Metallic storage tank and method for inspecting a metallic storage tank

Abstract

The present invention provides a metal storage tank and a method for inspecting the same, which prevents corrosion of a metal storage tank storing a content generating a corrosive gas. The metal storage tank of the present invention is characterized by comprising: a cylindrical side plate (2); a substantially circular ring-shaped reinforcing member (30) provided along an upper portion of an outer peripheral surface (2os) of the side plate (2); a roof plate (3) provided to cover the side plate (2) from above, an outer peripheral edge (3oe) of the roof plate (3) being joined to the top channel (30) in a first joining portion (C1) and the outer peripheral edge (3oe) being located at a position lower than a central portion of the roof plate (3); and a substantially circular ring-shaped closing member (40) provided along an upper portion of an inner peripheral surface (2is) of the side plate (2), an upper end portion (40U) of the closing member (40) being joined to an inner surface (3is) of the roof plate (3) in a second joining portion (C2).

Description

Technical Field

[0001] This invention relates to a metal storage tank for storing contents that generate corrosive gases, and a method for inspecting the metal storage tank.

[0002] This application claims priority to Japanese Patent Application No. 2020-198810, filed on November 30, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] As a metal storage tank for storing contents that generate corrosive gases, a sludge digestion tank is known. This sludge digestion tank is used to digest sludge composed of organic waste, such as sewage sludge from a wastewater treatment plant. As shown in Patent Document 1, the sludge digestion tank includes a tank body and an insulation layer. The tank body includes cylindrical side plates, a roof plate covering the upper part of the side plates, a roof plate support provided on the upper part of the side plates and supporting the roof plate, and a bottom plate disposed at the bottom of the inner side plates. The insulation layer covers the tank body from the outside. Furthermore, although Patent Document 2 does not explicitly describe a sludge digestion tank, it discloses a structure of a storage tank including a roof plate support.

[0004] If the tank body is kept at a suitable temperature while sludge is stored inside the tank body, the sludge is anaerobically decomposed into microorganisms, thus the sludge is digested and treated.

[0005] Patent Document 1: Japanese Patent No. 6259535

[0006] Patent Document 2: Japanese Published Patent No. 5-16157

[0007] During the process of anaerobic decomposition of sludge into microorganisms within the main body of the sludge digestion tank, that is, during the fermentation of sludge into methane, digestion gases such as methane are produced.

[0008] In addition to methane, the digestive gases produced by sludge also contain corrosive hydrogen sulfide gas.

[0009] The sludge digester contains sludge with a large amount of moisture, and is kept at a high temperature to increase microbial activity, resulting in a hot and humid environment. Consequently, water droplets often adhere to the inner surfaces of the roof and side panels of the digester.

[0010] Hydrogen sulfide gas produced by sludge dissolves in such water droplets, which may travel to the inner surface of the roof panel that slopes downwards towards the roof panel support and remain in the gap between the inner surfaces of the roof panel support and the roof panel. In this case, when the roof panel support and the roof panel are formed of metal such as steel, the joint created by welding or other processes between the roof panel and the roof panel support may be corroded from the inside of the tank body, and digestion gas may leak to the outside of the sludge digestion tank. Furthermore, since the joint between the roof panel and the roof panel support is usually welded only from the outside, a structure that is not resistant to corrosion from the inside is formed. In addition, the inner surface of the steel roof panel and the roof panel support are usually coated with anti-corrosion paint, but if the coating deteriorates, as mentioned above, the joint created by welding or other processes between the roof panel and the roof panel support may be corroded from the inside of the tank body, and digestion gas may leak to the outside of the sludge digestion tank. Summary of the Invention

[0011] The present invention was made in this context, and its object is to provide a structure for a metal storage tank that prevents corrosion of a metal storage tank containing contents that generate corrosive gases, and an inspection method that allows easy inspection of such a metal storage tank for any corrosion.

[0012] In order to solve the above problems and achieve this objective, the present invention proposes the following solution.

[0013] The first aspect of the present invention is a metal storage tank, characterized in that it comprises: a cylindrical side plate; a generally annular reinforcing member disposed along the upper part of the outer peripheral surface of the side plate; a roof plate configured to cover the side plate from above, the outer periphery being joined to the reinforcing member in a first joint and the outer periphery being located at a position lower than the center of the roof plate; and a generally annular blocking member disposed along the upper part of the inner peripheral surface of the side plate, the upper end of the blocking member being joined to the inner surface of the roof plate in a second joint.

[0014] According to the first aspect of the invention, when a container containing corrosive gases is stored, water droplets adhering to the inner surface of the roof panel and containing dissolved corrosive gases such as hydrogen sulfide will not remain in the gap between the reinforcing member and the roof panel, but will instead travel to the sealing member and the side plate and fall onto the contents within the storage tank. Therefore, the first joint, which is the junction between the reinforcing member and the roof panel, will not be corroded by corrosive gases from the inside of the storage tank. Thus, digestive gases will not leak from the corroded area to the outside. Furthermore, since the roof panel is supported by the sealing member in addition to the reinforcing member, it can be stably supported.

[0015] The second aspect of the present invention is characterized in that it further includes, in the first aspect: a through hole disposed on the roof panel and communicating with the space surrounded by the roof panel, the reinforcing member, the blocking member and the side panel; a pipe communicating with the through hole and enabling the through hole to open to the outside; and an opening and closing member disposed on the pipe and enabling the pipe to open and close to the outside, wherein the space is an airtight space when the pipe is closed.

[0016] According to a second aspect of the invention, by opening the opening / closing component and opening the through-hole to the outside, injecting compressed gas into the space, thereby closing the opening / closing component and shutting off the through-hole to the outside, the space can be made airtight and under high pressure relative to the outside. Therefore, it is possible to confirm whether there is any leakage of compressed gas from the space.

[0017] The third aspect of the invention is characterized in that, in the second aspect, the lower end of the inner peripheral portion constituting the inner periphery of the reinforcing member is joined to the outer peripheral surface of the side plate in a third joint, and the lower end of the blocking member is joined to the inner peripheral surface of the side plate in a fourth joint, wherein the third joint and the fourth joint are separated along the height direction of the side plate by a distance of about 3 to about 5 times the thickness of the side plate.

[0018] According to a third aspect of the invention, since the third joint and the fourth joint are sufficiently separated, the fourth joint is not affected by the heat of the third joint, and vice versa. Therefore, the strength of the third joint and the fourth joint can be appropriately maintained.

[0019] The fourth aspect of the invention is characterized in that, in any one of the first to third aspects, the inner surface of the roof panel, the inner circumferential surface of the closure member, and the second joint are coated with a corrosion-resistant coating.

[0020] According to the fourth aspect of the invention, corrosion can be prevented on the inner surface of the roof panel, the inner circumferential surface of the closure member, and the second joint.

[0021] The fifth aspect of the invention is characterized in that, in any one of the first to third aspects, the inner surface of the roof panel, the inner peripheral surface of the closure member, and the second joint are provided with a scale lining.

[0022] According to the fifth aspect of the invention, corrosion of the inner surface of the roof panel, the inner circumferential surface of the closure member, and the second joint can be prevented more reliably for a longer period of time.

[0023] The sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, the metal storage tank is a sludge digestion tank.

[0024] According to the sixth aspect of the present invention, the same effect as that according to the first to fifth aspects can be obtained for sludge digestion tanks.

[0025] The seventh aspect of the present invention is a method for inspecting a metal storage tank that stores contents that generate corrosive gases, characterized in that the third aspect includes: a compressed gas injection step, injecting compressed gas into the space; a foaming liquid coating step, coating the first joint, the second joint, the third joint, and the fourth joint with foaming liquid; and an observation step, observing whether the coated foaming liquid has foamed.

[0026] According to the seventh aspect of the present invention, it is possible to easily visually inspect metal storage tanks containing corrosive gases for corrosion. Furthermore, during the inspection of welded joints in the manufacture of the metal storage tank, it is also possible to easily visually inspect for any defects in the welds. In particular, since compressed gas at a pressure much higher than atmospheric pressure is injected, it is also possible to detect corrosion sites caused by gas leakage from the space that would be unknown at atmospheric pressure.

[0027] The eighth aspect of the present invention is characterized in that, in the seventh aspect, the pressure of the compressed gas is in the range of about 3.0 kPaG to about 5.0 kPaG.

[0028] According to the eighth aspect of the invention, since compressed gas with a pressure much higher than atmospheric pressure but not exceeding the design pressure of the roof panel is injected, it is possible to properly check for foaming. In particular, since compressed gas with a pressure much higher than atmospheric pressure is injected, it is also possible to detect corrosion sites caused by gas leaking from the space that would not be known at atmospheric pressure.

[0029] According to the present invention, corrosion of metal storage tanks containing contents that generate corrosive gases can be prevented, and corrosion of such metal storage tanks can be easily inspected. Attached Figure Description

[0030] Figure 1 This is a partial cross-sectional view illustrating one embodiment of the present invention.

[0031] Figure 2 yes Figure 1 An enlarged sectional view of the V section. Detailed Implementation

[0032] Below, refer to Figure 1 and Figure 2 This embodiment describes the metal storage tank 1 involved in the invention.

[0033] Figure 1This is a partial cross-sectional view of the metal storage tank (sludge digestion tank) 1 of this embodiment. Figure 2 yes Figure 1 The enlarged cross-sectional view of the V portion shows the vicinity of the outer periphery 3oe of the roof panel 3. Furthermore, in this embodiment, the case of a metal storage tank 1 being a sludge digestion tank is described as an example; however, as will be described later, the metal storage tank 1 is not limited to a sludge digestion tank.

[0034] The metal storage tank 1 comprises: a cylindrical side plate 2 centered on a centerline O perpendicular to the ground G; a generally annular top channel (reinforcing member) 30 disposed along the upper part of the outer peripheral surface 2os of the side plate 2; a roof plate 3, configured to cover the side plate 2 from above, the outer peripheral edge 3oe of the roof plate 3 being joined to the top channel 30 in a first joint C1 and the outer peripheral edge 3oe being located lower than the center of the roof plate 3; a generally annular blocking member 40 disposed along the upper part of the inner peripheral surface 2is of the side plate 2, the upper end 40U of the blocking member 40 being joined to the inner surface 3is of the roof plate 3 in a second joint C2; and a bottom plate 4 disposed to block the bottom of the side plate 2. These side plates 2, top channel 30, roof plate 3, blocking member 40, and bottom plate 4 are made of metal, using materials such as SS400 steel or stainless steel. The metal storage tank 1 is mounted on a base portion 13 disposed on the ground G. Here, "roughly circular" is not limited to a strict circular shape, but rather refers to a range that can be roughly considered as circular, such as an elliptical or polygonal circular shape.

[0035] The outer side of the side panel 2 is covered with polystyrene foam 20, and the outer side of the polystyrene foam 20 is further covered by the thermal insulation outer panel 5. Along the outermost edge of the side panel 2, i.e. the surface of the thermal insulation outer panel 5, a circumferential staircase 6 is spirally arranged from the ground G toward the roof panel 3.

[0036] The roof panel 3 is a cross-sectional roof with a center on the centerline O of the side panel 2 and an outer periphery 3oe located lower than the center. Although the roof panel 3 shown in the figure is formed as a convex spherical dome, it could also be conical, for example. A rotary drive device 10 is mounted at the center of the roof panel 3, and a rotary shaft 11 extends from the rotary drive device 10 into the metal storage tank 1 along the centerline O. The rotary shaft 11 is suspended at a distance from the bottom plate 4. On this rotary shaft 11, a plurality of stirring blades 12 are spaced apart in the direction of the centerline O. The rotary shaft 11 and the stirring blades 12 are rotated by the rotary drive device 10, thereby forming a downward flow around the centerline O of the metal storage tank 1 and an upward flow on the inner peripheral surface 2is of the side panel 2 in the sludge W held in the metal storage tank 1.

[0037] On the roof panel 3, a central roof staircase 8 is provided on the side closer to the outer periphery of the roof panel 3 than the rotary drive device 10. The central roof staircase 8 extends radially inward from the outer periphery 3oe of the roof panel 3 toward the center of the roof panel 3 to the metal storage tank 1. Furthermore, a central roof corridor 7 is provided along the circumference of the roof panel 3 from the outer periphery end of the central roof staircase 8. The outer side of the roof panel 3 is covered with polyurethane foam 100.

[0038] The blocking component 40 is a component formed by connecting the short sides of multiple generally rectangular flat steel bars to each other to create a generally circular shape. As an example, the short sides of flat steel bars with a length of approximately 100 mm, a long side length of approximately 2000 mm, and a thickness of approximately 6 mm are connected to each other by welding, resulting in a blocking component 40 with a circumference of approximately 72,000 mm. The size of the blocking component is not limited to this example and can be varied depending on the size of the metal storage tank 1 to which it is applied. Here, "generally rectangular" is not limited to a strict rectangle; it is acceptable as long as it is approximately rectangular. "Approximately 100 mm" is not limited to a strict 100 mm, but includes a range that is approximately 100 mm (e.g., a range of approximately 99 mm to 101 mm).

[0039] The top channel 30 is a component made of channel steel that connects to the upper end of the outer peripheral surface 2os of the side plate 2, with its groove facing downwards, machined into a generally annular shape. The outer peripheral edge 3oe of the roof plate 3 is joined to and supported at the upper end 70 of the top channel 30 in the first joint C1 along its circumferential direction. Furthermore, since the upper end 70 is a component constituting the top channel 30, it can be said that the outer peripheral edge 3oe of the roof plate 3 is joined to and supported on the top channel 30 in the first joint along its circumferential direction. In this embodiment, channel steel is used for the top channel 30, but angle steel can also be machined into a generally annular shape as in the prior art.

[0040] According to the structure of the metal storage tank 1 as described above, compared with the existing roof panel support using angle steel without the outer periphery 85 of the top channel 30, the area of ​​the longitudinal section of the top channel 30 is increased. Therefore, it is possible to support the rotary drive device 10, the rotary shaft 11, the multiple stirring blades 12, and more stably support the roof panel 3 with increased weight.

[0041] The upper end 2U of the side plate 2 is joined in the fifth joint C5 to the inner peripheral surface 60is of the inner peripheral portion 60 that forms the inner periphery of the top channel 30. The lower end 60L of the inner peripheral portion 60 is joined in the third joint C3 to the outer peripheral surface 2os of the side plate 2. The lower end 40L of the blocking member 40 is joined in the fourth joint C4 to the inner peripheral surface 2is of the side plate 2.

[0042] In this embodiment, the first joint C1, the second joint C2, the third joint C3, the fourth joint C4, and the fifth joint C5 are welded together, but the form of the joint is not limited to welding. In addition, similar to the first joint C1, the second joint C2, the third joint C3, the fourth joint C4, and the fifth joint C5 are joined around the circumference.

[0043] The third joint C3 and the fourth joint C4 are separated along the height direction of the side plate 2 (the direction of the center line O) by a distance of approximately 3 to approximately 5 times or more the thickness t of the side plate 2. Because the third joint C3 and the fourth joint C4 are sufficiently separated, the weld strength of the fourth joint C4 will not decrease due to the heat effect from the welded third joint C3, and the weld strength of the third joint C3 will not decrease due to the heat effect from the fourth joint C4. Therefore, the weld strength when welding the third joint C3 and the fourth joint C4 can be appropriately maintained. As an example, when using a side plate 2 with a thickness t of 6 mm, the third joint C3 and the fourth joint C4 are separated along the side plate 2 by a distance of 18 mm to 30 mm or more. Furthermore, the thickness t of the side plate 2 is not limited to 6 mm. Also, approximately 3 to approximately 5 times or more is not strictly 3 to 5 times or more, but refers to a range roughly considered to be 3 to 5 times or more. Therefore, when using a side plate 2 with a thickness t of 6 mm, the third joint C3 and the fourth joint C4 can also be separated along the side plate 2 by a distance of approximately 17.6 mm to 30.4 mm or more.

[0044] like Figure 2 As shown, there exists a space A surrounded by a roof panel 3, a top passage 30, a blocking component 40, and a side panel 2. Additionally, as... Figure 2 As shown, a through hole 50 communicating with space A is provided on the roof panel 3. The through hole 50 is connected to a pipe 55, which passes through the polyurethane foam 100 disposed on the upper part of the roof panel 3 and opens to the outside. Therefore, space A can open to the outside through the through hole 50 and the pipe 55. In addition, since an opening and closing component 90 is provided at the front end of the pipe 55, space A can be opened to the outside by opening the opening and closing component 90, or space A can be closed from the outside by closing the opening and closing component 90. When space A is closed to the outside, space A becomes airtight. Therefore, when performing corrosion inspections, etc., as described later, the presence of corrosion can be checked by checking the airtightness of space A. Here, as... Figure 2As shown, the pipe 55 is supported by flat steel 80 and is installed at approximately a right angle to the roof panel 3. Additionally, the opening and closing component 90 may be, for example, a resin cap embedded in the outer or inner circumferential surface of the front end of the pipe 55, a screw-on cap screwed onto the outer circumferential surface of the front end of the pipe 55, or a metal opening and closing valve. Here, "approximately a right angle" is not limited to a strict right angle, but includes a range that is approximately considered a right angle (e.g., a range of 89° to 91°).

[0045] The inner surface 3is of the roof panel 3, the inner peripheral surface 40is of the sealing member 40, and the second joint C2 are subjected to anti-corrosion treatment. This anti-corrosion treatment can be achieved by applying a corrosion-resistant coating or by applying a flake lining, which has a higher corrosion resistance than a corrosion-resistant coating. A flake lining refers to applying a coating of a specified thickness to the surface of the base material to be protected after mixing flake-shaped glass flakes into a liquid resin. By applying anti-corrosion treatment to the inner surface 3is of the roof panel 3, the inner peripheral surface 40is of the sealing member 40, and the second joint C2, corrosion by corrosive gases can be prevented. Furthermore, an anti-corrosion treatment can be applied to the fourth joint C4 in addition to the treatment of the inner surface 3is of the roof panel 3, the inner peripheral surface 40is of the sealing member 40, and the second joint C2.

[0046] Next, the function of the metal storage tank 1 with this structure will be explained.

[0047] The metal storage tank 1 stores organic sludge W inside. During the anaerobic decomposition of the organic sludge W into microorganisms, that is, during the fermentation of the organic sludge W into methane, digestion gases such as methane are produced. Here, in addition to methane gas, the digestion gases also contain corrosive hydrogen sulfide gas. Furthermore, in the following description, organic sludge W is sometimes referred to simply as sludge W.

[0048] The metal storage tank 1 contains sludge W with a large amount of moisture, and is kept at a high temperature to increase the activity of microorganisms, thus becoming a hot and humid environment. As a result, water droplets often adhere to the inner surface 3is of the roof plate 3 and the inner peripheral surface 2is of the side plate 2 of the metal storage tank 1.

[0049] If hydrogen sulfide gas produced by sludge W is dissolved in such a water droplet, and the droplet moves to the inner surface 3is of the roof panel 3 that slopes downward toward the top channel 30, then the droplet abuts against the blocking member 40. The upper end 40U of the blocking member 40 engages with the inner surface 3is of the roof panel 3 in the second joint C2, and the blocking member 40 extends downward along the side panel 2. The droplet then moves further to the blocking member 40 and downward along the side panel 2, passing the joint (fourth joint C4) between the lower end 40L of the blocking member 40 and the inner circumferential surface 2is of the side panel 2, and then moves downward along the side panel 2, finally falling onto and merging with the sludge W stored inside the metal storage tank 1.

[0050] Therefore, unlike existing technologies without the blocking component 40, water droplets containing corrosive gases will not remain in the gap between the roof panel and the roof panel support, thus preventing corrosion of the joint between the roof panel and the roof panel support from the inside. Consequently, digestion gases will not leak to the outside from the corroded joint between the roof panel and the roof panel support. Furthermore, since the blocking component 40 also supports the roof panel 3 in addition to the top channel 30, it can support the rotary drive device 10, the rotary shaft 11, the multiple stirring blades 12, and more stably support the increased weight of the roof panel 3.

[0051] Next, the inspection method for the metal storage tank 1 will be explained.

[0052] The following corrosion inspection was conducted using a metal storage tank 1 with space A being airtight when the opening and closing parts 90 are closed.

[0053] Open the opening / closing component 90 to inject compressed gas into space A from the outlet of a compressor (not shown) connected to pipe 55 (compressed gas injection step).

[0054] Next, a foaming liquid is applied to the visually inspectable first joint C1, second joint C2, third joint C3, and fourth joint C4, excluding the fifth joint C5 (foaming liquid application step). Soapy water can be used as an example of a foaming liquid. Then, the applied foaming liquid is visually inspected for foaming (observation step). Corrosion inspection is performed through this series of operations. When foaming of the foaming liquid applied to any one of the first joint C1, second joint C2, third joint C3, and fourth joint C4 is observed, it can be presumed that the area where foaming is observed in any one of the first joint C1, second joint C2, third joint C3, and fourth joint C4 has been corroded. Furthermore, the foaming liquid application step and the observation step can be performed simultaneously. That is, the foaming liquid can be applied during the foaming liquid application step, and the observation step, which visually confirms the foaming status of the applied areas, can also be performed at the same time.

[0055] Here, the pressure of the compressed gas is preferably in the range of about 3.0 kPaG to about 5.0 kPaG. In this case, since the pressure of the compressed gas is much higher than atmospheric pressure, and thus does not exceed about 5.0 kPaG, which is the design pressure of the roof panel 3, it is easy to observe whether there is foaming from the foaming liquid without damaging the roof panel 3. In particular, since the pressure of the compressed gas is much higher than atmospheric pressure, the slightly corroded parts are pressed outward from space A due to the pressure difference with the outside. Therefore, the compressed gas will also leak to the outside from the slightly corroded parts that cannot be detected at atmospheric pressure, thereby enabling the detection of the corroded parts and preventing the leakage of the gas. Here, the range of about 3.0 kPaG to about 5.0 kPaG is not limited to a strict range of 3.0 kPaG to 5.0 kPaG, but also includes a range that is roughly considered to be in the range of 3.0 kPaG to 5.0 kPaG (for example, a range of about 2.9 kPaG to 5.1 kPaG). Furthermore, compressed air is usually used as the compressed gas, but it is not necessarily limited to compressed air. Furthermore, while the inspection method for corrosion inspection of metal storage tanks is explained here, the same steps can be followed when inspecting for defects in the welded areas during the fabrication of metal storage tanks.

[0056] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the specific structure is not limited to these embodiments and their variations, and also includes designs that do not depart from the spirit of the present invention.

[0057] For example, the above embodiment uses the case where the metal storage tank 1 is a sludge digestion tank as an example, but it is not limited to this example. For example, the metal storage tank 1 of the present invention can be applied to all metal storage tanks that generate corrosive gases inside the metal storage tank 1. Therefore, it is not limited to the field of sludge treatment as long as the metal storage tank 1 used to store contents that generate corrosive gases is used, for example, it can also be applied to the field of food manufacturing and processing.

[0058] Here, the metal storage tank is conceived, for example, as the side plate 2, top channel 30, roof plate 3, sealing component 40 and bottom plate 4 of the storage tank are made of metal, but it is not necessarily limited to the case where all of them are made of metal, and it also includes the case where the storage tank is partially formed of materials other than metal.

[0059] In addition, although an example is shown with one through hole 50 on the roof panel 3, multiple through holes 50 may also be provided.

[0060] The inspection method for the metal storage tank 1 is not limited to the above-described inspection method. For example, compressed gas can be injected into space A at night when the temperature inside the metal storage tank 1 is unlikely to change due to sunlight, and the pressure change in space A can be monitored to infer whether there is corrosion at the welded joint.

[0061] Explanation of reference numerals in the attached figures

[0062] 1. Metal storage tank

[0063] 2 side panels

[0064] 3. Roofing panels

[0065] 4. Base plate

[0066] 10 Rotary drive unit

[0067] 11 Rotation axis

[0068] 12 Agitator blades

[0069] 30 top channels

[0070] 40 Blocking components

[0071] 50 through hole

[0072] 60 Inner Peripheral Region

[0073] 70 Upper end

[0074] 85 Peripheral part

[0075] 90 Opening and closing components

[0076] C1 First Joint

[0077] C2 Second Joint

[0078] C3 Third Joint

[0079] C4 Fourth Joint

[0080] C5 Fifth Joint

[0081] G Ground

Claims

1. A metal storage tank, characterized in that, include: Cylindrical side panels; A generally annular reinforcing member is provided along the upper part of the outer peripheral surface of the side plate; A roof panel is configured to cover the side panel from above, the outer periphery of the roof panel being joined to the reinforcing member in a first joint and the outer periphery being located lower than the center of the roof panel; as well as A generally annular closure member is disposed along the upper part of the inner circumferential surface of the side plate, and the upper end of the closure member is engaged to the inner surface of the roof panel in the second joint. The reinforcing component is a roughly annular component made by machining a channel steel that connects to the upper end of the outer peripheral surface of the side plate with the channel portion facing downwards. The metal storage tank has a space surrounded by the roof panel, the reinforcing member, the blocking member and the side panel. The roof panel is provided with a through hole communicating with the space. The through hole communicates with a pipe and opens to the outside. The front end of the pipe is provided with an opening and closing member that can be opened and closed and can make the space airtight.

2. The metal storage tank according to claim 1, characterized in that, Further includes: A through hole is provided on the roof panel and communicates with the space surrounded by the roof panel, the reinforcing member, the blocking member and the side panel; A pipe that communicates with the through hole and allows the through hole to open to the outside; as well as An opening and closing component is provided on the pipe to enable the pipe to be opened and closed to the outside. The space is an airtight space when the pipe is closed.

3. The metal storage tank according to claim 2, characterized in that, The lower end of the inner peripheral portion constituting the inner periphery of the reinforcing member is joined to the outer peripheral surface of the side plate in the third joint. The lower end of the blocking component is engaged with the inner circumferential surface of the side plate in the fourth joint. The third joint and the fourth joint are separated along the height direction of the side plate by a distance of 3 to 5 times the thickness of the side plate.

4. The metal storage tank according to any one of claims 1 to 3, characterized in that, The inner surface of the roof panel, the inner circumferential surface of the closure component, and the second joint are coated with a corrosion-resistant coating.

5. The metal storage tank according to any one of claims 1 to 3, characterized in that, The inner surface of the roof panel, the inner circumferential surface of the occluding member, and the second joint are lined with scales.

6. The metal storage tank according to any one of claims 1 to 3, characterized in that, The metal storage tank is a sludge digestion tank.

7. A method for inspecting a metal storage tank as described in claim 3, characterized in that, include: The compressed gas injection step involves injecting compressed gas into the space. The foaming liquid coating step involves coating the first joint, the second joint, the third joint, and the fourth joint with foaming liquid; and The observation step involves observing whether the applied foaming liquid foams. The metal storage tank stores the contents that generate corrosive gases.

8. The method for inspecting a metal storage tank according to claim 7, characterized in that, The pressure of the compressed gas is in the range of 3.0 kPaG to 5.0 kPaG.

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