Method for monitoring condition of internal Anti-corrosion coatings of pipelines during their operation

Abstract

FIELD: diagnostics.SUBSTANCE: invention relates to technical diagnostics of the condition of in-pipe anti-corrosion coatings and can be used in pipeline systems with the presence of control access units in the pipeline, ensuring the performance of classical gravimetric tests of corrosion witness samples. Through a corrosion control unit, initially embedded in the pipeline and designed for gravimetric monitoring of metal corrosion, a system of electrodes is introduced into the cavity of the operating pipeline with a coating on a hollow rod for conducting electrochemical impedance spectroscopy. The electrode system is lowered into the pipeline until it rests against the lower generatrix: in this manner the working dummy electrodes with the applied coating will be exposed to the aggressive aqueous phase and mechanical impurities carried away by the flow of the medium through the pipeline. Data on the electrochemical behaviour of the working electrodes, polarized from the counter electrode, are taken in the form of a Nyquist diagram or a Bode diagram. The appearance of these diagrams will signal the onset of coating destruction processes on the imitation samples and the development of subfilm corrosion of the sample metal. When ensuring the similarity criterion between the coating on the samples and the coating on the pipeline wall, the onset of these processes on the simulators will mean that the working coating in the pipeline will begin to deteriorate in a similar manner.EFFECT: tracking the onset of destruction of protective coatings of pipelines and the onset of corrosion development underneath them using electrochemical methods of influencing the coating and during the operation of the pipeline, i.e., in-situ in the area of the lower generatrix of the pipes, where the insulating layer is exposed to the aqueous phase and mechanical impurities.3 cl, 2 dwg

Description

[0001] The method relates to the field of technical diagnostics of the condition of in-pipe anti-corrosion coatings and can be used in pipeline systems of various purposes transporting corrosive-aggressive media with the presence of an operating system of access control units in the pipeline, ensuring the performance of classical gravimetric tests of corrosion witness samples.

[0002] Pipes whose internal surface in contact with the process fluid is insulated with a protective polymer coating are not fully protected against corrosion. Localized corrosive dissolution of the metal develops rapidly in areas of severe coating defects or slowly develops under seemingly intact coating if its barrier properties are insufficient for the operating conditions.

[0003] Severe through-and-through defects and discontinuities may occur in the coating due to improper pipeline installation, significant damage under adverse operating conditions not anticipated when selecting the protection system (e.g., intense frictional impact), or the development of manufacturing defects. The coating quality and its characteristics are not stable and consistent across the entire application area. This is due to the specifics of the technological process itself, the technical level of personnel, poor metal surface preparation before application, defects that arise during transportation and installation of pipelines, etc. Therefore, the appearance and development of defects such as thickness variations, discontinuities, peeling, blisters, and chipping are predetermined in the coating. The development and aggravation of these defects are influenced by severe external factors, such as ambient temperature, pressure fluctuations, and the hydroabrasive action of mechanical impurities at high flow rates.Therefore, it is extremely important to conduct periodic quality control of internal coatings during exposure to aggressive working environments.

[0004] Existing studies of coating properties are primarily limited to simulating corrosive environments in laboratory conditions followed by destructive testing of the coating. These harsh conditions lead to uncertainty about the actual condition and protective properties of coatings after exposure to aggressive environments. Destructive methods do not always correspond to real-world exposures and lead to significant discrepancies between the expected and actual results of protective coating application.

[0005] The development of more advanced coating compositions and application technologies requires the implementation of more sophisticated on-site and in-service monitoring systems that enable the correlation of gradual coating degradation and the onset of corrosion. Systems are needed to assess the technical condition of in-line anticorrosive coatings that are sensitive to the early stages of coating degradation in aqueous environments and the onset of subsurface corrosion. Pipeline sections where coating degradation is detected most quickly are potentially hazardous areas for accidents and should be prioritized for enhanced in-line inspection using flaw detectors.

[0006] There are currently no generally accepted, standardized methods for monitoring the integrity of internal anti-corrosion coatings on pipelines in the field. Such methods should allow for monitoring the coating condition (and preparation for it) without interrupting the pipeline's operational process.

[0007] The assessment methodology should characterize the insulation properties of the internal coating and their degradation over time under the influence of the medium composition and flow patterns in the pipe. This will overcome the challenges associated with the high labor intensity of directly determining the internal coating condition of existing pipelines (or the impossibility of doing so for small-diameter systems) in real time, as well as the need for traditional destructive testing of coating systems.

[0008] A prior art discloses a method and device for monitoring the technical condition of internal protective and insulating coatings on operating field pipelines [Russian Federation Patent for Invention RU 2718136 C1, IPC G01N 27 / 82, published March 30, 2020]. This method and device are intended for use in autonomous flaw detection devices inserted into operating pipelines through special launch / receive chambers and propelled by the flow of the working fluid. This method monitors the coating's condition by applying pulsed alternating current through two annular steel supply electrodes located directly at the coating's surface as the flaw detection device moves along the pipeline.The action of these measuring electrodes on the coating through a small electrolyte gap between them occurs in a closed volume of the working medium, formed by the electrically conductive end walls of the housing, which "cut off" the volume of the medium being measured from the surrounding flow. This is done so that the electrical resistance between the liquid within the measuring section and outside it is a multiple of the ohmic resistance of the liquid itself within the volume, measured from edge to edge, i.e., between the insulating end walls. Also located in the measuring space between the working electrodes is a reference electrode, electrically connected to the main volume of liquid in the pipeline.The coating condition is monitored using a measuring bridge circuit, which allows for the monitoring of the pipeline metal potential in the measurement area. This potential depends on the ohmic resistance values ​​of the "supply electrode-liquid in the small gap-coating-pipeline" and the capacitances of the "supply electrode-liquid in the small gap-coating-pipeline" resistances. This relationship is realized because the pipeline can be represented as an extended electrical capacitor, the plates of which are the pipe wall and the liquid product, and the dielectric is the protective coating layer on the metal. In the absence of through defects in the coating and stable ohmic resistance values, the measured pipe metal potential is close to zero. However, when the electrodes pass over areas without a coating on the metal, the capacitive component of the measurement in this area disappears, leading to a sharp multiple increase in the measured signal (the pipe potential in the measurement area).

[0009] The disadvantages of this non-destructive coating testing method during continuous pipeline operation include the mandatory requirement for a flaw detector launcher / receiver chamber—a specially designed component of the pipeline being inspected that allows inspection equipment to pass through its interior. Additionally, preliminary cleaning and pre-diagnostic inspection of the pipeline's interior with special scrapers are required. The pumped product pressure must allow the scraper to move through the pipeline. The instrumentation for this method is expensive, difficult to implement, and requires trained personnel. The method itself, implemented as part of a flaw detector, can only detect gross discontinuities and through-hole defects in the coating and is only applicable to medium- and large-diameter pipelines.

[0010] A device for simulating corrosion in a multiphase water-gas-oil flow for testing samples of internal protective coatings of drill pipes and oil pipelines is known [Patent for Utility Model CN ​​221224511 U IPC G01N 17 / 00, published on June 25, 2024]. The device is included in a laboratory flow rig for simulating liquid flow in oil pipelines and represents a section of a simulation pipeline with a variable wall thickness, included in the flow rig line. A groove is made in the thick-walled region on the inner wall, where a metal plate with an applied coating similar to that used to protect pipes is placed. The geometry of the inner surface of the coated sample repeats the geometry of the inner wall of the test section, and the sample itself is flush with it. Thus, the coated test specimen does not disturb the fluid flow inside the test section and the coating failure in a real pipe is modeled more accurately.When installing the coated specimen into the groove, a sealing resin is applied around the specimen's perimeter to prevent edge effects during coating degradation. The specimen is mounted and held on the outer surface of the test section using mounting screws, ensuring ease of installation and removal.

[0011] This solution is adapted for use in laboratory equipment in the form of a flow-through rig for simulating the flow of working fluids in pipes. Adopting this technical solution for installing a similar sample in a real pipeline with an internal polymer coating reveals two serious drawbacks. First, such a sample can only be installed along the upper generatrix of the pipeline, whereas the aqueous phase, which is aggressive to protective coatings in real horizontal pipelines (especially in oil field pipelines), predominantly coats the lower generatrix of each pipe. The effect of mechanical impurities on the integrity of the coating in this case is also impossible to reproduce. Second, the method only allows visual inspection of major damage to the coating during its removal from the pipeline.Or test the extracted sample in laboratory conditions using classical destructive methods (control of adhesion and electrical insulating properties of the coating).

[0012] A laboratory experimental setup for studying corrosion in a two-phase gas-liquid flow is known in the form of a flow-through loop stand with lines for the liquid and gas phases and their subsequent mixing in the experimental section, where a three-electrode device for measuring electrochemical corrosion is introduced into the internal volume, all electrodes of which are introduced through holes in the side wall of the imitation horizontal pipeline and connected from the outside to the interface of the electrochemical workstation via wired signal lines [Patent for Invention CN 103674822 A, IPC G01N 17 / 00, G01N 17 / 02, published on 03 / 26 / 2014]. The device implements an electrochemical study of corrosion processes on a special experimental coupon (witness sample), which is the working electrode in a three-electrode measurement circuit.A test sample, an auxiliary electrode that polarizes the working electrode by current flowing through the electrolyte, and a silver chloride reference electrode used as a standard for measuring the overvoltage of the other two electrodes are introduced into the pipeline cavity along its upper generatrix. The silver chloride reference electrode exhibits better stability under higher pressure conditions. After testing, the mass loss and appearance of the working electrode caused by corrosion in the flowing medium are measured. Electrochemical signals from the working electrode are also monitored, including corrosion potential, corrosion current density, slope of the cathodic and anodic characteristics, and pitting potential. These data are monitored periodically in situ in a high-temperature, high-pressure fluid flow.The conditions in the test section are close to real conditions of hydrocarbon production, including the nature of the medium flow and its fluidity, which allows for a more realistic and accurate reflection of corrosion.

[0013] This technical solution is also a laboratory rig and is designed to monitor pipe metal corrosion, not internal coating degradation. If some of this solution's features were applied to a real pipeline, corrosion (or coating degradation) would also be monitored only along the upper generatrix, which is not typically exposed to the factors most conducive to wear—water and mechanical impurities.

[0014] The closest technical solution to the claimed invention, adopted as a prototype, is a device for electrochemical testing using a classical three-electrode circuit for erosive and corrosive wear of specially shaped elements (welds, transitions, tees and defects) on the inner surface of underwater pipelines [Patent for invention CN 112903576 A, IPC G01N 17 / 02; G01 N27 / 416, published 06 / 04 / 2021].

[0015] This device, like one of the above-mentioned analogs, is built into a laboratory flow-through bench. The core of the device is a stainless steel tubing segment coated internally with an anodized coating of iridium and titanium oxides.

[0016] The tube segment acts as an auxiliary electrode. Two through holes located opposite each other, along the lower and upper generatrix, provide threaded mounting locations for the working and reference electrodes. One end of the working and reference electrodes is inserted into the tube segment, while the other ends are secured with screw connections to the mounting locations, which also contain terminal rods for connecting wires from the electrochemical workstation.

[0017] The pipeline section, according to the invention, is corrosion-resistant and simultaneously functions as an auxiliary electrode, part of a flow-through laboratory setup for pumping a model medium, and a reaction electrolytic cell. The internal diameter of the pipeline section is similar to the actual pipeline in which the conditions are simulated, ensuring the necessary similarity condition for the flow of the medium during the experiment.

[0018] The working surfaces of the working and reference electrodes face the inside of the test pipe section and are located opposite each other on the upper generatrix of the pipeline (working electrode, open at the bottom) and the lower generatrix (reference electrode, open at the top). The working electrode is made of the same material as the simulated object from the real pipeline, machined into a cylindrical shape, and seated in a mounting seat. Its working surface, in shape and size, matches the design of the specially shaped test pipeline; the reference electrode is silver chloride, machined into a cylindrical shape and seated in a mounting seat in the pipeline wall. The test surface of the working electrode and the inner wall can be coplanar relative to each other, or the surface of the working electrode can protrude above the pipe wall or be recessed relative to the inner wall.In the first case, this simulates wear of the heat-affected zone on a real welded pipe; in the second, wear of a branch or lateral from the main test section; and in the third, wear of a corrosion or metallurgical defect on the surface of a real object. The installation and removal of the working and reference electrodes is convenient, increasing test efficiency. Electrochemical information on the wear process includes recording the potentiodynamic polarization curve and electrochemical impedance.

[0019] This technical solution has some drawbacks. In addition to the prototype being a fragment of a laboratory flow rig, full implementation of such a solution in a real operating field or other pipeline is impossible, as access to the pipeline interior is only possible from above, via the upper generatrix of the pipe. Furthermore, in the proposed technical solution, the working electrode area is only directly adjacent to the surrounding plane of the corrosion-resistant alloy pipeline section, which acts as a polarizing auxiliary electrode, over a small, limited area, significantly reducing the effectiveness of current polarization of the working surface.

[0020] It can be concluded that the existing level of technology leaves room for improvement and leaves a need for more advanced methods for analyzing the quality of coatings on the inner surface of ground pipelines for various purposes in the field and devices suitable for implementing such a task.

[0021] The technical objective of the invention is to embody in the developed method and device all the best examples of the known prior art, while simultaneously eliminating the shortcomings of each of them.

[0022] The technical result is to track the onset of destruction of protective coatings of pipelines and the onset of corrosion development underneath them using electrochemical methods of influencing the coating and during the operation of the pipeline, i.e. in-situ in the area of ​​the lower generatrix of the pipes, where the insulating layer is exposed to the aqueous phase and mechanical impurities, ensuring minimal impact on the flow of the working medium and minimizing the cost and labor intensity of testing, as well as the requirements for the qualifications of maintenance personnel.

[0023] The technical result is achieved by a combination of known and new features, namely, that the monitoring of the technical condition of the internal coating of the pipeline is carried out inside the functioning pipeline in-situ in the flow of the working medium pumped by it by an electrochemical method and with the use of simulators in the form of witness samples with an applied coating, wherein the working electrodes in the form of simulators with an applied coating and a counter electrode that polarizes them are introduced into the operating pipeline through corrosion control units already present in the pipes, intended for gravimetric testing of metal witness samples so that the coating on the witness sample is in similar hydrochemical conditions compared to the coating on the pipe, that is, the flow of the medium tangentially washes the surface of the coating on the simulators;Indication of coating water absorption, the onset of degradation, and the initiation of subsurface corrosion is achieved by polarizing working samples with alternating current in a frequency range and measuring the total impedance of the electrolyte-coating-metal system. Monitoring is also performed by pipeline maintenance personnel, who conduct impedance spectroscopic measurements of the coating on simulators at specified intervals. The coating on the simulator is applied to specially prepared carbon steel samples under factory conditions similar to those used to apply the coating to the inner surface of pipes. This ensures compliance with the similarity criterion for the test object and the measurement object. The polarizing counter electrode is made of corrosion-resistant steel and is shaped and positioned relative to the working electrodes to ensure the most effective polarization of the coated samples by the operating current.

[0024] The electrodes are placed throughout the entire depth down to the lower generatrix of the pipeline, where the coating is exposed to the aqueous phase of the working medium and the mechanical impurities carried away by its flow.

[0025] While the similarity criterion between the simulators and the actual pipeline surface is met, this method and instrumentation for monitoring the continuity of coatings and subsurface corrosion will allow for the modeling and detection of damage caused by both operating conditions—the properties and characteristics of the working medium and its pumping mode—and the specifics of the factory coating application technology.

[0026] Detecting the acceleration of coating destruction and the onset of subsurface corrosion on a coated simulator will allow a section of the pipeline to be included in the pre-emergency category and included in the enhanced in-line diagnostics system, and if necessary, this section can be completely replaced to avoid an accident.

[0027] The working and reference electrodes are installed and removed through a pre-fabricated corrosion monitoring system on pipes, simplifying testing. Measurements, Nyquist and Bode diagrams, and recording are performed by the inspection team using an autonomous electrochemical workstation consisting of a potentiostat, a computer, and an autonomous voltage generator.

[0028] Reading and monitoring the electrochemical behavior of a coated simulator allows for the early detection of coating deformations, water absorption, cracks and pores, as well as corrosion on the metal beneath its surface, which are hidden by conventional in-line video diagnostics.

[0029] Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will understand that specific embodiments of the present invention may be modified or replaced with equivalents. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention shall be included within the scope of the legal protection of the claims of the present invention.

[0030] The essence of the invention is explained by the following drawings:

[0031] Fig. 1 - General view of the device for monitoring the condition of the protective anti-corrosion coating in the pipeline

[0032] Fig. 2 - General view and sectional view of the system of working electrodes with a coating and a counter electrode with signal electrical conductors from them.

[0033] The device for diagnosing the technical condition of the protective anti-corrosion coating in the pipeline 1 under investigation, shown in Fig. 1, includes a corrosion monitoring unit 2 already mounted on the pipe for gravimetric studies of metal corrosion witness samples, a hollow rod 3 with an electrode system fixed to it and placed in the pipeline, shown in Fig. 2 and consisting in turn of a counter electrode 4, two working electrodes-simulators 5, completely covered with a protective coating similar to that in the pipeline and fixed in a fluoroplastic gasket 6, electrically insulating the counter electrode; the electrode system is connected through this fluoroplastic gasket to a hollow connecting sleeve 7 by means of screws with a dielectric coating (not shown); signal wires 9 are also laid from each of the working electrodes and the counter electrode in the cavities of the sleeve and rod to electrical connectors 8 in the upper part of the corrosion monitoring unit 1.

[0034] Control of the technical condition of the coating using this device is carried out as follows:

[0035] Through corrosion monitoring lock unit 2, initially embedded in the pipeline and designed for gravimetric monitoring of metal corrosion, an electrode system for electrochemical impedance spectroscopy is introduced into the cavity of a working pipeline with coating 1 on a hollow rod 3. The electrode system is lowered into the pipeline until it rests against the lower generatrix. This exposes the working electrodes / simulators with the applied coating 5 to the aggressive aqueous phase (in the case of monitoring the coating of an operating oil pipeline) and mechanical impurities carried away by the pipeline flow. A negative voltage (cathode polarization) is applied to counter electrode 4, whose shape and relative position to the working electrodes allow for optimal polarization of the coated simulators at the beginning of the monitoring procedure. A positive voltage (anodic polarization) is applied to working electrodes 5.During periodic pipeline inspections, a workstation consisting of a potentiostat, a computer, and a portable generator are connected to a polarized electrode system via connectors 8 on the corrosion monitoring unit. Data on the electrochemical behavior of the working electrodes, polarized relative to the counter electrode, is collected in the form of a Nyquist diagram or Bode plot. The appearance of these plots will indicate the onset of coating degradation on the dummy samples and the development of subfilm corrosion of the sample metal. Provided the similarity criterion between the coating on the samples and the coating on the pipeline wall is met, the onset of these processes on the dummy samples will indicate similar degradation of the working coating in the pipeline, at least in the area of ​​the electrode system along the lower generatrix.

Claims

1. A method for monitoring the condition of internal anti-corrosion coatings of pipelines, carried out inside a functioning pipeline in-situ in the flow of the working medium pumped by it by an electrochemical method and using simulators in the form of test specimens with an applied coating, characterized in that the working electrodes in the form of test specimens with an applied coating and a counter electrode that polarizes them are introduced into the operating pipeline through corrosion monitoring units already present in the pipes, designed for gravimetric testing of metal test specimens so that the coating on the test specimen is in similar hydrochemical conditions compared to the coating on the pipe, that is, the flow of the medium tangentially washes the surface of the coating on the simulators, and the indication of water absorption of the coating,the onset of its destruction and the initiation of subsurface corrosion is carried out by polarizing working samples with alternating current in a range of frequencies and measuring the total impedance of the electrolyte-coating-metal system; monitoring is carried out by pipeline maintenance personnel at specified intervals, conducting impedance spectroscopic measurements of the coating on simulators.

2. A method for monitoring the condition of internal anti-corrosion coatings of pipelines according to paragraph 1, in which the coating on the simulator is applied to specially prepared samples made of carbon steel under factory conditions similar to the application of the coating to the internal surface of pipes, which ensures compliance with the similarity criterion for the test object and the measurement object.

3. A method for monitoring the condition of internal anti-corrosion coatings of pipelines according to paragraph 1, in which the placement of electrodes is carried out throughout the entire depth down to the lower generatrix of the pipeline, where the coating is exposed to the aqueous phase of the working medium and mechanical impurities carried away by its flow.

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