EP1054078A2

EP1054078A2 - Sensing and checking system for the safety condition of tanks

Info

Publication number: EP1054078A2
Application number: EP99830421A
Authority: EP
Inventors: Pietro Mingozzi
Original assignee: Plinoxotar Srl
Current assignee: Plinoxotar Srl
Priority date: 1999-03-25
Filing date: 1999-07-01
Publication date: 2000-11-22
Also published as: ITRM990188A1; EP1054078A3; IT1306844B1

Abstract

A sensing and checking system (B) of the safety conditions of tanks of the type comprising a cathodic corrosion protection apparatus (A), allowing the complete automation of the sensing activities with an improved checking safety and comprising: a data recognition and output unit (16), such data including a cathodic protection voltage (Vp) and a reference value (Vt) of a cathodic protection current, having a recognition storage (18), a storing recognition code of the tank (1); and a check unit (21), connectable to said data recognition and output unit (16), apt to record the measured values of said protection voltage (Vp) and of said reference value (Vt), comprising: a main storage storing a family of identification codes and the corresponding threshold value for said protection voltage (Vp); and means for comparing (31) said measured value with said threshold value.

Description

The present invention relates to a sensing and checking system of tank safety conditions, in particular of the type comprising a cathodic corrosion protection apparatus.
For instance, this type of systems are applied, to tanks stocking a liquid or gaseous fuel, e.g. LPG, for domestic consumption, located underground nearby the user.
Due to the aggressive environment deriving from the pure undergrounding, e.g. in yards or the like, this type of tanks can be purely undergrounded only under particular conditions of corrosion protection.
Usually, such protection is carried out by particular coatings, e.g. epoxy resin-based, associated to a cathodic protection apparatus comprising at least one anode, called expendable anode, made of a metallic material of very low electrochemical potential, e.g. magnesium, with respect to the material of the tank.
The functionality of the cathodic protection can be checked measuring the potential of the tank with respect to a reference electrode.
As it can be seen in the annexed figure 1 (Pourbaix diagram), if it is measured with respect to a Cu/CuSO₄ reference electrode, the potential must not exceed a threshold value of about 0.85 V.
Using the commercially available magnesium, with an electrochemical potential of -1.75 V, or an alloy thereof, with a potential of -1.60 V, a reference potential value predictable with respect to a steel tank having a variable potential from -0.50 to -0.70 V, is comprised between -0.90 and -1.55 V, i.e. well below the safety threshold.
On the other hand, as to the duration of such protection, it can be checked by the measure of the protection current supplied by the expendable anode that, being more electronegative than iron, is expended in lieu of the latter.
Therefore, as a first step, it is important for the expendable anode to possess an adequate mass that, notwithstanding consumption, may ensure a long life.
However, if the coating is in good condition, the current supplied by the anode does not exceed a threshold value indicative of the good state of preservation of the tank.
This association of protection members, coating and cathodic protection actually allows the burying for a long period of time, e.g. 20 years, with no need of a periodical visual inspection to check the condition of the tank surface.
Hence, it can be concluded that, by checking periodically that said voltage and current readings do not exceed the respective threshold values, the periodical visual inspection becomes in fact superfluous.
Obviously, the above conclusion holds true for any type of underground tank, in particular LPG tanks, of the horizontal or of the vertical type, regardless of the capacity.
Furthermore, it is understood that the inventive concept that will be defined hereinafter can be extended to all the tanks that, being located in a potentially corrosive environment, cannot be inspected easily during their operative life.
By way of example, an underground tank provided with this type of corrosion protection is illustrated with reference to figures 2 and 3, a side and a front view respectively with a cross section of the undergrounding, of the type having a horizontal cylindrical body used for LPG stocking.
In said figures, a tank 1 is undergrounded into a cavity 2, filled up with aggregate sand or with a similar filler, and resting onto a concrete slab 3 to which it is fastened, e.g., with pins 4 of galvanised steel, fixed in the supports 5 of the tank 1.
To such a tank 1, a cathodic corrosion protection apparatus generally indicated with A is applied, including the expendable anode 6, of the type made of magnesium and in direct contact with the ground of the cavity 2, and a reference Cu/CuSO₄ electrode 7.
The tank 1, the expendable anode 6 and the reference electrode 7 are respectively connected to a measuring spot 8 by corresponding first cable 9, second cable 10 and third cable 11, forming a first, a second and a third connection, respectively.
Said measuring spot 8 is located in a waterproof box C installed outside the protection cap 12 housing the instrument system of the tank 1. Such protection cap 12 and said waterproof box C, shown in a detailed perspective view in figure 4, are accessibly positionated, substantially at the ground surface level.
From the protection cap 12, a relief valve 13 protrudes, and the network pipe 14 delivering the gas to the respective burners branches out.
On the basis of the description of the tank 1 and of the protection apparatus A thereof, it is understood that the checking of the potential and of the current protection takes place respectively:
1. measuring, with a suitable voltage metering instrument, the voltage between the system tank 1 - expendable anode 6 and the third conductor 11, connected to the reference electrode 7; and
2. measuring the current circulating between the tank 1 and the expendable anode 6, upon disconnection of the first or of the third conductor 9, 11 and interposition of a suitable current metering system.
Usually this checking is carried out manually, uncovering the waterproof box C and applying a multimeter to the conductors 9, 10, 11. The sensed values have to be reported on a suitable periodical check card provided.
This operational mode can originate some uncertainties possibly hindering the ready comprehension of the performance of the checking steps.
In fact, such checking must necessarily be performed by trained staff, capable of handling the meters and wise to the content of said waterproof box, as well as to every respect of the procedure: the adjustment and the calibration of the multimeter, the disconnection and the reconnection of the disconnected cable, etc.
Moreover, this checking requires the use of a good multimeter in order to prevent misreadings, in particular for low current values, obviously affecting the costs.
Lastly, there cannot be the absolute certainty of a suitable card.
The technical problem underlying the present invention is that of providing a sensing and checking system of the safety conditions of underground tanks allowing to overcome the drawbacks mentioned with reference to the known art.
Such problem is solved by a sensing and checking system as above specified, characterised in that it comprises:

a data recognition and output unit, comprising a cathodic protection voltage and a reference value of a cathodic protection current, having a recognition memory storing an recognition code of the tank; and
a check unit connectable to said data recognition and output unit, apt to obtain the measured values of said protection voltage and of said reference value, comprising: a main storage, including a family of recognition codes and the corresponding threshold value for said protection voltage; and means for comparing said measured value of the protection voltage with the corresponding threshold value.

The main advantage of the sensing and checking system according to the present invention lies in the complete automation of the checking and of the data storage.
The present invention will hereinafter be described according to one of its preferred embodiments, given by way of example and without limitative purposes with reference to the annexed drawings wherein, besides the above mentioned figures:

figure 5 shows a perspective view of a detail of the system according to the present invention;
figure 6 shows a connection diagram referring to the system shown in figures 4 and 5; and
figure 7 shows a further connection diagram of said system.

With reference to figures 4 and 5, a sensing and checking system of the safety conditions of underground tanks is shown, indicated as B and associated to said cathodic protection apparatus A and to the above described tank 1.
At the box C and at the measuring spot 8, the three cables 9, 10, 11 performing said first, second and third conductors, are connected to an electronic circuit 16 through a connector D.
At the electronic circuit 16, the system B comprises a socket 17 connectable to a jack plug 20.
The socket 17 is formed e.g. on the lid C1 of the box C, that, in figure 5, is shown in an open condition, i.e. at the position provided for the electronic circuit 16.
Obviously, it is understood that inside the box C the location of the circuit 16 and of the socket 17 could be different, e.g. at a side wall thereof.
The electronic circuit 16, schematically shown in figure 7, is apt to perform a voltage between said first and third conductors 9, 11, i.e. said protection voltage Vp, and a current involving said first and second electric conductors 9, 10 associated to the second or third conductor 10, 11 in a disconnected condition, i.e. said protection current.
The electronic circuit 16 comprises a recognition read-only memory 18 storing the recognition data of the tank 1, and a shunt transducer 19 transforming said protection current into a corresponding transduced voltage Vt, i.e. into a reference value thereof.
Shortly, such electronic circuit 16 forms a data recognition and output unit, directly associated to the protection apparatus A in situ, i.e. connected to the tank 1, outputting said protection voltage Vp and a transduced voltage Vt representative of the protection current.
Said jack plug 20 belongs to a mobile check unit 21 of the system B, to which it is connected by a connection cable 22.
Thus the mobile check unit 21 can be connected to said data recognition and output unit 16, and it comprises a casing 23 containing a circuitry 24 globally shown in figure 6.
Said mobile check unit 21 further comprises a set of signal lights 25 that, for the purposes of the present invention, are equivalent to acoustic alarms.
The circuitry 24 comprises an input of the measuring signals Vt, Vp connected to a section of electronic circuit breakers 26 forwarding these signals to respective voltage amplifiers 27 and current amplifiers 28, both connected to a digital to analog converter 29 powered by a battery 30.
A microprocessor 31 is connected to the recognition memory 18 of the data recognition and output unit through the connection cable 22, to said converter 29 and to a storage unit 32 respectively.
Moreover, the microprocessor 31 is connected to a main storage 33, provided with a database including the program utilised by the microprocessor, the identification codes of all the data recognition and output units of a family of tanks subjected to a checking and the threshold value for the protection voltage Vp; a timing unit 34, reporting the current time data, i.e. the current date and time; and an interface 35 for the connection of the check unit to a processor not shown.
Furthermore, the microprocessor 31 controls the switching on and off of the light signallers 25.
The sensing and checking system B, with the respective data recognition and output unit and the check unit thereof, operates as follows.
The operator plugs the jack plug 20 of the check unit 21 into the socket 17 of the box C, thereby connecting the electronic circuit 16 of the data recognition and output unit to the inner components of the check unit 21.
Once the check unit 21 has been switched on by an switch not shown, the microprocessor 31 reads the recognition code stored in the recognition memory 18, after having performed some verifications, such as e.g.: the state of charge of the battery 30; the effective connection between the jack plug 20 and the socket 17 and the like. Possible errors are signalled by light signals and/or acoustic alarms.
To carry out the reading of the code, the check unit 21 supplies the recognition unit with the amount of power required to activate the recognition memory 18. Obviously, all of those steps are managed by the program of the microprocessor 31.
Once the recognition has been performed, it is stored in the storage unit 32 together with the current date and time.
Then, the readings of the protection voltage Vp and of the protection current are carried out.
The protection voltage Vp is sensed from the first and the third electric conductors 9, 11 through an input stage including said voltage amplifier 27 configured as voltage follower with a high input impedance, and then applied to the digital to analog converter 29.
In order to purge the effects of the offset voltage of the amplifier 27 from the measuring, the input of the voltage follower stage can be disconnected from the input signal of Vp and earthed by means of said section of electronic circuit breakers 26, controlled by the microprocessor 31.
The sequence of the measuring steps is as follows:
The input step, working as follower, is previously isolated from the input signal and earthed, by means of said set 26: the microprocessor 31 activates the measuring, through the analog to digital converter 29, of the tension at the output step, due to the voltage offset of the voltage amplifier 27. This data is stored.
Then, the microprocessor controls the electronic circuit breakers so that the input signal Vp is forwarded to the voltage follower stage; Then, by means of the analog to digital converter A/D 7, a measuring of the voltage at the output of this stage is carried out.
Therefore, the value of the protection voltage Vp is obtained by the microprocessor through the difference between the last measured value and the one stored as offset value.
Each measuring performed by the analog to digital converter 29 constitutes the average value of a large number of samplings, e.g., 100, and the relative conversions, carried out in such a manner as to be spread equally over a period of time of a predetermined length, e.g. 20 mins. Thus, the uncertainty of measurement due to the induced and sensed noises, deriving, e.g., from the industrial frequency (50 - 60 Hz) electric fields and the relative harmonics is sharply reduced.
On the other hand, as to the current measurement, it is converted into voltage Vt at the shunt transducer 19. This voltage signal Vt is amplified through a current amplification stage 28, characterised by two amplification levels calibrated and sortable by the microprocessor 31.
Said microprocessor 31 carries out a first voltage measurement setting the lowest gain of the amplifier 28. If the measured value allows a greater amplification, then the microprocessor 31 increases the gain of the current amplifier 28. Then the activation procedure of the measuring of the voltage offset by the amplifier 28 is activated, as above described for the other amplifier 27.
During these measuring procedures of the voltages Vt, Vp, the microprocessor keeps the light signal 25 in an on state, in particular the light corresponding to the data acquisition.
The voltages Vp, Vt thus obtained are stored in the same storage area already allocated for the tank recognition code and for the date.
Then the measured value of the protection voltage Vp is compared to the one stored in the main storage 33.
If the comparison does not satisfy the predetermined limits (figure 1), an alarm is activated, in correspondence of an alarm light, e.g. by means of the light signals 25.
On the contrary, a complete turning off of the preceding light, relative to the acquisition of the signals 25 indicates the successful completion of the verified storing.
A further alarm light, in the light signal 25, can indicate that the battery is flat.
After the completion of the checking cycles on the tanks recorded in the main storage 33, the content of the storage unit 32 can be unloaded into a processor memory through the suitable interface 35.
Of course, each record reports the recognition code, the date and time, so as to be easily queued to the previous records referred to the same tank, thus reconstructing the history of each checked tank.
It is understood that the connection between the check unit 21 and the data recognition and output unit 16 can take place, other than through the connection cable 22, also through other connection systems, as e.g., telephone connections, cellular telephones, satellite telephones and the like.
However, the verification unit as described can also be used by unskilled personnel, e.g. by the person in charge of the periodical tank filling, with a remarkable reduction of the costs and with a higher checking frequency.
Then, the accuracy requirements are transferred from the traditional measuring device to the manufacturer's calibration of the units 16, 21.
Furthermore, apart from the connection and the switching on of the verification unit, no other operation that might be overlooked are required. In particular, there is no need to open the waterproof box or to reconnect disconnected cables.
Furthermore, the recorded data cannot be corrected or altered in any way either by the operator or by the tank user or by their insertion on a computer database since, as the record areas of the relevant data are protected, the data writing is made possible exclusively following an acquisition from the mobile check unit 21.
To the above-described sensing and checking system of underground tank safety conditions, a person skilled in the art, in order to satisfy further and contingent needs, may introduce several further modifications and variants, all however comprised in the protective scope of the present invention, as defined by the annexed claims.

Claims

A sensing and checking system (B) of the safety conditions of tanks of the type comprising a cathodic corrosion protection apparatus (A) associated to a tank (1), characterised in that it comprises:

a data recognition and output unit (16), comprising a cathodic protection voltage (Vp) and a reference value (Vt) of a cathodic protection current, having a recognition storage (18) storing an recognition code of the tank (1); and

a check unit (21), connectable to said data recognition and output unit (16), apt to obtain the measured values of said protection voltage (Vp) and of said reference value (Vt), comprising: a main storage, storing a family of recognition codes and the corresponding threshold value for said protection voltage (Vp); and means (31) for a comparison of said measured value of the protection voltage with the corresponding threshold value.
The sensing and checking system (B) according to claim 1, wherein said tank (1) is located underground.
The sensing and checking system (B) wherein said tank (1) is apt to stock LPG.
The sensing and checking system (B) according to claim 1, wherein said data recognition and output unit (16) is housed inside a waterproof box (C).
The sensing and checking system (B) according to claim 1, wherein said threshold value is a transduced voltage (Vt) obtained with a shunt transducer(19).
The sensing and checking system (B) according to claim 1, wherein said data recognition and output unit (16) and check units (21) are connectable by a connection cable (22).
The sensing and checking system (B) according to claim 1, wherein said comparison means include a microprocessor (31).
The sensing and checking system (B) according to claim 1, wherein said check unit (21) includes a storage unit (32) to record said measured values (Vp, Vt) together with the respective recognition code of the tank (1).
The sensing and checking system (B) according to claim 1, wherein said check unit (21) comprises a timing unit (34), reporting the current time data apt to be recorded in said storage unit (32).
The sensing and checking system (B) according to claim 1, wherein said verification unit (21) comprises an interface (35) to unload the content of said storage unit (32).