FR2728546A1 - PROCESS FOR CHECKING THE GOOD CONDITION OF THE TANK OF A TANK - Google Patents

Abstract

A method of detecting the appearance of water on a part of the outer surface of a tank of a tank, preferably on the bottom of the tank. Process consisting in surrounding the tank in a sealed manner with an anhydrous fluid.

Description

Method for checking the good condition of the tank of a tank
The present invention relates to methods for checking the good condition of the tank of a tank, in particular buried tanks, as well as tanks provided with devices for checking the good state of the tank which use these processes.

 There is a known process for checking the good condition of the tank of an underground tank, which consists in observing the appearance of corrosion on the external wall of the tank using a camera, including the shots are transmitted to a monitor that is not buried.

 This process of the prior art has the drawbacks, on the one hand of being very crusty and on the other hand of preventing only after corrosion has taken place.

 The invention overcomes the drawbacks of the prior art by a method of controlling the tank of a tank which, while being much less complicated to implement than the previous method, makes it possible to warn the user even before the corrosion of the tank does not appear and thus makes it possible to preserve the tank for an almost unlimited lifetime.

 According to the invention, the method consists in detecting the appearance of water which condenses on a part of the external surface of the tank, and in particular on the bottom of the tank. It has now been understood that, when the tank contains a cold liquid, for example liquefied petroleum gas, the appearance of water which has condensed is a harbinger of corrosion. By working on the tank as soon as this sign appears, we are better able to maintain the tank in good condition than if we wait for the appearance of corrosion to intervene.

 An improvement of the method consists on the one hand in enveloping the external surface of the tank or part of this surface with a sealed envelope which defines with the external surface of the tank, or a part of this surface, a sealed enclosure which the '' an anhydrous fluid (air, nitrogen or other) is filled, via an inlet located on the envelope, and on the other hand to control the possible appearance of water which condenses on the external surface of the tank, or on a part of this external surface and more particularly on the part of the external surface of the tank corresponding to the bottom of the tank. The external surface is thus subjected to a medium such that it should not normally be able to appear there moisture , cause of appearance of water of condensation, early warning of corrosion and it is checked that effectively no water of condensation appears. If however, the tightness of the envelope or the surface of the tank were to fail and that humidity managed to be introduced into the enclosure supposed to be waterproof, one can intervene before corrosion starts. This process makes it possible to translate the phenomenon of corrosion into an appearance of water which can be measured by a simple physical quantity such as an electrical intensity.

 The invention also relates to a tank having a tank made of a corrodable material, for example of steel, of which at least part of the external surface is surrounded by an envelope which defines with it a sealed enclosure in which there is an anhydrous fluid. . The external surface, or at least said part of the external surface of the tank, which generally contains a cold liquid, for example liquefied petroleum gas, is thus protected from ambient humidity and from the corrosion which would result therefrom.

 An improvement of the tank according to the invention consists in that a detector of the presence of water on the external surface, and in particular the bottom thereof, is mounted inside the sealed enclosure. In practice, such a detection proves to be extremely difficult to carry out, since it is necessary to measure in the atmosphere of the enclosure, an extremely low humidity level due to the very low temperatures reached by the tank due to the evaporation of the liquefied gas it contains.

 In order to be able to measure traces of humidity, the tank detector according to the invention may consist of a layer of hygroscopic salt (chloride, nitrate, sulphate of alkali metal or the like) which is fixed on the external surface. of the tank by a known fixing means (glue, crimping, etc.) and with which two electrodes are brought into intimate contact at a distance from each other in a stainless material (gold, platinum, or the like) or plated with such material.

 Hygroscopic salt has a very low conductivity in crystallized form which becomes much greater when in solution. Electric current cannot pass between the two electrodes as long as the hygroscopic salt is in crystallized form. When condensed water appears, the salt dissolves and current can flow between the two electrodes.

 By connecting the electrodes by two conductors to an information means consisting of an electric circuit comprising a source of electric current and a means of detecting the passage of current, it can be known that condensation water has appeared.

 Generally, the tank of a tank is made of a corrodible material which conducts electricity. So that current cannot pass between the electrodes through the tank of the tank, we must ensure, when mounting the electrodes in intimate contact with the salt layer, that this salt layer completely isolates the electrodes of the external surface of the tank.

 An improvement of the detector of a tank according to the invention consists in placing between the external surface of the tank and the layer of salt a membrane which conducts heat but is electrically insulating. This membrane makes it possible to ensure the electrical insulation of the electrodes with respect to the external surface of the tank, while achieving thermal conduction which ensures that the salt layer is at a temperature equal to that of the external surface of the tank.

 An improvement of the detector consists in placing a removable fixing part, in particular a magnet, between this membrane and the external surface of the tank.

 Thanks to this magnet, the detector can be easily mounted under the tank by simply pressing the magnet which then supports the detector against the tank.

Likewise, the detector can simply be removed from the tank by moving the magnet away from the tank.

 In practice, it is convenient to have easy access to the data supplied by the detector, even though the detection is carried out inside the sealed envelope, preferably under the very bottom of the tank, itself buried.

 An improvement of the invention makes it possible to solve this problem by placing the information means outside the sealed enclosure, and in such a way that it is easily accessible by the user.

In order to further improve the resolution of the detector, that is to say the minimum quantity of water necessary for a current to be visible on the means for detecting the passage of current. according to an improvement of the invention, a means is added to the electrical circuit intended to amplify the current which passes through the electrodes when the salt has become conductive
According to one embodiment of the invention, this amplification means consists of a transistor (for example of type 2 N 222), the base of which is connected to an electrode, while the branch consisting of electric current source and means for detecting the passage of current is mounted between the collector and the emitter the collector being also connected to the other electrode Thus when a current enters the base of the transistor, it comes out amplified by the emitter before passing into the current flow detector
According to an improvement of the invention, the detector is provided with a memory means of the fact that current is passed between the electrodes and that, therefore. water appeared on the outer surface of the tank
This memorization allows the user of the tank to be informed that water has appeared at a given moment without having to consult the information means at this precise moment. This memorization means is particularly useful in cases where the detector detects an appearance of water when the user is not informing himself and before the user comes to inform himself, this water disappears
The electrical circuit of an embodiment of a detector provided with such a storage means consists of a tripole, for example a transistor, having the property that, if current enters through a first pole, the dipole constituted of the second and third poles is conductive and that, if current does not enter through the first blade, the dipole is not conductive, the first pole being connected to an electrode, one pole among the second and third blades being connected to the other electrode, of a memory switch controlled by the current, initially in the open position and which switches to the closed position when current leaves the pole of the terminal which is not connected to an electrode, from a current source electric and a current flow detection means, the pole of the tripole not connected to an electrode being connected to one of the terminals of the electric current source and to one of the terminals of the switch. The other terminal of the switch being connected to the current flow detection means, itself connected to the pole of the dipole which is connected to an electrode and to the other terminal of the electric current source.
In this montage. the storage means consists of the storage switch controlled by the current. The lamp serving as a means for detecting the passage of the current then remains permanently on, being supplied by the electric current source.
In practice. the source of electric current will discharge quickly, if allowed to flow continuously. If this discharge takes place before the user comes to inquire, the lamp will have gone out due to this discharge and he will wrongly conclude that the tank is working properly
In order to protect the electric current source from such a discharge, an improvement of the invention consists in placing in the electric circuit a means intended to prevent the electric current source from delivering current as soon as a current has been detected. .

 An embodiment of the electric circuit provided with such a means is as follows: it consists of a tripole, for example a transistor, having the property that, if current enters through a first pole, the dipole consisting of the second and third poles is conductive and if current does not enter through the first pole, the dipole is not conductive, the first pole being connected to one electrode, one pole among the second and third poles being connected to the other electrode , a memory switch excited by the current, initially in the open position and which switches to the closed position when current leaves the pole of the tripole which is not connected to an electrode, from a source of electric current and a current flow detection means, the pole of the pole not connected to an electrode being connected to one of the terminals of the electric current source and to one of the terminals of the switch, the other terminal of the switch being connected e by means of detection of the current flow, itself connected to the pole of the dipole which is connected to an electrode and to the other terminal of the electric current source., a non-flow switch with two positions open and closed, initially in the closed position and which passes into the open position when it is excited by current being mounted between the pole of the tripoli which is not connected to an electrode and the input of the first two-position switch controlled by the current and a switch manual controlling the flow of current in the current flow detection means.

 Thanks to this arrangement, the electric current source only delivers current for a very short period of time between the moment when the salt becomes conductive and the moment when the memory switch opens.

 The advantage of this arrangement is that after a condensation of water has been detected. the current source no longer delivers current, but the user is nevertheless informed that water has appeared during his absence. In fact, the memory switch controlled by the current has closed properly and when the user closes the manual switch, the source of electric current flows back into the current flow detection means and warns the user that current is passed through the circuit during its absence.

 Another embodiment consists in replacing the two switches excited by the current with a bistable relay with two branches, each branch having two open and closed positions, the first being initially in the closed position and the second initially in the open position and the first s opening and the second closing when the current enters the bistable relay.

 Thus, when the salt becomes conductive, a current enters the memory switch excited by the current (the branch of the relay), which is initially closed, which has the effect of opening it, while the second (the second ) closes.

 It can also happen that the detector detaches from the outer surface of the tank.

 An improvement of the tank detector according to the invention consists in providing this detector with a means of indicating that it has become detached from the tank.

 An embodiment of a detector fitted with such an indicating means comprises as indicating means a spring switch banded between the external surface of the tank and a stop integral with the detector, and conductors connecting it to each electrode.

 So when the detector and its integral stop move away from the surface of the tank, the spring switch relaxes and closes to let the current flow. Everything then takes place as if the detector had detected an appearance of water and the user is informed by the current flow detection means that an anomaly has appeared in the detector.

 When the detector does not detect anything, it may be because there is no condensation of water, but also because the information medium is defective.

 In order to provide the user with a signal warning him of an anomaly in the information medium, an improvement of the tank according to the invention consists of two conductors connected to the outside of the sealed envelope by a check switch and connected inside the envelope each to one of the electrodes. This allows, when the verification switch is closed, to act as if water appeared on the external surface of the tank and thus to verify that the information medium is operating normally. If this is not the case, the user knows that an anomaly exists and that an intervention is necessary.

 A variant of a tank comprising a device to warn the user that an anomaly is hindering its proper functioning consists of a detector which comprises a hygroscopic salt, two electrodes connected together by a resistance, of value less than that constituted by the salt undissolved and greater than that constituted by the dissolved salt, and preferably a sheath made of synthetic material chosen for its properties of high water absorption and low water desorption. A non-limiting example of a suitable material is a polyamide (nylon type).

 When condensation occurs on the outside surface of the tank, the condensed water easily penetrates the material of the sheath and modifies the resistance of the hygroscopic salt by bringing it to a value lower than that of the resistance placed between the two electrodes. In this way, the observation of the presence of condensation can be verified by a simple resistance measurement.

Three cases can arise: 1 ") the value of the overall resistance is greater than that of the resistance
series with the electrodes: the device is faulty due to a break in
circuit, 2 ") the value of the overall resistance corresponds to that of the resistance
series with the electrodes the sensor works and there was no
condensation; 3) the value of the overall resistance is lower than that of the resistance
series: there has been condensation.

 A simple ohmeter allows monitoring of both the circuit and the presence of condensation.

In the appended drawing given solely by way of example,
Figure 1 is a schematic sectional view of a tank according to the invention.

 Figure 2 is a schematic sectional view of a preferred embodiment of the detector according to the invention.

 Figure 3 is a diagram of a preferred embodiment of the electrical circuit of the tank according to the invention, corresponding to the part which is outside the sealed envelope.

 Figure 4 is a diagram of another possible embodiment of the detector.

 The tank shown in Figure 1 is designated as a whole by the reference 1. It comprises a tank 2 surrounded by an envelope 3 which defines with the outer surface 4 of the tank 2 a sealed enclosure 5 whose sealing is ensured by seals 6. An inlet (not shown), provided with a plug, makes it possible to introduce gas or anhydrous fluid into enclosure 5.

Under the bottom of the tank 2, is mounted a detector 7 of the appearance of water connected by conductors 8, 9 to an information means 10 making it possible to know whether the detector 7 has detected condensation. This information means 10 is easily accessible to the user of the tank by being close to the ground surface.
S.

 The detector (FIG. 2) consists of a membrane 11, electrically insulating and thermally conductive, for example SILPAD 400 manufactured by the company BERGQUIST, one of the faces of which is in permanent contact with the external surface 4 of the tank by the intermediary of a magnet 12, conductor of heat, while the other face 13 is covered with a layer 14 of hygroscopic salt (LiCI, NaCI, or the like), whose conductivity in solution is much greater than under crystallized form. In this layer are mounted two electrodes 15, 16 made of a stainless material (gold, platinum or the like), placed in intimate contact with the face 13 of the membrane 11. A plastic housing 17 covers the part inside the enclosure of the detector for protect the hygroscopic salt layer and can serve as a hygroscopic salt reserve.

 A spring-operated switch 18 has its spring 38 mounted compressed between the bottom of the housing 17 forming a stop and the external surface 4 of the tank with the interposition of a pusher 39 provided with a pallet 40. When the spring 38 relaxes because the bottom 17 moves away from the surface 4, the conductive pallet 40 comes into contact with two booms 41, and is connected by two conductors 19,20 to each of the electrodes. Two conductors 8, 9 connect the electrodes to the information means 10 after having passed through the sealed envelope 3 through sealed orifices.

 This information means 10 includes an electrical circuit 21 connected to the terminals of the conductors 8, 9 coming from the electrodes.

The conductor 8 is connected to the base of a transistor 22, the emitter of which is connected to a first branch 23a of a bistable relay 23 with two positions NF and
NO. This bistable relay branch 23a is connected by an electric wire on the one hand to a terminal of an electric current source 24 and on the other hand to the second branch of the bistable relay 23b with two positions NF and NO. The latter is connected by an electric wire to a lamp 25, serving as a means for detecting the passage of current, itself connected to a manual switch 26 itself connected to the collector of transistor 22. The second terminal of electric current source 24 is also connected to the collector of transistor 22. A branch comprising a reset switch 27 and an auxiliary coil 28 is mounted between the terminal of the electric current source which is also connected to the bistable relay 23.

The coil 29 is part of the bistable relay 23.

 Two other conductors 30, 31 are mounted on the terminals of the electrodes 15, 16 and connected, after having passed through the casing 3 in a sealed manner, by a check switch 32.

 The liquid or gas to be stored in the tank of the tank is introduced via an inlet 33, for example a liquefied petroleum gas and an anhydrous gas or fluid into the sealed enclosure. The tightness of the enclosure 5 ensures that the outer surface 4 of the tank 2 is never subjected to a humid atmosphere, which protects it against corrosion. If, however, moisture manages to enter the enclosure 5, it will ensue, due to the low temperature of the liquefied petroleum gases which are in the lower part of the interior of the tank, that water of condensation appears on the external surface of the tank, and in particular in the bottom of the tank where the temperature is the lowest This appearance of water is detected by the detector 7 of appearance of water. Via the conductors 8, 9, the information that water has been detected is transmitted to the lamp 25 which lets the user know that an intervention is necessary to avoid future corrosion of the tank 2.

 Under normal conditions (no appearance of water), the conductivity of the hygroscopic salt between the two electrodes 15,16 is very low and no current flows through the conductors 8,9 as much as two resistors 34,35 of high value are connected in series respectively with each electrode.

If water appears on the salt layer 14 of the detector 7, its conductivity increases greatly and there follows a current flow which enters the base of the transistor 22. The current exits amplified from the emitter of the transistor and enters in the first branch 23A with two bistable states of the bistable relay which then passes from the NF (closed) state which allows the current to flow, to the NO (open) state which prevents the current from passing. The current which has just passed through the first branch of the bistable relay also enters the second branch 23B of the bistable relay which passes from the NO state to the NC state. The circuit consisting of the electric current source 24, the lamp 25 and the manual switch 26 is then closed and current flows through the lamp 25 if the switch 26 is closed. The user, by closing this switch 26 , is then informed: - if the lamp comes on, that current has passed between the electrodes from the
last time the bistable relay 23 was in its normal position
(branch A closed, branch B open), (usually the last visit); - if the lamp does not light up and lights up when it closes the switch 32 of
check that no current has flowed since the last time the relay
bistable was put in normal position.

 The switch 32 short-circuits the electrodes and allows current to pass between them. By closing it, the user can then verify that the information means 10 is operating normally, if the lamp lights up. If that does not light up, it means that a fault exists in the information means (faulty cable, faulty components, etc.) and intervention is necessary there.

 Once these checks have been carried out, the user reopens the manual switch 26 and closes for a short time the reset switch 27 which resets the bistable relay in its normal position by supplying the auxiliary coil 29 of the relay.

 Thanks to the switch 26 and to the branch 23a, the source of electric current does not flow during the whole time between the moment when water has appeared and the moment when the user proceeds to his operations. This therefore ensures a very long battery life.

 When the user closes the switch 26 and the lamp comes on, this indicates a fault. Condensation may have occurred, as described above. Another cause is that the detector 7 has detached from the surface of the tank 2. In fact, if this occurs, the switch 18 with spring has its spring which decompresses thus bringing the switch to the closed position . Current then flows between the two electrodes and this energizes the lamp 25 in the same manner as if condensation had appeared.

 Thus, when pressing the switch 26, the user sees the lamp 25 light up, he knows that an intervention is necessary in the sealed enclosure to either dehumidify the enclosure or to reattach the detector to the tank.

 In FIG. 4, a resistor 36 is mounted between the electrodes (15, 16) in the hygroscopic salt 14 inside a sheath 37 made of a material highly absorbent of water and with low desorption.

 When condensations occur on the external surface of the tank of the tank, the condensed water easily penetrates the material of the sheath and modifies the resistance of the hygroscopic salt by bringing it to a value lower than that of the resistance 36. In this way, the observation of the presence of condensation can be verified by a simple resistance measurement.

Three cases can arise: 1 ") the value of the overall resistance is greater than that of the resistance 36: the
detector 7 is faulty due to a circuit break, etc.

2 ") the value of the overall resistance corresponds to that of the resistance 36: the
detector 7 is working and there has been no condensation.

3) the value of the overall resistance is lower than that of the resistance 36: there are
had condensation.

Claims (2)

 1. Method for checking the good condition of the tank (2) of a tank (1), characterized in that it consists in detecting the appearance of water on a part of the external surface (4) of the tank , preferably on the bottom of the tank.  2. Control method according to claim 1, characterized in that it consists in putting the part of the outer surface (4) of the tank in an anhydrous atmosphere.