Outer shell inspection device of double-shell tank

Abstract

To provide an inspection device for inner and outer shells of an underground buried double-shell tank, capable of inspecting a plurality of tanks at any time without requiring manual labor, using a nitrogen generation device and a pressure sensor provided in a control facility.SOLUTION: A controller 10 including a timer, a nitrogen separator 23 and a pressure sensor 20 are placed in a control facility 100, an ejector or pressure regulator is installed in a tank 1 (1a-1d), and the control facility and the tank are connected by nitrogen tubes 5 (5a-5d) and pressure tubes 6 (6a-6d) buried underground. The controller opens and closes a nitrogen supply valve 4 and a pressure detection valve 8 of each tank in accordance with registered inspection procedures, to switch a tank to be inspected, and depressurizes or pressurizes a shell gap of each tank in accordance with the registered procedures and detects and records the subsequent pressure change.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] This invention relates to an inspection device for the inner and outer shells of underground buried double-shell tanks, and in particular to said device which is particularly suitable for detecting leaks in the outer shell of so-called SF double-shell tanks which have an inner shell made of steel and an outer shell made of reinforced plastic. [Background technology]

[0002] SF double-shell tanks are tanks with a steel inner shell and an outer shell made of fiber-reinforced plastic (FRP) to form the tank body, with a narrow gap between the inner and outer shells (hereinafter referred to as the "shell gap"). Underground tank bodies can be damaged, such as by cracks, by external forces such as backfilling with soil when the tank is buried, earthquakes, and uneven subsidence of the ground. Such damage can cause serious accidents such as tank breakage, so it is necessary to detect the damage early and carry out the necessary repairs.

[0003] As a means of detecting damage to the tank shell, a detector tube is inserted from the top of the tank into the bottom of the shell gap, and a liquid sensor (e.g., a float sensor) is attached to the bottom of the detector tube that can detect both the contents leaking from the inner shell and the groundwater flowing in from the outer shell, and the output of the liquid sensor is monitored by a monitor installed in a control facility such as the service station office, thereby providing a leak detection device that detects damage to the shell (Patent Document 1).

[0004] However, the above-mentioned method cannot detect damage to the outer shell when the tank is installed in a place without groundwater or when the groundwater level drops. Therefore, as a method for confirming that the outer shell of a double-shelled tank is not damaged, the outer shell is inspected for leaks periodically (currently once every three years) by pressurizing or depressurizing the shell gap and observing the pressure change (Non-Patent Document 1).

[0005] In Patent Document 2, the applicant of the present application provides a means for safely and easily detecting leaks in double-shell tanks used for storing hazardous materials by pressurizing or creating negative pressure in the gap between the shells using a nitrogen gas cylinder. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2011-025987 A [Patent Document 2] JP 2019-202827 A [Non-patent literature]

[0007] [Non-Patent Document 1] Periodic inspection text for underground tanks, etc. [Non-Patent Document 2] Fire Safety No. 66 (March 28, 2007) DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0008] However, given that the required inspection of the outer hull for leaks every three years means, in the worst case scenario, that damage could remain undetected for three years after it occurs, during which time an earthquake could occur and destroy the tank, it would be desirable to be able to detect damage to the outer hull more frequently, and preferably continuously.

[0009] In addition, the test method takes time to complete, including the test pressure, the rate of pressurization and depressurization, the time to leave the tank after reaching the preset pressurization or depressurization value, and the measurement time thereafter, and the manual pressurization and depressurization of the shell gap and the subsequent pressure change are time-consuming. For operators who have installed multiple tanks, the inspection process requires a great deal of time and effort.

[0010] In addition, in the method proposed in Patent Document 2, in the case of pressurized testing, the nitrogen gas is pushed out in one direction, so there is no outflow of flammable gas into the control facility, but in the case of reduced pressure testing, the ejector is located in the control facility, so flammable gas will flow in and explosion prevention measures are necessary. Also, since inert gas is provided in a cylinder, the remaining amount must be managed.

[0011] The objective of this invention is to provide an inspection device that can automatically inspect the shells of double-shell tanks used to store hazardous materials for damage in a timely manner and without the need for human labor, and in particular to provide technology that can inspect multiple tanks continuously. [Means for solving the problem]

[0012] The inspection device of this invention is an apparatus for inspecting the shell for damage when there is no leakage of liquid into the shell gaps, and is an apparatus that can detect small damage before cracks in the outer shell or liquid leakage occur in places where there is no groundwater.

[0013] In this invention, the nitrogen gas used to inspect for shell damage is generated by supplying pressurized air supplied by a compressor to a nitrogen separator 23, thereby preventing a shortage of nitrogen gas when inspecting multiple tanks 1 (1a, 1b, 1c, 1d) and minimizing the risk of flammable gas leaking into the control facility (a facility mainly located on the ground, such as an office that monitors the liquid level and soundness of the tanks under its control; the same applies below and in the claims) 100 during decompression inspection.

[0014] The nitrogen separator 23 and pressure sensor 20 are placed in the control facility 100, and the control facility 100 and the tanks 1 (1a-1d) are connected with nitrogen tubes 5 (5a-5d) and pressure tubes 6 (6a-6d) buried underground, so that the multiple tanks 1 can be inspected with one pressure sensor 20 provided in the control facility 100. By opening and closing the nitrogen supply valve 4 and pressure detection valve 8 with the controller 10, inspection of multiple tanks can be performed in a timely manner without requiring manual labor.

[0015] The double-shell tank hull inspection device of this invention comprises a nitrogen tube 5 and a pressure tube 6 arranged between the control facility 100 and the manhole 19 of each tank, and each tank 1 has connection ports at its top for connecting to these tubes.

[0016] The control facility 100, which is equipped with a controller 10 including a timer, is equipped with a nitrogen separator 23 that separates nitrogen gas from air pressurized by a compressor, a pressure sensor 20 that detects the pressure in the shell gap 13, a nitrogen supply valve 4 that connects the nitrogen tube 5 and the nitrogen separator 23, and a pressure detection valve 8 that connects the pressure tube 6 to the pressure sensor 20.

[0017] The controller 10 opens and closes the nitrogen supply valve 4 to pressurize or depressurize the shell gap 13 of the tank 1 to be inspected, and opens and closes the pressure detection valve 8 to acquire, display, and record the pressure and pressure changes in the shell gap 13 of the tank 1 to be inspected.

[0018] In an apparatus for pressurizing the shell gap 13 of a tank to be inspected to inspect the shell for damage, a pressure regulator 35 connected to a nitrogen tube 5 is provided on the top of the tank to prevent excessive pressure from acting on the shell gap 13 of the tank to be inspected.

[0019] In an apparatus for inspecting a tank by reducing the pressure in the shell gap, an ejector 2 is provided at the top of the tank 1, with an inlet connected to a nitrogen tube 5 and a negative pressure generating port communicating with the shell gap 13 of the tank, and nitrogen gas is supplied to the ejector to reduce the pressure in the shell gap 13 of the tank to be inspected.

[0020] In an apparatus for inspecting multiple tanks 1 (1a-1d), multiple nitrogen supply valves 4 and pressure detection valves 8 are provided which sequentially switch between the nitrogen separator 23 and pressure sensor 20 in the control facility 100 and the multiple tanks and the nitrogen tubes 5 (5a-5d) and pressure tubes 6 (6a-6d).

[0021] In an apparatus for inspecting double-shelled tanks, which is equipped with a detector tube 15 that penetrates the top of the tank and communicates with the shell gap 13 at the bottom of the tank, a liquid sensor 16 located at the bottom of the detector tube, and an underground buried signal wire 18 that transmits the liquid detection signal from the liquid sensor to the control facility 100, the nitrogen tube 5 and pressure tube 6 can be attached to the signal wire 18 using the existing signal wire and disposed underground. Effect of the Invention

[0022] In the case of a depressurized inspection, the ejector is installed in the manhole at the top of the tank, so the nitrogen gas is pushed out, and just like in a pressurized inspection, no flammable gas flows into the control facility. Nitrogen gas is separated and purified from the air in the atmosphere and supplied to the ejector, so inspection work does not have to be stopped due to a lack of nitrogen gas.

[0023] Furthermore, inspection work can be carried out at any time without the need to prepare the necessary equipment and personnel, allowing damage to the shell to be detected early. By integrating the entire inspection process into a system, it is also possible to inspect multiple tanks at the same time or repeatedly, thereby increasing safety and significantly reducing the labor required for inspection work. [Brief description of the drawings]

[0024] [Figure 1] Flow diagram of the first embodiment [Diagram 2] Flow diagram of the second embodiment [Diagram 3] Flow diagram of the third embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described using a horizontal cylindrical double-shell tank as an example. Tank 1 shown in Figures 1 and 2 is a double-shell tank with a steel inner shell 11 and an outer shell 12 made of a fiber-reinforced plastic layer. The tank for storing liquid has an internal volume larger than the maximum storage amount of the liquid, and the inside of the tank is divided into a liquid phase L below the liquid level S at maximum storage and a gas phase G above the liquid level.

[0026] The outer shell 12 is in intimate contact with the outer surface of the inner shell of the gas phase portion G and is covered by the inner shell 11, leaving a shell gap 13, which is a minute sealed gap, between the outer shell 12 and the inner shell 11 of the liquid phase portion L. The shell gap 13 is narrower than the thickness of the outer shell or the inner shell, and is usually 1 mm or less.

[0027] The illustrated tank 1 is equipped with a known leak detection device 14 that detects the contents leaking from the inner shell 11 and groundwater flowing in from the outer shell. The leak detection device 14 includes a detector tube 15 that penetrates the top of the tank at a manhole 19 and communicates with the shell gap 13 at the bottom of the tank, a liquid sensor 16 installed at the bottom of the detector tube, and a signal line 18 that sends the detection signal of the liquid sensor 16 drawn through the detector tube 15 to a monitor 17 installed in the control facility. The signal line 18 is drawn into the control facility 100 through a protective pipe 31 buried underground.

[0028] If damage occurs to the inner shell 11 causing the contents to leak, or if groundwater flows into the shell gap 13 through a crack in the outer shell 12, the liquid will flow down to the bottom of the tank and be detected by the liquid sensor 16, and displayed on the monitor 17 at the control facility, making it possible to detect damage to the shell.

[0029] The inspection device of this invention is a device that inspects the soundness of the inner and outer shells by measuring the pressure change after pressurizing or depressurizing the shell gap 13 and leaving it to stand. Figure 1 shows an embodiment of a depressurization type device that inspects by making the shell gap negative pressure.

[0030] 1, pressurized air supplied from a compressor (not shown) is purified by a filter 21 and passes through a pressure regulator 22 to a nitrogen separator 23, and pressurized nitrogen gas separated from the pressurized air flows to a fixed orifice 24. The fixed orifice 24 makes it possible to stabilize the flow rate and concentration of the nitrogen gas.

[0031] The nitrogen gas that has passed through the fixed orifice 24 is used to drive the ejector 2 installed in the manhole 19 through a protective pipe 31 that is arranged between the control facility 100 and the manhole 19 of the tank 1. In the example shown in Figures 1 and 2, the nitrogen gas is also used as a pressurized gas that opens the pressure supply valve 4 and the pressure detection valve 8 that are driven by gas pressure.

[0032] When the solenoid valve 3 is opened by a command from the controller 10, the nitrogen supply valve 4 opens in conjunction, and the nitrogen gas flows into the ejector 2 through the nitrogen tube 5 and a check valve 32 provided on the tank side. The negative pressure port of the ejector 2 communicates with a sealed box 34 in which the upper end of the detector tube 15 is open via a check valve 33. The internal pressure of the sealed box 34 is detected by the pressure sensor 20 through the pressure tube 6 via the solenoid valve 7 of the control facility 100 and the pressure detection valve 8 linked thereto.

[0033] The reason why the nitrogen supply valve 4 is opened and closed via the solenoid valve 3, and the pressure detection valve 8 is opened and closed via the solenoid valve 7 is to ensure safety by preventing direct contact between the solenoid valve and gas leaking from the shell gap 13. In the figure, the solenoid valves 3 and 7 are drawn close to the nitrogen supply valve 4 and the pressure detection valve 8, but in reality, the nitrogen supply valve 4, the pressure detection valve 8, and the pressure sensor 20 are installed in an explosion-proof case installed away from the controller 10 and the solenoid valves 3 and 7.

[0034] In addition, the nitrogen tube 5 and the pressure tube 6 can be drawn into the protective tube 31 using the existing signal line 18, and a check valve 32 is provided in front of the ejector 2 to prevent backflow of gas in the shell gap when nitrogen gas is not being supplied.

[0035] The negative pressure generated by the nitrogen gas supplied to the ejector 2 reduces the pressure in the shell gap 13 through the detector tube 15. The pressure reduction speed and the time required to reach the test pressure can be set by the controller 10 by turning the solenoid valve 3 on and off at short intervals. The leakage of negative pressure when the solenoid valve 3 is closed is prevented by the check valve 33.

[0036] The pressure in the shell gap 13 after the shell gap 13 has been made negative is detected by the pressure sensor 20 by operating the solenoid valve 7 by the controller 10 at the required timing, and is displayed and recorded by the controller 10.

[0037] Fig. 2 shows an embodiment of a pressurized inspection device. Pressurized air supplied from a compressor (not shown) is purified by a filter 21, passes through a pressure regulator 22, and flows to a nitrogen separator 23, and the pressurized nitrogen gas separated by the nitrogen separator 23 flows to a fixed orifice 24. The nitrogen gas that passes through the fixed orifice 24 flows to a solenoid valve 3, and when the solenoid valve 3 is operated by a controller 10, the nitrogen gas that passes through the solenoid valve 3 operates a nitrogen supply valve 4, and the nitrogen gas passes through a check valve 32, is reduced in pressure to the pressure set by a pressure regulator 35, and passes through a detector tube 15 to pressurize the shell gap 13.

[0038] The pressure regulator 35 reduces the pressure to a level that will not damage the shell, and the safety valve 36 is set so that the pressure does not rise above 30 kPa. The pressurization time is adjusted by turning the solenoid valve 3 on and off with the controller 10. The pressure is maintained by the check valve 33 to prevent pressure leakage when the solenoid valve 3 is stopped.

[0039] The pressure in the shell gap 13 is sent to the control facility through the detector tube 15 and the pressure tube 6, and the pressure detection valve 8 is operated by the controller 10 via the solenoid valve 7, and the pressure is detected by the pressure sensor 20 and displayed and recorded by the controller 10.

[0040] 1 and 2 show the relationship between the control facility 100 and one tank 1, but the control facility 100 can be connected to multiple tanks 1 in a similar manner. Fig. 3 is a flow diagram showing the arrangement of equipment in a negative pressure inspection device for inspecting four tanks 1a-1d. The control facility 100 includes a nitrogen separator 23, a controller 10, and a gas distribution unit 110. Each tank 1 includes an ejector unit 200.

[0041] In the apparatus of Fig. 1 and Fig. 2, nitrogen gas is used as the gas to operate the nitrogen supply valve 4 and the pressure detection valve 8, but in the apparatus of Fig. 3, the nitrogen supply valve 4 and the pressure detection valve 8 are operated by pressurized air. That is, the pressurized air generated by a compressor (not shown) is passed through an air filter 21 and a pressure regulator 22, the pressure is detected by a pressure sensor 25, and the air is used to drive the nitrogen supply valves 4 (4a-4d) and the pressure detection valves 8 (8a-8d), and the air is supplied to a nitrogen separator 23 through a heater 26 and a constant flow controller 27, and the obtained pressurized nitrogen gas is supplied from the control side facility 100 to an ejector 2a provided in a manhole of the inspection target tank 1a through a nitrogen supply valve 4a and a nitrogen tube 5a belonging to the inspection target tank (assumed to be tank 1a) commanded by the controller 10.

[0042] The ejector unit 200 is provided in the manhole 19 of each of the four tanks, and is equipped with an ejector 2 (2a-2d), check valves 32, 33 provided on the drive side and negative pressure side, and a silencer 37 provided at the drive gas exhaust port. The pressure in the shell gap 13 is sent to the gas distribution unit 110 of the control facility 100 via the detection tube 15 and pressure tube 6, and is detected by the pressure sensor 20 when the pressure detection valve 8a corresponding to the tank 1a to be inspected is opened.

[0043] A controller 10 installed in the control facility 100 opens and closes the solenoid valve 3 for supplying nitrogen gas and the solenoid valve 7 for detecting shell gap pressure according to the registered inspection procedure. Four solenoid valves 3a-3d for supplying nitrogen gas and four solenoid valves 7a-7d for detecting shell gap pressure are provided for each of the four tanks 1a-1d. Although not shown in the figure, this type of piping is provided with an exhaust valve for releasing pressure.

[0044] The gas distribution unit 110 is a unit interposed between the control side facility 100 and the ejector unit 200 to ensure safety by isolating flammable gas and electricity that may leak into the ejector unit 200, and is provided with four nitrogen supply valves 4a-4d and four pressure detection valves 8a-8d that open and close in synchronization with the opening and closing operations of the solenoid valves 3, 7 of the control side facility 100.

[0045] A pressure sensor 20 for detecting the pressure in the shell gap of the tank to which the pressure tube 6 is connected is provided in the gas distribution unit 110, and the detection signal is sent to the controller 10 for display and recording.

[0046] Next, an embodiment of a tank inspection operation using the inspection device of this invention will be described. The inspection procedure is registered as a program in the controller, and the operator selects one of several registered programs to start the device. When a work standard is established, the registered program is created according to the standard, but it is also possible to perform inspection operations that include optional operations within the range of the standard, such as consecutively inspecting multiple tanks or repeatedly inspecting a specific tank.

[0047] In addition to registering work procedures for inspection work to be performed on each tank in accordance with the work standards, examples of additional work procedures that can be registered include, for example, repeated execution of a single tank, execution at intervals of a single tank, repeated execution of multiple tanks, sequential execution at intervals of multiple tanks, repeated execution of a combination of multiple tanks, and execution at intervals of a combination of multiple tanks.

[0048] Repeated inspection of a single tank involves repeating the procedures stipulated in the "Periodic Inspection Procedures for the Shell of a Tank" for a single tank. Step 1. Start the equipment and begin nitrogen purification. Step 2. Start pressurizing and depressurizing the pore pressure to 20 kPa (at a rate of about 1 kPa / min). Step 3. Check that the static pressure fluctuation is less than 15%. (Leave it for 15 minutes after pressurization and depressurization) Step 4. Check that the pore pressure fluctuation is less than 10%. (After step 3, for 15 minutes if pressurized, for 30 minutes if depressurized) Step 5. Check that the pressure fluctuation is less than 10% and pass. Step 6: Return to step 1, and start pressurizing and depressurizing to 20 kPa and repeat the inspection.

[0049] The interval testing for a single tank has the advantage that the shell can be determined to be sound until the pressure fluctuates by 10%, so repeated testing can be done less frequently, the number of times the compressor needs to be started can be reduced, and electricity costs can be saved. Step 1. Start the equipment and begin nitrogen purification. Step 2. Start pressurizing and depressurizing until the pore pressure reaches 20 kPa. Step 3. Verify that the static pressure fluctuation in the shell gap is less than 15%. Step 4. Verify that pore pressure fluctuation is less than 10%. Step 5. Check that the pore pressure fluctuation is less than 10% and pass. Step 6. After the pore pressure reaches the upper limit of the test pressure (pressure fluctuation 10%), return to step 1, start pressurizing and depressurizing to 20 kPa, and perform the test.

[0050] Repeated execution of multiple tanks involves repeating the procedure stipulated in the "Periodic Shell Inspection Procedure" for multiple tanks in sequence. Step 1. Start the equipment and begin nitrogen purification. Step 2. Start pressurizing and depressurizing tank 1a until the pore pressure reaches 20 kPa. Step 3. Verify that the pore pressure static pressure fluctuation of tank 1a is less than 15%. Step 4. Verify that the pore pressure fluctuation in tank 1a is less than 10%. Step 5. Check that tank 1a passes the pore pressure fluctuation test and is below 10%. Step 6. Start pressurizing and depressurizing tank 1b until the pore pressure reaches 20 kPa. Step 7. Verify that the static pressure fluctuation of the pore pressure in tank 1b is less than 15%. Step 8. Verify that the pore pressure fluctuation in tank 1b is less than 10%. Step 9. Check that Tank 2 passes the pore pressure fluctuation test and is below 10%. Step 10. If tanks 1b and below are present, follow the same procedure. After passing step 9, return to step 1 and repeat the inspection from tank 1a.

[0051] By repeatedly connecting multiple tanks, the shells of all the tanks can be checked simultaneously as long as they are sound, thereby shortening the time each tank has to wait for inspection. Step 1. Start the equipment and begin nitrogen purification. Step 2. Start pressurizing and depressurizing tank 1a until the pore pressure reaches 20 kPa. Step 3. Verify that the static pore pressure fluctuation of tank 1a is less than 15%. Step 4. Start pressurizing and depressurizing tank 1b until the pore pressure reaches 20 kPa. Step 5. Verify that the static pore pressure fluctuation of tank 1b is less than 15%. Step 6. Connect the shell gaps between tanks 1a and 1b and confirm that the static pressure fluctuation is less than 15%. Step 7. Verify that the pore pressure fluctuation in the combined tank is less than 10%. Step 8. Check that the pore pressure fluctuation in the combined tank is less than 10% and pass. Step 9. After the combined tank passes, repeat the inspection starting from tank 1a.

[0052] In addition to the advantages of the multiple tank coupling repeated execution, the multiple tank coupling interval execution has the advantage that the frequency of repeated inspections is reduced, the number of compressor starts is reduced, and electricity costs are saved. Step 1. Start the equipment and begin nitrogen purification. Step 2. Start pressurizing and depressurizing tank 1a until the pore pressure reaches 20 kPa. Step 3. Verify that the static pore pressure fluctuation of tank 1a is less than 15%. Step 4. Start pressurizing and depressurizing tank 1b until the pore pressure reaches 20 kPa. Step 5. Verify that the static pore pressure fluctuation of tank 1b is less than 15%. Step 6. Connect the shell gaps of tank 1a and tank 1b and confirm that the static pore pressure fluctuation is less than 15%. Step 7. Verify that the pore pressure fluctuation in the combined tank is less than 10%. Step 8. Check that the pore pressure fluctuation in the combined tank is less than 10% and pass. Step 9. After the pore pressure of the combined tank reaches the upper limit of the inspection pressure, inspection of tank 1a is started. [Explanation of symbols]

[0053] 1(1a-1d) Tank 4 Nitrogen supply valve 5(5a-5d) Nitrogen tube 6(6a-6d) Pressure tube 8 Pressure detection valve 10 Controller 13 Intershell space 15 Detector tube 16 Liquid Sensor 18 Signal Line 19 Manhole 20 Pressure Sensor 23 Nitrogen separator 35 Pressure Regulator 100 Control facility

Claims

1. An outer shell inspection device for a liquid storage facility includes an underground buried double-shell tank with a shell gap between the inner shell and the outer shell, and a control facility for monitoring the state of the tank, and uses nitrogen gas to pressurize or depressurize the shell gap formed between the inner shell and the outer shell to inspect for damage to the inner shell or the outer shell, A nitrogen tube and a pressure tube are provided between the control facility and the tank; The control facility includes a compressor, a nitrogen separator that separates nitrogen gas from the air pressurized by the compressor, a pressure sensor that detects the pressure in the shell gap, a nitrogen supply valve provided in a pipe connecting the nitrogen tube and the nitrogen separator, a pressure detection valve provided in a pipe connecting the pressure tube to the pressure sensor, and a controller including a timer; The nitrogen tube and the pressure tube are connected to the shell gap, The controller opens and closes the nitrogen supply valve and the pressure detection valve at time intervals set in the controller.

2. 2. The hull inspection device for a double-shell tank according to claim 1, wherein the tank is provided with a pressure detection valve between the nitrogen tube and the shell gap.

3. 2. The hull inspection device for a double-shell tank according to claim 1, wherein the tank is provided with an ejector having a pressurized gas inlet connected to the nitrogen tube and a negative pressure generating port connected to the shell gap.

4. 4. The outer hull inspection device for a double-shelled tank as described in claim 2 or 3, comprising a single control side facility, a plurality of the tanks, and the nitrogen tubes and pressure tubes arranged between each of the tanks and the single control side facility, and the single control side facility is equipped with a plurality of nitrogen supply valves and pressure detection valves that sequentially switch nitrogen separators and pressure sensors installed in the facility to the nitrogen tubes and pressure tubes of the multiple tanks.

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