JP2006030109A - Leakage testing apparatus of underground tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it has been impossible for an oil level gauge, which has been used and provided for the inside of an underground liquid storage tank for gasoline etc. for judging a leakage of a container on the basis of the amount of a liquid level rise as a conventional apparatus for judging the leakage of an underground tank sunk in underground water, to accurately detect the leakage since a liquid level only slightly rises when the quantity of underground water leaks into an underground tank is only a little. <P>SOLUTION: This leakage testing apparatus of tanks is constituted of a pressure reducing device for reducing the pressure inside an underground tank having a curved bottom surface storing a liquid lighter than underground water; a water level gauge provided for the deepest part inside the underground tank; and an arithmetic storage device for computing the quantity of underground water leakage to the underground tank on the basis of a water level detected by the water level gauge and the shape of the deepest part of the underground tank. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an underground tank leak test apparatus, and more particularly to an apparatus for checking whether there is a leak in an underground tank submerged in ground water, which is embedded in a gas station or the like.

Conventionally, when judging leakage of underground tanks that have been submerged in groundwater and in which liquids such as gasoline are stored, an oil level gauge was installed in the underground tank, and the groundwater leaked into the underground tank. As an apparatus for judging leakage of a tank based on the amount of rise in the liquid level, for example, there is one shown in Patent Document 1.
Japanese Patent Laid-Open No. 9-77198 (FIG. 1)

  However, if the amount of groundwater leaking into the underground tank is small, the amount of liquid rise in the entire underground tank is small, so that the above oil level gauge cannot detect leakage correctly.

  The present invention eliminates the above-mentioned drawbacks.

  In general, the underground tank has a cylindrical shape and a trunk length, that is, the center of the bottom is curved, and the horizontal cross-sectional area gradually increases from the bottom toward the top. Therefore, when there is a groundwater leak in the underground tank, the amount of rise in the level of groundwater stored at the bottom of the tank due to the leak is greater than the amount of rise in the liquid level of gasoline or the like. The present invention has been made paying attention to this point.

  The underground tank leakage test apparatus according to the present invention includes a decompression device for decompressing an underground tank having a curved bottom surface in which a liquid lighter than groundwater is stored, a water level gauge provided at the deepest portion of the underground tank, and the water level. It comprises an arithmetic storage device for calculating the amount of groundwater leakage to the underground tank from the water level detected by a meter and the shape of the deepest part of the underground tank.

  In the present invention, when a water level meter is provided at the deepest part of the underground tank, and there is a leakage of underground water to the underground tank, the amount of increase in the water level is greater than the amount of increase in the liquid level of gasoline or the like. Since the amount of leakage was determined by measuring the amount of change in the level of groundwater stored in the deepest part of the underground tank, there is a great advantage that the amount of leakage in the underground tank can be measured with high accuracy.

  Embodiments of the present invention will be described below with reference to the drawings.

  In FIG. 1, 1 is an underground tank buried in a gas station or the like, submerged in groundwater 2, 3 is a vent pipe communicating with the underground tank 1, 4 is an oil meter installed on the ground, and 5 is the oil meter. 4 is an oil suction pipe connecting between the lower part of the underground tank 1, 6 is an opening for inserting a measuring pipe provided in the ceiling part of the underground tank 1, and 7 is a decompression that can freely set a decompression value installed on the ground. A maintenance device, 8 is airtightly connected to the vent pipe 3, the decompression hose of the decompression maintenance device 7, 9 is an air release hose connected to the vent pipe 3 via the decompression maintenance device 7, and 10 is the underground tank A storage liquid 11 such as gasoline stored in 1 is hermetically inserted into the underground tank 1 from the opening 6 and is positioned at the deepest part in the underground tank 1, for example, a capacitive water level meter, 12 is the shape of the deepest part of the bottom of the underground tank Stores, arithmetic storage device for processing the leakage amount using the information from the shape and the water level gauge 11, 13 denotes a pressure gauge for measuring the pressure in the vapor phase in the underground tank 1.

  In the tank leakage test method of the present invention, first, the presence or absence of leakage of the tank wall in the gas phase portion above the stored liquid in the underground tank 1 is tested.

  The depressurization maintenance device 7 is driven to bring the underground tank 1 into a depressurized state, leaks into the underground tank through the tank wall of the gas phase within a predetermined period, and is stored at the bottom of the underground tank 1. The groundwater level is measured by the water level gauge 11 and the leakage amount of the groundwater is calculated by the calculation storage device 12 in which the shape of the deepest part of the underground tank 1 is stored in advance.

  Next, a test is conducted for the presence or absence of tank wall leakage in the liquid layer of the underground tank.

  In this case, the depressurization maintenance device 7 is driven so that the underground tank 1 is in a depressurized state, for example, the difference from the atmospheric pressure becomes more than the head of the stored liquid, and thereafter the gas phase of the underground tank 1 is increased. The amount of groundwater leakage is calculated in the same way as the presence or absence of tank wall leakage in the section.

  In general, the fall (suction port) of a drain water suction pipe (not shown) is installed upward about 100 mm from the tank bottom. Therefore, the water level accumulated at the tank bottom is considered to be 100 mm at the maximum. Therefore, even in a large tank, the precise measurement range is from the bottom of the tank to a height of 100 mm and the scale of the water level gauge should be, for example, 160 mm. Generally, the accuracy of the water level gauge is about 0.1% of the scale of the water level gauge. A high accuracy of 0.16 mm can be ensured. FIG. 2 is a side view of the underground tank 1 in which the water level gauge 11 is set. The position A is a position 100 mm from the tank bottom, and the position B is a position in the center of the tank. Changes in the water volume and liquid volume per 1 mm height at the A and B positions in the tank are as shown in Table 1 for each tank size.

  The amount of leakage per hour from a leak hole with a diameter of 0.3 mm is about 0.79 liters / hour (from the amount of leakage "Survey Report on Safety / Environmental Measures for Dangerous Goods Facilities Buried Underground") .

  Conventionally, in order to find a leak hole with a diameter of 0.3 mm or less, 3 hours to 4 hours at the earliest due to the poor liquid level rise rate and the poor accuracy of the water level gauge, and in some cases overnight and long time tests. Although it was necessary to carry out, it is difficult to put a tank in a dormant state for a long time in a tank in use at a gas station or the like. Therefore, in order to find out how accurately the liquid level should be measured in order to reduce the test time to about 1 hour, the height of the liquid to detect a leak amount of 0.79 liters in each type of tank The displacement height is obtained from Table 1 and shown in Table 2.

  If the scale of the water level gauge is 160 mm, the accuracy is 0.16 mm, so the test may be performed until the time when the displacement height of the liquid height is 0.16 mm or more. As is clear from Table 2, for example, when 0.79 liter of groundwater enters from a leak hole having a diameter of 0.3 mm in a 10 K liter tank at position A having a diameter of 1440 mm in a decompression test, the water level changes by 0.174 mm. Therefore, it is possible to determine the presence or absence of leakage in a test of about 1 hour. Similarly, at the A position of a large capacity 40 K liter tank, a water level change of 0.086 mm occurs. Therefore, it is possible to determine the presence or absence of leakage in a test of about 2 hours.

  As described above, in the present invention, when a water level meter is provided at the deepest part of the underground tank, and there is a leakage of underground water into the underground tank, the amount of increase in the water level is larger than the amount of increase in the liquid level of gasoline or the like. Become. Since the amount of leakage was determined by measuring the amount of change in the level of groundwater stored in the deepest part of the underground tank, there is a great advantage that the amount of leakage in the underground tank can be measured with high accuracy.

  Moreover, since a water level meter with a short scale can be used, a highly accurate measurement can be performed.

It is explanatory drawing of the leak test apparatus of the tank of this invention. It is a side view which shows the relationship between a tank and a water level gauge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Underground tank 2 Groundwater 3 Ventilation pipe 4 Oil meter 5 Oil suction pipe 6 Opening part 7 Depressurization maintenance apparatus 8 Decompression hose 9 Atmospheric release hose 10 Storage liquid 11 Water level meter 12 Computation storage device 13 Pressure gauge

Claims (1)

  A decompression device that depressurizes the inside of the underground tank having a curved bottom surface in which a liquid lighter than groundwater is stored, a water level gauge provided at the deepest part in the underground tank, the water level detected by the water level gauge, and the above-mentioned of the underground tank An underground tank leakage test apparatus comprising: an arithmetic storage device for calculating an amount of groundwater leakage into the underground tank from a deepest shape.

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