Thermal insulation structure and its construction method

Abstract

The present invention aims to provide an insulating structure that offers high insulation against outside air and is easy to install. [Solution] The thermal insulation structure (10) of the present invention comprises a plurality of thermal insulation layers (23, 26) having foamed polyurethane resin, and an intermediate layer (25) disposed in at least one of the gaps between the thermal insulation layers (23, 26), wherein the intermediate layer (25) has polyurea resin. The outermost layer, which is the outermost thermal insulation layer (26) among the thermal insulation layers (23, 26), may have an outer skin layer (28) formed integrally with the outermost layer on its outer surface, and the outer skin layer (28) may have polyurea resin.

Description

[Technical Field]

[0001] The present invention relates to an insulating structure and a method for constructing the same, which can be used, for example, in transport piping and storage tanks for cryogenic liquefied gases. [Background technology]

[0002] Conventionally, tanks have been used to store liquefied natural gas (hereinafter referred to as LNG as needed). Liquefied natural gas needs to be stored at temperatures below -163°C. Therefore, tanks and piping for storing LNG require an insulating structure with high thermal insulation performance. Furthermore, due to the storage and release of cryogenic LNG, the tanks and piping repeatedly contract and expand. Therefore, a structure capable of absorbing length fluctuations of the tanks and piping is required. As an example, Patent Document 1 discloses an invention relating to an insulating material that can be used for cryogenic tanks and piping.

[0003] The outer surface of the insulated structure of tanks and piping must have sufficient durability. Furthermore, insulating polyurethane resin, often using carbon dioxide as a foaming agent, is frequently used as the material for insulating structures. Because carbon dioxide has lower thermal conductivity than air, insulating polyurethane resin containing carbon dioxide within its bubbles is known to have improved insulation performance compared to resins containing air. However, if air enters this foamed polyurethane resin, the foaming gas within the resin replaces the air, reducing its insulation performance. Additionally, foamed polyurethane resin used as insulation becomes brittle due to hydrolysis when exposed to humid air. Furthermore, it deteriorates due to ultraviolet radiation from sunlight and oxidative degradation from contact with oxygen and ozone in the atmosphere. Therefore, the outer surface of insulating structures is often constructed using methods such as fixing metal exterior materials with fasteners or applying resin to glass cloth. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2001-248782 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the above insulation structures had the following problems: With the method of installing metal cladding, there was a possibility of gaps forming at the joints of the cladding, and damage due to rust formation, making it difficult to maintain high levels of insulation from the outside air over a long period of time. Furthermore, with the method of applying resin to glass cloth, it was difficult to achieve high durability because the material was prone to cracking due to expansion and contraction, and there was also the problem of increased moisture permeability due to cracking. In addition, the installation was very time-consuming, resulting in high costs, difficulty in shortening the construction period, and difficulty in repairs.

[0006] This invention was made to solve the above problems, and aims to provide an insulating structure and a method for constructing the same that has high insulation properties against outside air and can be easily installed. [Means for solving the problem]

[0007] To achieve the above objective, the thermal insulation structure of the present invention is An insulating structure that covers an object to be kept cold, Multiple insulation layers having foamed polyurethane resin, An intermediate layer is disposed in at least one of the gaps in the aforementioned thermal insulation layer, Equipped with, The aforementioned intermediate layer contains a polyurea resin.

[0008] According to the present invention, since the intermediate layer has a polyurea resin, it prevents air from entering the interior beyond the intermediate layer, and when the insulating structure is exposed to extremely low temperatures, it prevents the oxygen in the entering air from being cooled and generating liquid oxygen. Furthermore, the polyurea resin is very easy to apply by spraying or other methods, and is also easy to repair.

[0009] Also, in the present invention, The outermost layer, which is the outermost heat insulation layer among the heat insulation layers, has an outer skin layer integrally formed with the outermost layer on the outer surface. The outer skin layer may contain a polyurethane resin.

[0010] According to the present invention, since the outer skin layer contains a polyurethane resin, it can prevent the intrusion of air to the inside of the outer skin layer, and when the heat insulation structure is exposed to extremely low temperatures, it can more surely prevent the oxygen in the intruded air from being cooled and generating liquid oxygen inside the intermediate layer. In addition, the polyurethane resin can be easily applied by spraying or the like, and repair is also easy.

[0011] Also, in the present invention, The intermediate layer may contain glass fibers.

[0012] According to the present invention, even in the case of a heat insulation layer having a foamed polyurethane resin, an intermediate layer having a polyurethane resin can be easily formed on the heat insulation layer by arranging glass fibers and then applying the polyurethane resin.

[0013] The method for constructing a heat insulation structure covering a cryogenic object of the present invention is as follows. The heat insulation structure is as follows. A plurality of heat insulation layers having a foamed polyurethane resin, An intermediate layer disposed in at least one of the gaps between the heat insulation layers, And is provided with The intermediate layer is formed by attaching a glass mesh to the outer surface of the heat insulation layer and then applying a polyurethane resin.

[0014] According to the present invention, even in the case of a heat insulation layer having a foamed polyurethane resin, an intermediate layer having a polyurethane resin can be easily formed on the heat insulation layer by arranging a glass mesh and then applying the polyurethane resin.

Brief Description of the Drawings

[0015] [Figure 1] Side view of a tank in which the heat insulation structure according to the first embodiment of the present invention is installed. [Figure 2] Cross-sectional view of the surface of the tank of FIG. 1. [Figure 3] Cross-sectional view of a state in which the heat insulation structure according to the second embodiment of the present invention is attached to a pipe. [Figure 4] Perspective view of the heat insulation layer of FIG. 3. [Figure 5] Cross-sectional view showing a method of manufacturing the heat insulation layer of FIG. 3.

Mode for Carrying Out the Invention

[0016] <First Embodiment>

[0017] Referring to FIG. 1, a first embodiment in which the heat insulation structure 10 according to the present invention is applied to the tank 1 will be described. FIG. 1 shows a tank 1 capable of storing cryogenic substances. The cryogenic substance is, for example, liquefied natural gas (LNG). The substance stored in the tank 1 can be other than LNG as long as it is a liquid substance stored at a cryogenic temperature, and for example, liquefied hydrogen. The tank 1 may be either a tank 1 mounted on a ship or a tank 1 installed on land such as a plant.

[0018] The tank 1 is formed of a metal steel plate, such as nickel steel, stainless steel, aluminum alloy, etc. Nickel steel is, for example, a steel plate containing 9% nickel.

[0019] The tank 1 mounted on the ship is supported at two locations around both ends in the longitudinal direction. The tank 1 for storing LNG or the like at a cryogenic temperature repeats contraction and expansion each time LNG or the like is stored and released. Therefore, of the two support members 2 that support the tank 1, one support member 2 supports the tank 1 in a state where relative movement is impossible, and the other support member 2 supports the tank 1 in a state where relative movement in the longitudinal direction is possible.

[0020] The thermal insulation structure 10 will be described with reference to Figure 2. The thermal insulation structure 10 is provided on the outer surface of the tank 1. The thermal insulation structure 10 comprises a sealer layer 21, a first thermal insulation layer 23, an intermediate layer 25, and a second thermal insulation layer 26. The second thermal insulation layer 26 has a second core layer 27 and a second outer skin layer 28 formed on the outside of the second core layer 27. The first thermal insulation layer 23, the second core layer 27, and the second outer skin layer 28 of the thermal insulation structure 10 are formed by sequentially spraying them onto the outer surface of the tank 1.

[0021] The sealer layer 21 improves the adhesion of the sprayed first insulation layer 23. The sealer layer 21 is, for example, an epoxy primer.

[0022] The first insulation layer 23 is an insulation layer that is in contact with the cryogenic tank 1 via a sealer layer 21. The first insulation layer 23 is formed of a rigid foamed polyurethane resin made of hydrofluoroolefin (HFO). When liquefied hydrogen is stored in the tank 1, the thickness of the first insulation layer 23 is preferably 200 mm or more to maintain the appropriate properties of the polyurea resin of the intermediate layer 25 and to keep the temperature within an appropriate range. The foamed polyurethane resin is formed by a spraying method. HFO is used as a substitute material for CO2 because it has a lower global warming index than CO2.

[0023] Furthermore, HFO has thermal insulation properties and can be used as a foaming gas for thermal insulation materials. The density of the foamed polyurethane resin used in the first insulation layer 23 is 20 kg / m³. 3 ~80kg / m 3 It is within the range of 30 kg / m 3 ~70kg / m 3 Preferably, 40 kg / m 3 ~60kg / m 3This is more preferable. As the density of the foamed polyurethane resin increases, the thermal insulation decreases, but the volume change during contraction and expansion becomes smaller. When the volume change is small, relative movement between the part of the first insulation layer 23 that is in contact with the tank 1 and the part that is closer to the outer surface away from the tank 1 becomes difficult. As a result, the ability to follow contraction and expansion increases. The density of the foamed polyurethane resin used in the first insulation layer 23 is, for example, 50 kg / m³. 3 The thickness is 100 mm. The first insulation layer 23 may contain durability enhancers in addition to foamed polyurethane resin. Furthermore, the first insulation layer 23 can be made of a material other than foamed polyurethane resin, as long as it has equivalent or superior insulation properties.

[0024] The intermediate layer 25 is a layer positioned in the gap between the first insulation layer 23 and the second insulation layer 26. The intermediate layer 25 is formed by placing a glass mesh woven with glass fibers on the outer surface of the first insulation layer 23 and applying a polyurea resin. The presence of the intermediate layer 25 makes it easier for the first insulation layer 23 and the second insulation layer 26 to move relative to each other. The closer the intermediate layer is to the tank 1, where the insulation layers repeatedly contract and expand, the greater the amount of contraction and expansion. Therefore, the presence of the intermediate layer 25 allows the second insulation layer 26, which does not contract and expand as much as the first insulation layer 23, to move relative to the first insulation layer 23 easily. Consequently, if a crack occurs in the first insulation layer 23 due to the repeated contraction and expansion of the tank 1, the possibility of the crack spreading to the second insulation layer 26 can be reduced. In addition, because the intermediate layer 25 covers the entire circumference of the first insulation layer 23, the first insulation layer 23 can be effectively held even if a crack occurs in the first insulation layer 23.

[0025] Furthermore, because the intermediate layer 25 contains polyurea resin, it is possible to more reliably prevent air from entering the first insulation layer 23, thereby preventing the cooling of oxygen in the air within the first insulation layer 23 and the generation of liquid nitrogen, and thus preventing a decrease in insulation performance.

[0026] The second heat insulation layer 26 is the outer heat insulation layer in the heat insulation structure 10. Similar to the first heat insulation layer 23, the second core layer 27 is formed of a rigid foamed polyurethane resin made of hydrofluoroolefin (HFO). The thickness of the second core layer 27 is 200 mm or more and 400 mm or less, preferably 250 mm or more and 350 mm or less. The foamed polyurethane resin is formed by a spraying method. The density of the foamed polyurethane resin used for the second core layer 27 is 3 ~55 kg / m 3 in the range of, and preferably 15 kg / m3 to 45 kg / m 3 , and more preferably 25 kg / m 3 ~35 kg / m 3 .

[0027] The lower the density of the foamed polyurethane resin, the greater the volume change during contraction and expansion. When the volume change is large, relative movement becomes easier between the part closer to the tank 1 and the part closer to the outer surface away from the tank 1 in the second heat insulation layer 26. While the followability to contraction and expansion is increased, the heat insulation property is increased. The density of the foamed polyurethane resin used for the second core layer 27 is, for example, 30 kg / m 3 , and the thickness is 300 mm. The thickness, density, and components of the first heat insulation layer 23 and the second core layer 27 may be different. The second core layer 27 may have a durability improver or the like in addition to the foamed polyurethane resin. Note that the second core layer 27 can be used other than the foamed polyurethane resin as long as it is a substance with heat insulation property equal to or higher than that.

[0028] The second heat insulation layer 26 has a second outer skin layer 28 on the outer surface. The second outer skin layer 28 has a polyurethane resin. The thickness of the second outer skin layer 28 formed with the polyurethane resin is 1 mm or more and 3 mm or less. The polyurethane resin is applied by spraying on the second core layer 27 and is integrally formed with the second core layer 27. The polyurethane resin can be applied continuously to the tank 1 and the piping connected to the tank 1 without joints. Note that the second outer skin layer 28 may have a colorant, a durability improver, or the like in addition to the polyurethane resin.

[0029] Polyurea resin prevents the exchange of HFO (hydrofluoric acid) with air within the insulation layer of foamed polyurethane resin, thereby preventing a decrease in insulation performance. Polyurea resin has high strength and possesses various characteristics such as waterproofing, weather resistance, chemical resistance, elasticity, and quick drying. Because polyurea resin has low moisture permeability, it is less likely to allow moisture, which causes hydrolysis of polyurethane resin, to pass through. Furthermore, polyurea resin has chemical resistance and weather resistance, and is durable, so it can be used for a long period of time. In addition, because polyurea resin is elastic, even when applied to an object that expands and contracts insulated, it can follow the movement of the object and is less prone to cracking and other damage. Furthermore, because polyurea resin is quick-drying, it is possible to shorten the construction period compared to conventional methods in which resin is applied to metal exterior materials fixed with fasteners and to glass cloth. In addition, because polyurea resin is durable, it can reduce the cost of re-installation in the long term. Furthermore, even if a portion of the sprayed polyurea or polyurea sheet is damaged, the repair can be completed by applying hand-applied polyurea to the damaged area, making repairs simple and cost-effective.

[0030] The thickness of the second outer layer 28, which is formed using polyurea resin, will be described. The thermal insulation structure 10 is installed, for example, on a tank 1 mounted on a ship. The exterior material of the thermal insulation structure of an LNG fuel tank mounted on a ship is required by classification societies to have resistance to flame propagation based on standards such as ISO 5658-2, ASTM E84, and UL723. In the case of the test standard ISO 5658-2, the measured incident heat amount satisfies the standard set for bulkheads in FTP Code Annex 1, Part 5, which defines the fire test method for fire-resistant materials for ships, by making the second outer layer 28 of polyurea resin in the thermal insulation structure 10 of the present invention 3 mm or less in thickness. Furthermore, in order to obtain the above effect of polyurea resin to a certain extent, it is preferable that it be formed to be 1 mm or more in thickness, although this depends on the object to be cooled. That is, by making the thickness of the second outer layer 28 of polyurea resin 1 mm or more and 3 mm or less, the above effect of polyurea resin and the exceptional effect of satisfying the above standard can be obtained. A thickness of 3 mm is more preferable for the second outer layer 28. However, the thickness of the second outer layer 28, which is formed using polyurea resin, may be thicker than 3 mm in the case of structures other than the tank 1 installed on a ship, for example, a tank 1 on land installed in a plant, and may be, for example, 1 mm to 5 mm.

[0031] The protective layer 29 is a weather-resistant polyurethane resin-based coating layer provided on the second outer layer 28. For tanks 1 placed outdoors, a weather-resistant polyurethane resin-based coating layer made of known materials is applied on the second outer layer 28. The weather-resistant polyurethane resin-based coating layer can prevent UV degradation of the polyurea and the adhesion of dirt, etc. By preventing UV degradation of the polyurea, it is possible to prevent damage to the polyurethane resin layer due to external impacts, and also to prevent the polyurea from absorbing moisture into the polyurethane resin layer, thus preventing damage caused by moisture penetrating the inside of the insulation structure freezing and expanding due to the extremely low temperature of the liquefied gas. In the case of tanks 1 placed in a location other than outdoors, the protective layer 29 does not need to be applied. In this embodiment, the second insulation layer 26 corresponds to the "outermost layer, which is the outermost insulation layer among the multiple insulation layers."

[0032] Regarding the insulation layer of the insulation structure 10, the above describes a two-layer structure consisting of a first insulation layer 23 and a second insulation layer 26, but three or more insulation layers may be provided. If three or more insulation layers are provided, an intermediate layer 25 may also be provided as needed, and at least one gap between each insulation layer will have an intermediate layer 25. The thickness and density of each layer will be appropriately determined within the above numerical range. For example, the insulation structure may be composed of four layers of insulation layers stacked from the tank 1 side, from the first to the fourth layer, in which case an intermediate layer may be provided in the gap between the third and fourth insulation layers. In this case, the fourth insulation layer will be the outermost layer. In this case, the total thickness from the first to the third insulation layer may be set to 200 mm or more, so that even when liquefied hydrogen is stored in the tank 1, it can be used within an appropriate temperature in which the polyurea resin of the intermediate layer can maintain appropriate properties. Alternatively, for example, an intermediate layer may be provided in each of the gaps between the four stacked insulation layers, from the first to the fourth.

[0033] In this embodiment, since the second outer layer 28 does not contain metal, there is no need for a device to prevent galvanic corrosion caused by the potential difference with metal materials that make up the tank, piping, fixing brackets, etc.

[0034] [Construction method for insulation structure 10]

[0035] The construction method for the insulation structure 10 is described below. First, a sealer layer 21 is applied to the surface of the object to be kept cold, such as the tank 1. Once the sealer layer 21 is dry, foamed polyurethane resin is sprayed to form the first insulation layer 23. Once the first insulation layer 23 is dry, a glass mesh made of glass fibers is attached, and polyurea resin is sprayed over the glass mesh to form the intermediate layer 25. Generally, polyurea resin does not adhere directly to foamed polyurethane, making construction difficult. However, in this embodiment, the glass mesh attached to the outer surface of the first insulation layer 23 for strength reinforcement is effectively utilized to spray the polyurea resin. Therefore, the polyurea resin can be sprayed and fixed without using a special construction process specifically for polyurea for fixing the polyurea resin, making the polyurea resin spraying process easier to perform. Subsequently, foamed polyurethane resin is sprayed onto the intermediate layer 25 to form the second insulation layer 26. Once the second insulation layer 26 is dry, polyurea resin is painted to form the second outer layer 28. A protective layer 29 is applied to form the second outer layer. As a result, an insulating structure 10 is formed on the object to be kept cold.

[0036] Furthermore, this method for repairing an insulating structure is a method for repairing an insulating structure that has an outer layer covering the outer surface of an object to be kept cold and is formed containing polyurea resin, wherein the outer layer is either an outer layer formed in sheet form and attached to the outer surface of the object to be kept cold, or an outer layer formed by spraying, and the method includes a step of applying polyurea resin by hand to the outer side of the joints between sheet-like outer layers, or to any area where the sheet-like outer layer or sprayed outer layer material is missing.Therefore, polyurea resin can be easily applied by hand to the joints and missing areas of the insulating structure.As a result, it is possible to obtain a repair method that can maintain an insulating structure with high insulation performance against outside air and that is easy to apply.

[0037] <Second Example>

[0038] Referring to Figures 3 and 4, the second embodiment of the thermal insulation structure 50 according to the present invention applied to the piping 5 will be described. The main difference between the thermal insulation structure 50 and the first embodiment is that the thermal insulation layer, which is made of foamed polyurethane resin, is a molded product that is pre-formed by a mold, unlike the spraying method used for the thermal insulation structure 10 of the first embodiment. Figure 3 is a cross-sectional view of the thermal insulation structure 50 provided on the piping 5. Figure 4 is a perspective view of the second thermal insulation layer 56 provided on the thermal insulation structure 50.

[0039] Pipe 5 is a pipe made of metal steel capable of carrying cryogenic substances, for example, a steel pipe for LNG made of SUS steel. Cryogenic substances include, for example, liquefied natural gas (LNG). Other cryogenic substances besides LNG can be used to carry pipe 5, such as liquefied hydrogen. Pipe 5 may be either a pipe installed on a ship or a pipe installed on land, such as in a plant.

[0040] Referring to Figure 3, the thermal insulation structure 50 provided on the outer surface of the pipe 5 will be described. The thermal insulation structure 50 comprises a first thermal insulation layer 52, an intermediate layer 55, and a second thermal insulation layer 56. The thermal insulation structure 50 has a two-layer thermal insulation structure, with the first thermal insulation layer 52 provided on the outside of the pipe 5 and the second thermal insulation layer 56 provided on the outside of the first thermal insulation layer 52. As shown in Figures 3 and 4, both the first thermal insulation layer 52 and the second thermal insulation layer 56 are made of molded products that have been pre-formed by a mold. The shapes of the first thermal insulation layer 52 and the second thermal insulation layer 56 are similar members, differing only in their radial dimensions. The first thermal insulation layer 52 and the second thermal insulation layer 56 are shaped by dividing a hollow cylindrical member into two parts with a cross-section parallel to the central axis. The curvature of the outer surface of the first insulation layer 52 and the curvature of the inner surface of the second insulation layer 56 are approximately the same, and the first insulation layer 52 and the second insulation layer 56 are arranged relative to each other such that their respective centers of curvature are approximately the same, and the inner surface of the second insulation layer 56 is formed to be in contact with the outer surface of the first insulation layer 52.

[0041] The first insulation layer 52 is an insulation layer that is in direct contact with the cryogenic pipe 5. The first insulation layer 52 has a first core layer 53 and a skin layer 54 provided on the inside and outside of the first core layer 53, respectively. The second insulation layer 56 has a second core layer 57, a skin layer 54 provided on the inside of the second core layer 57, and a second outer skin layer 58 provided on the outside of the second core layer 57. The skin layer 54 is, for example, kraft paper. In addition to kraft paper, the skin layer 54 can also be a resin sheet or paper made by laminating a resin sheet onto kraft paper.

[0042] The first core layer 53 of the first insulation layer 52 is formed of a rigid foamed polyurethane resin made of hydrofluoroolefin (HFO). The combined thickness of the first insulation layer 52 and the second insulation layer 56 is 40 mm to 190 mm, preferably 45 mm to 95 mm. For example, the thickness of the first insulation layer 52 is 20 mm or more and 95 mm or less, preferably 22.5 mm or more and 47.5 mm or less. The thickness of the first insulation layer 52 and the second insulation layer 56 is determined within the above combined thickness range depending on the object to be kept cold, the installation location, etc. For example, the thickness of the first insulation layer 52 is 95 mm and the thickness of the second insulation layer 56 is 95 mm.

[0043] The first core layer 53 is formed by injecting foamed polyurethane resin into a mold. The density of the foamed polyurethane resin used in the first core layer 53 is 35 kg / m³. 3 ~75kg / m 3 It is within the range of 45 kg / m 3 ~65kg / m 3 This is preferable. As the density of the foamed polyurethane resin increases, the thermal insulation performance decreases, but the volume change during contraction and expansion becomes smaller. When the volume change is small, relative movement between the part of the first insulation layer 52 that is in contact with the pipe 5 and the part that is closer to the outer surface and away from the pipe 5 becomes difficult. As a result, the ability to follow contraction and expansion is improved. The first core layer 53 may contain durability improvers or the like in addition to the foamed polyurethane resin. Note that materials other than foamed polyurethane resin can be used for the first core layer 53 as long as they have equivalent or better thermal insulation properties.

[0044] When molding the first core layer 53, the surface layer 54 is attached to the inner surface of each of the molds before the foamed polyurethane resin is injected into the mold. As a result, the first insulation layer 52 is integrally molded with the first core layer 53 and the surface layer 54 on both sides of the first core layer 53. The surface layer 54 facilitates the release of the first core layer 53 from the mold. Furthermore, the surface layer 54, which is integrally molded on both sides of the first core layer 53, has the effect of facilitating relative movement of the first insulation layer 52 with respect to the piping 5 and the intermediate layer 55 in the insulation structure 50.

[0045] The intermediate layer 55 is a layer positioned in the gap between the first insulation layer 52 and the second insulation layer 56. The intermediate layer 55 has a glass mesh made of glass fibers and a polyurea resin. The intermediate layer 55, which is made of polyurea resin, prevents air from entering from the outside. If the polyurea resin in the intermediate layer 55 were absent and air entered the first insulation layer, and the temperature of liquefied natural gas or liquefied hydrogen was extremely low, such as below -183°C or below -253°C, the oxygen in the air would be cooled and liquefied, generating liquid oxygen. When liquid oxygen is generated in the first insulation layer 52, the air inside the first insulation layer 52 is replaced by a liquid with a higher thermal conductivity than air, increasing the thermal conductivity of the first insulation layer 52, reducing the overall cooling performance of the insulation structure, and furthermore, rigid polyurethane foam, which is difficult to burn in air, may become more flammable in the event of a fire due to the generated liquid oxygen. In other words, the presence of the intermediate layer 55 prevents air from entering the first insulation layer 52 and prevents an increase in thermal conductivity.

[0046] Furthermore, the presence of the intermediate layer 55 facilitates relative movement between the first insulation layer 52 and the second insulation layer 56. The closer the insulation layer is to the tank 1, which repeatedly contracts and expands, the greater the amount of contraction and expansion. Therefore, the presence of the intermediate layer 55 allows the second insulation layer 56, which does not contract and expand as much as the first insulation layer 52, to easily move relative to the first insulation layer 52. Consequently, the possibility of a crack occurring in the first insulation layer 52 being transmitted to the second insulation layer 56 can be reduced. In addition, because the intermediate layer 55 covers the entire circumference of the first insulation layer 52, the first insulation layer 52 can be effectively held in place even if a crack occurs in the first insulation layer 52.

[0047] The second insulation layer 56 is the outer insulation layer in the insulation structure 50. The second core layer 57, like the first insulation layer 52, is made of a rigid foamed polyurethane resin made of hydrofluoroolefin (HFO). The thickness, density, and composition of the second core layer 57 are the same as those of the first core layer 53. However, materials other than foamed polyurethane resin can be used for the second core layer 57, as long as they have equivalent or superior insulation properties. Also, like the first core layer 53, a skin layer 54 is provided on the inner surface of the second core layer 57. The thickness, density, and composition of the first core layer 53 and the second core layer 57 may be different.

[0048] The second outer layer 58, formed from polyurea resin, is integrally formed with the second insulation layer 56. Therefore, at the construction site, the construction work is completed simply by bonding and fixing the molded first insulation layer 52 and the second insulation layer 56 to the pipe 5 to be insulated with adhesive. Consequently, the construction period can be shortened compared to conventional methods that involve applying resin to steel plates and glass cloth attached with wires, etc.

[0049] The second insulation layer 56 has a second outer layer 58 on its outer surface. The second outer layer 58 contains polyurea resin. The thickness of the second outer layer 58, which is formed from polyurea resin, is 1 mm to 3 mm. The form of the polyurea resin of the second outer layer 58 is not particularly limited, and it can be formed in advance as a sheet or by spraying. When molding the second insulation layer 56, the inner surface layer 54 of the second core layer 57 and the outer surface second outer layer 58 are attached to the inner surface of the mold, and foamed polyurethane resin is injected into the mold to form the second insulation layer 56 integrally. In addition to polyurea resin, the second outer layer 58 may also contain colorants, durability enhancers, etc.

[0050] The characteristics and effects of the second outer layer 58 formed with polyurea resin are the same as those described in the first embodiment. The reason why the thickness of the second outer layer 58 formed with polyurea resin is 1 mm or more and 3 mm or less is the same as in the first embodiment. The thickness of the second outer layer 28 formed with polyurea resin may be thicker than 3 mm in the case of structures other than the piping 5 installed on a ship, for example, the piping 5 on land installed in a plant, and may be, for example, 1 mm or more and 5 mm or less.

[0051] The protective layer 59 is a weather-resistant polyurethane resin-based coating layer provided on the second outer layer 58. For pipes 5 placed outdoors, a weather-resistant polyurethane resin-based coating layer made of known materials is applied on the second outer layer 58. The weather-resistant polyurethane resin-based coating layer can prevent UV degradation and the adhesion of dirt, etc. By preventing UV degradation of the polyurea, it prevents damage to the rigid urethane foam due to external impacts. Furthermore, the polyurea resin prevents moisture absorption by the polyurethane resin layer, preventing damage caused by freezing and expansion of moisture that has penetrated into the insulation structure due to the extremely low temperature of liquefied gas. Note that for pipes 5 placed in locations other than outdoors, the protective layer 59 does not need to be applied. In this embodiment, the second insulation layer 56 corresponds to the "outermost layer, which is the outermost insulation layer among multiple insulation layers."

[0052] Referring to Figure 5, the manufacturing method of the second insulation layer 56 will be described. The second insulation layer 56 can be manufactured by any of the following methods. The second insulation layer 56 is produced by mixing raw materials, which are polyisocyanate, polyol, and HFO with low greenhouse effect used as a foaming agent for rigid urethane foam, in a semi-cylindrical space formed by a mold 101 and a mold 102 to generate a foaming stock, and injecting the foaming stock from an injection port 103 to obtain the insulation layer. When injecting the foaming stock, a sheet-like resin material having kraft paper as the surface layer 54 and polyurea resin as the second outer layer 58 is pre-loaded on the inner surfaces of the mold 101 and the mold 102, and the rigid urethane foam constituting the second core layer 57 foams and integrates with the surface layer 54 and the second outer layer 58 to produce the second insulation layer 56. In the case of the first insulation layer 52, kraft paper, which is the surface layer 54, is pre-loaded into the inner surfaces of the mold 101 and the mold 102, respectively. The second core layer 57, which is made of rigid polyurethane foam, is then foamed and integrated with the surface layer 54 to produce the first insulation layer 52.

[0053] Referring to Figure 5, an alternative manufacturing method for the second insulation layer 56 will be described. The alternative manufacturing method described below involves injecting a foaming stock solution into a recessed space of a mold 102 that does not have an injection port 103, placing the mold 101 on top to close the recessed space, and foaming the foaming stock solution to form the second insulation layer 56. The second insulation layer 56 is produced by mixing polyisocyanate, polyol, and HFO with low greenhouse effect as foaming agents for rigid polyurethane foam to generate the foaming stock solution, injecting the foaming stock solution into a mold having a semi-cylindrical space formed by the mold 101 and the mold 102, foaming and hardening within the mold, and then demolding to obtain the insulation layer. In the case of the first insulation layer 52, kraft paper, which is the surface layer 54, and a sheet-like resin material having polyurea resin, which is the second outer layer 58, are pre-loaded into the inner surfaces of the molds 101 and 102, respectively. The rigid urethane foam constituting the second core layer 57 is foamed and integrated with the surface layer 54 and the second outer layer 58 to produce the second insulation layer 56. In the case of the first insulation layer 52, kraft paper, which is the surface layer 54, is pre-loaded into the inner surfaces of the molds 101 and 102, respectively. The second core layer 57, which is made of rigid urethane foam, is foamed and integrated with the surface layer 54 to produce the first insulation layer 52.

[0054] Regarding the insulation layer of the insulation structure 50, the above describes a two-layer structure consisting of a first insulation layer 52 and a second insulation layer 56, but three or more insulation layers may be provided. If three or more insulation layers are provided, an intermediate layer 25 may also be provided as needed, and an intermediate layer 25 may be provided in at least one gap between each insulation layer. The thickness and density of each layer are determined appropriately within the above numerical range. For example, the insulation structure may be composed of four insulation layers stacked from the pipe 5 side, from the first to the fourth layer, in which case an intermediate layer may be provided in the gap between the third and fourth insulation layers. In this case, the fourth insulation layer becomes the outermost layer. Alternatively, for example, an intermediate layer may be provided in each of the gaps between all of the four insulation layers stacked from the first to the fourth layer.

[0055] In the thermal insulation structure 50 of this embodiment, since the second outer layer 58 and the surface layer 54 do not contain metal, there is no need for a device to prevent galvanic corrosion caused by the potential difference.

[0056] [Construction method for insulation structure 50]

[0057] The construction method for the insulation structure 50 is described below. First, two first insulation layers 52 are attached to the surface of the pipe 5 of the object to be insulated, connected in the circumferential direction. Although it is possible to apply adhesive to at least one of the central axial surfaces 62, 62 that are in contact with each other during attachment, it is preferable not to use adhesive in order to allow the insulation to follow the contraction of the pipe. Adhesive is not applied to the inner circumferential surface of the first insulation layer 52 so that the first insulation layer 52 can move relative to the pipe 5.

[0058] Then, a glass mesh made of glass fibers is placed on the outer surface of the first insulation layer 52 and polyurea resin is sprayed onto it. Generally, polyurea resin does not adhere directly to foamed polyurethane and is difficult to apply, but in this embodiment, the glass mesh attached to the outer surface of the first insulation layer 52 for strength reinforcement is effectively utilized to spray the polyurea resin. Therefore, the polyurea resin can be sprayed and fixed without using a special application process for polyurea resin fixing, making the polyurea resin spraying process easier to apply.

[0059] Subsequently, two second insulation layers 56 are joined circumferentially to the outer surface of the first insulation layer 52, and adhesive is applied to at least one of the contacting central axial surfaces 62, 62 to attach them. Adhesive is not applied to the inner circumferential surface of the second insulation layer 56 so that the second insulation layer 56 can move relative to the first insulation layer 52. The central axial surface 62 of the first insulation layer 52 and the central axial surface 62 of the second insulation layer 56 are installed offset from each other. By installing them with offset joints, cold air leakage can be prevented. The above is repeated along the longitudinal direction of the pipe 5 to construct the insulation structure 50 over the entire pipe 5 to be insulated. Along the longitudinal direction of the pipe 5, adhesive is applied to at least one of the contacting radial surfaces 63, 63 of the first insulation layers 52 and the second insulation layers 56 to fix them together. Subsequently, if necessary, a protective layer 59 is applied to the outer circumferential surface of the second insulation layer 56. As a result, an insulating structure 50 is formed on the object to be kept cold.

[0060] The first insulation layer 52 and the second insulation layer 56 may be cut from a molded foamed polyurethane resin base material and shaped to match the object to be insulated, such as the pipe 5. In that case, the second outer layer 58, made of sheet-shaped polyurea resin, may be attached to the outer surface of the second core layer 57 with an adhesive or the like to form the second insulation layer 56. In that case, the surface layer 54 may be attached to the inner surface of the second core layer 57 and the inner and outer surfaces of the first core layer 53 with an adhesive or the like, respectively, or it may be omitted.

[0061] Furthermore, the method for repairing the thermal insulation structure is a method for repairing a thermal insulation structure that covers the outer surface of an object to be kept cold and has an outer layer formed containing polyurea resin, wherein the outer layer is either an outer layer formed in sheet form and attached to the outer surface of the object to be kept cold, or an outer layer formed by spraying, and the method includes a step of applying polyurea resin by hand to the outer side of the joints between sheet-like outer layers, or to any area where the sheet-like outer layer or sprayed outer layer material is missing.Therefore, polyurea resin can be easily applied by hand to the joints and missing areas of the thermal insulation structure.As a result, it is possible to obtain a repair method that can maintain a thermal insulation structure with high insulation performance against outside air and that is easy to apply.

[0062] This method for repairing the insulation structure provides insulation structures 10 and 50 that offer high insulation against outside air and are easy to install.

[0063] In this embodiment, a foamed rigid polyurethane using hydrofluoroolefin (HFO), which has an extremely low environmental impact, as the foaming agent has been described. However, the foamed polyurethane of the present invention is not limited to this; for example, even if a foamed rigid polyurethane using hydrofluorocarbon (HFC) as the foaming agent is used, the effects of "preventing air from entering" and "facilitating construction" into the insulation layer inside the intermediate layer of the present invention can be achieved. [Explanation of symbols]

[0064] 1 tank 10. Insulated structure 21. Sealer layer 23. First insulation layer 25 Middle Class 26. Second insulation layer 27. Second Core Layer 28 Second integumentary layer 29 Protective layer 5 Piping 50 Insulated structure 52. First insulation layer 55 Middle Class 56. Second insulation layer 58 Second outer cortex 54 Epidermis

Claims

1. An insulating structure that covers an object to be kept cold, Multiple insulation layers having foamed polyurethane resin, An intermediate layer is placed in at least one of the gaps in the aforementioned thermal insulation layer, Equipped with, The aforementioned intermediate layer has a heat insulating structure containing polyurea resin.

2. The thermal insulation structure according to claim 1, The outermost of the aforementioned insulation layers, which is the outermost insulation layer, has an outer layer formed integrally with the outermost layer on its outer surface. The aforementioned outer layer has a polyurea resin, providing an insulating structure.

3. The thermal insulation structure according to claim 1 or claim 2, The aforementioned intermediate layer has a heat insulating structure containing glass fibers.

4. A method for constructing an insulating structure that covers an object to be kept cold, The aforementioned thermal insulation structure is Multiple insulation layers having foamed polyurethane resin, An intermediate layer is placed in at least one of the gaps in the aforementioned thermal insulation layer, Equipped with, The method for constructing an insulating structure is to form the intermediate layer by attaching glass fibers to the outer surface of the insulating layer and then applying a polyurea resin.

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