Barrier structure and barrier sheet for liquefied natural gas cargo tank

Abstract

A barrier sheet for an LNG cargo tank includes a first barrier sheet so as to form a secondary barrier of the cargo tank and a second barrier sheet attached on the first barrier sheet. Each of the first and second sheets includes first and second metal layers and a glass cloth layer interposed between the first and second layers and bonded to the first and second metal layers.

Claims

1. A barrier structure for a liquefied natural gas cargo tank, the barrier structure comprising: an insulation panel fixed to the cargo tank and comprising lower insulation panels adjacent to each other with a flat joint interposed therebetween and an upper insulation panel stacked over the lower insulation panels; a first barrier sheet attached between the upper insulation panel and the lower insulation panels, a second barrier sheet attached on the first barrier sheet over the flat joint, and an adhesive layer disposed between the first barrier sheet and the second barrier sheet and bonding the first barrier sheet to the second barrier sheet, wherein each of the first barrier sheet and the second barrier sheet comprises a first metal layer, a second metal layer, and a glass cloth layer interposed between the first metal layer and the second metal layer, wherein a lower surface of the first metal layer of the second barrier sheet directly contacts the adhesive layer, wherein the first metal layer of the first barrier sheet directly contacts the lower insulation panels, wherein a portion of an upper surface of the second metal layer of the first barrier sheet directly contacts the upper insulation panel and another portion of the upper surface of the upper surface of the second metal layer of the first barrier sheet directly contacts the adhesive layer, and wherein a lower surface of the second metal layer of the first barrier sheet directly contacts the glass cloth layer of the first barrier sheet.

2. The barrier structure of claim 1, wherein the first and second metal layers are formed of aluminum, and have a thickness of about 0.03 to 0.2 mm.

3. The barrier structure of claim 1, wherein the first and second metal layers are formed of stainless steel, and have a thickness of about 0.05 to 0.1 mm.

4. The barrier structure of claim 1, wherein the adhesive layer is configured as a liquid adhesive for the secondary barrier or a synthetic resin film having an adhesive applied thereon.

5. The barrier structure of claim 1, wherein the glass cloth layer is formed of prepreg which is fabric reinforced composite materials.

6. The barrier structure of claim 1, wherein the glass cloth layer has a thickness of about 0.15 to 0.4 mm such that the first and second barrier sheets satisfy a mechanical property for the secondary barrier.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a diagram for explaining a barrier structure formed in a conventional LNG cargo tank;

(2) FIG. 1B is a cross-sectional view of triplexes and insulation panels formed in the barrier structure of FIG. 1A;

(3) FIG. 2 illustrates a barrier sheet used in a barrier structure of an LNG cargo tank in accordance with an embodiment of the present invention;

(4) FIG. 3 is a cross-sectional view of a barrier structure of the LNG cargo tank employing the barrier sheet shown in FIG. 2; and

(5) FIG. 4 is a graph showing a sealing characteristic of the barrier sheet shown in FIG. 2.

DETAILED DESCRIPTION

(6) Hereinafter, a barrier structure and barrier sheet for an LNG cargo tank in accordance with an embodiment of the present invention will be described in detail with reference to FIG. 2 to FIG. 4, in which same or like reference numerals refer to the same components throughout the accompanying drawings.

(7) While the embodiments of the present invention have been described, they are exemplary ones only and do intend not to limit the scope of the present invention.

(8) FIG. 2 illustrates a barrier sheet used in a barrier structure of an LNG cargo tank in accordance with an embodiment of the present invention.

(9) Referring to FIG. 2, a barrier sheet 100 of the LNG cargo tank in accordance with an embodiment of the present invention may have a sandwich structure or stacked structure of thin layers to form a secondary barrier of the LNG cargo tank. That is, the barrier sheet 100 in accordance with the embodiment may include a first metal layer 101, a glass cloth layer 102, and a second metal layer 103, which correspond to the stacked thin layers.

(10) The barrier sheet 100 may have a thin plate shape such as a belt or strip shape to be coupled to another sheet for the secondary barrier of the LNG cargo tank.

(11) The first and second metal layers 101 and 103 of the barrier sheet 100 may be formed of aluminum or stainless steel. The first and second metal layers 101 and 103 may have a thickness of about 0.03 to 0.2 mm when they are formed of aluminum.

(12) In exemplary embodiment, when the thickness of the first and second layers 101 and 103 is smaller than 0.03 mm, it is highly likely that pin holes are formed while the first and second layers 101 and 103 are manufactured and handled. Meanwhile, when the thickness of the first and second layers 101 and 103 is larger than 0.2 mm, the flexibility of the barrier sheet 100 rapidly decreases. When the secondary barrier is constructed, it may become difficult to deal with a level difference between top and lower insulation panels 20 and 21.

(13) Further, the first and second metal layers 101 and 103 may have a thickness of about 0.05 to 0.1 mm when being formed of stainless steel. In this regard, the numerical values for the thickness may include values optimized by considering the manufacturing process, the handling process, and the level difference, in correspondence to stainless steel.

(14) Therefore, when the manufacturing process, the handling process, and the level difference are considered, it is understood that the numerical values for the thickness of the first and second metal layers 101 and 103 may correspond to critical values at which the first and second metal layers 101 and 103 may exhibit a superior mechanical property to the existing triplex (for example, the conventional sample) which will be described below with reference to Table 1 and exhibit an excellent sealing characteristic which will be described with reference to FIG. 4.

(15) Meanwhile, the glass cloth layer 102 may be interposed between the first and second metal layers 101 and 103 via an adhesive. The glass cloth layer 102 may be formed of prepreg which is fiber reinforced composite materials. Further, the glass cloth layer 102 may have an optimized thickness of about 0.15 to 0.4 mm such that the barrier sheet 100 in accordance with the embodiment satisfies a superior mechanical property and an excellent sealing characteristic when the secondary barrier is constructed.

(16) FIG. 3 is a cross-sectional view of a barrier structure forming the secondary barrier of the LNG cargo tank using the barrier sheet illustrated in FIG. 2.

(17) Referring to FIG. 3, the barrier structure in accordance with the embodiment of the present invention includes insulation panels 20 and 21, a first barrier sheet 300, and a second barrier sheet 310. The insulation panels 20 and 21 include lower insulation panels 20 adjacent to each other with a flat joint 22 interposed therebetween and an upper insulation panel 21 stacked over the lower insulation panel 20. The first barrier sheet 300 is attached between the upper and lower insulation panels 21 and 20 so as to form the secondary barrier of the LNG cargo tank. The second barrier sheet 310 is attached on the first barrier sheet over the flat joint 22.

(18) The first barrier sheet 300 in accordance with the embodiment is strictly managed after the first barrier sheet 300 has been previously attached or coupled to the surface of the lower insulation panel 20 so as to have a rigid characteristic, during the manufacturing process. Then, the first barrier sheet 300 is managed without a flexural deformation even while it is shipped to the field. Therefore, the above-described leakage path is rarely formed.

(19) Further, the second barrier sheet 310 having a supple characteristic is manufactured in such a shape as to be rolled and then unrolled for use. Therefore, the second barrier sheet 310 may be bonded and attached to the first barrier sheet 300 so as to form the secondary barrier of the LNG cargo tank.

(20) Each of the first and second barrier sheets 300 and 310 may include the first metal layer 101, the glass cloth layer 102, and the second metal layer 103, as described above with reference to FIG. 2.

(21) As the thicknesses of the first and second metal layers 101 and 103 in the first and second barrier sheets 300 and 310 are properly selected, the first and second barrier sheets 300 and 310 may have rigid and supple characteristics. In other words, the thicknesses of the first and second metal layers 101 and 103 in the barrier sheet 300 may be set to a large value within the above-described thickness range, and the thicknesses of the first and second metal layers 101 and 103 in the second barrier sheet 310 may be set to a smaller value than the first barrier sheet 300 within the above-described thickness range, which may result in that the first and second barrier sheets 300 and 310 have rigid and supple characteristics, respectively.

(22) Furthermore, when the second barrier sheet 310 is bonded over the first barrier sheet 300 or ends of the barrier sheets are connected and bonded to each other, the barrier sheets may be bonded to each other through an adhesive layer 200. The adhesive layer 200 may be formed by applying a commercial liquid adhesive for the secondary barrier onto the first metal layer 101 in the second barrier sheet 310 or the second metal layer 103 in the first barrier sheet 300 and then heating and pressurizing the applied liquid adhesive using a surface heater such as a ceramic heater (not illustrated).

(23) Alternatively, the adhesive layer 200 may be formed by bonding an adhesive film in which a synthetic resin film has an adhesive applied the surface thereof, to the first metal layer 101 in the second barrier sheet 310 or the second metal layer 103 in the first barrier sheet 300.

(24) According to the above-described barrier structure, when the first and second barrier sheet 300 and 310 are used to construct the secondary barrier of the LNG cargo tank, the second metal layer 103 of the first barrier sheet 300 and the first metal layer 101 of the second barrier sheet 310 are bonded to each other through the adhesive layer 200. When an interlayer adhesion defect occurs in the first and second barrier sheets 300 and 310 each including the glass cloth layer 102 coupled between the first and second metal layers 101 and 103 due to a manufacturing error, a movable gap Q may be formed between the first metal layer 101 and the glass cloth layer 102 or the second metal layer 103 and the glass cloth layer 102.

(25) However, although the gap Q or crack is formed in the first and second barrier sheets 300 and 310 constructed in the field due to repeated thermal stresses, gas and/or liquid L stored in the internal space of the cargo tank does not leak.

(26) That is because, although the gas and/or liquid L stored in the internal space of the cargo tank may flow between the first metal layer 101 and the glass cloth layer 102 or the second metal layer 103 and the glass cloth layer 102 along the gap Q, the first metal layer 101 in the second barrier sheet 310 and the second metal layer 103 in the first barrier sheet 300 are bonded to each other through the adhesive layer 200.

(27) Under the supposition that there are no problems in forming the adhesive layer 200, liquid tightness and/or air tightness may be maintained by the second and first metal layers 103 and 101 in the first and second barrier sheet 300 and 310 and the adhesive layer 200. Accordingly, gas and/or liquid L does not leak toward the pores of the flat joint 22 or an external space of the cargo tank through the pores of the flat joint 22.

(28) The mechanical properties and sealing characteristics of the first and second barrier sheets 300 and 310 having the above-described thicknesses were tested as follows. This test was performed on a sample corresponding to the first and second barrier sheets in accordance with the embodiment and a sample corresponding to the triplex for the secondary barrier of the conventional cargo tank, under test conditions of about 25 C. of a room temperature and about 170 C. of an ultra-low temperature, based on a test standard of ASTM D3039 (test speed: 2.0 mm/min).

(29) The test result was measured by the universal testing machine (UTM) of ISNTRON Corporation.

(30) Table 1 shows the test results of the sample in accordance with the embodiment of the present invention and the triplex for the secondary barrier of the conventional cargo tank. Referring to Table 1, it can be seen that the sample in accordance with the embodiment of the present invention has a much higher tensile strength and a much higher strength corresponding to an elasticity coefficient than the triplex for the secondary barrier of the conventional cargo tank, in both of room temperature and ultra-low temperature environments.

(31) TABLE-US-00001 TABLE 1 Tensile strength Elastic coefficient Warp Weft Warp Weft Characteristic direction direction direction direction Unit Mpa Mpa Room Prior art 211.3 168.4 10100 8771 temperature Present 302.5 25879 invention Ultra-low Prior art 389.2 335.5 11371 7229 temperature Present 461.3 29948 invention

(32) FIG. 4 is a graph showing the sealing characteristic of the first and second barrier sheets in accordance with the embodiment of the present invention.

(33) Referring to FIG. 4, it can be seen that the sealing characteristic of the sample in accordance with the embodiment hardly change even though repeated thermal loads, for example, 60, 120, or 300 times of thermal loads are repeated, which means that the sample has excellent air tightness and liquid tightness characteristics.

(34) While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.