Cathodic protection apparatus and related process

Abstract

The present disclosure proposes a cathodic protection apparatus that allows to solve at least in part the drawbacks encountered in the protection of a metal structure because it allows to detect the IR-free potential by means of an "instant off on coupon" technique and to regulate the cathodic protection current supplied so that the detected IR-free potential is maintained at a regulation value. A cathodic protection process that can be implemented by means of the apparatus of this disclosure is also described.

Description

[0001] CATHODIC PROTECTION APPARATUS AND RELATED PROCESS

[0002] TECHNICAL FIELD

[0003] This disclosure concerns the field of cathodic protection of metal structures and more specifically an IR-free potential cathodic protection apparatus, which allows the implementation of a related process.

[0004] BACKGROUND

[0005] Cathodic Protection is an electrochemical process that allows a metallic material to be brought to a state of immunity (or controlled corrosion rate, therefore in general, to a state of effective cathodic protection), thus ensuring a prolonged life cycle and greater operational efficiency of the protected metal infrastructures.

[0006] Any electrochemical process has at least one anode and at least one cathode and a circulating electric current. In this process the cathode does not undergo physical alterations, while the anode is consumed. Cathodic Protection with a forced current, by circulating a continuous electric current through a cathodic protection apparatus, makes the structure to be protected from corrosion as a Cathode (hence the name Cathodic Protection). The diagram in Figure 1 briefly illustrates how a Cathodic protection apparatus works.

[0007] The power supply FEEDER is the element of the cathodic protection apparatus responsible for supplying the current needed to make the protected metal structure as the cathode of the electrochemical process. The power supplies receive the alternating current (AC) as input and transform it into a direct current (DC), to be able to protect the structure.

[0008] To understand when the Cathodic Protection is effective, it is necessary to measure the electrochemical potential of the metal structure with a voltage measurement between the structure and a reference electrode: with cathodic protection, the electrical potential of the structure will be shifted towards more negative values, until it reaches the threshold values indicated by the regulations. This measurement has a specific value, in the specific site where it is carried out, for this reason in the case of a structure with a certain extension (such as, for example, underground pipe networks for the transport and distribution of gas) there must be multiple measurement points in which to carry out the measurement: for cathodic protection to be effective on the entire structure, effective protection potentials must be measured on all the identified measurement points.

[0009] The measurement of the potential, in the presence of active cathodic protection, is called the “On Potential” measurement. A diagram illustrating how cathodic protection apparatuses are currently constructed is shown in figure 2. They essentially comprise: an anode dispersion electrode; a reference electrode; at least one electrical connector connectable to the metal structure to be protected in at least one respective measuring point; a central control unit configured to circulate a cathodic protection current between the anode dispersion electrode and the metal structure to be protected and to detect a difference in electrical potential between the reference electrode and the measuring point.

[0010] The central control unit receives a reference signal representative of a reference value to be attained at the measuring point and regulates the intensity of the cathodic protection current supplied to the metal structure as a function of the reference value and of the detected difference in electrical potential. As illustrated in Figure 2, such regulation is typically performed by a control board comprising a PID (Proportional, Integral, Derivative) type controller that receives the reference signal and the detected difference in electrical potential to generate a corresponding error signal as the difference between the reference signal and the detected difference in electrical potential, as well as a regulator that, adjusts the intensity of the cathodic protection current as a function of the error signal .

[0011] In some more recent devices, with the sole purpose of isolating the control board from the signals coming from the place where the reference electrode and the metal structure to be protected are installed, there are analog-to-digital and digital-to-analog conversion circuits for greater protection from any overvoltages. In the most common devices on the market, the difference in electrical potential between the reference electrode and the measuring point is directly supplied to the control board because the analog-to-digital and digital-to-analog conversion circuits are not present.

[0012] However, the difference in electrical potential between the reference electrode and the measuring point does not represent the real potential of the structure, but is the sum of the real potential value (called “IR-free potential”) plus an unwanted component that is added, given by the voltage drop (V=I*R) generated by the current circulating in the ground (I) between the reference electrode and the protected structure (which therefore represents a resistance R):

[0013] On Potential = IR-free Potential + IR

[0014] The reference standards indicate potential values that must be reached to be in a condition of effective cathodic protection, and always refer to the IR-free Potential. For this reason, there are various measurement techniques to measure the IR-free Potential. The ON-OFF techniques are based on the interruption of the protection current, so that the ohmic drop (IR) is cancelled in a very short time (typically in the order of a millionth of a second) while the overvoltage of the reduction reaction in longer times. When the circulation of current is temporarily interrupted, the ohmic drop is temporarily cancelled and the IR-free Potential is measured.

[0015] Among these techniques, the most effective is the so-called “instant-off on coupon” measurement, which involves the use of an external potential probe, also called "coupon", which is an object characterized by a metal surface of known area, electrically connected to the structure to be protected, positioned near or incorporated into the reference electrode.

[0016] Current power supplies provide the following operating modes: o Manual o Regulation al a constant voltage-, the output voltage V supplied by the power supply is regulated and therefore the current supplied I will be simply given by the formula I :::: V7R where R is the total resistance of the electrical circuit, at. the ends of the power supply, whose main components are the resistance of the structure to be protected and the resistance of the ground in which it is buried. Obviously in this regulation, the current supplied wall depend strongly on the seasonality wet / dry ground) and on specific variations in the resistance of the ground as a result of weather conditions (rain, heat, etc.). In this regulation, the presence of a reference electrode to perform a measurement of the On potential is not necessary. o Automatic: in the “automatic” operating modes, the device has a measurement circuit that allows the device, depending on the type of regulation chosen, to have feedback on the effect of its regulation, modifying its output voltage to keep the chosen parameter constant. These are the possible regulation modes: o Regulation at a constant current the device is given an output current value I to be kept constant, the device has a measurement channel that reads the value of the current actually supplied and varies its output voltage V over time to keep the current constant at the set value I at all times. In this regulation, the presence of a reference electrode to carry out an On potential measurement is not necessary'. o Regulation at a constant potential', the device is given a local On potential value to be kept constant, the device has a measurement channel that reads the On potential measurement and varies the supplied current I over time to keep the On potential constant at all times at the set value. In this regulation, the presence of a reference electrode to carry out the On potential measurement is necessary'. o Regulation at a constant potential with base current the device is given a local On potential value to be kept constant and a minimum current (base current) to be always delivered; the device has a measurement channel that reads the On potential measurement and varies the delivered current I over time to keep the On potential constant at the set value at all times, unless the delivered current drops to the set base current value, in which case the device will continue to deliver this minimum current even if the On potential does not correspond to the one indicated. In this regulation, the presence of a reference electrode to carry out the On potential measurement is necessary.

[0017] In all the described automatic operating modes, the reference (current or potential) is a local quantity, and the regulation of the device output is managed, in the most modern power supplies, through a PID (Proportional Integral Derivative) control algorithm, which compares the present reading of the quantity taken as a reference and the value set as the regulation target, modifying the current supply to follow' the set value. This type of management mainly has two technical limitations:

[0018] 1. The regulation at a constant potential is based on the On potential: this means that the PID algorithm tracking also considers IR voltage drops in the comparison, which do not represent a real change in the protection of the structure (IR-free potential), and this leads to an “over-reaction” of the device, which therefore tends to vary its current supply more times than necessary, often resulting in more current than necessary, with the following disadvantages: a. Higher electricity consumption, b. Excess current supplied to the metal structure, which can generate overprotection of the cathode, which in turn causes other technical problems, c. Increase in interference generated towards other metal structures, whose cathodic protection systems will in turn be forced to react to the interference by increasing the supplied current, in turn increasing the interference generated towards other metal structures;

[0019] 2. The regulation at a constant potential is based on a local potential, but cathodic protection must be effective on the entire metal structure and the power supply has no information on the effect that the current it is supplying actually has on the structure: this analysis is usually managed a posteriori by expert technicians, who, depending on measurements and checks carried out along the grid, can decide to change the reference value (setpoint) indicated as the target local potential for the power supply,

[0020] SUMMARY

[0021] A cathodic protection apparatus, defined in claim 1, has been found and is the subject of this disclosure, which allows to solve at least in part the above-mentioned drawhacks encountered in the protection of a metal structure because it allows to detect the IR-free potential by means of an “instant off on coupon” technique and to regulate the cathodic protection current supplied so that the detected IR-free potential is maintained at a regulation value.

[0022] The apparatus of this disclosure comprises an electrical monitoring device connectable to the structure at a measuring point and to an external potential probe (coupon), which provides an electrical “off’ potential present on the external potential probe when the external potential probe (coupon) is temporarily disconnected from the structure, and which further includes: - an analog-to-digital conversion circuit configured to receive the “off’ electrical potential and the electrical potential present on the reference electrode of the apparatus, to generate a digital signal representative of the IR-free potential of the tnetal structure at the measurement point obtained as the difference between the “off” electrical potential and the electrical potential present on the reference electrode,

[0023] - a digital -to-analog conversion circuit configured to generate an analog signal corresponding to the digital signal representative of the IR-free potential of the metal structure at the measurement point, which is transmitted to a control unit of the apparatus.

[0024] The control unit of the apparatus is configured to:

[0025] - control the electrical monitoring device so as to temporarily disconnect the coupon from the metal structure to be protected,

[0026] - receive the analog signal representative of the IR-free potential and receive a regulation signal representative of a regulation value (setpoint) for the measurement point,

[0027] - regulate an intensity of the cathodic protection current delivered to the metal structure as a function of the regulation value and the IR-free potential.

[0028] More in detail, this disclosure provides a cathodic protection apparatus for protecting a metal structure, said apparatus comprising: an anodic dispersing electrode; a reference electrode, an external potential probe "coupon", which can be electrically connected to the metal structure to be protected; at least one electrical connector, configured to be connected to the metal structure to be protected in at least one respective measurement point so as to be at a same electric potential of said measurement point, a central control unit, comprising an adjustable power supply configured to supply a cathodic protection current and to circulate said cathodic protection current between said anodic dispersing electrode and the metal structure to be protected, wherein the adjustable power supply is configured to supply said cathodic protection current with an intensity determined by a command signal provided by the adjustable power supply of the central control unit, and wherein said central control unit is connected to said reference electrode and to said external potential probe "coupon" and is configured to detect an electrical potential difference between said reference electrode and said external potential probe "coupon"; an electrical monitoring device distinct and separated by the central control unit, directly connected via respective electrical lines to said at least one electrical connector, to said reference electrode and to said external potential probe "coupon", said electrical monitoring device comprising a switch and being configured to:

[0029] - connect, through said switch, said external potential probe "coupon" to said electrical connector,

[0030] - detect a respective external electric potential present on said external potential probe and a respective electric potential present at said at least one electrical connector when said at least one electrical connector is connected in said at least one measurement point,

[0031] - open on command said switch to interrupt a current circulating between said connector and said external potential probe "coupon", and

[0032] - provide an "off' electrical potential present on the external potential probe when said switch is open and the external potential probe "coupon" is disconnected from said electrical connector; said electrical monitoring device further comprising:

[0033] - an analog-digital conversion circuit configured to receive said "off electrical potential and the electrical potential present on the reference electrode, and to generate a digital signal representative of the IR-free potential of the metal structure in said measurement point obtained as the difference between the “off’ electrical potential and the electrical potential present on the reference electrode,

[0034] - a digital-analog conversion circuit configured to generate an analog signal, corresponding to the digital signal, representative of the detected IR-free potential of the metal structure at said measurement point; wherein said control unit is configured to

[0035] - command said electrical monitoring device to open / close said switch,

[0036] - receive said analog signal representative of the detected IR-free potential and receive a regulation signal representative of a regulation value "setpoint" for said measurement point,

[0037] - generate said command signal to adjust an intensity of the cathodic protection current supplied to said metal structure, said command signal being generated as a function of said regulation value and said IR-free potential.

[0038] According to one aspect, the central control unit includes a central control unit comprising:

[0039] - a PID type controller configured to receive said analog signal and said regulation signal, and to generate an error signal as a difference between the analog signal and the regulation signal,

[0040] - a regulator configured to receive said error signal and to adjust the intensity of the cathodic protection current based on said error signal.

[0041] According to one aspect, the central control unit is configured to be connected to a cloud server so as to receive said regulation signal from the cloud server and to transmit to said cloud server values of the IR-free potential of the metal structure in at least said measurement point.

[0042] It is further disclosed a process of cathodic protection that may be implemented using the apparatus of this disclosure.

[0043] More precisely, the process of cathodic protection according to the present disclosure comprises the steps of: providing and installing a cathodic protection apparatus; with the electrical monitoring device:

[0044] - circulating a cathodic protection current between the anodic dispersing electrode and the metal structure to be protected,

[0045] - detecting an electrical potential difference between the reference electrode and the external potential probe "coupon",

[0046] - detecting a respective external electric potential present on the external potential probe and a respective electric potential present in said at least one measurement point,

[0047] - opening on command the switch that connects the external potential probe "coupon" to the electrical connector connected to the metal structure to be protected at the measurement point, to interrupt a current circulating between them, - providing an "off electrical potential present on the external potential probe when said switch is open and the external potential probe "coupon" is disconnected from said electrical connector; with the digital-analog conversion circuit, generating an analog signal representative of the IR-free potential of the metal structure in said measurement point obtained as the difference between the "off electrical potential and the electrical potential present on the reference electrode; with the central control unit:

[0048] - receiving a regulation signal representing a regulation value for said measurement point,

[0049] - generating the regulation signal for the adjustable power supply for adjusting an intensity of the cathodic protection current supplied to said metal structure as a function of said regulation value and said IR-free potential.

[0050] According to one aspect, the apparatus comprises a plurality of electrical connectors connected at respective measurement points to the metal structure to be protected and a plurality of said electrical monitoring devices, and wherein the central control unit is configured to be connected to a cloud server so as to receive the regulation signal from the cloud server and to transmit to said could server values of the IR-free potential of the metal structure in at least one measurement point of said measurement points, the process further comprising the following operations: detecting the IR-free potential of the metal structure in at least one measurement point of said measurement points; determining said regulation value as a function of at least one value of said values of the IR-free potential.

[0051] According to one aspect, the process comprises the following steps: selecting a measurement point among said monitored measurement points and defining a respective regulation value and a respective variation interval defining a maximum deviation between the IR-free potential detected at the selected measurement point and the respective regulation value; detecting said IR-free potential in the selected measurement point and, if the IR- free potential detected in the selected measurement point exceeds the respective regulation value by more than said maximum deviation, varying a current intensity of cathodic protection provided to the structure until the difference between said detected IR-free potential and said regulation value is not less than the maximum deviation.

[0052] According to one aspect, the step of detecting said IR-free potential at the selected measurement point is performed by the related monitoring device at the measurement point when queried periodically at regular time intervals by said server.

[0053] According to one aspect, the step of detecting said IR-free potential in the selected measurement point is performed autonomously by the relevant monitoring device, which signals to said server only when the difference between said detected IR-free potential and said regulation value exceeds the maximum deviation.

[0054] The apparatus and method of the present disclosure are more precisely defined in the appended claims.

[0055] BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a basic diagram illustrating a cathodic protection apparatus connected to a metal structure to be protected.

[0057] Figure 2 is a block diagram of operation of a cathodic protection apparatus implementing a control method with constant On Potential.

[0058] Figure 3 illustrates a protection apparatus according to the present disclosure, suitable for implementing a control method to maintain the constant IR-Free potential on the metal structure to be protected.

[0059] Figure 4 is a flow chart illustrating a control method with constant On Potential, of a known type.

[0060] Figure 5 is a flow chart schematically illustrating the control method according to the present disclosure.

[0061] Figure 6 shows a block diagram illustrating an embodiment of a control method according to the present disclosure.

[0062] Figure 7 shows another block diagram illustrating another embodiment of a control method according to the present disclosure.

[0063] DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0064] In order to overcome and solve at least partially the technical problems set forth above, this disclosure illustrates a cathodic protection apparatus, which in addition to the standard operating modes described above, allows a further automatic operating mode: º Regulation at a constant IR-free potential, the power supply also manages the connection of a coupon at the input, and integrates the measurement circuitry of the remote monitoring devices that allow the instant-off measurement to be carried out on coupons to have the ER-free Potential. The peculiarity of the circuit allows a measurement to be carried out on cycles of a few milliseconds, thus allowing the possibility of carrying out the measurement several times within a second and being able to use this reference at the input to the PID circuit to allow this value to be followed instead of the ON Potential.

[0065] To better understand the differences with a “standard” device, the operating block diagrams of one of these apparatuses at constant On Potential are shown (Fig. 2) and of an apparatus according to the present disclosure that can operate at a constant IR-Free potential (Fig. 3). The regulation at a constant IR-free potential therefore allows the tracking of the PID algorithm to consider in the comparison only the real polarization variation of the protected structure, thus eliminating the effect of the IR ohmic voltage drops. Consequently, the power supply of the device, which supplies the protection current, will “react” by varying the current supplied only when really necessary.

[0066] The device illustrated in figure 3 can operate by implementing different cathodic protection procedures, which vary depending on how the current supplied is regulated, for example according to the following combinations: º Regulation at a constant IR-free potential with base current, in addition to performing a constant IR-free potential regulation, the possibility of indicating a minimum cathodic protection current to be supplied ahvays is added, for an operation similar to that described in the constant potential regulation with base current. º Regulation at a constant IR-free potential with safety limits: in addition to performing a constant IR-free potential regulation, the possibility of indicating a minimum current and a maximum current is added, within which to limit the regulation carried out according to the PID algorithm, to ensure the continuous supply of at least the minimum current, and in addition the possibility of also establishing a maximum current that can be supplied by the device's power supply during the regulation (for safety or technical reasons).

[0067] The operation of cathodic protection with power supplies in automatic mode requires that they work to maintain a constant quantity (current, On potential, IR-free potential) that is measured locally. However, effective cathodic protection must be guaranteed over the entire metal structure to be protected, in the case of gas or oil pipeline networks, over the entire structure to be protected, which can also extend over several tens of km2.

[0068] .According to one aspect of this disclosure, in order to have effective cathodic protection on a metal structure that has a relatively large surface area, several measuring points on the structure to be protected are identified where potential measurements can be made, in order to verify that in all these points an IR-free potential value compliant with the minimum required by the regulations is respected. Based on these collected values, the regulation values (setpoints) of the power supplies in automatic operation that supply the respective cathodic protection currents are calibrated to ensure that effective protection IR-free potential values are reached on all the measuring points. In the currently used devices, this calibration is done and maintained even for several years, so this calibration tends to be very conservative, with the risk that the chosen setpoints lead to constantly supplying more current than necessary’, in order to be sure to guarantee cathodic protection on the entire structure. Figure 4 schematically illustrates the management of cathodic protection according to current practice, in which the regulation value (setpoint), i.e. the current that the T / R power supply must supply, is established by an operator and is kept constant for long periods of time.

[0069] According to an aspect of this disclosure, illustrated schematically in figure 5, multiple measurement points are arranged on the structure to be protected and among all the measurement points, the most critical ones are identified, to be monitored more frequently or to be equipped with remote monitoring devices for continuous control, so that if effective cathodic protection is guaranteed on these points, it can be reasonably assumed that the entire structure is adequately protected.

[0070] On the basis of this principle, a dynamic control and management algorithm of the setpoint of cathodic protection apparatuses is proposed, with the aim of ensuring effective cathodic protection of the entire structure at all times, supplying at all times the minimum current necessary for this purpose. This objective is achieved by using as a reference given to a power supply in automatic operation of a device no longer the measurement of a local signal, but the measurement of a remote signal, coming from one or more critical points identified in the cathodic protection system, assumed as the point to be monitored.

[0071] Figure 5 schematically illustrates a process according to the present disclosure. Conveniently, the setpoint value used will be chosen so as to guarantee the minimum current supply to have effective cathodic protection on the entire structure to be protected. All this can be done for example with the device of the present disclosure illustrated in figure 3, but it can also be implemented with different types of devices, such as those without an external potential probe (coupon). More generally, the process can be implemented using the following elements: º A cathodic protection power supply with remote control, therefore with a remote communication channel always "on". º A measurement point equipped with a remote monitoring device with a power supply such as to make possible a remote communication channel always "on“ or with the possibility of several switch-ons during the day. º A management unit, which for example can be a server / cloud that runs a management algorithm.

[0072] According to one aspect, the management algorithm can also be executed by the device itself that manages the monitoring devices at the various measuring points, without requiring a connection to a remote server.

[0073] Figure 6 shows an example of a flowchart of an algorithm according to the present disclosure that implements a synchronous management (“Time driven”), whilst figure 7 shows an example of a flowchart according to the present disclosure of an asynchronous management (“Event driven”). According to one aspect, the management algorithm will work in this way: º For a remote point, which will conveniently be the most critical point of the structure to be protected, a regulation potential Eref.remwill be defined for the observed quantity that will be: o The On Potential, if the measuring point is not equipped with coupons or the remote monitoring device is not able to perform the instant-off measurement on coupons, or o The ER-free Potential, if the measuring point is equipped with coupons and the remote monitoring device is able to perform the instant-off measurement on coupons; º For the remote point, a “dead band” will be defined, i.e. a variation range of the On Potential or IR-free Potential at the remote point considered admissible, for which the relative regulation value (setpoint) is not changed as long as the observed quantity (On Potential or IR-free Potential) remains within this range; º The power supply of the cathodic protection apparatus is set to automatic operation (in the previously described modes with constant current or constant potential with / without base current); º At regular set intervals (figure 6) or as soon as it is detected at the measuring point that it detects that the observed quantity is outside the dead band (figure 7), the monitoring device at the remote measuring point is put in communication with the power supply that must supply the protection current. º In the case in which communication occurs at regulated intervals (figure 6), if at the time of communication the observed quantity is within the dead band, everything is left unchanged and the communication channel is closed;

[0074] • Whether communication occurs at regular intervals (figure 6) or only when the observed quantity is outside the dead band (figure 7), if it is verified that the observed quantity is outside the dead band for a minimum interval of time settable in the algorithm (time intervals that can also be asymmetrical with respect to exceeding the upper and lower limit of the dead band), the power supply that supplies the cathodic protection current begins to vary its intensity until the observed quantity at the remote point returns to the setpoint value Eref.rem. At this point:

[0075] ■ If the power supply was previously set to constant current, the new constant current value set will correspond to the last current value supplied that allowed Eref.remto be reached,

[0076] ■ If the power supply was previously set to constant potential (with or without base current), º If the regulation is performed at constant ON Potential (standard power supplies), the value of the local On Potential corresponding to the Eref.remvalue is saved and this value is set as the setpoint, possibly keeping the value of the base current unchanged (if present);

[0077] « If the regulation is performed at constant IR-free Potential (which can be done with the power supply of this disclosure illustrated in figure 3), the value of the local IR-free potential corresponding to the Eref.remvalue is saved and this value is set as the setpoint, possibly keeping the value of the base current unchanged (if present).

[0078] ■ Once the power supply setpoint is reset, the communication channel is closed waiting for the next regulation cycle / event.

[0079] The above described algorithms can also be implemented using a cathodic protection apparatus that can selectively connect to multiple remote monitoring devices connected to respective measurement points. According to one aspect, in this case the criterion for choosing the “dominant” point can be the following: º All points can have a potential equal to or more negative than their respective Eref.remregulation values; º Regulation stops when the measuring point with the potential that most exceeds its respective Eref.remis brought back to its Eref.remvalue.

[0080] Conveniently, a device of this disclosure of the type illustrated in figure 3 will be used with multiple monitoring devices at the various measurement points, but the management algorithm shown in figures 6 and 7 can also be implemented on a device that detects the On Potential.

[0081] Optionally, multiple devices of different types can also be used. In this case, for each device it is possible to indicate one or more reference points, and each power supply will be managed as described above. Alternatively, or even in addition, with an artificial intelligence engine it is possible to manage more complex balancing rules between the various apparatuses, also as a function of predicted values based on the history' of measurements carried out over time, and not only on the measured real-time values.

Claims

CLAIMS1. A cathodic protection apparatus for protecting a metal structure, said apparatus compri sing: an anodic dispersing electrode; a reference electrode; an external potential probe "coupon", which can be electrically connected to the metal structure to be protected; at least one electrical connector, configured to be connected to the metal structure to be protected in at least one respective measurement point so as to be at a same electric potential of said measurement point; a central control unit, comprising an adjustable power supply configured to:- supply a cathodic protection current and to circulate said cathodic protection current between said anodic dispersing electrode and the metal structure to be protected, wherein the adjustable power supply is configured to supply said cathodic protection current with an intensity determined by a command signal provided by the adjustable power supply of the central control unit, and wherein said central control unit is connected to said reference electrode and to said external potential probe "coupon" and is configured to- detect an electrical potential difference between said reference electrode and said external potential probe "coupon"; an electrical monitoring device distinct and separated by the central control unit, directly connected via respective electrical lines to said at least one electrical connector, to said reference electrode and to said external potential probe "coupon", said electrical monitoring device comprising a switch and being configured to:- connect, through said switch, said external potential probe "coupon" to said electrical connector,- detect a respective external electric potential present on said external potential probe and a respective electric potential present at said at least one electrical connector when said at least one electrical connector is connected in said at least one measurement point,- open on command said switch to interrupt a current circulating between said connectorand said external potential probe "coupon", and- provide an "off’ electrical potential present on the external potential probe when said switch is open and the external potential probe "coupon" is disconnected from said electrical connector; said electrical monitoring device further comprising:- an analog-digital conversion circuit configured to receive said "off" electrical potential and the electrical potential present on the reference electrode, and to generate a digital signal representative of the IR-free potential of the metal structure in said measurement point obtained as the difference between the “off’ electrical potential and the electrical potential present on the reference electrode,- a digital-analog conversion circuit configured to generate an analog signal, corresponding to the digital signal, representative of the detected IR-free potential of the metal structure at said measurement point; wherein said control unit is configured to- command said electrical monitoring device to open / close said switch,- receive said analog signal representative of the detected IR-free potential and receive a regulation signal representative of a regulation value "setpoint" for said measurement point,- generate said command signal to adjust an intensity of the cathodic protection current supplied to said metal structure, said command signal being generated as a function of said regulation value and said IR-free potential.

2. The cathodic protection apparatus according to claim 1, wherein said central control unit includes a central control unit comprising:- a PID type controller configured to receive said analog signal and said regulation signal, and to generate an error signal as a difference between the analog signal and the regulation signal,- a regulator configured to receive said error signal and to adjust the intensity of the cathodic protection current based on said error signal.

3. The cathodic protection apparatus according to one of the previous claims, wherein said central control unit is configured to be connected to a cloud server so as to receive said regulation signal from the cloud server and to transmit to said cloud server valuesof the IR-free potential of the metal structure in at least said measurement point.

4. A process of cathodic protection of a metallic structure, said process comprising the operations of: providing and installing a cathodic protection apparatus according to one of the preceding claims; with said electrical monitoring device:- circulating a cathodic protection current between the anodic dispersing electrode and the metal structure to be protected,- detecting an electrical potential difference between the reference electrode and the external potential probe "coupon”,- detecting a respective external electric potential present on the external potential probe and a respective electric potential present in said at least one measurement point,- opening on command the switch that connects the external potential probe "coupon” to the electrical connector connected to the metal structure to be protected at the measurement point, to interrupt a current circulating between them,- providing an "off electrical potential present on the external potential probe when said switch is open and the external potential probe "coupon" is disconnected from said electrical connector; with said digital-analog conversion circuit, generating an analog signal representative of the IR-free potential of the metal structure in said measurement point obtained as the difference between the "off” electrical potential and the electrical potential present on the reference electrode; with said central control unit:- receiving a regulation signal representing a regulation value for said measurement point,- generating the regulation signal for the adjustable power supply for adjusting an intensity of the cathodic protection current supplied to said metal structure as a function of said regulation value and said IR-free potential.

5. The process according to claim 4, wherein the apparatus comprises a plurality of electrical connectors connected at respective measurement points to the metal structure to be protected and a plurality of said electrical monitoring devices, and wherein thecentral control unit is configured to be connected to a cloud server so as to receive the regulation signal from the cloud server and to transmit to said could server values of the IR-free potential of the metal structure in at least one measurement point of said measurement points, the process further comprising the following operations: detecting the IR-free potential of the metal structure in at least one measurement point of said measurement points; determining said regulation value as a function of at least one value of said values of the IR-free potential .

6. The process according to claim 5, comprising the following operations: selecting a measurement point among said monitored measurement points and defining a respective regulation value (Eref.rem) and a respective variation interval defining a maximum deviation between the IR-free potential detected at the selected measurement point and the respective regulation value (Eref.rem); detecting said IR-free potential in the selected measurement point and, if the IR-free potential detected in the selected measurement point exceeds the respective regulation value (Eref.rem) by more than said maximum deviation, varying a current intensity of cathodic protection provided to the structure until the difference between said detected IR-free potential and said regulation value (Eref.rem) is not less than the maximum deviation.

7. The process according to claim 6, wherein said operation of detecting said IR-free potential at the selected measurement point is performed by the related monitoring device at the measurement point when queried periodically at regular time intervals by said server.

8. The process according to claim 6, wherein said operation of detecting said IR-free potential in the selected measurement point is performed autonomously by the relevant monitoring device, which signals to said server only when the difference between said detected IR-free potential and said regulation value (Eref.rem) exceeds the maximum deviation.

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