JP5222061B2 - Structure of joints provided between multiple thermal insulation panels arranged on the outer wall of a cryogenic tank - Google Patents

Description

  The invention which concerns on a claim is related with the structure of the joint part provided between the some heat insulation panels arrange | positioned on the outer wall of low temperature tanks, such as a LNG (liquefied natural gas) tank.

  A so-called low-temperature tank that contains a low-temperature substance such as LNG inside has a widely adopted heat-insulating structure in which a plurality of heat-insulating panels are arranged in a planar shape covering the outer wall and a joint material is provided between each heat-insulating panel. ing. For example, as shown in FIG. 3C, a large number of rectangular parallelepiped heat insulation panels 11 are spread on the outer wall 1 a of the low temperature tank 1, and the joint material 12 is sandwiched between adjacent heat insulation panels 11. By inserting joint material and eliminating the gap between the heat insulation panels, the possibility of convection of gas in the gap is reduced and the heat insulation performance is secured. In order to make it easy to adjust the installation position of the insulation panel during construction, and to realize the dimensional change of the insulation panel due to temperature changes when the tank is used, some joint materials such as glass wool are flexible. It is used.

About the heat insulation structure above, in recent years, in order to improve heat insulation performance, the thickness of a heat insulation panel etc. tends to increase. As the thickness of the thermal insulation panel increases, the thickness of the joint material increases accordingly. About the heat insulation panel without gas permeability, since gas does not flow in the inside, there is no possibility of convection generation. However, the flexible joint material as described above usually has high gas permeability, so even if the joint material is sandwiched between the heat insulating panels in a compacted state, gas can flow inside the joint material. That is, convection may occur.
In particular, in a joint material that has become extremely thick and has an increased volume, the fluidity of the gas is extremely increased, and as a result, convection inside the joint material can no longer be ignored. When convection occurs, the heat input to the low-temperature tank increases due to convection heat transfer, so that there is a possibility that the expected heat insulation performance cannot be obtained even though the thickness of the heat insulation panel and the like is increased.

Patent Document 1 below proposes to use a light-weight organic foam obtained by reacting an organic polyol or an isocyanate component as a joint material that can be used for heat insulation of a low-temperature tank or the like. These materials have gas barrier properties as well as flexibility, and are preferable in terms of both preventing gaps between the heat insulating panels and preventing convection inside the joint material.
Patent Document 2 describes a heat insulating plate having a structure in which a bag of an aluminum vapor-deposited film enclosing gas is inserted into a double wall structure made of synthetic resin. A multilayer pleat for preventing convection is formed inside the bag.
JP 2000-110988 A Japanese Patent Laid-Open No. 7-103388

  Patent Document 1 proposes that a specific joint material having flexibility and gas barrier properties is preferable in terms of both preventing gaps and preventing convection. However, the types of lightweight organic foams that have gas barrier properties as well as flexibility are limited, and the range of selection is extremely limited. This is because materials having gas barrier properties are generally poor in flexibility. Moreover, even if the material has flexibility, if the resilience is high, the construction work of the heat insulation panel cannot be easily performed. If it is not a so-called low-resilience joint material that recovers over time after compression deformation, when adjusting the mounting position of the heat insulation panel, it will resist the large repulsive force of the joint material until it is fixed with stud bolts, etc. This is because it must continue to be added to the insulation panel.

  The heat insulating plate described in Patent Document 2 is a double-walled structure in which a gas-filled bag is placed, and since it is not flexible, it can be used between heat insulating panels in a heat insulating structure of a low-temperature tank. Can not. Moreover, although the multilayer pleat for preventing a convection is formed in the bag body, since it does not partition the space inside the bag body, it is considered that the convection cannot be completely prevented.

  The invention according to the claims provides a structure of the joint portion that prevents the occurrence of convection in the joint material even when the thickness of the heat insulation panel or the like is increased, thereby ensuring high heat insulation performance. In particular, it aims to expand the choice of joint materials that can be used, thereby facilitating the construction work of insulation panels.

The structure of the joint part according to the invention is a structure of a joint part provided between a plurality of heat insulating panels arranged on the outer wall of the cryogenic tank, and the joint material is divided into a plurality of sections by a surface orthogonal to the thickness direction of the joint material. The partition material is provided between the divided joint materials. The “thickness” of the joint material is a dimension in the same direction as the thickness of the heat insulating panel, that is, a dimension from the inside to the outside of the tank, and corresponds to a dimension between the low temperature side and the high temperature side.
According to the present invention, it is possible to effectively prevent the occurrence of convection in a joint material while using a joint material having a gas permeability coefficient comparable to that of a conventional joint material.
When the gas permeation coefficient is not limited to a joint material, or a material similar to the conventional one may be used, options for the joint material are greatly expanded. In addition, the joint material can be adopted from the one having flexibility and low repulsion, and the construction work including adjustment of the mounting position of the heat insulating panel can be facilitated. These points are significantly different from the technique of Patent Document 1.

The case where another joint material having a small gas permeability coefficient is used as the partition material is also included. Further, as shown in FIG. 11, the joint material itself may be shaped like a honeycomb structure to be finely divided.
If the joint material is divided by a surface that intersects the thickness direction, and the partition material as described above is provided on the divided surface, even if the joint material is thickened together with the heat insulating panel as described above, the convection in the joint material Is effectively prevented from occurring. This is because if the joint material is divided by the partition material that does not allow gas to permeate, the range in which the gas can move is partitioned in the thickness direction, that is, the heat input direction, and convection is less likely to occur. For this reason, the joint structure having such a convection prevention measure has high heat insulation performance, and when the thickness of the heat insulation panel is increased, the performance is enhanced as expected. Since it is not necessary to use a special joint material having a low gas permeability coefficient, the choice of usable joint materials is wide, and therefore, it is easy to easily perform the construction work of the heat insulation panel.

For each of the joint materials divided into a plurality of sections, it is preferable that the upper limit of the joint material thickness and gas permeability coefficient is set so that the corrected Rayleigh number does not exceed the critical value of convection generation.
The modified Rayleigh number is a dimensionless number determined by the gas permeability coefficient of the material, the dimensions of the material, the temperature difference between the high temperature side and the low temperature side, the body expansion coefficient of the gas inside, the kinematic viscosity coefficient, and the temperature diffusivity. It is said that it is easy to generate convection. The inventors have confirmed that the occurrence of convection can be prevented by determining the size of the division section of the joint material so that the corrected Rayleigh number does not exceed the critical value of convection generation in each section. That is, by using the corrected number of relays as an index, it is possible to minimize the number of divisions and effectively prevent convection from occurring at low cost.

As the joint material, an EPDM (ethylene / propylene / diene monomer) -based semi-continuous foam or polyether-based soft urethane, which is a low-rebound foam, is used. As the partition material, a gas barrier resin, metal foil, It is preferable to use either non-woven fabric or Japanese paper.
EPDM semi-continuous foam or polyether soft urethane, which is a low resilience foam, has flexibility and low resilience, and has a property of restoring over time after being deformed by compression. Therefore, if they are used as joint materials, the gaps between the heat insulation panels can be eliminated appropriately, the installation position of the heat insulation panel can be easily adjusted during construction, and the dimensions of the heat insulation panel accompanying the temperature change when the tank is used There is no hindrance to change.
When a material such as the resin is used as the partitioning material, the gas movement range inside the joint material is partitioned and the occurrence of convection is effectively prevented.

  It is preferable to have an adhesive on one or both sides of the partition material. This is advantageous in joining the sections of the divided joint material. That is, when joint materials are integrated using the adhesiveness of these partition materials, the work of inserting between the heat insulating panels is easy.

It is suitable that the thickness of each joint material divided into a plurality of compartments is thinner than the high temperature side (outside side) as the compartment on the low temperature side (side closer to the tank). Yes. The “thickness” of the section here also means a dimension in the same direction as the thickness of the heat insulating panel, that is, a dimension from the inside to the outside of the tank.
On the low temperature side, the convection tends to be strong due to the high gas density. Therefore, it is preferable to make the thickness of the compartment thinner than the high temperature side as described above so that the effect of preventing convection is enhanced. On the high temperature side, by making each section thicker than the low temperature side and reducing the number of divisions, it is possible to reduce the cost required for joining partition materials.

It is desirable that the joint portion structure is applied to all joint portions provided in the low temperature tank.
In the integrated low-temperature tank, the joint material is connected like a net, so the convection that occurs in one part is also transmitted to the joint material in the other part, forming a general circulation throughout the tank, and heat insulation performance There is a risk of a significant drop. In order to prevent such general circulation convection, the convection prevention measure according to the present invention is preferably applied to all the joint materials provided in the tank.

The structure of the joint part may be applied only to the joint part provided in the vertically lower part of the low-temperature tank.
In order to prevent general circulation convection, it is also effective to apply the convection prevention measure according to the present invention to only some joint materials. For example, the vertical lower part of a low temperature tank tends to be the starting point of general circulation convection, so if convection prevention measures are taken there, the convection of the entire tank will be prevented by treating only some joint materials, and the heat insulation performance will be improved. It is possible to secure. If measures to prevent convection are applied only to some joint materials, it is much more advantageous in terms of cost and construction period than to implement them entirely.
The vertically lower portion of the low-temperature tank has a low-temperature wall surface of the tank main body at a position above the vertical, and the joint material is present with the vertical direction below the thickness direction. For this reason, the force of the upper gas moving downward is strong, and therefore, it tends to be the starting point of convection in general circulation, particularly in a spherical or horizontal cylindrical tank. If a convection prevention measure is applied to the portion that tends to be the starting point in this way, it is possible to effectively prevent convection of the general circulation and to exhibit high heat insulation performance.

The joint portion design method according to the present invention is a joint portion design method provided between a plurality of heat insulating panels arranged on the outer wall of a low-temperature tank, and the corrected Rayleigh number in the joint material does not exceed the critical value of convection generation. Thus, the upper limit of the thickness of the joint material and the gas permeation coefficient is set.
By doing so, it is possible to reliably prevent the occurrence of convection in the joint material. In addition, it is unavoidable to use a joint material having poor flexibility by setting the gas permeability coefficient to be lower than necessary, or to invest excessive cost in the joint material.

Regarding the structure of the joint material, an EPDM semi-continuous foam which is a low resilience foam having a gas permeability coefficient of 2 × 10 ⁻¹⁰ [m ² ] or less (preferably 1 × 10 ⁻¹¹ [m ² ] or less). It is advantageous if a body or polyether-based soft urethane is used.
EPDM semi-continuous foam or polyether soft urethane, which is a low resilience foam, has flexibility and low resilience as described above, and has the property of being restored over time after being deformed by compression. Therefore, using them as joint materials is convenient for eliminating gaps between the heat insulation panels, adjusting the mounting position of the heat insulation panels during construction, and for changing the dimensions of the heat insulation panels without hindrance when using the tank. . The above-mentioned materials having a gas permeability coefficient of 2 × 10 ⁻¹⁰ [m ² ] or less are not particularly rare unless the coefficient is limited to zero, so that an appropriate material can be easily selected.
When the joint material having a small gas permeability coefficient as described above is used, convection at the joint material can be prevented in many cases without any special measures for preventing convection. That is, when the thickness of the joint material and the temperature difference in the thickness direction are not more than a certain level (for example, the thickness is 400 mm and the temperature difference is 230 ° C.), it is possible to prevent convection and to provide high heat insulation without dividing the joint material. Performance can be obtained.

According to the structure of the joint part of the invention, it is possible to prevent the occurrence of convection in the joint material and to ensure high heat insulation performance. In addition, joint materials can be used from a wide range of options, and it is possible to facilitate the installation work of the heat insulation panel.
In general, when the thickness of a heat insulating panel or the like is increased in order to increase the heat insulating performance, convection is likely to occur in the joint portion, and the heat insulating thickness may be further increased to cover it. According to the structure of the invention, the heat insulation thickness can be greatly reduced as compared with the case where convection prevention measures are not taken. Therefore, not only can the material cost be reduced, but also the total weight of the low temperature tank can be reduced, or the capacity of the tank can be increased by that amount.
The joint material is divided into a plurality of sections by a surface orthogonal to the thickness direction of the joint material, and a partition material is provided between the divided joint materials. Therefore, the joint material is limited to a material having a small gas permeability coefficient. No need to use it. And also when making a joint material thick with a heat insulation panel, generation | occurrence | production of the convection in a joint material is prevented effectively, and heat insulation performance can be made high.

If EPDM semi-continuous foam or polyether soft urethane, which is a low-resilience foam having a gas permeability coefficient of 2 × 10 ⁻¹⁰ [m ² ] or less, is used for the joint material, other special convection is used. Even without taking preventive measures, convection in the joint material can be prevented in many cases, and high heat insulation performance can be secured. Since the selection range of the joint material is not particularly narrow, it is advantageous for the construction work of the heat insulation panel.

  The structure of the joint portion may be applied to all joint portions provided in the low-temperature tank, or may be provided only to the joint portion provided in the vertical lower portion of the low-temperature tank. If it is implemented only for a part, the necessary cost can be suppressed or the construction period can be shortened.

  An embodiment according to the invention will be described with reference to the drawings. Each of FIGS. 1A and 1B is a perspective view showing a structure in the vicinity of the joint material 12, and FIG. 2 is a perspective view in the vicinity of the joint material 12 showing another structure. FIG. 3 is a diagram showing the low temperature tank 1 and the structure adopted therein, FIG. 3 (a) is an overall front view of the low temperature tank 1, and FIG. 3 (b) is an enlarged plan view showing a part of the surface of the tank 1. (C) is a cc cross-sectional view in the same (b). 4-10 is explanatory drawing which shows the test done in employ | adopting the structure of FIGS. 1-3, and its result.

  The low temperature tank 1 shown in FIG. 3 is a spherical marine LNG tank. On the outside of the outer wall 1a (FIG. 3C) of the tank body, more than several thousand heat insulating panels 10 are laid. The heat insulating panel 10 has an inner and outer two-layer structure in which an outer layer 21 made of rigid polyurethane foam is formed on an inner layer 11 made of phenol foam. Between the inner layers 11 of the adjacent heat insulating panels 10, a joint material 12 made of soft polyurethane foam is sandwiched, and between the outer layers 21, an injection foam material 22 made of rigid polyurethane foam is filled. A wire mesh 19 exists between the inner layer 11 and the outer layer 21.

  The heat insulating panel 10 and the injected foaming agent 22 do not have gas permeability, but the joint material 12 has gas permeability. The thermal insulation panel 10 is placed along the outer wall 1a of the tank 1 so that it undergoes large heat shrinkage after construction, and the installation position must be adjusted before it is fixed with stud bolts (not shown) during construction. Therefore, the joint material 12 is required to have sufficient flexibility and low resilience.

  When using the joint material 12 having gas permeability, as shown in FIG. 1 (b), depending on the thickness S of the joint material 12 and the temperature difference between the low temperature side and the high temperature side, the gas is generated inside the joint material 12. Or air may cause convection and reduce the heat insulation performance. Therefore, in the low temperature tank 1 shown in FIG. 3, only the joint portion shown in FIG. 1 (a) is provided in all joint materials 12 or only in the joint portion provided in the vertical lower portion of the low temperature tank which is likely to be the starting point of general circulation convection. The structure of is going to be applied. That is, the joint material 12 is divided into a plurality of sections (three sections of S1, S2, and S3 in the illustrated example) by a surface that intersects the thickness direction, and the gas permeability coefficient is covered so that the entire surface is covered without omission. Is provided with a partition member 13 having zero or very small, that is, a gas barrier property. By doing so, it is possible to prevent convection from occurring inside the joint material 12 while using a material having high gas permeability and excellent flexibility and low resilience as the joint material 12.

Examples of suitable materials for the joint material 12 and the partition material 13 having a low gas permeability include the following.
As joint material 12:
a) EPDM (ethylene / propylene / diene monomer) semi-continuous foam which is a low-rebound foam. For example, OP-131 (Sanka Corporation).
b) Polyether-based soft urethane foam with low resilience. For example, 806EA (Kurabo).
As partition material 13:
1) Polyimide tape (single-sided or double-sided adhesive tape). For example, Kapton (registered trademark, Toray DuPont).
2) Fluororesin tape (single-sided or double-sided adhesive tape). For example, polytetrafluoroethylene or Teflon (registered trademark, DuPont).
3) Other double-sided adhesive tape. For example, non-woven fabric or Japanese paper with an adhesive.
4) The partition material 13 is not a film-like material as described above, but a partition material made of another joint material (for example, the material a) or b) having a gas permeability coefficient smaller than that of the joint material 12. It is also possible to use the material 14 as shown in FIG.

  When a double-sided adhesive tape is used on each divided surface in each section S1, S2... Of the divided joint material 12, all the sections S1, S2. The handling becomes easy.

  The effect of the convection prevention measure of dividing the joint material 12 and providing the partition material 13 (or 14) was confirmed by the test shown in FIG. That is, for the joint material with and without the convection prevention measure, the internal temperature distribution between the low temperature side (−196 ° C.) and the high temperature side (30 ° C.) is measured and compared. did. The results are shown in FIGS. 5 (a) and 5 (b). If there is no convection, the isotherm will be parallel to the low temperature surface, and there will be no temperature difference in height (in the direction of gravity).

The division position of the joint material employed in the example of FIG. 1A is determined using the corrected number of R Rays as an index as follows.
In the case of convection inside a porous body sandwiched between vertical walls having different temperatures as shown in FIG. 6, the following simple calculation formula is established within the range where Darcy's law is established.
Nu = 0.313R ^1/2 (R> Rcr = 10)… (Number of Nusert)
R = (gβΔθs ³ / νa) (k / sL) (corrected number of relays)
g: Gravity acceleration β: Body expansion coefficient ν: Kinematic viscosity coefficient
a: Temperature diffusivity
k ： Gas permeability coefficient (Source: Heat transfer engineering data revised 4th edition (221p), Japan Society of Mechanical Engineers)
The condition where Nu = 1 (R = 10) is the convection generation limit (critical value), and in the calculation, the condition where Nu <1 (R <Rcr = 10) deviates from the possible range of convection.

また、表２にしたがって目地材を区画S1・S2・S3・S4に４分割する場合にも、修正レーレー数Rおよびヌセルト数Nuが上記の臨界値以下となり、対流発生が回避される。この場合、目地材の内部での温度分布は図７のようになる。

For example, a joint material (temperature difference 230 ° C, gas permeability coefficient k = 5 × 10 ^-8 (m ² )) with a height L of 700 mm and a width (thickness) s of 400 mm on a surface perpendicular to the thickness direction Consider the case of dividing into multiple sections. If no division is performed, R = 175.76 and Nu = 4.15, and convection is unavoidable.
When the above joint material is divided into three sections S1, S2, and S3 according to Table 1 (and a partition material is put on each divided surface), the modified Rayleigh number R and the Nusselt number Nu are less than the above critical values, Convection will not occur.

In addition, when the joint material is divided into four sections S1, S2, S3, and S4 according to Table 2, the corrected Rayleigh number R and the Nusselt number Nu are not more than the above critical values, and convection generation is avoided. In this case, the temperature distribution inside the joint material is as shown in FIG.

  When the joint material is divided into a plurality of pieces as shown in Tables 1 and 2, the thickness of each divided section is set so that the low temperature side (side closer to the tank) is thinner than the high temperature side (outside). Yes. This is because the corrected Rayleigh number in each section does not exceed the critical value for convection generation. This is a treatment that matches the tendency that the gas density is high and the convection tends to be strong on the low temperature side.

Even when the joint material is not divided at all, the occurrence of convection can be prevented depending on the thickness of the joint material, the temperature difference in the thickness direction, the gas permeability coefficient of the joint material, and the like.
For example, when calculating the joint material (temperature difference 230 ° C) of 700mm in height and 400mm in width (thickness) and having a small gas permeability coefficient of k = 2 × 10 ^-10 (m ² ),
R = 7.03, Nu = 0.8299
And it is determined that there is no convection. If the material has a gas permeability coefficient smaller than this value, the condition of Nu <1 is secured, so that convection can be prevented. In that case, if the conditions of the joint material are determined, the maximum gas permeation coefficient (critical value) effective for preventing convection can be calculated backward.

In the case where the joint material is arranged horizontally as shown in FIG. 8, the following simple calculation formula is applied.
If the top is cold and the bottom is hot, like the bottom of a spherical tank,
R = (gβΔθL ³ / νa) (k / L ² )
And the critical value is
Rcr = 4π ² = 39.5
It becomes. (Source: Thermophysical Handbook (178p))

For example, when using joint material (temperature difference 230 ° C) with a thickness L of 400mm without dividing it,
R = 307.58
Therefore, the occurrence of convection is inevitable.
Therefore, if such a joint material is divided into five parts L1 to L5 as shown in FIG. 9 and Table 3 and a partition material is inserted, the corrected Rayleigh number R falls below the critical value, and convection is avoided.

For the joint material arranged on the vertical low-temperature surface (tank outer wall surface) as shown in FIG.
Assuming that the temperature difference of the joint material is 200 ° C (-163 ° C to 37 ° C) in the horizontal direction and the length of the joint material between the heat insulation panels (vertical direction) is 900 mm, the gas permeability coefficient k is 5 × 10 ^-8 ( m ² ) when using conventional joint material
The maximum thickness that does not need to be divided is approximately 133 mm.
The maximum thickness that can be divided into two is approximately 300mm.
The recommended ratio when splitting into two is: Low temperature side 3: High temperature side 7
(When the corrected number of Rrays is the same)
It is.
In addition, when the temperature difference of the joint material is 230 ° C (-193 ° C to 37 ° C) in the horizontal direction and the length of the joint material between the heat insulation panels (vertical direction) is 900mm,
The maximum thickness that does not need to be divided is approximately 100 mm.
The maximum thickness that can be divided into two is approximately 200mm.
The recommended ratio when splitting into two is: Low temperature side 23.5: High temperature side 76.5
It becomes.

It is a figure which shows embodiment of invention, and each of FIG. 1 (a), (b) is a perspective view which shows the structure of the joint material 12 vicinity which is the principal part of a heat insulation structure. It is a perspective view of the joint material 12 vicinity shown about the heat insulation structure of a form different from Fig.1 (a). 3A and 3B are views showing the low temperature tank 1 and the heat insulating structure employed therein, in which FIG. 3A is an overall front view of the low temperature tank 1, FIG. 3B is an enlarged plan view showing a part of the surface of the tank 1, and FIG. ) Is a sectional view taken along line cc in FIG. It is explanatory drawing shown about the content of the test which confirms the effect of invention. 5A and 5B are diagrams showing the results of a test for confirming the effect of the invention. It is a conceptual diagram which shows the temperature distribution etc. of a porous body in order to demonstrate the correction | amendment Rayleigh number R. FIG. It is a diagram which shows temperature distribution about the joint material which divided | segmented and put the partition. It is explanatory drawing which shows the joint material arrange | positioned horizontally. It is a diagram which shows temperature distribution about the joint material of the horizontal arrangement | positioning which divided | segmented and put the partition. It is explanatory drawing which shows the joint material arrange | positioned to the perpendicular low-temperature surface. It is explanatory drawing which shows the joint material made into the honeycomb structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low temperature tank 1a Outer wall 10 Thermal insulation panel 11 Inner layer 21 Outer layer 12 Joint material 13 Partition material S1, S2, S3 ... Partition

Claims (9)

A structure of a joint portion provided between a plurality of heat insulating panels arranged on the outer wall of the low-temperature tank, wherein the joint material is divided into a plurality of sections by a surface orthogonal to the thickness direction of the joint material, That a partition material was provided between the joint materials ;
And, for each of the joint materials divided into a plurality of sections, the upper limit of the joint material thickness and gas permeability coefficient is set so that the corrected Rayleigh number does not exceed the critical value of convection generation, Structure of joints A structure of a joint portion provided between a plurality of heat insulating panels arranged on the outer wall of the low-temperature tank, wherein the joint material is divided into a plurality of sections by a surface orthogonal to the thickness direction of the joint material, That a partition material was provided between the joint materials;
And the joint material is EPDM semi-continuous foam or polyether soft urethane, which is a low-resilience foam, and the partition material is any one of resin, metal foil, nonwoven fabric, or Japanese paper having gas barrier properties. Be
Structure of joints characterized by The joint material is an EPDM semi-continuous foam or polyether soft urethane, which is a low-resilience foam, and the partition material is any one of a gas barrier resin, metal foil, nonwoven fabric, or Japanese paper. The joint structure according to claim 1 , The joint structure according to claim 2 or 3 , wherein an adhesive is provided on one or both sides of the partition material.   5. The joint structure according to claim 1, wherein the thickness of each joint material divided into a plurality of sections is thinner at a lower temperature side than at a higher temperature side.   The joint structure according to any one of claims 1 to 5, wherein the joint structure is applied to all joint parts provided in the low-temperature tank.   The structure of the joint part according to any one of claims 1 to 5, wherein the joint part structure is provided only on the joint part provided in a vertically lower part of the low-temperature tank.   A method for designing a joint provided between a plurality of heat insulating panels arranged on the outer wall of a low-temperature tank, wherein the thickness of the joint material is adjusted so that the corrected number of Rayleigh in the joint material does not exceed the critical value for occurrence of convection. And design method of joint part, characterized by setting upper limit of gas permeability coefficient EPDM which is a structure of a joint part provided between a plurality of heat insulating panels arranged on the outer wall of a low-temperature tank, and has a gas repellent coefficient of 2 × 10 ⁻¹⁰ [m ² ] or less in the joint material. Of joint parts characterized by the use of a semi-continuous foam or polyether-based soft urethane

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