US 3150794 A
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Description (OCR text may contain errors)
Sept. 29, 1964 E. M. SCHLUMBERGER ETAL 3,150,794
- MEMBRANE TANKS Filed April 18, 1962 'II'III'I'I'IIIIIIIIIIIJ III]! '5' A Home y United States Patent 3,150,794 MEMBRANE TANKS Etienne Maurice Schlumberger, London, England, and Arnold Jozef Willem Ploum, LIle Residentielle de Villennes-sur-Seine, Seine-et-Oise, France, assignors to Conch International Methane Limited, Nassau, Bahamas, a Bahamian company Filed Apr. 18, 1962, Ser. No. 188,481 Claims priority, application Great Britain June 20, 1961 Claims. (Cl. 2209) This invention relates to membrane tanks for containing fluids at a temperature considerably below ambient temperature.
In the storage of very cold liquids in large metal tanks, difiiculties arise due to the stresses set up in the tank walls following contraction and expansion of the metal if these walls are restrained. This is particularly so with so-called membrane tanks which comprise thin metal walls and floor resting against a thermal insulation layer, which layer takes the weight of the contents of the tank, the metal walls and floor merely acting as a barrier preventing the liquid coming into contact with the thermal insulation. Clearly in such tanks the thin metal walls and floor have to be fixed to the supporting insulation at appropriate points and, if fiat metal sheet is used, then on contraction severe stresses are set up in the sheet which, if great enough, lead to permanent deformation or even to rupture.
Similar problems arise when thin metal sheet is used as a barrier to prevent escape of cold gases in the case of a rupture of, or a leak from, a vessel containing cold low-boiling liquids, i.e. where a thin metal sheet tank is used as a secondary barrier around a primary container. For the sake of convenience, such thin metal sheet tanks are also herein called membrane tanks.
To avoid the severe stresses arising in such cases, it is possible to use a metal sheet provided with protrusions which deform on contraction but return to their original shape on subsequent expansion. Examples of such pro trusions are corrugations, wrinkles or dimples formed in the sheet.
Generally, in a membrane tank the thermal insulating layer supporting the thin metal walls and floor has flat surfaces, for example plywood sheets, in contact with the thin metal walls and floor, and when these metal walls and floor are provided with protrusions there will be spaces between these flat surfaces and the metal walls and floor. In fact, if there are protrusions on the outside of the metal walls and floor, there is only point or line contact with the load-bearing flat surfaces of the thermal insulation.
The foregoing means that very high loads have to be carried by those parts of the said metal sheet which touch the load-bearing flat surfaces, and it is an object of the present invention to spread these loads more evenly.
Similarly, where a membrane tank is used as a sec ondary barrier, not only will point and line contact occur outside the tank where the primary container rests on the floor of the membrane tank, but it will also occur inside the tank. In this case, point and line contact results in very heavy loads on the floor of the membrane tank which may well cause collapse of the protrusions. Also, if the primary container should rupture, the membrane tank will have to transmit the hydrostatic load and again this load must be evenly spread.
Accordingly, the present invention provides a membrane tank for containing fluids at a temperature considerably below ambient temperature comprising a container constructed of metal sheet provided with protrusions surrounded by, and supported on, load-bearing surfaces which are part of a thermal insulation system, the
spaces between the outside of the protrusions and the load-bearing surfaces being filled with a resilient filler.
The protrusions on the inside of the tank may also be filled with a resilient filler, this being particularly useful when a primary container is sited within the membrane tank. The roof of the tank and means for filling and emptying may be of any conventional type, but preferably the tank is fitted with a rigid metal roof and a trunk in the roof through which the filling and emptying conduits pass.
The metal employed will depend on the temperature to which the tank is to be subjected. For storing the liquefied natural gas, nitrogen or helium at about atmospheric pressure, stainless steel and aluminum alloys are particularly suitable.
The resilient filler may be any material which retains some degree of resiliency at the low temperature to which the tank is to be subjected. Polyurethanes and polyvinyl chlorides, particularly of the foamed variety, are suitable for this purpose. Resin bonded fibres, for example, resin bonded glass fibres, may also be used. The filler may be applied to that surface of the sheet which is to be adjacent to the load-bearing surface of the surrounding insulation to fill the hollows of the protrusions before the tank is constructed. Alternatively, with some types of resilient fillers, it is possible to coat the load-bearing surfaces and press the metal sheets in place so that the filler takes up the hollows of the protrusions and then fabricate the tank in situ.
The invention is illustrated with reference to the accompanying drawings which show a cross-section of a corner of the lower part of a tank of this invention. In the illustrated embodiment, the metal sheets are provided with protrusions of the dimple type.
FIG. 1 shows the corner of a tank in which the membraneconstitutes the liquid container and FIG. 2 shows a similar view of a modification wherein a primary container is located within the membrane tank.
In this specification, the term dimple means a small hollow in a sheet, the depth of which hollow is substantially greater than the thickness of the sheet, thus resulting a corresponding protuberance on the other side of the sheet. It also means the said corresponding protuberance.
The tank is a prismatic tank having four side walls and a floor constructed of dimpled stainless steel sheet surrounded and supported by a thermal insulation system. The thermal insulation system comprises balsa wood panels 1 and 2 having bonded to their inner faces plywood panels 3, 4, 5 and 6. The dimpled metal sheet of the side wall 7 is affixed to the plywood panel 4 at 8 by any suitable means. Similarly, the dimpled metal sheet of the floor 9 is affixed to the plywood panel 5 at 10. The corner between the floor and the side wall is then sealed up by a gutter-like strip 11 with transverse corrugations 12.
According to the present invention, the spaces between the dimpled sheet 7 and the plywood facing 3 and between the dimpled sheet 9 and the plywood facing 6 are filled with a resilient filler 13 such as foamed polyurethane or polyvinyl chloride, or resin bonded glass fibre. If desired, the space between the strip 11 and the panels 4 and 5 may also be filled with a resilient filler.
FIG. 2 shows an arrangement generally similar to FIG. 1, but for the case where a primary container 14 is situated within the membrane tank 7, and the protrusions on the inside of the dimpled sheet 7 are also filled with a resilient filler 15. In practice, the primary container 14 may also be provided with any suitable means for accommodating thermal expansion and contraction, being shown only diagrammatically to indicate the relationship of the respective elements.
Sheet having protrusions used in the present invention may be prepared from any type of sheet metal which is suitable for the intended purpose. Examples of metals which may be provided with protrusions in this fashion are steel, stainless steel, aluminum and its alloys and copper and its alloys. For very low temperature operation, stainless steel and aluminum alloys are particularly suitable. T he protrusions may be formed in the sheet by any suitable method such as pressing or rolling.
The thermal insulation may be of any suitable type such as balsa wood, quippo, cork, foamed plastics, glass, asbestos, jute fibres, mineral wool or cellular gypsum. Where the thermal insulation material has structural strength, such as balsa wood, quippo and corkboard, it may be used directly to support the dimpled metal sheets, but it is preferably lined with a stronger material such as plywood, on which lining the metal sheets are supported. Where loose thermal insulating materials are used, then a supporting surface of a strong material, such as plywood, must be constructed to take the Weight of the metal sheet tank and its contents.
It will be clear that, instead of metal sheet provided with dimples, metal sheet provided with corrugations or wrinkles or similar protrusions can be used if desired.
1. A membrane tank for containing fluids at a temperature considerably below ambient temperature comprising a container constructed of thin metal sheet provided with thermal-stress-relieving protrusions, and thus presenting an irregular surface; thermal insulating material having substantially non-resilient load-bearing surfaces externally surrounding said container and supporting said container by engagement with only those portions of said irregular surface which protrude toward said insulating material, so that there are spaces in some areas between the outside of the container and the load-bearing surfaces; and a resilient filler substantially completely occupying said spaces, said filler being sufficiently deformable so as to distribute a fluid load in said tank, in a uniform manner, from said metal sheet to said load-bearing surfaces.
2. A membrane tank as claimed in claim 1 in which the resilient filler is foamed polyurethane or polyvinyl chloride or resin bonded glass fibre.
3. A membrane tank as claimed in claim 1 in which the protrusions are dimples in the metal sheet.
4. A membrane tank as claimed in claim 1 in which the protrusions are corrugations in the metal sheet.
5. A membrane tank as claimed in claim 1 in which the protrusions are wrinkles in the metal sheet.
6. A generally rectangular membrane tank having flat walls and a flat floor for containing large volumes of fluids at a temperature considerably below ambient temperature comprising a container constructed of metal sheet provided with protrusions surrounded by, and supported on load-bearing surfaces which are part of a thermal insulation system, the spaces between the outside of the protrusions and the load-bearing surfaces being filled with a resilient filler, the protrusions on the inside of the tank being also filled with a resilient filler.
7. A membrane tank as claimed in claim 6 provided inside with a primary container.
8. A membrane tank as claimed in claim 6 in which the resilient filler is foamed polyurethane or polyvinyl chloride or resin bonded glass fibre.
9. A membrane tank as claimed in claim 6 in which the protrusions are dimples in the metal sheet.
10. A membrane tank as claimed in claim 6 in which the protrusions are corrugations in the metal sheet.
11. A membrane tank as claimed in claim 6 in which the protrusions are wrinkles in the metal sheet.
12. A membrane tank as claimed in claim 1, in which the load-bearing surfaces are substantially smooth, flat surfaces, said tank being substantially prismatic in shape.
References Cited in the file of this patent UNITED STATES PATENTS 1,186,572 Guibert June 13, 1916 1,453,284 Robe May 1, 1923 2,131,632 Lindell Sept. 27, 1938 2,393,964 Boardman Feb. 5, 1946 2,889,953 Morrison June 9, 1959 2,963,873 Stowers Dec. 13, 1960 3,039,418 Versluis June 19, 1962 FOREIGN PATENTS 860,815 Great Britain Feb. 8, 1961 860,816 Great Britain Feb. 8, 1961