US3659817A

US3659817A - Tank for liquid cargo

Info

Publication number: US3659817A
Application number: US21688A
Authority: US
Inventors: Willem P Hendal; Lionel R Prew
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1969-03-31
Filing date: 1970-03-23
Publication date: 1972-05-02
Anticipated expiration: 1989-05-02
Also published as: FR2040099A5; NO126341B; DE2014428A1; NL7004255A; GB1221911A; SE360454B

Abstract

Means are disclosed for storing and transporting liquid cargo, which means include a substantially cylindrical tank and means for supporting such tank from an overhead load-bearing structure with the cylindrical axis of the tank normally horizontal and in which the means for supporting the tank give rise to tensile stresses in the tank wall and reduced bending stresses, whereby the tank wall may be made thinner for a given cargo. Various embodiments of such means are described, all of which include at least two circular arrays each of at least four load-bearing elements, which elements of each array extend upwardly and tangentially from the cylindrical tank wall in a common vertical plane perpendicular to the cylindrical axis of the tank and are attached between the load-bearing structure and the tank wall under tension. Preferred features of such embodiments are disclosed.

Description

Unlted States Patent 1151 3,659,817 Hendal et al. 1451 May 2, 1972 [54] TANK FOR LIQUID CARGO 2,954,003 9/1960 Farrel] et a1 ..1 14 74 A 1721 Willem Hendal, Amsterdam, Nether- 5332112 1811322 Efiffiiiiiiji: .2/

lands; Lime Famham England 2,967,152 1/1961 Matsch et al. ..114/74 A ux [73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: Mar. 23, 1970 [21] App1.No.: 21,688

[30] Foreign Application Priority Data Mar. 31, 1969 Great Britain ..16,619/69 [52] 11.8. C1. ..248/317, 114/74 A, 220/18, 248/D1G. 1 [51} int. Cl ..F16m l/00 [58] Field ofSearch ..248/317, 119 R, 146,318; 114/74 R, 74 T, 74 A; 220/15, 14, 18; 280/5 R, 5 G, 5 C, 5 E

[56] References Cited UNITED STATES PATENTS 3,225,953 12/1965 Wolfe ..220/18 X 2,814,410 11/1957 Hansen ..220/15 Primary Examiner.|. Franklin Foss Attorney-J. l-l. McCarthy and T. E. Bieber [5 7] ABSTRACT Means are disclosed for storing and transporting liquid cargo, which means include a substantially cylindrical tank and means for supporting such tank from an overhead load-bearing structure with the cylindrical axis of the tank normally horizontal and in which the means for supporting the tank give rise to tensile stresses in the tank wall and reduced bending stresses, whereby the tank'wall may be made thinner for a given cargo. Various embodiments of such means are described, all of which include at least two circular arrays each of at'least four load-bearing elements, which elements of each array extend upwardly and tangentially from the cylindrical tank wall in a common vertical plane perpendicular to the cylindrical axis of the tank and are attached between the loadbearing structure and the tank wall under tension. Preferred features of such embodiments are disclosed,

17 Claims, 20 Drawing Figures Patented May 2, 1972 3,659,817

9 Sheets-Sheet 1 INVENTORS;

WILLEM P. HENDAL LIONEL R. PREW Patented May 2, 1972 3,659,817

I 9 Sheets-Sheet 2 INVENTORS:

WILLEM P. HENDAL LIONEL R. PREW Patented May 2, 1972 3,659,817

9 Sheets-Sheet 3 FIG. 8

FIG. ll

INVENTORS:

WILLEM P. HENDEL LIONEL R. PREW FIG. 9

Patented May 2, 1972 9 Sheets-Sheet 4 INVENTORS:

WILLEM F? HENDEL LIONEL R. PREW Patented May 2, 1972 3,659,817

9 Sheets-Sheet 5 FIG. l2

INVENTORS:

WILLEM P. HENDEL LIONEL R. PREW Patented May 2, 1972 3,659,817

9 Sheets-Sheet 6 I F I 7| 5 FIG. I4

INVENTORS:

WILLEM P. HENDEL LIONEL R.PREW

Patented May 2, 1972 9 Sheets-Sheet 9 FIG. l9

FIG. 20

INVENTORS WILLEM P. HENDEL LIONEL R. PREW TANK FOR LIQUID CARGO The invention relates to a tank of substantially cylindrical shape for the storage and/or transportation of liquid cargo, in particular of cold liquids, such as liquefied natural gas.

The invention is aimed at a new method of fastening a tank of this type to a load-bearing structure in such a way that deformations of the tank or of the load-bearing structure do not result in undesired mechanical stresses. Deformations occur upon changes in the quantity of cargo contained in the tank, upon movements of the tank, upon external forces being exerted on the load-bearing structure, upon changes in the temperature of the cargo or of the surroundings. These deformations occur to a high degree in the overseas transport of liquefied natural gas. For this reason the following is concerned mainly with one or more tanks for cryogenic applications on board ships, although the invention is by no means limited hereto. Similar problems also occur with floating storages or with vehicles for land transport, the invention providing a solution for these problems as well. Moreover, tanks according to the invention can also be used for heated liquid cargo, such as sulphur or bitumen.

The invention therefor relates to a tank of substantially cylindrical shape for the storage and/or transportation of liquid cargo, in particular of cold liquids, such as liquefied natural gas, which tank is suspended in an approximately horizontal position from a load-bearing structure by means of at least two sets of load-bearing elements in a circular array, which elements are in tension and are directed approximately tangential with respect to the cylindrical tank wall. The points of attachment to the tank of those load-bearing elements which belong to a particular set as mentioned hereinabove being located approximately on a circumferential line of the tank, which circumferential line is the line of intersection of a plane perpendicular to the center axis of the tank and the wall of thetank, which loadbearing elements from the horizontal plane through the relevant point of attachment to the tank are directed upwards.

If the invention relates to a moving tank, such as for instance, on an oceangoing vessel, then the terms horizontal and vertical are used in relation to a tank in the position of rest, for instance on board a vessel in still water,

As the load-bearing elements are directed tangential, in the points of attachment to the tank they give rise to tensile stresses in the material of the tank wall, not to bending stresses. This is extremely important, because now the wall thickness of the tank can be much smaller than in the case of that wall having to resist bending'stresses. Bending stresses in the tank wall would occur, for instance, if the tank were placed on stools or were fastened by tie rods or supporting rods not being directed tangential. Continuously varying bending stresses caused, for instance, by the continual variations of the position of a vessel at sea, would then lead to recurrent locally occurring deflections of the tank wall. In order to avoid fatigue phenomena in the material under these conditions, the tank would have to be so constructed as to have a very high rigidity. This would have very important consequences, such as, for instance, a large weight ofthe tank and high cost of construction owing to the necessity of using additional material. This last-named disadvantage will count particularly heavily if, for cryogenic applications, special materials have to be employed,

Also of importance is that the load-bearing elements are directed upwards. As a result of this, all load-bearing elements are in tension and by appropriate positioning of those elements it can be ensured that the tensile stresses in the tank wall are well distributed. The location of the points of attachment on the said circumferential lines of the tank is to a high degree promotive in this respect.

A tank according to the invention therefore is connected to the load-bearing structure by the load-bearing elements only. The stiffness of the tank does not influence the stifi ness of the load-bearing structure and vice versa. This is of importance particularly with respect to vessels equipped with tanks according to the invention. Both the vessel and the tanks may,

independently of each other, be so designed that the construction is optimum with respect to the requirements concerning strength, as a result of which large savings are obtained.

It is of importance that each set of load-bearing elements in a circular array comprises at least four elements which are positioned mirror-symmetrical with respect to the vertical plane through the center axis of the tank.

It is also of importance that the points of attachment to the tank of the load-bearing elements belonging to a particular set are in symmetrical positions with respect to the horizontal plane through the center axis of the tank.

Furthermore, it is of importance in this connection that the said circumferential lines are in symmetrical positions with respect to the longitudinal center vertical plane of the tank.

The points of attachments to the tank of all load-bearing elements are preferably located on lines running parallel to the center of the tank.

The measures described hereinbefore are conductive to an even and symmetrical distribution of forces in the tank wall. These measures become more important according as the tank becomes larger.

Bending stresses in the tank wall are kept small if the deviation from the tangential direction of the load-bearing elements is at most 1. Here it is of importance that the angle between the radius to the point of attachment to the tank of a loadbearing element and the larger part of that element which remains clear of the tank wall is smaller than a small part of that element being in contact with the tank wall from the point of attachment. With slight oscillatory movements of the tank about the longitudinal axis the load-bearing elements may uncoil without a risk of those elements being torn off.

Bending stresses in the tank wall are likewise reduced if the distance between the point of attachment of a load-bearing element and the last point of contact of that load-bearing element before that element becomes clear of the tank has been chosen so that the projection of the point of attachment on the radius through the last point of contact coincides with the point of intersection of that radius with the center line of the cross section of the tank wall. This measure will hereinafter be elucidated with the aid of a figure.

It is preferred that the load-bearing elements be fastened to the tank at the points of attachment by means of fastening elements which are Hat and which are fastened onto the tank in such a way that they project as little as possible. In this way bending moments in the points of attachment are kept very small.

The load-bearing elements may consist of level bands with a flat surface tangential to the wall of the tank. Under the influence of a lateral movement of a point of attachment, for instance due to thermal effects, the loadbearing band in question will then bend to a slight degree which band owing to its flat, level shape, it is capable of doing easily. A conducive effect in this respect is likewise reached by providing for each load-bearing element to have at least one pivot.

A high strength in the longitudinal direction and a capacity for easy bending are attained by employing cables as loadbearing elements or by employing chains as load-bearing elements.

The tank may be provided at the location of the said circumferential lines with ring-shaped stiffeners. The load-bearing elements may be fastened to those ring-shaped stiffeners. The tank may also be provided with internal transverse plates with holes which plates may be connected to the stiffener rings. Such plates restrict movements in the liquid cargo in the tank.

If a particular set of load-bearing elements in a circular array comprises four elements then the points of attachments of those elements may coincide with points whose radii are at angles of, respectively, 45, 225 and 315 with respect to a horizontal radius of the relevant circumferential line. If six load-bearing elements are employed, then the points of attachment of those elements may coincide with points whose radii are at angles of, respectively, 45, 135, 180, 225 and 315 with respect to a horizontal radius of the relevant circumferential line. Thus, in this case there are two load-bearing elements which are directed vertical. These may have a larger load-bearing capacity than the other load-bearing elements.

In the case of a tank being suspended in a vessel, the center line of the tank being approximately parallel with the longitudinal axis of the vessel, it is of importance that in each set of load-bearing elements in a circular array elements of equal maximum load-bearing capacity are present, of which elements the points of attachment coincide with points whose radii are at angles with respect to a horizontal radius of the relevant circumferential line being at most equal to the maximum rolling angle of the vessel that is likely to occur. in that case one may employ a set of ten load-bearing elements in a circular array, of which elements the points of attachment coincide with points whose radii are at angles, respectively, 0, 30, 60, 120, 150, 180, 210, 240, 300 and 330 with respect to a horizontal radius of the relevant circumferential line. Then, next to the two load-bearing elements that are directed vertical there are located elements which with respect to the former elements are at an angle of 30", which angle is the maximum rolling angle that is likely to occur. By providing for the load-bearing elements indicated by the

angles

0, 30, 150, 180, 210 and 330 to have the same maximum load-bearing capacity it is ensured that each load-bearing element which in the absolute sense can take the vertical position is capable of resisting the maximum tensile force that may occur.

In the case of tanks being positioned so that the centre axis of the tank are parallel with the transverse axis of the vessel the dipping angle of the vessel takes the place of the rolling angle mentioned hereinbefore.

A set of load-bearing elements in a symmetrical circular array will as a rule offer sufficient resistance to oscillatory movements of the tank about the longitudinal axis. Oscillatory movements would lead to load-bearing elements on one side of the tank becoming slack and being bent, which can happen only if the centre axis of the tank also moves in the upward direction. Gravity as a rule is sufficiently strong to render oscillatory movements impossible. Extra safety in this respect may be provided by equipping each set of load-bearing elements in a circular array with tangentially directed elements by which it is connected to the load-bearing structure, which last-mentioned elements from the horizontal plane through the relevant point of attachment to the tank are directed downward or horizontal. These connecting elements are not load-bearing elements and they are in tension alternatively only, when the tank is rotated about a longitudinal axis. The connecting elements may consist of elongations of some of the load-bearing elements. Connecting elements may also have their points of attachment at the lowest and/or the highest point of the relevant circumferential line whereby each pair of connecting elements are in line with each other.

A tank according to the invention provided with level bands as load-bearing elements, will generally be sufficiently protected to oscillatory movements about the transverse axis of the tank. The level band touch the wall of the tank by a flat surface, as a result of which there is a very high resistance to movements in the longitudinal direction of the tank. The shape of the level bands may be rendered more suitable in this respect, for instance by providing for the flat surface to be fastened to the load-bearing structure by a wide base.

Extra safety against oscillatory movements about the transverse axis of the tank is obtained when one or more sets of load-bearing elements comprise elements being at an acute angle with respect to a plane perpendicular to the center axis of the tank, which elements are positioned mirror-symmetrical with respect to the longitudinal centre perpendicular plane of the tank. The said acute angle may have a value in the range from to 45. The load-bearing elements remain tangential to the wall of the tank. It is possible for all elements belonging to the said sets of load-bearing elements in a circular array to be at the said acute angle. Thus, for instance, provision may be made for the two extreme sets of load-bearing elements to comprise elements positioned so as to be at an acute angle. It may also be sufficient for this purpose to take a set in the middle of the tank.

A tank having very large dimensions for instance a length of 50 m and a diameter of 15 m will in general be suspended by more than two sets of load-bearing elements. It may then be desirable that for fastening the load-bearing elements to the load-bearing structure means should be present which bring about approximately equal loads in all points of fixture to the load-bearing structure of load-bearing elements whose points of attachment to the tank are located on a straight line parallel to the centre axis of the tank. Owing to, for instance, sagging of the tank, the load on the load-bearing elements located at the site where that sagging occurs would increase considerably, as a result of which there would be a risk of overloading, which may be prevented by designing the load-bearing elements and the load-bearing structure in such a way that there is a large reserve of load-bearing capacity. This is very expensive and the means according to the invention eliminate this disadvantage. The said means may consist of helical springs, of pneumatic elements, of hydraulic elements or of combinations of these. The action of these means will be further elucidated with the aid of the figures to be discussed hereinafter.

The said means may also consist of a cable for each series of load-bearing elements whose points of attachment are located on one straight line of the tank, of which cable the ends are fastened to the load-bearing structure, which cable is supported by a first series of pulleys which are likewise fastened to the load-bearing structure, and which cable carries a second series of pulleys to which the relevant series of loadbearing elements are fastened, the pulleys of the two series .being placed in a staggered arrangement such that the cable is zigzag or square-wave shaped. The pulleys of the second series may be fastened at the points of attachment to the tank, in which case the load-bearing elements are made up entirely by the cables.

One or more cables as discussed may be combined with a set of load-bearing elements in a circular array near either end of the tank, which elements are not connected to the cables, but directly to the load-bearing structure, one end of each cable being movable connected to the load-bearing structure. The present sets of load-bearing elements preferably will comprise load-bearing elements which are at the aforementioned acute angle with respect to a plane perpendicular to the center axis of the tank. Owing to the rotatability of the pulleys, upon deflection of the tank or of the load-bearing structure, the cable distributes the load evenly over all the points of attachment connected to the cable. Movable connection of one end of each cable is here required in order that the entire required length of the cables is always readily available, since the ends of the tank are not carried by the cables. All the aforementioned means for effecting approximately equal loads may be provided with stopping devices which are capable of limiting the movements of the points of attachment to the tank to a maximum value. These stopping devices are a safety measure. The means discussed here will also be further elucidated hereinafter with the aid of some figures.

The aforementioned circumferential line of the tank may be a circle. A tank of which the said circumferential line is an ellipse with a vertical major axis is likewise very suitable.

A tank according to the invention may in a simple manner and at a low cost be provided with an insulating layer. As the tank is suspended and for the rest remains entirely clear of its surroundings, an insulating layer provided on the outside need not be load-bearing. The insulating material thus may be chosen on the basis of its thermal properties; mechanical properties, such as load-bearing capacity and brittleness are not of importance.

With an insulation provided on the outside, the load-bearing elements protrude through the insulation and here it is of importance that at least that part of each load-bearing element which is inside the insulation is made of temperature-resisting material. This material may be nickel steel.

The advantages of the tank being suspended so as to be clear of its surroundings are particularly evident in cryogenic applications, such as storage or transportation in a tank of liquefied natural gas, for instance at atmospheric pressure, where the temperature of the cargo is -l 60C.

A suitable embodiment is obtained when a layer of material providing thermal insulation is present on the outside of a wall which completely envelops the tank, an annular space remaining between the enveloping wall and the tank wall, which enveloping wall is fastened to the tank near the sets of load-bearing elements in a circular array, which enveloping wall does not otherwise touch the tank, and which wall is provided with expansion grooves each time on either side of the fixtures to the tank. An important advantage of this construction is that the said space between the two walls may be used for catching and discharging product that may be leaking from the tank. That space may also very suitably be used for the installation of or providing the connection to equipment for the detection of product leaking from the tank. Then, on the basis of the indication of that equipment, measures such as removal by pumping, reduction of pressure, etc. may be taken at a very early stage. By providing the enveloping wall with expansion grooves as indicated, it is ensured that in that wall substantial stresses due to deformation of the tank will not develop.

External ring-shaped stiffeners may be present to which the enveloping wall is fastened, which stiffeners protrude through the enveloping wall to which protruding parts the load-bearing elements are fastened.

In the case of a tank according to the invention being suspended in a vessel, the load-bearing structure may consist of bulkheads and/or longitudinal and transverse beams forming part of the ships structure. Each tank may then remain completely clear of neighboring parts of the ships structure, such as cofferdams, bulkheads, walls, beams and the transverse frames. It is very suitable for the tanks to be positioned with their center axis parallel to the longitudinal axis of the vessel.

One will aim at a situation where the space in the vessel is filled as far as possible with tanks according to the invention. To reach this aim one may employ, for instance, tanks with a carrying capacity of 5000 tons apiece. Pump lines may easily be installed below decks between the tanks. Furthermore, at least a part of the space between the shell of the vessel and the tank(s) may be suited for liquid cargo having a temperature approximately equal to the ambient temperature. In this case one will aim at a situation where the quantity of liquid outside the tank is at most so large that the buoyancy force exerted on the tank by that liquid is equal to or smaller than the combined weight of the tank and the cargo contained therein. The loadbearing elements are designed so as to take a tensile load and at an excessive upward force difficulties will arise. These difficulties can be obviated by providing, in addition, load-bearing tangential elements designed so as to take a tensile load due to an upward force exerted on a tank. In the overseas transportation of natural gas the said space between the tank(s) and the shell of the vessel may be of great importance if use is made of a so-called cold carrier which makes it possible for the energy in the form of cold being liberated upon the vaporization of liquefied natural gas to be utilized again and again. If, for instance, pentane, at ambient temperature, is used as cold carrier, then this may be stored in the said interveing space, the liquified natural gas then being contained in the tanks. Upon the delivery of the natural gas, owing to the vaporization the temperature of the cold carrier is decreased and this cold liquid is transported in the tanks to the production area of the gas, where the cold carrier is used for the condensation of natural gas.

Tanks according to the invention may very suitably be used in a floating storage. This may be a vessel in which the tanks are placed, or specially constructed floating bodies comprising one or more tanks. The tanks according to the invention can likewise very suitable be placed on vehicles for overland transport, such as road trucks and railway cars.

The invention will now be further elucidated with the aid of a number of figures.

FIGS. 1, 2, 3 and 4 show difierent positions of load-bearing elements in a circular array.

FIG. 5, shows a detail of a load-bearing element.

FIGS. 6 and 7 are diagrammatic representations of a tank with ring-shaped stiffeners.

FIGS. 8 and 9 are diagrammatic representations of another embodiment of load-bearing elements.

FIGS. 10, ll, 12, 13, 14, 15, 16, 17 and 18 showexamples of means which bring about approximately equal loads at the points of fixture to the load-bearing structure.

FIGS. 19 and 20 show a tank with load-bearing elements equipped with insulation.

In FIG. 1, item 1 represents a perpendicular cross section through a circular-cylindrical tank wall. A load-bearing structure 2, is here represented as a square frame that may be constituted by, for instance, a transverse frame in a vessel. By four load-bearing elements which are in tension which elements are designated as 3, the tank is suspended from the load-bearing structure 2. The load-bearing elements 3 are directed tangential with respect to the cylindrical tank wall and from the horizontal plane through the relevant points of attachment 4 to the tank are directed upwards. The points of attachment 4 are located on a circumferential line of the tank, which here coincides with the perpendicular cross section 1. The points of attachment 4 are in symmetrical positions with respect to the horizontal plane through the center axis of the tank and the load-bearing elements 3 are positioned mirror-symmetrical with respect to the vertical plane through the centre axis of the tank. The points of attachment of the load-bearing elements 3 coincide with points whose radii are at angles of, respectively, 45", 255 and 315 with respect to a horizontal radius of the relevant circumferential line.

FIG. 2 shows a view of a part of the tank with surroundings, of which FIG. 1 represents the cross section according to a a. The tank 5 is provided near one end, 6, with a set, 7, offour load-bearing elements, 3, in a circular array, which are fastened to the load-bearing structure 2. Here, the load-bearing elements 3 are level bands, with a flat surface tangential to the wall of the tank. The tank 5 is provided at the other end with a set of load-bearing bands in a circular array similar in shape to the set 7 which is not further indicated. The two sets are positioned symmetrical with respect to the centre plane perpendicular to the axis of the tank. It is possible for a plurality of sets of load-bearing elements to be present. The points of attachment to the tank of all load-bearing elements then are always located on generating lines of the tank.

In FIG. 3 a set of six load-bearing elements is designated as 8. The points of attachment of these elements coincide with points whose radii are at angles of, respectively, 0, 45, 135, 225 and 315 with respect to a horizontal radius. Here there are two vertical load-bearing elements, which have a larger load-bearing capacity than the other elements.

In FIG. 4 a set of 10 load-bearing elements in a circular array is designated as 9. The points of attachment of these elements coincide with points whose radii are at angles of, respectively, 0, 30, 60, 120, 210, 240, 300 and 330 with respect to a horizontal radius. Sets of load-bearing elements of this composition are suitable for suspension of a tank in a vessel. The maximum rolling angle of the vessel that is likely to occur is 30, which implies that the load-bearing elements indicated by the angles, defined hereinbefore, of 0, 30, 150, 180, 210 and 330 may be subjected to the same maximum load. These elements may therefore be designed so as to be stronger than the other elements.

Also indicated in this set of load-bearing elements are two connecting elements, 10, which are directed horizontal and which have their points of attachment at the lowest point of the array. These elements 10 provide extra safety against oscillatory movements of the tank about the longitudinal axis.

In FIG. 5, item 11 represents a part of a perpendicular cross section through a tank. By this figure the surroundings of a point of attachment of a load-bearing element to the tank are represented and elucidated in detail. The load-bearing element 12 has a geometrical point of attachment 13. Between the

points

14 and 15 the load-bearing element 12 is in contact with the tank wall 11. As a result, the angle of the element 12, that is to say of the larger part of that element which remains clear of the tank wall, is somewhat smaller than 90 with respect to the radius through point 13. The point 15 is the last point of contact of the load-bearing element 12 before it becomes clear of the tank wall 11. The distance between the

points

13 and 15 has been chosen to be so that the projection of the point 13 on the radius through point 15 coincides with the point of intersection of this radium with the center line 16 of the tank wall 1 1. The distance between the

points

13 and 15 has been chosen to be so that the projection of the point 13 on the radius through point 15 coincides with the point of intersection of this radium with the center line 16 of the tank wall 1 1. As a result the high tensile stress in the element 12 is conducted through the center of the tank wall, owing to which that wall remains as far as possible free from bending stresses. This method of attachment is of importance particularly with very large tanks, Then the curvature of the tank all at the site of the point of attachment is much less than that indicated in FIG. 5, and the angle between the radii to the

points

13 and 15 will be smaller than 1.

In FIG. 6 the tank 17 is equipped with two sets, 18 and 19, of load-bearing bands. The tank is equipped with ring-shaped

stiffeners

20 and 21 provided on the outside. The

sets

18 and 19 differ in constructional design it being the intention to show various different embodiments. The set 18 has a ringshaped stiffener 20 with, in each point of attachment, two load-

bearing elements

22 and 23. These are fastened by pivots to, respectively, the tank in a point of attachment 24 and the load-bearing structure in point 25. The application of pivots has the advantage that in case of expansion of the tank in the radial direction it is not necessary for the load-bearing elements to be bent. The set 19 has a ring-shaped stiffener 21 having a U-shaped cross section. Each load-bearing element here consists of a rod 26 which is fastened by

pivots

27 and 28 to, respectively, the point of attachment to the tank and the point of fixture to the load-bearing structure.

FIG. 7 shows a view of a part of the set 18 in the direction of the center axis of the tank. T0 the ring-shaped stiffener 23 are fastened by pivots 24, the load-bearing elements 22. For one of the load-bearing elements 22 the pivot is shown by which that element is fastened to the load-bearing structure.

In FIG. 8 two embodiments are represented of load-bearing elements which are at an acute angle with respect to a plane perpendicular to the centre axis of the tank. The part 29 of a tank is equipped with load-bearing elements, of which the element 30 has the shape of a level band which in the tangential direction runs from the tank to the load-bearing structure 31. A second load-bearing element 32 has a V-shape, the two halves running, in the tangential direction, from the tank to the load-bearing structure 31. This arrangement prevents movements of the tank in the longitudinal direction. A similar effect is obtained by means as indicated for one end of the tank 33 with a load-bearing element 34. Just like the element 35, this element is connected to the load-bearing structure 36. The other end of the tank 33, which end is not shown, is equipped with load-bearing elements which are positioned mirror-symmetrical with respect to the center plane perpendicular to the axis of the tank.

FIG. 9 shows a view of the two sets of load-bearing elements. l-lere item 37 represents the tank wall, 38 the loadbearing structure and 39 and 40 projections of the load-

bearing elements

32 and 30. The elements 34 and may likewise be represented by the

projections

39 and 40. From FIG. 9 it is obvious that all load-bearing elements are directed tangential with respect to the tank wall.

FIG. 10 shows an example of a structure where means are present which bring about approximately equal loads in all the points of fixture to the load-bearing structure. Here the loadbearing structure is a transverse bulkhead 41 of a vessel, pro vided with two apertures, 42 and 43, bounded by hexagons. In each aperture a tank is present. Near the tank 44 a part of a set of load-bearing elements 45 is represented. These elements 45 are fastened by means of springs 46 to projections 47 of the transverse bulkhead 41. When the distance between a point of attachment 48 and a projection 47 changes, for instance owing to deflection of the tank, the tensile force in a loadbearing element 45 will hardly change, because the relevant spring 46 accommodates this change in distance. All the loadbearing elements of a tank may be equipped in this way. In the case of sagging of the middle part of the tank the tension to which the load-bearing bands at that location are subjected will hardly increase. Nor will the tension to which the loadbearing bands of the relevant set are subjected increase when a force is exerted on the tank that produces torsion. This tank 44 is also equipped with two connecting elements 49 that are directed horizontal.

In the case represented here, the tank 44 is surrounded by a hexagonal enveloping structure 50 to which insulating material may be applied. The springs 46 are shut off from their surroundings by a cap 51 and a flexible tube 52. Similar flexible tubes, 53, are also present at the connecting elements 49. This enclosure is of importance with a view to preventing condensation phenomena.

In FIG. 11 the load-bearing elements 54, whose points of attachment to the tank are located on a generating line of the tank, are fastened to the load-bearing structure 55 by hydraulic elements 56 which communicate. Now it is impossible for a difference in tensile force to occur between those load-bearing elements.

FIG. 12 indicates how, by a simple control system, the position of a tank provided with hydraulic elements can be influenced in the vertical direction. Here the tank 57, where in each set four load-bearing elements, 58, are present in a circular array, is suspended by elastic hydraulic elements 59. The load-bearing elements positioned at an angle of 45 are connected to hydraulic elements of which the surface area of the piston is (1) 0.414 4),, where dz, is the surface area of the piston of the other hydraulic elements, connected to the loadbearing elements being directed vertical. Thus pressure equalization may occur within a particular set of load-bearing elements. The hydraulic elements are interconnected via a chamber 60, which chamber, in turn, is connected by a tube to a liquid-containing reservoir 61 which is separated by a diaphragm 62 from a gas-containing reservoir 63 which is connected via a control valve 64 to a vessel containing gas of which the pressure is higher than the atmospheric pressure. When the pressure of the gas in the vessel 63 increases, liquid is forced to the hydraulic elements 59, as a result of which the tank 57 is caused to move upwards. The pressure of the gas in reservoir 63 can be adjusted by means of a distance meter 66, via controller 67 and valve 64. If the measured distance becomes too small, then the valve 64 will admit gas pressure to the chamber 63 to an increasing extent and, consequently, force more liquid into the hydraulic elements 59. If the distance becomes too large, then gas pressure will be released by valve 64. In this way each load-bearing band can be adjusted at the prescribed level.

FIGS. 13 and 14 show the use of cables with pulleys for suspending the tank. The tank 68 is suspended from the loadbearing structure 69 by means of cables 70 that are tangential to the tank. At the points of attachment are located pulleys 71. At the points of fixture to the load-bearing structure 69 there are located pulleys 72. The pulleys 71 are fastened in ringshaped stiffeners 73. The cables 70 in passing over the

relevant pulleys

71 and 72 follow a zigzag course. Owing to the pulleys being capable of rotating freely, the tension in a cable will be the same in all points thereof, as a result of which the loads in all points of fixture are equally large, irrespective of the relative movements of load-bearing structure and tank. This holds for each individual cable in the arrangement shown.

Suspension by means of cables may also be combined with suspension by means of other elements, such as level bands. Each set of load-bearing elements may then consist of a combination of this type, as represented diagrammatically in FIG. 15. A set of load-bearing elements for the tank 74 comprises four level bands 75 which are fastened to the load-bearing structure 76, which may be a transverse bulkhead. Two vertical level bands 77 are fastened by pulleys 78 which are carried by cables 79 which in turn are carried by pulleys 80 fastened to the load-bearing structure 76. FIG. 16 represents a lateral view of a tank suspended in this way, where the numerals used before denote the components then described. The cables here have a square-wave shape. Each cable is connected to a tensioning device 81 that is fastened to the load-bearing structure 76 and that is loaded by a weight 84. The tensioning device 81 consists of two coaxial wheels which are interconnected, of which the wheel 82, having the smaller radius, is connected to the cable 79. The wheel 83, having the larger radius, is connected to the weight 84. By an appropriate choice of the lengths of the radii it can be ensured that the weight 84 need not be excessively large. The weight 84 can be prevented from performing oscillating movements by, for instance, guide wheels 85. In this way it is ensured that the tension on the cables always has the desired value, irrespective of the positions of the points of attachment. The same method of tensioning cables may be applied when near the ends of the tank are present a set of load-bearing elements in a circular array that are not connected to the cables, intermediate sets of load-bearing element being either entirely or partly equipped with cables. The rotation of each pulley will remain very small, because it is only deformations of the tank or the load-bearing structure which have to be followed. For reasons of safety stopping devices may be installed, which in a calamity prevent an excessive downward movement of the tank. In FIG. 17, the level load-bearing bands 86 are connected to the tank, which is not indicated. The

pulleys

87 and 88 carry the cable 89. The pulleys 88 are fastened to the load-bearing structure 90. Also fastened to the load-bearing structure 90 are the holders 91 through which the cable 89 passes. Fastened to the cable are the blocks 92, which are located inside the holders 91. These blocks 92 are entirely clear of the holders 91 under conditions of normal operation. However, they prevent the cable from slipping.

If a tank is suspended by two sets of load-bearing bands, then rotatable yokes and level load-bearing bands may be used instead of pulleys and cables, as indicated in FIG. 18. The tank 93 is equipped with ring-shaped stiffeners 94 with rotatable yokes 95. Pivots 96 and a rotatable yoke 97 are fastened to the load-bearing structure 98. The level load-bearing bands 99 are again tangential to the tank. Here again, owing the yokes being capable of rotating freely, it is ensured that the load is the same in all points offixture.

In FIGS. 19 and the tank 100 is suspended by means of two sets 101 of load-bearing elements 102 from a transverse bulkhead 103 of a vessel. The tank 100 is surrounded by an enveloping wall 104 in such a way that a space 105 remains, which space has the shape of an annular slit. The wall 104 carries an insulating layer 106. The wall 104 is fastened to the tank 100 near the sets of load-bearing elements 101. If at those locations the tank is provided with ring-shaped stiffeners, then the wall 104 may be fastened to those stiffeners. The wall 104 is on either side of its fixtures provided with expansion grooves 107. The insulating layer is not loaded by the weight of the tank and/or of the cargo. Consequently, the insulating material may consist of, for instance, material having a very low mechanical strength.

Granular material may be used in a second enveloping wall is present which bounds the insulating layer on the outside. The deformations of the tank 100 and the wall 104 do not influence each each other. The space 105 may be used for leak detection or for the discharge of product that may have leaked from the tank. The tank with insulation remains entirely clear of its surroundings, so that, for instance, deformation of the shell of the vessel may occur without the tank or the insulation thereof being affected. The load-bearing elements, as far as located in the cold zone, are made of cold-resisting material, for instance, steel containing 8 percent nickel.

We claim as our invention: 1. Means for storing and transporting liquid cargo, said means comprising:

a. a tank having a wall of substantially cylindrical shape and a given cylindrical axis;

b. an overhead load-bearing structure, and

0. support means for supporting said tank on said load-bearing structure with said given cylindrical axis normally horizontal, said support means comprising at least two circular arrays each of at least four load-bearing elements, each load-bearing element of each of said arrays extending upwardly and tangentially from the cylindrical tank wall in a common vertical plane which is perpendicular to said given axis and each being attached between said load-bearing structure and said tank wall under tension.

2. Means for storing and transporting liquid cargo as claimed in claim 1 wherein said arrays of load-bearing elements of said support means are arranged in pairs which are on opposite sides of and equally spaced from the vertical plane passing through the center of said given cylindrical axis perpendicularly thereto.

3. Means for storing and transporting liquid cargo as claimed in claim 1 wherein said load-bearing elements of said sets are positioned mirror-symmetrically with respect to the vertical plane in which said given cylindrical axis has it locus.

4. Means for storing and transporting liquid cargo as claimed in claim 1 wherein the points of attachment of said load-bearing elements to said tank are positioned symmetrically with respect to the horizontal plane in which said given cylindrical axis has its locus.

5. Means for storing and transporting liquid cargo as claimed in claim 2 wherein the point of attachment to said tank of each load-bearing element in one of said arrays lies on a different one of a plurality of lines each passing through the point of attachment to said tank of a different one of the loadbearing elements of another of said arrays, said lines being parallel to said given cylindrical axis.

6. Means for storing and transporting liquid cargo as claimed in claim 1 wherein the directions in which said loadbearing elements extend from said tank deviate from directions tangential to said wall of said tank by an amount no greater than 1.

7. Means for storing and transporting liquid cargo as claimed in claim 6 wherein the angle between each radius of said tank passing through a point of physical attachment of one said load-bearing element to said tank and the associated load-bearing element is less than 8. Means for storing and transporting liquid cargo as claimed in claim 7 wherein the projection of the point at which each of said load-bearing elements is physically attached to said wall of said tank onto a radius of said tank taken through the last point of physical contact between such loadbearing element and said wall of said tank coincides with the point of intersection of such radius with said cylindrical axis of said tank.

9. Means for storing and transporting liquid cargo as claimed in claim 1 wherein said load-bearing elements have high tensile strength and low strength in directions transverse to the direction in which said load-bearing elements extend.

10. Means for storing and transporting liquid cargo as claimed in claim 1 wherein said load-bearing elements are adapted to pivot at the points of attachment thereof to said wall of said tank.

11. Means for storing and transporting liquid cargo as claimed in claim 1 wherein said tank includes a stiffener member having dimension defining a ring lying in one of said common vertical planes associated with one of said arrays of load-bearing elements.

12. Means for storing and transporting liquid cargo as claimed in claim 11 wherein said stiffener member includes an apertured plate extending within and across said tank.

13. Means for storing and transporting liquid cargo as claimed in claim 4 including means for maintaining substantially equal loads on said load-bearing structure at the point of attachment of each of said load-bearing elements to said loadbearing structure.

14. Means for storing and transporting liquid cargo as claimed in claim 5 including means for maintaining substantially equal loads on said load-bearing structure at all points of attachment to said load-bearing structure of each of a series of load-bearing elements comprising all load-bearing elements having points of attachment to the tank which lie on a particular one of the plurality of parallel lines.

15. Means for storing and transporting liquid cargo as claimed in claim 14 wherein said means for maintaining substantially equal loads comprises a plurality of helical springs, each helical spring operatively connected to one of said series of load-bearing elements and to said load-bearing structure.

16. Means for storing and transporting liquid cargo as claimed in claim 14 wherein said means for maintaining substantially equal loads comprises a plurality of hydraulic cells interconnected in pressure communication, at least one of said cells being operatively connected to each of said series of load-bearing elements.

17. Means for storing and transporting liquid cargo as claimed in claim 14 wherein said means for maintaining substantially equal loads comprises a cable for each series of loadbearing elements having points of attachment to the tank which lie on one of said parallel lines; a supporting series of pullies fastened to the load-bearing structure for supporting said cable; a second series of traveling pullies movably riding upon said cable, one of said traveling series of pullies being affixed to each of the relevant series of load-bearing elements; one end of said cable being fixedly attached to one of said tank or load-bearing structure and the other end of said cable being connected to a means for maintaining a substantially constant tension in said cable, whereby substantially equal support forces are maintained on each of said traveling pullies.

Claims

1. Means for storing and transporting liquid cargo, said means comprising: a. a tank having a wall of substantially cylindrical shape and a given cylindrical axis; b. an overhead load-bearing structure, and c. support means for supporting said tank on said load-bearing structure with said given cylindrical axis normally horizontal, said support means comprising at least two circular arrays each of at least four load-bearing elements, each load-bearing element of each of said arrays extending upwardly and tangentially from the cylindrical tank wall in a common vertical plane which is perpendicular to said given axis and each being attached between said load-bearing structure and said tank wall under tension.

5. Means for storing and transporting liquid cargo as claimed in claim 2 wherein the point of attachment to said tank of each load-bearing element in one of said arrays lies on a different one of a plurality of lines each passing through the point of attachment to said tank of a different one of the load-bearing elements of another of said arrays, said lines being parallel to said given cylindrical axis.

6. Means for storing and transporting liquid cargo as claimed in claim 1 wherein the directions in which said load-bearing elements extend from said tank deviate from directions tangential to said wall of said tank by an amount no greater than 1*.

7. Means for storing and transporting liquid cargo as claimed in claim 6 wherein the angle between each radius of said tank passing through a point of physical attachment of one said load-bearing element to said tank and the associated load-bearing element is less than 90*.

8. Means for storing and transporting liquid cargo as claimed in claim 7 wherein the prOjection of the point at which each of said load-bearing elements is physically attached to said wall of said tank onto a radius of said tank taken through the last point of physical contact between such load-bearing element and said wall of said tank coincides with the point of intersection of such radius with said cylindrical axis of said tank.

13. Means for storing and transporting liquid cargo as claimed in claim 4 including means for maintaining substantially equal loads on said load-bearing structure at the point of attachment of each of said load-bearing elements to said load-bearing structure.

17. Means for storing and transporting liquid cargo as claimed in claim 14 wherein said means for maintaining substantially equal loads comprises a cable for each series of load-bearing elements having points of attachment to the tank which lie on one of said parallel lines; a supporting series of pullies fastened to the load-bearing structure for supporting said cable; a second series of traveling pullies movably riding upon said cable, one of said traveling series of pullies being affixed to each of the relevant series of load-bearing elements; one end of said cable being fixedly attached to one of said tank or load-bearing structure and the other end of said cable being connected to a means for maintaining a substantially constant tension in said cable, whereby substantially equal support forces are maintained on each of said traveling pullies.