JP3997333B2 - Leak position detection method - Google Patents

Description

【００３２】
を共に満足する点となる。Ｖは予め測定可能であるので、(1)、(2)を連立方程式として解くことにより、漏洩点の座標(x,y)を定めることができる。
【００３３】
通常、タンク１は、内圧が正となるような前提の下で設計されているので、所定以上の負圧をかけると、凹みや破壊等が発生する恐れがある。よって、これらの検査を行うに際しては、タンク１の内圧を監視し、内圧が所定以上の負圧にならないようにする必要がある。もし、所定以上の負圧になったとき、まだ、漏洩が続いているような場合には、更に油３の液面レベルを下げて、この負圧より高い圧力で漏洩が止まるようにして測定を行う。
【００３４】
また、タンク１の内圧を下げて漏洩が止まった場合、さらに圧力を下げ続けると、今度は漏洩箇所から外気がタンク１内に流入し、その流入に伴ってＡＥが発生する。この場合も、ＡＥは一端観測されなくなり、再び観測され始めるようになる。よって、前述したのと同様、先頭波が観測される時刻を測定することにより、漏洩位置を特定することができる。このような場合も、タンク１の内圧を監視し、内圧がタンクの構造に影響を与えない程度に留まるように、油３の液面レベルを下げる必要がある。
【００３５】
以上述べたような方法の他に、タンク１の底板４の下方、即ち底板４と基礎２の間に加圧された気体を送り込み、そのときのＡＥを測定することによって漏洩の発生箇所を特定することもできる。
【００３６】
通常、底板４と基礎２の間には隙間があるので、測定に先立ってまずこの隙間をシールする。そして、シールを一部取り除き、そこから窒素等、タンク１内に入っても危険な状態を発生しないような気体を加圧して送り込む。
【００３７】
すると、タンクの底板４の下側の圧力が上昇するので、漏洩が止まるか少なくなり、その時点でＡＥセンサ７Ａ、７Ｂ、７Ｃで漏洩に伴うＡＥが検出されなくなる。そして、さらにタンクの底板４の下側の圧力が上昇すると、加圧された気体が漏洩箇所を通してタンク１内に流入し始め、それによるＡＥが発生する。よって、このＡＥの先頭波が各ＡＥセンサ７Ａ、７Ｂ、７Ｃで検出された時刻を特定することにより、前述したのと同じ手法により漏洩箇所を特定することができる。
【００３８】
この方法は、タンクが固定屋根式でなく、移動屋根式の場合も使用することができる。すなわち、移動屋根式のタンクの場合は、タンク内の圧力は屋根の重さで決定されてしまうので、内圧を変えることができず、前記第１の手段から第４の手段の方法は使用することができない。しかし、加圧された空気を底板の下から送り込む方法は、有効に使用することができる。
【００３９】
以上、各実施の形態を述べたが、いずれの方法も、漏洩によって連続しているＡＥの発生を一端止め、再び発生したＡＥの先頭波の到達時刻を複数の位置で測定し、それから漏洩位置を検出することで共通している。
【００４０】
なお、図１に示すタンクにおいては、液体である油が貯留されているが、本発明は、気体のみが収容されているタンク、ＬＰＧのように液体とそれが気化した蒸気が貯蔵されているタンクにも使用することができる。また、石油等の液体が貯留されているタンクにおいても、ガス放出管６の代わりに、大気解放管等の管を使用し、そこから吸気することによってタンクの内圧を下げることにより使用することができる。
【００４１】
【発明の効果】
以上説明したように、本発明によれば、底板を有するタンクにおいて、底板から流体が漏洩している場合に、その漏洩位置をＡＥを使用して検出可能な新規な方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態の例である漏洩位置検知方法を適用する設備の概要を示す図である。
【図２】腐食によって発生するＡＥの波形を３箇所の異なる位置に設置したＡＥセンサで検知した例を示す図である。
【図３】流体の漏洩により発生するＡＥの波形を３箇所の異なる位置に設置したＡＥセンサで検知した例を示す図である。
【図４】直径５mmの孔からの漏洩があった場合に、検出された漏洩位置をプロットしたものを示す図である。
【符号の説明】
１…タンク
２…基礎
３…油
４…底板
５…孔
６…ガス放出管
７Ａ、７Ｂ、７Ｃ…ＡＥセンサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a leak position detection method for detecting a position where a leak occurs in a bottom plate in an oil tank, an LPG tank, an LNG tank, etc. having a bottom plate.
[0002]
[Prior art]
Some oil tanks, LPG tanks, LNG tanks and the like have a bottom plate, and the bottom plate is usually placed on a foundation. In a tank of this type, when a hole is opened in the bottom plate due to corrosion or the like, the fluid inside the tank leaks from there to the foundation side. Normally, such holes are small and the amount of leakage is small, but if left for a long period of time, there is a risk of soil contamination and the like, so it is necessary to detect the leakage as soon as possible and repair the tank.
[0003]
A method for detecting AE (acoustic emission) has been developed as a method for detecting the leakage of fluid from the tank bottom plate. This utilizes the fact that acoustic radiation is generated when a hole opens in a tank and fluid leaks from it, and that sound waves propagate through the outer wall of the tank. AE can be detected at multiple locations on the outer wall of the tank. By installing an AE sensor and detecting AE generated along with fluid leakage, it is detected that leakage has occurred.
[0004]
[Problems to be solved by the invention]
According to the experiment results of the inventors, such a technique can detect leakage even when a hole of about 1 mmφ is opened in a cylindrical flat bottom tank having a diameter of about 10 m. However, since AE generated due to leakage is a continuous wave, there is a problem in that the position where leakage occurs cannot be specified even if AE sensors are arranged at a plurality of positions.
[0005]
Originally, the non-destructive inspection technology by AE was developed for the purpose of detecting the occurrence position of mechanical defects and corrosion. FIG. 2 shows an example in which AE waveforms generated by corrosion are detected by AE sensors installed at three different positions. As described above, AE generated due to mechanical defects and corrosion is a pulse-like one generated at a certain time interval. Therefore, if the time at which this pulse occurs is detected at different positions, From the time difference between the pulse detection times and the transmission speed of the AE, the position where the mechanical defect or corrosion occurs can be calculated.
[0006]
On the other hand, AE generated by fluid leakage is as shown in FIG. FIG. 3 is a diagram illustrating an example in which an AE waveform generated due to fluid leakage is detected by AE sensors installed at three different positions. As described above, if the waveforms are continuous, it is impossible to determine which points of the waveform measured at each location correspond to each other. Therefore, the leakage position determination based on the difference in the detection time of the AE is not possible. Can not.
[0007]
FIG. 4 shows a plot of the detected leak position when there is a leak from a hole with a diameter of 5 mm. In the figure, a circle indicates a tank bottom plate, and a position indicated by a cross indicates an actual hole position. On the other hand, the detected leak position is plotted as a point, but the plotted point varies over a wide range of the tank bottom plate, and the relationship with the true leak position is not seen (note that The unit of the vertical axis and the horizontal axis is m).
[0008]
Thus, if the leak position cannot be determined even if the occurrence of the leak can be detected, it is necessary to visually find the leak position when repairing the tank. However, the tank has a diameter of 10 to 80 m, and it takes a lot of labor and time to visually find a hole having a diameter of several mm or less in the bottom plate.
[0009]
The present invention has been made in view of such circumstances, and provides a novel method capable of detecting the leakage position using AE when a fluid leaks from the bottom plate in a tank having the bottom plate. This is the issue.
[0010]
[Means for Solving the Problems]
A first means for solving the above-described problem is a method for detecting leak positions of fluid leaking from a tank bottom plate, wherein AE sensors are provided at a plurality of positions of the tank, and the pressure in the tank is set to these AE sensors. The pressure in the tank is then increased again, the regenerated AE head wave is detected by each AE sensor, the time when the AE head wave was detected by each AE sensor, and each AE sensor. In the leak position detecting method characterized by detecting the leak position of the fluid from the installation position of the AE sensor , the pressure in the tank is lowered until AE is not detected before the pressure in the tank is lowered. In this case, the liquid level of the liquid stored therein is lowered to such an extent that the structure of the tank is not changed (claim 1).
[0011]
In this means, AE sensors are installed at a plurality of positions in the tank, and the pressure in the tank is lowered until AE is no longer detected by these AE sensors. If the pressure is increased again from this state, AE is detected again by these sensors. The time of the detected first waveform of the AE (referred to as the first wave) corresponds to the time when the regenerated AE arrives at each AE sensor for the first time. Therefore, if the time difference between the time when these AE sensors detect the leading wave and the position of each AE sensor are known, the speed of AE propagating through the outer wall of the tank can be measured in advance, so that the fluid leak position can be detected. it can.
[0013]
When the liquid is stored in the tank, if the liquid level is high, the tank may have a high negative pressure when the pressure in the tank is decreased until AE is no longer detected. Normally, a tank is designed to be applied with a positive pressure, and therefore, when a high negative pressure is applied, structural changes such as deformation and mechanical damage may occur in the tank structure.
[0014]
Therefore, in such a case, in the present means, the liquid level of the liquid stored inside is lowered before the pressure in the tank is lowered. Then, even if the pressure in the tank is the same, the pressure applied to the bottom plate is reduced by the liquid head difference, so that AE is not detected even if the pressure in the tank is not reduced so much.
[0015]
The liquid level may be lowered to such an extent that the tank structure is not changed when the pressure in the tank is reduced until AE is no longer detected.
[0016]
The second means for solving the above-mentioned problem is a method for detecting leak positions of fluid leaking from the tank bottom plate, wherein AE sensors are provided at a plurality of positions of the tank, and the pressure in the tank is set to these AE sensors. The AE is reduced to a level at which the AE is not detected, the pressure in the tank is further reduced, and the regenerated AE head wave is detected by each AE sensor. The time when the AE head wave is detected by each AE sensor and each AE A leakage position detection method characterized by detecting a fluid leakage position from a sensor installation position, when the pressure is reduced until AE is regenerated before the pressure in the tank is reduced. The liquid level of the liquid stored inside is lowered to such an extent that the structure of the tank is not changed (claim 2).
[0017]
In the first means, after the pressure in the tank is lowered to a level at which AE is not detected by the AE sensor, the pressure is increased again, and the leading wave of AE generated due to leakage is detected. In this means, on the contrary, after the pressure in the tank is lowered to a level at which AE is not detected by the AE sensor, the pressure is further lowered, and the head of the AE generated due to the suction of outside air from the leaked portion. Waves are detected and processed. The position specifying method is the same as that of the first means.
[0019]
The technical idea of this means is the same as that of the first means . However, in this means, since the minimum value of the pressure is when AE is regenerated, the liquid level of the liquid is lowered to such an extent that the tank structure is not changed at this time.
[0020]
A third means for solving the above-mentioned problem is a method for detecting the leak position of the fluid leaking from the tank bottom plate, and sending pressurized gas to the lower surface side of the tank bottom plate, and this pressurized gas Is detected by each AE sensor provided at a plurality of positions in the tank, and the AE front wave is detected by each AE sensor. In the leak position detection method , which detects the fluid leak position from the set time and the installation position of each AE sensor , the AE is restarted before the pressurized gas is sent to the lower surface side of the tank bottom plate. When the pressure of the pressurized gas is increased until it is generated, the liquid level of the liquid stored inside is reduced to such an extent that the structure of the tank is not changed. (Contract Section 3).
[0021]
In this means, first, pressurized gas is sent to the lower surface side of the tank bottom plate. Then, as the pressure on the bottom surface of the tank bottom plate rises, the amount of fluid leakage in the tank decreases, and finally there is no leakage. At this time, one end AE is not detected. When the pressure further rises, this time, the fed gas begins to flow into the tank, and AE is generated at this time. In this means, the leading wave of this AE is detected, and the fluid leakage position is detected in the same manner as in the first means.
[0022]
This means is particularly effective for floating roof tanks. The reason is that it is difficult to apply the first and second means to a floating roof type tank. Of course, this means can be applied to a fixed roof tank.
[0024]
Also in this means, when the liquid is stored, it is preferable to lower the liquid level beforehand because the pressure of the gas to be fed can be reduced and the influence on the tank can be reduced.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of equipment to which a leakage position detection method according to an embodiment of the present invention is applied, and shows a fixed roof type oil tank. (B) is a plan view, and (a) is an AA cross-sectional view.
[0026]
The tank 1 is provided on the foundation 2, and LGP 3 is stored therein. It is assumed that the bottom plate 4 of the tank 1 has a hole 5 from which leakage has occurred. The tank 1 is a steel cylindrical tank.
[0027]
In order to detect this leakage location, first, AE sensors 7A, 7B, and 7C are provided at three locations around the tank 1. The height of the mounting position is the same, and the position of each sensor is (X1, Y1), (X2, Y2), (X3, Y3) when (x, y) coordinates are taken on the horizontal plane at this height. .
[0028]
These AE sensors 7A, 7B, and 7C detect AE, and if an AE that accompanies leakage is detected, work is performed to identify the leakage position. First, the stored oil 3 is extracted or discharged as a gas from the gas discharge pipe 6 to lower the liquid level of the oil 3. Next, the internal pressure in the tank 1 is lowered by increasing the discharge amount from the gas discharge pipe 6.
[0029]
At this time, the AE is monitored by the AE sensors 7A, 7B, and 7C, and the release of the gas from the gas discharge pipe 6 is stopped when the AE associated with the leakage is not detected. And the gas is blown in reverse from the gas discharge pipe 6, and the inside of the tank 1 is pressurized. When the internal pressure of the tank 1 starts to increase again and reaches a predetermined pressure, AE associated with leakage starts to occur again. Each AE sensor monitors the start of the generation of the AE, and measures the generation start time of the AE, that is, the arrival time of the leading wave of the AE.
[0030]
Assuming that the arrival times of the leading waves of AE observed by the AE sensors 7A, 7B, and 7C are t _A , t _B , and t _C respectively, and the sound velocity in the bottom and side walls of the tank 1 is V, the leakage point (x , y)
[0031]
[Expression 1]

[0032]
It is a point that satisfies both. Since V can be measured in advance, the coordinates (x, y) of the leakage point can be determined by solving (1) and (2) as simultaneous equations.
[0033]
Normally, the tank 1 is designed under the premise that the internal pressure is positive. Therefore, when a negative pressure higher than a predetermined value is applied, there is a risk of dents or destruction. Therefore, when performing these inspections, it is necessary to monitor the internal pressure of the tank 1 so that the internal pressure does not become a negative pressure higher than a predetermined value. If leakage continues even when the negative pressure exceeds the specified level, the level of oil 3 is further lowered and measured so that the leakage stops at a pressure higher than this negative pressure. I do.
[0034]
In addition, when the internal pressure of the tank 1 is lowered and the leakage is stopped, if the pressure is further reduced, the outside air flows into the tank 1 from the leaked portion, and AE is generated along with the inflow. Also in this case, the AE is not observed once and starts to be observed again. Therefore, as described above, the leakage position can be specified by measuring the time when the leading wave is observed. Even in such a case, it is necessary to monitor the internal pressure of the tank 1 and lower the liquid level of the oil 3 so that the internal pressure remains at a level that does not affect the tank structure.
[0035]
In addition to the method described above, the location of the leak is specified by sending pressurized gas below the bottom plate 4 of the tank 1, that is, between the bottom plate 4 and the foundation 2, and measuring the AE at that time. You can also
[0036]
Usually, since there is a gap between the bottom plate 4 and the foundation 2, this gap is first sealed before measurement. Then, a part of the seal is removed, and a gas such as nitrogen that does not generate a dangerous state even when entering the tank 1 is pressurized and sent.
[0037]
Then, since the pressure below the bottom plate 4 of the tank increases, the leakage stops or decreases, and at that time, the AE associated with the leakage is not detected by the AE sensors 7A, 7B, and 7C. When the pressure on the lower side of the bottom plate 4 of the tank further rises, the pressurized gas begins to flow into the tank 1 through the leaked portion, thereby generating AE. Therefore, by specifying the time at which the leading wave of this AE is detected by each AE sensor 7A, 7B, 7C, the leak location can be specified by the same method as described above.
[0038]
This method can also be used when the tank is not a fixed roof type but a moving roof type. That is, in the case of a movable roof type tank, since the pressure in the tank is determined by the weight of the roof, the internal pressure cannot be changed, and the methods of the first to fourth means are used. I can't. However, the method of feeding pressurized air from under the bottom plate can be used effectively.
[0039]
As described above, each embodiment has been described. In any of the methods, generation of continuous AEs due to leakage is temporarily stopped, arrival times of leading waves of the generated AEs are measured again at a plurality of positions, and then leakage positions are detected. It is common to detect.
[0040]
In addition, although the oil which is a liquid is stored in the tank shown in FIG. 1, this invention stores the liquid and the vapor | steam which it vaporized like LPG, the tank in which only gas is accommodated. It can also be used for tanks. Also, in a tank in which a liquid such as petroleum is stored, a pipe such as an atmospheric release pipe is used instead of the gas release pipe 6 and the internal pressure of the tank is lowered by sucking from the pipe. it can.
[0041]
【The invention's effect】
As described above, according to the present invention, when a fluid leaks from a bottom plate in a tank having a bottom plate, a novel method can be provided in which the leak position can be detected using AE. .
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of equipment to which a leakage position detection method as an example of an embodiment of the present invention is applied.
FIG. 2 is a diagram showing an example in which an AE waveform generated by corrosion is detected by AE sensors installed at three different positions.
FIG. 3 is a diagram showing an example in which an AE waveform generated due to fluid leakage is detected by AE sensors installed at three different positions.
FIG. 4 is a diagram showing a plot of detected leak positions when there is a leak from a hole having a diameter of 5 mm.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Tank 2 ... Base 3 ... Oil 4 ... Bottom plate 5 ... Hole 6 ... Gas discharge pipe 7A, 7B, 7C ... AE sensor

Claims (3)

A method for detecting leakage positions of fluid leaking from a tank bottom plate, wherein AE sensors are provided at a plurality of positions in the tank, and the pressure in the tank is lowered to a level at which AE is not detected by these AE sensors. The pressure of the AE is increased again, the regenerated AE head wave is detected by each AE sensor, and the fluid leak position is detected from the time when the AE head wave was detected by each AE sensor and the installation position of each AE sensor. In the leak position detection method characterized in that , when the pressure in the tank is lowered until AE is no longer detected before the pressure in the tank is lowered, the tank structure is not changed. A leakage position detection method characterized by lowering the liquid level of the liquid stored inside. A method for detecting leakage positions of fluid leaking from a tank bottom plate, wherein AE sensors are provided at a plurality of positions in the tank, and the pressure in the tank is lowered to a level at which AE is not detected by these AE sensors. The pressure of the AE is decreased, the regenerated AE head wave is detected by each AE sensor, and the fluid leakage position is detected from the time when the AE head wave was detected by each AE sensor and the installation position of each AE sensor. In the leak position detection method characterized by the above, when the pressure is reduced until the AE is regenerated before the pressure in the tank is reduced, it is stored in the tank so as not to change the structure of the tank. A leakage position detecting method, characterized by lowering a liquid level of a liquid that has been used. A method for detecting the leak position of a fluid leaking from a tank bottom plate, in which a pressurized gas is sent to the lower surface side of the tank bottom plate, and this pressurized gas flows into the tank through a leak point on the tank bottom plate. The AE head wave generated by the AE sensor is detected by each AE sensor provided at a plurality of positions of the tank, and from the time when the AE head wave is detected by each AE sensor and the installation position of each AE sensor, In the leak position detection method , the pressure of the pressurized gas is increased until AE is regenerated before the pressurized gas is sent to the lower surface side of the tank bottom plate. In this case, the leak level detection method is characterized in that the liquid level of the liquid stored therein is lowered to such an extent that the tank structure is not changed.

Images