Title of Invention

"MEMBRANE UNIT FOR LIQUID GAS STORAGE TANKS"

Abstract

A membrane unit for LNG storage tanks is disclosed. In the membrane unit, a plurality of horizontal and vertical corrugation units, having the same profile, are alternately and regularly formed on the membrane unit. In each of the horizontal and vertical corrugation units, two outer corrugations, having the same profile and the same size, linearly and parallely extend at both sides of each corrugation unit, with an intermediate gap being defined between the two outer corrugations. Two central corrugations, each having the same length as that of each of the outer coxrugarions, extend in opposite directions from the central portion of the intermediate gap while leaving a middle land at the center between the outer and central corrugations. An anchor hole is formed at the center of the middle land. A cell is defined by two vertical corrugation units and two horizontal corrugation units, with a length of each outer corrugation within the cell being longer than 1/2 of the width of the cell. The membrane unit allows the horizontal and vertical corrugation units to effectively resist external stress while effectively removing an undesirable stress concentration from the anchors in the anchor holes.

Full Text

MEMBRANE UNIT FOR LIQUID NATURAL GAS STORAGE TANKS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates, in general, to a membrane unit for LNG (liquid natural gas) storage tanks and, more particularly, to a membrane unit having a T-shaped corrugation pattern designed to minimize the stress applied to anchors. Description of rhe Prior Art As well known to those skilled in the art, a membrane unit for LNG storage tanks is a specifically designed structural member, which completely prevents undesirable LNG leakage while effectively resisting m.echanical stress, gas and liquid pressures of LNG in addition to thermal stress derived from contact with cryogenic liquid having a temperature of -1620C. Such membrane units are interiorly mounted to the sidewall and bottom wall of an LNG storage tank. Fig. 1 is a plan view of a conventional Kawasaki membrane unit for LNG storage tanks. As shown in the drawing, the Kawasaki membrane unit is formed with a plurality cf horizontal and vertical corrugation units,, which are alternately arranged on the membrane unit and each corrugation unit consists of two parallel corrugations 3 and 4. In the - 1A - Kawasaki membrane unit, each horizontal corrugation unit horizontally extends between two vertical corrugation units, with regular gaps being formed between the horizontal and vertical corrugation units. An anchor hole 5 is formed at the center of each cell defined by the horizontal and vertical corrugation units and is used for anchoring the membrane unit to the interior wall of an LNG storage tank. When the Storage tank, the horizontal and vertical corrugation units are deformed as shown by the dotted lines in Fig. 1. Fig. 2 is a plan view of a conventional Mitsubishi membrane unit for LNG storage tanks. As shown in the drawing, the conventional Mitsubishi membrane unit is formed with a plurality of horizontal and vertical corrugation units, each corrugation unit consisting of a single corrugation 5, 6. In the Mitsubishi membrane unit, each horizontal corrugation 5 horizontally extends between two vertical corrugations 6. Ar. anchor hole 7 is formed at the center of each cell defined by the horizontal and vertical corrugations 5 and 6 and is used for anchoring the membrane unit to the interior wall of an LNG storage tank. In the Mitsubishi membrane unit, the horizontal and vertical corrugations 5 and 6 com.pletely come into contact with each other, thus allowing the membrane unit to more effectively expand and contract when the membrane unit is stressed by the pressure of the tank, 2 In each of the two conventional membrane units, an anchor hole, used for anchoring the membrane unit to the interior wail of an LNG storage tank, is formed at the center of each ceil defined by the horizontal and vertical corrugation units, thus accomplishing a desired operational stability against a thermal strain behavior. However, when the thermal strain behavior asymmetrically and ununiformly distorts each of the two conventional membrane units in accordance with stressed conditions, a great amount of stress is undesirably concentrated at the anchors of each membrane unit and deteriorates the stability of the membrane unit at the anchored points. SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, ana an object of the present invention is to provide a membrane unit ¦^ ¦. for LNG stcrage tanks, of which the anchor holes are ¦r respectively formed at the middle lands of -he horizontal and vertical corrugation units, thus allowing nhe horizontal and vertical corrugation units to effectively resist external stress while effectively removing an undesirable stress concentration from the anchors held in the anchor holes. In order to accomplish the above object, the present 3 invention provides a membrane unit for LNG storage tanks, comprising; a plurality of horizontal and verticai corrugation units having the same profile and being alternately and regularly formed on the membrane unit, each of the horizontal and verticai corrugation units consisting of: two outer corrugations having the same profile and the same size, and linearly and parallely extending at both sides of each corrugation unit, with an intermediate gap being defined between the two outer corrugations; two central corrugations each having the same length as that of each of the outer corrugacionSf the two central corrugations extending in opposite directions from a central portion of the intermediate gap between the two outer corrugations while leaving a middle land at a center between the outer and central corrugations; and an anchor hole formed at a center of the m.iddle land. In the membrane unit, a cell is defined by two vertical corrugation units and two horizontal corrugation units, with a length of each outer corrugation within the cell being longer than 1/2 of a width of the cell. In addition, ail the corrugations of the vertical and horizontal corrugation units have the same cross-section, or a semicircular cross-section or an elliptical cross-section. 4 BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The above and other objects, features and other advantages of the present invention wLL be more clearly understood from the following detailed description taKen in conjunction with the accompanying drawings, in which: Fig. 1 is a plan view of a conventional Kawasaki membrane unit for LNG storage tanks; Fig. 2 is a plan view of a conventional Mitsubishi meinbrane unit for LNG storage tanks; fig. 3 is a perspective view of a membrane unit for LNG storage tanks in accordance with the preferred embodiment of the present invention; Fig. 4 is a plan view of the merribrane unit for LNG storage tanks of the present invention; Fig. 5 is a sectional view taken along the line A-A of Fig, 4, showing a vertical corrugation unit formed on the membrane unit of this invention; and Fig. 6 is a sectional view taken along rhe line B-B of Fig. 4, showing a horizontal corrugation unit formed on the membrane unit of this invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS figs. 3 and 4 are views of a membrane unit for LNG 5 storage tanks in accordance with the preferred embodiment of the present, invention. As shown in the drawings, the membrane unit 20 of this invention is formed with a plurality of horizontal and vertical corrugation units having the same profile. That is, the vertical corrugation units each consist of two outer corrugations 21 and 22, having the same profile and the same size. The above two outer corrugations 21 and 22 linearly and parallely extend at both sides of each vertical corrugation unit, with an intermediate gap being defined between the two outer corrugations 21 and 22. Upper and lower central corrugations 23 and 24, each having the sa.'ne lengtn as that of the outer corrugations 21 and 22, extend upwardly and downwardly from the central portion of the intermediate gap between the two outer corrugations 21 and 22 while leaving a middle land at the center between the corrugations 21. 22 / 23 and 24. An anchor hole 25 is formed at the center of each middle land left at the center between the corrugations 21, 22 , 23 and 24. Cr. the other hand, the horizontal corrugation units, navinq the same profile a3 that; of the vertilcal corrugation unirs, are alternately and horizontally formed on the membrane unit at positions between Che vertical corrugation units. That is, the horizontal corrugation units horizontally extend 6 outside the outer corrugations 21 and 22 of the vertical corrugation units while horizontally extending at the intermediate gaps between the outside ends of the upper and lower central corrugations 23 and 24 of the vertical corrugation units. In the drawings, both outer corrugations of each horizontal corrugation unit are designated by the numerals 31 and 32, both central corrugations are designated by the numerals 33 and 34, and the anchor hole formed at each middle land is designated by the numeral 35, In the membrane unit 20 of this invention, a square cell is defined by two vertical corrugation units and two horizontal corrugation units. Within each cell, the length E of each outer corrugation of the vertical and horizontal corrugation units is longer than 1/2 of the width D of the square cell. As shown in Figs. 5 and 6, all the corrugations of the vertical and horizontal corrugation units have the same cross-section. In the present invention, the corrugations of the corrugation units may have a semicircular cross-section or an elliptical cross-section without affecting the functioning of this invention. In the above membrane unit 20 of this invention, one vertical corrugation unit and one horizontal corrugation unit form a T-shaped corrugation pattern and each has a triply corrugated section at two portions. That is, in the case of 7 each vertical corrugation unit as an example, the three corrugations 21, 12 and 23, or 21, 22 and 24 form the triply corrugated section. Within each square cell, four outer corrugations are respectively arranged along the four sides of the cell while not coming into contact with each\ other at the corners, with the length E of each outer corrugation being longer than 1/2 of the width D of the cell. Due to such a specifically designed structure, the membrane unit 20 of this invention is effectively free from an undesirable stress concentration at the end portions of the outer corrugations within each cell. In addition, the central corrugations 25 and 24, 33 and 34 of each corrugation unix: are designed to be spaced apart from the inside ends thereof, with a middle land being left between the inside ends. An anchor hole 25, 35 is formed at each of the middle lands of the corrugation units. Therefore, finally the m.embrane unit 20 of "this invention is free from an undesirable stress concentration at the anchors (not shown) installed at the anchor holes 25 and 35. That is, even when the external stress conditions for the membrane unit 20 are undesirably changed, the anchor holes 25 and 35 are less stressed than the other portions of the corrugation units, thus allowing the anchors to be stably held in the anchor holes 25 and 35 even in the event of changed external stress conditions. In other words, the anchors held 8 in the anchor holes 25 and 35 are effectively protected by the corrugations surrounding the middle lands of the corrugation units, thus being stably held at their designated positions even in the event of the changed external stresses. When the membrane unit 20 contracts due to an interior pressure of an ING storage tank, the horizontal and vertical corrugation units are deformed as shown by the dotted lines in Tig. 4. As best seen in Fig. 4, the lands around the anchors are less deformed than the other portions of the corrugation units. This finally allows the anchors, held in the anchor holes 25 and 35, to be effectively protected even in the event of changed external stresses. As described above, the present invention provides a membrane unit for LNG storage tanks. In the membrane unit, a plurality of horizontal and vertical corrugation units, having the same profile^ are alternately formed, with an anchor hole being formed at the middle land of each of the horizontal and vertical corrugation anits. When the membrane unit contracts due to a thermal strain behavior, the membrane unit allows the horizontal and vertical corrugation units to effectively resist external stress while effectively removing an undesirable stress concentration from the anchors held in the anchor holes. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those 9 skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 10 We Claim: 1. A mesmbrane unit for LNG storage tanks, comprising: a plurality of horizontal and vertical corrugation units having the same profile and being alternately and regularly formed on said membrane unit, each of said horizontal and vertical corrugation units characterized by comprising: two outer corrugations having the same profile and the same size, and linearly and parallely extending at both sides of each corrugation unit, with an intermediate gap being defmed between the two outer corrugations; two central corrugations each having the same length as that of each of said outer corrugations, said two central corrugations extending in opposite directions from a central portion of said intermediate gap between the two outer corrugations while leaving a middle land at a center between the outer and central corrugations; and an anchor hole formed at a center of said middle land. 2. The membrane unit as claimed in claim I, wherein a cell is defined by two vertical corrugation units and two horizontal corrugation units, with a length of each outer corrugation within the ceil being longer than ½ of a width of said cell. 3. The membrane: unit as claimed in claim 1, wherein ai the corrugation of the vertical and horizontal corrugation units have the same cross-section, or a semicircular cross-section or an elliptical cross-section. A membrane unit for LNG storage tanks is disclosed. In the membrane unit, a plurality of horizontal and vertical corrugation units, having the same profile, are alternately and regularly formed on the membrane unit. In each of the horizontal and vertical corrugation units, two outer corrugations, having the same profile and the same size, linearly and parallely extend at both sides of each corrugation unit, with an intermediate gap being defined between the two outer corrugations. Two central corrugations, each having the same length as that of each of the outer coxrugarions, extend in opposite directions from the central portion of the intermediate gap while leaving a middle land at the center between the outer and central corrugations. An anchor hole is formed at the center of the middle land. A cell is defined by two vertical corrugation units and two horizontal corrugation units, with a length of each outer corrugation within the cell being longer than 1/2 of the width of the cell. The membrane unit allows the horizontal and vertical corrugation units to effectively resist external stress while effectively removing an undesirable stress concentration from the anchors in the anchor holes.

Documents:

00918-cal-1999 abstract.pdf

00918-cal-1999 claims.pdf

00918-cal-1999 correspondence.pdf

00918-cal-1999 description[complete].pdf

00918-cal-1999 drawings.pdf

00918-cal-1999 form-1.pdf

00918-cal-1999 form-18.pdf

00918-cal-1999 form-2.pdf

00918-cal-1999 form-26.pdf

00918-cal-1999 form-3.pdf

00918-cal-1999 form-5.pdf

00918-cal-1999 letter patent.pdf

00918-cal-1999 ptiority document others.pdf

00918-cal-1999 ptiority document.pdf