Title:
CONTAINERS FOR LIQUEFIED GASES
United States Patent 3595424
Abstract:
An insulated container such as used in marine tankers for cryogenic liquids comprising an inner metal tank surrounded and supported by thermal insulation characterized in that less lightly stressed parts of the insulation comprise rigid foamed-plastic material sprayed in situ while more highly stressed parts thereof are of load-bearing thermal insulation of higher strength.
US Patent References:
Spherical type insulated container for liquefied gases
Jackson - October 1945 - 2386958
Insulated container
Hemp - September 1949 - 2481664
Apparatus for the maintenance of liquefied petroleum products and method of manufacture thereof
Clauson - September 1960 - 2952987
Insulated space and elements employed therein
Dosker - February 1963 - 3079026
Insulated container
Morrison - October 1963 - 3106307
Spherical type insulated container for liquefied gases
Jackson - October 1945 - 2386958
Insulated container
Hemp - September 1949 - 2481664
Apparatus for the maintenance of liquefied petroleum products and method of manufacture thereof
Clauson - September 1960 - 2952987
Insulated space and elements employed therein
Dosker - February 1963 - 3079026
Insulated container
Morrison - October 1963 - 3106307
Application Number:
04/801495
Publication Date:
07/27/1971
Filing Date:
02/24/1969
View Patent Images:
Export Citation:
Assignee:
Conch International Methane Limited (Nassau, BA)
Primary Class:
Other Classes:
220/901, 220/560.040, 114/74A
International Classes:
F17C3/02; F17C3/00; B65D25/00
Field of Search:
220/9F,9A,10,15 114/74A 62/45
US Patent References:
| 3147878 | Cryogenic storage tank | September 1964 | Wissmiller | |
| 3150795 | Membrane tanks | September 1964 | Schlumberger | |
| 3241703 | Liquefied gas storage tank | March 1966 | Korin et al. | |
| 3362560 | Refrigerating apparatus | January 1968 | Burrus et al. | |
| 3399800 | Tank for liquefied gas | September 1968 | Gilles | |
| 3502239 | THERMALLY INSULATED CONTAINER FOR TRANSPORTING LOW TEMPERATURE LIQUIDS | March 1970 | Worboys |
Primary Examiner:
Leclair, Joseph R.
Assistant Examiner:
Garrett, James R.
Claims:
I claim
1.
2.
3. A container according to claim 2, in which at least one mat of open-mesh reinforcing material is incorporated in the foam insulation, with the edges of the mat securely anchored to the adjacent load-bearing insulating material.
4. A container according to claim 3, wherein the tank is a self-supporting tank and wherein the load-bearing insulation extends beneath the tank and part way up each sidewall thereof, said load-bearing insulation being liquidproof to constitute a secondary barrier against leakage of liquid cargo from the tank.
5. A container according to claim 3 wherein the tank is a membrane tank and the load-bearing thermal insulating material extends around the corner edges thereof, said corner edges being anchored in said load-bearing insulating material.
1.
2.
3. A container according to claim 2, in which at least one mat of open-mesh reinforcing material is incorporated in the foam insulation, with the edges of the mat securely anchored to the adjacent load-bearing insulating material.
4. A container according to claim 3, wherein the tank is a self-supporting tank and wherein the load-bearing insulation extends beneath the tank and part way up each sidewall thereof, said load-bearing insulation being liquidproof to constitute a secondary barrier against leakage of liquid cargo from the tank.
5. A container according to claim 3 wherein the tank is a membrane tank and the load-bearing thermal insulating material extends around the corner edges thereof, said corner edges being anchored in said load-bearing insulating material.
Description:
This invention relates to containers for the bulk storage or transport of liquids at temperatures greatly differing from ambient temperature. The invention is primarily intended for containers for very cold liquids, such as liquefied gases, e.g. natural gas, at near atmospheric pressure; but it may also be applicable to containers for housing warm liquids. For convenience, reference will be confined in the following to containers for cold liquids. Such containers are used, for example, in marine tankers, for the transport of liquefied gases.
Containers of the kind concerned, for the bulk storage or transport of liquids at temperatures greatly differing from ambient temperature, each comprises a tank surrounded and supported, at least from below, by thermal insulation within an outer rigid shell. The present invention is concerned with the thermal insulation of such a container. The containers are of one or two distinct types. In one type, the container comprises a self-supporting tank; that is to say one which, while supported from below, has sufficient structural strength to hold the liquid within the tank and withstand the hydrostatic pressures and inertia forces, without depending upon any other means outside the tank for aid in supporting the walls of the tank against buckling. The insulation beneath the tank carries the load of the weight of the tank, and loads involved in holding the tank in place against horizontal movement, e.g. arising from the motion of a tanker at sea. The tank is of a material, e.g. metal, which is not subject to cold embrittlement. The tank is thermally insulated externally by thermal insulation which lines the outer rigid shell, e.g. the cargo hold of a tanker, so as to define a containing space within which the tank is located.
The other type of container is known as an integrated tank container and comprises a housing of solid load-bearing thermal insulation lined with a thin and flexible fluidtight membrance tank of sheet material, e.g. metal, which is not subject to cold embrittlement and which is not self-supporting but is supported against internal loads due to hydrostatic pressures and inertia forces, by the surrounding solid insulation. The insulation lines and is itself supported by, the outer rigid shell so that the insulation directly transmits to the latter all the pressure exerted by the fluid upon the walls of the membrane tank. More important, the tank is rigidly anchored at the corners to hold it against contraction on cooling, and the insulation at the corners takes the local loads arising from such anchorage.
In either type of container, the thermal insulation may be of any appropriate material capable of carrying the loads imposed upon it. It is usually required to be fluidtight and impermeable to the cold liquid cargo so as to constitute a secondary barrier which will itself contain a liquid, e.g. to prevent it from contacting the hull of a tanker, in the event of failure of the tank. A number of thermal insulation materials and constructions are known for use for this purpose. One known material comprises blocks or panels, for example of balsa wood faced with plywood, mounted upon spaced securing strips, e.g. of wood, secured to the outer rigid shell. The gaps between the panels are sealed by compressed plastics material. Such a construction is described in U.S. Pat. No. 3,112,043.
A disadvantage of this and other known thermal insulation materials which satisfy said requirement is that they are expensive to construct.
An object of this invention is to provide a container having thermal insulation which is a satisfactory secondary barrier but which is less expensive to construct.
According to the present invention there is provided a thermally insulated container of the kind concerned, in which less highly stressed sections of the thermal insulation comprise rigid foamed-plastics material sprayed in situ internally on the outer rigid shell while more highly stressed sections of the thermal insulation are of nonfoamed load-bearing thermal insulation material of higher strength.
The invention is based on the realization that the same thermal insulation material does not need to be used for different sections of the insulation because there are different requirements for such different sections. For example, in the case of a self-supporting tank the bottom section of the insulation supporting the bottom of the tank requires to be of high compressive strength to support the tank and the liquid cargo, but the other sections of the insulation do not support any loads and do not require to have such a high compressive strength. Likewise in the case of the integrated tank container the corner sections of the insulation require to be of high strength in order to accept the local loads involved in anchoring the tank against contraction due to cooling.
The rigid foamed-plastics material may be applied by spraying, using conventional spray equipment and the desired thickness of foamed material may be built up layer by layer. For increased strength and resistance to cracking, mats of hessian or similar mesh material can be incorporated into the foamed material between successive layers during the spraying operation. A number of such mats can be included in the overall thickness of the foamed material.
Advantageously, the foamed-plastics material comprises a multilayer construction with at least one surface layer of higher density than the other layers. The layers of foamed-plastics material are preferably rigid polyurethane closed cell foams. In addition to being an efficient thermal-insulation material, polyurethane foam is effective as a barrier to liquefied gases.
Preferably the layers making up the thickness of the insulation have a density in the range of 50 to 130 kilograms per cubic meter and one or both of the surface layers has a density greater than 100 kilograms per cubic meter, and preferably in the range of 110 to 130 kilograms per cubic meter.
In accordance with an important feature of the invention, the lines of junction between sections of foamed plastics material and sections of unfoamed load-bearing thermal insulating material should be spaced from the lines of the corner of the shell (and of the tank contained therein) so that the junction is located in a plane portion of the total insulation and not in the angle of a corner.
Thus, in the case of a self-supporting tank the section of the thermal insulation lining the bottom of the outer shell and supporting the bottom of the tank is of nonfoamed load-bearing material of high compressive strength, and this extends around the lower corners of the shell to line the lower portions of the walls of the outer shell, while the sections of the thermal insulation lining the remainder of the sidewalls of the shell and, if desired, the top of the shell also are of rigid foamed-plastics material. The vertical corners may be directly sprayed with foamed-plastics material, or the treatment of these corners may be facilitated by the insertion of preformed fillets of foamed-plastics material glued into and filling the sharp angles of the corners. The foamed-plastics material may be internally lined with another thermal-insulation material, for example glass fiber or rock wool, and this material is preferably used also, instead of foamed plastics, over the top of the tank. The nonfoamed load-bearing sections of the thermal insulation may comprise plywood-faced balsa panels, the gaps between which are sealed.
In the case of a membrane tank container in which the corners of the membrane tank are rigidly anchored to the insulation in the corners of the outer rigid shell, such that the membrance tank is held against overall dimensional change notwithstanding temperature variations, the insulation on the faces adjoining the corners of the shell will be of a material which is load-bearing and of tensile, shear and compressive strength sufficient to transmit to the shell the loads imposed upon the corners of the insulation by reason of the anchorage thereto of the corners of the membrane tank. The walls of the shell, other than the corners, are lined by rigid foamed-plastics material as specified above, the lines of junction extending across the walls and being spaced from the corners. The material of high tensile, shear and compressive strength forming the corners of the thermal insulation may be constituted by plywood-faced balsa panels. The polyurethane foam constituting the walls between the load-bearing corners may be faced on its inner surface adjacent the tank by balsa panels.
In accordance with a further important feature of the invention, at the junction between a section of foamed-plastics material and a section of nonfoamed load-bearing thermal insulation material, in a tank of either of the types specified, the plane of junction extends obliquely to the plane of the wall of the shell so that the thickness of one section of the insulation progressively diminishes and thickness of the adjoining section progressively increases.
In this even, the edges of the mats of hessian or the like at the junction with a section of nonfoamed load-bearing thermal insulation material are preferably rigidly anchored to the latter. This may be effected in any number of ways. The relevant edge face of the nonfoamed insulation material may be formed with slots to receive the marginal portions of the mats which are retained therein by wedges or adhesive. Alternatively, the marginal portion of the mat may be attached to said edge face by adhesive. Extra mats of hessian may be incorporated in the polyurethane foam adjacent this junction.
In order that the invention may be more clearly understood two specific constructional examples will now be described with reference to the accompanying drawings, wherein:
FIG. 1 is a vertical cross-sectional view through a marine tanker incorporating a freestanding cargo tank.
FIG. 2 is a detail vertical sectional view on a much larger scale through the thermal insulation of the tank of FIG. 1 showing the junction between a section of foamed-plastics material and a section of nonfoamed load-bearing material.
FIG. 3 is a detail vertical sectional view on a much larger scale through the thermal insulation of the tank of FIG. 1 showing the arrangement at the top of a sidewall thereof, the view being broken diagonally so as to show a complete upper corner and a complete lower corner.
FIG. 4 is a vertical cross-sectional view through a marine tanker incorporating a membrane cargo tank, broken and shifted diagonally to enable a larger scale.
Corresponding components in the different figures are designated by the same references throughout these figures. Dimensions are quoted merely by way of example and not in limitation.
In FIG. 1 there is shown a marine tanker having an outer hull 1 and an inner hull 2. Disposed within a cargo hold 3 defined within the inner hull and transverse bulkheads is a self-supporting tank indicated generally at 4. This is of metal which is not subject to cold embrittlement and of sufficient thickness and suitably stiffened to contain the liquid. The tank is surrounded by thermal insulation, generally designated 5, which lines the cargo hole 3. FIG. 1 is not drawn to scale, i.e. the insulation is shown on a larger scale than the tanker for clarity. There is a space S of approximately 1 meter width all around the tank between the exterior surface of the tank and the internal surface of the cargo hold 3.
The thermal insulation 5 comprises a section A lining the bottom and extending for a short distance up the walls of the cargo hold and sections B forming the rest of the walls of the thermal insulation lining the walls of the cargo hold. Section A comprises timber ground strips 6 attached at regular intervals to the cargo hold. Mounted upon the strips are relatively thick panels 7 of balsa wood faced with plywood, with the gaps therebetween sealed by compressed plastics material 8, all for example, as disclosed in U.S. Pat. No. 3,112,043, constituting a secondary barrier against leakage of liquid cargo. Interposed between the bottom of the tank and the panels 7 is a layer of balsa wood 9.
Each section B comprises a constant thickness of e.g. approximately 10 centimeters (depending on the density) of rigid closed-cell foamed polyurethane 10 lining the main portions of the walls of the cargo hold and itself lined with glass fiber or rock wool 11 of a thickness, e.g. of 15 centimeters.
In installing the insulation the section A is constructed in known manner. The tank 4 is then mounted in the cargo hold and the sections B of the insulation are formed.
The walls of the cargo hold are first shotblasted or wire brushed to provide a clean surface to receive a rigid closed-cell polyurethane foam, for example, Shell Caradal S1 and Shell Caradate 30 and having a density in the range of 50 to 130 kilograms per cubic meter. This polyurethane foam is sprayed on to the inner surface of the cargo hold layer by layer until a desired thickness of the foam has been built up.
Either the inner or the outer surface layer may be of polyurethane foam of a higher density, e.g. in the range of 110 to 130 kilograms per cubic meter than the remainder of the foam. The inner layers incorporate two mats 12 of hessian or similar mesh, e.g. of 1 centimeter mesh size, one of which is disposed e.g. 18 millimeters from the inner surface and the other which is disposed e.g. 6 millimeters from the inner surface.
As shown in FIG. 2, at the junction between sections A and B of the insulation the line of junction extends at an angle to the plane of the wall of the cargo hole 3 other than a right angle, e.g. 10°, so that the thickness of one section progressively diminishes as the thickness of the adjoining section increases. Thus, the edges 7a of the end panels 7' of section A are formed at this angle.
As shown in FIG. 3, a block 13 is provided at the upper location of each wall secured to the latter. The opposite ends of the hessian mats 12 are secured to the junction panels 7' of section A and to the block 13, e.g. entering slots 7b formed therein. Extra mats 14 of short length are incorporated in the polyurethane foam at the ends thereof and secured to block 13 and grounds 6' (FIG. 2) of junction panels 7' of section A. A vertical panel 15 depends for a short distance from block 13 and a large horizontal panel 16 extends to the top of tank 4 and is connected to panel 15 by hinge 17 as known per se. Layers of glass fiber or rock wool are provided above and below the panel 16 and the upper layer extends over the top of tank.
Referring now to FIG. 4 there is again shown a marine tanker having an outer hull 1 and an inner hull 2. In this case there is disposed within a cargo hold 3 defined within the inner hull and transverse bulkheads a membrane tank, generally indicated at 18. This is of thin metal which is not subject to cold embrittlement. The tank is surrounded and supported against hydrostatic loads and inertia forces by the thermal insulation, generally designated 5, which lines the cargo hold 3. FIG. 4 is not drawn to scale, i.e. the insulation is shown on a much larger scale than the tanker for clarity.
The thermal insulation comprises corner sections C and wall sections D. The corner sections C are each identical with section A in FIG. 1 comprising panels secured to ground strips 6 and balsa wood interposed between the panels and tank. The corners of the membrane tank 18 are anchored, so that it is held against overall dimensional change, by means of angle section anchoring members 19 secured to hardboard blocks 20 secured to the panels. The panels are of sufficient tensile, shear and compressive strength to transmit the loads to the cargo hold. The wall sections D are identical with sections B in FIG. 1 comprising polyurethane foam as described with reference to FIG. 1, except that instead of an internal layer of glass fiber or rock wool there is an internal layer 21 of thin balsa panels. The vertical corners, not shown in this drawing are identical with the corner sections C and the sections A in FIG. 1.
It will be seen that for both of the above-described type of containers the portions of insulation which are relatively highly stressed under working conditions are of the more expensive load-bearing construction, but the greatest part of the insulated area is of less expensive foam-plastic construction, both parts being effective as insulation and as a liquid-retaining barrier.
Containers of the kind concerned, for the bulk storage or transport of liquids at temperatures greatly differing from ambient temperature, each comprises a tank surrounded and supported, at least from below, by thermal insulation within an outer rigid shell. The present invention is concerned with the thermal insulation of such a container. The containers are of one or two distinct types. In one type, the container comprises a self-supporting tank; that is to say one which, while supported from below, has sufficient structural strength to hold the liquid within the tank and withstand the hydrostatic pressures and inertia forces, without depending upon any other means outside the tank for aid in supporting the walls of the tank against buckling. The insulation beneath the tank carries the load of the weight of the tank, and loads involved in holding the tank in place against horizontal movement, e.g. arising from the motion of a tanker at sea. The tank is of a material, e.g. metal, which is not subject to cold embrittlement. The tank is thermally insulated externally by thermal insulation which lines the outer rigid shell, e.g. the cargo hold of a tanker, so as to define a containing space within which the tank is located.
The other type of container is known as an integrated tank container and comprises a housing of solid load-bearing thermal insulation lined with a thin and flexible fluidtight membrance tank of sheet material, e.g. metal, which is not subject to cold embrittlement and which is not self-supporting but is supported against internal loads due to hydrostatic pressures and inertia forces, by the surrounding solid insulation. The insulation lines and is itself supported by, the outer rigid shell so that the insulation directly transmits to the latter all the pressure exerted by the fluid upon the walls of the membrane tank. More important, the tank is rigidly anchored at the corners to hold it against contraction on cooling, and the insulation at the corners takes the local loads arising from such anchorage.
In either type of container, the thermal insulation may be of any appropriate material capable of carrying the loads imposed upon it. It is usually required to be fluidtight and impermeable to the cold liquid cargo so as to constitute a secondary barrier which will itself contain a liquid, e.g. to prevent it from contacting the hull of a tanker, in the event of failure of the tank. A number of thermal insulation materials and constructions are known for use for this purpose. One known material comprises blocks or panels, for example of balsa wood faced with plywood, mounted upon spaced securing strips, e.g. of wood, secured to the outer rigid shell. The gaps between the panels are sealed by compressed plastics material. Such a construction is described in U.S. Pat. No. 3,112,043.
A disadvantage of this and other known thermal insulation materials which satisfy said requirement is that they are expensive to construct.
An object of this invention is to provide a container having thermal insulation which is a satisfactory secondary barrier but which is less expensive to construct.
According to the present invention there is provided a thermally insulated container of the kind concerned, in which less highly stressed sections of the thermal insulation comprise rigid foamed-plastics material sprayed in situ internally on the outer rigid shell while more highly stressed sections of the thermal insulation are of nonfoamed load-bearing thermal insulation material of higher strength.
The invention is based on the realization that the same thermal insulation material does not need to be used for different sections of the insulation because there are different requirements for such different sections. For example, in the case of a self-supporting tank the bottom section of the insulation supporting the bottom of the tank requires to be of high compressive strength to support the tank and the liquid cargo, but the other sections of the insulation do not support any loads and do not require to have such a high compressive strength. Likewise in the case of the integrated tank container the corner sections of the insulation require to be of high strength in order to accept the local loads involved in anchoring the tank against contraction due to cooling.
The rigid foamed-plastics material may be applied by spraying, using conventional spray equipment and the desired thickness of foamed material may be built up layer by layer. For increased strength and resistance to cracking, mats of hessian or similar mesh material can be incorporated into the foamed material between successive layers during the spraying operation. A number of such mats can be included in the overall thickness of the foamed material.
Advantageously, the foamed-plastics material comprises a multilayer construction with at least one surface layer of higher density than the other layers. The layers of foamed-plastics material are preferably rigid polyurethane closed cell foams. In addition to being an efficient thermal-insulation material, polyurethane foam is effective as a barrier to liquefied gases.
Preferably the layers making up the thickness of the insulation have a density in the range of 50 to 130 kilograms per cubic meter and one or both of the surface layers has a density greater than 100 kilograms per cubic meter, and preferably in the range of 110 to 130 kilograms per cubic meter.
In accordance with an important feature of the invention, the lines of junction between sections of foamed plastics material and sections of unfoamed load-bearing thermal insulating material should be spaced from the lines of the corner of the shell (and of the tank contained therein) so that the junction is located in a plane portion of the total insulation and not in the angle of a corner.
Thus, in the case of a self-supporting tank the section of the thermal insulation lining the bottom of the outer shell and supporting the bottom of the tank is of nonfoamed load-bearing material of high compressive strength, and this extends around the lower corners of the shell to line the lower portions of the walls of the outer shell, while the sections of the thermal insulation lining the remainder of the sidewalls of the shell and, if desired, the top of the shell also are of rigid foamed-plastics material. The vertical corners may be directly sprayed with foamed-plastics material, or the treatment of these corners may be facilitated by the insertion of preformed fillets of foamed-plastics material glued into and filling the sharp angles of the corners. The foamed-plastics material may be internally lined with another thermal-insulation material, for example glass fiber or rock wool, and this material is preferably used also, instead of foamed plastics, over the top of the tank. The nonfoamed load-bearing sections of the thermal insulation may comprise plywood-faced balsa panels, the gaps between which are sealed.
In the case of a membrane tank container in which the corners of the membrane tank are rigidly anchored to the insulation in the corners of the outer rigid shell, such that the membrance tank is held against overall dimensional change notwithstanding temperature variations, the insulation on the faces adjoining the corners of the shell will be of a material which is load-bearing and of tensile, shear and compressive strength sufficient to transmit to the shell the loads imposed upon the corners of the insulation by reason of the anchorage thereto of the corners of the membrane tank. The walls of the shell, other than the corners, are lined by rigid foamed-plastics material as specified above, the lines of junction extending across the walls and being spaced from the corners. The material of high tensile, shear and compressive strength forming the corners of the thermal insulation may be constituted by plywood-faced balsa panels. The polyurethane foam constituting the walls between the load-bearing corners may be faced on its inner surface adjacent the tank by balsa panels.
In accordance with a further important feature of the invention, at the junction between a section of foamed-plastics material and a section of nonfoamed load-bearing thermal insulation material, in a tank of either of the types specified, the plane of junction extends obliquely to the plane of the wall of the shell so that the thickness of one section of the insulation progressively diminishes and thickness of the adjoining section progressively increases.
In this even, the edges of the mats of hessian or the like at the junction with a section of nonfoamed load-bearing thermal insulation material are preferably rigidly anchored to the latter. This may be effected in any number of ways. The relevant edge face of the nonfoamed insulation material may be formed with slots to receive the marginal portions of the mats which are retained therein by wedges or adhesive. Alternatively, the marginal portion of the mat may be attached to said edge face by adhesive. Extra mats of hessian may be incorporated in the polyurethane foam adjacent this junction.
In order that the invention may be more clearly understood two specific constructional examples will now be described with reference to the accompanying drawings, wherein:
FIG. 1 is a vertical cross-sectional view through a marine tanker incorporating a freestanding cargo tank.
FIG. 2 is a detail vertical sectional view on a much larger scale through the thermal insulation of the tank of FIG. 1 showing the junction between a section of foamed-plastics material and a section of nonfoamed load-bearing material.
FIG. 3 is a detail vertical sectional view on a much larger scale through the thermal insulation of the tank of FIG. 1 showing the arrangement at the top of a sidewall thereof, the view being broken diagonally so as to show a complete upper corner and a complete lower corner.
FIG. 4 is a vertical cross-sectional view through a marine tanker incorporating a membrane cargo tank, broken and shifted diagonally to enable a larger scale.
Corresponding components in the different figures are designated by the same references throughout these figures. Dimensions are quoted merely by way of example and not in limitation.
In FIG. 1 there is shown a marine tanker having an outer hull 1 and an inner hull 2. Disposed within a cargo hold 3 defined within the inner hull and transverse bulkheads is a self-supporting tank indicated generally at 4. This is of metal which is not subject to cold embrittlement and of sufficient thickness and suitably stiffened to contain the liquid. The tank is surrounded by thermal insulation, generally designated 5, which lines the cargo hole 3. FIG. 1 is not drawn to scale, i.e. the insulation is shown on a larger scale than the tanker for clarity. There is a space S of approximately 1 meter width all around the tank between the exterior surface of the tank and the internal surface of the cargo hold 3.
The thermal insulation 5 comprises a section A lining the bottom and extending for a short distance up the walls of the cargo hold and sections B forming the rest of the walls of the thermal insulation lining the walls of the cargo hold. Section A comprises timber ground strips 6 attached at regular intervals to the cargo hold. Mounted upon the strips are relatively thick panels 7 of balsa wood faced with plywood, with the gaps therebetween sealed by compressed plastics material 8, all for example, as disclosed in U.S. Pat. No. 3,112,043, constituting a secondary barrier against leakage of liquid cargo. Interposed between the bottom of the tank and the panels 7 is a layer of balsa wood 9.
Each section B comprises a constant thickness of e.g. approximately 10 centimeters (depending on the density) of rigid closed-cell foamed polyurethane 10 lining the main portions of the walls of the cargo hold and itself lined with glass fiber or rock wool 11 of a thickness, e.g. of 15 centimeters.
In installing the insulation the section A is constructed in known manner. The tank 4 is then mounted in the cargo hold and the sections B of the insulation are formed.
The walls of the cargo hold are first shotblasted or wire brushed to provide a clean surface to receive a rigid closed-cell polyurethane foam, for example, Shell Caradal S1 and Shell Caradate 30 and having a density in the range of 50 to 130 kilograms per cubic meter. This polyurethane foam is sprayed on to the inner surface of the cargo hold layer by layer until a desired thickness of the foam has been built up.
Either the inner or the outer surface layer may be of polyurethane foam of a higher density, e.g. in the range of 110 to 130 kilograms per cubic meter than the remainder of the foam. The inner layers incorporate two mats 12 of hessian or similar mesh, e.g. of 1 centimeter mesh size, one of which is disposed e.g. 18 millimeters from the inner surface and the other which is disposed e.g. 6 millimeters from the inner surface.
As shown in FIG. 2, at the junction between sections A and B of the insulation the line of junction extends at an angle to the plane of the wall of the cargo hole 3 other than a right angle, e.g. 10°, so that the thickness of one section progressively diminishes as the thickness of the adjoining section increases. Thus, the edges 7a of the end panels 7' of section A are formed at this angle.
As shown in FIG. 3, a block 13 is provided at the upper location of each wall secured to the latter. The opposite ends of the hessian mats 12 are secured to the junction panels 7' of section A and to the block 13, e.g. entering slots 7b formed therein. Extra mats 14 of short length are incorporated in the polyurethane foam at the ends thereof and secured to block 13 and grounds 6' (FIG. 2) of junction panels 7' of section A. A vertical panel 15 depends for a short distance from block 13 and a large horizontal panel 16 extends to the top of tank 4 and is connected to panel 15 by hinge 17 as known per se. Layers of glass fiber or rock wool are provided above and below the panel 16 and the upper layer extends over the top of tank.
Referring now to FIG. 4 there is again shown a marine tanker having an outer hull 1 and an inner hull 2. In this case there is disposed within a cargo hold 3 defined within the inner hull and transverse bulkheads a membrane tank, generally indicated at 18. This is of thin metal which is not subject to cold embrittlement. The tank is surrounded and supported against hydrostatic loads and inertia forces by the thermal insulation, generally designated 5, which lines the cargo hold 3. FIG. 4 is not drawn to scale, i.e. the insulation is shown on a much larger scale than the tanker for clarity.
The thermal insulation comprises corner sections C and wall sections D. The corner sections C are each identical with section A in FIG. 1 comprising panels secured to ground strips 6 and balsa wood interposed between the panels and tank. The corners of the membrane tank 18 are anchored, so that it is held against overall dimensional change, by means of angle section anchoring members 19 secured to hardboard blocks 20 secured to the panels. The panels are of sufficient tensile, shear and compressive strength to transmit the loads to the cargo hold. The wall sections D are identical with sections B in FIG. 1 comprising polyurethane foam as described with reference to FIG. 1, except that instead of an internal layer of glass fiber or rock wool there is an internal layer 21 of thin balsa panels. The vertical corners, not shown in this drawing are identical with the corner sections C and the sections A in FIG. 1.
It will be seen that for both of the above-described type of containers the portions of insulation which are relatively highly stressed under working conditions are of the more expensive load-bearing construction, but the greatest part of the insulated area is of less expensive foam-plastic construction, both parts being effective as insulation and as a liquid-retaining barrier.