Liquefied gas piping unit and assembly method for same

Abstract

A piping unit (1) for transferring liquefied gas comprises: first double piping (3A) that is provided with a first inner pipe (5A) through which liquefied gas passes and a first outer pipe (9A) which covers the first inner pipe (5A) with a vacuum layer (7) therebetween; second double piping (3B) that is provided with a second inner pipe (5B) through which the liquefied gas passes and a second outer pipe (9B) which covers the second inner pipe (5B) with a vacuum layer (7) therebetween, the second inner pipe (5B) being connected to the first inner pipe (5A); a cover pipe (13) that covers a connection part (11) of the first inner pipe (5A) and the second inner pipe (5B) with a vacuum layer (23) therebetween; and a communication path (35) that communicates the vacuum layer (7) of the first double piping (3A), the vacuum layer (7) of the second double piping (3B), and the vacuum layer (7) inside the cover pipe (13).

Description

Liquefied gas piping unit and assembly method thereof Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-028624, filed February 28, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a piping unit for liquefied gas and a method for assembling the same.

[0003] Conventionally, the use of a double-wall vacuum insulated pipe has been proposed as a pipe for transporting liquefied gases such as liquefied natural gas and liquefied hydrogen (see, for example, Patent Document 1). This double wall pipe has a structure in which an inner pipe is covered by an outer pipe with a vacuum insulation layer in between, so that high thermal insulation is obtained and the temperature rise of the low-temperature liquefied gas flowing inside the inner pipe can be effectively suppressed.

[0004] Generally, such double piping is manufactured by dividing the entire piping into multiple blocks, and then connecting these blocks to form a piping unit. By configuring it in this way, a vacuum layer is formed in each block, so if vacuum deterioration occurs after the piping is installed and put into operation, it is easy to identify the cause.

[0005] Furthermore, double piping requires accessories for support and maintaining the gap between the inner and outer pipes, and double piping for liquefied gas requires a high level of vacuum between the inner and outer pipes, making the installation of a piping unit consisting of double piping complicated. Therefore, in the past, the double piping that makes up each block was generally transported to the installation site after assembly, and installation at the installation site was then performed with only simple tasks such as connecting the double piping together. This improves the accuracy and efficiency of the assembly and installation of double piping units, which require advanced skills.

[0006] Japanese Patent Application Laid-Open No. 2022-064652

[0007] However, when re-evacuating a double piping unit that has already been installed in a given facility, depending on the location of the cause of vacuum deterioration, extensive scaffolding installation work may be required, or connecting a vacuum pump may be difficult. Furthermore, when re-evacuating the entire double piping for periodic maintenance, etc., a vacuum pump must be connected to each of the multiple blocks. Furthermore, such facilities contain many double piping units, and the number of vacuum spaces that need to be re-evacuated is extremely large. Therefore, in large-scale double piping, the period for checking vacuum deterioration and re-evacuating the double piping may be long.

[0008] In order to solve the above-mentioned problems, an object of the present disclosure is to improve the efficiency of the re-evacuation work for a double piping unit that is manufactured by dividing it into a plurality of blocks.

[0009] In order to achieve the above object, the piping unit for liquefied gas according to the present disclosure is a piping unit for transporting liquefied gas, comprising: a first double pipe including a first inner pipe through which the liquefied gas passes and a first outer pipe covering the first inner pipe via a vacuum layer; a second double pipe including a second inner pipe through which the liquefied gas passes and a second outer pipe covering the second inner pipe via a vacuum layer, the second inner pipe being connected to the first inner pipe; a cover pipe covering the connection portion between the first inner pipe and the second inner pipe via a vacuum layer; and a communicating passage connecting the vacuum layer of the first double pipe, the vacuum layer of the second double pipe, and the vacuum layer in the cover pipe.

[0010] It should be noted that any combination of at least two elements disclosed in the claims and / or the specification and / or the drawings is included in the present disclosure, and in particular, any combination of two or more of the claims set forth in the claims is included in the present disclosure.

[0011] The present disclosure will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation purposes and should not be used to define the scope of the present disclosure. The scope of the present disclosure is defined by the accompanying claims. In the accompanying drawings, the same part numbers in multiple drawings indicate the same parts.

[0023] FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a liquefied gas piping unit according to one embodiment of the present disclosure.

[0024] FIG. 2 is a flow chart showing an outline of a method for assembling the liquefied gas piping unit of FIG. 1.

[0025] FIG. 3 is a vertical cross-sectional view showing an example of the state of the liquefied gas piping unit in the vacuum breaking step of the assembly method of FIG. 2.

[0026] FIG. 4 is a flow chart showing an outline of a method for assembling the liquefied gas piping unit of FIG. 4.

[0027] FIG. 5 is a diagram explaining a configuration for facilitating on-site re-evacuation of the liquefied gas piping unit according to one embodiment of the present disclosure.

[0028] FIG. 6 is a diagram showing details of section VII of FIG.

[0012] A preferred embodiment of the present disclosure will now be described with reference to the drawings. FIG. 1 shows a liquefied gas piping unit 1 according to one embodiment of the present disclosure. In the following description, this liquefied gas piping unit 1 will be simply referred to as the "piping unit 1." The piping unit 1 is used to transfer liquefied gas. The piping unit 1 includes a plurality of double pipes 3 connected to each other. That is, the piping unit 1 is composed of a plurality of double pipes 3, which are blocks. Each double pipe 3 includes an inner pipe 5 through which liquefied gas passes and an outer pipe 9 that covers the inner pipe 5 via a vacuum layer 7. The piping unit 1 further includes a cover pipe 13 that covers a connection portion 11 between the double pipes 3. In the following description, the vacuum layer 7 formed in the double pipe 3 will be referred to as the "piping vacuum layer 7."

[0013] In this specification, one double pipe 3 of two double pipes 3 connected to each other will be referred to as the "first double pipe 3A," and the other double pipe 3 will be referred to as the "second double pipe 3B." Furthermore, the inner pipe 5 and outer pipe 9 of the first double pipe 3A will be referred to as the "first inner pipe 5A" and the "first outer pipe 9A," respectively, and the inner pipe 5 and outer pipe 9 of the second double pipe 3B will be referred to as the "second inner pipe 5B" and the "second outer pipe 9B," respectively. However, since the first double pipe 3A and the second double pipe 3B may have the same structure, when describing matters common to these double pipes 3, they will simply be referred to as the "double pipe 3," the "inner pipe 5," and the "outer pipe 9."

[0014] The piping unit 1 is used in liquefied gas storage facilities such as liquefied gas storage ships and onshore liquefied gas storage bases. In this specification, the term "liquefied gas storage ship" refers to a ship that has the function of storing liquefied gas. In addition to liquefied gas carriers, liquefied gas storage ships also include, for example, liquefied gas fuel ships and bunkering ships that supply liquefied gas to other ships. However, the liquefied gas storage facility is not limited to ships as long as it has the structure and function to store liquefied gas, and may be, for example, an onshore liquefied gas storage facility or a plant that uses liquefied gas.

[0015] The liquefied gas transported by the piping unit 1 may be, for example, liquefied petroleum gas (LPG, approximately −45°C), liquefied ethylene gas (LEG, approximately −100°C), liquefied natural gas (LNG, approximately −160°C), liquefied hydrogen (LH ２ , about −250° C.), and liquefied helium (LHe, about −270° C.). In this embodiment, liquefied hydrogen is transferred through the piping unit 1.

[0016] The first double pipe 3A and the second double pipe 3B are connected by connecting the first inner pipe 5A of the first double pipe 3A and the second inner pipe 5B of the second double pipe 3B. Specifically, in each double pipe 3, the end of the inner pipe 5 protrudes from the outer pipe 9, and the end of the first inner pipe 5A protruding from the first outer pipe 9A and the end of the second inner pipe 5B protruding from the second outer pipe 9B are connected to each other. In the following description, the end of the first inner pipe 5A protruding from the first outer pipe 9A is referred to as the "first protruding portion 15A," and the end of the second inner pipe 5B protruding from the second outer pipe 9B is referred to as the "second protruding portion 15B." In addition, in this specification, the first protruding portion 15A and the second protruding portion 15B, which are connected to each other, are collectively referred to as the "connection portion 11." In this embodiment, the first protruding portion 15A and the second protruding portion 15B are connected by welding. However, the first protrusion 15A and the second protrusion 15B may be connected in other ways.

[0017] The cover tube 13 covers the connection portion 11 between the first inner tube 5A and the second inner tube 5B. The cover tube 13 covers the connection portion 11 in a hermetically sealed manner. In this embodiment, as shown in the example shown in the figure, the cover tube 13 extends beyond the "connection portion 11" and covers the ends of the first outer tube 9A and the second outer tube 9B. This ensures a heat conduction distance and improves thermal insulation. However, the shape of the cover tube 13 is not limited to the example shown in the figure. For example, the outer diameter of the cover tube 13 may be the same as the outer diameter of the first outer tube 9A and the second outer tube 9B. In this case, for example, a step may be formed at the ends of the first outer tube 9A and the second outer tube 9B to reduce the outer diameter, and the cover tube 13 may be inserted into this step to connect them.

[0018] Each outer pipe 9 is provided with an outer pipe vacuum port 17 for evacuating the space between the outer pipe 9 and the inner pipe 5 to form a piping vacuum layer 7. The outer pipe vacuum port 17 is located in a portion of each outer pipe 9 that is not covered by the cover pipe 13. In this example, the outer pipe vacuum port 17 is formed by an opening 19 that penetrates the pipe wall of the outer pipe 9 and a seal-off valve 21 attached to this opening 19.

[0019] The cover tube 13 is also provided with a cover tube vacuum port 25 for evacuating its internal space to form a vacuum layer 23. In the following description, the vacuum layer 23 formed inside the cover tube 13 will be referred to as the "cover tube vacuum layer 23." In the illustrated example, the cover tube vacuum port 25 is located approximately in the center of the cover tube 13 in the axial direction. However, the location of the cover tube vacuum port 25 is not limited to this example. In this example, the cover tube vacuum port 25 is formed by an opening 27 penetrating the wall of the cover tube 13 and a seal-off valve 29 attached to this opening 27.

[0020] In this embodiment, the cover pipe 13 includes a plurality of divided bodies 31. Specifically, in this example, the cover pipe 13 is formed from two divided bodies 31 that are cut in half along a plane including the axis of the cover pipe 13. Forming the cover pipe 13 from the divided bodies 31 facilitates the assembly work of the piping unit 1, which will be described in detail later. However, it is not essential that the cover pipe 13 be formed from the divided bodies 31, and the cover pipe 13 may be formed as a single pipe body. Furthermore, when the cover pipe 13 is formed from a plurality of divided bodies 31, the manner of division is not limited to the above example.

[0021] The piping unit 1 according to this embodiment includes a communication passage 35 that connects the piping vacuum layer 7 of the first double piping 3A, the piping vacuum layer 7 of the second double piping 3B, and the cover tube vacuum layer 23. Specifically, in this embodiment, the communication passage 35 is formed in the portions of the first outer pipe 9A and the second outer pipe 9B that are covered by the cover pipe 13. More specifically, the communication passage 35 is formed by communication holes 39 formed in the walls of the first outer pipe 9A and the second outer pipe 9B, which can be closed with block plugs 37. As will be described in detail later, each communication hole 39 is closed with a block plug 37 shown by a dashed line in the figure during the assembly of the piping unit 1. However, when the assembly of the piping unit 1 is complete, the block plug 37 is removed and each communication hole 39 is open. Note that instead of being blockable with a block plug, the communication holes 39 may be closed by attaching a vacuum flange.

[0022] Next, a method for assembling the piping unit 1 according to the present embodiment will be described. In the following description, each step may be referred to as "step S-N" (N: integer) as needed, but "N" is a number added for convenience in distinguishing between steps, and does not necessarily represent the chronological relationship between steps unless otherwise specified.

[0023] 2, the assembly method according to this embodiment includes the steps of preparing a required number of double pipes 3, for example, two double pipes 3, connecting the first inner pipe 5A and the second inner pipe 5B, breaking the vacuum in the pipe vacuum layers 7 of the first double pipe 3A and the second double pipe 3B, covering the connection portion 11 with a cover pipe 13, and drawing a vacuum from at least one of the cover pipe 13, the first outer pipe 9A, and the second outer pipe 9B. In the following description, these steps are referred to as the "double pipe preparation step S1," the "inner pipe connection step S2," the "vacuum breaking step S3," the "cover step S4," and the "vacuum drawing step S5," respectively.

[0024] In the double pipe preparation step S1, the inner pipe 5 and the outer pipe 9 are assembled, and then the space between the inner pipe 5 and the outer pipe 9 is evacuated with the communicating passage 35 closed to fabricate the double pipe 3. When assembling the inner pipe 5 and the outer pipe 9, structural components such as a spacer to ensure a gap between the inner pipe 5 and the outer pipe 9, and an expansion / contraction member such as a bellows to absorb the difference in thermal contraction between the inner pipe 5 and the outer pipe 9 may be used as needed. In this example, the communicating passage 35 is closed by inserting a blocking plug 37 into the communicating hole 39. The vacuum is drawn by connecting a vacuum pump to a vacuum port provided in the outer pipe 9. The vacuum layer 7 is formed by drawing the vacuum.

[0025] In the inner pipe connecting step S2, the first inner pipe 5A and the second inner pipe 5B are connected by connecting the first protruding portion 15A of the first inner pipe 5A and the second protruding portion 15B of the second inner pipe 5B. As described above, the first protruding portion 15A and the second protruding portion 15B are connected by welding, for example, but other methods may also be used.

[0026] In the vacuum breaking step S3, the connecting passages 35 of the first double pipe 3A and the second double pipe 3B are opened to break the vacuum in each pipe vacuum layer 7. In this example, as shown in FIG. 3 , the vacuum breaking is performed by attaching an operator 41 to the seal-off valve 21 of the outer pipe vacuum port 17, operating the operator 41 to open the seal-off valve 21, and removing the block plug 37 inserted in the connecting hole 39 of the outer pipe 9. More specifically, the operator 41 opens the seal-off valve 21 and supplies dry gas from a dry gas cylinder connected to the operator 41 to the vacuum layer 7. Once the vacuum layer 7 reaches atmospheric pressure or higher, the block plug 37 is opened. During this operation, it is preferable to continue supplying dry gas at a minute flow rate to prevent moisture from entering. By performing the vacuum breaking procedure in this manner, the block plug 37 can be easily removed and the connecting passage 35 can be opened. Note that the vacuum breaking method is not limited to the above example; for example, it may be performed simply by removing the block plug 37 inserted in the connecting hole 39 of the outer pipe 9.

[0027] In this embodiment, when breaking the vacuum, dry gas is introduced into the piping vacuum layer 7. Specifically, in this example, a dry gas supply source 43 is connected to the operator 41, and then the above-described vacuum breaking operation is performed. In this embodiment, nitrogen gas is used as the dry gas, but the type of dry gas is not limited to this. In addition, in the illustrated example, a dry gas cylinder is used as the dry gas supply source 43, but the dry gas supply source 43 is not limited to this and may be, for example, a balloon filled with dry gas.

[0028] Then, in a covering step S4, the connection portion 11 between the first inner tube 5A and the second inner tube 5B is covered with a cover tube 13. Then, in a vacuuming step S5, a vacuum is drawn from at least one of the cover tube 13, the first outer tube 9A, and the second outer tube 9B. In this embodiment, a vacuum pump is connected to the cover tube vacuum port 25, and a vacuum is drawn from the cover tube 13. In this embodiment, the formation of the communication passage 35 allows vacuuming from only one of the cover tube 13, the first outer tube 9A, and the second outer tube 9B to form vacuum layers in all of the first double pipe 3A, the second double pipe 3B, and the cover tube 13, and to connect these vacuum layers. However, vacuuming may also be performed from either the first outer pipe 9A or the second outer pipe 9B. Alternatively, vacuuming may also be performed from, for example, two of the cover tube 13, the first outer pipe 9A, and the second outer pipe 9B.

[0029] Fig. 4 shows a liquefied gas piping unit 1 according to another embodiment of the present disclosure. In the following explanation, mainly only the differences from the embodiment explained with reference to Figs. 1 to 3 will be explained, and explanation of the configuration common to the embodiment will be omitted.

[0030] In this embodiment, the communication passage 35 is formed by each of the connecting pipes 45 that connect the cover pipe 13 to the portions of the first outer pipe 9A and the second outer pipe 9B that are not covered by the cover pipe 13. In this example, each of the connecting pipes 45 is provided with an on-off valve 47.

[0031] Next, a method for assembling the piping unit 1 according to the other embodiment described above will be described. In the following description, mainly only the differences from the embodiment described with reference to Figures 1 to 3 will be described, and a description of the configuration common to the embodiment will be omitted.

[0032] 5 , the assembly method according to this embodiment includes the steps of preparing a required number of double pipes 3, for example, two double pipes 3, connecting a portion of the cover pipe 13 to the first double pipe 3A and the second double pipe 3B with the connecting pipe 45, connecting the first inner pipe 5A and the second inner pipe 5B, covering the connection portion 11 between the first inner pipe 5A and the second inner pipe 5B with the remaining portion of the cover pipe 13, evacuating the interior space of the cover pipe 13, and opening the connecting pipe 45. In the following description, these steps will be referred to as the "double pipe preparation step S11," "double pipe connection step S12," "inner pipe connection step S13," "cover step S14," "cover pipe evacuation step S15," and "connecting pipe opening step S16," respectively.

[0033] In the double pipe preparation step S11, the inner pipe 5 and the outer pipe 9 are combined, and then the space between the inner pipe 5 and the outer pipe 9 is evacuated to produce the double pipe 3. When combining the inner pipe 5 and the outer pipe 9, structural components such as a spacer to ensure a gap between the inner pipe 5 and the outer pipe 9, and an expansion / contraction-permitting member such as a bellows to absorb the difference in thermal contraction between the inner pipe 5 and the outer pipe 9 may be used as needed.

[0034] In the double pipe connecting step S12, a portion of the cover pipe 13 is connected to the first double pipe 3A and the second double pipe 3B by the connecting pipe 45 in a closed state. In this example, the closed state of the connecting pipe 45 is achieved by closing the on-off valve 47. The "portion of the cover pipe 13" connected in the double pipe connecting step S12 is, for example, one of the divided bodies 31 when the cover pipe 13 is formed from multiple divided bodies 31. Furthermore, the connecting pipe 45 and each of the above pipes are connected by, for example, welding, but other methods may also be used.

[0035] In the inner pipe connecting step S13, the first inner pipe 5A and the second inner pipe 5B are connected by connecting the first protruding portion 15A of the first inner pipe 5A and the second protruding portion 15B of the second inner pipe 5B. As described above, the first protruding portion 15A and the second protruding portion 15B are connected by welding, for example, but other methods may also be used.

[0036] In the covering step S14, the connection portion 11 between the first inner pipe 5A and the second inner pipe 5B is covered with the remaining portion of the cover pipe 13. Here, the "remaining portion of the cover pipe 13" refers to all the divided bodies 31 other than the divided body 31 connected to the connecting pipe 45, for example, when the cover pipe 13 is formed from a plurality of divided bodies 31.

[0037] In the cover tube evacuation step S15, a vacuum pump is connected to the cover tube vacuum port 25 to evacuate the cover tube 13, thereby forming the internal space of the cover tube 13 as a cover tube vacuum layer 23.

[0038] In the connecting pipe opening step S16, the closed connecting pipe 45 is opened. In this example, the connecting pipe 45 is opened by opening the on-off valve 47, and the communication passage 35 is formed, so that all the vacuum layers of the first double pipe 3A, the second double pipe 3B, and the cover pipe 13 can be communicated with each other.

[0039] 2 and 3, the method according to this embodiment shown in Fig. 5 allows the vacuum layers to communicate with each other without breaking the vacuum in the double piping 3. Therefore, there is no risk of moisture entering the piping vacuum layer 7 during the assembly process, and it is possible to omit the step of suppressing the inflow of moisture during vacuum breaking as described above.

[0040] Next, a method for efficiently re-vacuuming the piping unit 1 installed by the above method will be described. Figure 6 is a diagram illustrating a configuration for facilitating re-vacuuming of the piping unit 1 on-site. For simplicity, details of the piping unit 1 and other elements are omitted from the illustration. The re-vacuuming method according to this embodiment is a method for re-vacuuming a plurality of piping units 1, and includes the steps of leading the vacuum layers 7, 23 in the plurality of piping units 1 to a common work area and evacuating the vacuum layers 7, 23 in the piping units 1 using a common vacuum pump P.

[0041] In the example shown in Figure 6, in a liquefied gas storage facility, which is an example of a liquefied gas piping system, multiple piping units 1 are installed in two tiers of piping racks 51, one above the other, which are located higher than the ground level (GL). The arrangement of the multiple piping units 1 is not limited to the example shown in the figure. The multiple piping units 1 on each tier are connected to each other by any of the methods described above with reference to Figure 2 or Figure 5. The number of piping units 1 to be connected can be determined arbitrarily.

[0042] A representative vacuum point is determined for each vacuum space formed by a plurality of interconnected piping units 1. The representative vacuum point may be, for example, the outer pipe vacuum port 17 or the cover pipe vacuum port 25 of the piping unit 1 shown in Fig. 1. Alternatively, the representative vacuum point may be a dedicated vacuum port separately provided on the outer pipe 9 or the cover pipe 13. The representative vacuum point may also be a portion where the vacuum piping 53 is directly connected to the outer pipe 9 or the cover pipe 13 by, for example, welding.

[0043] A vacuuming pipe 53 is connected to the representative vacuuming point. Three vacuuming pipes 53 are shown in FIG. 6 . More specifically, the vacuuming pipes 53 are connected to one upper piping unit 1, one lower piping unit 1, and a piping unit 1 (not shown). As shown in the detailed view of FIG. 7 , the vacuuming pipe 53 connected to the upper piping unit 1 is connected to a cover pipe 13, which serves as the representative vacuuming point. These multiple vacuuming pipes 53 extend to a common work area. In this example, each vacuuming pipe 53 extends to a common work area near the ground level. The term "work area" here refers to an individual site where a vacuum pump is used to perform re-vacuuming of a piping unit 1. The term "common work area" refers to a work area where re-vacuuming of multiple piping units 1 can be performed sequentially or simultaneously without moving the vacuum pump. There may be multiple work areas, and the number of work areas can be determined arbitrarily based on the number and arrangement of piping units, ease of maintenance, and other factors. The location of the work site is not limited to being on the ground, but may be on a walkway or scaffolding within the liquefied gas storage facility.

[0044] The evacuation pipe 53 has an access vacuum port 55 for connecting a vacuum pump P. The access vacuum port 55 is provided with a vacuum valve. The vacuum valve may be, for example, an angle-type vacuum valve, a straight-type vacuum valve, or a seal-off valve. The multiple access vacuum ports 55 are arranged adjacent to each other in a common work area. By sequentially connecting the vacuum pump P to multiple adjacent access vacuum ports 55 in one common work area, it is possible to continuously re-evacuate the multiple vacuum spaces formed by the connected vacuum layers 7, 23. Alternatively, by simultaneously connecting the vacuum pump P to multiple adjacent access vacuum ports 55 in one common work area, it is possible to simultaneously re-evacuate the multiple vacuum spaces formed by the connected vacuum layers 7, 23.

[0045] The access vacuum port 55 does not necessarily have to be located near the ground level, but if it is located in a work area near the ground level, evacuation work can be performed without lifting the vacuum pump onto a framework, piping rack, etc. Therefore, movement of the vacuum pump P is minimized and made easy, and there is no need to provide an access walkway or maintenance deck for maintenance on the piping rack 51, which was previously required, making maintenance easier and improving the safety of the facility. Note that if re-vacuuming can be performed from the representative vacuum point, the evacuation piping 53 and access vacuum port 55 as shown in Figure 6 may be omitted.

[0046] A piping unit 1 for liquefied gas according to a first aspect of the present disclosure is a piping unit 1 for transporting liquefied gas, and comprises: a first double piping 3A including a first inner pipe 5A through which the liquefied gas passes and a first outer pipe 9A that covers the first inner pipe 5A via a vacuum layer; a second double piping 3B including a second inner pipe 5B through which the liquefied gas passes and a second outer pipe 9B that covers the second inner pipe 5B via a vacuum layer, the second inner pipe 5B being connected to the first inner pipe 5A; a cover pipe 13 that covers a connection portion 11 between the first inner pipe 5A and the second inner pipe 5B via a vacuum layer; and a communication passage 35 that communicates the vacuum layer of the first double piping 3A, the vacuum layer of the second double piping 3B, and the vacuum layer in the cover pipe 13.

[0047] According to this configuration, in a piping unit having multiple double pipes 3, the vacuum layers in the connected double pipes and the cover pipe are connected by a communication passage, so that re-evacuation can be performed on any one of the pipes rather than on each pipe individually, thereby improving the efficiency of the re-evacuation work.

[0048] The liquefied gas piping unit 1 according to the second aspect of the present disclosure is the liquefied gas piping unit 1 according to the first aspect, wherein the communication passage 35 is formed in the portion of the first outer pipe 9A and the second outer pipe 9B that is covered by the cover pipe 13. According to this configuration, the efficiency of the re-vacuuming operation is improved with a simple structure.

[0049] The liquefied gas piping unit 1 according to the third aspect of the present disclosure is the liquefied gas piping unit 1 according to the second aspect, wherein the communication passage 35 is formed by a communication hole 39 formed in each pipe wall of the first outer pipe 9A and the second outer pipe 9B, and the communication passage 35 is formed by a communication hole 39 that can be closed by a blocking plug 37. According to this configuration, the communication passage 35 can be blocked by the blocking plug 37 and each double pipe 3 can be evacuated once, so that re-evacuation in the assembly process can be performed via a short vacuum break, thereby improving the efficiency of the assembly work.

[0050] The liquefied gas piping unit 1 according to a fourth aspect of the present disclosure is the liquefied gas piping unit 1 according to the first aspect, wherein the communication passage 35 is formed by a connecting pipe 45 that connects the cover pipe 13 to the portions of the first outer pipe 9A and the second outer pipe 9B that are not covered by the cover pipe 13, and an on-off valve 47 is provided on the connecting pipe 45. With this configuration, there is no need to break the vacuum during the assembly process of the piping unit 1, and it is possible to suppress the intrusion of moisture into the vacuum layer.

[0051] A method for assembling a liquefied gas piping unit 1 according to the first aspect of the present disclosure is a method for assembling a liquefied gas piping unit 1 according to the second or third aspect, comprising: preparing the first double pipe 3A by combining the first inner pipe 5A and the first outer pipe 9A, and evacuating the space between the first inner pipe 5A and the first outer pipe 9A with the communicating passage 35 closed to form the vacuum layer; preparing the second double pipe 3B by combining the second inner pipe 5B and the second outer pipe 9B, and evacuating the space between the second inner pipe 5B and the second outer pipe 9B with the communicating passage 35 closed to form the vacuum layer; connecting the first inner pipe 5A and the second inner pipe 5B; opening the communicating passage 35 to break the vacuum in the vacuum layers of the first double pipe 3A and the second double pipe 3B; covering a connection portion 11 between the first inner pipe 5A and the second inner pipe 5B with the cover pipe 13; drawing a vacuum from at least one of the cover tube 13, the first outer tube 9A and the second outer tube 9B.

[0052] According to this configuration, the connecting passage 35 can be blocked with the blocking plug 37 and each double pipe 3 can be evacuated once, so that re-evacuation can be performed during the assembly process via a short vacuum break, thereby making the assembly work more efficient.

[0053] A method for assembling a liquefied gas piping unit 1 according to a second aspect of the present disclosure is the same as the method according to the first aspect, except that breaking the vacuum includes flowing dry gas into the vacuum layer. With this configuration, flowing dry gas into the vacuum layer can suppress the intrusion of moisture into the vacuum layer.

[0054] A method of assembling a liquefied gas piping unit 1 according to a third aspect of the present disclosure is a method of assembling a liquefied gas piping unit 1 according to a fourth aspect, comprising: preparing the first double pipe 3A by combining the first inner pipe 5A and the first outer pipe 9A and evacuating the space between the first inner pipe 5A and the first outer pipe 9A to form the vacuum layer; preparing the second double pipe 3B by combining the second inner pipe 5B and the second outer pipe 9B and evacuating the space between the second inner pipe 5B and the second outer pipe 9B to form the vacuum layer; connecting a part of the cover pipe 13, the first double pipe 3A, and the second double pipe 3B with the connecting pipe 45 in a closed state; connecting the first inner pipe 5A and the second inner pipe 5B; covering a connection portion 11 between the first inner pipe 5A and the second inner pipe 5B with the remaining part of the cover pipe 13; evacuating the internal space of the cover pipe 13; and opening the connecting pipe 45. According to this configuration, there is no need to break the vacuum in the assembly process of the piping unit 1, and it is possible to suppress the intrusion of moisture into the vacuum layer.

[0055] The method for re-vacuuming a liquefied gas piping unit 1 according to the first aspect of the present disclosure is a method for re-vacuuming a liquefied gas piping unit 1 according to any one of the first to fourth aspects, and includes guiding the vacuum layers in a plurality of the liquefied gas piping units 1 to a common work area and using a common vacuum pump to evacuate the vacuum layers in the liquefied gas piping units 1. According to this configuration, for example, by arranging a plurality of access vacuum ports of piping for re-vacuuming together, the vacuum layers in the plurality of piping units 1 can be accessed in a common work area, and therefore, the plurality of vacuum spaces can be efficiently re-vacuumed without moving the vacuum pump or with minimal movement of the vacuum pump.

[0056] A liquefied gas piping system according to a first aspect of the present disclosure is a liquefied gas piping system including a plurality of liquefied gas piping units 1 according to any one of the first to fourth aspects, and includes a vacuum piping 53 connected to at least one of the liquefied gas piping units 1 and directing the vacuum layers in the plurality of liquefied gas piping units 1 to a common work area, and an access vacuum port 55 provided on the vacuum piping 53 and configured to be connected to a vacuum pump in the common work area. With this configuration, similar to the above-described re-vacuuming method, the vacuum layers in the plurality of piping units 1 can be accessed in the common work area, so that re-vacuuming of the plurality of vacuum spaces can be performed efficiently.

[0057] As described above, the preferred embodiments of the present disclosure have been described with reference to the drawings, but various additions, modifications, and deletions can be made without departing from the spirit of the present disclosure. Therefore, such additions, modifications, and deletions are also included in the scope of the present disclosure.

Claims

1. A piping unit for transporting liquefied gas, comprising: a first double pipe having a first inner pipe through which the liquefied gas passes and a first outer pipe that covers the first inner pipe with a vacuum layer interposed therebetween; a second double pipe having a second inner pipe through which the liquefied gas passes and a second outer pipe that covers the second inner pipe with a vacuum layer interposed therebetween, the second inner pipe being connected to the first inner pipe; a cover pipe that covers the connection between the first inner pipe and the second inner pipe with a vacuum layer interposed therebetween; and a communication passage that communicates the vacuum layer of the first double pipe, the vacuum layer of the second double pipe, and the vacuum layer in the cover pipe.

2. A piping unit for liquefied gas according to claim 1, wherein the communication passage is formed in the portion of the first outer pipe and the second outer pipe that is covered by the cover pipe.

3. A piping unit for liquefied gas according to claim 2, wherein the communication passage is formed by a communication hole formed in the wall of each of the first outer pipe and the second outer pipe, the communication hole being capable of being blocked by a blocking plug.

4. A piping unit for liquefied gas according to claim 1, wherein the communication passage is formed by a connecting pipe that connects the cover pipe to the portions of the first outer pipe and the second outer pipe that are not covered by the cover pipe, and an opening / closing valve is provided on the connecting pipe.

5. A method for assembling a piping unit for liquefied gas as defined in claim 2 or 3, comprising: preparing the first double pipe by combining the first inner pipe and the first outer pipe, and forming the vacuum layer by evacuating the space between the first inner pipe and the first outer pipe with the communicating passage closed; preparing the second double pipe by combining the second inner pipe and the second outer pipe, and forming the vacuum layer by evacuating the space between the second inner pipe and the second outer pipe with the communicating passage closed; connecting the first inner pipe and the second inner pipe; opening the communicating passage to break the vacuum in the vacuum layers of the first double pipe and the second double pipe; covering the connection between the first inner pipe and the second inner pipe with the cover pipe; and drawing a vacuum from at least one of the cover pipe, the first outer pipe, and the second outer pipe.

6. A method for assembling a liquefied gas piping unit according to claim 5, wherein said breaking the vacuum includes causing dry gas to flow into said vacuum layer.

7. A method for assembling a piping unit for liquefied gas as described in claim 4, comprising: preparing the first double pipe by combining the first inner pipe and the first outer pipe and evacuating the space between the first inner pipe and the first outer pipe to form the vacuum layer; preparing the second double pipe by combining the second inner pipe and the second outer pipe and evacuating the space between the second inner pipe and the second outer pipe to form the vacuum layer; connecting a part of the cover pipe, the first double pipe, and the second double pipe with the connecting pipe in a closed state; connecting the first inner pipe and the second inner pipe; covering the connecting portion of the first inner pipe and the second inner pipe with the remaining part of the cover pipe; evacuating the internal space of the cover pipe; and opening the connecting pipe.

8. A method for re-vacuuming a plurality of liquefied gas piping units as described in claim 1, comprising: directing the vacuum layers within the plurality of liquefied gas piping units to a common work area; and evacuating the vacuum layers within the liquefied gas piping units using a common vacuum pump.

9. A liquefied gas piping system comprising a plurality of liquefied gas piping units as described in claim 1, comprising: a vacuum piping connected to at least one of said liquefied gas piping units and guiding the vacuum layers in said plurality of liquefied gas piping units to a common work area; and an access vacuum port provided on said vacuum piping and configured to be connected to a vacuum pump in said common work area.

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