Liquefied gas carrier

Abstract

A double-shell tank (3) mounted on a hull of a liquefied gas carrier includes an inner tank (4) including an inner tank main body portion (41) and an inner tank dome (42), an outer tank (5) including an outer tank main body portion (51) and an outer tank dome (52), and a support member provided between the outer tank main body portion (51) and the inner tank main body portion (41). The outer tank dome (52) is divided into a fixed portion (52A) and a movable portion (52B) by a bellows (55), and the movable portion (52B) is coupled to the inner tank dome (42). A tank cover (7) includes a cylindrical portion (72) through which the outer tank dome (52) is inserted, and a resilient member (8) is interposed between the cylindrical portion (72) and a dome flange (56) provided to the movable portion (52B) of the outer tank dome (52). A plurality of displacement measuring mechanisms (9) for measuring displacement of the movable portion (52B) of the outer tank dome (52) relative to the tank cover (7) are arranged on a circumference surrounding the outer tank dome (52).

Description

Technical Field

[0001] This invention relates to a liquefied gas transport vessel comprising a double-shell tank. Background Technology

[0002] It has long been known that there are liquefied gas transport vessels that include double-shell tanks. For example, Patent Document 1 discloses a liquefied gas transport vessel in which double-shell tanks mounted on the hull are covered by a tank cover.

[0003] In the liquefied gas transport vessel disclosed in Patent Document 1, a vacuum layer is formed between the inner and outer tanks of the double-shell tank as a heat insulation layer. More specifically, the inner tank includes an inner tank body for storing liquefied gas and an inner tank dome protruding upward from the inner tank body, and the outer tank includes an outer tank body surrounding the inner tank body and an outer tank dome surrounding the inner tank dome. The inner tank dome is used to collect and is penetrated by various pipes such as liquefied gas transfer pipes and electrical pipes.

[0004] Furthermore, in the double-shell tank of Patent Document 1, a bellows is assembled on the outer tank dome. Through this bellows, the outer tank dome is divided into a movable upper part and a fixed lower part. When liquefied gas is introduced into the inner tank, the inner tank thermally contracts. The movable part of the outer tank dome is connected to the inner tank dome via a connecting member in such a way that it moves together with the inner tank dome during thermal contraction.

[0005] Furthermore, in the double-shell tank of Patent Document 1, a support member is provided between the outer tank body and the inner tank body to support the inner tank body from below.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2015-4383

[0009] Patent Document 2: Japanese Patent Application Publication No. 2019-151191 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, in a structure like the liquefied gas transport ship in Patent Document 1, it is difficult to directly visually inspect the support components between the outer tank body and the inner tank body of the double-shell tank. Therefore, there is a desire to check whether the support components are malfunctioning.

[0012] Therefore, the object of the present invention is to provide a liquefied gas transport vessel capable of confirming whether the support components between the outer tank body and the inner tank body of a double-shell tank are malfunctioning.

[0013] Methods for solving problems

[0014] To address the aforementioned issues, the inventors of this invention conducted in-depth research and discovered that, in the case of a structure where the outer dome penetrates the canister as disclosed in Patent Document 2 (for ships), the movable portion of the outer dome shifts together with the inner dome. Therefore, by measuring the relative displacement of the movable portion of the outer dome relative to the canister, it is possible to determine whether the support components between the outer and inner main bodies are malfunctioning. This is because if the relative displacement of the movable portion of the outer dome relative to the canister does not conform to the design value during the thermal shrinkage of the inner canister, it can be considered that the support components are malfunctioning. This invention was made based on this viewpoint.

[0015] That is, the liquefied gas transport vessel of the present invention is characterized in that the liquefied gas transport vessel has: a hull; a double-shell tank mounted on the hull; and a tank cover covering the double-shell tank, the double-shell tank comprising: an inner tank including an inner tank body portion for storing liquefied gas and an inner tank dome projecting upward from the inner tank body portion; an outer tank including an outer tank body portion surrounding the inner tank body portion and an outer tank dome surrounding at least the lower portion of the inner tank dome, a heat insulation layer being formed between the outer tank and the inner tank; a support member disposed between the outer tank body portion and the inner tank body portion, supporting the inner tank body portion from below; and a bellows dividing the outer tank dome. The liquefied gas transport vessel is assembled to the outer dome in the manner of a fixed part on the lower side and a movable part on the upper side; and a connecting member that connects the movable part of the outer dome to the inner dome. The tank cover includes a cylindrical part through which the outer dome is inserted. The liquefied gas transport vessel also has: a dome flange disposed on the movable part of the outer dome and extending above the cylindrical part from the movable part; an annular elastic member sandwiched between the cylindrical part of the tank cover and the dome flange; and a plurality of displacement measuring mechanisms arranged on the circumference surrounding the outer dome for measuring the displacement of the movable part of the outer dome relative to the tank cover.

[0016] According to the above structure, for example, during the heat shrinking of the inner tank, the elastic member sandwiched between the cylindrical part of the can cover and the dome flange is flattened, and the movable parts of the inner and outer tank domes are displaced downwards. Then, the displacement of the movable part of the outer tank dome is measured as the relative displacement with respect to the can cover by multiple displacement measuring mechanisms. Moreover, multiple displacement measuring mechanisms are arranged on the circumference surrounding the outer tank dome. Therefore, it is possible to confirm whether the relative displacement of the movable part of the outer tank dome with respect to the can cover meets the design value during the heat shrinking of the inner tank, thereby confirming whether there are any defects in the support members between the outer and inner tank main bodies.

[0017] Invention Effects

[0018] According to the present invention, a liquefied gas transport vessel is provided that is capable of confirming whether the support member between the outer tank body and the inner tank body of the double-shell tank is malfunctioning. Attached Figure Description

[0019] Figure 1 This is a side view of a liquefied gas transport vessel according to one embodiment of the present invention.

[0020] Figure 2 yes Figure 1 A cross-sectional view of a portion of the liquefied gas transport vessel shown.

[0021] Figure 3 It is along Figure 2 A cross-sectional view along line III-III.

[0022] Figure 4 It is along Figure 3 A cross-sectional view along line IV-IV.

[0023] Figure 5 It is an external view of the cylindrical part of the can's dome and the outer groove dome.

[0024] Figure 6 These are cross-sectional views of the inner and outer groove domes in the modified example. Detailed Implementation

[0025] Figure 1 This invention illustrates a liquefied gas transport vessel 1 according to one embodiment of the present invention. The liquefied gas transport vessel 1 includes a hull 2 ​​and two double-shell tanks 3 mounted on the hull 2. In this embodiment, the double-shell tanks 3 are arranged along the length of the vessel, but if the vessel is wide, they can also be arranged along the width. Furthermore, the number of double-shell tanks 3 mounted on the hull 2 ​​can be one or more.

[0026] The two double-shelled tanks have the same structure as each other. For example... Figure 2 As shown, each double-shell tank 3 includes an inner tank 4 and an outer tank 5 that surrounds the inner tank 4. A heat insulation layer 31 is formed between the inner tank 4 and the outer tank 5.

[0027] In this embodiment, the heat insulation layer 31 is a vacuum layer. For example, the outer surface of the inner groove 4 may be covered with a vacuum heat insulation material (e.g., a multilayer sheet formed by alternating layers of radiation shielding film and spacers) within the vacuum space between the inner groove 4 and the outer groove 5, creating a gap where no object exists between the vacuum heat insulation material and the inner surface of the outer groove 5. Alternatively, pearlite, which is a granular heat insulation material, may be filled into the vacuum space.

[0028] In this embodiment, each double-shell container 3 is a cylindrical shape that is longer in the horizontal direction. However, the shape of the double-shell container 3 can be spherical, cubic, or cuboid.

[0029] Specifically, the inner tank 4 includes an inner tank body 41 for storing liquefied gas and an inner tank dome 42 protruding upward from the inner tank body 41. The outer tank 5 includes an outer tank body 51 surrounding the inner tank body 41 and an outer tank dome 52 surrounding at least the lower part of the inner tank dome 42. In this embodiment, the outer tank dome 52 surrounds the entire inner tank dome 42.

[0030] Liquefied gases include, for example, liquefied petroleum gas (LPG, approximately -45°C), liquefied ethylene gas (LEG, approximately -100°C), liquefied natural gas (LNG, approximately -160°C), liquefied oxygen (LO2, approximately -180°C), liquefied hydrogen (LH2, approximately -250°C), and liquefied helium (LHe, approximately -270°C).

[0031] The inner groove main body 41 includes a main body extending horizontally in a certain cross-sectional shape and a hemispherical closing portion that closes the openings on both sides of the main body. However, the closing portion can be a plane perpendicular to the main body or it can be disc-shaped. The inner groove dome 42 protrudes upward from the main body of the inner groove main body 41. In this embodiment, the protruding direction of the inner groove dome 42 is parallel to the vertical direction, but it can also be slightly inclined relative to the vertical direction.

[0032] The outer groove main body 51 has a shape that is an enlargement of the inner groove main body 41. That is, the outer groove main body 51 includes: a main body that extends horizontally in a certain cross-sectional shape and has a diameter larger than that of the inner groove main body 41; and a hemispherical closing portion that closes the openings on both sides of the main body. The outer groove dome 52 also has a shape that is an enlargement of the inner groove dome 42. Alternatively, the outer groove main body 51 may not have the shape that is an enlargement of the inner groove main body 41, and the outer groove dome 52 may not have the shape that is an enlargement of the inner groove dome 42.

[0033] The inner dome 42 is used to collect various piping such as cryogenic fluid transfer piping, electrical piping, etc. 11 (refer to) Figure 3 ,exist Figure 3 Only one pipe is shown as a representative part in the diagram, and it is penetrated by these pipes 11. In this embodiment, the outer groove dome 52 surrounds the entire inner groove dome 42, so the outer groove dome 52 is also penetrated by the pipes 11.

[0034] The hull 2 ​​has two upward-opening cargo holds 21. The cargo holds 21 are arranged along the length of the ship and are separated from each other by a bulkhead 22. Moreover, a double-hulled tank 3 is arranged inside each cargo hold 21.

[0035] Inside each cargo hold 21, a pair of saddles 23, separated from each other along the length of the ship, are provided. The saddles 23 support the outer main body 51 of the outer trough 5 of the double-shell tank 3. In addition, a pair of support members 32 are provided between the inner trough 4 and the outer trough 5 of the double-shell tank 3 to support the inner trough main body 41 from below. In this embodiment, the support members 32 are provided at the same position as the saddles 23, but the support members 32 may also be provided at a different position than the saddles 23.

[0036] Furthermore, the number and shape of the support members 32 can be appropriately changed according to the shape of the double-shell tank 3. For example, if the double-shell tank 3 is spherical, only one support member that appears to be cross-shaped (i.e., the shape of two intersecting arcs) can be provided between the outer tank body 51 and the inner tank body 41.

[0037] A can cover 7 is disposed above each double-shell tank 3. Each can cover 7 covers the corresponding double-shell tank 3 from above, forming a holding space 70 that, together with the corresponding cargo compartment 21, encloses the double-shell tank 3. The outer main body 51 of the aforementioned outer channel 5 is located below the can cover 7, and the outer channel dome 52 penetrates through the can cover 7.

[0038] The holding space 70 is filled with an inert gas. Nitrogen, argon, or similar gases can be used as the inert gas filling the holding space 70. The inert gas serves to prevent negative pressure formation in the holding space 70 and condensation on the surface of the double-shell tank 3. In particular, when the cryogenic fluid stored in the inner tank body 41 is liquefied hydrogen, the inert gas filling the holding space 70 also serves to prevent the formation of liquefied oxygen around the double-shell tank 3.

[0039] However, the holding space 70 may also be filled with a gas other than an inert gas (e.g., dry air). Alternatively, the holding space 70 may be left unfilled, and the gas within the holding space 70 may be ordinary air.

[0040] Next, refer to Figures 3 to 5 The construction of the inner groove dome 42, the outer groove dome 52, and their surrounding structures is described in detail. Furthermore, the centerline 50 of the outer groove dome 52 coincides with the centerline 40 of the inner groove dome 42.

[0041] The inner groove dome 42 includes a tubular peripheral wall 43 that rises from the inner groove main body 41 and a top wall 44 that closes the upper opening of the peripheral wall 43. Similarly, the outer groove dome 52 includes a tubular peripheral wall 53 that rises from the outer groove main body 51 and a top wall 54 that closes the upper opening of the peripheral wall 53.

[0042] In the illustration, the aforementioned pipe 11 passes through the top wall 44 of the inner groove dome 42 and the top wall 54 of the outer groove dome 52. However, the pipe 11 can also be bent 90 degrees inside the inner groove dome 42 and pass through the peripheral wall 43 of the inner groove dome 42 and the peripheral wall 53 of the outer groove dome 52.

[0043] A bellows 55, which undulates vertically, is assembled on the peripheral wall 53 of the outer dome 52. The bellows 55 divides the outer dome 52 into a fixed part 52A on the lower side and a movable part 52B on the upper side. The movable part 52B is the part through which the piping 11 passes.

[0044] The movable portion 52B of the inner groove dome 42 and the outer groove dome 52 is connected by an annular connecting member 6. In this embodiment, the connecting member 6 includes: an inner ring 61 that protrudes radially outward from the peripheral wall 43 of the inner groove dome 42; an outer ring 63 located below the inner ring 61 and protruding radially inward from the peripheral wall 53 of the outer groove dome 52; and a cylindrical partition wall 62 that connects the outer periphery of the inner ring 61 to the inner periphery of the outer ring 63.

[0045] However, the structure of the connecting component 6 can be modified appropriately. For example, the connecting component 6 can also be a cylindrical component sandwiched between the top wall 44 of the inner groove dome 42 and the top wall 54 of the outer groove dome 52.

[0046] The can cover 7 includes: a top 71, which is opposed to the bottom of the cargo compartment 21 through the double-shell can 3; and a cylindrical portion 72, which is internally inserted through the outer groove dome 52 and protrudes upward from the top 71.

[0047] A dome flange 56 is provided on the movable part 52B of the outer dome 52, which protrudes radially outward from the peripheral wall 53. The dome flange 56 extends from the movable part 52B toward the top of the cylindrical part 72 of the can cover 7.

[0048] An annular elastic member 8 is sandwiched between the cylindrical portion 72 and the dome flange 56 of the can cover 7. The elastic member 8 seals the space between the cylindrical portion 72 and the dome flange 56 of the can cover 7 and is capable of significant elastic deformation in the vertical direction. For example, expandable rubber can be used as the elastic member 8.

[0049] Multiple displacement measuring mechanisms 9 are arranged on the circumference surrounding the outer groove dome 52 (the circumference centered on the center line 50 of the outer groove dome 52). These displacement measuring mechanisms 9 are used to measure the displacement of the movable part 52B of the outer groove dome 52 relative to the can cover 7.

[0050] In this embodiment, the four displacement measuring mechanisms 9 are arranged at 90-degree intervals. However, the number of displacement measuring mechanisms 9 can be two, three, or even five or more.

[0051] Furthermore, in this embodiment, the displacement measuring mechanism 9 is disposed around the cylindrical portion 72 of the tank cover 7. The displacement measuring mechanism 9 is disposed on the dome flange 56 in such a way that it moves together with the movable portion 52B of the outer groove dome 52. However, the displacement measuring mechanism 9 may also be disposed on the cylindrical portion 72 of the tank cover 7 in such a way that it does not move even if the movable portion 52B of the outer groove dome 52 moves.

[0052] In this embodiment, each displacement measuring mechanism 9 is a scale with graduations not only along the vertical direction but also along the horizontal direction. However, it is also possible to have graduations only along the vertical direction on the scale. In addition, various displacement measuring mechanisms other than scales can be used as the displacement measuring mechanism 9. For example, the displacement measuring mechanism 9 can also be a contact displacement gauge, a non-contact displacement gauge, or rubber with a grid-like mesh.

[0053] More specifically, two of the four displacement measuring mechanisms 9 are configured to be connected to a plane that passes through the centerline 50 of the outer groove dome 52 and is parallel to the ship's length direction, while the remaining two are configured to be connected to a plane that passes through the centerline 50 of the outer groove dome 52 and is parallel to the ship's width direction.

[0054] On the other hand, although not shown in the figure, reference marks are formed on the outer peripheral surface of the cylindrical portion 72 of the canister 7 by means of engraving or the like, on a plane parallel to the length direction of the ship and on a plane parallel to the width direction, passing through the center line 50 of the outer groove dome 52. The position of the reference marks is measured using the aforementioned ruler.

[0055] In the LPG transport vessel 1 with the structure described above, for example, during the heat shrinking of the inner tank 4, the elastic member 8 sandwiched between the cylindrical portion 72 of the tank cover 7 and the dome flange 56 is flattened, and the movable portion 52B of the inner tank dome 42 and the outer tank dome 52 is displaced downward. Then, the displacement of the movable portion 52B of the outer tank dome 52 is measured by the displacement measuring mechanism 9 as the relative displacement relative to the tank cover 7. Moreover, the displacement measuring mechanism 9 is arranged on the circumference surrounding the outer tank dome 52. Therefore, it is possible to confirm whether the relative displacement of the movable portion 52B of the outer tank dome 52 relative to the tank cover 7 meets the design value during the heat shrinking of the inner tank 4, thereby confirming whether the support member 32 between the outer tank main body 51 and the inner tank main body 41 is malfunctioning.

[0056] Furthermore, in this embodiment, since the four displacement measuring mechanisms 9 are arranged at 90-degree intervals, the inclination of the movable part 52B of the outer groove dome 52 relative to the can cover 7 can also be confirmed.

[0057] Furthermore, in this embodiment, the displacement measuring mechanism 9 uses a scale with graduations formed along the vertical and horizontal directions, thus enabling instantaneous measurement of the displacement in the vertical and horizontal directions at the measuring location.

[0058] (Modified Example)

[0059] This invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of this invention.

[0060] For example, such as Figure 6 As shown, the outer groove dome 52 may only surround the lower part of the inner groove dome 42. In this case, the outer groove dome 52 is only composed of the peripheral wall 53 on which the bellows 55 is assembled, and the connecting member 6 may be an annular plate that connects the upper end of the peripheral wall 53 to the peripheral wall 43 of the inner groove dome 42. Additionally, as... Figure 6 As shown, in the case where the outer groove dome 52 only surrounds the lower part of the inner groove dome 42, although the figure is omitted, a heat insulation structure (e.g., multiple partition plates arranged vertically) is provided inside the inner groove dome 42.

[0061] Furthermore, the insulation layer 31 does not necessarily need to be a vacuum layer; the space between the inner groove 4 and the outer groove 5 can also be filled with a gas with low thermal conductivity, such as argon. However, if the insulation layer 31 is a vacuum layer, its thermal insulation performance can be improved.

[0062] Alternatively, the displacement measuring mechanism 9 can be disposed inside the cylindrical portion 72 of the canister 7 and around the peripheral wall 53 of the outer groove dome 52 or around the bellows 55. However, in this case, the operator needs to enter the holding space 70 to visually confirm the displacement measuring mechanism 9. Moreover, this requires replacing the inert gas in the holding space 70 with air. In contrast, if the displacement measuring mechanism 9 is disposed around the cylindrical portion 72 of the canister 7 as described in the above embodiment, the operator can visually confirm the displacement measuring mechanism 9 from the outside of the holding space 70, and therefore it is not necessary to replace the inert gas in the holding space 70 with air.

[0063] (Summarize)

[0064] The liquefied gas transport vessel of the present invention is characterized in that it comprises: a hull; a double-shell tank mounted on the hull; and a tank cover covering the double-shell tank, the double-shell tank comprising: an inner tank including an inner tank body portion for storing liquefied gas and an inner tank dome projecting upward from the inner tank body portion; an outer tank including an outer tank body portion surrounding the inner tank body portion and an outer tank dome surrounding at least the lower portion of the inner tank dome, a heat insulation layer being formed between the outer tank and the inner tank; a support member disposed between the outer tank body portion and the inner tank body portion, supporting the inner tank body portion from below; and a bellows, which divides the outer tank dome into sections. The lower fixed part and the upper movable part are assembled to the outer groove dome; and a connecting member connects the inner groove dome to the movable part of the outer groove dome. The tank cover includes a cylindrical part through which the outer groove dome is inserted. The liquefied gas transport vessel also has: a dome flange disposed on the movable part of the outer groove dome and extending above the cylindrical part from the movable part; an annular elastic member sandwiched between the cylindrical part of the tank cover and the dome flange; and a plurality of displacement measuring mechanisms arranged on the circumference surrounding the outer groove dome for measuring the displacement of the movable part of the outer groove dome relative to the tank cover.

[0065] According to the above structure, for example, during the heat shrinking of the inner tank, the elastic member sandwiched between the cylindrical part of the can cover and the dome flange is flattened, and the movable parts of the inner and outer tank domes are displaced downwards. Then, the displacement of the movable part of the outer tank dome is measured as the relative displacement with respect to the can cover by multiple displacement measuring mechanisms. Moreover, multiple displacement measuring mechanisms are arranged on the circumference surrounding the outer tank dome. Therefore, it is possible to confirm whether the relative displacement of the movable part of the outer tank dome with respect to the can cover meets the design value during the heat shrinking of the inner tank, thereby confirming whether there are any defects in the support members between the outer and inner tank main bodies.

[0066] Alternatively, the aforementioned multiple displacement measuring mechanisms may include four displacement measuring mechanisms arranged at 90-degree intervals. Based on this structure, the inclination of the movable part of the outer tank dome relative to the tank cover can also be determined.

[0067] Alternatively, the aforementioned multiple displacement measuring mechanisms can be configured as graduated scales along the vertical direction. Based on this structure, the amount of displacement in the vertical direction at the measurement location can be instantly determined.

[0068] Alternatively, graduations can be formed along the horizontal direction on the aforementioned scale. Based on this structure, the horizontal displacement at the measurement location can be instantly determined.

[0069] For example, the aforementioned multiple displacement measuring mechanisms can also be disposed on the aforementioned dome flange.

[0070] Alternatively, the hull may have a cargo hold containing the aforementioned double-shell tank. The tank cover, together with the cargo hold, forms a retaining space enclosing the double-shell tank. This retaining space is filled with inert gas, and the plurality of displacement measuring mechanisms are arranged around the cylindrical portion of the tank cover. With this structure, since the displacement measuring mechanisms can be visually confirmed from the outside of the retaining space, it is not necessary to replace the inert gas in the retaining space with air.

[0071] Alternatively, the aforementioned insulation layer could be a vacuum layer. This structure improves the insulation performance of the insulation layer.

Claims

1. A liquefied gas transport vessel, wherein, This liquefied gas transport vessel has the following features: hull; Double-hulled tanks, mounted on the hull; and A can cover that covers the double-shell can. The double-shell tank comprises: The inner tank includes an inner tank body for storing liquefied gas and an inner tank dome protruding upward from the inner tank body; An outer groove includes an outer groove main body that surrounds the inner groove main body and an outer groove dome that surrounds at least the lower part of the inner groove dome, and a heat insulation layer is formed between the outer groove and the inner groove. A support component is disposed between the outer groove main body and the inner groove main body, and supports the inner groove main body from below; A bellows, which is assembled to the outer groove dome in such a way that the outer groove dome is divided into a fixed part on the lower side and a movable part on the upper side; as well as A connecting component connects the movable part of the outer groove dome to the inner groove dome in such a way that the movable part of the outer groove dome and the inner groove dome move together. The can cover includes a cylindrical portion through which the outer groove dome is inserted. This liquefied gas transport vessel also features: A dome flange is provided on the movable part of the outer groove dome and extends from the movable part toward the top of the cylindrical part; An annular elastic member is sandwiched between the cylindrical portion of the canister and the dome flange; and Multiple displacement measuring mechanisms are arranged on the circumference surrounding the outer groove dome for measuring the displacement of the movable part of the outer groove dome relative to the can cover.

2. The liquefied gas transport vessel according to claim 1, wherein, The plurality of displacement measuring mechanisms includes four displacement measuring mechanisms arranged at 90-degree intervals.

3. The liquefied gas transport vessel according to claim 1 or 2, wherein, The plurality of displacement measuring mechanisms are scales with graduations formed along the vertical direction.

4. The liquefied gas transport vessel according to claim 3, wherein, The scale also has graduations along the horizontal direction.

5. The liquefied gas transport vessel according to claim 1 or 2, wherein, The plurality of displacement measuring mechanisms are disposed on the dome flange.

6. The liquefied gas transport vessel according to claim 1 or 2, wherein, The hull has a cargo hold, within which the double-hulled tank is installed. The can cover, together with the cargo compartment, forms a retaining space that encloses the double-shell tank. The retaining space is filled with an inert gas. The plurality of displacement measuring mechanisms are arranged around the cylindrical portion of the can cover.

7. The liquefied gas transport vessel according to claim 1 or 2, wherein, The insulation layer is a vacuum layer.

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