Potential probe and method for measuring the cathodic protection potential applied to a buried metal structure

Abstract

Probe (1) for measuring the cathodic protection potential applied to a buried metal structure comprising: a first pair of electrodes (4,5) arranged with axes H4, H5 lying on a first plane P1; a second pair of elongated electrodes (6,7) arranged with axes H6, H7 lying on a second plane (P2) perpendicular to the first plane P1; a fifth central elongated electrode (10) which has an axis H10 whose track passes through a central point C; the fifth electrode (10) is configured to be connected to the buried metal structure in order to simulate a defect of the cladding on which the measurement is to be made. A processing unit (15) calculates the value of the field DDP REAL IR Free which depends on the cathodic protection alone by eliminating the effect of the potential drop induced by the interfering electric field present in the ground and makes this value measurable with any device on the market today.

Description

[0001] "POTENTIAL PROBE AND METHOD FOR MEASURING THE CATHODIC PROTECTION

[0002] POTENTIAL APPLIED TO A BURIED METAL STRUCTURE. "

[0003] Cross-Reference to Related Patent Applications

[0004] This patent application claims priority of the Italian patent application No. 102024000017335 filed on July 25, 2024, the content of which is incorporated by reference herein.

[0005] Technical field

[0006] The present invention refers to an electrochemical potential probe and a method for measuring the effectiveness of the cathodic protection systems applied to a buried metal structure with purification of the value acquired from the error induced by the presence of voltage drops in the ground through the analysis of the same and their elimination by electronic processing of the acquired data.

[0007] Background of the invention

[0008] The use of cathodic protection systems for the protection of buried metal structures has been a well-established technique for years and is regulated by national and international standards and, in Italy, by specific legislations that make the technique mandatory in the natural gas transport, distribution and storage sector with regular checks by the competent authorities.

[0009] Examples of cathodic protection systems are for example known from documents: WO2021107776 Al, US4823072 A and W02007107652 A2.

[0010] A buried metal structure has a natural and spontaneous tendency to degrade due to corrosion. Typically the metal reacts with water and oxygen to produce metal oxides as corrosion products. Cathodic protection is an electrochemical technique that, by imposing a direct current on the surface of the buried structure, allows to reduce the corrosion phenomenon up to negligible values. In particular, a protection current is imposed on the metal structure by forcibly introducing electrons into the metal that compensate for those that would be ’’lost" during the corrosion process. In this way the surfaces of the metal structure in contact with the ground do not oxidize.

[0011] The measurement of the electrochemical potential of buried structures is necessary in order to evaluate the effectiveness of the cathodic protection systems.

[0012] This measurement is carried out by comparing the electrochemical potential of the buried structure and subjected to cathodic protection with the potential of a reference electrode.

[0013] Typically, the reference electrode consists of an electrochemical copper / copper sulphate couple in saturated solution (Cu / CuSCg) contained in a casing provided with a porous baffle in order to allow ionic transport.

[0014] The measurement of potential is inevitably influenced by the presence of electric fields in the ground that can be induced by external interferences (e.g. current leakage from electrically driven transport systems) or by the same cathodic protection current that is operating on the structure.

[0015] These electric fields generate a measurement error represented by the potential drop, known as "IR" which in turn depends on the resistivity of the ground, on the physical distance between the active part of the electrode (porous baffle) and the first defect present on the buried structure, and on the circulating current density.

[0016] Since the distance from the first defect is not determinable, due to the randomness of the arrangement of the defect of the claddings, it is not possible to predict the value of the potential drop which can also assume significant values, rendering the measurements carried out with classic methods unusable.

[0017] The reference standard requires that the measured potential values be purified of the ohmic drop contribution providing a potential value defined as IR-FREE. To date, the correction of the measured potential value is carried out, according to current standard (UNI EN ISO 15589-1), using a polarisation plate arranged at a predetermined distance from the reference electrode and electrically connected with the buried structure.

[0018] The reference electrode and polarisation plate assembly is defined as a "potential probe" in accordance with UNI 11094:2019 standard.

[0019] However, the correction value thus obtained is often inaccurate since, depending on the geometry of the probe and the local current intensity, a residual error remains, linked to physical factors, which cannot be eliminated, and which can assume significant values.

[0020] Aim of the present invention is to realise a measurement system based on a potential probe that succeeds in obtaining an IR-Free value on the basis of the actual instantaneous assessment of the IR value present at the probe and its elimination by mathematical processing obtained thanks to an electronic processing unit associated with the probe.

[0021] The measurement system will allow that:

[0022] • the effects due to the geometry of the probe are eliminated.

[0023] • the measurement from the IR ohmic drop is significantly reduced if not completely eliminated.

[0024] • the effects of the electrical interference on the measurement to be minimized.

[0025] • it is possible to carry out reliable measurements even in the state of active cathodic protection. • measurable values are returned from any device (multimeter, remote measurement, remote control) currently on the market.

[0026] The above aim is achieved by the present invention in that it relates to a system for measuring the cathodic protection potential applied to a buried metal structure of the type described in claim 1.

[0027] The present invention also relates to a method for measuring the cathodic protection potential applied to a buried metal structure of the type described in claim 6.

[0028] Brief description of the drawings

[0029] The invention will be shown with reference to the accompanying drawings which represent a preferred embodiment thereof wherein:

[0030] Figure 1 schematically shows a probe for measuring the cathodic protection applied to a buried metal structure realized according to the present invention;

[0031] Figure 2 shows the principle of operation of the probe of Figure 1 and of the method;

[0032] Figure 3 shows, in partially exploded perspective view, a probe realized in accordance with the technical indications of the present invention; and

[0033] Figure 4 shows, in top and bottom view and in longitudinal section, the probe of Figure 3.

[0034] Preferred embodiment example

[0035] According to the present invention and with reference to Figures 1 and 2, a probe 1 for measuring the cathodic protection potential applied to a buried metal structure (not shown, for example pipes belonging to a gas distribution system) is described, comprising: - a first pair of straight electrodes 4,5 arranged with axes H4, H5 lying on a first plane Pl (perpendicular to the plane of Figure 1); and

[0036] - a second pair of straight electrodes 6,7 arranged with axes Hg, H7lying on a second plane P2 perpendicular to the first plane Pl (also the second plane P2 is perpendicular to the plane of Figure 1);

[0037] The electrodes 4,5 and 6,7 are arranged in such a way that the straight lines R1 and R2 passing through the tracks of the axes EU, Hsand He, H7 respectively and lying on a plane perpendicular to the planes Pl and P2 intersect at a central point C equidistant from the axes H4, H5and He, H7and define four quadrants QI, Q2, Q3 and Q4 each delimited by a pair of four directrices DI, D2, D3, D4 which are generated from the central point C and are perpendicular with respect to the two adjacent ones.

[0038] In this way, the tracks of the axes H4, H5 He, H7 lie on the same circumference having centre C.

[0039] In particular, the quadrant QI is delimited by the directrices DI and D2, the quadrant Q2 is delimited by the directrices D2 and D3, the quadrant Q3 is delimited by the directrices D3 and D4 and the quadrant Q4 is delimited by the directrices D4 and DI.

[0040] In the prototype made, the circumference has a circular area of approximately 78.5 cm2.

[0041] A fifth central metal electrode 10 (acting as a polarization plate) has an axis H10 whose track passes through the point C. The fifth central electrode 10 is configured to be connected to the buried metal structure (not shown) in order to be representative of a defect of the cladding on which the measurement is to be made. The fifth central electrode is formed, for example, by a hemisphere of carbon steel (the same material from which the pipes are formed) placed centrally between the reference electrodes 4,5 and 6,7. Each electrode 4,5, 6,7 belonging to the first or second pair is made - with known techniques and therefore not further detailed - by an electrochemical copper / copper sulphate pair in saturated solution (Cu / CuSCU) arranged in a plastic casing provided with a porous baffle at the base (this casing will be detailed later).

[0042] The electrode 1 is of the active type and comprises a processing unit 15 which receives the signals coming from all the five electrodes and measures the potential value El, E2, E3 and E4 present on the electrodes 4,6, 5 and 7 respectively. The electronic unit 15 is adapted to perform the following operations when the sensor is buried and is used to measure the cathodic potential:

[0043] - measure a first vector Vi provided by the potential difference (E1-E3) between the first pair of electrodes 4,5 and measured along the straight line R1 with the positive pole of the measurement positioned on the electrode 4;

[0044] - measure a second vector V2 provided by the potential difference (E2-E4) between the second pair of electrodes 6,7 and measured along the straight line R2 with the positive pole of the measurement positioned on the electrode 6;

[0045] - carry out the vector sum between the first vector Vi and the second vector V2 obtaining a resultant vector Vm = Vi+V2 that expresses by means of a vector the electric field DCE referring to the four quadrants QI, Q2, Q3 and Q4. The measured value DCE of electric field is stored.

[0046] The electric field DCE (whose effect is to be removed from the measurement of the potential) is the cathodic one.

[0047] The electronic unit 15 is further configured to choose one of the electrodes of the first pair 4,5 and the second pair 6, 7 with which to measure the potential on the fifth electrode 10 and select a directrix.

[0048] The choice is determined by calculating: the potential difference with sign DdPl between the first and second electrode of the first pair (4 and 5); the potential difference with sign DdP2 between the first and second electrodes of the second pair (6 and 7); determining the absolute value Vmax of the potential drops between the electrodes of the first and second pair.

[0049] In more detail, the criterion used for the choice of the electrode between the four electrodes and the selection of the directrix is as follows:

[0050] • If Vmax=DdPl the chosen electrode is the first 4 of the first pair 4,5 and the directrix is D3;

[0051] • If Vmax=-DdPl the chosen electrode is the second 5 of the first pair and the directrix is DI;

[0052] • If Vmax=DdP2 the chosen electrode is the first 6 of the second pair and the directrix is D2; and

[0053] • If Vmax=-DdP2 the chosen electrode is the second 7 of the second pair 6,7 and the directrix is D4.

[0054] The measurement of potential drop comprises a component caused by the Electric Field present in the ground and falling on the measurement directrix identified (DI in the example) and another component deriving from the cathodic protection in place.

[0055] The angle that the direction of the electric field DCE (whose value has been determined previously, see above) forms with respect to the above determined directrix is then determined. The angle is determined with the following formula:

[0056] Formula 1: Formula 2:

[0057] If DdPl / 2 > DdP2 / 2 formula 1 is used.

[0058] Otherwise DdPl / 2 < DdP2 / 2 formula 2 is used.

[0059] The projection IRDI of the electric field DCE previously determined on the selected directrix Di and with the previously determined angle a is then determined, for example using the formula:

[0060] Formula 3 ]rRr>Di= —Ddp—l cosa

[0061] Formula 4 „ IrRr>DI= —Dd-p—2 cosa

[0062] If Ddpl>Ddp2 formula 3 is used otherwise (Ddpl<Ddp2) formula 4 is used.

[0063] Finally, the value of the potential drop Ve~io measured between the chosen electrode and the fifth electrode 10 is corrected by subtracting from this potential drop Ve-io the projection IRm in order to detect the value of the field DDP REAL IR Free which depends on the cathodic protection alone.

[0064] This DDP REAL Free value represents the final measurement free from the effect of the field:

[0065] DDP RealIRFree= Ve- 10 — IRDI

[0066] This value will be measurable with any device on the market today. Figure 3 shows a cylindrical tubular casing 17 housing the two pairs of electrodes 4,5 and 6, 7. There are four partition baffles 18 delimiting the space within the cylindrical tubular casing 17 into four chambers within each of which a respective electrode 4,5,6 and 7 is housed.Along the axis of the cylindrical casing 17 runs a cable for connection to the fifth electrode 10. Each chamber is delimited by an end wall 20 of the cylindrical casing 17 on which a respective opening 21 opens, closed by a porous baffle 23 allowing the passage of ions. A cylindrical casing 30 arranged coaxial to the axis of the casing 17 houses the electronic circuit 15 and is arranged in contact with a second end wall 24 of the casing 17.

[0067] Numerals

[0068] 1 probe 1 for measuring the cathodic protection potential

[0069] 4, 5 first pair of electrodes

[0070] H4, H5axes

[0071] Pl first plane

[0072] 6,7 second pair of electrodes

[0073] Hs, H7axes

[0074] P2 second plane

[0075] R1 and R2 straight lines

[0076] QI, Q2, Q3 and Q4 four quadrants

[0077] DI, D2, D3, D4 directrices

[0078] 10 fifth electrode (coupon)

[0079] H10 axis

[0080] Vifirst vector Gcfull gradient

[0081] 15 processing unit

[0082] 17 cylindrical casing

[0083] 20 first end wall 21 opening

[0084] 23 porous baffle

[0085] 24 second end wall

[0086] 30 cylindrical casing

Claims

CLAIMS1. Probe (1) for measuring a cathodic protection potential applied to a buried metal structure comprising:- a first pair of electrodes (4,5) arranged with axes H4, H5 lying on a first plane Pl; and- a second pair of electrodes (6,7) arranged with axes He, H? lying on a second plane (P2) perpendicular to the first plane Pl; the electrodes (4,5 and 6,7) are arranged in such a way that the straight lines R1 and R2 passing through the tracks of the axes H4, Hsand He, H7 respectively and lying on a plane perpendicular to the planes Pl and P2 intersect at a central point C equidistant from the axes H4, H5and He, H7and define four quadrants QI, Q2, Q3 and Q4 each delimited by a pair of four directrices DI, D2, D3, D4 which are generated from the central point C and are perpendicular one to the two adjacent ones;- a fifth central electrode (10) which has an axis H10 whose track passes through the central point C; the fifth central electrode (10) is configured to be connected to said buried metal structure in order to simulate a defect in the cladding on which the measurement is to be made; a processing unit (15) configured to: i) receive at least one potential value El, E3, E2 and E4 present on the first and second electrodes of the first pair and on the first and second electrodes of the second pair respectively (4,6, 5 and 7); ii) perform the following operations when the metal structure is buried and is used to measure the cathodic potential: a) measure a first vector Vi provided by the potential difference (E1-E3) between the first pair of electrodes (4,5) and measured along the straight line R1;b) measure a second vector V2 provided by the potential difference (E2-E4) between the second pair of electrodes (6,7) and measured along the straight line R2; c) carry out the vector sum between the first vector Viand the second vector V2 obtaining a resultant vector Vmthat expresses by means of a vector the electric field DCE referring to the four quadrants QI, Q2, Q3 and Q4; d) store the measured value DCE; e) choose one of the electrodes of the first pair (4,5) and the second pair (6, 7) with which to make the final measurement of the potential on the fifth central electrode(10) and select a directrix Di by calculating: el) a first potential difference with sign DdPl between the first and second electrodes of the first pair (4 and 5); e2) a second potential difference with sign DdP2 between the first and second electrodes of the second pair (6 and 7); e3) an absolute value Vmax of the potential drops between the electrodes of the first and second pair; said processing unit (15) is further configured to: f) determine an angle a that the direction of the electric field DCE forms with respect to the selected directrix Di; g) determine a projection 1RDI of the electric field DCE previously determined on the selected directrix Di and with the previously determined angle a; h) correct a value of the potential drop Ve-io measured between the chosen electrode and the fifth central electrode (10) by subtracting from this potential drop Ve~ 10 the projection IRDiin order to detect the value of a field DDP REAL IR Free which depends on the cathodicprotection alone; said DDP REAL Free value represents a final measurement free from the effect of the field:DDP RealIRFree= Fe-10- IRDt .2.- Probe according to claim 1, wherein the processing unit (15) is configured to use the following criterion for choosing the electrode and selecting the directrix Di:• If Vmax=DdPl the chosen electrode is the first (4) of the first pair (4,5) and the directrix Di is D3;• If Vmax=-DdPl the chosen electrode is the second (5) of the first pair and the directrix Di is DI;• If Vmax=DdP2 the chosen electrode is the first (6) of the second pair and the directrix Di is D2; and• If Vmax=-DdP2 the chosen electrode is the second (7) of the second pair (6,7) and the directrix Di is D4.3.- Probe according to claim 2 wherein the processing unit (15) is configured to determine the angle a that the direction of the electric field DCE forms with respect to the selected directrix Di with the following formula:Formula 1:DdpiFormula 2: a = tan1Ddp2If DdPl / 2 > DdP2 / 2 Formula 1 is used; otherwise Formula 2 is used.4.- Probe according to claim 3 wherein the processing unit (15) is configured to determine the projectionof the electric fieldDCE previously determined on the selected directrix Di and with the angle a previously determined according to the formula:> ,„ DdplFormula 3 IRDi= —— ■cosaFormulaIf Ddpl>Ddp2 Formula 3 is used otherwise Formula 4 is used.5.- Probe according to any one of the preceding claims, wherein each electrode consists of an electrochemical copper / copper sulphate pair in saturated solution (Cu / CuS04).6.- Probe according to any one of the preceding claims, wherein a cylindrical tubular casing (17) is provided, housing the first and second pair of electrodes; four partition baffles (18) are provided, delimiting the space within the cylindrical tubular casing (17) into four chambers within each of which a respective electrode (4,5,6 and 7) is housed; each chamber is delimited by an end wall (20) of the cylindrical casing (17) on which a respective opening (21) opens, which is closed by a porous baffle (23) allowing the passage of ions; along the axis of the cylindrical casing (17) runs a cable for connection to the fifth electrode (10).7.- Probe according to claim 6 wherein an additional cylindrical casing (30) is provided arranged coaxial to the axis of the casing (17) and housing the processing unit (15).8.- Method (1) for measuring the cathodic protection applied to a buried metal structure comprising the steps of:- providing a first pair of electrodes (4,5) arranged with axes H4, HS lying on a first plane Pl; and- providing a second pair of electrodes (6,7) arranged with axes Hg, H7lying on a second plane (P2) perpendicular to the first plane Pl; the electrodes (4,5 and 6,7) are arranged in such a way that thestraight lines R1 and R2 passing through the tracks of the axes H4, H5and He, H-?respectively and lying on a plane perpendicular to the planes Pl and P2 intersect at a central point C equidistant from the axes H4, Heand He, H-?and define four quadrants QI, Q2, Q3 and Q4 each delimited by a pair of four directrices DI, D2, D3, D4 which are generated from the central point C and are perpendicular one to the adjacent ones;- providing a fifth central electrode (10) which has an axis H10 whose track passes through the point C; the fifth central electrode (10) being configured to be connected to said buried metal structure in order to simulate a defect in the cladding on which the measurement is to be made;- detecting the potential value El, E3, E2 and E4 present on the first and second electrodes of the first pair and on the first and second electrodes of the second pair respectively (4,6, 5 and 7);- measuring a first vector Vi provided by the potential difference (E1-E3) between the first pair of electrodes (4,5) and measured along the straight line Rl;- measuring a second vector V2 provided by the potential difference (E2-E4) between the second pair of electrodes (6,7) and measured along the straight line R2;- carrying out the vector sum between the first vector Viand the second vector V2obtaining a resultant vector Vm that expresses by means of a vector the electric field DCE referring to the four quadrants QI, Q2, Q3 and Q4;- storing the measured value DCE;- choosing one of the electrodes of the first pair (4,5) and the second pair (6, 7) with which to make the final measurement of the potential on the fifth central electrode (10) and select a directrix Di by calculating: i) a first potential difference with sign DdPl between the first and second electrodes of the first pair (4 and 5);ii) a second potential difference with sign DdP2 between the first and second electrodes of the second pair (6 and 7);- iii) the absolute value Vmax of the potential drops between the electrodes of the first and second pair;- determining an angle a that the direction of the electric field DCE forms with respect to the selected directrix Di; determining a projection IRDiof the electric field DCE previously determined on the selected directrix Di and with the previously determined angle a; correcting the value of the potential drop Ve-io measured between the chosen electrode and the fifth central electrode (10) by subtracting from this potential drop Ve-io the projection IRDiin order to detect a value of the field DDP REAL IR Free which depends on the cathodic protection alone; this DDP REAL Free value represents a final measurement free from the effect of the field:DDP RealIRFree— Ve-10— lRDi9.- Method according to claim 8, wherein the choice of the probe and the selection of the directrix Di is carried out according to the following criterion:• If Vmax=DdPl the chosen electrode is the first (4) of the first pair (4,5) and the directrix Di is D3;• If Vmax=-DdPl the chosen electrode is the second (5) of the first pair and the directrix Di is DI;• If Vmax=DdP2 the chosen electrode is the first (6) of the second pair and the directrix Di is D2; and• If Vmax=-DdP2 the chosen electrode is the second (7) of the second pair (6,7) and the directrix Di is D4.10.- Method according to claim 9, comprising the step of determining the angle a that the direction of the electric field DCEforms with respect to the determined directrix with the following formula:Formula 1:Formula 2:If DdPl / 2 > DdP2 / 2 Formula 1 is used and otherwise Formula 2 is used.11.- Method according to claim 10, wherein the projection lRatof the electric field DCE previously determined on the selected directrix Di and with the previously determined angle a is obtained according to the formula:FormulaFormulaif Ddpl>Ddp2 Formula 3 is used otherwise Formula 4 is used.

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