Patent Grant
12173414
The present disclosure is directed to cathodic protection systems and methods.
Metal structures spontaneously oxidize in the presence of oxygen and common electrolytes such as water or soil. Oxidation turns metals into their oxide form (e.g., rust), which disintegrates and can cause structures to fail. This process, called corrosion, affects bridges, tanks, pipelines, sea walls, and other civil structures. The cost of corrosion was estimated at 2.7% of US GDP, or $450B in 2013. Cathodic protection (CP) systems prevent corrosion by providing an input of energy in the form of electric current from a more electrically active metal (sacrificial anode) or DC power supply (impressed current). It can be difficult to monitor how well a CP system is working because the structure/anodes are buried in soil, underwater, or encased in concrete, making them difficult to inspect.
Some embodiments are directed to a system comprising a cathodic protection system having an anode and configured to protect a protected structure from corrosion. The system comprises a monitoring circuit operatively coupled to the cathodic protection system. The monitoring circuit comprises an electrical-to-optical transducer. The electrical-to-optical transducer is configured to generate a light signal in response to electrical current flowing between the protected structure and the anode of the cathodic protection system, the protected structure and a reference electrode, or the reference electrode and the anode.
Some embodiments are directed to a method comprising protecting a protected structure from corrosion using a cathodic protection system comprising an anode. The method comprises monitoring for corrosion at the protected structure using a monitoring circuit comprising an electrical-to-optical transducer. The method also comprises generating, by the electrical-to-optical transducer, a light signal in response to electrical current flowing between the protected structure and the anode, the protected structure and a reference electrode, or the reference electrode and the anode. The method further comprises communicating the light signal to a remote data acquisition system via a fiber-optic link.
The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments.
The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.
A wide array of electrochemical sensors exist for monitoring corrosion based on open circuit potential, surface potential, concrete resistivity, polarization resistance, noise analysis, and galvanic current. These approaches are hampered by issues with durability, sensitivity to electromagnetic interference (EMI), and stability over the very long (>25 year) timescales associated with the lifetime of a civil structure.
Embodiments of the disclosure are directed to systems and methods for monitoring the status of a CP system. Embodiments of the disclosure differ from conventional electrochemical sensors in that a corrosion signal detected by the CP circuitry is converted to a light signal which is transmitted by an optical fiber, a detection and transmission method which is stable over long timescales in harsh environments and immune to EMI. For example, commercial off the shelf (COTS) telecom-grade laser diodes have a lifetime of 10{circumflex over ( )}6 hours (>100 years).
Fiber optic sensors based on a fiber Bragg grating (FBG) have been demonstrated for corrosion sensing as they are rugged, immune to EMI, and can be easily multiplexed in arrays. However, FBGs are sensitive to strain and temperature only, which makes them difficult to couple to corrosion-related processes. Embodiments of the disclosure differ from FBG-based fiber sensors in that an FBG is a passive element: for an FBG sensor, an optical pulse is injected from the outside, and certain spectral components are reflected back. According to various embodiments, there is no FBG and the optical signal can be generated directly using at least some of the current from the CP system. In some implementations, an optical pulse may be injected from the outside to provide power (e.g., Power-Over-Fiber or POF) and/or trigger the start of a measurement. It is noted that fiber optic current sensors based on the Faraday effect are not sensitive enough to measure the small currents associated with corrosion.
Sacrificial anodes with built in current monitors are commercially available and can form part of a remote-monitoring cathodic protection (RMCP) system. These conventional systems communicate with a base station via a wired connection or a wireless connection. Such systems are powered via solar power, wind power, or electrical power from a rectifier (for impressed current). In some cases, RMCP nodes are equipped with a GSM or satellite transmitter to wirelessly transmit information about the state of the node.
Embodiments of the disclosure differ from these systems in that the corrosion signal is transduced to an optical signal and transmitted over optical fiber. Compared to commercial RCMP systems, fiber optic transmission provides a way to transmit signals with low loss over long distances (10-100 km) which is compatible with buried/submerged structures such as pipelines, tanks, bridge piers, and sea walls. Wireless GSM or satellite signals cannot propagate long distances underground or underwater due to absorption. The fiber connection also provides for the delivery of power to the sensor (e.g., via a POF arrangement), for transmission of a trigger signal, and to multiplex with existing fiber infrastructure, including other sensors.
Embodiments of the disclosure are directed to systems and methods for measuring the current flowing in a cathodic protection system using an optical transducer powered at least in part by the CP system. A cathodic protection system slows or halts corrosion by making the protected structure (e.g., steel) the cathode in an electrochemical circuit, such that electrons flow from an anode to the steel. This requires an input of energy. The energy is supplied by either spontaneous electron flow from a more active “sacrificial” anode (see
A unique aspect of the present disclosure is placement of a light source (e.g., a laser diode or LED) in series with the CP circuitry shown in the figures which generates light when current flows. The light signal produced by the light source can by communicated to a remote data acquisition system/analyzer via a fiber-optic link. One or more characteristics of the light signal can be analyzed to determine the presence, absence, and extent of corrosion at that protected structure (e.g., steel structure).
The system 100 also includes a monitoring circuit 110 operatively coupled to the CP system 101. The monitoring circuit 110 includes an electrical-to-optical transducer 112. By way of example, and with reference to
The electrical-to-optical transducer 112 is configured to generate a light signal 114 in response to electrical current flowing between the protected structure 104 and the sacrificial anode 102 of the CP system 101. As will be described hereinbelow, the light signal 114 is communicated to a data acquisition system/analyzer via a fiber-optic link. The data acquisition system/analyzer is typically situated at a monitoring station remote from the system 100.
As is best shown in
For sacrificial anode CP systems, such as that shown in
The ICCP system 201 includes a DC power source 115 electrically connected to the inert anode 202 and the protected device 104. The inert anode 202 is driven by the DC current provided by the DC power source 115. The DC power source 115, which can be referred to as a rectifier, is configured to develop a high potential difference between the surface of the protected structure 104 to be protected and the inert anode 202. The DC power source 115 is used to generate the electric current and this current provides cathodic protection to the protected structure 104. It is noted that impressed current systems provide better results relative to sacrificial CP systems when a large current is required for cathodic protection.
For impressed current, the voltage is set by the DC power source 115 and can be 24 V or more. The current flowing in the circuit is determined by the resistivity of the electrolyte 105. The NACE specification for a structure to be considered protected is a potential of −850 mV vs copper sulfate electrode. If the potential is too negative (e.g., <−1 V vs Ag/AgCl), then the protected structure is overprotected, which degrades coatings and can weaken the structure through hydrogen embrittlement. The typical impressed current required to protect a steel structure is around 22 mA/m2.
The system 200 also includes a monitoring circuit 110 operatively coupled to the CP system 201. The monitoring circuit 110 includes an electrical-to-optical transducer 112 coupled in series with the DC power source 115, the anode 202, and the protected structure 104 via electrical connections 106, 108. The electrical-to-optical transducer 112 can include an LED, a laser diode or a superluminescent device, for example. As previously discussed, the electrical-to-optical transducer 112 is configured to generate a light signal 114 in response to electrical current flowing between the protected structure 104 and the sacrificial anode 202 of the CP system 201. The light signal 114 is communicated to a data acquisition system/analyzer via a fiber-optic link. The data acquisition system is typically situated at a monitoring station remote from the system 200.
As illustrated, the coupling circuit 302 is electrically coupled to the anode 102/202 and the protected structure 104 via electrical connections 106, 108. The coupling circuit 302 is also electrically coupled to the electrical-to-optical transducer 112. The coupling circuit 302 can include a voltage converter configured to step up a voltage generated in response to the electrical current flowing between the protected structure 104 and the anode 102/202. The voltage converter of the coupling circuit 302 can be configured to drive the electrical-to-optical transducer 112 with the stepped-up voltage.
According to some embodiments, the system 300 can include a power subsystem 304. The power subsystem 304 can be configured to supply power to the monitoring system 110. For example, the power subsystem 304 can include an energy harvesting device. According to various embodiments, the energy harvesting device can include one or more of a photovoltaic cell circuit, a thermoelectric circuit, a piezoelectric circuit, and a hysteretic circuit configured to harvest energy from galvanic corrosion. The power subsystem 304 can include an energy storage device coupled to receive and store energy from the energy harvesting device. The energy storage device can include one or both of a battery and a capacitor (e.g., a supercapacitor).
The energy harvesting device circuit can combine an energy storage element, such as a capacitor, with a DC-DC converter to step up the low voltage signal from the energy harvesting device. The stored energy can be used to generate short bursts of power to acquire and transmit data in the form of a light signal 114. Off-the-shelf energy harvesting/power management ICs can run on an input voltage as low as 0.020 V and produce an output voltage of 3.3 V or more (with a correspondingly reduced average current).
As is further shown in
In some embodiments, the power subsystem 304 can include a Power-Over-Fiber apparatus configured to convert optical energy carried by the 502 optical fiber into electrical energy. The electrical energy converted from optical energy is used to provide power to the monitoring circuit 110. As was previously discussed, the light signal 114 generated by the electrical-to-optical transducer 112 is communicated to a remote data acquisition system via the fiber-optic link 502. This same fiber-optic link 502 can be used as the optical link of the Power-Over-Fiber apparatus.
The semiconductor light source of the electrical-to-optical transducer 112 converts electrical current into light. A suitable semiconductor light source is a commodity telecom laser diode which operates at 1550 nm with a forward voltage of 1 V, a threshold current of 10 mA, and an electro/optical conversion efficiency of around 3%. Low threshold 850 nm VCSELs in research have thresholds of <1 mA at drive voltages of <2 V. This driving voltage and current is broadly compatible with the power supplied by a cathodic protection system (˜1 V, 10 s of mA). The power consumption of a laser diode is around 20 mW (e.g., compare this to a wireless GSM transmitter which requires >1000 mW in a remote area).
According to some embodiments, a CP system of the present disclosure can provide sufficient power to run a laser diode as the electrical-to-optical transducer 112. Some embodiments of the disclosure aim to harvest some of the electrical energy from a CP system to drive a light source to sense the status of the CP system. For example, the light emission may provide a readout of the current flowing from anode to cathode. This provides both a qualitative verification that the circuit is complete and also a quantitative measure of how corrosive the environment is (e.g., more corrosion leads to more current which leads to more light emission).
The process flow 600 also involves energy harvesting and power management 602, typically implemented by coupling circuitry of the CP system. The process flow 600 further involves encoding 606 an electrical signal indicative of current flow between the anode and the protected structure. The encoded electrical signal is communicated to an electrical-to-optical transducer 608 which converts the encoded electrical signal to a corresponding light signal. The light signal is transmitted to a data acquisition and control facility 612 via a fiber-optic link 610.
The data acquisition and control facility 612, which typically includes an analyzer (see, e.g., block 506 of
In some implementations, the voltage controlled switch 706 can be closed by coupling the voltage controlled switch 706 to a photovoltaic cell. In some implementations, a light pulse (e.g., a trigger stimulus) can be sent into the electrical-to-optical transducer 112 via a fiber-optic link which closes the voltage controlled switch 706 and discharges the capacitor 704. As such, data is read out of the electrical-to-optical transducer 112 only when triggered. Accordingly, the power consumption of the overall CP system is extremely low.
The conclusion is that the Mg sacrificial anode 906 both protected the steel wool 903 and drove the LED 912 to emit light, providing a positive indication that the steel wool 903 was protected (or alternatively, that the beaker was full of electrolyte, completing the circuit). This was a somewhat unrealistic demonstration because Mg (high driving voltage) in seawater (high conductivity) with a short path length (low resistance) provides a very large current and also overprotects the steel wool 903. An actual monitor system would use a sacrificial anode that is more appropriate for that environment (e.g., Mg in high resistivity soil, Zn in seawater), which would generate a smaller current, hence the usefulness of power management or external power, which could be supplied over the same fiber as the read out signal (e.g., via a Power-Over-Fiber arrangement).
As an example use case, in a sacrificial anode system both steel and anode are buried and difficult to access, making inspection difficult or impossible. In this case, a laser diode and single mode fiber can be installed on the electrical path connecting the anode to steel at the time of anode installation. Coupling the laser diode to a single mode optical fiber allows the fiber to be deployed above ground at the time of anode installation and connected to a test station that could be many kilometers away. During its normal life, the anode supplies electrons which cause the laser diode to emit. When the sacrificial anode is consumed, the flow of current stops, and the laser diode stops emitting, indicating that the anode must be replaced. Both types of cathodic protection systems (sacrificial anode and impressed current) are frequently deployed in arrays of many anodes, and 1550 nm laser diodes can be readily multiplexed via single mode fibers and wavelength-division multiplexing to effectively cover a whole structure, enabling one to pinpoint which sections are corroding most rapidly. This allows better use of the limited time available for inspection.
One common application for sacrificial anodes is in water heaters. The high temperature inside a water heater presents a corrosive environment, so a sacrificial anode is usually installed to prevent the water heater tank from corroding and eventually rupturing. A sacrificial CP system of the present disclosure can be implemented in water heaters.
Besides detecting the status of the anode, another way to implement various embodiments of the disclosure is to detect changes in the electrolyte. For example, some transformers are buried in underground vaults and protected from corrosion via one or more sacrificial anodes. In this configuration, the electrolyte completing the CP circuit is air or dry soil, which has a low conductivity and therefore a low rate of corrosion. If an extreme weather event such as a hurricane fills the vault with seawater, the electrolyte conductivity increases, more current flows through the circuit, and the light source turns on. This could be detected via an indicator light at the surface that tells a technician that there is seawater in the vault. This detection system would not depend on external power, which may be relevant after an extreme weather event where there is no power. This same methodology can be applied to detect saltwater intrusion into wells or aquifers, where a sudden increase in conductivity could trigger an alarm. Currently, saltwater intrusion is measured intermittently using groundwater samples or aerial surveys. Embodiments of the disclosure can provide an effective approach to continuously monitor for saltwater intrusion.
Although reference is made herein to the accompanying set of drawings that form part of this disclosure, one of at least ordinary skill in the art will appreciate that various adaptations and modifications of the embodiments described herein are within, or do not depart from, the scope of this disclosure. For example, aspects of the embodiments described herein may be combined in a variety of ways with each other. Therefore, it is to be understood that, within the scope of the appended claims, the claimed invention may be practiced other than as explicitly described herein.
All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims may be understood as being modified either by the term “exactly” or “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein or, for example, within typical ranges of experimental error.
The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. Herein, the terms “up to” or “no greater than” a number (e.g., up to 50) includes the number (e.g., 50), and the term “no less than” a number (e.g., no less than 5) includes the number (e.g., 5).
The terms “coupled” or “connected” refer to elements being attached to each other either directly (in direct contact with each other) or indirectly (having one or more elements between and attaching the two elements). Either term may be modified by “operatively” and “operably,” which may be used interchangeably, to describe that the coupling or connection is configured to allow the components to interact to carry out at least some functionality (for example, a radio chip may be operably coupled to an antenna element to provide a radio frequency electric signal for wireless communication).
Terms related to orientation, such as “top,” “bottom,” “side,” and “end,” are used to describe relative positions of components and are not meant to limit the orientation of the embodiments contemplated. For example, an embodiment described as having a “top” and “bottom” also encompasses embodiments thereof rotated in various directions unless the content clearly dictates otherwise.
Reference to “one embodiment,” “an embodiment,” “certain embodiments,” or “some embodiments,” etc., means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.
The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the disclosure.
As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
As used herein, “have,” “having,” “include,” “including,” “comprise,” “comprising” or the like are used in their open-ended sense, and generally mean “including, but not limited to.” It will be understood that “consisting essentially of” “consisting of,” and the like are subsumed in “comprising,” and the like. The term “and/or” means one or all of the listed elements or a combination of at least two of the listed elements.
The phrases “at least one of,” “comprises at least one of,” and “one or more of” followed by a list refers to any one of the items in the list and any combination of two or more items in the list.
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