WO2007064212A1

WO2007064212A1 - Panel tank for storage of fluids

Info

Publication number: WO2007064212A1
Application number: PCT/NO2005/000446
Authority: WO
Inventors: Pål G. BERGAN; Kåre BAKKEN
Original assignee: Det Norske Veritas As
Priority date: 2005-12-01
Filing date: 2005-12-01
Publication date: 2007-06-07
Also published as: EP1977155A1

Abstract

The present invention regards a tank for storing of fluid, capable of withstanding thermal expansion and contraction, for instance for storing of LNG, comprising means for filling and emptying the tank and for placement within an outer supporting, load carrying structure (20) enclosing the tank. The sides forming walls, roof and or floor of the tank comprise panel elements (1) comprising at least a double barrier (2,3) and which barriers (2,3) of neighboring panel elements (1) are connected to each other by barrier strips (6) with properties which allow for contraction and expansion of the individual panel elements and form a leakage proof connection between the barriers of neighboring panel elements.

Description

Panel Tank for Storage of Fluids

The present invention regards a tank for storage of a fluid, which tank is positioned within an outer supporting structure, for instance a structure of a vessel, a void in the ground or another outer supporting structure. The tank comprises filling and emptying means and is also formed to withstand expansion and contraction due to temperature variations, for instance occurring in connection with storage of Liquefied Natural Gas (LNG).

There is a need for storage of fluid in tanks which are able to withstand large temperature variation and thus undergo large contractions and expansions for example for storing LNG at cryogenic temperature and near atmospheric pressure. Such tanks are needed in many areas of the LNG value chain: fixed and floating offshore production facilities (liquefaction facility), onshore production and storage facilities, waterborne transportation on ships, fixed and floating offshore import terminal facilities, and onshore import terminals and re-gasification facilities. Floating storage tanks on ships and floating terminal experiencing different levels of filling represent a particular challenge; this is because motion of the tank and, thus, the fluid, sets up waves that hit the inner tank surface. High, dynamic sloshing and slamming pressures in corner regions can create damage to the wall and the insulation, particularly for large tanks. It is known that these phenomena represent a serious problem for the currently most used type of tanks on ships, the so-called membrane tanks.

For ships or offshore production facilities, the shape of the tank is important as the tanks normally would be located inside the structure. It therefore is an advantage if the tank system can be adapted to different geometric shapes. Another important aspect is efficient fabrication and installation of the tanks. The possibility of extensive preproduction of elements and rapid installation gives a potential for overall reduced costs and production time.

Purpose

The main purpose of the present invention is to provide a new type of tank structure to form a highly efficient, double barrier tank adaptable to be placed within most external structures. A further purpose is to provide a tank with reduced stress/load on the insulation, preferably with very small stress/loads directly on the insulation.

It is still another aim to provide a tank with a double barrier against leakage and which may be leakage tested before use and where one may detect any leakage and decide the position of such leakage.

Another aim is to provide a tank which can be prefabricated in parts or in sections and be rapidly installed at the final location, such as onboard ships, floating 5 000446

terminals or on sites on land. It is also an aim to provide a tank wherein one easily may replace elements of the tank in case of damage to a part of the tank. Another aim is to provide a tank system capable of being adapted to different surrounding spaces, as cargo holds in ships, containment spaces on floating platforms, segmented spaces at land-based plants, etc.

General part

These purposes and aims are achieved by means of the invention as defined in the following claims.

The invention regards a tank for storing of fluid, which may withstand expansion and contraction due to temperature changes occurring for instance with storing of LNG. The tank comprises means for filling and emptying the tank. The tank system is adaptable for placement within a containment space of an outer supporting, load carrying structure. This containment space may be prismatic with straight, rounded or faceted corners, or, it may have other shapes such as cylindrical shape. This outer supporting structure may be a hull of a vessel, a void within a structure in a floating or stationary platform or a void within a structure onshore. The outer supporting structure encloses the tank structure according to the invention.

According to the invention the tank sides forming walls, roof and or floor of the tank, positioned within the outer supporting structure, comprise panel elements. These panel elements comprise at least a double barrier in the form of at least two barriers plates, but it may also be a triple or quadruple barrier, formed by layers of barrier plates.

To form the tank, the panel elements with the barrier plates are connected to each other by barrier strips with properties that allow for contraction and expansion of the individual barrier plates and form a leakage proof connection between neighboring panel elements. A barrier strip connects a barrier element, i.e. a barrier plate of one panel element to a barrier element, i.e. a barrier plate of another panel element, and another barrier strip connects a second barrier plate of the one panel element to a second barrier plate of the other panel element. This principle applies to all joining zones between panel elements and for all layers of barriers that the panel elements consist of.

The design of the panel elements may vary, depending on the type of fluid to be stored and/or the intended location and use of the tank. In one embodiment a panel element comprises of a double layer of connected barrier plates forming a double barrier preferably in the form of a sandwich structure, flanges attached to and arranged between the barrier plates along the edges of the barrier plates for attachment of the barrier strips, and a support and attachment structure for the barrier plates connected to and or incorporated into the panel element, which support and attachment structure is positioned between the barrier plates and an outer surrounding structure. The support and attachment structure is preferably formed in such a manner that it forms spaces within the support and attachment structure, between the barrier plates and the outer supporting structure. These spaces are thus suitable for being filled with insulation material and in the preferred embodiment filled with insulation. There may typically also be an additional plate type layer that holds the insulation in place within the support and attachment structure for the plates.

In a preferred embodiment the panel elements comprises a sandwich structure, where the two outer layers or skins of the sandwich structure form two barrier plates of the tank. The two outer layers are in a leakage proof manner connected to two outer layers or skins of a sandwich structure of neighboring panel elements by barrier strips, thereby forming a double barrier for the tank. The sandwich structure may be formed with a core of a corrugated structure between the two outer layers. In other embodiments the sandwich structure may have beams (webs) stretching from one outer layer to the other layer and or there may be a porous material between the two layers. Preferably the sandwich structure comprises a corrugated structure with ridges or girders running across the longer distance between two edges of the panel element. The ridges thereby stretches across a longitudinal axis of the panel element, mainly parallel with a short edge of the panel element, thus the load carrying takes place mainly in the shortest span direction. In different embodiments of the panel elements the barrier plates may be formed by metal plates, composite barrier plates or combinations of these and other possibilities. In the case of corrugated core there are preferably also end flange elements, at least arranged at the two shorter edges of the panel element, but possibly at all four edges. By having the barrier of the tank formed by a sandwich structure one achieves a structure where there are no or minimal stresses on the insulation of the tank, since the sandwich structure is mainly self supporting.

The support and attachment structure may be formed by beam elements, columns, corrugated webs or a sandwich structure or combinations of these different structures. The support and attachment structure may comprise of beam elements along the outer edges of the panel element. Alternatively the siipport and attachment structure is integrated in the panel elements forming a box-like panel element. The support and attachment structure will always with an integrated or separate configuration relative to the panel element, be positioned between the barrier plates and the outer supporting structure. In embodiments there will be insulation arranged in spaces formed between the elements forming the support and attachment structure either this support and attachment structure is integrated into the panel element or not. In all embodiments of the panel elements there may be means to detect any leakage through any of the barriers of the panel elements. These means may be adapted to detect leakages specific for any panel element or between panel elements to determine the position of the leakages, or means arranged to detect leakages for any of the barriers of the tank. By having a double barrier one may also test leak tightness of the barriers prior to filling the tank with the fluid to be stored in the tank. This is largely beneficial since one by this may perform improvement and repairs to the barriers during construction of the tank without having to fill and empty the tank for fluid. Leak testing may be done in several ways, one possibility is pressurizing or depressurizing the void between the barriers with a fluid and measure the pressure or gas leakage, or adding a fluid between the barriers and visually detect if there are any leakage into or out of the barriers.

The barrier plates of the panel element are directly or indirectly connected to the support and attachment structure along the edges of the barrier plates where this connection is made in such a way that it allows for necessary relative motion due to relative thermal deformations. This connection and support may be formed by point connections, as columns or connection lines as beams, allowing the barrier plates to undergo thermal contraction and expansion. When the support and attachment structure is integrated in the panel element and forms a box structure around the edges of the panel element, the connection will not allow for movement between the barrier plates and the support and attachment structure. In the case where the support and attachment structure is not a part of the panel element the connection between the panel element and a support and attachment structure will allow for some movement between the panel element and the support and attachment structure, dependent on the construction of the support and attachment structure.

Also the connection between the support and attachment structure, either integrated in the panel elements or separate from these, and the outer supporting structure may allow for some thermal contraction and expansion variation between these elements. This connection to the outer supporting structure may also be formed by non- metallic elements.

The flexible barrier strips have two main functions: to provide a leakage proof seal between the panel elements, and to allow for thermal contraction and expansion of the barrier plates of the panel elements and the panel elements. To serve these purposes, flexibility and suitable shape are important factors. The barrier strips must be fixed or connected to the panel element's barriers or barrier plates in a way which assures sufficient strength and leak tightness. The flexibility of the barrier strips can be provided through bending of a flexible corrugation or by in-plane flexibility of the barrier strips. Both the material and the thickness of the barrier strips can be varied to obtain the desired properties of the barrier strips with respect to both flexibility and leakage resistance. The barrier strips connecting neighboring panel elements are welded or glued or otherwise continuously connected to the panel elements, to form a leakage proof connection and gas barrier.

The panel elements should be made and dimensioned in accordance with the fluid properties, fluid static and dynamic pressures according to the part of the tank where they are placed and which fluids and use, the tank is intended for. The shape and design of the panel elements can also be varied depending on which part of the tank they should form. Larger elements experience more accumulated thermal contraction/expansion over the extension of the panel elements, which may be accounted for in the overall tank design. The overall form of the panel elements may be flat, single or double curved or a combination of these. The panel elements may also be formed with curved portions to correspond to the shape of the outer structure. Curved panel element or panel elements with a curved section may for instance be used in the transition between the wall and either the roof or the floor. The panel elements should preferably be of rectangular shape with proportions 1:2, 1 :3 or 1 :4 or a higher ratio, but may have other proportions or be quadratic. The thickness and strength of the floor, wall and roof elements can be different, as they may experience different loading conditions. In a preferred embodiment, the transition zones are curved, which provide a better performance in relation to fluid dynamic impact loads such as sloshing. A specific feature of the invention is that the panel elements in a preferred embodiment in at least a portion of tank are arranged in a pattern where only three or less panel elements are joined at one position, and where the panel elements are rectangular with the length of one edge a multiple of the other edge and where the panel elements are arranged in a pattern where a shorter edge of one panel element is abutting a longer edge of a neighboring panel forming an L-shape of these two panel elements. When combing several pairs, the element lay-out will resemble a fish bone pattern. This pattern has the advantage over the conventional pattern for membrane tanks, that all connection zones will be discontinuous with T- intersections instead of X-inter sections. This is particularly an advantage with respect to obtaining a simplified barrier strip geometry at the intersections and thereby more leakage safe connections between the panel elements.

The layout of the panel elements in terms of size, geometric proportions and patterns is important since these parameters are essential for the magnitude and forms of deformation that must be accommodated for in the plate sections. The invention will now be explained in more detail with reference to the following drawings where:

Fig. 1 shows an elevated view of a part of a panel element according to a first embodiment, Fig. 2 shows a cross section of part of a panel element,

Fig. 3 shows a cross section of a first embodiment of the joining of two panel elements of an embodiment similar to that shown in fig. 1 attached to an outer supporting structure, Fig. 4 shows a more detailed view of a part of the configuration in fig. 3,

Fig. 5 shows a cross section of another joining of two panel elements with a separate support and attachment structure, attached to an outer supporting structure,

Fig. 6 and 7 show two different patterns for arranging the panel elements, Fig. 8 show a third rectangular pattern for arranging the panel elements, Fig. 9 shows a sketch for arranging of panel elements in a corner of a tank,

Fig. 10 shows a cross section of another way of arranging panel elements in a corner of a tank,

Fig. 11 shows the structure of panel element arranged on a beam and column type support and attachment structure, and Fig. 12 shows an elevated sketch and part cross section of the joining of panel element arranged as in fig. 11.

Similar elements are given the same reference numerals in all the figures.

In fig. 1 there is shown an elevated view of a part of a panel element 1 according to a first embodiment of the invention. The panel element 1 comprises of a first barrier plate 2 and a second barrier plate 3, with a connected corrugated structure 4 in between the two barrier plates 2, 3, and a support and attachment structure incorporated into the panel element 1. There is between the first and second barrier plates 2, 3 also arranged end flange elements 5 shown at two edges of the panel element 1, which edges are mainly parallel to the ridges formed by the corrugated structure. There may be end flange elements 5 between the barrier plates on all the four edges of the panel element. These end flange elements 5 have several functions as stiffening the barrier plates and the panel element, form an attachment position for barrier strips and so further. The support and attachment structure comprises in this embodiment of a box shaped structure 16, which may be formed by for instance plate elements with pressed corrugations, an extruded element or connected beam elements or formed in a different manner, comprising insulation 11 in any space formed within the box shaped structure 16. There is also an attachment plate 19 attached to the panel element 1 along the edges of the box shaped structure 16, there will be given and explanation of the attachment plate 19 in the explanation of fig. 4. In fig. 2 there is shows a cross section of part of a panel element. This cross section may form part of the panel element as shown in fig. 1 or be a cross section of a part of a second embodiment of the panel element. The cross section shows a first barrier plate 2 and a second barrier plate 3 and a corrugated structure 4 in between these two barrier plates 2, 3, which in this embodiment is forming a sandwich structure. The connection between the outer barrier plates and the internal corrugated structure may typically be done by welding, for instance laser welding. In other embodiments the barrier plates may be attached to each other by beam shaped elements forming a sandwich structure and or even with a porous material between the barrier plates, the important element is allowing of fluid transport between the barrier plates thereby allowing for detection of leakages across the barrier plates or barrier strips.

Fig. 3 and 4 show a cross section and a more detailed cross section of one possible embodiment of connection of panel elements according to the embodiment shown in fig. 1, attached to an outer supporting structure. In this figure there is shown two panel element 1,1', which both comprises of a first barrier plate 2, and a second barrier plate 3, and a corrugated structure 4, seen clearly in the cross section of one of the panel elements 1. This also indicates that the corrugated structure of the other panel element is oriented transverse to the first panel element. There are end flanges 5 close to all the edges of the barrier plates 2,3. The panel elements 1,1 ' further comprise a support and attachment structure, comprising of a box structure 16 formed along the edges of the panel elements 1,1 ' and insulation 11 arranged within the box structure 16, with an additional plate 12 holding the insulation within the box structure 16. There is in addition attachment means for attaching the panel elements to an outer supporting structure 20. In this embodiment there is also arranged insulation 11 ' in voids created between the different panel elements 1,1 ', see fig. 3. There may be leakage detection means 21 arranged in voids formed between the neighbouring panel elementsl,l', between the barriers of the tank.

The two panel elements 1, 1' are connected to each other by barrier strips 6 connecting a first barrier plate 2 of one panel element 1 to a first barrier plate 2 of the other panel element 1 ' and a second barrier strips 6 connecting the two second barrier plates 3. As best seen from fig. 4 this connection may be done by having the barrier plates 2,3 attached the flanges of the barrier plates 2,3. The barrier strips 6 are formed with a bend to allow for contraction and expansion of the barrier plates 2,3 relative to each other.

The panel elements 1 are attached to the outer supporting structure 20 with attachment means , i.e. bolt arrangements, allowing for some movement of the parts relative to each other. This is achieved by having an attachment tray 14 attached or welded to the outer supporting structure 20, with an internal insulation pad 15 within the attachment tray 14, faced towards the support and attachment structure of the panel element 1. The panel elements 1,1 ' comprise an attachment plates 19 along their edges faced toward the outer supporting structure, which will be fastened to the outer supporting structure 20 within the attachment tray 15, while at the same time allowed to move in a direction mainly parallel with the plane of the panel element 1 within the attachment tray 15. The walls formed by the box structure 16 are flexible in their transverse direction to allow for thermal contraction of the sandwich structure.

In fig. 5 there is shown a different embodiment of connection of neighbouring panel elements 1. These panel elements comprises of a first barrier plate 2 and a second barrier plate 3 with a corrugated structure 4 in between the barrier plates 2,3. There are also arranged end flanges 5 in between the barrier plates 2, 3 at the edges of these. The panel element further comprises connection flanges 8 for attachment to, in this embodiment, a separate support and attachment structure. The connection flanges 8 are formed and arranged in such a manner that a beam structure 17, formed by I-shaped beams, forming part of the support and attachment structure , may be positioned with an end within the connection flanges 8 allowing for movement in one plane but preventing movement in other planes. The separate support and attachment structure with beam structure 17 and insulation 11 but without an additional plate, is attached to the outer support structure 20 in a similar manner as in the embodiment shown in fig. 4, with bolt connections and attachment tray. The barrier strips 6 connecting the barrier plates 2, 3 are formed with a U- formed bends allowing for contraction and expansion of barrier plates 2, 3.

The panel elements will according to a preferred embodiment of the invention be arranged in a pattern as seen in fig. 6 and 7, breaking up any longer lines of connection between the panel elements. The panel elements 1 are preferably formed with a shorter edge 101 of the panel element 1 abutting a longer edge 102 of a neighbouring panel element 1 '. This pattern gives a L-shape of two neighbouring panel elements where one shorter edge 101 is abutting a longer edge 102 either these panel elements have a dimension of rectangular shape of 1:2 as seen in fig. 6 or 1 :3 as seen in figure 7, forming a fishbone pattern.

In other embodiment the panels are arranged in a rectangular pattern rather than a fish-bone pattern as seen in figure 8. The various previous embodiments shown in form of beam and box support systems can also be applied when the pattern is rectangular; however, there is one exception and that applies to the barrier strips. These strips will have to be rather elastic since there will be stretching and contraction in the zone of the X-shaped intersections. Alternatively, for instance when the barrier strips are made of metal alloy, there will have to be a doubly curved corrugation of the barrier strips at the intersections. Use of such corrugation is known technology from LNG membrane tanks. In fig. 9 there is shown an embodiment of panel element forming a corner of a tank, where regular panel elements 1 are planar panel elements, while panel element 110 are formed as single curved panel element or comprises a single curved section of the panel element. There is also a double curved panel element 120 arranged in the corner where the three sides of the tank meet.

In a different embodiment the corners of the tank are sharp or faceted rather than rounded as shown in figure 9. Figure 10 shows how a corner may be shaped in 90 degrees or, in principle, any other angle that is consistent with the actual shape of the external supporting structure. The figure shows how the panels meet at the corner and how the barrier strips may be attached in this case. How this will look if the angle for instance is 45 degrees rather than 90 degrees is self evident. In this way the transition between the floor or ceiling and the walls may be shaped with a panelled 45 degree intersection plane and thereby be adapted to shapes of holds that are common for ships (e.g. with wing and hopper type tanks).

Fig. 11 show an arrangement where some panel elements 1 are arranged on a separate support and attachment structure, comprising of a beam structure 17 and columns 18 adapted to be attached to an outer support structure (not shown) There are only shown four panel element, but beam structure 17 and columns 18 for more than four panel elements. One can in this embodiment also see that an internal corrugated structure in the sandwich structure always is arranged with ridges transverse to a longer edge of the panel element, and therefore by orientation of the different panel elements being oriented transverse to the corrugated structures of some of the neighbouring panel elements. Fig. 12 shows a part cross section of a connection as shown in fig. 11. The panel elements 1 comprise a first barrier plate 2 and a second barrier plate 3 with a corrugated structure 4 in between the barrier plates 2, 3. The panel elements are attached to a separate support and attachment structure comprising of a beam structure 17 along the edges of the panel elements 1, 1 ' with insulation in between the beam structure 17 with an additional plate 12 holding the insulation within the beam structure. This additional plate 12 may form an additional barrier for the tank in addition to the barriers formed by the barrier plates 2,3. In this embodiment the support and attachment structure comprising of an additional column structure 18 attached to an outer supporting structure (not shown). In this figure one may also see barrier strip 6 connecting the first barrier plates 2 of the two neighbouring panel elements 1.

The invention has now been explained with different embodiments, a skilled person will however understand that there may be performed alterations and changes to these embodiments that are within the scope of the invention as defined in the following claims. The panel strips may be .planar with properties allowing for contraction and expansion of the barrier plates in the plane of the panel elements. In other embodiments the panel strips may be formed with different bending configuration than a U-bend, for instance more like a V-formed, double U-bend, or other configuration. There may be different form of the panel elements forming one tank. It is also possible to form parts of the tank in a different manner than with panel elements, as having floor and walls with panel elements and roof with a different structure. There may be leakage detection means arranged in any void created between the barriers when assembling a tank, and the different void may be separated in individual void, partly connected forming sections of voids or a fully connected void between the barriers. The panel elements are preferably positioned in a fish-bone pattern, but may also be laid with a brick pattern or rectangular pattern.

Claims

1. Tank for storing of fluid, capable of withstanding thermal expansion and contraction, for instance for storing of LNG, comprising means for filling and emptying the tank and for placement within an outer supporting, load carrying structure (20) enclosing the tank, characterised in that sides forming walls, roof and or floor of the tank comprise panel elements (1) comprising at least a double barrier (2,3) and which barriers (2,3) of neighboring panel elements (1) are connected to each other by barrier strips (6) with properties which allow for contraction and expansion of the individual panel elements and form a leakage proof connection between the barriers of neighboring panel elements.

2. Tank according to claim 1, characterised in that there are leakage detection means (21) connected to an internal space formed by the two barriers (2,3) of the tank and one or series of panel elements

3. Tank according to claim 1 or 2, characterised in that the panel element (1) comprises a sandwich plate structure comprises two outer layers of the sandwich structure forming the barriers or barrier plates (2,3) of the panel element (1), and which barrier plates (2,3) in a leakage proof manner are connected to corresponding neighboring outer barrier plates (2,3) of neighboring panel elements (V), thereby forming a double barrier for the tank.

4. Tank according to claim 3, c h ar a ct e r i s e d i n that the sandwich structure is formed with a corrugated structure (4), beams and or a porous solid material between the two barrier plates (2,3), and with possible openings allowing for leak detection of the space between the two barrier plates (2,3) forming the barriers.

5. Tank according to claim 4, c h a r a c t e r i s e d i n that the panel elements (1) are rectangular and the internal corrugated structure (4) comprises ridges running perpendicular to the longer edges of the panel element (1).

6. Tank according to one of the claims 1-5, characterised in that the panel elements (1) further comprises a support and attachment structure in a box shaped fashion (16) and insulation (11), arranged in between elements forming the support and attachment structure.

7. Tank according to one of the preceding claims, characterised in that the barrier plates (2,3) of the panel elements (1) are supported along their edges by the support and attachment structure, comprising for instance a beam structure (17) where the beam structure (17) is attached to the outer supporting structure (20) in such a way that the beam structure (17) itself may contract and expand in accordance with thermal variations without generating significant thermal stresses.

8. Tank according to claim 6, characterised in that each panel element (1) is a fully self-contained box-type element, comprising a sandwich structure comprising barrier plates (2,3), which sandwich structure is connected to box structure (16) forming box walls along its edges, which box walls form part of the support and attachment structure and with thermal insulation (11) in the space formed by the box walls, and where the box walls are flexible in their transverse direction to allow for thermal contraction of the sandwich structure and where the box walls are connected to the outer support structure (20) in such a way as to reduce heat flux.

9. Tank according to one of the preceding claims, characterised in that at least one panel element (1) is curved or formed with curved sections to correspond to the shape of the outer structure.

10. Tank according to one of the preceding claim, c h a r a c t e r i s e d i n that panel elements (1,1') ^are rectangular with the length of one edge (102) a multiple of the other edge (101) and where the panel elements (1,1') are arranged in a pattern where a shorter edge (101) of one panel element (1) is abutting a longer edge (102) of a neighboring panel (T) forming a L-shape of these two panel elements (1,1').

11. Tank according to one of the preceding claims, characterised in that the barrier strip (6) joining barrier plates (2,2';3,3') of two panel elements (1,1') is formed with a curved section, allowing for contraction and expansion of the distance between the connection points of the barrier plates (2,2';3,3') of two neighboring panel elements (1,1').

12. Tank according to one of the claims 1-11, characterised in that the barrier strip (6) joining barrier plates (2,2';3,3⁵) of two panel elements (1,1'), is formed as a plate formed element with at least a part of the barrier strip in a material elastically allowing for contraction and expansion of the distance between the connection points of the barrier plates (2,2' ;3, 3') of two neighboring panel elements (1,1').