Support of tanks in vessels

A system for support of a vertical cargo tank resting on an insulation layer against the hull of a vessel is arranged such that vertical forces are supported through the base of the tank. Horizontal forces are supported by support point pairs. These pairs are designed to direct applied forces generally through the middle of the shell of the tank in order not to apply bending moment to the shell of the tank. The base of the tank is flexible to generally distribute transferring forces from the tank directly to the bottom of the vessel in order not to apply bending moment to the shell of the tank or to the bottom of the vessel.

Not Applicable

BACKGROUND

The present disclosure relates to a system for the support of tanks for liquids in vessels. More particularly the disclosure relates to a system for bearing or support of vertical forces on tanks for liquids in vessels at the base of the tanks and for horizontal forces at few places so that the bearing of forces that arise are transferred in an advantageous manner to the construction of the vessel.

It is advantageous that the capacities of a ship are exploited in the most efficient way while safety is maintained. The design and therefore the fastening of tanks thereto are influenced by the liquid that is to be transported. This is influenced by the environment that the liquid requires. Liquids that are to be transported may be, for example, foodstuffs that require cooling in order to maintain quality, while other liquids require an over- or under-pressure. An energy carrier such as a liquefied natural gas (LNG) transport vessel requires a tank having a storage temperature of around −160° C. at atmospheric pressure. For carbon dioxide (CO2) transportation, a requirement is, for staying fluent, a temperature of −60° C. in addition to a pressure of about 600 kPa. When transporting other liquids, other conditions apply. Together with dimensions and weight of such tanks, this lay the foundation for even minor improvements may result in large economic profit and competitive advantages.

In the art is known to use hardwood to transfer support forces from a tank to hull as pure pressure via hardwood layers or synthetic materials with similar properties. It is essential that the materials in these layers have very good temperature insulating properties and that they can endure the pressure that they are subjected to.

Hardwood is a suitable material for this purpose, but there are many synthetic alternatives. The products DEHONIT® and PERMALI, which are trademarks of the German company “Deutshe Holzveredlung Schmeing” are examples of products for such use.

Tanks intended for transport of liquids with boats are often formed as spheres, cylinders or prisms. U.S. Reissue Pat. No. RE 29424 describes supporting of tanks having a cylinder shaped cross section that rest on a skirt with opposite sides firmly fastened to a hull of a ship, claim1. The '030 reissue patent describes another form of support, where a number of support units along a horizontal circumference of the tank is put into opposite positioned sleeves.

Vessels may also comprise high vertical cylinder shaped tanks. High tanks may be advantageous for transporting liquids because it will then have better opportunity to adapt the amount of liquid that may be transported with a given hull of a vessel. In addition there are of course other technical problems to addressed as a consequence of using such high tanks. An example of such consequences may be conditions regarding the stability of the vessel. Another and important example is the vertical and horizontal support of such high tanks.

International (PCT) Application Publication No. WO 2010/020431 describes a device for storing a self supporting vertical tank for LNG. It comprises a support arrangement that enables a horizontal relative motion between the tank and the foundation. In this way the tank may contract and expand according to the temperature of the tank without unwanted tension to appear.

The foregoing International Application also describes an arrangement with vertical support faces that are distributed evenly around the tank in two heights. In this way the tank is supported when horizontal forces are applied and pitching is prevented.

A disadvantage with self supporting big and high vertical tanks is that they result in large local load because it is not straightforward to distribute the load. Normally the load is either applied to a ring on the bottom of a ship or to the sidewalls of the hull of the ship. This is described in the '431 PCT publication.

There are mainly two different versions of cryogenic tank design for transport of LNG that are being used today. One is a self supporting tank while the other is a so called membrane type. The most common self supporting type is the Moss tank with a design owned by the Norwegian company Moss Maritime and is a spherical tank. One advantage with self supporting tanks like the Moss tank is that they are robust. One disadvantage is that they are not very efficient in that much space is wasted in the hull with spherical tanks.

The French company Gaz Transport & Technigaz (GTT) own some important designs of membrane type tanks. A membrane tank has a layer of corrugated metal that can maintain its proportions in a wide temperature range so that the tank can fill out the space inside a hull and thus rest on the inner bottom and on the walls of the hull. This results in a very efficient utilization of the space in a ship. Disadvantages of membrane tanks today are that they have a history of leakage and they are not as robust as self supporting tanks. Maintenance on membrane tanks therefore has to be done at frequent intervals and this adds to the cost of running such ships.

SUMMARY

A system for support of a cargo tank in a vessel according to one aspect include a cargo tank having a generally flat and generally flexible base. The system includes support elements substantially evenly distributed underneath the base of the tank. Each support element comprises an insulation layer transferring pressure generally evenly distributed from the contents of the tank, through the bottom structure of the vessel and on to water pressure exerted on an outer bottom of the vessel. The cargo tank comprises at least two pairs of tank pressure faces fastened to a tank shell, wherein at least one pair of the tank pressure faces is arranged transversely and wherein at least one pair of the tank pressure faces is arranged longitudinally in the vessel. An insulation layer is arranged proximate to each of the tank pressure faces.

A corresponding hull pressure face is arranged proximate to each of the insulation layers on the other side of each of the insulation layers. Each hull pressure face is fastened to a ship side or to a bulkhead, wherein each tank pressure face and each corresponding hull pressure face is aligned so that an orthogonal line of force is directed generally tangentially to a middle of the tank shell so that the insulation layers can transfer pressure without transferring substantial bending moment from the support loads to the cargo tank structure or to the bottom of the vessel and, at the same time, thermally insulate between the cargo tank and the vessel.

DETAILED DESCRIPTION

A support system for different shapes of load tanks in vessels like carrier ships and storage ships is described. Without this being a limitation on the scope of the present disclosure, described embodiments are particularly suited for cooled liquids, e.g., liquid natural gas (LNG).

One important advantage of a system according to the present disclosure for vertical high tanks may be that vertical pressure comprising large static components is supported separately from horizontal pressure, mainly induced by dynamic movement of the vessel.

An important feature for tanks for storing, for example, LNG, is that there is substantially no metallic contact between loaded tanks and the structure of the vessel. This may be important when the liquid that is to be transported has a temperature which is lower than common steel in ships may endure without degrading some of the material properties of such steel. The liquid that is to be transported may, for instance, be LNG having a typical storage temperature of about −160° C. Another typical liquid that may be transported is carbon dioxide (CO2) having a typical storage temperature of −60° C. at a pressure of 600 kPa. All support forces from tank to the hull of the vessel are generally transferred as pure pressure straight through hardwood layers or synthetic materials having similar properties. It is important that the material in these layers have suitable temperature insulating properties and that they are able to withstand the pressure they are to be subjected to. Hardwood is a well suited material for this purpose, but there are synthetic materials available as well.

In a first example embodiment, the vessel is a ship equipped with number of cylinder shaped tanks being arranged vertically. A support system for cylinder shaped cargo tanks designed for cooled liquid gas in transport ships and storage ships is presented.

FIG. 1shows a typical alongside cross section of a hold for tanks in a gas carrier. Between two transverse bulkheads5, for example, four such tanks may be arranged. All support forces in the present example are foreseen to be in three horizontal planes. The number of planes may be altered when desirable. InFIGS. 1 and 2, all vertical forces are supported using a suitable number of transverse webs14. The number and the size of these webs14may depend upon the size of cargo tanks4,40and the structure of the bottom of the ship, possibly a double bottom construction as may be required by regulatory authorities, and a main deck6. The planes2and3may be arranged to support all horizontal forces including pitching moment.

FIG. 2presents a typical detail from one of more vertical support elements13below the cargo tank4,40. The support element13may comprise a transverse web14, welded to the inner bottom of a bulkhead7aligned with the main webs of the ship and a corresponding web16welded to the bottom of the cargo tank4,40. Between these two webs may be installed a bottom insulation layer15made of hardwood or a material with similar mechanical and thermal insulating properties. The webs may secured against tilting by means of the support elements13that may be aligned with double bottom stiffening ribs12in the bottom of the ship and a cargo tank bottom stiffener rib17. The support elements13may support only vertical force and the bottom insulation layer15insulates the cargo tank4,40from the structure of the ship.

The base of the vertical tank4,40is generally flat and may be generally flexible. Underneath this base may be disposed a number of generally evenly distributed support elements. The pressure from the contents of the tank may be substantially evenly distributed to the support elements and further through the bottom structure of the vessel41and then to the water pressure on the outer bottom10of the vessel. In this way there no substantial bending moment is transferred from a tank to the structure of the vessel. If the tank bottom had a rigid construction, this would be difficult to achieve. Common self-supporting tanks known in the art prior to the present disclosure normally have support frames covering only part of the tank, e.g., in a ring underneath and covering the outer part of the base of the tank.

The reference number in the drawings named “support point pair”8is a word structure shown inFIGS. 4 and 5. A support point pair8may comprise two main components, the first being a hull support pair24and the second being a tank support pair25. The hull support pair24comprises a number of generally parallel profiles being welded or otherwise anchored to a transverse bulkhead5or to the hull of the ship41,141. Orthogonally to these profiles may be arranged two opposite surfaces of contact. The tank support pair25comprises, in a similar fashion, an number of generally parallel profiles being welded or otherwise anchored to the tank shell23of the cargo tank4,40,104. Orthogonally to these profiles may also be arranged surfaces of contact on two opposite sides. Between the one surface of contact of the hull support pair24and the corresponding surface of contact of the tank support pair25, an insulation layer26is arranged with a purpose of spreading the applied forces over the two surfaces of contact. A corresponding insulation layer26may be arranged between the remaining two surfaces of contact. With this construction, forces and reaction forces are supported in two opposite directions. In this example, the hull support pair24may be designed with an outer extension having a recess for receiving the inner extension of the tank support pair25. A variation of this construction may be to swap the design of the hull support pair24and the tank support pair25.

The number of support point pairs8in the planes2and3shown in the drawings may be minimized to two in each plane, but in some cases three or more may be more suitable. In principle, the least number of support points that are necessary to support horizontal movements of a vertical tank is four, preferably angularly separated by about 90 degrees, distributed in two planes. In this first embodiment, the construction is preferably carried out horizontal support point pairs8. InFIGS. 17 to 21, with details fromFIGS. 4 and 5, the construction of the presented cross sections are orthogonal to the presented forces that are acting. In these drawings one may observe that the support, with positive force, is carried out in such a way that a force in one direction, e.g., from the cargo tank4,40,104, and upward inFIGS. 4 and 5, is directed toward the hull of the ship going from the tank pressure face38, through the insulation layer26; and further on to the hull pressure face39. Assuming the pressure is directed the other way, from the cargo tank4,40,104and downward inFIG. 4; toward the hull of the ship, the pressure is directed from the lower tank pressure face38, through the insulation layer26and further on to lower hull pressure face39further down in the same drawings.

FIG. 3presents a horizontal cross section through a typical hold and a typical cargo tank4,40. Just one cargo tank4,40is shown in the drawing, but the number thereof may vary in other examples.FIG. 3represents cross sections in both planes2and3, these planes possibly being similar. Each plane will have at least two support point pairs8, arranged with a mutual angle that is generally orthogonal, one of the support point pairs being designed to support alongside load and the other transverse load.

FIG. 4shows a detail of a typical support point pair8andFIG. 5shows the same detail in exploded view. A support point pair8may comprise a tank support pair25, comprising a number of parallel faces, each being welded or fastened in some other way to a tank shell23of a cargo tank4,40,104, possibly combined with ring stiffeners (not shown) on the tank. A compatible frame or hull support pair24with recess for the tank support pair25on the tank4,40,104may be welded to the inside of the ship side19. The recess in the frame on the ship makes room for an insulation layer26made of hardwood (or other material having similar mechanical and thermal insulating properties) on each side. The insulation layer26is foreseen to transfer only general pressure, orthogonally to the faces of the insulation layer26, so that the insulation layer26on the front side of a support point pair8receives loads that are directed forward, while the insulation26on the back side receives the loads that are directed backward.

Support point pairs8in this present embodiment address only horizontal forces while all vertical forces are transferred through the construction below plane1. The support point pairs8are designed to be as long as required to accept a construction where a center in the reaction force from the ship is generally tangential to the middle of the tank shell23. This results in that no torque is applied into the tank shell23, but that the force goes tangentially directly into the tank shell23as pressure. This provides a substantially even distribution of stress in the tank shell23.

Overturning or tipping is counteracted by the support point pairs8in plane3taking on more force than those in plane2.

The construction has enough flexibility in the insulation layers26,15, to transfer substantially all forces, including forces from deformation, e.g. initiated by temperature variations and the moving of the ship41, without undesirable stress being imparted upon the cargo tank(s)4,40or the ship. The cargo tank(s) may expand or shrink freely in the radial direction without imparting to the corresponding support point pair8any additional force. This is particularly important when expecting substantial temperature variations as for, e.g., LNG.

FIGS. 6,7and8illustrate schematically how loads are transferred to the vessel hull. The total applied vertical load29may be transferred in plane1by the vertical support elements shown inFIG. 2. Horizontal static and dynamic loads may be transferred through the support point pairs8in planes2and3.

When the cargo tank4,40has applied thereto a horizontal transverse load30in the starboard direction as inFIG. 8(for example due to the ship heeling over in starboard direction), the foregoing transverse load will generally be supported on the starboard side of the support point pair8arranged on the transverse bulkhead5. The horizontal transverse reaction load31results in a rotating torque33applied to the tank4,40that secondarily may be supported aft by the support point pair8arranged at the longitudinal bulkhead20on the ship side19. This secondary reaction load is referenced by numeral32. Part of the transverse loads are naturally be supported by the vertical support elements13having applied thereto an increased load on the starboard side compared to the port side.

Similarly, a horizontal side load34applied to the tank4,40will be substantially supported by the support point pair8at the longitudinal bulkhead. The reaction load35will in this example result in a torque37applied to the tank4,40which is supported by a secondary reaction load36in the support point pair8arranged at the transverse bulkhead5.

Support point pair8in plane3may in such cases absorb substantially the whole load, and the support point pairs8in plane2will only contribute in extreme cases in which the whole of the tank is influenced to slide or move horizontally. If the support in plane1prevents the tank from sliding or moving horizontally, one omit arranging the support in plane2.

Forces directed upward may appear if damage occurs and water gets into the hold outside a tank4,40. If the tank is exposed to water on the outside and the tank is not sufficiently filled so that it does not float, additional support point pairs8may be added to prevent the tank4,40from floating inside the hold. This is not shown in the figures relating to this first embodiment, but reference is made to the following embodiments where this is described.

In a second example embodiment, the vessel is a ship equipped with a number of cylinder shaped tanks that are placed horizontally. The embodiment is a simple support system for lying cylinder shaped cargo tanks designed for cooled liquids in gas and storage ships. The cooled liquid may for instance be LNG.

FIG. 13presents a typical longitudinal cross section of a hold in an LNG carrier. Between two transverse bulkheads5there may be arranged e.g. two cargo tanks104. All support forces in this embodiment may be distributed or transferred in three planes. This may be changed on demand.

In the present embodiment a construction with support point quads9is used in addition to the construction with support point pairs8as described earlier herein.

InFIGS. 15 and 16the construction of a support point quad9is presented. It is constructed in a similar way as the support point pair8, but it has in addition a corresponding support arrangement orthogonally to the support point pair8so that the combined construction supports loads and reaction loads in four directions generally orthogonally to each other. A person skilled in the art will observe that possible variations to this are feasible, for example, a construction with three symmetrical or asymmetrical directions. Another variation may be carried out with a circular version of the tank support and with a corresponding circular arrangement of the hull support. This is not shown on the drawings. Such variations may be a starting point for different embodiments that are not described further herein, but may be adapted to different movement patterns of vessels41,141equipped with cargo tanks4,104of different sizes and shapes. As a person skilled in the art will understand that all such embodiments and variations have insulation layers26corresponding to their tank pressure faces and hull pressure faces for transferring forces.

Support point pairs8may also be arranged on the fore and/or aft end surfaces of cargo tanks. This is not shown in the drawings or described further in the embodiments. The different support point pairs8in one vessel may not be designed equally, but may be adapted to different requirements.

The construction may be designed with flexibility and tolerances to handle all loads, including loads resulting from deformations, that may be initiated, e.g., by temperature variations and the movement of the vessel, without undesirable strain being transferred onto the cargo tank4,40,104or ship41,141. The cargo tank may in principle expand or shrink freely in its radial or axial direction without adding any additional strain to any of the support point pairs8or support point quads9. This is important when the tanks may be large temperature variations as with e.g. LNG.

FIGS. 17-21illustrate schematically how load is transferred between the tanks and the hull of the ship. The general force of gravity129is transferred in plane102, as shown inFIGS. 17 and 18. Horizontal static and dynamic forces,130,134, are transferred through support point pairs8and through support point quads9.

When the cargo tank104has a horizontal transverse load130applied toward starboard as inFIG. 21, e.g., because the ship is heeling over in starboard direction, with further reference toFIG. 13, such transverse load130will primarily be supported by a support point quad9and a support point pair8on the lower side of tank104, where the included hull support quad124and the hull support pair24may be fastened to the inner bottom of the ship7.

The horizontal transverse reaction load131in turn apply a rotating torque133to the tank resulting in a secondary reaction load132from the ship supported at the upper part of the support point pair arranged at the port side. Part of the applied horizontal transverse load130will be supported by vertical reaction forces128and will provide a larger load on the starboard side than on the port side of the vessel.

While vertical tanks may have a flexible base, horizontal tanks are generally completely self supporting. Both horizontal and vertical applied forces acting on big tanks4,40,104should be applied as close to the tank shell23as possible, preferably by letting the forces act along the middle of the shell23, so that bending forces are not transferred into the tank. This may be obtained in the present example through the construction of the support point pair8and the support point quad9, allowing the forces to act along the center line27of the support point pair and quad8,9tangential to the center line of the tank4,40,140. The length of the hull support pair24, the hull support quad124, the tank support pair25and the tank support quad125may vary to a large extent depending on the shape of the tank. It may even be split in separate halves for long designs, including long horizontal tanks.

FIG. 19illustrates the upward directed forces146that may appear provided damage arises resulting in water seeping into the hold outside the tank. Provided the tank104subject to such forces is not filled sufficiently to preventing it from floating, the part of the support pair8that is in plane103will prevent the tank from floating inside the hold.

Support points in the present description is to imply a limited area for support and not a literal point.

REFERENCES

While the invention has been described with reference to a limited number of embodiments, those skilled in the art will readily devise other embodiments which do not exceed the scope of the present invention. Accordingly, the invention shall be limited in scope only by the attached claims.