US 3302358 A
Description (OCR text may contain errors)
Feb. 7, 1967 R. G. JACKSON 3,302,358
THERMAL INSULATION STRUCTURES Filed Nov. 26, 1963 2 Sheets-Sheet l Robert G. Jackson Se 55 BY /i/Mb of 70am ATTORNEY Feb. 7, 1967 y I R. G. JACKSON 31,302,358
THERMAL INSULATION STRUCTURES Filed NOV. 25, 1963 2 Sheets-Sheet 2 INVENTOR Rober? G. Jackson ATTORNEY United States Patent G 3,302,358 THERMAL INSULATIN STRUCTURES Robert Glover Jackson, Hornchnrch, Essex, England, assignor to Couch International Methane Limited, Nassau, Bahamas, a Bahamian company Filed Nov. 26, 1963, Ser. No. 325,931 Claims priority, application Great Britain, May 6, 1963, 17,834/ 63 Claims. (Cl. 52-573) This invention relates to a thermal insulation system which is suitable for forming the walls of tanks for storing liquefied gases.
In the specification of copending U.S. patent application Serial No. 285,279 of French et al., led June 4, 1963, now Patent No. 3,184,094, an extensible sheet is described, which sheet contains an enclosed area bounded entirely by non-intersecting but meeting corrugations, the corrugations extending linearly beyond the enclosed area. This form of sheet solves the problem of relieving thermal stresses when a sheet is subject to great temperature changes, but does not of itself provide any thermal insulation. It is a major object of the present invention to provide a thermally insulated structure suitable for forming the walls of tanks for storing liquefied gases and other lowtemperature liquids, which structure has the advantages of the above-described sheet in relieving thermal stresses, and in addition, provides good thermal insulation.
According to the present invention, the thermal insulation structure comprises a dened sheet, which is an extensible sheet including an enclosed area bounded entirely by non-intersecting but meeting corrugations, the corrugations extending linearly beyond the enclosed area, a second sheet spaced a short distance from the extensible sheet, transversely spaced walls between said sheets for defining vacuum-tight enclosures between said sheets, and load bearing insulation contained in said enclosures. An extensible sheet is defined as a sheet which when under stress will be more extensible than allowed by the modulus of elasticity of the material itself, due, in eifect, to controlled bending of the sheet at areas of corrugation. The term corrugation includes simple folds.
In the preferred embodiment of the invention, in the extensible sheet, the adjacent corrugations form two sets of co'rrugations at right angles to one another. Opposite corrugations terminating in the periphery of an enclosed area are preferably parallel, i.e., the enclosed area is a rectangle, or preferably a square, although other polygonal shapes may be used, as shown in the above-mentioned copending application.
The specic nature of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:
FIG. l is a perspective view of a thermal insulation structure in which the extensible sheet has one enclosed area bounded by corrugations;
FIG. 2 is a sectional side elevation of the structure of FIG. l taken vertically through line 2 2 of FIG. l;
FIG. 3 is a sectional side elevation similar to FIG. 2, but of an alternative structure to that shown in FIG. l;
FIG. 4 is a plan view of a thermal insulation structure in which the extensible sheet has five enclosed areas bounded by corrugations;
FIG. 5 is a sectional side elevation of the structure of FIG. 4 taken vertically through line 5-5 of FIG. 4;
FIG. 5a is a sectional view taken on line Sa--Sa of FIG. 4, of a modiiied form of the structure having a single tray;
FIG. 6 is a perspective view of a modified form of the invention;
FIG. 7 is a detail view in section showing the structure of the supporting pins; and
FIG. 7a is a detail view of a modified supporting pin.
In FIG. l, an extensible sheet ll of a suitable material, eg., stainless steel, has four adjacent corrugations, 2, 3, 4 and 5, which form two sets of corrugations at right angles to one another. The corrugations have in this case symmetrical proles, and in the center of the sheet the corrugations enclose a square area 6, whose plane lies in the plane of the extensible sheet. Opposite corrugations 2, 4 and 3, 5 respectively are offset as shown, and each of the corrugations 2, 3, 4, and 5 terminates in the periphery of square area 6.
Extensible sheet I can suitably be fabricated as by bending and welding together suitable sections of stainless steel, and need not be heat treated after the welding.
Fixed to the bottom of the extensible sheet l by weld ing along the edges 1l are separate trays, two of which are indicated at S and 9. In FIG. 2, the side walls Of the tray 8 are indicated at @a and 8c, and the bottom at 8b. Similarly for tray 9, the side walls are indicated at Stn and 9c and the bottom at 9b. Blocks i0 of rigid open cell plastic material such as polyvinyl chloride are used as insulation and substantially fill the enclosures bounded by the extensible sheet and the trays. The enclosures are evacuated through nipples l2 which are thereafter sealed.
When extensible sheet ll is contracted or extended, corrugations 2, 3, 4 and 5 open or close, and bending moments about axes perpendicular to the plane of the sheet are induced in the sides of the corrugations at the corners of square area 6. These bending moments cause square area 6 to rotate about its center of area at point 7, thereby enabling each corrugation to move longitudinally as a whole, and the extensible sheet to be extensible in all directions, as explained in the above copending application.
In FIG. 3, the trays 8 and 9 are of a different shape, suitable for fabrication by stamping, and the enclosures are preferably substantially lled with stabilized particles of perlite as a thermal insulation. The top and bottom sheets may be provided with dimples, as shown at l5, or any other form of minor deformation, to relieve thermal stresses, and this may similarly b-e done with any of the forms of the invention. A corrugated bridging and sealing strip 4a may be secured, as by welding, between the bottoms of adjacent trays, to provide a continuous second wall, in effect.
In FIG. 4 an extensible sheet having four small enclosed areas 21, 22, 23 and 24, and one large enclosed area 25 is shown. The other areas 26, 27, 28, 29, 30, 31, 32 and 33 are bounded partially by the corrugations and partially by the edges of the sheet. The sheet is preferably supported by pins extending from the centers 7 of the respective areas as better shown in FIG. 7.
In FIG. 5, the trays 40, 41, 44 and 43, welded respectively to the areas 30, 31, 24 and 33 are shown. As in the structures illustrated in FIGS.. l and 2, the trays are substantially filled with blocks of open cell rigid polyvinyl chloride 34. FIG. 5a shows a structure similar to that of FIG. 5, but having a single tray 56 for a number of enclosed areas corresponding to the face structure of FIG. 4.
FIG. 6 shows at i6 and 17 the manner in which the corrugations 4 may be curved outwardly of the enclosed area.
FIG. 7 shows a preferred manner -of supporting the extensible sheets on a rigid backing 51, itself preferably made of insulating material such as balsa wood. Bushings 52 are inserted into the backing 51. Each bushing has an internal snap ring 52a for engagement in a circumferential recess in peg 53, there being one such peg extending from each point 7 at the center of area of each area 6, 2l, 25', etc. Thus thermal expansion and contraction forces on the sheets are free to cause parti-al u rotation of the supported areas. Pegs 53 may be made hollow, and used for evacuating the respective enclosures, after which they may be sealed in any usual or known manner.
FIG. 7a shows a'modiiied form of pin construction in which the peg 53 extends through the tray 56 to the extensible sheet 57. This construction can `be used where there is only one tray (or second sheet) extending over a number of enclosed areas, in which case there will be only .one peg located in the middle of each such tray and in the middle of an enclosed area, so that there will be only one relative rotation between the extensible sheet and the tray.
Adjacent corrugations can have any desired profile, which can by symmetrical or unsymmetrical, as shown for example in FIGS. 5 and 6 respectively. When corrugations terminating within the sheet to form a corner have unsymmetric-al profi-les, they are arranged so that the same sides of the profile are in a clockwise direction and the other sides of the profiles are in the anti-clockwise direction.
The area bounded by the corrugations can lie either in or out of the plane of the extensible sheet; that is, it can be bounded by the flanks or sides of the corrugations, or by the crests of the corrugations. When adjacent corruga'tions are mutually at right angles to each other, the enclosed area can be a square or a square with triangular fianges. The enclosed area will rotate about its center of area when the extensible sheet is contracted or expanded by stresses.
The enclosed area may be of any shape, having any number of sides. However, to minimize the stresses set up in the sheets when they contract at low temperatures, it is preferable if the sides of the enclosed areas are equal in length and also preferable if the enclosed area is in the center of a sheet. Preferred shapes are triangles or hexagons as shown in the above copending application, and especially quadrilaterals, eg., squares.
The average of the ratios yof the length of each corrugation bounding each enc-losed area to the total length of each corrugation is preferably less than 1:2, e.g., about 1:4. The end portions of the coirugations may if desired by curved before meeting an adjacent corrugation, preferably curved outwardly of the enclosed area, as shown at I6 and 1i7 in FIG. 6. When referring to sheets substantially the same shape as the enclosed area, the curvature of the corrugations is for this purpose ignored, i.e., the sheet is considered to be of the same shape as the enclosed area except for the rounded corners. In 'order to obtain the best results, the c-orrugations should extend f linearly beyond the enclosed area to the sides of the sheet, or at least extend to nearly the sides of the sheet.
The extensible sheet, preferably metal, can be fabricated by suitably pressing a flat metal sheet or bending and welding together suitable metal sections. The extensible metal sheet can be of any thickness appropriate to the stresses to be taken by it and to the degree of extensibility required. Preferred extensible metal sheets are fabricated from steels, but other metals possessing desired structural strengths can be used, for example aluminum or alloys of aluminum.
For many applications it is desirable if the thermal insulation structures are such that the extensible sheet has a plurality of enclosed areas. Such sheets may -be either a composite extensible sheet comprising a plurality of defined sheets joined to one lanother and spaced in side-by-side and end-to-end relationship so that each of the corrugations of each of the defined sheets is in line with and meets a corrugation in a contiguous sheet, or may be an extensible sheet comprising a plurality of Zones, each having the features of, and corresponding to the defined sheet in which the Zones are placed in side-by-side and end-to-end relationship so that each of the corrugations of each zone is in line with, and meets a corrugation in a contiguous zone. Because ofthe geometry, the defined sheet or the zone corresponding to the defined sheet, also has to be one which is substantially the same shape as its enclosed area, in which the corrugations extend to the sides of the sheet and in which the enclosed area is in the center ofthe sheet and has sides which are equal in length. In the extensible composite sheet referred to above, the individaul defined sheets are preferably welded together. The extensible sheet comprising a plunality of Zones (or the extensible composite sheet), may be made by welding sheets together along Ithe corrugations. In this case, corrugations which are curved outwardly Vof the enclosed area before meeting an adjacent corrugation, as shown in FIG. 6, are ian advantage, because such sheets can be fabricated by `stamping and are therefore exactly the same in size and they can be welded together along the corrugations.
If desired, the extensible sheets used in the thermal insulation structure of this invention may be provided with one or more, preferably a series, of protrusions, e.g., dimples, in its surface to further counteract the effect of contraction or expansion due to large temperature changes, as shown by way of example in FIG. 3.
The second sheet, i.e., the sheet which need not have an enclosed area, should preferably be fiexible. Suitable forms of flexible sheet Iare for example, dimpled sheets or corrugated sheets. These second sheets are also preferably of metal, especially those me-tals which do not become embrittled at low temperatures, for example aluminum or stainless steel. Other materials, e.g., certain plastics such as Teflon (ifourinated hydrocarbons) or epoxy fiber glass, may also be used. The second sheet may be thinner or thicker than the first sheet.
Where the temperature changes yare not likely to be great or where the separation between the sheets is fairly large, the sec-ond sheet will not normally undergo any excessive strains or stresses due to temperature changes. In other cases, however, it is preferable if there is not one second sheet, but a series of separate second sheets all lying in the same plane, there being a second sheet for each area defined in the corrugations of the extensible sheet, and each area defined by the corrugations and edges of the extensible sheet, the second sheets being of substantially the same area as the corresponding defined areas of the extensible sheet.
The extensible sheet is preferably spaced with respect to the second sheet or sheets so that the corrugated portions of the sheet project out of the extensible sheet in a direction :away from the second sheet or sheets.
The transversely spaced walls may be separate strips as 8a, 8c, 9a, etc., secured to Iboth sheets so as to define the vacuum tight enclosures. In such cases, it is preferable if the strips are secured to the sheets at or near the region where the corrugations define the enclosed areas and around the perimeter of the extensible sheet. These strips should preferably be of thin sheet metal so as to minimize conduction of heat therethrough. The preferred method of securing the walls to the sheet is by welding.
In a preferred form of the invention, the transversely spaced walls are extensions of the second sheet as shown at 13, 14 in FIG. 3. In other words, these second sheets are in the form of trays of substantially the same area as the enclosed areas of the other sheet (extensible sheet) dened by the corrugations and by the corrugations and edges of the sheets. These trays are secured (e.g., by welding) onto the edges of the other sheet (extensible sheet) at or near the region where the corrugations define the enclosed areas of the sheet, and round the perimeter of the extensible sheets.
The .trays may 'be ones in which the walls are substantially at right angles to the base of the tray, similar to FIG. 2. Alternatively, they may lbe ones in which the walls are rounded, curving outwardly from the base of the tray, the edges of the walls preferably being flattened out in a direction parallel to and away from the base of the tray, as shown in FIG. 3.
With trays, it is possible to secure to each pair of adjacent tray bases (e.g., by welding) sealing strips of metal as shown at 4a in FIG. 3, each strip being provided with a protrusion such as a corrugation so as to bridge the gaps between each pair of adjacent tray bases. In this manner, an extra barrier is formed, should leakage of liquid occur through the extensible sheet, load bearing insulation and walls of the tray.
If either the separate strips or the trays are secured to portions of the corrugations of the extensible sheet having one or more enclosed areas, which are not substantially nearer the enclosed areas of the sheet than the peaks of the corrugations, then the extensible sheet having one or more enclosed areas should preferably have one or more protrusions (eg, dimples) on its surface. This is because the xing of the transverse walls to portions of the corrugations other than the enclosed areas of the sheet would tend to restrict the movement of the corrugations and so tend to prevent rotation of the enclosed areas. Consequently there should be one or more, e.g., a series, of protrusions in the surface of the enclosed areas to accommodate changes in the shape of the sheet. It is for this reasons therefore that it is preferable if the transverse walls are secured to or near the edges of the extensible sheet where the corrugations define the enclosed areas of the sheet.
The load bearing insulation should be rigid to undergo compressive forces, due to air and uid pressure acting on the external surfaces of the insulation through the flexible metal. In order that an effective vacuum may be mounted in the enclosures between the sheets, the insulation should also be preferably an open cell structure.
Examples of suitable insulation are `open cell rigid plastics, e.g., polyvinyl chloride foams, polyurethane foams, urea foams, polyethylene foams or plystyrene foams. Other suitable load bearing insulating stabilized particles of silicious materials of low thermal conductivity, eg., perlite (expanded lava) or vermiculite (expanded mica). Alternatively, fiber glass can be used. When using filaments of insulating material such as fiber glass, it is preferable if the general direction of the filaments is transverse to the shortest path between the sheets, eg., if the general direction is su'bstantially parallel to one or more sheets, and also if the filaments run in directions transverse to one another. In this way, the mass of fiber glass is capable `of absorbing any compressive forces.
To obtain the best insulating properties, the vacuumtight enclosures should be evacuated, preferably through an aperture or nipple in the second sheet, which is thereafter sealed when the evacuation procedure is completed. If possible, .the evacuation should preferably be delayed until after any construction work is completed, so that there is little danger of the vacuum being substantially destroyed.
One or more walls of a container suitable for the storage of a liquefied gas can be fabricated from any of the above-described thermal insulation structures of the invention. These containers may normally be used as a primary container supported by a secondary container of load bearing thermal insulating material. The methods used for constructing such containers are similar to those described in the above-mentioned copending application for constructing containers from the extensible sheets of that invention. Where the primary container is provided with pegs for rotatable securement in recesses of the walls of the secondary container, these pegs should be secured to the second sheet or sheets of the thermal insulation structure, care being taken not to impair the vacuum tightness of the enclosures. In this case, the material of the second sheet should be at least as thick and strong as that of the first sheet. The containers thus constructed may be used as storage tanks in the hold of a ship, or as land tanks for storing liquefied gases.
It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.
1. A thermal insulation structure for use under conditions of great temperature change, comprising (a) a composite extensible sheet in which there are a plurality of individual extensible sheets,
(b) each individual extensible sheet comprising a number of substantially plane areas including an enclosed area of the same geometric shape as said individual sheet,
(c) the enclosed area being bounded entirely by noncrossing but angularly meeting corrugations, which corrugations extend linearly beyond the enclosed area and extend .to the sides of the individual sheet,
(d) the individual extensible sheets being joined to one another and disposed in side-'by-side and endto-end relationship so that each of the corrugations of each individual sheet is in line with and meets a corrugation in a contiguous individual extensible sheet,
(e) a composite second sheet disposed with its face in spaced opposed parallel relation to the face of the composite extensible sheet; said composite second sheet including a plurality of individual second sheet elements each coextensive with an individual one of said plane areas,
(f) transversely spaced walls between the individual plane areas of said composite extensible sheet and said second sheet elements for dening vacuum tight enclosures between said areas and said elements;
(g) the second sheet elements and transversely spaced walls being in the form of trays of substantially the same base area as the substantially plane areas of the individual extensible sheets, the walls of each tray constituting the transversely spaced walls between the sheets defining vacuum tight enclosures; and
(h) load bearing insulation contained in said enclosures.
2. A structure as claimed in claim l, in which the extensible sheet is spaced with respect to the second sheet so that the corrugated portions of the sheet project out of the extensible sheet in a direction away from the second sheet.
3. A structure as claimed in claim 1, in which the second sheets are in the form of trays having walls which are rounded, curving outwardly from the base of the tray, the edges of the walls being flattened out in a direction parallel to and away from the base of the tray.
4. A structure as claimed in claim ll, in which sealing strips, each provided with a corrugation, are welded to each pair of adjacent tray bases so as to bridge the gaps between each pair of adjacent tray bases.
5. A structure as claimed in claim 1, in which the insulation has an open cell structure.
References Cited bythe Examiner UNITED STATES PATENTS 2,576,698 11/1951 Russom. 3,179,549 4/1965 Strong et al 220-10 X 3,184,094 5/1965 French et al 220-9 FOREIGN PATENTS 924,803 5/1963 Great Britain.
THERON E. CONDON, Primary Examiner.
JAMES R. GARRETT, Examiner.
R. A. JENSEN, Assistant Examiner.