Secondary barrier for liquefied gas storage tanks

Abstract

The present invention relates to a secondary barrier for a liquefied gas storage tank, the secondary barrier for a liquefied gas storage tank comprising: (a) a barrier layer containing one or more polymers selected from the group consisting of metal or (b) polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene vinyl alcohol, and nylon; and fiber layers laminated on both sides of the barrier layer and containing one or more fibers selected from the group consisting of glass fiber, polyethylene fiber, polyparaphenylene benzobisoxazole (PBO) fiber, aramid fiber, and carbon fiber, wherein the fiber layers are fixed by an adhesive layer that matches the surface characteristics.

Description

[Technical field]

[0001] The present invention relates to a secondary barrier for a liquefied gas storage tank. [Background technology]

[0002] Normally, after production, hydrocarbons such as natural gas and ethylene are liquefied at low temperatures and stored and transported in the form of liquefied gas. For example, natural gas can be handled in the form of liquefied gas by cooling it to -163°C. For this reason, floating marine structures and ships that produce or transport liquefied gas require a storage tank structure that can stably store the liquefied gas at low temperatures.

[0003] The inner wall surface of the liquefied gas storage tank is provided with an insulating wall for heat insulation and a barrier structure for liquid-tightness of the stored liquefied gas, and a secondary barrier structure has been utilized. A secondary insulating wall and a secondary barrier may be laminated on the inner wall surface of the liquefied gas storage tank, and a primary insulating wall and a primary barrier may be laminated on the secondary barrier, and the primary barrier may be in contact with the liquefied gas. The secondary barrier can provide an airtight structure that prevents the liquefied gas from leaking, and can be installed to withstand about two weeks even if the primary barrier is damaged, until the ship moves to the port and unloads the liquefied gas.

[0004] 1, a conventional secondary barrier has a structure in which adhesive layers 11 are formed on both sides of a metal barrier layer 10 such as an aluminum foil or stainless steel sheet, and a fiber layer 12 containing glass fiber is laminated on the adhesive layer 11. A polyurethane-based adhesive is used as the adhesive layer 11 used to laminate the metal barrier layer 10 and the fiber layer 12.

[0005] The polyurethane or epoxy adhesives used in the construction process of the secondary barrier create hard, sharp corners after curing. 12 When exposed to direct or indirect heat and cold, the secondary barrier is damaged by repeated contraction and expansion. 12The breakage of the secondary barrier means the breakage of the secondary barrier, and the damage of the secondary barrier leads to the leakage of liquefied gas and huge repair costs. For this reason, attempts have been made to improve the durability of the secondary barrier by changing the material of the fiber layer of the secondary barrier, but there is a problem that conventional adhesives cannot bond a fiber layer containing a fiber material having surface properties different from those of glass fiber to the surface of the metal barrier layer.

[0006] In addition, the barrier layer 10 is a thin metal layer of several tens to several hundreds of micrometers and has low tear strength, which makes it vulnerable to damage due to breakage. The barrier layer 10 made of a metal material is easily corroded by moisture, so it can be damaged by moisture in the surrounding air that condenses when handling cryogenic liquefied gas, and the strength of the entire secondary barrier can be reduced when the barrier layer is exposed to seawater when damage occurs to the outer hull wall. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a secondary barrier that exhibits excellent tensile strength, shear strength and durability even in an extremely low temperature environment by using a barrier layer or fiber layer containing a corrosion-resistant polymer, and a manufacturing method thereof. [Means for solving the problem]

[0008] A secondary barrier according to one aspect of the present invention is for a liquefied gas storage tank, and includes a barrier layer containing one or more polymers selected from the group consisting of (a) a metal or (b) polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene vinyl alcohol, and nylon, and fiber layers laminated on both sides of the barrier layer, and the fiber layers may be fixed by an adhesive layer.

[0009] Specifically, the barrier layer may include metal and the fiber layer may include polyethylene fibers.

[0010] Specifically, the blocking layer may have a thickness of 50 to 200 μm.

[0011] Specifically, the polyethylene fibers may be 200 to 1600 denier.

[0012] Specifically, the barrier layer may include one or more polymers selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene vinyl alcohol, and nylon.

[0013] Specifically, the polymer has a density of 0.9 to 1.7 g / cm 3 The density of the powder may be 0.01 to 0.01.

[0014] Specifically, the blocking layer may be at least partially vapor-deposited with one or more metals or metal oxides selected from aluminum, copper and oxides thereof.

[0015] Specifically, the fiber layer may include one or more fibers selected from the group consisting of glass fibers, polyethylene fibers, polyparaphenylene benzobisoxazole fibers, aramid fibers, and carbon fibers.

[0016] Specifically, the adhesive layer may include at least one of linear low density polyethylene and ethylene vinyl acetate.

[0017] Specifically, the adhesive layer may have a melting point lower than the melting point of the fiber layer, and the melting point of the adhesive layer may be 90 to 120°C.

[0018] Yet another aspect of the present invention is a liquefied gas storage tank including the secondary barrier according to the above-mentioned aspect of the present invention, characterized in that a secondary insulation barrier fixed to a hull, a secondary barrier, a primary insulation barrier and a primary barrier are arranged in that order.

[0019] Specifically, the secondary barrier may be disposed on the secondary insulating wall by being glued, and the primary barrier may be disposed on the primary insulating wall by being welded. Effect of the Invention

[0020] The present invention provides a secondary barrier having excellent durability and life even in an extremely low temperature environment by using a polyethylene fiber layer having superior tensile strength compared to conventional glass fibers, and also achieves weight reduction due to its low specific gravity, thereby improving workability and fuel efficiency during operation.

[0021] In addition, the present invention can solve the problem of poor adhesion to metal surfaces without damaging the polyethylene fiber layer by adhering the polyethylene fiber layer to the metal barrier layer using a polyethylene-based adhesive layer having a melting point relatively lower than that of the polyethylene fiber layer.

[0022] In addition, the present invention provides a secondary barrier having improved durability and life due to excellent tear strength even in cryogenic environments by using a polymer barrier layer having superior corrosion resistance and tear strength compared to conventional metal or alloy materials, and also achieves weight reduction due to its low specific gravity, thereby improving workability and operating fuel efficiency. [Brief description of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view of a conventional secondary barrier including a fibrous layer. [Diagram 2] FIG. 2 is a cross-sectional view of a secondary barrier according to the present invention. [Diagram 3] 1 is a conceptual diagram showing a method for manufacturing a secondary barrier according to the present invention. [Figure 4] 1 is a conceptual diagram showing a method for manufacturing a secondary barrier according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The object, particular advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments in conjunction with the accompanying drawings. In this specification, when referring to the components in each drawing, it should be noted that the same components are referred to by the same numbers as much as possible even if they are displayed in different drawings. In addition, when describing the present invention, if it is determined that a detailed description of related publicly known technology unnecessarily obscures the gist of the present invention, the detailed description will be omitted.

[0025] In the following, the liquefied gas may be LNG, ethane, hydrogen, etc., which have a low boiling point.

[0026] In the following, high pressure, low pressure, high temperature, low temperature, high strength and low strength are relative values ​​and do not indicate absolute values.

[0027] In the following, liquefied gas carrier is an all-encompassing expression for cargo-carrying ships, merchant ships and ships capable of producing natural gas at sea.

[0028] In the following, the term "secondary barrier" refers to a barrier placed on a secondary insulating wall fixed to the hull, and can collectively refer to a rigid secondary barrier (RSB) that is installed to cover a secondary insulating wall, and a flexible secondary barrier (FSB) that is installed to cover two or more RSBs.

[0029] In the following, metallic material may refer generically to a single metal or to an alloy containing two or more metals.

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0031] FIG. 1 is a cross-sectional view of a conventional secondary barrier.

[0032] Referring to FIG. 1, the secondary barrier has a structure in which a barrier layer 10 made of a metal material is placed at the center, and an adhesive layer 11 and a fiber layer 12 are laminated in this order on both sides of the barrier layer 10 .

[0033] The barrier layer 10 may be, but is not limited to, an aluminum foil or stainless steel sheet, and may be made of austenitic stainless steel, copper alloy, or other material whose crystals have a face-centered cubic structure and are suitable for cryogenic environments. However, barrier layer 10 made of such metals has limitations in that it has low tear strength and is vulnerable to corrosion.

[0034] Adhesive layer 11 is a polyurethane adhesive, which may be a thermoplastic polyurethane adhesive (TPU) that is melted by heat to bond barrier layer 10 and fiber layer 12 together and then hardens.

[0035] The fiber layer 12 may be a woven fabric layer whose strength is improved by impregnating glass fibers with resin and hardening them. When liquefied gas leaks and contacts the secondary barrier, thermal contraction stress is concentrated in the adhesive layer 11, and the contraction stress and peeling stress of the adhesive layer 11 are transmitted to the fiber layer 12 bonded to the adhesive layer 11, resulting in a limited and short durability life.

[0036] FIG. 2 is a cross-sectional view of a secondary barrier 1 according to the present invention.

[0037] The secondary barrier 1 according to the present invention comprises a barrier layer 10 containing one or more polymers selected from the group consisting of (a) a metal or (b) polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene vinyl alcohol, and nylon, and a fiber layer 30 laminated on both sides of the barrier layer 10, and the fiber layer 30 is fixed to the barrier layer 10 by an adhesive layer 20.

[0038] With reference to FIG. 2, Example 1 is directed to a secondary barrier including a metal barrier layer and a fiber layer including polyethylene fibers, and Example 2 is directed to a secondary barrier including a barrier layer including a polymer.

[0039] Example 1. Secondary barrier containing a polyethylene fiber layer

[0040] The secondary barrier 1 according to this embodiment includes a barrier layer 10, and may be formed by laminating an adhesive layer 20 and a fiber layer 30 on both sides of the barrier layer 10.

[0041] The barrier layer 10 is made of a metal material like the conventional secondary barrier described above, and serves to prevent leakage of liquefied gas by making the secondary barrier 1 liquid-tight and airtight. The barrier layer 10 may include aluminum foil, copper foil, stainless steel sheet such as SUS304, copper alloy such as beryllium copper, etc.

[0042] The thickness of the blocking layer 10 may be 50 to 200 μm. If the thickness of the blocking layer 10 is less than 50 μm, the strength of the blocking layer 10, which provides liquid-tightness for the secondary barrier 1, will be significantly reduced, resulting in a problem of reduced durability, while if the thickness is more than 200 μm, it will be difficult to wind up the secondary barrier 1 during its manufacture and construction, resulting in a problem of reduced workability.

[0043] Furthermore, an epoxy primer can be applied to the surface of the barrier layer 10 to improve the adhesive strength between the adhesive layer 20 (described below) and the barrier layer 10.

[0044] The fiber layer 30 is disposed and laminated on the adhesive layer 20 formed on both sides of the barrier layer 10, and may contain polymer fibers. Since the fiber layer 30 forms the surfaces of both sides of the secondary barrier 1, the strength of the fiber layer 30 may have a direct effect on the durability and life of the secondary barrier 1.

[0045] Specifically, the fiber layer 30 may be a woven layer containing polyethylene fibers, which are polymeric fibers. Preferably, the polyethylene fibers may be ultra-high molecular weight polyethylene fibers (UHMWPE fibers). Ultra-high molecular weight polyethylene fibers have a molecular weight of 3.5 million to 7.5 million, and have been used in fields where high tear strength and excellent cut resistance are required. By focusing on the fact that such ultra-high molecular weight polyethylene fibers have excellent tensile strength and tear strength and are lightweight, a woven fabric layer is woven from the fibers and used as the fiber layer 30 for the secondary barrier 1, the effect of increasing the durability life of the secondary barrier 1 can be ensured.

[0046] The physical properties of the ultra-high molecular weight polyethylene fiber used in the fiber layer 30 of this embodiment are compared with those of the glass fiber that has been mainly used in conventional fiber layers, as shown in Table 1 below.

[0047] [Table 1]

[0048] As shown in Table 1, in this embodiment, a material having a higher elastic modulus and tensile strength but a significantly lower density than glass fiber is used as the material for the fiber layer 30, which ensures better tensile strength for the secondary barrier 1 as described below, while also improving workability through its light weight.

[0049] The polyethylene fibers contained in the fiber layer 30 according to this embodiment may have an average thickness of about 200 to 1600 denier (D). Denier is the linear mass unit when 1 g of polyethylene fiber is stretched to 9,000 m. If the polyethylene fibers have a thickness of about 200 denier or less, the tensile strength at cryogenic temperatures (-170°C) drops sharply, whereas if the polyethylene fibers have a thickness of more than 1600 denier, winding becomes difficult during the manufacturing and construction of the secondary barrier 1, resulting in a problem of reduced workability. Preferably, the polyethylene fibers have an average thickness of about 200 to 800 denier or less. The tensile strength of the polyethylene fibers by thickness will be described later.

[0050] However, since the polyethylene fiber layer 30 has a relatively low surface energy compared to conventional fiber layers containing glass fibers, it is difficult to adhere it to the metal surface constituting the barrier layer 10. Therefore, in this embodiment, the adhesion between the polyethylene fiber layer 30 and the barrier layer 10 is realized by using an adhesive layer 20 described below.

[0051] The adhesive layer 20 is disposed on both sides of the barrier layer 10 to bond and bond the above-mentioned fiber layer 30 to the barrier layer 10. The adhesive layer 20 may be disposed by applying an adhesive composition to both sides of the barrier layer 10 or by laminating separate layers such as an adhesive film or sheet.

[0052] The polyethylene fibers constituting the fiber layer 30 have a melting point (140°C) significantly lower than that of conventional polyurethane adhesive films (165°C), making them unable to adhere to the barrier layer 10, and have poor adhesion properties due to their non-polar surface characteristics. For this reason, in this embodiment, a polyethylene-based compound, which is a polymer of the same series, is used as the adhesive layer 20 to solve the poor adhesion problem of the fiber layer 30.

[0053] Specifically, the adhesive layer 20 may be formed of an adhesive composition, adhesive film, or adhesive sheet containing a polyethylene-based compound. The polyethylene-based compound may be a thermoplastic compound having a polyethylene chain as a backbone.

[0054] Preferably, the polyethylene-based compound is a main chain polymer containing polyethylene to which one or more functional groups are attached as side chains, and the compound may be at least partially modified by the attachment of a polar functional group. At least a portion of the compound is modified, which may mean that the functional group is crosslinked to the compound by a method such as graft polymerization to form a branch.

[0055] For example, adhesive layer 20 may be a polyolefin having one or more polar functional groups polymerized therein, or the entire polyolefin may be rendered polar by polymerizing one or more functional groups therein.

[0056] For example, the adhesive layer 20 may be formed using an adhesive film containing at least one of linear low density polyethylene (LLDPE) and ethylene vinyl acetate (EVA).

[0057] Furthermore, the adhesive layer 20 may contain a polymer having a melting point of 90 to 120° C. The fiber layer 30 containing polyethylene fibers has a melting point of about 140° C., and has the same series of polymer as the fiber layer 30 as its backbone to improve adhesion to the fiber layer 30, but is formed of a polymer having a lower melting point than the fiber layer 30, so that the secondary barrier 1 can be manufactured even under relatively low temperature conditions. For this reason, by disposing the adhesive layer 20 of this embodiment between the fiber layer 30 and the barrier layer 10 and applying heat, only the adhesive layer 20 can be melted, and the fiber layer 30 and the barrier layer 10 can be bonded together without damaging the polyethylene fibers and the fiber layer 30 containing them.

[0058] In this embodiment, an aluminum foil having a thickness of 70 μm was used as the metal layer 10, and an adhesive film containing LLDPE having a melting point of about 115° C. and a fiber layer containing polyethylene fiber 30 were sequentially pressed and laminated on both sides. Then, the formation of the adhesive layer 20 and the adhesive strength to the adjacent layer were confirmed at various temperatures through a heating furnace, and the results are shown in Table 2 below.

[0059] [Table 2]

[0060] As shown in Table 2, the adhesive layer 20 itself is not formed at temperatures lower than the melting point of the adhesive film (115°C), and the adhesive film melts and solidifies at a temperature corresponding to the melting point to form the adhesive layer 20, which exhibits the greatest adhesive strength at 130°C and then decreases. It can be seen that the adhesive strength of the adhesive layer 20 formed is not necessarily proportional to the heating temperature. When forming the adhesive layer 20 according to this embodiment, it was confirmed that the adhesive layer 20 exhibits an adhesive strength of up to 5 MPa at room temperature and up to 25 MPa at cryogenic temperatures (-170°C).

[0061] The thickness of the adhesive layer 20 may be 0.05 to 0.25 mm. If the thickness of the adhesive layer 20 is less than 0.05 mm, the bonding strength between the blocking layer 10 and the fiber layer 30 will be significantly reduced, resulting in a problem of reduced durability, while if the thickness is more than 0.25 mm, it will be difficult to wind up the secondary barrier 1 during its manufacture and construction, resulting in a problem of reduced workability.

[0062] Example 2. Secondary barrier containing a polymeric barrier layer

[0063] The secondary barrier 1 according to this embodiment includes a barrier layer 10, and may be formed by laminating an adhesive layer 20 and a fiber layer 30 on both sides of the barrier layer 10.

[0064] The barrier layer 10 may be a polymer barrier layer 10 containing a polymer, and can serve to prevent the leakage of liquefied gas by making the secondary barrier 1 liquid-tight and airtight. For example, the barrier layer 10 has a density of 0.9 to 1.7 g / cm 3 Conventional metallic barrier layers may comprise one or more polymers having a density of about 2.7 g / cm. 3 The density of the barrier layer 10 is as high as 100%, and the weight of the barrier layer 10 reaches several tons when applied to a liquefied gas storage tank. In this embodiment, a polymer having excellent corrosion resistance is used as the barrier layer 10, which ensures excellent tear strength compared to metal and is lightweight, thereby improving workability.

[0065] Specifically, the barrier layer 10 according to the present embodiment includes one or more polymers selected from the group consisting of polyethylene (PE), polyethylene terephthalate (PET), polyvinyl alcohol (PVA), ethylene vinyl alcohol (EVOH), and nylon, and can improve tear strength and exhibit excellent resistance to corrosion compared to conventional metal materials such as aluminum. The main properties of the conventional metal materials and the polymer materials for use in the barrier layer 10 according to the present embodiment are shown in Table 3 below. The gas barrier properties and corrosion resistance were ranked as excellent: 5, good: 4, average: 3, weak: 2, and corroded or fragile: 1.

[0066] [Table 3]

[0067] The polyethylene may be a high molecular weight polyethylene having a molecular weight of 1 million to 7 million, or may be an ultra-high molecular weight polyethylene (UHMWPE) having a molecular weight of 3.5 million to 7.5 million. Ultra-high molecular weight polyethylene has a molecular weight of about 0.9 to 1.0 g / cm. 3 It has a density of about 1.1 to 1.5 g / cm, making it suitable for use at extremely low temperatures and offering excellent resistance to corrosion, including water resistance, chemical resistance, and abrasion resistance. 3 It has a density of about 1.0 to 1.3 g / cm, making it suitable for use at extremely low temperatures and highly water resistant. 3 It has a density of about 1.0 to 1.3 g / cm, making it suitable for use at extremely low temperatures and providing excellent gas barrier properties. 3 Nylon has a density of about 1.1 to 1.7 g / cm, making it suitable for use at extremely low temperatures and providing excellent gas barrier properties. 3 It has a density of 100 μm, is suitable for use at cryogenic temperatures, and has excellent gas barrier properties and water resistance. The nylon may be, for example, nylon-6, nylon-66, nylon-MXD6, etc.

[0068] Furthermore, the blocking layer 10 according to this embodiment may be formed by depositing one or more metals selected from aluminum and copper or oxides thereof on at least a portion of the blocking layer 10. As the metal oxide, ceramics containing aluminum oxide may be used. Thus, the blocking layer 10 may be a polymer layer containing the above-mentioned polymer, and a blocking layer 10 may be formed by depositing a metal on at least a portion of its surface. The deposition of the metal may be either chemical deposition or physical deposition. It is preferable to deposit the metal on both sides of the blocking layer 10.

[0069] Among the polymers that can be used for the barrier layer 10, polyethylene and polyethylene terephthalate may have relatively low gas barrier properties compared to polyvinyl alcohol, ethylene vinyl alcohol, and nylon. By depositing a metal or an oxide thereof on the surface of such polyethylene and polyethylene terephthalate, the gas barrier properties of the barrier layer 10 can be increased, and the liquid-tight and air-tight performance of the secondary barrier 1 can be improved. However, the present embodiment is not limited thereto, and the gas barrier properties can be further increased by depositing a metal or an oxide thereof on the surface of polyvinyl alcohol, ethylene vinyl alcohol, and nylon, which have relatively excellent gas barrier properties. In addition, the deposition of a metal or an oxide thereof on the barrier layer 10 not only improves the gas barrier properties of the barrier layer 10, but also relatively increases the surface energy of the barrier layer 10, thereby improving the adhesive strength to the adhesive layer 20, which will be described later.

[0070] The adhesive layer 20 is formed on both sides of the barrier layer 10 to bond and adhere the fibrous layer 30, which will be described later, to the barrier layer 10. The adhesive layer 20 may be formed by applying an adhesive composition to both sides of the barrier layer 10, or by laminating separate layers such as an adhesive film or sheet.

[0071] When the barrier layer 10 contains a polyethylene-based polymer such as polyethylene or polyethylene terephthalate, it has a relatively low surface energy compared to conventional barrier layers made of metal materials, making it difficult to adhere to the fiber layer 30 via the adhesive layer 20. Therefore, in this embodiment, when the barrier layer 10 contains at least one of polyethylene and polyethylene terephthalate, a polyethylene-based compound, which is a polymer of the same series, is used as the adhesive layer 20 to solve the poor adhesion problem of the barrier layer 10.

[0072] Specifically, the adhesive layer 20 may be formed of an adhesive composition, an adhesive film, or an adhesive sheet containing a polyurethane-based or polyethylene-based compound. The adhesive layer may be a thermoplastic one.

[0073] Preferably, the polyethylene compound has one or more functional groups attached to a polyethylene main chain as side chains, and the compound may be at least partially modified by attachment of a polar functional group. The compound being at least partially modified may mean that the functional group is crosslinked to the compound by a method such as graft polymerization to form a branch.

[0074] The secondary barrier 1 according to this embodiment may include the adhesive layer 20 of the above-mentioned embodiment 1, and the detailed description is substituted for the above-mentioned embodiment.

[0075] When the barrier layer 10 contains at least one of polyvinyl alcohol, ethylene vinyl alcohol, and nylon, a thermoplastic polyurethane adhesive can be used to form the adhesive layer 20 and adhere it to the fiber layer 30. Even when the barrier layer 10 contains polyethylene or polyethylene terephthalate, a polyurethane adhesive can be used if at least a portion of the surface of the barrier layer 10 is vapor-deposited with a metal such as aluminum or copper or an oxide thereof as described above.

[0076] The fiber layer 30 is disposed and laminated on the adhesive layer 20 formed on both sides of the barrier layer 10, and the fiber layer 30 may include one or more fibers selected from the group consisting of glass fiber, polyethylene fiber, polyparaphenylene benzobisoxazole fiber (PBO), aramid fiber, and carbon fiber.

[0077] For example, the glass fibers may be E or S glass, the polyethylene fibers may be ultra-high molecular weight polyethylene fibers, etc. The fibrous layer 30 may also be a blend of fibers including one or more of the fibers described above.

[0078] Preferably, the fiber layer 30 may be a woven layer containing polyethylene fibers as polymer fibers. Most preferably, the polyethylene fibers may be ultra-high molecular weight polyethylene fibers. Ultra-high molecular weight polyethylene fibers have a molecular weight of 3.5 million to 7.5 million, and have been used in fields where high tear strength and excellent cut resistance are required. By focusing on the fact that such ultra-high molecular weight polyethylene fibers have excellent tensile strength and tear strength and are lightweight, a woven fabric layer is woven from the fibers and used as the fiber layer 30 for the secondary barrier 1, the effect of increasing the durability life of the secondary barrier 1 can be ensured.

[0079] When the fiber layer 30 contains polyethylene fibers, it is preferable that the adhesive layer 20 uses a polyethylene-based adhesive as described above. When the fiber layer 30 contains at least one of glass fibers, polyparaphenylene benzobisoxazole fibers, aramid fibers, and carbon fibers, a conventional polyurethane-based adhesive can be used.

[0080] A liquefied gas storage tank according to an embodiment of the present invention may have a secondary insulation wall, a secondary barrier wall, a primary insulation wall and a primary barrier arranged in that order and fixed to the hull, and the secondary barrier may be according to the above-mentioned embodiments.

[0081] The insulating wall constitutes the wall surface of the liquefied gas storage tank and includes a thermal insulating material to provide thermal insulation for the liquefied gas stored in the liquefied gas storage tank. The secondary insulating wall may be constructed so that one or more of its surfaces is fixed to the hull of the liquefied gas carrier, and the secondary barrier 1 may be disposed on the insulating wall. The secondary barrier 1 including the RSB and the FSB may be disposed in a form of being adhered to the insulating wall.

[0082] Specifically, the RSB may be placed on the insulating wall via an adhesive layer, and the FSB may be placed on the RSB via an adhesive layer.

[0083] The RSB can be provided to cover the upper surface of the insulating wall to provide liquid-tightness, and the FSB can be provided to cover the gaps between the multiple RSBs provided on the multiple insulating walls, respectively, to provide air-tightness.

[0084] The RSB and FSB of the secondary barrier 1 may be determined according to the shape and size of the applied liquefied gas storage tank and the shape and size of the insulating wall, and may be a wide plate or a narrow and long strip, but is not limited thereto, and the shape and size of the RSB and FSB do not necessarily have to be the same.

[0085] FIG. 3 is a conceptual diagram showing a manufacturing apparatus 100 for the secondary barrier 1 according to an embodiment of the present invention.

[0086] The secondary barrier 1 manufacturing apparatus 100 may include a barrier layer roll 110, a fiber roll 120, an adhesive film roll 130, a roll press 140, a heating furnace 150, etc. The secondary barrier 1 can be manufactured continuously using the apparatus 100.

[0087] The barrier layer 10 may be supplied in a wound form on a barrier layer roll 110, and the fibrous layer 30 containing polyethylene fibers may be supplied in a wound form on a respective fibrous layer roll 120. The respective rolls may be arranged so that the fibrous layer 30 is laminated on both sides of the barrier layer 10, and the adhesive layer 20 may be supplied wound in the form of a film on a roll 130 before the fibrous layer 30 is arranged. The adhesive film roll 130 may be supplied so that the adhesive film is arranged between the barrier layer 10 and the fibrous layer 30.

[0088] Although not shown, the fiber layer 30 may be corona-treated by passing it between electrodes to which high frequency and high voltage output is applied to generate a corona discharge, or the surface of the fiber layer 30 may be plasma-treated using various reactive gases, and then laminated together with the blocking layer 10 and the adhesive layer 20. By such a surface treatment of the fiber layer 30, the low surface energy of the polyethylene is increased, and then the fiber layer 30 is bonded to the adhesive layer 20, thereby further increasing the adhesive strength to the blocking layer 10.

[0089] After the adhesive layer 20 is formed on both sides of the barrier layer 10, the fiber layer 30 is arranged and simultaneously pressed by a roll press 140 and passed through a heating furnace 150 to manufacture the secondary barrier 1.

[0090] FIG. 4 is a conceptual diagram showing a manufacturing apparatus 200 for the secondary barrier 1 according to another embodiment of the present invention.

[0091] The secondary barrier 1 manufacturing apparatus 200 includes a barrier layer roll 210, a fiber layer It may include a roll 220, an adhesive injection tank 230, a roll press 240, a heating furnace 250, etc. As with the previous embodiment, the apparatus 200 may be utilized to continuously manufacture the secondary barrier 1.

[0092] In the following, the differences from the above-mentioned embodiment will be mainly described, and the common contents will be substituted for the contents of the above-mentioned embodiment.

[0093] The adhesive injection tank 230 may store an adhesive suitable for the polyethylene fiber fabric having poor adhesion characteristics as described above, and supply the adhesive in accordance with the speed at which the barrier layer 10 unravels as the barrier layer roll 210 rotates to form the adhesive layer 20.

[0094] After the adhesive layer 20 is formed on both sides of the barrier layer 10, the fiber layer 30 is placed and pressed by a roll press 240, and then passed through a heating furnace 250 to manufacture the secondary barrier 2.

[0095] Thus, the present embodiment provides an apparatus 100, 200 for the continuous production of a secondary barrier 1 including an adhesive layer 20 and a production method utilizing same.

[0096] Experimental Example 1. Manufacture and properties of secondary barrier according to Example 1

[0097] In the following, a secondary barrier was manufactured according to the process shown in Fig. 3, and its tensile strength was confirmed at room temperature and low temperature. An aluminum foil with a thickness of 70 μm was used as the barrier layer, and an LLDPE film was laminated on both sides of the aluminum foil, and then a fiber layer made of ultra-high molecular weight polyethylene fiber was laminated. The laminate was placed in a heating furnace and heated at 130°C to manufacture a secondary barrier. At this time, ultra-high molecular weight polyethylene fibers with thicknesses of about 200, 400, and 800 denier were prepared, and named Examples 1-1 to 1-3, respectively.

[0098] As a comparative example, a secondary barrier having a laminated fiber layer containing conventional glass fiber was used. The barrier layer was the same as in the example, but the adhesive layer was a thermoplastic polyurethane adhesive film laminated thereon and heated at 180°C or higher to produce a secondary barrier.

[0099] The tensile strength of the secondary barriers according to the examples and comparative examples was measured at room temperature and at a cryogenic temperature (-170°C) and is shown in Table 4 below.

[0100] [Table 4]

[0101] As shown in Table 4, the secondary barrier according to Example 1-1 exhibited a similar tensile strength to the secondary barrier according to the comparative example, and the secondary barriers according to Examples 1-2 and 1-3 exhibited superior tensile strength to the comparative example under all temperature conditions. In particular, it was confirmed that the tensile strength of the secondary barrier 1 according to Example 1-3 was 79% higher than that of the conventional secondary barrier at room temperature and about 47% higher at cryogenic temperatures.

[0102] Both Examples 1-2 and 1-3 showed superior tensile strength compared to the Comparative Example. However, the secondary barrier according to Example 1-2, which has a relatively thin thickness and therefore exhibits superior workability, was selected and subjected to a tensile fatigue test to evaluate the durability life, which was then compared with the secondary barrier according to the Comparative Example.

[0103] The stress shown in Table 5 below was repeatedly applied to each secondary barrier sample at room temperature and low temperature (-110℃), and the number of times the stress was applied until fatigue failure occurred in the sample (durability life) was shown.

[0104] [Table 5]

[0105] As shown in Table 5, the secondary barrier according to Example 1-2 was confirmed to exhibit a very high durability life despite being subjected to a relatively large stress at room temperature and low temperature (-110°C) conditions compared to the secondary barrier according to the comparative example.

[0106] The above-described embodiment 1 of the present invention provides a secondary barrier 1 having a structure in which a fiber layer 30 containing polyethylene fiber and an adhesive layer 20 for fixing the fiber layer 30 are laminated on a blocking layer 10. In addition, the secondary barrier 1 according to this embodiment can ensure excellent tensile strength and durability even in an extremely low temperature environment, and can be used in place of the widely known Mark-III type triplex.

[0107] Experimental Example 2: Manufacturing and physical properties of secondary barrier according to Example 2

[0108] A secondary barrier was manufactured according to the process shown in Figure 3, and the tensile strength (UTS), elongation (elongation at UTS), elastic modulus, and shear strength were confirmed under room temperature (23°C) and cryogenic temperature (-170°C) conditions, and are shown in Table 2 below. An ethylene vinyl alcohol film with a thickness of 100 μm was used as the barrier layer, and LLDPE films were laminated on both sides of it, and then a fiber layer made of ultra-high molecular weight polyethylene fibers was laminated. The laminate was poured into a heating furnace and heated at 130°C to manufacture the secondary barrier.

[0109] As a comparative example, a secondary barrier including a conventional aluminum metal barrier and a glass fiber layer was used. The comparative example was measured for the warp and woof parts of the glass fiber layer woven in the secondary barrier.

[0110] [Table 6]

[0111] A secondary barrier for application to a liquefied gas storage tank is required to have a tensile strength of about 172 MPa at 23° C. and about 235 MPa or more at -163° C. The secondary barrier according to Example 2 has a tensile strength that is about 217% better at 23° C. and about 165% better at -170° C. than the reference value, which is superior to the comparative example that only has a tensile strength that is about 127% to 150% better than the reference value.

[0112] In addition, the secondary barrier for application to the liquefied gas storage tank preferably has an elongation rate of 2% or more under the above-mentioned temperature and tensile strength conditions. The secondary barrier according to the present embodiment exhibited an elongation rate of about 7-9%, which was confirmed to be superior to the comparative example, which showed an elongation rate of about 4-5%.

[0113] In addition, it is preferable that the secondary barrier applied to the liquefied gas storage tank has an elastic modulus of about 20 GPa or less. It was confirmed that the secondary barrier according to Example 2 has a lower elastic modulus than the secondary barrier according to the comparative example, and in particular, it maintains an elastic modulus of less than 20 GPa even under extremely low temperature conditions, and has excellent tear resistance.

[0114] The shear strength (MPa) of the secondary barrier according to Example 2 was lower than that of the Comparative Example. This is because the secondary barrier according to the Comparative Example uses glass fiber and a metal barrier film, which are easy to adhere to. Considering that the shear strength requirement for application to a liquefied gas storage tank must be greater than about 3.5 MPa, the secondary barrier according to this Example is at a level suitable for practical application.

[0115] In the above-described second embodiment of the present invention, a polymer having a relatively low specific gravity is used for the barrier layer 10, which has been conventionally made of a metal material, and therefore superior tear resistance and corrosion resistance can be ensured compared to a metal barrier layer. In addition, a relatively thin metal can be vapor-deposited on a portion of the barrier layer 10 containing a polymer, thereby improving the gas barrier properties of the barrier layer 10. This makes it possible to reduce the weight of the secondary barrier including the barrier layer 10, thereby improving the ease of installation of the secondary barrier and the operational efficiency of the ship.

[0116] The present invention has been described in detail above through specific examples. However, these are for the purpose of specifically explaining the present invention, and the present invention is not limited thereto. It is clear that modifications and improvements can be made by those having ordinary skill in the art within the technical spirit of the present invention.

[0117] The present invention is not limited to the embodiments described above, and may include combinations of the embodiments described above or combinations of at least one of the embodiments described above with known techniques as further embodiments.

[0118] Any simple variations or modifications of the present invention belong to the scope of the present invention, and the specific protection scope of the present invention will be made clear by the appended claims. [Explanation of symbols]

[0119] 1 Secondary Barrier 10. Barrier Layer 11 Adhesive layer 12 Fiber layer 20 Adhesive layer 30 Fiber layer 100, 200 Secondary barrier manufacturing equipment 110, 210 Barrier layer roll 120, 220 Fiber layer roll 130 Adhesive film roll 230 Adhesive injection tank 140, 240 roll press 150, 250 heating furnace

Claims

1. A secondary barrier for a liquefied gas storage tank, comprising: a barrier layer comprising a metal; and a fiber layer laminated on each side of the barrier layer, The fiber layer is fixed by an adhesive layer; the fibrous layer comprises polyethylene fibers; The secondary barrier, wherein the adhesive layer comprises at least one of linear low density polyethylene and ethylene vinyl acetate.

2. As a secondary barrier for liquefied gas storage tanks, a barrier layer comprising at least one polymer selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene vinyl alcohol, and nylon; A fiber layer is laminated on each side of the barrier layer, The fiber layer is fixed by an adhesive layer; The secondary barrier, wherein the fiber layer comprises at least one fiber selected from the group consisting of polyethylene fiber, polyparaphenylene benzobisoxazole fiber, aramid fiber, and carbon fiber.

3. The secondary barrier according to claim 1, wherein the barrier layer has a thickness of 50 to 200 μm.

4. A secondary barrier according to claim 1 or 2, characterized in that the polyethylene fibres are 200 to 1600 denier.

5. The polymer has a mass of 0.9 to 1.7 g / cm 3 3. The secondary barrier of claim 2, having a density of

6. The blocking layer is 3. The secondary barrier according to claim 2, characterized in that at least a portion of the secondary barrier is vapor-deposited with one or more metals or metal oxides selected from aluminum, copper and oxides thereof.

7. The adhesive layer is having a melting point lower than the melting point of the fibrous layer; The secondary barrier according to claim 1, wherein the melting point of the adhesive layer is 90 to 120°C.

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