinal connecting corrugations, which connect the plurality of rectangular unit corrugations to each other, and transverse and longitudinal extending corrugation, which are extended to the edges of the metal membrane panel from the transverse and longitudinal bulging portions of the outermost unit corrugations which are positioned adjacent to the edges of the metal membrane panel.
The transverse and longitudinal connecting corrugations may be increased in width from the centers thereof toward the unit corrugations, and the transverse and longitudinal extending corrugations may be increased in width from the edges of the metal membrane panel toward the unit corrugations.
The unit corrugations, the transverse and longitudinal connecting corrugations, and the transverse and longitudinal extending corrugations may be shaped to have any of semicircular, elliptical and parabolic sections, and portions where the unit corrugations, the transverse and longitudinal connecting corrugations, and the transverse and longitudinal extending corrugations are connected to a flat surface of the metal membrane panel may be shaped to have a concave-curved section.

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a perspective view showing a metal membrane panel according to the present invention;
FIG. 2 is a top plan view of the metal membrane panel of FIG. 1;
FIG. 3 is an enlarged perspective view of the metal membrane panel of FIG. 1;
FIG. 4 is an enlarged top plan view of the metal membrane panel of FIG. 3;
FIG. 5 is an enlarged top plan view showing a connecting corrugation section of the metal membrane panel according to the present invention;
FIG. 6 is a cross-sectional view of the metal membrane panel according to the present invention;
FIG. 7 is a perspective view of the metal membrane panel according to the present invention, which is attached on a plywood;
FIG. 8 is a view showing a result of an elastic stress analysis of the metal m embrane panel according to the present invention; and
FIG. 9 is a perspective view showing a conventional metal membrane panel.

Best Mode for Carrying Out the Invention

This invention will be described in further detail by way of example with reference to the accompanying drawings.
FIG. 1 is a perspective view showing a metal membrane panel according to the present invention, FIG. 2 is a top plan view of the metal membrane panel of FIG. 1, FIG. 3 is an enlarged perspective view of the metal membrane panel of FIG. 1, FIG. 4 is an enlarged top plan view of the metal membrane panel of FIG. 3, FIG. 5 is an enlarged top plan view showing a connecting corrugation section of the metal membrane panel according to the present invention, FIG. 6 is a cross-sectional view of the metal membrane panel according to the present invention, and FIG. 7 is a perspective view of the metal membrane panel according to the present invention, which is attached on a plywood.
As showing in the drawings, the metal membrane panel "A" according to the present invention includes a plurality of rectangular unit corrugations 10 which enable low stress regions to be formed on inside and outside thereof, and a plurality of transverse corrugations 20 and a plurality of longitudinal corrugations 30, which serves to connect the plurality of unit corrugations 10 to each other.
Each of the unit corrugations 10 is comprised of combination of longitudinal bulging portion 11 and transverse bulging portion 12 such that the longitudinal and transverse bulging portions 11 and 12 defines a rectangular bulging strip, as viewed from plan view, which is gently rounded at corners thereof. The unit corrugations 10 are arranged to be spaced from each other by predetermined intervals. As mentioned above, the corners of the unit corrugations 10, at which the longitudinal bulging portions 11 are connected to the transverse bulging portions 12, are gently curved, so as to disperse and alleviate stress concentrating on the corners and to allow an easy operation of manufacturing the metal membrane panel "A".
The unit corrugations 10 are constructed such that the unit corrugations 10 are positioned at points where the transverse corrugations 20 intersect the longitudinal corrugations 30. Consequently, low stress regions are formed inside and outside the unit corrugations 10. More specifically, since an inside area of the unit corrugation 10 is smoothly curved at corners thereof, thereby defining a closed curve, the unit corrugation 10 enables a low stress to be distributed on the inside and outside areas thereof, which is equal to or less than 1/5 of the maximum stress which may otherwise occur at the intersection of the transverse and longitudinal corrugations 20 and 30.
The transverse and longitudinal corrugations 20 and 30 are comprised of transverse and longitudinal connecting corrugation sections 40 and 50, which are adapted to connect adjacent unit corrugations to each other, and transverse and longitudinal extending corrugation sections 60 and 60', which are extended to edges of the metal membrane panel "A" from the longitudinal and transverse bulging portions 11 and 12 of the outermost unit corrugations 10 which are positioned adjacent to the edges of the metal membrane panel "A", respectively. In this configuration, the transverse and longitudinal connecting corrugation sections 40 and 50 and the transverse and longitudinal extending corrugation sections 60 and 60' are arranged such that the transverse connecting corrugation sections 40 are aligned with the transverse extending corrugation sections 60 and the longitudinal connecting corrugation sections 50 are aligned with the longitudinal extending corrugation sections 60'.
According to the present invention, since the unit corrugations 10, which has low stress regions on inside and outside areas thereof, are provided at points where the transverse and longitudinal corrugations 20 and 30 intersect, a spacing between the adjacent transverse extending corrugation sections 60 and a spacing between the adjacent longitudinal extending corrugation sections 60' are increased. Consequently, the number of the extending corrugation sections 60 and 60' formed on welding edges of the metal membrane panel "A" is reduced to about 1/2 of the number of the corresponding corrugations of a conventional metal membrane panel, thereby enabling easy application of an automatic welding.
As shown in FIG. 6, the unit corrugations 10, the transverse and longitudinal connecting corrugation sections 40 and 50, and the transverse and longitudinal extending corrugation sections 60 and 60' are shaped to have any of semicircular, elliptical and parabolic sections, and portions where the unit corrugations 10, the transverse and longitudinal connecting corrugation sections 40 and 50, and the transverse and longitudinal extending corrugation sections 60 and 60' are connected to a flat surface of the metal membrane panel "A" are shaped to have a concave-curved section.
Widths of the transverse and longitudinal connecting corrugation sections 40 and 50 and the transverse and longitudinal extending corrugation sections 60 and 60' are continuously increased toward junction portions 13 where the transverse and longitudinal connecting corrugation sections 40 and 50 and the transverse and longitudinal extending corrugation sections 60 and 60' are connected to the unit corrugations 10. Accordingly, the transverse and longitudinal connecting corrugation sections 40 and 50 and the transverse and longitudinal extending corrugation sections 60 and 60' are shaped to have curved lines at the junction portions, as viewed from above, thereby preventing localized stress concentration and improving a workability of the metal membrane panel "A". In other words, the transverse and longitudinal connecting corrugation sections 40 and 50 are increased in width from the centers thereof toward the junction portions while forming gently curved outlines at the junction portions, and the transverse and longitudinal extending corrugation sections 60 and 60' are also increased in width from the edges of the metal membrane panel "A" toward the junction portions, as shown in FIG. 5.
In application, the metal membrane panel "A" according to the present invention, which is constructed in the above-described manner, is attached to an insulated wall to constitute an internal surface of an insulated LNG cargo tank. At this point, the metal membrane panel "A" is placed on a plywood 70 such that the metal membrane panel "A" is positioned at metal attaching strips 71 which are arranged on the plywood 70 into a lattice pattern, as shown in FIG. 7. The metal membrane panel "A" is joined to other adjacent metal membrane panels "A" by lap welding, thereby constructing a sealed wall. At this time, the metal membrane panels "A", which placed on the plywood 70, are joined to each other by intermittent welding without additional joining devices, and then the resulting metal membrane panels "A" are attached to an insulated cargo tank.
FIG. 8 shows a result of an elastic stress analysis of the metal membrane panel according to the present invention. In performing this elastic stress analysis, an MSC/NASTRAN program is used, and an SUS304L stainless panel having a size length 3m x width 1m is used. FIG. 8 shows stress variations at various positions according to temperature variations from a roan temperature to -162°C As seen in FIG. 8, curved and connected portions of the metal membrane panel exhibit the maximum stress while flat surface areas of the metal membrane panel exhibit relatively low stress.

Industrial Applicability

As described above, the present invention provides a metal membrane panel of an insulated LNG cargo tank, in which a plurality of unit rectangular corrugations, which are shaped to have curved corners, are arranged on the metal membrane panel at predetermined intervals such that the unit rectangular corrugations are positioned at intersections of transverse and longitudinal corrugations and connected to them, and junctions of the unit corrugations and the transverse and longitudinal corrugations are shaped to have gently curved outlines, so as to alleviate stress concentration acting on the transverse and longitudinal corrugations and to facilitate a manufacturing operation of the metal membrane panel. Consequently, an insulated cargo tank, which is achieved by combination of the metal membrane panels, is improved in reliability. Furthermore, since the number of corrugations formed on edge areas of the metal membrane panels to be welded is decreased, weldability is improved during a welding process.

Claims

A metal membrane panel (A) of an insulated LNG cargo tank, comprising:
a plurality of rectangular unit corrugations (10) arranged on the panel to be spaced from each other by predetermined intervals, each of the plurality of rectangular unit corrugations (10) being comprised of a pair of transverse bulging portions (12) and a pair of longitudinal bulging portions (11) and being shaped to have gently curved comers;

transverse and longitudinal connecting corrugations (40, 50), which connect the plurality of rectangular unit corrugations (10) to each other; and

transverse and longitudinal extending corrugations (60, 60'), which are extended to edges of the metal membrane panel (A) from the transverse and longitudinal bulging portions (12, 11) of the outermost unit corrugations which are positioned adjacent to the edges of the metal membrane panel (A).
The metal membrane panel (A) as set forth in claim 1, wherein the transverse and longitudinal connecting corrugations (40, 50) are increased in width from the centers thereof toward the unit corrugations (10), and the transverse and longitudinal extending corrugations (60, 60') are increased in width from the edges of the metal membrane panel (A) toward the unit corrugations (10).
The metal membrane panel (A) as set forth in claim 1 or 2, wherein the unit corrugations (10), the transverse and longitudinal connecting corrugations (40, 50), and the transverse and longitudinal extending corrugations (60, 60') are shaped to have any of semicircular, elliptical and parabolic sections, and portions where the unit corrugations (10), the transverse and longitudinal connecting corrugations (40, 50), and the transverse and longitudinal extending corrugations (60, 60') are connected to a flat surface of the metal membrane panel (A) are shaped to have a concave-curved section.