NO126341B - - Google Patents

Description

Tank for storage and/or transport of liquid cargo.

This invention relates to a tank with an essentially cylindrical shape for the storage and/or transport of liquid cargo, particularly cold liquids, such as liquefied natural gas.

The purpose of the invention is to attach a tank of this type to a load-bearing structure in such a way that deformations of the tank or the load-bearing structure will not cause unwanted mechanical stresses. Deformations occur after changes in the amount of cargo in the tank, after movements of the tank, after external forces begin to act on the load-bearing structure, and as a result of changes in the temperature of the cargo or the ambient temperature. These deformations occur to a great extent during sea transport of liquefied natural gas" For this reason, the following mainly relates to one or more tanks for cryogenic use on board ships, but the invention is not limited to this. Similar problems occur with liquid cargo or with vessels for road transport, and the invention also provides a solution to such problems. Furthermore, tanks according to the invention can also be used for heated liquid cargo, such as sulfur or asphalt.

The invention therefore relates to a tank with an essentially cylindrical shape for the storage and/or transport of liquefied cargo, in particular cold liquids such as liquefied natural gas, which tank is suspended in an approximately horizontal position in a load-bearing structure by means of at least two sets of load-bearing elements arranged in a circular pattern, which elements are under tension and are directed approximately tangentially to the cylindrical wall of the tank. The attachment points between the tank and these load-bearing elements belonging to a certain set as mentioned above are arranged approximately on a circumferential line of the tank which is the line of intersection of a plane perpendicular to the central axis of the tank and the wall of the tank, and which load-bearing elements proceed from the horizontal plane through relevant attachment points on the tank and is directed upwards.

If the invention relates to a moving tank, such as on a seagoing vessel, the terms horizontal and vertical are meant to refer to a tank that is at rest, e.g. on board a vessel in still water.

When the load-bearing elements are directed tangentially at the attachment points on the tank, they will cause tensile stresses in the tank wall material, but not bending stresses. This is extremely important because the wall thickness of the tank can then be much smaller than in the case where the wall must withstand bending stresses. Bending stresses in the tank wall will e.g. occur when the tank is placed on racks or fixed by means of tie rods or support rods that are not aligned tangentially. Continuously varying bending stresses are caused e.g. by continuous variation of a vessel's position at sea, which will lead to constant repeated local bends in the tank wall. In order to avoid fatigue phenomena in the material under such conditions, the tank had to be made with very high rigidity. However, this has the very important consequence that the weight becomes large and the construction costs higher, because more material is needed. These disadvantages will weigh particularly heavily if special materials must be used, such as for cryogenic use.

It is also important that the load-bearing elements are directed upwards - As a result, all load-bearing elements are under tension and an appropriate placement of these elements will ensure that the tensile stresses in the tank wall are correctly distributed. The location of the attachment points on the aforementioned circumference of the tank is extremely important in this regard.

Therefore, a tank according to the invention is connected to the load-bearing structure only by means of load-bearing elements. The rigidity of the tank does not influence the rigidity of the load-bearing structure or vice versa. This is particularly important in connection with vessels that are equipped with tanks in accordance with the invention. Both the vessel and the tanks can be constructed independently of each other so that both achieve the best possible construction in terms of strength while at the same time making large savings possible.

It is important that each set of load-bearing elements in a circular pattern comprises at least four elements which are arranged mirror-symmetrically in relation to the vertical plane through the central axis of the tank.

It is also important that the attachment points on the tank for the load-bearing elements belonging to a particular set are in symmetrical positions in relation to the horizontal plane through the central axis of the tank.

Furthermore, it is important in this connection that the said perimeter lines are in symmetrical positions in relation to the longitudinal vertical center plane of the tank.

The attachment points for all load-bearing elements are preferably arranged on lines that extend parallel to the central axis of the tank.

The precautions mentioned above will contribute to an even and symmetrical distribution of forces in the tank wall. These precautions become more important when the tank gets bigger.

Bending stresses in the tank wall are kept small if the deviation from the tangential direction for the load-bearing elements is a maximum of 1 degree. Here it is important that the angle between the radius of the attachment point on the tank for a load-bearing element and the largest part of this element that goes clear of the tank wall is less than 90 degrees, and the smallest part of this "element is in contact with the tank wall out With small swinging movements of the tank about the longitudinal axis, the load-bearing elements will be able to -"unwind" without the risk of them being torn off.

Bending stresses in the tank wall are also reduced when the distance between the attachment point and the last contact point for the load-bearing element before it leaves the tank is chosen so that the projection of the attachment point on the radius through the last contact point coincides with the point of intersection between the radius and the center line of the tank wall cross section . This precaution must be illustrated in more detail below with the help of a figure"

It is preferable that the load-bearing elements are attached to the tank at attachment points by means of attachment elements which are flat and which are attached to the tank in such a way that they protrude as little as possible. In this way, bending moments in the attachment points are kept very small.

The load-bearing elements can consist of flat bands with a smooth surface tangential to the tank wall, Under the influence of lateral movement of a fastening point, e.g. as a result of thermal action, the relevant load-bearing belt will bend less because, due to its flat, even shape, it can easily carry out a movement. A similar effect in this connection is also achieved by arranging at least one pivot point for each load-bearing element.

A great strength in the longitudinal direction and the ability to bend easily is achieved by using cables as load-bearing elements or by using chains or chains.

The tank can be equipped at the location of the aforementioned perimeter lines with annular struts. The load-bearing elements can be attached to these annular struts. The tank can also be equipped with internal transverse plates with holes that can be connected to ring stiffeners. Such plates prevent movement of the liquid load in the tank.

If a certain set of load-bearing elements in a circular pattern includes four elements, the attachment points for these elements can coincide with the point whose radii have angles of or

45, 135, 225 and 315 degrees with a horizontal radius for the relevant circumference. If six load-bearing elements are used, the attachment points for these elements can coincide with points whose radius forms angles of 0, 45, 135, 180, 225 and 315 degrees with a horizontal radius in the relevant circumference. In this

In this case, there are therefore two load-bearing elements that are aligned vertically. These elements can have greater load-bearing capacity than the other load-bearing elements.

In the case of a tank suspended in a vessel where the centerline of the tank is approximately parallel to the longitudinal axis of the vessel, it is important that in each set of load-bearing elements in a circular pattern there are elements with the same maximum load-carrying capacity and whose attachment points coincide with points if radii form an angle with a horizontal radius in the relevant circumferential line that does not exceed the maximum roll angle that can be expected for the vessel in question. In this case, a set of ten load-bearing elements can be used in a circular pattern, where the elements at the attachment points coincide with points whose radii form angles of 0, 30, 60, 120, 150, 180, 210, 240, 300 and 330 degrees with a horizontal radius for the relevant circumference. After the two load-bearing elements which are aligned vertically, elements form an angle of 30 degrees with the first-mentioned elements, where the mentioned angle is the maximum roll angle that can be counted on. When arranging the load-bearing elements at angles of 0, 30, 150, 180, 210 and 330 degrees to achieve the same maximum load-bearing capacity, it is ensured that each load-bearing element that can assume a vertical position is able to withstand the maximum tensile force that can occur.

In the case of tanks that are arranged so that the tank's center axis is parallel to the vessel's transverse axis, the tank's pitch angle will take the place of the roll angle.

A set of load-bearing elements in a symmetrical circular pattern will usually provide sufficient resistance to the tank's swinging movements about the longitudinal axis. Swinging movements will cause load-bearing elements on one side of the tank to loosen and bend, which can only happen if the center axis of the tank also moves in an upward direction. As a rule, the weight is sufficiently great to make turning movements impossible. Additional security in this respect can be achieved by equipping each set of load-bearing elements in a circular pattern with tangentially directed elements by means of which this is connected to the load-bearing structure, which latter elements are directed downwards or horizontally out of the horizontal plane through the relevant attachment point on the idea. These connecting elements are not load-bearing elements and they are subjected to tension only in the event that the tank is rotated about a longitudinal axis. The connecting elements can consist of extensions of some of the load-bearing elements. Connecting elements may have their attachment points at the lowest and/or highest point of the relevant circumferential line, whereby each pair of connecting elements is aligned with each other.

A tank in accordance with the invention equipped with flat belts as load-bearing elements will normally be adequately protected against swinging movements about the transverse axis of the tank. The tape touches the wall of the tank with a smooth surface so that there will be very great resistance to movements in the longitudinal direction of the tank. The shape of the bands can be made more appropriate in this connection, e.g. by providing these smooth surfaces to be attached to the load-bearing structure with a wide base.

Extra security against swinging movements about the transverse axis of the tank is achieved when one or more sets of load-bearing elements comprise elements that form an acute angle with a plane perpendicular to the central axis of the tank, which elements are arranged mirror-symmetrical in relation to the longitudinal perpendicular mid-plane of the tank. This acute angle can have a value range from 10 to 45 degrees.

The load-bearing elements remain tangential to the tank wall.

It is possible for all elements belonging to the aforementioned sets of load-bearing elements in a circular pattern to acquire the aforementioned acute angle. It can e.g. an arrangement is made for two outer sets of load-bearing elements comprising elements arranged so that they will have an acute angle. It may also be sufficient for this purpose to arrange a set in the middle of the tank.

A tank with very large dimensions, e.g. a length of

50 m and a diameter of 15 m, will usually be suspended using more than two sets of load-bearing elements. It may then be desirable to arrange devices for the load-bearing elements or for the load-bearing structure which will ensure approximately the same load on all attachment points for the load-bearing structure for load-bearing elements whose attachment points on the tank are arranged in a straight line parallel to the center axis of the tank. As a result of e.g. suspension of the tank, the load on the load-bearing elements arranged at the place where the suspension occurs will be much greater with the risk of overloading, which can be avoided by designing the load-bearing elements and the load-bearing structure so that a large reserve is obtained with regard to carrying capacity. However, it is a very expensive solution and the device according to the invention eliminates this disadvantage. The devices can consist of helical springs, pneumatic elements, hydraulic elements or a combination of these. The effect of these devices will be explained in more detail below with the help of figures.

The aforementioned devices can also consist of a cable for each row of load-bearing elements on which attachment points are arranged

a straight line on the tank, and whose cable ends are attached to the load-bearing structure, and where the cable is carried by a first row of line sheaves which are also attached to the load-bearing structure, and where the cable carries a second row of line sheaves that the respective rows of load-bearing elements are attached to, and where the line disks in the two rows are arranged offset from each other with a position so that the cable runs in a zigzag or meander shape. The line sheaves in the second row can be attached to the attachment points on the tank, in which case the load-bearing elements consist entirely of cables.

One or more cables as mentioned can be combined with a set of load-bearing elements in a circular pattern near each end of the tank, where the elements are not attached to the cables, but directly to the load-bearing structure, and where one end of each cable is movably connected to it load-bearing construction. The sets of load-bearing elements then preferably comprise load-bearing elements that form an acute angle, as previously mentioned, with a plane that runs perpendicular to the central axis of the tank. As a result of the line sheaves' rotatability, the cable will distribute the load evenly over all attachment points connected to the cable, despite bending of the tank or the load-bearing structure. Movable connection at one end of each cable is required here to ensure that the entire required length of cable is always available, because the ends of the tank are not supported by the cables. All the previously mentioned devices for achieving approximately uniform loads can be equipped with stopping devices which can limit the movements at the attachment points on the tank to a certain maximum value. These stop devices are a safety measure. The devices mentioned here will be explained in more detail below in connection with some of the figures.

The above-mentioned circumference of the tank can be a circle. A tank in which the aforementioned circumferential line is an ellipse with a vertical main axis is just as appropriate.

A tank in accordance with the invention can be provided with an insulating layer in a simple and inexpensive way. As the tank is suspended and is otherwise completely clear of the surroundings, an insulating layer arranged on the outside does not need to be load-bearing. The insulating layer can thus be chosen on the basis of the layer's thermal properties, while mechanical properties, such as load-carrying capacity and fragility, are of no importance.

When insulation is arranged on the outside, the load-bearing elements protrude through the insulation and here it is important that at least the part of each load-bearing element that is inside the insulation consists of temperature-resistant material. This material can e.g. be nickel steel.

The advantage of a tank suspended so that it is clear of its surroundings is particularly clear in connection with cryogenic applications, such as the storage or transport of liquefied gas in a tank, e.g. at atmospheric pressure where the temperature in the load is -160°Ci

A suitable embodiment is obtained when a layer of material constituting thermal insulation is located on the outside of a wall that completely surrounds the tank, where there is an annular space between the casing and the tank wall and where the casing wall is attached to the tank near the sets of load-bearing elements in a circular pattern, and where the enclosure wall does not otherwise touch the tank, . and which wall is equipped with expansion slots each time on each. side of the fasteners on the tank. An important advantage of this design is that the space between the tank and the enclosure wall can be used to capture and then remove products that may leak out of the tank. The room can also be used for installations or for

j

arrange connection with equipment to detect leaks from the tank. On the basis of indications on such equipment, the necessary precautions can then be taken, such as pumping, pressure reduction, etc., which can be done at a very early stage. By supplying the casing wall with expansion slots as mentioned, it is ensured that this wall does not develop stresses as a result of deformations in the tank.

Outer annular struts can be arranged and the enveloping wall can be attached to these, which then pass through the wall to which the projecting parts of the load-bearing elements are attached.

In the case of a tank in accordance with the invention suspended aboard a vessel, the load-bearing structure may consist of bulkheads and/or transverse and longitudinal beams which form part of the ship's structure. Each tank can then go completely clear of adjacent parts of the ship's construction, such as cofferdams, transverse bulkheads, walls, deck beams, transverse frames etc. It is very appropriate to arrange the tanks with their axes running parallel to the longitudinal axis of the vessel.

The purpose may be to achieve that the space in the vessel is as full as possible. with tanks according to the invention. To achieve this purpose, it can e.g. tanks with a capacity of 5,000 tonnes per piece. Pump lines can be easily installed below deck between the tanks. Furthermore, at least part of the space between the tank and the ship's hull can be used for liquid cargo with a temperature that roughly corresponds to the ambient temperature. In this case, one will seek to achieve that the amount of liquid outside the tank is at least so large that the buoyancy force or buoyancy force exerted by the liquid against the tank is equal to or less than the total weight of the tank and the load in it. The load-bearing elements are designed so that they take up tensile loads if sufficiently large forces in the upward direction should occur and cause difficulties. These difficulties can also be avoided by additional load-bearing tangential elements which are designed so that they take up tensile loads as a result of an upward force exerted against a tank. When transporting natural gas by sea, the aforementioned space between the tank or tanks and the vessel's hull cladding can be of great importance if a so-called cold barrier is used, which makes it possible for the energy - in the form of cold - to be released after evaporation of liquid natural gas to be used again . In the case of e.g. pentane at ambient temperature as an agent in the cold barrier, the pentane gas can be stored in the said room,

while the natural gas in a liquid state will be stored in the tanks. After delivery of natural gas, as a result of evaporation, the temperature of the cold barrier will decrease and this cold liquid is transported in the tanks to the production area for gas, where the cold barrier is used to condense natural gas.

Tanks produced in accordance with the invention are

very suitable for use in liquid storage. This can be a vessel in which the tanks are placed or specially designed floating bodies comprising one or more tanks. The tanks in accordance with the invention can also very appropriately be placed on vehicles for land transport, such as road vehicles and rail vehicles.

The invention shall be explained in more detail by means of examples

with reference to the drawings, where:

Fig. 1, 2, 3 and 4 show different positions of load-bearing elements in a circular pattern, fig. 5 a detail of a load-bearing element, fig. 6 and 7 schematically show a tank with annular struts, and fig. 8 and 9 schematically show another embodiment of the load-carrying elements. Fig. 10 - 18 show examples of devices which ensure approximately the same load on the attachment points on the load-bearing structure, and fig. 19 and 20 show a tank with load-bearing elements equipped with insulation.

In fig. 1 schematically shows a perpendicular cross-section through a cylindrical tank wall with a circular cross-section. The wall is denoted by 1. A load-bearing construction 2 is shown here as a square frame which e.g. can consist of a cross frame in a\vessel. Four load-bearing elements which are tension elements are denoted by 3. The tank is suspended by means of these elements in the load-bearing construction 2. The elements 3 are directed tangentially to the cylindrical tank wall and the elements extend upwards from the horizontal plane through the relevant attachment points 4 on the tank. The attachment points are arranged on a circumferential line of the tank that coincides with the vertical cross-section 1. The attachment points 4 are arranged symmetrically in relation to the horizontal plane through the central axis of the tank and the load-bearing elements 3 are arranged mirror-symmetrically in relation to the vertical plane through the central axis of the tank. The attachment points for the load-bearing elements 3 coincide with points whose radii form angles of respectively 45, 135, 225 and 315 degrees with a horizontal radius for the relevant circumference.

Fig. 2 shows part of the tank with surroundings. Fig. 1 is a cross-section along the line a-a' in fig. 2. The tank 5 is equipped at one end 6 with a set 7 consisting of four load-bearing elements 3 arranged in a circular pattern and which are attached to the load-bearing structure 2. The load-bearing elements 3 are flat bands with a smooth surface that fall tangentially towards the wall of the tank. The tank 5 is equipped at the other end with a set of load-bearing elements which are also arranged in a circular pattern as in the element set 7, but which are not further shown. The two sets are arranged symmetrically in relation to the center plane which is perpendicular to the axis of the tank. - It is possible that several such sets of load-bearing elements can be arranged. The attachment points for the load-bearing elements will always be arranged on the generatrix of the tank.

In fig. 3 is a set of six load-bearing elements denoted by 8. The attachment points for these elements coincide with points whose radii form angles of respectively 0, 45, 13 5, 18 0, 225

and 315 degrees with a horizontal radius. Here there are two vertical load-bearing elements that have a greater load capacity or carrying capacity than the other elements.

In fig. 4 is a set of ten load-bearing elements in a circular pattern denoted by 9. The attachment points for these elements coincide with points whose radii form angles of respectively 0, 30, 60, 120, 150, 180, 210, 240, 300 and 330 degrees with a horizontal radius. Set of load-bearing elements in this assembly is suitable for suspending a tank in a vessel. The maximum roll angle for the vessel that can be expected to occur is 30 degrees, which means that the load-bearing elements that here form angles of 0, 30, 150, 180, .210 and 330 degrees will be exposed to the same maximum load. These elements can therefore be made stronger than the other elements.

As shown in this set of load-bearing elements, there are two connection elements 10 which are aligned horizontally and whose attachment points are at the lowest point of the pattern. These elements 10 provide additional security against swinging movements of the tank about the longitudinal axis.

In fig. 5 shows at 11 part of a vertical cross-section through a tank. The attachment points and the area around the attachment points are shown in detail. The load-bearing element 12 has a geometric attachment point 13. Between points 14 and 15, the load-bearing element 12 is in contact with the tank wall 11. As a result, the angle for the element 12, i.e. for the largest part of the element that clears the tank wall, is somewhat less than 90 degrees measured to the radius through point 13. Point 15 is the last point of contact between the load-bearing element 12 before it clears the tank wall 11. The distance between points 13 and 15 is chosen so that the projection of point 13 on the radius through the point 15 coincides with the intersection of this radius with the center line 16 of the tank wall 11. As a result, the tensile stress, which can be large in the element 12, is directed through the center of the tank wall so that the wall is kept free from bending stresses to the greatest extent possible. This attachment method is particularly important for very large tanks. The curvature of the tank wall at the location of the attachment point is then much smaller than indicated in fig. 5 and the angle between the radii of points 13 and 15 will be less than 1 degree.

The tank 17 shown in fig. 6 is equipped with two sets

18, 19 load-bearing bands. The tank is equipped with two ring-shaped struts 20 and 21 arranged on the outside<*>. The sets 18 and 19 are designed differently in order to show different designs. The set 18 has an annular stiffener 20 with two load-bearing elements 22, 23 at each attachment point. These are attached by means of pivots to the tank, respectively, at attachment point 24 and attachment point 25 on the load-bearing construction. The advantage of the use of pivots is that the load-bearing elements do not need to be bent in the event of expansion of the tank in the radial direction. The set 19 has an annular stiffener 21 with a U-shaped cross-section. In this case, each load-bearing element consists of a rod 2 6 which, by means of pivot pins 27, 28, is attached to the attachment points respectively. on the tank and the load-bearing structure. x

Fig. 7 shows a part of the set 18 in the direction of the central axis of the tank. The load-bearing elements 2 2 are attached to the annular stiffener 23 by means of pivot pins 24. For one of the load-bearing elements 22, a pivot pin 25 is shown for attachment to the load-bearing construction.

In fig. 8 shows two designs with load-bearing elements that form an acute angle with a plane perpendicular to the central axis of the tank. The tank's part 29 is equipped with load-bearing elements, of which the element 30 is designed as a flat band which runs in the tangential direction from the tank towards the load-bearing structure 31,

Another load-bearing element 32 is V-shaped, and the two halves run in the tangential direction from the tank to the load-bearing structure 31. This device prevents movements of the tank in the longitudinal direction. A similar effect is achieved by means of devices for one end of the tank 33 with a load-bearing element 34. Like the element 35, this element is connected to the load-bearing structure 36. The other end of the tank 33, which is not shown, is equipped with similar load-bearing elements which are arranged mirror-symmetrical in relation to the tank's mid-plane, which is perpendicular to the tank's central axis. Fig. 9 shows a diagram of two sets of load-bearing elements. 37 is the wall of the tank and 38 the load-bearing structure and 39 and 40 are projections of the load-bearing elements 32 and 30. The elements 34 and 35 can be like 39 and 40. From fig. 9 clearly shows that all load-bearing elements are directed tangentially in relation to the tank wall. Fig. 10 shows an example of a structure where there are devices that ensure approximately equal load on all attachment points on the load-bearing structure. In this case, this load-bearing construction consists of a transverse bulkhead 41 in a vessel equipped with two openings 42 and 43 which are limited by hexagon-shaped outlines. In each opening there is a tank» Near the tank 4^ there is part of a set of load-bearing elements 45. These elements 45 are attached by means of springs 46 to projections 47 on the transverse bulkhead 41. When the distance between an attachment point 48 and a projection 47 changes, e.g. as a result of bending the tank, the tensile force in a load-bearing element 45 will hardly change because the relevant spring 46 takes up the change in distance. All the load-bearing elements for the tank can be equipped in this way. In the case of sagging of the middle part of the tank, the tension in the load-carrying straps at this point is unlikely to increase. Nor will the tension increase in the load-bearing straps in the relevant set when the tank is subjected to torsional forces. The tank 44 is thus equipped with two connecting elements 49 which are directed horizontally,

In this case, the tank 44 is surrounded by a hexagonal enclosure 50 which can be provided with insulating material. The springs 46 are isolated from their surroundings by means of caps 51 and flexible tubes 52. Similar flexible tubes 53 are found on the connecting elements 49. This design is important with regard to preventing the occurrence of condensation.

In the embodiment according to fig. 11, the load-bearing elements 54 are arranged on a generatrix line for the tank and are attached to the load-bearing construction 55 by means of hydraulic elements 5 6 which are connected to each other. Here it is clear that no difference can arise in the tensile forces between the different load-bearing elements.

Fig. 12 shows a simple control system or control system that can be used to influence the position of a tank in the vertical direction when the tank is equipped with hydraulic elements. The tank is denoted by 57 and is equipped with four load-bearing elements 58 in each set. The elements are arranged in a circular pattern and are suspended in elastic hydraulic elements 59. The load-bearing elements arranged at an angle of 45 degrees are connected by hydraulic elements whose surface area of the piston is = nj414<|>^, where is the surface area of stamped in the other hydraulic elements which are connected to the vertically directed load bearing elements. Therefore, pressure equalization can take place within-for a specific set of load-bearing elements. The hydraulic elements are connected to each other through a chamber 60 which in turn is in connection with a pipe to a container 61 which contains liquid and which is separated by a membrane 62 from a container 63 which contains gas and which through a control valve 64 is in connection with a container containing gas under pressure higher than atmospheric pressure. When the gas pressure in the container 63 increases, liquid is forced into the hydraulic elements 59 with the result that the tank 57 is forced to move upwards. The gas pressure in the container 63 can be set using a distance meter 66 through a control element 67 and a valve 64. If the measured distance becomes too small, the valve 64 can transfer gas pressure to the chamber 63 to increase the pressure and thus force more liquid into the hydraulic elements 59. If the distance becomes too large, the gas pressure can be reduced through the valve 64. In this way, the load-carrying bands can be adjusted to the required level.

Fig. 13 and 14 show the use of cables and cable washers for suspending the tank. The tank 68 is suspended in the load-bearing construction 69 by means of cables 70 which extend tangentially to the tank. Cable sheaves 71 are attached to the attachment points. Cable sheaves 72 are found at the attachment points on the load-bearing structure 69. The sheaves 71 are attached in ring-shaped stiffeners 73. The cables 70 which

is passed over the cable pulleys 71 and 72 follows a zigzag-shaped pattern. As the cable sheaves can rotate freely, the tension in a cable will be

the same in all places - and thus the load on all attachment points will also be the same regardless of the relative movements of the tank and the load-bearing structure.

Suspension using cables can also be combined with suspension using other elements, such as flat bands.

Each set of load-bearing elements can then consist of a combination

of this type, as shown schematically in fig. 15. A set of load-bearing elements for the tank 74 comprises four flat bands 7 5 which are attached to the load-bearing construction 7 6 which may be a transverse bulkhead.

Two vertical flat bands 77 are attached to cable sheaves 78 which are carried

of cables 79 which are in turn carried by cable sheaves 80 which are attached to the load-bearing structure 76. Fig. 16 is a side view of a tank suspended in this way. In fig. 16, the same reference number is used as in fig. 15.

The cables here have a meander-shaped course. Each cable is on the one hand connected to the load-bearing structure 76. On the other hand, it is connected to a tension device 81 which is attached to the load-bearing structure 76 and loaded with a weight 84. The tension device 81 comprises two coaxial wheels which are connected to each other, where the wheel 82 with the smallest radius is in connection with the cable 79. The wheel B3, which has the largest radius, is in connection with the weight 84. Appropriate selection of the radius lengths ensures that the weight 84 does not need to be too large. The scale can be prevented from swinging, e.g. by means of guide pulleys 85" In this way,

res that the tension in the cables always has the predetermined value regardless of the position of the attachment points. The same way of tensioning the cables can be used when near the ends of the tank there are arranged sets of load-carrying elements which are placed in a circular pattern and which are not in connection with the cables, intermediate sets of load-carrying elements can be fully or partially equipped with cables .

The rotation of each cable pulley will be very small because

only the deformation of the tank or the deformation of the load-bearing structure must be taken into account. For safety's sake, stopping devices can be arranged to prevent the tank from falling too far in the event of an accident.

According to fig. 17, the tank, which is not shown, is connected by load-bearing flat bands 86. The cable pulleys 8 7 and 8 8 carry the cable 89. The pulleys 88 are attached to the load-bearing structure 90. To the load-bearing structure 90 holders 91 are also attached through which the cable 89 passes . Blocks 92 are attached to the cable and are located inside the holders 91. These blocks 92 go completely clear of the holder

ne 91 when operation is normal. However, they prevent the cable from releasing the load.

If a tank is suspended by two sets of load-carrying straps, swivel forks and flat load-carrying straps can be used instead of cables and pulleys. According to fig. 18, the tank 93 is equipped with annular stiffeners 94 with rotatable yokes 95. Pivot pins 96 and a rotatable yoke 97 are attached to the load-bearing structure 98. The load-bearing bands 99 extend tangentially to the tank. As the yokes can be turned or swung freely, it is certain that the load will be the same at all attachment points.

According to fig. 19 and 20, the tank 100 is suspended by means of

two sets 101 of load-bearing elements 102 in a transverse bulkhead 103 in a vessel. The tank 100 is surrounded by an enclosure wall 104 so that

a space 105 with an annular cross-section is formed. The wall 104 carries an insulation layer 106. The wall 104 is attached to the tank 100

near the sets with the load-bearing elements 101. If the tank of dis-

where places are equipped with annular stiffeners, the wall 104 can be attached to these stiffeners. The wall 104 is equipped on each side of the fasteners with expansion grooves 107. The insulation layer is not loaded by the weight of the tank nor by the weight of the load. The insulation layer must therefore consist of material with very little mechanical strength.

Granulated material can be used if another enclosure wall is present which limits the insulation layer on the outside. Deformations of the tank 100 and the wall 104 do not affect each other. The space 105 can be used for equipment to detect leaks or for emptying the product that may have leaked out of the tank. The tank with the insulation is completely clear of its surroundings, i.e. that deformation of the vessel's hull will not be able to affect the tank and the insulation. If the load-bearing elements are located in the cold zone, they can be made of cold-resistant material, e.g. 8% nickel steel.

Claims (17)

1. Tank with an essentially cylindrical shape for the storage and/or transport of liquid cargo, especially cold liquids, such as fly-tendeg or natural gas, which tank is suspended in an approximately horizontal position in a load-bearing structure, characterized in that the tank is equipped with i at least two sets of load-bearing elements .(3) arranged in a circular pattern, which elements are under tension and are directed essentially tangentially in relation to the tank wall (15/ where the load-bearing elements' attachment points (4J on the tank belonging to a particular set is arranged approximately on a circumferential line of the tank, which circumferential line is the line of intersection between a plane perpendicular to the central axis of the tank and the wall of the tank, and which load-bearing elements (3) from the horizontal plane through the relevant attachment points (4) of the tank are directed upwards. <*> 2. Tank according to claim 1, characterized in that each set of load-bearing elements (31 in a circular pattern comprises at least four elements which are arranged mirror-symmetrical in relation to the vertical plane passing through the central axis of the tank. 3. Tank according to claim 2, characterized in that the angle between the radius of the tank's (11) attachment point (13) for a load-bearing element (12) and the largest part of this element that goes clear of the tank's wall is less than 90 degrees, and where a small part of this element is in contact with the tank wall from the attachment point (13). 4. Tank according to claim 3, characterized in that the distance between the attachment point (13) of a load-bearing element (12) and the last contact point (15) before the load-bearing element (12) leaves the tank is chosen so that the projection of the attachment point (13) on the radius through the last contact point (15) coincides with the point of intersection of this radius with the center line (16) of the cross section of the tank wall (11). 5. Tank according to one or more of the preceding claims, characterized in that the load-bearing elements consist of flat bands (30) with a flat surface which is tangential to the tank wall. 6. Tank according to one or more of claims 1-5 arranged for suspension in a vessel, characterized in that in each set of the load-bearing elements (9) in a circular pattern there are elements with the same maximum load-bearing capacity / which elements' attachment points coincide with points whose radii form angles with a horizontal radius for the circumference line in question and which angles do not exceed the maximum roll angle for the vessel that can be expected to occur. 7. Tank according to one or more of the preceding claims, characterized in that each set of load-bearing elements (9) in a circular pattern also includes tangentially directed elements (10)/ by means of which the tank is connected to the load-bearing construction (2), which latter elements (10) from the horizontal plane through the relevant attachment points on the tank are directed downwards or horizontally. 8. Tank according to one or more of the preceding claims, characterized in that one or more sets of load-bearing elements comprise elements (32) which form an acute angle, e.g. 10-45°, with a plane that is perpendicular to the central axis of the tank, which elements (32) are arranged mirror-symmetrical in relation to the central perpendicular plane of the tank. 9. Tank according to claim 8, characterized in that all elements (32) belonging to said set of load-bearing elements in a circular pattern form the same acute angle. 10. Tank according to one or more of the preceding claims, with at least three sets of load-bearing elements, characterized in that the load-bearing elements (45) on the load-bearing structure (41) are equipped with devices (46,56,59,79-80) which provides an approximately equal load on all the attachment points for load-bearing elements in the various sets which lie on a straight line running parallel to the central axis of the tank. 11. Tank according to claim 10, characterized in that the aforementioned devices consist of helical springs (46), pneumatic elements (56) or hydraulic elements (59). 12. Tank according to claim 10, characterized in that the said devices consist of a cable (79) for each row of load-bearing elements whose attachment points are arranged in a straight line, and where the ends of the cables (79) are attached to the load-bearing structure (76) , and where the cable is supported by a first row of cable sheaves (80), which is also attached to the load-bearing structure, and which cable carries another row of cable sheaves (78), to which sheaves the respective rows of load-bearing elements (77) are attached , with the washers (78,80) in the two rows arranged in a staggered position so that the cable runs in a zigzag or meander curve. 13. Tank according to claim 12, characterized in that the cable pulleys in the second row (71) are attached to the tank's attachment points (68). 14. Tank according to claim 12 or 13, characterized in that near the end of the tank a set of load-bearing elements is arranged in a circular pattern, which elements are not connected by cables, but directly to the load-bearing structure, and where one end of each cable is movably connected to the load-bearing structure. 15. Tank according to one or more of claims 9-14, characterized in that the said devices are equipped with stopping devices (91,92) which can limit the movement of the attachment points on the tank to a determined maximum value. 16. Tank according to one or more of the preceding claims, characterized in that a layer of material that forms thermal insulation is arranged on the outside of a wall that completely surrounds the tank, where an annular space is formed between the casing wall and the tank wall, where the casing wall is attached to the tank near the sets of load-bearing elements in a circular pattern, and where the surrounding wall does not otherwise touch the tank, and which wall is provided with expansion slots on both sides of the fasteners of the tank. 17. Tank according to one or more of the preceding claims arranged for suspension in a vessel, characterized in that the load-bearing structure where the tank is suspended consists of transverse bulkheads and/or longitudinal and transverse beams which form part of the ship's construction.