GB2032506A

GB2032506A - Tank

Info

Publication number: GB2032506A
Application number: GB7841417A
Authority: GB
Original assignee: Kvaerner Brug AS
Current assignee: Kvaerner Brug AS
Priority date: 1978-10-20
Filing date: 1978-10-20
Publication date: 1980-05-08

Abstract

A tank 14, particularly a large storage tank for containing liquids under pressure, for example liquefied gases, comprises two or more shells 14a, 14b connected in the vertical plane of intersection therebetween, each of these shells constituting a section of a spherical shell. The tank is supported in the transition zones between adjacent shells 14a, 14b by a bearing structure, for example a vertical wall 15, around the entire circumference thereof. A vertical, internal tank partition wall or internal stiffener may be provided in the plane of intersection between the tank shells, this partition or stiffener constituting a portion of the bearing structure. <IMAGE>

Description

SPECIFICATION Tank The invention relates to a tank, particularly a large storage tank, e.g., for containing liquids under pressure. Such liquids might for example by liquefied gases, especially ethylene and liquefied petroleum gas.

Large spherical tanks which are supported in various ways are known in the art. For land-based installations, it is most common to support such spherical tanks by means of a truss or on pillars. A disadvantage of this method of supporting a spherical tank is that the legs of the structure are expensive, and the structure is difficult to calculate, especially at the points of support.

On board ships, spherical tanks are supported by means of vertical skirts, or they are suspended in expensive articulated structures. Such supporting means can also be used for installations on land.

A tank of spherical shape is preferable for many applications. Compared with other tank configurations, a spherical tank has the lowest surface-to-volume ratio, and the mechanical stresses caused by internal pressure are lower than with any other configuration. The low surface-to-volume ratio results in less heat transfer from the surroundings to the contents in the tank, which is important when cooled, liquefied gases are stored in the tank.

Furthermore, owing to the favorable stress distribution in a spherical tank, the thickness of the plates required for the tank shell can be reduced.

These advantageous characteristics have made the spherical configuration very well suited for the storage and transportation of many media. The known supporting means for the tanks (i.e. skirts and articulated structures) are satisfactory on board a vessel, but for land installations they become too expensive.

A disadvantage of spherical tanks is that one cannot fully utilise the available surface area or space. This is not only true for tanks on board a vessel, where the spaces for such tanks are delimited by approximately plane surfaces, but it also applies to land installations.

A primary aim of the invention, therefore, is to provide a tank having a supporting means which is inexpensive and easy to calculate from the structural point of view, and which at the same time utilises the favorable stress distribution of a spherical shell and leads to a better utilisation of space.

According to the invention, a tank comprising two tank shells connected in a vertical plane of intersection therebetween, each of said tank shells constituting a portion of a spherical shell, said tank being supported in the transition zone between the tank shells, is characterised in that the tank is rigidly supported by a bearing structure in the transition zone, around the entire circumference thereof. Thus, for purposes of calculation, each of the adjacent part-spherical tank shells can be considered as being fixed in a vertical wall.

The tank may comprise at least one additional tank shell, also constituted by a portion of a spherical shell, which is connected in a vertical plane of intersection to one of, or a respective one of, the first mentioned tank shells. In this case the tank may be supported by a further bearing structure in the transition zone between the additional tank shell and the first mentioned tank shell to which it is connected, this further bearing structure also extending around the entire circumference of its associated transition zone.

In order to stiffen the structure, a vertical tank partition wall or stiffener can optionally be provided inside the tank, at the plane of intersection between adjacent tank shells. The vertical tank partition wall or stiffener then constitutes a part of the bearing structure.

Preferably, an annular member is welded into the or each transition zone, support of the tank then being effected via this or these annular members. In cross section, the annular member preferably has the configuration of a three-armed star, two of the arms then constituting portions of the respective part-spherical tank shells, and the third arm projecting into the tank and serving to stiffen and reinforce the tank. The third arm can constitute a part of a tank partition wall or stiffener when such are found inside the tank.

Welding an annular member into the or each transition zone is advantageous, because the transition zones between the part-spherical tank shells are, from the structural point of view, subject to high stresses.

The angle of intersection between adjacent part-spherical tank shells, or the angle between the tangents of the part-spherical tank shells in the transition zone between two adjacent shells, has no definite critical value, but it is preferred that the angle be below 1000, and preferably around 90".

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which Figures 1 and 2 are purely schematic drawings, in elevation and plan view, respectively, of a tank constructed and supported in accordance with the invention, Figure 3 shows a calculation model for such a tank structure, Figure 4 is a schematic drawing showing one possible embodiment and support for a tank according to the invention, Figures 5 and 6 are elevation and plan views, respectively, of a tank of the type shown in Figures 1 and 2, Figure 7 is a cross section through the line Vil-VIl on Figure 5, Figure 8 is a cross-section on a larger scale of the area encircled and designated VIII in Figure 5, Figure 9 shows a modified embodiment in which a tank partition wall or stiffener has been provided; the cross-section corresponds to the cross-section in Figure 8, Figure 10 is a schematic plan view of a tank supported on board a ship, and Figure 11 is a schematic elevation view of a vessel having two types of tanks according to the invention mounted on board.

Figures 1 and 2 show a tank which is outwardly defined by two part-spherical shell sections 1 and 2. The tank is supported in the transition zone 3 between the two shell sections 1 and 2. The support is only schematically indicated, but it can comprise, e.g., a vertical wall structure 6 which surrounds the transition zone.

Reference numerals 4 and 5 indicate practical braces for the bearing wall 6.

A tank of this type can be calculated by means of a calculation model as shown in Figure 3, in which a part-spherical shell section A is fixed to a vertical wall 6. Calcuations have shown that in such a shell, one obtains an ideal distribution of stresses and shear force in the structure.

Figure 4 shows an embodiment of a tank composed of three part-spherical shell sections 7, 8 and 9. The tank is supported in the transition zones 10 and 11 between the shell sections 7, 8 and 9; one support 12 is indicated as a fixed support, e.g., of the type shown schematically in Figure 1, while the other support 13 is a support permitting movement.

The supports for both embodiments can be realised through techniques that are known per se, and no further discussion of the support structure should therefore be necessary. In Figures 5, 6 and 7, however, a practical embodiment of a support structure of the general type shown in Figures 1 and 2 has been shown.

The tank 14 is supported in the transition zone between two part-spherical shell sections and in reality is fixed in a vertical wall 1 5 which extends around the transition zone. The wall 1 5 has a stiffening flange 1 6 which slopes outwards at the lower portion thereof to form a bracing portion 17. In Figure 7, the wall 15 is shown as having openings 1 8. The wall can naturally be made in many other ways which will be obvious to one skilled in the art.

Figure 8 shows a detail of Figure 5 in crosssection. Welded into the transition zone between the two shell sections 1 4a and 1 4b is an annular member 19, which in cross section has the configuration of a three-armed star. Two of the arms constitute respective portions of the shell sections 14a and 14b, while the third arm 20 projects into the tank and functions as a stiffening member.

Figure 9 shows a modified embodiment of the transition zone, in which the zone is provided with an auxiliary support structure. tnside the tank of Figure 9, a partition wall 21 has been arranged in order to stiffen this area, which is subject to high structural stresses. The wall is provided with openings or outlets 22. Otherwise, the same reference numerals are used in Figure 9 as in Figure 8.

Figure 10 shows a tank of the type shown in Figures 1 and 2, rigidly affixed to a bulkhead 25 on board a vessel whose sides are designated 26 and 27, respectively. The bulkhead 25 may extend only around the outside of the tank, or it can continue inside the tank as a tank partition or stiffener, as described above in connection with Figure 9.

Figure 11 shows an example of a way in which two tanks may be supported on board a ship. The aft tank 28 is supported in the manner depicted in Figure 4, on a bulkhead 29, comparable to the bulkhead 25 in Figure 10, to provide fixed support for the tank in one transition zone, while in the other transition zone the tank is supported in a way which permits the possibility of movement for the tank relative to the ship. The forward tank 30 is supported in the same way, in principle, as the tank in Figure 10, i.e., the two part-spherical shell sections are rigidly attached to a bulkhead 31 on the ship.

As can be seen from Figure 11, the partspherical shell sections do not necessarily need to have the same diameter.

Claims

1. A tank comprising two tanks shells connected in a vertical plane of intersection therebetween, each of said tank shells constituting a portion of a spherical shell, said tank being supported in the transition zone between the tank shells, characterised in that the tank is rigidly supported by a bearing structure in the transition zone, around the entire circumference thereof.

2. A tank according to claim 1, comprising a vertical, internal tank partition wall or Internal stiffener in the plane of intersection between said tank shells, said partition or stiffener constituting a portion of the bearing structure.

3. A tank according to claim 1 or 2, in which the support is effected via an annular member welded into the transition zone.

4. A tank according to claim 3, in which the annular member in cross-section has a threearmed star configuration, two of which arms constitute portions of the respective tank shells, whereas the third arm projects into the tank.

5. A tank according to claim 4 when dependent on claim 2, in which said third arm constitutes a portion of the tank partition wall or stiffener.

6. A tank according to any of the preceding claims, comprising at least one additional tank shell, also constituted by a portion of a spherical shell, connected in a vertical plane of intersection to one, or a respective one, of the first mentioned tank shells.

7. A tank according to claim 6, in which the tank is supported by a further bearing structure in the transition zone between the additional tank shell and the first mentioned tank shell to which it is connected, said further bearing structure extending around the entire circumference of its associated transition zone.

8. A tank constructed and arranged substantially as herein described with reference to, and as illustrated in, Figures 1 and 2, Figure 4, Figures 5 to 8, Figures 5 to 7 and 9, Figure 10 or Figure 11 of the accompanying drawings.