Method and measurement configuration for determining the internal corrosion rate of steel structures

Abstract

A method for measuring the internal corrosion rate of a steel pipeline is disclosed in which a calibration constant is determined under laboratory conditions, field conditions are then modeled using the calibration constant to determine the corrosion rate, and the corrosion rate is then determined under field conditions in a manner similar to that under laboratory conditions. The present invention also provides a measurement setup for determining the calibration constant and corrosion rate for the internal corrosion rate of a steel pipeline (1), which is applicable for carrying out the method under both laboratory and field conditions. The setup includes a polarization and measurement unit (5) having a two-channel power output (2), a potential measurement input (3), and a ground connection (4), a control and data storage unit (6), and three probes (8) equipped with counter electrodes (7). At least one of the probes (8) further includes a reference electrode (9).

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the internal corrosion rate of steel pipelines, in the application of which calibration constants are determined under laboratory conditions, then field conditions are modeled under laboratory conditions using the calibration constants to determine the corrosion rate, and then the corrosion rate is determined under field conditions in a similar manner as under laboratory conditions.

[0002] The present invention further relates to a measurement setup for determining the calibration constant and corrosion rate for the internal corrosion rate of steel pipelines, which is applicable for carrying out the method under laboratory and field conditions. The setup comprises a polarization measurement unit having a two-channel power output, a potential measurement input and a ground connection, a control and data storage unit, and three probes with counter electrodes. At least one of the probes further comprises a reference electrode. [Background technology]

[0003] The corrosion rate of the inner surface of a pipeline is typically determined by coupons, LPR techniques, and ER techniques (corrosion monitoring). A common imperfection in all three solutions is that the corrosion rate of a separate specimen introduced into the system is measured, rather than the corrosion rate of the pipe wall itself. This means that the measurements are subject to significant uncertainty. The solution is to polarize the pipe wall itself in an appropriate manner and determine the polarization resistance of the pipe wall from this polarization, from which the corrosion rate can be calculated using the LPR method or any other commonly used electrochemical polarization technique.

[0004] The corrosion rate in an industrial environment can be determined essentially by three technical solutions:

[0005] (1) Mass loss measurement. During this process, test pieces (so-called coupons) of known mass are placed in a corrosive medium, and after a certain time they are removed, washed, weighed, and the corrosion rate is calculated from the mass loss. The advantage of this method is that it is a simple and direct measurement. The disadvantage is that it takes time, provides delayed information, or does not provide any information about the consequences of changes in the corrosive medium, thus reducing the possibility of intervention. This method can be used in all types of media (oil, gas, water).

[0006] (2) The essence of the ER (electrical resistance) method is that the test specimen is a metal wire, the resistance of which is measured very accurately. The corrosion rate is calculated from the change in the resistance of the wire. This method is also relatively time-consuming and inaccurate. The advantage of this method is that it can be used in oily and gaseous media, as well as mass loss measurements. Its use in aqueous media is very limited.

[0007] (3) LPR (Linear Polarization Resistance) Measurement. The technological development described here is based on this method. Its essence is that a voltage difference is generated between two electrodes placed in a corrosive medium, and the current response is measured. If the voltage perturbation is sufficiently small (<15 mV) and certain other conditions are met, the current response is linear (as if measured with an equivalent circuit of an ohmic resistor and capacitor), and a specific so-called polarization resistance is negatively correlated with the corrosion rate at the electrode's surface (the lower the resistance, the greater the corrosion rate). The application of this method requires a minimum of two electrodes, called the working electrode and the counter electrode. Optionally, a third, non-polarized electrode can be used; this electrode is only required for potential measurement. This is the reference electrode. If a reference electrode is used, the potential signal is measured at the working electrode relative to it (however, current still flows between the working and counter electrodes).

[0008] To apply this method accurately, the solution resistance must be known and corrected (subtracted from the overall resistance). To do this, two measurements are often made, both using alternating current: one at a high frequency (about 1000 Hz) and one at a low frequency (about 1 Hz). In the high-frequency measurement, only the solution resistance is measured; in the low-frequency measurement, the sum of the two types of resistance is measured. (The surface resistance of the electrode, which is related to the corrosion rate, is actually zero and is pseudo-short-circuited during the high-frequency measurement due to the so-called double-layer capacitance that arises in the parallel connection.) The difference between the two results gives the electrode's polarization resistance, which is related to the current as follows:

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[0009] In practice, in an LPR corrosion monitoring procedure, the working and counter electrodes are typically threaded steel rods at one end, screwed into a suitably formed steel support, isolated from each other and from the support, and connected to the corrosion rate meter by suitable wires. http: / / www.corrscience.com / products / corrosion / intro-to-corrosion / linear-polarisation-resistance-monitoring-lpr / )

[0010] This paper describes a method developed for pipeline corrosion monitoring. In this method, one of the electrodes in the monitoring system is the pipe wall itself. This allows for measuring the polarization resistance of the pipe wall (at the expense of installing a third reference electrode) and directly monitoring the corrosion rate of the pipe wall. This is necessary because pipe walls that have existed for a long period of time (often decades) may exhibit quite different corrosive behavior than the monitoring electrode, which must be replaced at least every two years (perhaps much more frequently in highly corrosive media). The technical value, reliability, and information richness of electrochemical measurements performed directly on the pipe wall clearly make them worthwhile for certain conditions. When the pipe wall is the working electrode, the use of a reference electrode is mandatory. In this case, one electrode of a standard two-electrode probe is the counter electrode, and the other is the reference electrode.

[0011] (1) If the pipe wall itself is used as the monitoring electrode, a very complex and possibly time-varying potential distribution can occur on it, polarizing individual surface areas to significantly different degrees and making the approximate determination of the polarized surface uncertain (the corrosion rate determination can be very inaccurate anyway, and therefore, while the requirements for technical measurement accuracy are at least moderate, the uncertainty in the size of the corroding surface and the wide range of potentials will in any case result in errors that are unacceptable or significantly reduce the value resulting from the benefits of the method of the present invention). Therefore, the proposed method uses three probes, installed at clearly defined distances and positions from each other, rather than one probe, to make the potential distribution in the geometric environment of the intermediate active working electrode more uniform and enable a more accurate determination of the relevant corroding surface.

[0012] (2) When the pipe wall is polarized (e.g., through electrodes built into the LPR probe), it is difficult to calculate the polarization resistance of the pipe wall because the surface area of ​​the polarized pipe wall section or the distribution of the polarization current cannot be determined in advance. Therefore, it is necessary to apply three electrodes equidistantly spaced along the busbar of the pipe wall to generate a roughly symmetrical and uniform potential and current distribution within the space of the intermediate electrode.

[0013] More specifically, the corrosion rate can be determined from the value of polarization resistance according to the following relationship between polarization resistance and corrosion current:

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[0014] The corrosion rate is determined from the value of the corrosion current using the following formula:

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[0015] To measure LPR in an industrial environment, probes positioned in a known manner are used. Two types of designs are generally used: two-electrode and three-electrode. The probes are installed in the pipeline in a known manner.

[0016] The operation of an LPR probe is as follows: a time-varying voltage (typically a triangular signal with an amplitude of 10 mV to 15 mV and a frequency of approximately 1 Hz or less) is emitted between the two electrodes of the LPR probe from a power supply with a controllable output. The voltage and current are then measured again. If a third electrode is present in the probe, this is used as a reference electrode, and the potential of another electrode is measured against it. From the current and voltage values, the electrical resistance of the system (knowing the surface of the probe) is calculated, which consists of two terms: the ohmic resistance of the solution and the polarization resistance.

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[0017] Solution resistance R Ω is either ignored (which does not cause significant error in aggressive saline solutions with good conductivity) or its value can be determined by high frequency impedance measurements as shown in EIS measurements.

[0018] Similar probes to those used for LPR measurements are used for industrial EIS measurements, the differences being in the measurement electronics and polarization waveform.

[0019] The transfer function (impedance) of an electrochemical corrosion system to a low amplitude (maximum 10-15 mV) AC voltage (preferably sinusoidal) perturbation can be represented by a so-called equivalent circuit. The equivalent circuit of a corrosion system is represented by the polarization resistance (RP ) and interfacial double layer capacitance (C DL ) are connected in parallel, and the ohmic resistance of the solution (R Ω ) can be well modeled by a circuit coupled in series with them. The impedance of this equivalent circuit is:

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[0020] There are other configurations tailored to specific needs, but their common feature is that the electrodes are always inserted into the corrosion system in isolation from it. In some cases, a three-electrode probe is used, where the third electrode serves only as a reference electrode (the potential of the unloaded electrode can be treated as constant for short periods during the measurement).

[0021] WO 2015200899(A1) (Linear Polarization Resistance Flex Sensors and Methods that Involve Structure as Working Electrode) discloses linear polarization resistance sensors and methods that further include the configuration of a working electrode. This document uses LPR and / or EIS and / or other electrochemical polarization methods.

[0022] The common feature of this application and the present invention is that both use the same measurement calculation method (LPR and / or EIS and / or other electrochemical polarization methods) that is widely known and has been used for decades. Both polarize the structural material (pipe wall) to determine the corrosion rate.

[0023] However, there are significant differences between the two patents. The physical implementation, the sensors used, the electrodes, the measurement configuration, the auxiliary materials used, and the mechanical configuration (e.g., fixation) do not show similarity. Another important difference is that in the case of the above-mentioned patent, the film containing the electrodes must be fixed to the structural material, which is very technically problematic, while the sensor of the present invention can be installed using a standard threaded access fitting.

[0024] Chinese Patent Specification No. 108535178 discloses an apparatus and method for on-line monitoring of the corrosion rate of a pipeline. The apparatus includes an electrochemical test system, a piece hanging system, corresponding valves, a flow meter, etc. The method for on-line monitoring of the corrosion rate is (1) a step of attaching a counter electrode and a corrosion test piece to be monitored and adjusting the flow rate of the liquid flowing through the apparatus so that the flow rate of the liquid flowing through the apparatus matches the flow rate of the liquid in the pipeline of the system; (2) a step of measuring the linear polarization resistance using the linear polarization method; (3) a step of measuring the solution resistance between the electrodes using the constant current method; (4) a step of dividing the measured value by 2 to obtain the anodic polarization resistance (R); (5) a step of obtaining the B value in consideration of the weight loss correction process of the test piece; (6) according to Equation I<corr=B / R, the corrosion rate I <corr>and calculating Includes.

[0025] The value obtained in step (4) is subtracted from the linear polarization resistance. The advantage of this device and method is that the anodic polarization resistance R can be accurately measured, and the B value can be determined using a weight loss correction process for the test specimen, thereby enabling accurate and continuous online monitoring of the internal corrosion rate of the pipeline in real time.

[0026] The above-mentioned methods use separate test electrodes to monitor pipeline corrosion, and not the pipe wall itself, which is an essential difference in measurement technology.

[0027] U.S. Patent No. 10,031,066 (B1) discloses a system and method for monitoring corrosion of a structure by using the structure itself as part of an electromechanical measurement. According to some implementations, a linear polarization resistance (LPR) sensor device is presented for directly monitoring corrosion on a structure. According to a particular innovation in this implementation, the sensor device may include three electrodes: a counter electrode, a reference electrode, and a working electrode consisting of the structure being monitored. In further embodiments, each electrode may be configured on a polymer flexible substrate cable, such as polyimide, and each electrode may be made of a noble metal, e.g., gold-plated copper, or a metal system whose outer surface does not oxidize upon environmental exposure.

[0028] The solution described in this patent is suitable for use on corroding steel surfaces to measure corrosion rates. The main difference between the above application and the present invention is that the counter and reference electrodes required for the measurement are placed very close to a surface of a specific shape (rectangular), and the size of the usable surface area of ​​the opposite working electrode is defined, eliminating the limitation on the test surface (to a definable value). This method is not suitable for the use of built-in electrodes for industrial purposes. Summary of the Invention [Problem to be solved by the invention]

[0029] The object of the present invention is essentially to develop a method and measurement configuration for determining the corrosion rate of pipelines that is more accurate and economical than conventional methods, which also makes it possible to replace electrodes less frequently. [Means for solving the problem]

[0030] It has been found that the disadvantages of LPR measurement methods can be significantly reduced by the method of the present invention when one of the electrodes of the monitoring system is the pipe wall itself, three additional probes are installed axially adjacent to each other in a row, and the two outer probes limit the range of the middle probe approximately symmetrically with respect to the distance between the probes. It has also been found that when the corrosion rate of the pipe wall is measured rather than the corrosion rate of the probe material, a more realistic representation of the corrosion rate and more accurate results can be obtained compared to known solutions. Advantageously, the metallic material of the probe is formed of a corrosion-resistant metal. Furthermore, it has been found that by adjusting the surface polarized by the intermediate counter electrode as described in the present invention, the corrosion rate can be determined more accurately because both the intensity of the polarization current and the size of the polarization surface are known.

[0031] Therefore, the present invention is a method for determining the calibration constant of a measurement configuration for determining the internal corrosion rate of a steel pipeline. This is preferably performed using linear polarization resistance measurement (LPR) and / or electrochemical impedance spectroscopy (EIS), where the solution resistance is preferably determined by EIS measurement, and the polarization resistance value obtained by the LPR method is corrected using this value. In this process, two outer probes and one middle probe are used through the pipeline wall, galvanically isolated from the pipeline. The probes include a counter electrode, and at least the middle probe also includes a reference electrode. The polarization resistance is calculated using the first equation:

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[0032] This process uses a pipeline consisting of three pipe sections (two outer pipe sections and an intermediate pipe section). Probes are inserted into each section of the pipeline in a row along the steel pipeline busbar, equidistant from each other. The distance is at most 150% of the pipeline diameter. The boundary of the pipe section is formed at half the distance between the probes. The intermediate probe is placed within the intermediate pipe section, half the distance between the outer probes. During the procedure, a calibration measurement is first performed on the calibration model. During this time, the pipe sections are galvanically isolated from each other. The counter electrode of the outer probe is in a non-polarized state. To determine the polarization resistance (LPR), the natural corrosion potential is measured between a reference electrode and the pipeline at ground potential. The voltage applied between the counter electrode of the intermediate probe and ground potential is then selected so that the polarization of the pipe relative to the reference electrode is ±5-20 mV relative to the corrosion potential. The polarization potential (EE) between the reference electrode of the intermediate probe and the pipeline connected to ground potential is then measured. corr The value of the polarization resistance (R) and the current (J) thus generated are measured. From the measurement results, the polarization resistance (R P ) is determined. The solution resistance is then determined by impedance spectroscopy, after which the polarization resistance per unit area is corrected by the ohmic resistance of the solution. The corrosion current (J) is then calculated using the second equation: corr ) is calculated, from which the corrosion rate is determined. Field conditions are then modeled under laboratory conditions by removing the galvanic isolation between the pipe sections, leaving the electrical connections of the intermediate probe used in the calibration measurement unchanged, and coupling the counter electrodes of the two outer probes in parallel. A voltage is applied between the parallel-coupled counter electrodes and ground potential so that the value of the polarization resistance determined by the output current and measured polarization on the intermediate probe is substantially equal to the value of the polarization resistance determined in the calibration measurement. The calibration constant of the system is then determined by calculating the quotient of the current intensity values ​​measured on the two outer probes and the current intensity value measured on the intermediate probe.

[0033] The present invention further provides a method for determining the internal corrosion rate of a steel pipeline under field conditions using the calibration constants determined by the above-described method. In this method, two outer probes and one intermediate probe are used through the pipeline wall, galvanically isolated from the pipeline. The probes include counter electrodes, and at least the intermediate probe also includes a reference electrode. The annual corrosion rate is calculated using a third equation:

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[0034] The present invention further provides a method for determining the internal corrosion rate of a steel pipeline using the method described above, in which a calibration constant is determined under laboratory conditions, the calibration constant is then used to model field conditions under laboratory conditions and the corrosion rate is determined, and the corrosion rate is then determined under field conditions as under the laboratory modeling conditions.

[0035] The present invention further provides a measurement configuration for determining the calibration constant and corrosion rate for the internal corrosion rate of a steel pipeline under laboratory and field conditions using the above-described method. The configuration comprises a polarization and measurement unit having a two-channel power output, a potential measurement input, and a ground connection; a control and data storage unit; and three probes with counter electrodes. At least one probe further comprises a reference electrode. The pipeline comprises three pipe sections: two outer pipe sections and one intermediate pipe section. The probes are positioned equidistant from each other in a row along the busbar of the steel pipeline within the pipeline sections. The distance between them is at most 150% of the pipeline diameter. The section boundaries are formed at half the probe distance. The electrodes are electrically insulated from each other and from the pipeline. The intermediate probe located in the intermediate pipe section comprises a reference electrode and a counter electrode. The reference electrode is connected to the input of the electrometer, and the counter electrode is connected to the first power output. The pipeline is coupled to the ground connection. For calibration measurement configurations under laboratory conditions, the pipe sections are galvanically isolated from one another, preferably by spacers inserted into the pipeline. The outer probe is fixed to the pipeline in an unpolarized state. For modeling field conditions under laboratory conditions and measurements under field conditions, the individual pipe sections are galvanically connected to one another. The counter electrodes of the outer probes are combined and connected to a second power output. The output of the control and data storage unit is connected to the input of the polarization and measurement unit.

[0036] A detailed description of the present invention will now be given with reference to the accompanying drawings. [Brief explanation of the drawings]

[0037] [Figure 1] 10A-10C are partial side cross-sectional views of possible probe designs. [Figure 2] FIG. 1 is a schematic diagram of a calibration measurement setup. [Figure 3] FIG. 1 is a schematic diagram of a measurement setup for modeling field conditions under laboratory conditions. [Figure 4] FIG. 1 is a schematic diagram of one setup for performing measurements under field conditions. DETAILED DESCRIPTION OF THE INVENTION

[0038] The method according to the present invention can be applied to determine the internal corrosion rate of a steel pipeline 1. A suitable measurement configuration has also been developed to implement this method. A method for determining calibration constants under laboratory conditions, which can be used to accurately determine the corrosion rate of steel pipes in the field, has also been developed. Under laboratory conditions, this process is carried out using linear polarization resistance measurements (LPR), preferably electrochemical impedance spectroscopy (EIS). In the latter, the solution resistance is determined, and the polarization resistance value obtained by measuring the linear polarization resistance is corrected using this value. During the measurement, two outer probes 15 and an intermediate probe 14 are used through the pipeline 1 wall, galvanically isolated from the pipeline 1. Probe 8 is equipped with a counter electrode 7, and at least the intermediate probe 14 is also equipped with a reference electrode 9 (Figure 1). A pipeline 1 consisting of three pipe sections (two outer pipe sections 10 and an intermediate pipe section 11) is used. The probes 8 are inserted equidistant from each other into each pipe section 10, 11 of the steel pipeline 1 in a row along the busbar of the steel pipeline 1. The distance is at most 150% of the diameter 12 of the pipeline 1, preferably equal to the length of the diameter 12. The diameter 12 refers to the inner diameter of the pipe. In a given case, if the distance corresponds to the outer diameter being measured, it does not imply a significant inaccuracy. Naturally, the probes 8 may be arranged at a different distance than suggested, even further apart, but this may reduce the accuracy of the measurement. The boundary 13 between the pipe sections 10 and 11 is formed at half the distance between the probes 8. The middle probe 14, located within the middle pipe section 11, is positioned within the middle pipe section 11 at half the distance between the outer probes 15. The procedure begins with a calibration measurement performed under laboratory conditions on a calibration model. During this time, the pipe sections 10 and 11 are galvanically isolated from each other. The counter electrode 7 of the outer probe 15 remains unpolarized (Figure 2). To determine the polarization resistance (LPR), the natural corrosion potential is measured between the reference electrode 9 and the pipeline 1, which is connected to ground potential.The voltage used for the measurement (coupled between the counter electrode 7 of the intermediate probe 14 and ground potential) is then selected to be ±5 to 20 mV relative to the corrosion potential. The polarization potential (EE) between the reference electrode 9 of the intermediate probe 14 and the pipeline 1 connected to ground potential. corr The value of the current (J) thus generated is measured. From the measurement results, the first equation:

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[0039] Further, a method for determining the internal corrosion rate of a steel pipeline 1 under field conditions using the calibration constant determined by the above-described method is provided. In this method, two outer probes 15 and an intermediate probe 14 are used through the wall of the pipeline 1, galvanically insulated from the pipeline 1. The probe 8 further includes a counter electrode 7, and at least the intermediate probe 14 includes a reference electrode 9. The probes 8 are inserted into the pipeline 1 in a line along the busbar of the steel pipeline 1, equidistant from each other. The distance between them is at most 150% of the diameter 12 of the pipeline 1. The intermediate probe 14 is positioned within the pipeline 1 at half the distance between the outer probes 15. The natural corrosion potential is measured. The currents applied to the intermediate probe 14 and the outer probe 15 are then adjusted to different values ​​so that the potentials generated therebetween are 5 to 20 mV, the ratio of which corresponds to the value of the calibration constant. By maintaining this condition, the polarization potential is measured between the reference electrode 9 and ground potential. Preferably, the polarization potential is selected to be ±5 mV to ±20 mV relative to the corrosion potential. The polarization resistance of the space surrounding the intermediate probe 14 is calculated using the polarization value calculated from the current applied to the intermediate probe 14 and the potential of the reference electrode 9. From the high-frequency (1-10 kHz) electrochemical impedance spectroscopy data, the solution resistance is calculated using the same configuration as for electrochemical impedance measurements. The quotient of the current applied to the two outer probes 15 and the current applied to the intermediate probe 14 is set equal to the value of a calibration constant. The solution resistance is calculated with respect to the intermediate probe 14, and this value is used to correct the value of the polarization resistance. The corrected polarization resistance value thus obtained is calculated relative to the surface area polarized by the intermediate probe 14. (J corr ) After determining the correction current, the third equation:

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[0040] The invention further relates to a measurement setup for determining the calibration constant of the internal corrosion rate of a steel pipeline 1 in order to carry out the above-mentioned method, which consists of a polarization and measurement unit 5 having a two-channel power output 2, a potential measurement input 3 and a ground connection 4, a control and data storage unit 6 and three probes 8 with counter electrodes 7.

[0041] The polarization and measurement unit 5 is a unit with two power outputs 2, the output voltages of which can be set independently of each other relative to a common earth connection 4. At least one potential measurement input 3 also measures the voltage relative to the earth connection 4. The earth connection 4 is connected to the pipe 1.

[0042] The control and data storage unit 6 controls and evaluates the three measurement processes carried out with the polarization and measurement unit 5. The control and data storage unit 6 also stores the data, evaluates the data if necessary and ensures its transmission.

[0043] The measurement system consists of three probes 8, which are completely identical in design but have different connections. The distance between the probes 8 must not exceed 150% of the inner diameter 12 of the pipeline 1. The probe 8 has two electrodes: a counter electrode 7 and a reference electrode 9. The counter electrode 7 and the reference electrode 9 are electrically insulated from each other and from the pipeline 1. The counter electrode 7 is formed of a metal electrode with a relatively large surface area. Preferably, but not necessarily, the counter electrode 7 is made of stainless steel, or in some cases structural steel. Its function is to close the circuit that polarizes the pipeline 1. The reference electrode 9 is a ring with a smaller surface area made of stainless steel or some other metal, whose potential is stable in the medium transported in the pipeline 1. Its function is to measure the potential of the pipeline 1. In some cases, a commercially available reference electrode 9 (e.g., silver / silver chloride) may be used. In a practical embodiment, the connection of the reference electrode 9 would also extend into the container of the probe 8, but in Figure 1 it is shown outside for better traceability. The three probes 8 are identical in design, but their use is different. The reference electrode 9 of the middle probe 14 is always connected to the input 20 of the polarization and measurement unit 5. If the polarization and measurement unit 5 comprises several potential measurement inputs 3, the reference electrodes 9 of the two outer probes 15 can also be connected to increase the accuracy of the measurement and evaluation, but this is not necessary. This embodiment is not shown for clarity.

[0044] The counter electrodes 7 of the probes 8 are electrochemically polarized relative to the inner wall of the pipeline 1, resulting in almost no current flow between them. Each counter electrode 7 polarizes a specific portion of the wall of the pipeline 1. The counter electrodes 7 of the two outer probes 15 limit the area that can be polarized by the counter electrode 7 of the middle probe 14. The percentage of the surface polarized by the counter electrodes 7 of the two outer probes 15 and the counter electrodes 7 of the middle probe 14 can be varied by controlling the current applied to the counter electrodes 7 of the two outer probes 15 and the counter electrodes 7 of the middle probe 14. The objective is to polarize exactly half of the pipe wall surface area enclosed by the counter electrodes 7 of the two outer probes 15 with the counter electrode 7 of the middle probe 14. This adjustment can be made by changing the value of the potential applied to the first power output 16 and the second power output 18, which polarize the counter electrodes 7 of the two outer probes 15 and the counter electrodes 7 of the middle probe 14. The optimum ratio is obtained in a calibration measurement procedure. The corrosion rate can be determined by any of the well-known electrochemical methods, but for practical reasons it is preferred to use linear polarization measurements (LPR) and / or electrochemical impedance spectroscopy (EIS), or a combination of the two (e.g., the solution resistance is determined by EIS measurements and the polarization resistance values ​​obtained by the LPR method are corrected using this value).

[0045] Thus, as described above, at least one probe 8 is further provided with a reference electrode 9. The pipeline 1 comprises three pipe sections: two outer pipe sections 10 and an intermediate pipe section 11. The probes 8 are inserted into each of the sections 10, 11 of the pipeline 1 in a line along the busbar of the steel pipeline 1, at equal distances from each other. This distance is at most 150% of the diameter 12 of the pipeline 1. The boundary 13 between the pipe sections 10, 11 is formed at half the distance between the probes 8. The counter electrodes 7 are electrically isolated from each other and from the pipeline 1. The intermediate probe 14 located in the intermediate pipe section 11 comprises the reference electrode 9 and the counter electrode 7. The reference electrode 9 is connected to the input 3 of the electrometer, and the counter electrode 7 is connected to the first power output 16. The pipeline 1 is coupled to the ground connection 4. In the calibration measurement configuration (FIG. 2), the pipe sections 10, 11 are preferably galvanically isolated from each other by a spacer 17 inserted within the pipeline 1. The outer probe 15 is fixed in the pipeline 1 in an unpolarized state. When modeling field conditions under laboratory conditions, the individual pipe sections 10, 11 are galvanically connected to each other. The counter electrode 7 of the outer probe 15 is galvanically connected and coupled to the second power output 18. The output 19 of the control and data storage unit 6 is connected to the input 20 of the polarization and measurement unit 5. This configuration allows field conditions to be modeled so that connection points 21 are formed on the pipe sections 10, 11. These are galvanically coupled to a short circuit 22 during modeling of field conditions under laboratory conditions (Figure 3). Of course, the galvanic connection between the individual pipe sections 10, 11 can also be established by removing the spacer 17, but applying the short circuit 22 is easier and faster. Optionally, the outer probe 15 equipped with the counter electrode 7 is also equipped with a reference electrode 9. In this case, each of the reference electrodes 9 should measure the same value, ignoring local variations in the ohmic losses of the solution, which depend on the calibration constant. Measurements using the reference electrode 9 of the outer probe 15 can be additional control data for the linearity of the system, which can be used to compensate for the loss of accuracy caused by application in polluted industrial water.

[0046] To determine the optimal current output ratio between the first power output 16 and the second power output 18 (counter electrode 7 in probe 8), a calibration measurement system for determining calibration constants was developed. A schematic diagram of this is shown in Figure 2. This configuration models the system's geometric conditions; the difference is that two insulating spacers 17 are symmetrically inserted into the pipeline 1 between the probes 8, and connection points 21 are formed to provide the possibility of a cable connection that shorts the insulating spacers 17. The calibration layout has two measurement modes: a real-field measurement mode and an isolated calibration mode. When the insulating spacers 17 are shorted by a short circuit 22, the system essentially measures as if it were being measured on a continuous pipeline 1. When the short circuit 22 is removed, the intermediate pipe section 11 is electrically isolated from the adjacent outer pipe section 10. In this case, the corrosion rate in the intermediate pipe section 11 can be measured in a clearly defined, discrete area using one of the electrochemical corrosion rate measurement methods described above. When the exact corrosion rate of the intermediate pipe section 11 is determined in the calibration mode, this value can be compared with the corrosion rate value obtained in the real field mode, and if necessary, the measurement input parameters (potential ratio and current ratio of the counter electrodes 7 of the intermediate probe 14 and the two outer probes 15) can be changed accordingly.

[0047] The solution according to the invention is illustrated by the following embodiment.

[0048] In a first step, the current ratio (i.e., the calibration constant) is determined by the measurement configuration of the measurement device and the method according to the invention. The calibration constant is determined in the measurement mode shown in Figure 2. In this example, the inner diameter 12 of the pipe is 100 mm and the length of the pipe sections 10, 11 separated by the spacer 17 is also 100 mm. Although it is a desirable requirement that the diameter 12 of the pipe 1 and the distance between the probes 8 are equal, in principle the calibration constant can be determined in a similar way for any pipe diameter and diameter / electrode distance ratio. The surface area of ​​the intermediate pipe section 11 separated by the spacer 17 is 3140 cm 2 The natural potential measured with respect to ground potential is several times 10 mV to 100 mV. The electrode design described above is used because it would be too complicated to design a measurement setup with commonly used so-called non-standard electrodes. As a result, safety issues at high voltages would arise. First, the polarization resistance (LPR) is determined by the first equation. To this, an offset (polarization) of ±5 to 20 mV is performed at the potential value relative to the corrosion ("natural") potential measured with the reference electrode 9 of the intermediate probe 14, and the resulting current is measured with a high internal resistance voltmeter (>10 MΩ). The measurement results are as follows: [Table 1]

[0049] In practice, this measurement is usually performed automatically, and typically a sawtooth signal with a frequency of 0.1-1 Hz is used to vary the voltage (polarization), the amplitude of which varies within the voltage range. From the measurement results, the first equation:

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[0050] To determine the corrosion current, a second equation is used.

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[0051] Using the value of the corrosion current, the corrosion rate is calculated using the third equation:

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number

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[0052] where K is the corrosion rate (its dimensions: [mass / time / length] 2 ], characteristic units of measurement: g / year / cm 2 ) and A is the corrosion surface (dπl) (characteristic unit of measurement: cm 2 )

[0053] For the 10cm intermediate pipe section 11, A is 314cm 2 where n is the stoichiometric number (oxidation number) of the corrosion process, which has a value of 2 for iron and steel, F is Faraday's constant, which has a value of 96494 As / mol, and M Fe is the molar mass of iron (55.845 g / mol) and s is the number of seconds in a year (31,536,000).

[0054] The pipe sections 10, 11 are then connected to the short circuit 22, and the two outer probes 15 are coupled in parallel to the second power output 18. It is then determined how many times the current delivered to the two outer probes 15 and the middle probe 14 should be applied, so that the resulting current output at the middle probe 14 and the measured polarization (the potential deviation measured at the reference electrode 9 relative to its natural, unpolarized state) and the polarization resistance calculated from these data should be as close as possible to the measured and previously calculated polarization resistance value of 0.729 Ω shown in the table. The quotient of the current values ​​applied to the two outer probes 15 and the middle probe 14 is then recorded. This value is the calibration constant for the system.

[0055] The corrosion rate is then determined under field conditions using the calibration constant. Under field conditions, the pipe is not segmented by the insulating spacer 17, as shown in Figure 4. Therefore, when measurements are performed under field conditions, the two outer probes 15 are also connected as shown in Figure 3. The current applied to the middle probe 14 and the current applied to the outer probe 15 are adjusted so that their ratio corresponds to the value of the calibration constant. By maintaining this condition, the current is measured at several different polarization values ​​(as shown in the table), and the polarization resistance of the space between the middle probe 14 is calculated using the polarization resistance value calculated from the current applied to the middle probe 14 and the potential of the reference electrode 9. From the high-frequency (1-10 kHz) electrochemical impedance spectroscopy data, the solution resistance is calculated using the same configuration. For electrochemical impedance measurements, the quotient of the current applied to the two outer probes 15 and the current applied to the middle probe 14 must match the value of the calibration constant. By maintaining this, the solution resistance relative to the middle probe 14 can be calculated with high accuracy, and its value is used to correct the polarization resistance value. The corrected polarization resistance value thus obtained is calculated for the surface area polarized by the intermediate probe 14. This surface value can be easily calculated using the relationship A=dπl, where d is the diameter 12 of the pipeline 1 and l is the sensor distance l, which is also equal to the distance between the probes 8. If the distance between the electrodes is not equal to the diameter, a different formula should be applied: A=dπl, where l is the sensor distance l. As a result, the value obtained is the polarization resistance per unit area, from which the corrosion rate can be calculated using the first, second, and third equations.

[0056] It should be emphasized that the geometries of the calibration measuring device and the field measuring device are similar if the geometry of the operating pipeline meets the requirements (i.e., the distance between the probes 8 is substantially proportional to the pipe diameter 12). Therefore, the calibration constants can be applied to pipes 1 of any diameter if the distance between the probes 8 is substantially equal to the inner diameter 12 of the pipe 1.

[0057] The advantages of the measurement system and calibration measurement device and method according to the present invention over currently operating industrial systems are as follows:

[0058] In currently operating industrial corrosion rate measurement systems (LPR systems, EIS systems, and ER systems), the working electrode (whose corrosion rate is determined) is placed within the probe. Therefore, the probe measures the corrosion rate of the working electrode, not the pipe wall. Therefore, it is impossible to determine the surface area of ​​the pipe wall to which the measurement results apply. Because the material quality, geometry, history (time spent in the system), and surface condition of the working electrode can differ significantly from the relevant parameters of the pipe wall, the measurement results only provide information about the corrosion rate of the pipe wall with significant uncertainty. In contrast, in the system of the present invention, measurements are made directly on the pipe wall, resulting in the corrosion rate, thus providing significantly more reliable results.

[0059] In currently operating systems, electrodes break down relatively quickly (partly due to corrosion, partly due to their geometry, and partly due to material thickness), so they typically need to be replaced every 6 to 12 months. After replacement, the material of the new electrode is completely different from that of the already worn electrode. The lifespan of the electrodes in the probe is limited because they must be made of a material that is somewhat corrosive. In the system of the present invention, pipe wall corrosion is measured directly by polarizing the pipe wall, and the electrodes (counter and reference electrodes) can be made of stainless steel, which allows for reliable operation over several years and significantly reduces system reliability, availability, and operating costs.

[0060] Currently operating systems (LPR, EIS and ER systems) give inaccurate results due to severe localized corrosion. The system according to the present invention is, on the one hand, able to detect the presence of localized corrosion (by monitoring the change in the potential of the pipe wall over time) and, on the other hand, provides accurate data on the average corrosion rate even in the case of severe localized corrosion.

[0061] Current corrosion monitoring systems (except for mass loss measurement systems) cannot be used in media containing hydrogen sulfide, mainly because iron sulfide precipitates on the surface, creating a conductive coating that changes the electrical resistance of the probe. In the case of the system according to the invention, a geometric separation can be achieved (the electrodes can be spaced farther apart) or insulating elements can be installed to which iron sulfide does not adhere, resulting in satisfactory measurement results.< / corr>

Claims

1. 1. A method for determining calibration constants of a measurement configuration that can be used to determine the internal corrosion rate of a steel pipeline by performing linear polarization resistance measurements (LPR) and / or electrochemical impedance spectroscopy (EIS), The solution resistance is determined by EIS measurement, and the value of polarization resistance obtained by LPR method is corrected using the value of the solution resistance, and in the process, two outer probes and one middle probe are used through the wall of the pipeline that is galvanically isolated from the pipeline, and each of the outer probe and the middle probe includes a counter electrode, and at least the middle probe further includes a reference electrode, and the polarization resistance is calculated by a first formula: [Equation 1] is determined by the formula (EE ｃｏｒｒ ) is the polarization potential value, and the corrosion current (J ｃｏｒｒ ) under laboratory conditions yields the second formula: [Equation 2] is determined by the formula Ａ and b Ｃ are the Tafel slopes of the base 10 logarithms of the anode and cathode, respectively, 1. A method comprising: A pipeline (1) consisting of three pipe sections (10, 11), two outer pipe sections (10) and one intermediate pipe section (11), is used, and the outer probe and the intermediate probe are inserted into each pipe section (10, 11) of the pipeline (1) in a line along the generatrix of the pipeline (1) at equal distances from each other, the distance being at most 150% of the diameter (12) of the pipeline (1), the boundary (13) between the outer pipe section (10) and the intermediate pipe section (11) is formed at half the distance between the outer probes and the intermediate probe, and the intermediate probe (14) is inserted into the intermediate pipe section at a position half the distance between the outer probes (15). The method includes first performing a calibration measurement on a calibration model, during which the outer pipe section (10) and the intermediate pipe section (11) are galvanically isolated from each other, and the counter electrode (7) of the outer probe (15) is in a voltage-free state, and determining the polarization resistance involves measuring a natural corrosion potential between the reference electrode (9) and the pipeline (1) at ground potential, and then selecting a voltage to be applied between the counter electrode (7) of the intermediate probe (14) and the ground potential during the measurement to be ±5 to ±20 mV relative to the corrosion potential, and determining a polarization potential (EE) between the reference electrode (9) of the intermediate probe (14) and the pipeline (1) connected to the ground potential. ｃｏｒｒ The value of the polarization resistance (R Ｐ ) is determined by the first equation, then the solution resistance is determined by impedance spectroscopy, then the polarization resistance per unit area is corrected by the ohmic resistance of the solution, then the corrosion current (J ｃｏｒｒ ) is calculated using a second equation, and the corrosion rate is determined from the result; then the field conditions are modeled under laboratory conditions by removing the galvanic isolation between the outer pipe section (10) and the intermediate pipe section (11), keeping unchanged the electrical connection of the intermediate probe (14) used for the calibration measurement, and coupling the counter electrodes (7) of the two outer probes (15) in parallel; a voltage is applied between the parallel coupled counter electrodes (7) and the ground potential so that the value of the polarization resistance determined by the output current on the intermediate probe (14) and the measured polarization is substantially equal to the value of the polarization resistance determined in the calibration measurement; then the calibration constant is determined by calculating the quotient of the value of the current intensity measured at the two outer probes (15) and the value of the current intensity measured at the intermediate probe (14).

2. 10. A method for determining the internal corrosion rate of a steel pipeline under field conditions using the calibration constants determined by the method of claim 1, wherein two outer probes (15) and one intermediate probe (14) are used through a wall of the pipeline (1) galvanically isolated from the pipeline (1), each of the outer probes and the intermediate probe including a counter electrode (7), and at least the intermediate probe including a reference electrode (9), and the annual corrosion rate is calculated using a third equation: [Equation 3] where K is the corrosion rate, n is the oxidation number of the iron and steel corrosion process, F is the Faraday constant, and M Ｆｅ is the molar mass of iron, A is the corrosion surface (dπl) to which the intermediate probe is accessible, d is the diameter (12) of the pipeline (1), l is the sensor distance (l), and s is the number of seconds per year; The outer probe and the intermediate probe are inserted into the pipeline (1) in a line along the busbar of the pipeline (1) at an equal distance from each other, the distance being at most 150% of the diameter of the pipeline (1), the intermediate probe (14) is placed in the pipeline (1) at a position half the distance between the outer probes (15), and the natural corrosion potential is measured; then, the currents applied to the intermediate probe (14) and the outer probe (15) are adjusted to different values ​​so that the potential generated therebetween is 5 to 20 mV, and the ratio of these corresponds to the value of a calibration constant; by maintaining this condition, the polarization potential is measured between the reference electrode (9) and the ground potential, and the corrosion potential is calculated. The polarization resistance of the space between the intermediate probes (14) is calculated using the polarization value calculated from the current applied to the intermediate probe (14) and the potential of the reference electrode (9), which is selected to be ±5 to ±20 mV. In the same configuration, the solution resistance is calculated from high-frequency (1 to 10 kHz) electrochemical impedance spectroscopy data. For the electrochemical impedance measurement, the quotient of the current applied to the two outer probes (15) and the current applied to the intermediate probe (14) is set to a value equal to the value of a calibration constant. Then, the solution resistance is calculated for the intermediate probe (14). The value of the solution resistance is used to correct the value of the polarization resistance. The corrected polarization resistance thus obtained is calculated for the surface area polarized by the intermediate probe (14), and the corrosion current (J ｃｏｒｒ ), and then determining the annual corrosion rate by a third equation.

3. 3. A method for determining the internal corrosion rate of a steel pipeline using the method of claims 1 and 2, characterized in that calibration constants are determined under laboratory conditions, then field conditions are modeled under laboratory conditions using the calibration constants to determine the corrosion rate, and then the corrosion rate is determined under field conditions in a manner similar to the laboratory modeling.

4. A measurement setup for determining calibration constants and corrosion rates for internal corrosion rates of steel pipelines under laboratory and field conditions using the methods of claims 1, 2 and 3, A measurement setup consisting of a polarization and measurement unit (5) with a two-channel power output (2), a potential measurement input (3) and a ground connection (4), a control and data storage unit (6), and three probes (8) each equipped with a counter electrode (7), consisting of two outer probes (15) and one middle probe (14), at least one of which further comprises a reference electrode (9), The pipeline (1) consists of three pipe sections, two outer pipe sections (10) and one intermediate pipe section (11), the outer and intermediate probes are arranged in the outer pipe section (10) and the intermediate pipe section (11) in a row along a generatrix of the pipeline (1) at an equal distance from each other, the distance being at most 150% of the diameter (12) of the pipeline (1), the boundary (13) between the outer pipe section (10) and the intermediate pipe section (11) is formed at half the distance between the outer and intermediate probes, the counter electrodes (7) are electrically insulated from each other and from the pipeline (1), the intermediate probe (14) arranged in the intermediate pipe section (11) consists of a reference electrode (9) and a counter electrode (7), the reference electrode (9) is connected to the potential measurement input (3) and the counter electrode (7) is connected to a first power output (16). and the pipeline (1) is coupled to the earth connection (4), and in the case of a calibration measurement configuration under laboratory conditions, the outer pipe section (10) and the intermediate pipe section (11) are galvanically isolated from each other, advantageously by means of a spacer (17) inserted in the pipeline (1), and the outer probe (15) arranged in the outer pipe section (10) is fixed in the pipeline (1) in a voltage-free state, while in the case of modeling field conditions under laboratory conditions and measuring under field conditions, the outer pipe section (10) and the intermediate pipe section (11) are galvanically connected to each other, and the counter electrodes (7) of the outer probe (15) are galvanically connected to each other and coupled to a second power output (18), and further an output (19) of the control and data storage unit (6) is connected to an input (20) of the polarization and measurement unit (5).

5. 5. A measurement arrangement according to claim 4, characterized in that connection points (21) are provided on the outer pipe section (10) and on the intermediate pipe section (11), and a short circuit (22) is installed between the connection points (21) of the outer pipe section (10) and the intermediate pipe section (11), respectively, during modelling of field conditions under laboratory conditions.

6. 5. A measurement arrangement according to claim 4, characterized in that during modelling of field conditions under laboratory conditions, the spacers (17) are removed from the outer pipe section (10) and the intermediate pipe section (11).

7. A measuring arrangement according to any one of claims 4 to 6, characterized in that the outer probe (15) further comprises a reference electrode (9).

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