System and method for managing stray currents

Abstract

An example system includes an electrically insulating coating disposed on a metallic substrate to be protected from corrosion; a covering anode disposed on the electrically insulating coating and configured to conduct electricity; an electron source interconnected with the metallic substrate at a negative terminal and to the covering anode at a positive terminal, the electron source configured to apply a voltage to cause the metallic substrate to act as a cathode in an impressed current cathodic protection system; a first controller to control the electron source to apply the voltage; a second controller interconnected with the covering anode and the metallic substrate, the second controller configured to: detect a stray current received at the covering anode; and in response to detecting the stray current, cooperate with the first controller to adjust the voltage supplied by the electron source.

Description

SYSTEM AND METHOD FOR MANAGING STRAY CURRENTSFIELD

[0001] The specification relates generally to corrosion protection systems, and more particularly to a system and method for managing stray currents.BACKGROUND

[0002] Stray currents (or interference currents) may be defined as currents that follow paths other than their intended circuit. When stray current is discharged, corrosion will occur. Stray current corrosion may be observed in rail transit systems, pipeline systems and electric distribution systems, among others.SUMMARY

[0003] According to an aspect of the present specification an example system includes: an electrically insulating coating disposed on a metallic substrate to be protected from corrosion; a covering anode disposed on the electrically insulating coating and configured to conduct electricity; an electron source interconnected with the metallic substrate at a negative terminal and to the covering anode at a positive terminal, the electron source configured to apply a voltage to cause the metallic substrate to act as a cathode in an impressed current cathodic protection system; a first controller to control the electron source to apply the voltage; a second controller interconnected with the covering anode and the metallic substrate, the second controller configured to: detect a stray currentreceived at the covering anode; and in response to detecting the stray current, cooperate with the first controller to adjust the voltage supplied by the electron source.

[0004] According to another aspect of the present specification, an example method includes: applying, by a first controller via an electron source, a voltage to the ICCP system to cause a metallic substrate to be protected by the ICCP system to act as a cathode to protect the metal substrate from corrosion; detecting, at a covering anode of the ICCP system, a stray current; and in response to detecting the stray current, adjusting the current supplied by the electron source.BRIEF DESCRIPTION OF DRAWINGS

[0005] Implementations are described with reference to the following figures, in which:

[0006] FIG. 1 depicts a schematic diagram of an example impressed current cathodic protection system with stray current management.

[0007] FIG. 2 depicts a schematic diagram of an example interaction of an external system emitting stray current with the system of FIG. 1 .

[0008] FIG. 3 depicts a schematic circuit diagram of the system of FIG. 1 .

[0009] FIG. 4 depicts a flowchart of an example method of stray current management in an impressed current cathodic protection system.DETAILED DESCRIPTION

[0010] Stray current may originate from almost any electrical systems that use grounds or groundings, such as electric rail ways, light-rail systems, cathodic protection systems,electrical welding machines and other grounded direct current (DC) electric sources. Stray currents may leave their intended path because the current finds a path with low resistance, such as a buried metal pipe or some other metal structure, or an electrolyte with low resistance, such as salt water. The stray current may flow to and from that structure. Stray currents may cause accelerated corrosion to occur where they leave the metal structure and enter the surrounding electrolyte. The site where the current enters the structure will become cathodic in nature, while the site where the current leaves the metal will become anodic. For example, systems such as buried pipelines, ship hulls or other metallic structures that share an electrolytic environment with some sources of stray current may be at risk of stray current corrosion or other effects.

[0011] In another example, an on-board electric welding machine can create stray currents in a ship and can cause an accelerated attack of the hull of the ship as the stray currents generated at the welding electrodes pass out of the hull through the water back to a grounded DC line located on shore. Work boats or construction barges that do welding of structures or pipelines in the water can cause severe stray-current damage to the structure.

[0012] Another example is a steel-hulled vessel moored to a cathodic-protected dock facility. The dock's cathodic protection system can cause stray current damage to the vessel.

[0013] Stray currents are usually thought of as being DC currents. However, severe damage can also be caused by alternating currents (AC). Alternating currents are induced onto pipelines that run parallel and close to power lines.

[0014] In accordance with the present disclosure, an impressed current cathodic protection (ICCP) system may be configured to manage stray current received at the ICCP system. In particular, the ICCP system includes a covering anode separated by an electrically insulating layer from a metallic substrate to be protected. The covering anode acts as a Faraday cage to keep voltage resulting from stray current at an exterior surface of the ICCP system (i.e., at the covering anode) to limit stray current corrosion of the metallic substrate. Further, the covering anode and the metallic substrate act as a capacitor, allowing the system 100 to store electricity generated by the stray current at the surface (i.e., the covering anode). The stray current may therefore be used as the impressed current or a portion thereof in the ICCP system, and hence the system may adjust (i.e., reduce) a voltage supplied by the ICCP system source.

[0015] Thus, the total voltage at the covering anode may be maintained at a predefined target level to reduce the likelihood of localized and concentrated discharge of current to return to the external system from which the stray current was received. In some examples, the system may further include a battery configured to harvest and store excess electricity resulting from the stray current from the covering anode to maintain the predefined target level of voltage at the covering anode. The stored electricity may subsequently be used as a power or energy source in the ICCP system to reduce the overall power consumption of the system.

[0016] FIG. 1 depicts a system 100 for managing stray current in accordance with the present disclosure. In particular, the system 100 is an impressed current cathodic protection (ICCP) system configured to protect a metallic substrate 104. For example, themetallic substrate 104 may be a pipe (e.g., for an underground pipeline or the like), a vehicle or vessel (e.g., a marine vessel, such as a ship, a car, or the like) or other similar metallic substrate which may be prone to corrosion.

[0017] The system 100 further includes an electrically insulating layer 108 applied on the substrate 104. The electrically insulating layer 108 may itself serve to protect the substrate 104 from corrosion. In some examples, the electrically insulating layer 108 may include a series of coatings and / or layers configured to protect the substrate 104. However, damage to the electrically insulating layer 108 and other coatings over time may allow defects to form, thereby exposing the substrate 104. Accordingly, the system 100 further includes a covering anode 112 and an electron source 116 which is connected at a negative terminal to the substrate 104 and at a positive terminal to the covering anode 112. The electron source 116 is configured to protect the substrate 104 via ICCP.

[0018] In particular, the electrically insulating layer 108 separates the substrate 104 and the covering anode 112 to prevent current from flowing through the system 100. When a defect develops in both the electrically insulating layer 108 and the covering anode 112 (e.g., a crack or similar) that allows an electrolyte to interconnect the covering anode 112 and the substrate 104, an electrochemical cell is formed and allows current to flow from the positive terminal of the electron source 116 to the covering anode 112, through the electrolyte and the substrate 104, and return to the negative terminal of the electron source 116. That is, current is impressed or applied to the substrate 104 via the covering anode 112 and the electrolyte to cause the substrate 104 to act as a cathode in the ICCPsystem 100. The flow of electrons from the electron source 116 to the substrate 104 protects the substrate 104 from corrosion.

[0019] The system 100 may further include a first controller 120 integrated with or interconnected to the electron source 116 to control the application of current in the system 100. For example, the first controller 120 may include any suitable microcontroller, microprocessor, central processing unit (CPU), field programmable gate array (FPGA), application-specific integrated circuit (ASIC), multiple cooperating processors and / or integrated circuits, or the like. The controller 120 may cooperate with a memory, including a combination of volatile (e.g., random access memory or RAM) and non-volatile memory (e.g., read-only memory or ROM, electrically erasable programmable read-only memory or EEPROM, flash memory), having instructions stored thereon which when executed cause the system 100 to realize the functionality described herein. All or some of the memory may be integrated with the controller 120. The controller 120 may further cooperate with a communications interface (not shown) which may be configured for wireless (e.g., satellite, radio frequency, Bluetooth, Wi-Fi, or other suitable communications protocols) or wired communications and may include suitable hardware (e.g., transmitters, receivers, network interface controllers, and the like) to allow the controller 120 to communicate with other computing devices. The specific components of the communications interface may be selected based on the types of communication links that the controller 120 communicates over.

[0020] Preferably, the system 100 may also include sensors embedded in the covering anode 112 to detect when an active current flows through the covering anode 112 to thesubstrate 104, thereby indicating a defect in the system 100 (i.e., in the covering anode 112 and the electrically insulating layer 108). For example, such a system is described in PCT / IB2021 / 061321 , the contents of which are incorporated herein by reference. Additionally, the sensors may be spaced apart in the covering anode 112, and respective strengths of signals (e.g., electrochemical current draw signals) detected by the sensors may allow the location of the defect to be identified.

[0021] In practice, the system 100 may be deployed to protect a substrate 104 such as a pipe of a pipeline or the like which may be buried underground for protection from water and other electrolytes present in the earth. Additionally, other external systems and infrastructure may be located nearby which may affect or otherwise influence the performance of the system 100.

[0022] For example, referring to FIG. 2, an example external system 200 is depicted in relation to the system 100, which is buried in the ground. The external system 200 is, in the present example, an electric rail line. In other examples, the external system 200 may include other systems which themselves produce or employ an active current, such as other ICCP systems, utility lines, and the like.

[0023] In the present example, current is provided by a supply 204 via an overhead line 208 to a railcar 212. The current is intended to return via the rails 216 to the supply 204. However, as the rails 216 are situated on the ground, if the rails 216 are not properly insulated and / or the insulation has some deficiencies, then some stray current 220 may leak from the rails 216 and enter the system 100 or other buried systems.

[0024] The stray current 220 may flow along the system 100. In traditional systems, the stray current 220 may discharge from the system 100 at a site 224 (illustrated in dotted lines), to follow a lower resistance path along the metallic structure of the system 100 for a length prior to returning to the supply 204. Accordingly, the discharge of the stray current 220 may tend to be local and concentrated. Thus, in traditional systems, the discharge of the stray current 220 may cause an anodic region in the system 100 which may therefore cause corrosion. Further, due to the localization of the discharge of the stray current 220, the stray current corrosion may be accelerated at the site 224 of the discharge (i.e., as compared to corrosion due to emission of stray current from the system 100 itself).

[0025] However, in the system 100, the covering anode 112, which blankets the body of the substrate 104, acts as a Faraday cage to keep the voltage or electricity resulting from the stray current 220 to the exterior surface of the system 100 (i.e., to the covering anode 112, as opposed to the substrate 104, which may contain fluid). Thus, stray current- induced corrosion at the surface of the substrate 104 is mitigated via the structure of the system 100.

[0026] In addition to the risks of stray current corrosion, the system 100 has the electron source 116 which itself is configured to apply a current. Accordingly, after absorbing the stray current 220, an excess of current (i.e., the combination of the stray current 220 and the applied current from the system 100 itself) may be present in the system 100. This excess of current may make control systems and / or other electronic components of the system 100 vulnerable to damage.

[0027] Accordingly, returning to FIG. 1 , in accordance with the present disclosure, the system 100 may further include a secondary controller 124 configured to manage the voltage resulting from the stray current entering the system 100 above a target voltage level. In particular, two conductive material surfaces or layers (i.e., the substrate 104 and the covering anode 112) are separated by a non-conductive layer (i.e., the electrically insulating layer 108). Accordingly, protective layers and the substrate 104 effectively form a capacitor. The modelled capacitor is therefore capable of storing and harvesting the electric potential from the stray currents.

[0028] In particular, the secondary controller 124 is generally configured to detect stray current (or otherwise excess voltage above the target voltage level) at the covering anode 112. For example, the controller 124 may be interconnected with the line from the positive terminal of the electron source 116 and / or the surface of the covering anode 112 and hence may detect current levels via one or more analog-to-digital converters (ADCs), passive analog circuits or the like. In particular, the stray current may affect the voltage at the covering anode 112, and hence the stray current may be detected by detecting a voltage change in the covering anode 112. In response to detecting the stray current, the controller 124 may cooperate with the controller 120 to adjust the voltage supplied by the electron source 116.

[0029] Thus, rather than supplying current solely via the electron source 116, the current to support the ICCP operation (i.e., to impress current from the anode 112 to the substrate 104) may be supplemented by voltage resulting from the stray current received at the anode 112. In some examples, the system 100 may track a target voltage level (i.e.,optimized according to the ICCP operation). Accordingly, the controller 124 and the controller 120 may cooperate to reduce the voltage supplied by the electron source 116 such that a total voltage (i.e., the voltage resulting from the stray current and the supplied voltage) equal the target voltage level. In other examples, the voltage supplied by the electron source 116 may be terminated entirely, for example if the voltage resulting from the stray current exceeds the target voltage level.

[0030] In some examples, the system 100 may further include a battery 128 configured to store and discharge energy as appropriate. For example, when the voltage resulting from the stray current exceeds the target voltage level, the controller 124 may direct excess voltage to the battery 128 to be converted and stored as energy for subsequent use. Further, when the voltage resulting from the stray current is below the target voltage level, the controller 124 and the controller 120 may cooperate to discharge voltage from the battery 128 rather than from the electron source 116.

[0031] One or both of the controllers 124 and 120 may store a predefined set of metrics, such as bands of stray current levels, battery levels, target voltage levels, and the like, as well as rules defining how to control the application of current by the electron source 116, direction of voltage / current for storage in the battery 128, release of energy stored in the battery 128, or the like. In some examples, the controllers 124 and 120 may be integrated with one another, rather than being implemented as separate controllers.

[0032] Turning to FIG. 3, a schematic circuit diagram of the system 100 is depicted. As noted above, the combination of the substrate 104, the electrically insulating layer 108 and the covering anode 112 acts as a modelled capacitor 300. When a defect occurs inthe electrically insulating layer 108 and the covering anode 112, the defect allows the formation of an electrochemical cell which may act as a consumer 304 in the system 100.

[0033] Electrically, the controller 120 is connected to the electron source 116 (i.e., a main power supply 308) and to the modelled capacitor 300 and the consumer 304. The main power supply 308 may supply electricity to the controller 120 for supplying current in the ICCP system. The controller 120 is thus enabled to control the current supplied based on the detected stray current. That is, the controller 120 may convert the input voltage from the main power supply 308 to a suitable output voltage, for example according to a cooperated determination with the controller 124 based on the stray current, to supply the consumer 304 and charge and discharge the modelled capacitor 300 (e.g., to reduce power consumption and control the electrochemical cell parameters). The controller 120 may further be configured to monitor and regulate the input voltage of the consumer 304.

[0034] In some examples, the lines between the controller 120 and the modelled capacitor 300 may each contain inductors 312-1 and 312-2 to protect the electronic components of the controller 120. The properties of the inductors 312-1 and 312-2 may be calculated according to the system specifications and the type of interferences. For example, the inductors 312-1 and 312-2 may stabilize the voltage prior to feeding the voltage to the consumer 304.

[0035] The system 100 may further include an additional line 316 interconnecting the controller 120 to the consumer 304 to sample the voltage from the consumer 304 and provide the sampled data to the controller 120. Thus, the controller 120 may monitor astatus of the consumer 304 and take appropriate actions according to the sampled voltage.

[0036] The system 100 further includes the controller 124 connected to the battery 128 and to the modelled capacitor 300 and the consumer 304. The controller 124 is fed by the voltage resulting from the stray currents stored on the surface of the modelled capacitor 300. For example, stray current on the covering anode 112 may appear as voltage at the input of the controller 124. The controller 124 may then capture the stray current, accumulate electricity and store the electricity in the battery 128. The controller 124 may further be integrated with an ADC or a passive analog circuit to detect the stray current, and may communicate with the controller 120 according to the detected stray current.

[0037] Turning now to FIG. 4, the functionality implemented by the system 100 will be discussed in greater detail. FIG. 4 illustrates a method 400 of managing stray current. The method 400 will be discussed in conjunction with its performance in the system 100. In other examples, the method 400 may be performed by other suitable devices or systems.

[0038] At block 405, the system 100 detects a stray current, such as the stray current 220, at the covering anode 112. For example, the stray current 220 may be detected via an ADC circuit, a passive analog circuit, or the like associated with the second controller 124. For example, a voltage resulting from the stray current may be identified upon detecting a voltage level above a predefined target voltage level. That is, the system 100 may expect that the predefined target voltage level is supplied by the electron source 116, andhence any voltage above the target voltage level is detected as a result of receipt of the voltage resulting from the stray current 220 at the covering anode 112. In other examples, other manners of detecting the stray current 220 are also contemplated.

[0039] At block 410, the system 100 determines whether a storage condition for the stray current 220 is met. The storage condition may represent criteria for which the detected stray current is to be harvested and stored in the battery 128. For example, the storage condition may include the battery 128 being depleted below a predefined energy level, the amount of detected voltage resulting from the stray current 220 being above a predefined storage level, or the like. In other examples, other storage conditions and / or combinations of the above and similar are also contemplated.

[0040] If the determination at block 410 is affirmative, that is the storage condition for the voltage resulting from the stray current 220 is met, then the system 100 proceeds to block 415. At block 415, the system 100 is configured to harvest the stray current 220 and store the converted energy in the battery 128. For example, the voltage resulting from the stray current 220 may be stored at the surface of the modelled capacitor 300 - i.e., at the covering anode 112 - and accumulated by the controller 124 for storage in the battery 128.

[0041] If the determination at block 410 is negative, that is the storage condition for the voltage resulting from the stray current 220 is not met, and / or after the performance of block 415, the system 100 proceeds to block 420. At block 420, the system 100 determines whether an energy release condition is met. The energy release condition may represent criteria for which energy in the battery 128 is configured to be released toapply an impressed current for the ICCP operation for protection of the substrate 104. For example, the energy release condition may include the battery 128 being above a predefined energy level, the main power supply 308 being below another predefined energy level, the amount of voltage resulting from the stray current 220 being below a predefined level, or the like. In other examples, other energy release conditions and / or combinations of the above and similar are also contemplated.

[0042] If the determination at block 420 is affirmative, that is, the energy release condition is met, then the system 100 proceeds to block 425. At block 425, the system 100, and more particularly, the second controller 124, is configured to release energy from the battery 128 to supply the impressed current for the ICCP operation of the system 100.

[0043] If the determination at block 420 is negative, that is the energy release condition is not met, and / or after performance of block 425, the system 100 proceeds to block 430. In some examples, performance of blocks 415 and 425 may be mutually exclusive (i.e., if voltage resulting from the stray current is harvested, then the battery 128 may not be simultaneously configured to release energy), and hence the system 100 may proceed from block 415 directly to block 430. At block 430, the system 100, and more particularly, the controllers 120 and 124 in cooperation, may adjust the emitted voltages to achieve the a predefined target voltage level.

[0044] That is, the system 100 may determine a total voltage level, for example including application of voltage from the electron source 116, the battery 128 and the stray current 220. If the total voltage level exceeds the predefined target voltage level, then one or both of the controllers 120 and 124 may adjust the voltage applied by the electron source 116and the battery 128, respectively, to be reduced until the target voltage level is achieved. In some examples, the controllers 120 and 124 may follow a set of predefined rules defining prioritization of emission of voltage by the electron source 116 or the battery 128. For example, when the battery 128 has sufficient energy stored therein, the controllers 120 and 124 may prioritize application of voltage from the battery 128 to allow the battery 128 to have capacity to be recharged with excess stray current, if excess stray current is incurred. In other examples, other prioritization rules are also contemplated.

[0045] As described herein, an ICCP system may be equipped with a secondary controller and optionally a battery to detect and manage stray current from external systems. In particular, the controller may cooperate with the main controller of the ICCP system to limit voltage applied to the covering anode of the ICCP system to a predefined target voltage level. Excess voltage induced from the stray current above the predefined target level may be managed, for example by harvesting storing the excess voltage in a battery and / or adjusting the voltage applied by the ICCP system itself to maintain the predefined target voltage level. This may allow the ICCP system to limit stray current corrosion, since there is a limited buildup of voltage at the covering anode above the predefined target voltage level, and hence current may be less likely to leave the system in a localized and concentrated manner. Further, the harvested energy may be stored and subsequently released to apply voltage to the system instead of the main power source for increased longevity and sustainability of the system.

[0046] The scope of the claims should not be limited by the embodiments set forth in the above examples but should be given the broadest interpretation consistent with the description as a whole.

Claims

CLAIMS1 . A system comprising: an electrically insulating coating disposed on a metallic substrate to be protected from corrosion; a covering anode disposed on the electrically insulating coating and configured to conduct electricity; an electron source interconnected with the metallic substrate at a negative terminal and to the covering anode at a positive terminal, the electron source configured to apply a voltage to cause the metallic substrate to act as a cathode in an impressed current cathodic protection system; a first controller to control the electron source to apply the voltage; a second controller interconnected with the covering anode and the metallic substrate, the second controller configured to: detect a stray current received at the covering anode; and in response to detecting the stray current, cooperate with the first controller to adjust the voltage supplied by the electron source.

2. The system of claim 1 , further comprising an analog-to-digital converter configured to detect the stray current at the covering anode and detect a voltage change resulting from the stray current.

3. The system of claim 1 , wherein the first and second controllers are configured to cooperate to adjust a total voltage comprising (i) the voltage applied by the electron source, and (ii) a voltage resulting from the stray current to achieve a predefined target voltage level.

4. The system of claim 1 , further comprising a battery interconnected with the second controller, the battery configured to store electricity resulting from the stray current as energy.

5. The system of claim 4, wherein the second controller is configured to: determine whether a storage condition is met; and when the storage condition is met, harvest stray current and the electricity from the stray current to be stored in the battery as energy.

6. The system of claim 4, wherein the second controller is further configured to control the battery to release an applied voltage such that a total voltage comprising (i) the voltage applied by the electron source, (ii) a voltage resulting from the stray current, and (iii) the applied voltage from the battery, achieves a predefined target voltage level.

7. The system of claim 6, wherein the second controller is configured to: determine whether an energy release condition is met; andwhen the energy release condition is met, release the applied voltage from the battery.

8. The system of claim 1 , wherein the first controller and the second controller are integrated.

9. A method in an impressed current cathodic protection (ICCP) system, the method comprising: applying, by a first controller via an electron source, a voltage to the ICCP system to cause a metallic substrate to be protected by the ICCP system to act as a cathode to protect the metal substrate from corrosion; detecting, at a covering anode of the ICCP system, a stray current; and in response to detecting the stray current, adjusting the voltage supplied by the electron source.

10. The method of claim 9, further comprising detecting the stray current by detecting a voltage change at the covering anode from a predefined target voltage level.11 . The method of claim 10, wherein adjusting the voltage comprises adjusting a total voltage comprising (i) the voltage applied by the electron source, and (ii) a voltage resulting from the stray current, to achieve the predefined target voltage level.

12. The method of claim 9, further comprising: harvesting electricity from the stray current and storing the electricity as energy in a battery of the ICCP system.

13. The method of claim 12, further comprising: determining whether a storage condition is met; and harvesting and storing electricity from the stray current in response to determining that the storage condition is met.

14. The method of claim 12, further comprising: controlling the battery to release an applied voltage such that a total voltage comprising (i) the voltage applied by the electron source, (ii) a voltage resulting from the stray current, and (iii) the applied voltage from the battery, achieves a predefined target voltage level.

15. The method of claim 14, further comprising: determining whether an energy release condition is met; and releasing the applied voltage from the battery in response to determining that the energy release condition is met.

Images