Secondary barrier for liquefied gas storage tank

Abstract

The present invention provides a secondary barrier for liquefied gas storage tank, characterized by comprising: a blocking layer containing (a) metal or (b) one or more polymers selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and nylon; and a fiber layer laminated on both sides of the blocking layer, containing one or more fibers selected from the group consisting of glass fiber, polyethylene fiber, poly-p-phenylene benzobisoxazole fiber (PBO), aramid fiber, and carbon fiber, the fiber layer being fixed by an adhesive layer suitable for surface properties.

Description

Technical Field

[0001] This invention relates to a secondary barrier for liquefied gas storage tanks. Background Technology

[0002] Generally, hydrocarbons such as natural gas and ethylene are liquefied at low temperatures after production and stored and transported as liquefied gas (LPG). For example, natural gas can be cooled to -163°C and used as LPG. Therefore, floating offshore structures or ships that produce or transport LPG require a storage tank structure for stably storing LPG at low temperatures.

[0003] The internal walls of the liquefied petroleum gas (LPG) storage tank are equipped with heat-insulating walls and a barrier structure for liquid-tightening the stored LPG, employing a two-stage barrier structure. Secondary heat-insulating walls and secondary barriers can be stacked on the internal walls of the LPG storage tank, and primary heat-insulating walls and primary barriers can be stacked on top of the secondary barriers. The primary barriers can be in contact with the LPG. The secondary barriers provide an airtight structure to prevent LPG leakage, and even if the primary barriers are damaged, the system can withstand approximately two weeks until the ship moves to port and unloads the LPG.

[0004] Reference Figure 1 Existing secondary barriers employ a structure in which an adhesive layer 11 is formed on both sides of a metal blocking layer 10, such as aluminum foil or stainless steel sheet, and a fiber layer (glass cloth) 12 containing glass fibers is laminated on the adhesive layer 11. The adhesive layer 11 used for laminating the metal blocking layer 10 and the fiber layer 12 utilizes a polyurethane-based adhesive.

[0005] Polyurethane or epoxy adhesives used in the construction of the secondary barrier form hard, sharp edges after bonding and curing. The fiber layer 11 is repeatedly subjected to cooling and heating, causing contraction and expansion, which leads to tearing and damage to the secondary barrier. Fracture of the fiber layer 11 means fracture of the secondary barrier, resulting in liquefied gas leakage and significant repair costs. Therefore, attempts have been made to improve the durability of the secondary barrier by changing the material of the fiber layer; however, existing adhesives have limitations in bonding fiber layers containing fiber materials with different surface properties than glass fibers to the surface of the metal barrier layer.

[0006] Furthermore, the barrier layer 10 is a thin metal layer of tens to hundreds of micrometers, resulting in low tear strength and susceptibility to damage caused by tearing. The metallic barrier layer 10 is also susceptible to corrosion by moisture. Therefore, with the use of extremely low-temperature liquefied gas, there is a risk of damage due to condensation of moisture in the surrounding air, or a reduction in the overall strength of the secondary barrier due to exposure to seawater when the hull is damaged. Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The present invention is proposed to solve the problems of the prior art mentioned above. The purpose of the present invention is to provide a secondary barrier and a method for manufacturing the same. The secondary barrier uses a blocking layer or fiber layer containing a non-corrosive polymer, thereby exhibiting excellent tensile strength, shear strength and durability even in extremely low temperature environments.

[0009] Technical solutions to the problem

[0010] A secondary barrier according to one aspect of the present invention is used in a liquefied gas storage tank. The secondary barrier may include: a blocking layer comprising (a) a metal or (b) one or more polymers selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer and nylon; and a fiber layer laminated on both sides of the blocking layer, the fiber layer being fixed by an adhesive layer.

[0011] Specifically, the blocking layer may contain metal, and the fiber layer may contain polyethylene fibers.

[0012] Specifically, the thickness of the blocking layer can be 50 to 200 μm.

[0013] Specifically, the polyethylene fiber can be 200 to 1600 denier.

[0014] Specifically, the blocking layer may comprise one or more polymers selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and nylon.

[0015] Specifically, the polymer can have a concentration of 0.9 to 1.7 g / cm³. 3 The density.

[0016] Specifically, at least a portion of the blocking layer may be deposited with one or more metals or metal oxides selected from aluminum, copper and their oxides.

[0017] Specifically, the fiber layer may comprise one or more fibers selected from the group consisting of glass fiber, polyethylene fiber, poly(p-phenylenebenzodioxazole) fiber, aramid fiber, and carbon fiber.

[0018] Specifically, the adhesive layer may comprise at least one of linear low-density polyethylene and ethylene vinyl acetate copolymer.

[0019] Specifically, the adhesive layer may have a lower melting point than the fiber layer, and the melting point of the adhesive layer may be 90 to 120°C.

[0020] According to another aspect of the present invention, a liquefied gas storage tank including the secondary barrier of the present invention is characterized in that a secondary heat insulation wall, a secondary barrier, a primary heat insulation wall and a primary barrier fixed to the hull are arranged in sequence.

[0021] Specifically, the secondary barrier can be bonded and disposed above the secondary insulation wall, and the primary barrier can be welded and disposed above the primary insulation wall.

[0022] Invention Effects

[0023] This invention uses a polyethylene fiber layer with superior tensile strength compared to existing glass fibers, thereby providing a secondary barrier with excellent durability even in extremely low temperature environments, while achieving lightweighting due to its low specific gravity, thus improving workability and fuel efficiency.

[0024] In addition, the present invention utilizes a polyethylene-based adhesive layer having a melting point lower than that of the polyethylene fiber layer to bond the polyethylene fiber layer to the metal blocking layer, thereby solving the problem of difficult bonding to the metal surface without damaging the polyethylene fiber layer.

[0025] In addition, the present invention uses a polymer barrier layer with superior corrosion resistance and tear strength compared to existing metal or alloy materials, thereby providing a secondary barrier with improved durability due to its excellent tear strength even in extremely low temperature environments, while achieving lightweight due to its low specific gravity, thereby improving workability and fuel efficiency. Attached Figure Description

[0026] Figure 1 It is a cross-sectional view of the secondary barrier including the existing fiber layer.

[0027] Figure 2 This is a cross-sectional view of the secondary barrier of the present invention.

[0028] Figure 3 This is a conceptual diagram illustrating a method for manufacturing the secondary barrier according to the present invention.

[0029] Figure 4 This is a conceptual diagram illustrating a method for manufacturing the secondary barrier according to the present invention. Detailed Implementation

[0030] The objectives, specific advantages, and novel features of this invention will become clearer through the following detailed description and preferred embodiments in conjunction with the accompanying drawings. It should be noted that, even when shown in different drawings, reference numerals are added to the constituent elements of the various drawings in this specification, and the same reference numerals are assigned to the same constituent elements whenever possible. Furthermore, in the process of describing this invention, detailed descriptions of related well-known technologies are omitted if they are deemed likely to obscure the spirit of the invention.

[0031] The following liquefied gas can be LNG, ethane, hydrogen, etc., which have low boiling points.

[0032] In the following text, high pressure, low pressure, high temperature, low temperature, high strength, and low strength are relative terms and do not represent absolute values.

[0033] Hereafter, "liquefied gas carrier" refers to all vessels, including cargo ships, merchant ships, and ships capable of producing natural gas at sea.

[0034] The secondary barrier is arranged above the secondary thermal insulation wall fixed to the hull and may include an RSB (Rigid Secondary Barrier) covering the secondary thermal insulation wall and an FSB (Flexible Secondary Barrier) covering two or more RSBs.

[0035] In the following text, metallic materials may refer to a single metal or an alloy containing two or more metals.

[0036] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0037] Figure 1 This is a cross-sectional view of the existing secondary barrier.

[0038] Reference Figure 1 The secondary barrier has a structure with a metal material blocking layer 10 as the center, and an adhesive layer 11 and a fiber layer 12 stacked sequentially on both sides of the blocking layer 10.

[0039] The barrier layer 10 can be aluminum foil or stainless steel sheet, but is not limited to these. It can use crystals with a predominantly face-centered cubic structure suitable for extremely low temperature environments, such as austenitic stainless steel or copper alloys. However, the barrier layer 10 composed of such metals has limitations such as low tear strength and susceptibility to corrosion.

[0040] The adhesive layer 11 is a polyurethane-based adhesive, which may be a thermoplastic polyurethane adhesive (TPU) that is cured after bonding the barrier layer 10 and the fiber layer 12 by heat melting.

[0041] The fiber layer 12 can be a fabric layer whose strength is increased by impregnating glass fibers with resin and curing. When the liquefied gas flows out and comes into contact with the secondary barrier, the thermal shrinkage stress is concentrated in the adhesive layer 11, and the shrinkage stress and the peel stress of the adhesive layer 11 are transferred to the fiber layer 12 bonded to the adhesive layer 11, thereby exhibiting the limitation of low durability.

[0042] Figure 2 This is a cross-sectional view of the secondary barrier 1 of the present invention.

[0043] The secondary barrier 1 of the present invention includes: a blocking layer 10 comprising (a) a metal or (b) one or more polymers selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer and nylon; and a fiber layer 30 stacked on both sides of the blocking layer 10, the fiber layer 30 being fixed to the blocking layer 10 by an adhesive layer 20.

[0044] Reference Figure 2 This describes Example 1, which includes a secondary barrier comprising a metal blocking layer and a fiber layer comprising polyethylene fibers, and Example 2, which includes a secondary barrier comprising a blocking layer comprising polymers.

[0045] Example 1. Secondary barrier comprising a polyethylene fiber layer

[0046] The secondary barrier 1 in this embodiment includes a blocking layer 10, and an adhesive layer 20 and a fiber layer 30 can be stacked on both sides of the blocking layer 10.

[0047] The barrier layer 10, like the existing secondary barriers mentioned above, is made of a metallic material and serves to prevent liquefied gas from flowing out through the liquid-tight and gas-tight seals of the secondary barrier 1. The barrier layer 10 may include aluminum foil, copper foil, stainless steel sheets such as SUS304, or copper alloys such as beryllium copper.

[0048] The thickness of the blocking layer 10 can be from 50 to 200 μm. If the thickness of the blocking layer 10 is less than 50 μm, the strength of the liquid-tight blocking layer 10 responsible for the secondary barrier 1 will decrease significantly, resulting in a decrease in durability. If the thickness of the blocking layer 10 is greater than 200 μm, winding becomes difficult during the manufacturing and construction of the secondary barrier 1, resulting in a decrease in workability.

[0049] In addition, the bonding strength between the adhesive layer 20 and the blocking layer 10 can be improved by applying an epoxy primer to the surface of the blocking layer 10.

[0050] The fiber layer 30 is stacked on the adhesive layer 20 formed on both sides of the barrier layer 10, and may include polymer fibers. The fiber layer 30 forms both sides of the secondary barrier 1, and thus the strength of the fiber layer 30 can directly affect the durability of the secondary barrier 1.

[0051] Specifically, the fiber layer 30 is a polymer fiber, which may be a fabric layer containing polyethylene fibers. Preferably, the polyethylene fibers may be ultra-high molecular weight polyethylene fibers (UHMWPE fibers). UHMWPE fibers have a molecular weight of 3.5 million to 7.5 million and, due to their high tear strength, have been used in applications requiring excellent cut resistance. Considering the excellent tensile strength, tear strength, and lightweight characteristics of this UHMWPE fiber, using this fiber to weave a fabric layer and using it as the fiber layer 30 of the secondary barrier 1 can ensure an increase in the durability of the secondary barrier 1.

[0052] The physical properties of the ultra-high molecular weight polyethylene fiber used in the fiber layer 30 of this embodiment and the glass fiber mainly used in existing fiber layers were compared, as shown in Table 1 below.

[0053] Table 1

[0054]

[0055] As shown in Table 1, in this embodiment, a material with a higher modulus of elasticity and tensile strength than glass fiber, while having a significantly lower density, is used as the material for the fiber layer 30, as described later, thereby ensuring superior tensile strength of the secondary barrier 1, while improving workability due to its light weight.

[0056] Furthermore, the polyethylene fibers included in the fiber layer 30 of this embodiment can be polyethylene fibers with an average thickness of 200 to 1600 deniers (D). Denier is a linear mass unit when 1g of polyethylene fiber is stretched to 9,000m. If the thickness of the polyethylene fiber is less than 200 deniers, a sharp decrease in tensile strength occurs at extremely low temperatures (-170°C). If the thickness of the polyethylene fiber is greater than 1600 deniers, winding becomes difficult during the manufacture and construction of the secondary barrier 1, resulting in a decrease in workability. Preferably, polyethylene fibers with an average thickness of 200 to 800 deniers can be used. Tensile strength will be explained later according to the thickness of the polyethylene fiber.

[0057] On the other hand, since this polyethylene fiber layer 30 has a relatively lower surface energy than fiber layers containing existing glass fibers, it is difficult to bond to the metal surface constituting the blocking layer 10. Therefore, in this embodiment, the bonding between the polyethylene fiber layer 30 and the blocking layer 10 is achieved using the adhesive layer 20 described later.

[0058] The adhesive layer 20 is disposed on both sides of the blocking layer 10, bonding the aforementioned fiber layer 30 and the blocking layer 10 together. The adhesive layer 20 can be disposed on both sides of the blocking layer 10 by coating an adhesive composition or by laminating separate layers such as adhesive films or adhesive sheets.

[0059] The polyethylene fibers constituting the fiber layer 30 have a significantly lower melting point (140°C) than existing polyurethane adhesive films (165°C), making them unable to bond to the blocking layer 10. Due to their non-polar surface properties, they exhibit poor adhesion characteristics. Therefore, in this embodiment, a polyethylene-based compound, which is a homogeneous polymer, is used as the adhesive layer 20, thereby solving the problem of poor adhesion of the fiber layer 30.

[0060] Specifically, the adhesive layer 20 can be formed from an adhesive composition, adhesive film, or adhesive sheet containing a polyethylene-based compound. The polyethylene-based compound can be a thermoplastic material with a polyethylene chain as the backbone.

[0061] Preferably, the polyethylene-based compound is a compound comprising a main-chain polymer containing polyethylene and one or more functional groups as side chains, wherein at least a portion of the compound can be modified by the combination of polar functional groups. Modification of at least a portion of the compound may refer to the formation of branches by crosslinking the compound through graft polymerization or similar methods.

[0062] For example, the adhesive layer 20 may become polar by polymerizing one or more polar functional groups in the polyolefin or by polymerizing one or more functional groups.

[0063] For example, adhesive layer 20 can be formed using an adhesive film comprising at least one of linear low-density polyethylene (LLDPE) and ethylene vinyl acetate copolymer (EVA).

[0064] Furthermore, the adhesive layer 20 may contain a polymer with a melting point of 90 to 120°C. The fiber layer 30, containing polyethylene fibers, has a melting point of approximately 140°C. By using a polymer of the same series as the fiber layer 30 as the main chain, the adhesive force to the fiber layer 30 is improved. Since the adhesive layer 20 is formed from polymers with melting points lower than those of the fiber layer 30, the secondary barrier 1 can be manufactured even under relatively low temperature conditions. Therefore, by arranging the adhesive layer 20 between the fiber layer 30 and the barrier layer 10 and heating it, only the adhesive layer 20 can be melted, and the fiber layer 30 and the barrier layer 10 can be bonded without damaging the polyethylene fibers and the fiber layer 30 containing polyethylene fibers.

[0065] According to this embodiment, an aluminum foil with a thickness of 70 μm is used as the metal layer 10. After pressing and stacking an adhesive film containing an LLDPE with a melting point of about 115°C and a fiber layer 30 containing polyethylene fibers on both sides, the formation of the adhesive layer 20 and the adhesion strength with the adjacent layers are confirmed by heating in a furnace, as shown in Table 2 below.

[0066] Table 2

[0067] Heating temperature (°C) Bond strength (MPa) 110 Adhesive layer not formed 115 7.2 120 8.9 130 13.3 140 12.1 145 Fiber layer damage

[0068] As shown in Table 2, the adhesive layer 20 itself cannot be formed at temperatures below the melting point of the adhesive film (115°C). The adhesive film begins to melt at the temperature corresponding to its melting point and then solidifies to form the adhesive layer 20, exhibiting the highest adhesive strength at 130°C, which subsequently decreases. It can be seen that the adhesive strength of the formed adhesive layer 20 is not necessarily proportional to the heating temperature. In the case of forming the adhesive layer 20 of this embodiment, it was confirmed that the adhesive layer 20 exhibits a maximum adhesive strength of 5 MPa at room temperature and a maximum adhesive strength of 25 MPa at extremely low temperatures (-170°C).

[0069] The thickness of the adhesive layer 20 can be from 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 decrease significantly, resulting in reduced durability. If the thickness of the adhesive layer 20 is greater than 0.25 mm, winding will become difficult during the manufacturing and construction of the secondary barrier 1, resulting in reduced workability.

[0070] Example 2. Secondary barrier including a polymer blocking layer

[0071] The secondary barrier 1 in this embodiment includes a blocking layer 10, and an adhesive layer 20 and a fiber layer 30 are formed by stacking on both sides of the blocking layer 10.

[0072] The barrier layer 10 can be a polymer barrier layer containing a high molecular weight, which can prevent liquefied gas from flowing out through the liquid-tight and gas-tight layers of the secondary barrier 1. For example, the barrier layer 10 can contain a high molecular weight polymer containing 0.9 to 1.7 g / cm³. 3 One or more polymers with a density of approximately 2.7 g / cm³. Existing metal blocking layers are formed from metals such as aluminum and exhibit a density of approximately 2.7 g / cm³. 3 The density is so high that when applied to liquefied gas storage tanks, the weight can reach tens of tons. In this embodiment, a highly corrosion-resistant polymer is used as the barrier layer 10 to ensure superior tear strength compared to metal, while its light weight improves workability.

[0073] Specifically, the barrier layer 10 of this embodiment comprises one or more polymers selected from the group consisting of polyethylene (PE), polyethylene terephthalate (PET), polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), and nylon. Compared with existing metallic materials such as aluminum, it can improve tear strength and exhibit excellent resistance to corrosion. The main characteristics of existing metallic materials and the polymeric materials used in the barrier layer 10 of this embodiment are shown in Table 3 below. Gas barrier properties and corrosion resistance are expressed as follows: Excellent: 5, Good: 4, Average: 3, Weak: 2, Corroded or fragile: 1.

[0074] Table 3

[0075]

[0076] Polyethylene can be high molecular weight polyethylene with a molecular weight of 1 million to 7 million, or ultra-high molecular weight polyethylene (UHMWPE) with a molecular weight of 3.5 million to 7.5 million. UHMWPE has a molecular weight of approximately 0.9 to 1.0 g / cm³. 3 With a density suitable for use at extremely low temperatures, polyethylene terephthalate exhibits excellent resistance to water, chemicals, abrasion, and corrosion. It has a density of approximately 1.1 to 1.5 g / cm³. 3 Its density is suitable for use at extremely low temperatures, and it exhibits excellent water resistance. Polyvinyl alcohol has a density of approximately 1.0 to 1.3 g / cm³. 3 Its density is suitable for use at extremely low temperatures, and it exhibits excellent gas barrier properties. The ethylene-vinyl alcohol copolymer has a density of approximately 1.0 to 1.3 g / cm³. 3 Its density makes it suitable for use at extremely low temperatures, and it exhibits excellent gas barrier properties. Nylon has a density of approximately 1.1 to 1.7 g / cm³. 3 It has a density suitable for use at extremely low temperatures, and exhibits excellent gas barrier properties and water resistance. For example, nylon can be nylon-6, nylon-66, nylon-MXD6, etc.

[0077] Furthermore, the blocking layer 10 of this embodiment can be a layer formed by depositing at least a portion of one or more metals selected from aluminum and copper, or their oxides, on the blocking layer 10. As a metal oxide, a ceramic containing aluminum oxide can be used. Therefore, the blocking layer 10 can be a polymer layer containing the aforementioned polymer, or a layer formed by depositing metal on at least a portion of the surface of the blocking layer 10. The metal deposition can be either chemical deposition or physical deposition. Preferably, metal can be deposited on both sides of the blocking layer 10.

[0078] Among the polymers that can be used as the barrier layer 10, polyethylene and polyethylene terephthalate can have relatively lower gas barrier properties than polyvinyl alcohol, ethylene-vinyl alcohol copolymers, and nylon. By depositing a metal or its oxide on the surface of such polyethylene and polyethylene terephthalate, the gas barrier properties of the barrier layer 10 can be increased, thereby improving the liquid tightness and gas tightness of the secondary barrier 1. However, this embodiment is not limited to this; for the surfaces of polyvinyl alcohol, ethylene-vinyl alcohol copolymers, and nylon, which have relatively excellent gas barrier properties, the gas barrier properties can also be further increased by depositing a metal or its oxide. In addition, the deposition of a metal or its oxide on the barrier layer 10 can not only improve the gas barrier properties of the barrier layer 10, but also provide an effect of improving the adhesion to the adhesive layer 20 described later by relatively increasing the surface energy of the barrier layer 10.

[0079] The adhesive layer 20 is formed on both sides of the blocking layer 10 and can bond the fiber layer 30 (described later) to the blocking layer 10. The adhesive layer 20 can be arranged on both sides of the blocking layer 10 by coating an adhesive composition or by laminating separate layers such as adhesive films or adhesive sheets.

[0080] When the blocking layer 10 comprises a polyethylene-based polymer such as polyethylene or polyethylene terephthalate, it is difficult to bond it to the fiber layer 30 via the adhesive layer 20 because the blocking layer has a relatively lower surface energy than that of conventional metallic materials. Therefore, in this embodiment, when the blocking layer 10 comprises at least one of polyethylene and polyethylene terephthalate, a polyethylene-based compound, which is a homogeneous polymer, is used as the adhesive layer 20, thereby solving the problem of the difficult bonding of the blocking layer 10.

[0081] Specifically, the adhesive layer 20 may be formed from an adhesive composition, adhesive film, or adhesive sheet comprising a polyurethane-based or polyethylene-based compound. The adhesive layer may be made of a thermoplastic material.

[0082] Preferably, the polyethylene-based compound is a compound in which one or more functional groups are bonded as side chains to the polyethylene main chain, and at least a portion of the compound can be modified by the bonding of polar functional groups. Modification of at least a portion of the compound may refer to the crosslinking of the functional groups with the compound through graft polymerization or other methods to form branches.

[0083] The secondary barrier 1 in this embodiment may include the adhesive layer 20 of the aforementioned embodiment 1, and the aforementioned embodiment is used instead of detailed description.

[0084] When the blocking layer 10 comprises at least one of polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and nylon, a thermoplastic polyurethane adhesive can be used to form an adhesive layer 20 to bond it to the fiber layer 30. Alternatively, when the blocking layer 10 comprises polyethylene or polyethylene terephthalate, as previously described, a polyurethane adhesive can be used if a metal such as aluminum or copper or its oxide is deposited on at least a portion of the surface of the blocking layer 10.

[0085] The fiber layer 30 is stacked on the adhesive layer 20 formed on both sides of the blocking layer 10. The fiber layer 30 may contain one or more fibers selected from the group consisting of glass fiber, polyethylene fiber, poly(p-phenylene benzodioxazole) fiber (PBO), aramid fiber and carbon fiber.

[0086] For example, the glass fiber can be E or S-glass, and the polyethylene fiber can be ultra-high molecular weight polyethylene fiber. The fiber layer 30 can also be a mixture of fibers containing one or more of the aforementioned fibers.

[0087] Preferably, the fiber layer 30, as a polymer fiber, can be a fabric layer containing polyethylene fibers. Most preferably, the polyethylene fibers can 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, due to their high tear strength, have been used in fields requiring excellent cut resistance. Considering the excellent tensile strength, tear strength, and light weight of such ultra-high molecular weight polyethylene fibers, using these fibers to weave a fabric layer and using it as the fiber layer 30 of the secondary barrier 1 can ensure an increase in the durability of the secondary barrier 1.

[0088] When the fiber layer 30 contains polyethylene fibers, the adhesive layer 20 preferably uses the aforementioned polyethylene-based adhesive. When it contains at least one of glass fibers, poly(p-phenylene benzodioxazole) fibers, aramid fibers, and carbon fibers, existing polyurethane-based adhesives can be used.

[0089] In the liquefied gas storage tank of this invention, the secondary heat insulation wall, the secondary barrier, the primary heat insulation wall and the primary barrier fixed to the hull can be arranged in sequence, and the secondary barrier can be as described in the previous embodiment.

[0090] The insulating wall forms the wall of the liquefied gas storage tank and includes insulating material, providing insulation for the liquefied gas stored in the tank. The secondary insulating wall can be constructed such that it is fixed to the hull of the liquefied gas transport vessel on one or more sides, and the secondary barrier 1 can be arranged above the insulating wall. The secondary barrier 1, including RSB and FSB, can be arranged above the insulating wall in an adhesive manner.

[0091] Specifically, an RSB can be arranged above the insulation wall using an adhesive layer, and an FSB can be arranged above the RSB using an adhesive layer.

[0092] The RSB is arranged to cover the upper surface of the insulation wall, thereby providing a liquid tightness. The FSB is arranged to cover the gaps between the plurality of RSBs respectively disposed above the plurality of insulation walls, thereby providing an air tightness.

[0093] The RSB and FSB of the secondary barrier 1 can be determined according to the shape and size of the liquefied gas storage tank and the shape and size of the insulation wall. They can be wide plates or narrow and long strips, but are not limited to these. The shape and size of the RSB and FSB are not necessarily the same as each other.

[0094] Figure 3 This is a conceptual diagram illustrating a secondary barrier 1 manufacturing apparatus 100 according to an embodiment of the present invention.

[0095] The manufacturing apparatus 100 for the secondary barrier 1 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 continuously manufactured using the apparatus 100.

[0096] The blocking layer 10 can be supplied in the form of being wound on a blocking layer roll 110, and the fiber layer 30 containing polyethylene fibers can be supplied in the form of being wound on each fiber layer roll 120. The rolls can be arranged to laminate the fiber layer 30 on both sides of the blocking layer 10. Before the fiber layer 30 is arranged, the adhesive layer 20 can be supplied in the form of a film wound on a roll 130. The adhesive film roll 130 can be supplied such that the adhesive film is arranged between the blocking layer 10 and the fiber layer 30.

[0097] Although not illustrated, the fiber layer 30 can be configured to undergo corona treatment between electrodes that generate corona discharge by applying a high-frequency, high-voltage output, or to undergo plasma treatment on the surface of the fiber layer 30 using various reactive gases before being laminated together with the blocking layer 10 and the adhesive layer 20. This surface treatment of the fiber layer 30 increases the low surface energy of the polyethylene before bonding it to the adhesive layer 20, thereby further increasing the adhesion to the blocking layer 10.

[0098] After forming adhesive layers 20 on both sides of the barrier layer 10, fiber layers 30 are arranged and pressurized by a roll press 140, and a secondary barrier 1 can be manufactured by a heating furnace 150.

[0099] Figure 4 This is a conceptual diagram illustrating a secondary barrier 1 manufacturing apparatus 200 according to another embodiment of the present invention.

[0100] The manufacturing apparatus 200 for the secondary barrier 1 may include a barrier layer roll 210, a fiber roll 220, an adhesive injection tank 230, a roll press 240, a heating furnace 250, etc. Similar to the aforementioned embodiments, the apparatus 200 can be used to continuously manufacture the secondary barrier 1.

[0101] The following description focuses on the differences from the aforementioned embodiments, using the content of the aforementioned embodiments instead of the common content.

[0102] As previously described, the adhesive injection tank 230 stores an adhesive suitable for polyethylene fiber fabrics with difficult-to-bond properties, and then supplies it in a manner that matches the unwinding speed of the barrier layer 10 as the barrier layer roll 210 rotates to form the adhesive layer 20.

[0103] After forming adhesive layers 20 on both sides of the blocking layer 10, fiber layers 30 are arranged and pressed by a roll press 240, and a secondary barrier 2 can be manufactured by a heating furnace 250.

[0104] As described above, this embodiment provides an apparatus 100, 200 for continuously manufacturing a secondary barrier 1 including an adhesive layer 20, and a manufacturing method thereunder.

[0105] Experimental Example 1. Manufacturing and Physical Performance Confirmation of the Secondary Barrier in Example 1

[0106] The following is through, as Figure 3 The process illustrated creates a secondary barrier, and tensile strength under both room temperature and low temperature conditions is confirmed. A 70 μm thick aluminum foil is used as the barrier layer, and after laminating LLDPE films on both sides, a fiber layer formed of ultra-high molecular weight polyethylene fibers is laminated. The laminate is injected into a furnace and heated to 130°C, thereby creating the secondary barrier. The ultra-high molecular weight polyethylene fibers are then set to thicknesses of 200, 400, and 800 deniers, and are designated Examples 1-1 to 1-3, respectively.

[0107] As a comparative example, a secondary barrier was used, which consisted of a layer of fiber containing existing glass fibers. The barrier layer was the same as in the embodiment, and was heated to above 180°C after the adhesive layer, i.e., a thermoplastic polyurethane adhesive film, was laminated, thereby creating the secondary barrier.

[0108] The tensile strength of the secondary barriers of the manufactured examples and comparative examples was measured under normal temperature and extremely low temperature (-170°C) conditions, as shown in Table 4 below.

[0109] Table 4

[0110]

[0111] As shown in Table 4, the secondary barrier of Example 1-1 exhibited similar tensile strength to the secondary barrier of the comparative example, while the secondary barriers of Examples 1-2 and 1-3 exhibited superior tensile strength compared to the comparative example under all temperature conditions. In particular, it was confirmed that the tensile strength of the secondary barrier 1 of Examples 1-3 was 79% higher at room temperature and approximately 47% higher at extremely low temperatures compared to existing secondary barriers.

[0112] Examples 1-2 and 1-3 both exhibited superior tensile strength compared to the comparative examples. However, the secondary barrier of Example 1-2, which had a relatively thinner coarseness and exhibited superior workability, was selected. Its durability was evaluated by tensile fatigue testing and compared with the secondary barrier of the comparative examples.

[0113] Under ambient and low temperature (-110℃) conditions, the stresses in Table 5 below were repeatedly applied to each secondary barrier specimen, indicating the number of stresses applied until fatigue failure of the specimen (durability).

[0114] Table 5

[0115]

[0116] As shown in Table 5, it was confirmed that although the secondary barriers of Examples 1-2 were subjected to relatively greater stress than the secondary barriers of the comparative examples under normal temperature and low temperature (-110°C) conditions, they still exhibited significantly higher durability than the secondary barriers of the comparative examples.

[0117] As described above, Embodiment 1 of the present invention provides a secondary barrier 1 with a structure in which a fiber layer 30 comprising polyethylene fibers and an adhesive layer 20 for fixing the fiber layer 10 are laminated on a blocking layer 10. Furthermore, the secondary barrier 1 of this embodiment can ensure excellent tensile strength and durability even in extremely low temperature environments, thus replacing the well-known Mark-III Flex system.

[0118] Test Example 2. Manufacturing and Physical Performance Validation of the Secondary Barrier in Example 2

[0119] The following is through, as Figure 3 The secondary barrier was fabricated using a process that confirmed its tensile strength (UTS: Ultimate Tensile Strength), elongation (elongation at UTS), modulus of elasticity, and shear strength under ambient temperature (23°C) and extremely low temperature (-170°C) conditions, as shown in Table 2 below. A 100 μm thick ethylene-vinyl alcohol copolymer film was used as the barrier layer. After laminating LLDPE films on both sides of the film, a fiber layer composed of ultra-high molecular weight polyethylene fibers was laminated. The laminate was injected into a furnace and heated to 130°C, thereby fabricating the secondary barrier.

[0120] As a comparative example, a secondary barrier consisting of an existing aluminum metal barrier layer and a glass fiber layer was used. For this comparative example, the warp and weft portions of the glass fiber layer woven in the secondary barrier were measured, as shown below.

[0121] Table 6

[0122]

[0123] Secondary barriers for liquefied gas storage tanks are required to have a tensile strength of approximately 172 MPa at 23°C and approximately 235 MPa or higher at -163°C. The secondary barrier of Example 2 exhibits a tensile strength approximately 217% higher than the baseline at 23°C and approximately 165% higher at -170°C, demonstrating superior performance compared to comparative examples that only exhibit tensile strength approximately 127% to 150% higher than the baseline.

[0124] Furthermore, the secondary barrier for the liquefied gas storage tank preferably has an elongation of 2% or more under the stated temperature and applied tensile strength conditions. It was confirmed that the secondary barrier of this embodiment exhibits an elongation of approximately 7% to 9%, which is superior to the comparative example exhibiting an elongation of approximately 4% to 5%.

[0125] Furthermore, the secondary barrier used in liquefied gas storage tanks preferably has an elastic modulus of about 20 GPa or less. Compared with the secondary barrier of the comparative example, the secondary barrier of Example 2 has an even lower elastic modulus, and in particular, it maintains an elastic modulus of less than 20 GPa even under extremely low temperature conditions, thus confirming excellent tear resistance.

[0126] The shear strength (MPa) of the secondary barrier in Example 2 is lower than that of the comparative example. This is because the secondary barrier of the comparative example uses easily bondable glass fiber and metal blocking membrane. Considering that the shear strength requirement for liquefied gas storage tanks should be greater than about 3.5 MPa, it can be seen that the secondary barrier of this example is at a level suitable for practical use.

[0127] Compared to the barrier layer 10 utilizing existing metallic materials, Embodiment 2 of the present invention, as described above, uses a polymer with a relatively low specific gravity, thereby ensuring superior tear resistance and corrosion resistance compared to metallic barrier layers. Furthermore, the gas-blocking properties of the barrier layer 10 can be improved by depositing a thin layer of metal on a portion of the polymer-containing barrier layer 10. This achieves a lightweight secondary barrier including the barrier layer 10, thereby improving the ease of installation of the secondary barrier and the operational efficiency of the vessel.

[0128] The present invention has been described in detail above through specific embodiments, which are used to specifically illustrate the present invention. The present invention is not limited thereto. Obviously, those skilled in the art to which the present invention pertains can make modifications or improvements.

[0129] The present invention is not limited to the embodiments described above. Obviously, it may include a combination of the embodiments or a combination of at least one of the embodiments and known technologies as another embodiment.

[0130] Simple variations or modifications of this invention are all within the scope of this invention, and the specific scope of protection of this invention will be clearly defined by the appended claims.

[0131] Explanation of reference numerals in the attached figures

[0132] 1: Secondary barrier; 10: Blocking layer

[0133] 11: Adhesive layer 12: Fiber layer

[0134] 20: Adhesive layer; 30: Fiber layer

[0135] 100, 200: Secondary barrier manufacturing device

[0136] 110, 210: Blocking layer roll

[0137] 120, 220: Fiber layer roll

[0138] 130: Adhesive film roll; 230: Adhesive injection tank

[0139] 140, 240: Roller Press

[0140] 150, 250: Heating furnace

Claims

1. A secondary barrier, which is a secondary barrier for liquefied gas storage tanks, wherein, include: The blocking layer contains metal; as well as Fiber layers are stacked on both sides of the blocking layer. The fiber layer is fixed by an adhesive layer. The fiber layer comprises polyethylene fibers. The adhesive layer uses a homogeneous series of high-molecular-weight polyethylene compounds. The adhesive layer has a lower melting point than the fiber layer.

2. The secondary barrier according to claim 1, wherein, The thickness of the blocking layer is 50 to 200 μm.

3. The secondary barrier according to claim 1, wherein, The polyethylene fiber is 200 to 1600 denier.

4. The secondary barrier according to claim 1, wherein, The adhesive layer comprises at least one of linear low-density polyethylene and ethylene vinyl acetate copolymer.

5. The secondary barrier according to claim 4, wherein, The melting point of the adhesive layer is 90 to 120°C.

6. A secondary barrier, which is a secondary barrier for liquefied gas storage tanks, wherein, include: The blocking layer comprises one or more polymers selected from the group consisting of polyethylene, polyethylene terephthalate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and nylon. as well as Fiber layers are stacked on both sides of the blocking layer. The fiber layer is fixed by an adhesive layer. The fiber layer comprises one or more fibers selected from the group consisting of polyethylene fibers, poly(p-phenylenebenzodioxazole) fibers, aramid fibers, and carbon fibers. The adhesive layer has a lower melting point than the fiber layer.

7. The secondary barrier according to claim 6, wherein, The polymer has a content of 0.9 to 1.7 g / cm³. 3 The density.

8. The secondary barrier according to claim 6, wherein, At least a portion of the blocking layer is deposited with one or more metals or metal oxides selected from aluminum, copper and their oxides.

9. The secondary barrier according to claim 6, wherein, The adhesive layer comprises at least one of linear low-density polyethylene and ethylene vinyl acetate copolymer.

10. The secondary barrier according to claim 9, wherein, The melting point of the adhesive layer is 90 to 120°C.

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