US3004509A - Ships designed for the transport of liquefied gases - Google Patents

Description

Oct. 17, 1961 R LEROUX 3,004,509

SHIPS DESIGNED FOR THE TRANSPORT 0F LIQUEFIED GASES Filed March 3, 1958 4 Sheets-Sheet l INVENTOR RENE LEROUX PAVE ATTOR NEY S R. LEROUX Oct. 17, 1961 SHIPS DESIGNED FOR THE TRANSPORT OF LIQUEFIED GASES 4 Sheets-Sheet 2- Filed March 5, 1958 INVENTOR RENE LEROUX /W, W fix/4M ATTORNEYS w R. LEROUX Oct. 17, 196i SHIPS DESIGNED FOR THE TRANSPORT OF LIQUEFIED GASES 4 Sheets-Sheet 3 Filed March 3, 1958 INVENTOR RENE LEROUX ATTORNEYS Oct. 17, 1961 RJLEROUX 3,004,509

SHIPS DESIGNED FOR THE TRANSPORT 0F LIQUEFIED GASES Filed March 5, 1958 4 Sheets-Sheet 4 FIG] INVENTOR RENE LEROUX I {NM ATTORNEYS Unite The present invention relates to a ship designed for the transport of liquefied gases, such as butane, propane, ethane, methane and ammonia, these gases being under pressure and at a temperature equal to or less than the exterior temperature.

The invention consists essentially in the use of a large tank having the shape of a double cylinder, fixed to the ship, with its generator lines parallel to the axis of the ship and its section formed by two equal and cosecant circles which are limited to their external arcs and are completed by their common chord; orany construction, the mean fibre of which would be constituted by the combination of the circles and their chord, as described above.

Along the common chord, a device ensures the rigid connection of the two generators of intersection of the double cylinders; this device may be constituted by a lower runner and an upper runner, coupled by vertical stifieners which may be reduced to stanchions, or by a flat longitudinal bulk-head of suitable thickness, so as to withstand the vertical stresses due either to pressure or to gravity, or to the internal depression. As this bulk-head will not be made to withstand a difference in pressure, it will be provided with orifices, preferably at its upper part, in order to ensure equality of pressure on each side, while however the two volumes of liquid are kept separate, which isfavourable to stability. I

' In order to use the shape of the ship to the best advantage, the circular cylinders are extended towards the front by intersecting cones having also a bi-circular transverse section, the coupling being formed by fractions of a sphere or of a torus.

With the form having a bi-circular section, the moment of the system of applied forces at every point of the wall is nil, which avoids all deformation due to pressure, excepta general expansion. The moment of the system of applied forces is zero on the lines of intersection as a result of the presence of the stanchions or of the bulkhead, which enables the tangential forces of the walls of the cylinder to be balanced, the resultant of these forces being contained in the plane of the bulkhead.

The double secant cylinder shape enclosed by a hull is in accordance with the rules of navigating safety commissions which, up.to the present time, have specified that tanks containing liquefied gases should not be in direct contact with the water of the external medium. In fact, the enclosure of a single cylinder in a hull would result in a ship having transverse dimensions which would not correspond to the usual standards, the breadth being too small with respect to the depth.

The arrangement which consists in causing the cylinder to project above the deck would also be faulty, since it would considerably weaken the deck of the ship by a too large cover and would make it necessary either to leave the tank exposed to the heat of the sun, or to cover it by a bulky superstructure badly arranged for the general strength of the ship.

The enclosure of two tangential cylinders by a hull would result on the contrary in a ship which is too wide with respect to its depth, with a large loss in volume.

It is advantageous to include the tank in a hull of normal proportions, which is possible with the form which is the object of the invention, and which avoids the addition of heavy and expensive side ballast tanks. It is easy tates atet 3,094,509 Patented Oct. 17, 1961 the tanks.

The thickness of the walls of the tank is calculated in accordance with the usual rules: if this thickness is correctly calculated to withstand tearing along a generator line, it is twice too large as compared with the result of the calculation made for a transverse section. It is therefore an advantage to profit by this margin, and to make the tank contribute to the strength of the hull of the ship.

The elimination of the bending moments of the system of forces external to the surfaces and on its intersection is only theoretical. The fact that the reservoir is fixed to the hull modifies this situation slightly.

In order to ensure indeformability, it is thus necessary to add to the construction a series of transverse brackets (for example one for each frame) ensuring the rigidity of the angles between the walls of the cylinder and the flat bulkhead around the two intersection lines of the cylinder.

The coupling of the tank to the outer hull must take account of the elastic expansions of the tank under the action of internal pressure and of thermal contractions due to cooling. It may thus happen that a certain slip takes place between the tank and the outer hull. This slip must be allowed for, whilst at the same time the tank is permitted to participate in the stresses produced by the longitudinal deformation of the ship.

If the classification companies specify the support of an external hull with scantlings almost equal to standard scantlings, the tank must be coupled to the hull by frames which are rigid in the transverse sense while retaining a certain flexibility in the longitudinal direction; this result is achieved by using transverse bulkheads or brackets for the coupling of the cylinder, to the exclusion of any longitudinal support.

If on the other hand, the classification companies allow the scantlings of the outer hull to be considerably reduced, making the latter similar to a submarine ballast-tank, for example, the hull may itself be subjected to deformations and it is possible to couple the tanks rigidly to the hull.

Other features and objects of this invention will more readily appear from a detailed description of the invention with reference being made to the accompanying drawings in which:

FIG. 1 is a view in transverse vertical section of a vessel embodying the features of the invention.

FIG. 2 is a view similar to FIG. -1 but taken at a different location to show the tubular stanchion,

FIG. 3 is a fragmentary cross-sectional view in side elevation showing details of the deck, tank and tubular stanchion,

FIG. 4 is a view similar to FIG. 1 but showing a layer of insulating material applied to the tank.

FIG. 5 is a view similar to FIG. 2 but with thermal insulation added as shown,

FIG. 6 is view similar to FIG. 3 also with the insulation added,

FIG. 7 is a top-plan view partly in section of a vessel made according to the invention, and

FIG. 8 is a fragmentary top-plan view partly in section, showing details of the transverse supports for the tank.

In the drawings, the reference character 1 indicates the hull of a vessel having a deck 2, and enclosing an elongated tank 3 fabricated from two parallel and intersecting cylinders. Conduits 13 and 14 are provided for filling and discharging the tank. The tank 3 is supported by means of spaced transverse bulkheads 8 and by means of radiant flexible supports '9 for permitting a certain amount of expansion and contraction of the tank.

In the accompanying drawings, the distance apart of the axes of the cylinders has been chosen, by way of example, equal to the radius of the cylinders. This arrangement (which is not absolutely essential) gives a good general overall size and enables the bulkhead to be given a thickness identical with that of the cylinders. a 1

The construction of the ship according to the invention may be carried out by using tanks working at more or less high pressures and containing gases liquefied at more or less low temperatures; the general principles specified above remain however valid in all cases.

The construction of the ship may include thermal insulation of the tank; depending on the quality of the insulating material employed, it will be applied either to the outside or the inside of the tank. Certain insulating materials such as glass wool can only be used on the outside, While others which have greater mechanical strength such as cork or balsa wood or relatively stiff plastic insulating materials such as clegesel can be applied as desired at the most favourable position. However, the transport of liquefied gases at very low temperature necessitates internal application of the insulating material so as to protect the steel against the efiect of intense cold. I

In the latter case, the difficulty is encountered of maintaining the flat bulkhead or the stanchions at normal temperatures; even if these members are protected on all their faces, it is however certain that at the end of a certain time, the temperature of the steel of which they are made will fall to a dangerous extent. In order to avoid this drawback, a system of stanchions will be adopted, formed in accordance with FIGS. 2, 3, 5 and 6 by hollow pillars 7 coupling the upper and lower runners 4 which are fabricated along the intersections of the secant cylinders and connected with transversereinforcing brackets 10; these stanchions may be simple tubes of suitable diameter. These stanchions 7 will be thermally insulated by insula tion material 5 (FIGS. 5 and 6) on their outer faces which are inside the reservoir. They will be open at their two extremities, so that their internal faces will be in contact with air or with the liquid contained in the ballast tank.

Under these conditions, the steel of the pillars will be protected against low temperatures, exactly in the same manner as the wall of the tank.

The invention is also applicable'to the case of use of the same principle with a larger number of secant cylinders parallel to the stays or bulkheads which ensure the rigidity of the couplings, the diameters of these cylinders not being necessarily equal.

In practice, it is verified that the tangential forces acting on the walls of any pair of secant and therefore parallel cylinders subjected to the same pressure have a resultant which falls in the secant plane. This property makes it possible to pass from a single cylinder to an assembly of cylindrical sections of a smaller thickness, resulting in the limit in the total elimination of the initial cylinder, whilst maintaining the sum of the resultant moments at zero. This arrangement enables the difiiculties of shaping thick steel sheet to be reduced, since for the same useful section the thickness of the sheet to be shaped is smaller.

Finally, in order to provide for the case of a partial pressurein the" tank with respect to the external pressure, the double cylinder may he provided with frames and flat bulkheads of pillars to prevent any possibility of buckling.

What I claim is:

1. A cargo vessel for transporting liquefied gases, comprising in combination a hull, an elongated pressureresistant tank disposed longitudinally within said hull and mounted in spaced relation thereto, said tank being formed by at least two horizontally disposed cylinders of circular cross section having their axes generally parallel to the axis of the vessel, said cylinders intersecting and joining with one another to form a single integrated tank, and at least one elongated hollow stanchion mounted along the common chord of said cylinders with the ends thereof passing through and being connected to said cylinders at their points of intersection, the interior of said stanchion being in free communication Withthe space between said tank and said hull.

2. A cargo vessel for transporting liquefied gas cornprising in combination a hull, an elongated pressure resistant tank disposedlongitudinally within said hull and mounted in spaced relation thereto, said tank being formed by at least two horizontally disposed cylinders of circular cross section having their axes parallel to the axis of the vessel, said cylinders intersecting and joining with one another to forma single integrated tank, the inner surface of said tank being covered with thermal insulating material a runner formed along each line of intersection of said cylinders, a plurality of tubular stanchions mounted along the common chord of said cylinders having their interior in free communication with the space formed between said tank and said hull and their outer surfaces covered with thermal insulating material, the extremities of said stanchions being fixed respectively to said nmners, and at least two intersecting conical shells connecting with said cylinders to close the forward ends thereof.

References Cited in the file of this patent UNITED STATES PATENTS

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