A HEAT-INSULATED CONTAINER FOR LIQUEFIED GASES

Abstract: A heat-insulated container for storage or transport of liquefied gases comprising a rigid outer shell (2), a heat-­ insulating lining (3) of rigid polyurethane foam arranged along the inner side of the rigid outer shell (2), and a porous reinforcement laminate (5) provided at least on the inner sur­ face (4) of the heat-insulating lining (3), wherein said porous reinforcement laminate (5) comprises a cured epoxy resin formulation (10) and at least two plies (8 and 9) of woven cloth of glass-fibre material laid on top of each other, which plies differ as to mesh size and thread thickness in such a manner that the plies (8 and 9) cannot nest when laid on top of each other.

Description: A HEAT-INStJLATED CONTAINER FOR LIQUEFIED GASES The invention relates to a heat-insulated container for storage or transport of liquefied gases, comprising a rigid outer shell and a heat-insulating lining of rigid polyurethane foam arranged along the inner side of the rigid outer shell. Containers of this kind are known, wherein the heatinsulating lining is a of such a quality that it is adapte#d -to be- in direct contact with the liquefied gas stored in the container. When it is desired to store liquefied gases, for example, at temperatures lower than minus 60 C, it is necessary to provide at least the inner surface of the heat-insulating lining with a porous reinforcement laminate, in order to inhibit the formation of cracks in the heat-insulating lining. It is an object of the invention to provide a reinforcement laminate for use in a container of the above kind, which reinforcement laminate is-of a special construction so that it can be easily applied to the heat-insulating lining and so that it combines high stiffness with high porosity at the service conditions. For this purpose, a heat-insulated container for storage or transport of liquefied gases comprising a rigid outer shell a heat-insulating lining of rigid polyurethane foam arranged along the inner side of the rigid outer shell, and a porous reinforcement laminate provided at least on the inner surface of the heat-insultaing lining, wherein said porous reinforcement ls-min- ate comprises, according to the invention, a cured epoxy resin formulation and at least two plies of woven cloth of glass-fibre material laid on top of each other, which plies differ as to mesh size and thread thickness in such a manner that the plies cannot nest when laid on top of each other. The invention will be described more in detail with reference to the accompanying drawings, wherein: Figure 1 shows schematically a vertical cross-section of a heat-insulated container provided with a reinforcement laminate according to the invention. Figure 2 show schematically in detail a cross- section of part of the heat-insulating lining of the container according to figure 1, provided with an embodiment of a reinforcement laminate according to the invention. In figure 1, the steel outer hull of a ship for transporting liquefied gas is indicated by the reference numeral 1, whereas the steel inner hull of the ship is indicated by the reference numeral 2. The inner hull 2, connected to the outer hull 1 in conventional manner, forms the rigid outer shell of a container for liquefied gas. The said rigid outer shell 2 is provided with a heat-insulating lining 3 of rigid polyurethane foam. The top of the container is provided with 'a heat-insulated dome 7. In containers of this kind, the liquefied gas is normally in direct contact with the heat-insulating lining 3 However, when the temperature of the liquefied gas -to be stored is very 0 low, for example lower than minus 60 C, it is necessary to provide the inner surface 4 of the heat-insulating lining 3 with a reinforcement laminate 5, comprising a cured epoxy resin formulation and a glass-fibre material. The purpose of the laminate 5 is to arrest cracks in the polyurethane foam and to inhibit the formation of cracks at the inner surface 4 of the heat-insulating lining 3 during the filling of the container with liquefied gas, when the container is cooled down from ambient temperature to the very low temperature of the liquefied gas to be stored in the container. In the case of storage of liquefied natural gas at about atmospheric pressure, this temperature is as low as about minus 1600C. This reinforcement laminate must be sufficiently stiff to perform its function as a crack inhibitor and as a crack arrester properly. Furthermore, the reinforcement laminate must have a high degree of porosity. During normal use of the container, some liquefied gas will penetrate through the reinforcement laminate and will collect behind the reinforcement laminate. When at a later stage the liquefied gas is removed from the container, so that the temperature of the container rises to ambient temperature, the liquefied gas collected behind the reinforcement laminate will evaporate rapidly. If the reinforcement laminate is not sufficiently porous, the evaporated gas cannot escape quickly through the pores of the laminate, so that the pressure of the gas behind the laminate rises to a high value. This high back pressure may destroy the reinforcement laminate. In order to obtain the necessary stiffness of the laminate one could use in theory a single thick and coarse ply of woven cloth of glass-fibre material. ¯ Such a thick and coarse ply would, however, be too heavy to handle and when used on the side- or top walls of the container, it would fall off from the heat-insulating lining during the wet stage of the epoxy resin. The required stiffness of the reinforcement laminate could also be-obtained by using a plurality of thin and fine plies of woven cloth of glass-fibre material laid on top of each other. It has been found, however, that in that case it is very difficult to obtain a laminate of sufficient porosity. Consequently, it is necessary to compromise in order to obtain: a. a laminate having a high stiffness, b. a laminate having a high porosity, c. a laminate which can be applied at low cost to the heat-insulating lining without great difficulties. Serious investigations and tests have revealed that the above problem can be solved in a satisfactory manner by using a reinforcement laminate comprising a cured epoxy resin formulation and at least two plies of woven cloth of glass-fibre material laid on top of each other, which plies differ as to mesh size and thread thickness in such a manner that the plies cannot nest when laid on top of each other. In figure 2 an embodiment of the reinforcement laminate 5 according to the invention is shown. This laminate 5 comprises a thin and fine ply 8 of woven cloth of glass-fibre material secured to the inner surface 4 of the heat-insulating lining 3 by means of a cured epoxy resin formulation 10 and a somewhat thicker and coarser ply 9 of woven cloth of glassfibre material laid on top of the ply 8 and secured thereto by means of a cured epoxy resin formulation 10. The plies 8 and 9 differ as to mesh size and thread thickness in su#ch a manner that the plies 8 and 9 cannot nest. The glass content of the reinforcement laminate 5 is in the range of from 40 to 65% w/w. Plies of a plain weave construction can be used, for example, for ply 8 can be used woven cloth of glass-fibre material having a nominal thickness of 0.36 mm, a nominal weight of 332 git2, 3.9 warp threads/10 mm and 3.9 weft threads/10 mm, and for ply 9 can be used a woven cloth of glass-fibre material having a nominal thickness of 0.74 mm, 2 a nominal weight of 386 gim , 2.8 warp threads/10 mm and 2.8 weft threads/10 mm. The glass cloth used for ply 8 is, for example, glass-cloth type Y 384 and glass cloth used for ply 9 is, for example, glass cloth type Y 961, both marketed by Fothergill and Harvey, Littleborough, Lancashire, England, but other manufacturers offer identical glass cloths but under other code names. These glass cloths are made to a British Standard Specification It is observed that instead of plies of plain weave construction, it is possible to use plies of interlocked weave construction, for example, leno, mock leno or lograft. An embodiment of the reinforcement laminate according to the invention is manufactured in the following manner: 1. To the clean sanded, smooth and skin-free surface 4 of the heat-insulating lining of rigid polyurethane foam, 2 a quantity of 320 g/m2 of an epoxy resin mixture is applied as evenly as possible by using a roller or by spraying. 2. One ply of glass cloth type Y 384 is laid into the wet epoxy resin mixture. Air bubbles are smoothed out. 3. The glass cloth is then rolled with a split washer roller or a finned roller to wet out the glass cloth and to contact the glass cloth with the polyurethane foam surface 4. 4. A quantity of 60 g/m2 of epoxy resin mixture is applied to the glass cloth to cover any dry spots and to even the epoxy resin distribution. 5. The glass cloth is rolled again with a split washer roller or a finned roller to complete wet out and to--con- tact the glass cloth with the surface 4 of the polyure thane foam. 6. A quantity of 100 g/m2 of epoxy resin mixture is applied to the first ply of glass cloth. 7. One ply of glass cloth type Y 961 is laid into the wet or gelled epoxy resin mixture. Air bubbles are-smoothed out. 8. The glass cloth is compacted with a split washer roller or a finned roller. 2 9. A quantity of 80 g/m2 of epoxy resin mixture is applied to the glass cloth to cover any dry spots and to even the resin distribution. 10. The laminate is finally compacted by means of a split washer roller or a finned roller. 11. The epoxy resin mixture is allowed to cure. When the temperature of the liquefied gas is very low, more in particular when the temperature of the liquefied gas is lower than about minus 600C, the reinforcement laminate 5 is always required on the inner surface 4 of the heat-insulating lining .3, but is some cases, depending on the design, such a reinforcement laminate may also be required within the heat-insulating# lining 3 at some distance from the inner surface 4. The manufacture of the last-mentioned reinforcement laminate is similar to the manufacture of the reinforcement laminate 5 on the inner surface 4 of the heat-insulating lining, the only difference being that further layers of polyurethane foam are sprayed onto the reinforcement laminate after it has been applied. The reinforcement laminate arranged within the heat-insulating lining 3 acts both as a crack inhibitor and as a crack arrester. A suitable epoxy resin formulation for use in the invention is described in the following example: Material Parts bz weight Epoxy resin: EPIKOTE 828 100 Flexibilizer: Flexibilizer 151 50 Thixotropic agent: Aerosil 380 5 Curing agent: A modified Cycloaliphatic amine 46 EPIKOTE 828 is a glycidyl polyether of 2,2-bis (4-hydroxyphenyl) propane having an epoxy equivalent weight of 182-194 0 and a viscosity of 100-150 poises at 25 C. EPIKOTE is a re gistered trade mark. Flexibilizer 151 is a flexibilizing epoxy resin ncomponent having an epoxy equivalent weight of 700. It is observed that the invention can be applied to containers without a so-called inner tank as described in the above. However, instead it can be applied as well to containers provided with an inner tank (normally made of a suitable metal), wherein the liquefied gas is only in direct contact with the insulation in case of failure and leakage of the inner tank.

Claims: CLAIMS 1. A heat-insulated container for storage or transport of liquefied gases comprising a rigid outer shell, Åa heat-insulating lining of rigid polyurethane foam arranged along the inner side of the rigid outer shell, and a porous reinforcement laminate provided at least on the inner surface of the heat-insulating lining, characterized in that said porous reinforcement laminate comprises a cured epoxy resin formulation and at least two plies of woven cloth of glass-fibre material laid on top of each other, which plies differ as to mesh size and thread thickness in such a manner that the plies cannot nest when laid on top of each other. 2. The container as claimed in claim 1., wherein the glass content of the reinforcement laminate is in the range of from 40 to 65% w/w. 3. The container as claimed in any one of the claims 1 to 2, wherein the plies of woven cloth of glass-fibre material are of a plain weave construction. 4. The container as claimed in claim 3, wherein one ply of woven cloth of glass-fibre material has a nominal thickness 2 of 0.36 mm, a nominal weight of 332 g/m , 3.9 warp threads/10 mm and 3.9 weft threads/1O#xnm. and wherein an adjacent ply of woven cloth of glass-fibre material has a nominal thickness of 0.74 mm, 2 a nominal weight of 386 g/m2, 2.8 warp threads/10 mm and 2.8 weft threads/10 mm. 5. A heat-insulated container for storage or transport of liquefied gases, substantially as described with particular reference to the accompanying drawings.

Inventors: COLLINS, MICHAEL HARRY
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1981
Main classification: F17C3
IPC codes: F17C3, F16L59