Device and method for measuring time constant of metal interface capacitance under dynamic DC interference

Abstract

The present invention provides a device and method for measuring the time constant of metal interface capacitance under dynamic DC interference. The device comprises: a metal sample buried in a soil simulation medium, a reference electrode and an auxiliary electrode, a dynamic DC power supply, a circuit breaker, and a data recorder. The dynamic DC power supply is used to provide an experimental current flowing into and out of the metal sample; the data recorder is used to collect the power-on potential and power-off potential E of the metal sample in real time when the circuit breaker is connected and disconnected. off ; By integrating E of multiple dynamic DC power supply interference cycles during the measurement period off , get a dynamic DC power interference cycle E off The invention solves the problem that the prior art studies the charge and discharge capacitance effect of the double electric layer of the metal interface by measuring the electrochemical impedance spectrum of the metal in the laboratory, but cannot reflect the corrosion behavior of the metal sample in the process of alternating positive and negative currents in real time.

Description

Technical Field

[0001] The invention belongs to the technical field of buried metal pipeline corrosion measurement, and in particular relates to a device and method for measuring a metal interface capacitance time constant under dynamic direct current interference. Background Art

[0002] Due to the complexity and unpredictability of the stray current leakage path in the urban rail transit system, the prediction and protection of dynamic DC stray current interference corrosion has also become a difficult problem to ensure the safe operation of buried steel pipelines in recent years. Since the position of the train on the track changes continuously during operation, the DC stray current generated by the rail transit system has dynamic fluctuation characteristics. For buried pipelines, stray currents will flow in and out of the same position of the pipeline at different times, causing alternating positive and negative polarization on the exposed metal surface at the coating defect, which is reflected in the measurement results of the pipe-to-ground potential or the test piece current, and is manifested as dynamic positive and negative fluctuations of potential or current. Another type of stray current interference to buried steel pipelines, namely AC interference, also has alternating positive and negative fluctuation characteristics. In the research on the effect of frequency on corrosion under AC interference, it is basically that the corrosion rate gradually decreases with the increase of AC frequency, because most of the AC current is non-Faraday current and is used for the charging and discharging of the interface double layer, and only a small part of the AC current is related to metal dissolution (Faraday current). For dynamic DC stray current interference, it also has the characteristics of alternating positive and negative fluctuations. The charging and discharging capacitance effect of the interfacial double layer may also play an important role in inhibiting metal corrosion.

[0003] The prior art generally measures the electrochemical impedance spectrum (EIS) of metals in the laboratory, uses impedance spectrum fitting software and selects appropriate equivalent circuits to fit the data, obtains the parameters of the components such as resistance, capacitance and inductance in the equivalent circuit, and studies the charge and discharge capacitance effect of the double electric layer of the metal interface. However, since the AC impedance spectrum EIS is scanned when the corrosion system reaches a stable open circuit potential, it takes about 30 minutes to scan the AC impedance spectrum after the experiment, and it is impossible to reflect the corrosion behavior of the metal sample in the process of alternating positive and negative currents in real time. In addition, the double electric layer structure of the metal / electrolyte interface is related to the arrangement of charges on both sides of the interface, and the specific arrangement structure of charged particles or dipoles on the interface is greatly affected by the electrode potential and pH value. In the process of alternating positive and negative currents, there are fluctuations in the polarization potential and the near-surface pH value, and the size of the capacitance may also change, which is also the electrochemical information that the simulation results of the AC impedance spectrum cannot reflect. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a device and method for measuring the time constant of metal interface capacitance under dynamic DC interference.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions.

[0006] In a first aspect, the present invention provides a device for measuring the time constant of metal interface capacitance under dynamic DC interference, comprising: a metal sample buried in a soil simulation medium, a reference electrode and an auxiliary electrode, a dynamic DC power supply, a circuit breaker, and a data recorder; one output end of the dynamic DC power supply is electrically connected to the metal sample through the circuit breaker, and the other output end is electrically connected to the auxiliary electrode, and is used to provide an experimental current flowing into and out of the metal sample by outputting a voltage signal with a positive-negative voltage width ratio of 1:1 and an interference period of T; the on-off ratio of the circuit breaker is a:1, and the on-off period is T1; the data recorder is connected in parallel between the metal sample and the reference electrode, and is used to collect the on-potential E of the metal sample in real time when the circuit breaker is connected and disconnected with a period of T2. on and the power-off potential E off ; By integrating E of multiple dynamic DC power supply interference cycles during the measurement period off , get a dynamic DC power interference cycle E off A curve that changes with time, based on which the metal interface capacitance time constant is calculated; wherein T2 <T1 / (a+1),T1<T / 2,a> 1.

[0007] Furthermore, we can obtain E in a dynamic DC power supply interference cycle. off Methods for time-varying curves include:

[0008] Get the E of N dynamic DC power supply interference cycles for integration during the measurement period off ,in,

[0009] N=[T,T1] / T

[0010] Where, [T, T1] represents the least common multiple of T and T1, [T, T1] ≠ T;

[0011] Only the last E is retained in a circuit breaker on-off cycle. off , the jth E of the ith dynamic DC power supply interference cycle off Indicated as E off (t i +(i-1)T+(j-1)T1), where t i For the first E off The collection time, t i =T1-mod((i-1)T,T1), mod(a,b) represents the remainder when a is divided by b;

[0012] The E of the ith dynamic DC power supply interference cycle off Shift left along the time axis by (i-1)T, the jth E offChanges to E off (t i +(j-1)T1), 0≤t i +(j-1)T1≤T;E off (t i +(j-1)T1) is the integrated dynamic DC power supply interference cycle E off Curve changing with time, 2 adjacent E off The time interval is T1 / N; where i=1,2,…,N, j=1,2,…,int(T / T1), and int() is the rounding function.

[0013] Furthermore, 2 E off , shielding the first E in each circuit breaker on-off cycle off , keep the second E off .

[0014] Furthermore, the metal interface capacitance time constant τ is equal to the time constant τ calculated based on the curve in the positive half cycle and the negative half cycle of the dynamic DC power supply interference cycle. + and τ - The sum.

[0015] Furthermore, τ + The calculation methods include:

[0016] Calculate E in the positive half cycle off The maximum value E max+ ;

[0017] Calculate E from the positive half cycle off The initial value E 0+ The time required to change to E1 is τ + ; Where E1=E 0+ +0.63(E max+ -E 0+ ).

[0018] Furthermore, τ - The calculation methods include:

[0019] Calculate E in the negative half cycle off The minimum value of E min- ;

[0020] Calculate E from the negative half cycle off The initial value E 0- The time required to change to E2 is τ - ; Where E2 = E min- +0.37(E 0- -E min- ).

[0021] Furthermore, the method for analyzing the corrosion risk according to the relative size of the dynamic DC power supply interference period T and the metal interface capacitance time constant τ includes:

[0022] When T≤τ, most of the current is charged and discharged through the metal interface capacitor, and the current is not a non-Faraday current; only a small part of the current flows through the reaction resistor to cause corrosion, and the corrosion risk is relatively small;

[0023] When T>τ, most of the current flows through the interface reaction resistance, which is a Faraday current and has a greater corrosion risk.

[0024] Furthermore, the duration of the measurement period is 13h, T=1h, T1=130s, T2=1s, a=64.

[0025] Furthermore, the metal sample is made of X70 pipeline steel pipe, processed into a cylindrical shape with a diameter of 11.3 mm and a length of 5 mm, and the working surface is an area of ​​1 cm 2 The back of the circular metal surface is electrically connected to the copper wire, and the current density flowing out and into the metal sample surface is 10mA / cm 2 .

[0026] In a second aspect, the present invention provides a method for measuring a metal interface capacitance time constant using the device, comprising the following steps:

[0027] The dynamic DC power supply outputs interference signals according to the set interference cycle and positive and negative voltage width ratio, providing experimental current flowing into and out of the metal sample; the circuit breaker works according to the set on-off cycle and on-off ratio;

[0028] During the measurement period, the data recorder collects the energized potential E of the metal sample in real time according to the set period when the circuit breaker is connected and disconnected. on and the power-off potential E off ;

[0029] E of multiple dynamic DC power supply interference cycles during the measurement period off Integrate to get a dynamic DC power interference cycle E off A curve varying with time, based on which the metal interface capacitance time constant is calculated.

[0030] Compared with the prior art, the present invention has the following beneficial effects.

[0031] The present invention provides a metal sample buried in a soil simulation medium, a reference electrode and an auxiliary electrode, a dynamic DC power supply, a circuit breaker and a data recorder. The dynamic DC power supply is used to provide an experimental current flowing into and out of the metal sample. The circuit breaker works with a set on-off cycle and on-off ratio. The data recorder is used to collect the on-potential and off-potential of the metal sample in real time when the circuit breaker is turned on and off. By integrating the E values ​​of multiple dynamic DC power supply interference cycles within a measurement period, the dynamic DC power supply is used to provide an experimental current flowing into and out of the metal sample. The circuit breaker works with a set on-off cycle and on-off ratio. The data recorder is used to collect the on-potential and off-potential of the metal sample in real time when the circuit breaker is turned on and off. off , a curve of the off-power potential changing with time in a dynamic DC power supply interference cycle is obtained, and the metal interface capacitance time constant is calculated based on the curve. The present invention measures the metal interface capacitance time constant based on real-time monitoring of the off-power potential of the metal sample, and can evaluate the corrosion behavior caused by dynamic DC stray interference in real time based on the time constant, solving the problem that the existing technology obtains parameters such as equivalent resistance, capacitance and inductance by measuring the electrochemical impedance spectrum of the metal in the laboratory, and studies the charging and discharging capacitance effect of the double electric layer of the metal interface, but cannot reflect the corrosion behavior of the metal sample in the process of alternating positive and negative currents in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a block diagram of a device for measuring the time constant of metal interface capacitance under dynamic DC interference according to an embodiment of the present invention. In the figure, 1 is a metal sample, 2 is a reference electrode, 3 is a soil simulation medium, 4 is an auxiliary electrode, 5 is a data recorder, 6 is a dynamic DC power supply, and 7 is a circuit breaker.

[0033] Figure 2 Real-time monitoring of E in multiple dynamic DC power supply interference cycles on 、E off Waveform diagram.

[0034] Figure 3 E is a dynamic DC power supply interference cycle off A curve that changes over time.

[0035] Figure 4 Schematic diagram of the time constant calculation principle.

[0036] Figure 5 The present invention is a flowchart of a method for measuring the metal interface capacitance time constant by using the device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer and more understandable, the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Figure 1 The present invention is a block diagram of a device for measuring the time constant of metal interface capacitance under dynamic DC interference according to an embodiment of the present invention, comprising: a metal sample 1 buried in a soil simulation medium 3, a reference electrode 2 and an auxiliary electrode 4, a dynamic DC power supply 6, a circuit breaker 7, and a data recorder 5; one output end of the dynamic DC power supply 6 is electrically connected to the metal sample 1 through the circuit breaker 7, and the other output end is electrically connected to the auxiliary electrode 4, and is used to provide an experimental current flowing into and out of the metal sample 1 by outputting a voltage signal with a positive-negative voltage width ratio of 1:1 and an interference period of T; the on-off ratio of the circuit breaker 7 is a:1, and the on-off period is T1; the data recorder 5 is connected in parallel between the metal sample 1 and the reference electrode 2, and is used to collect the on-potential E of the metal sample 1 in real time when the circuit breaker 7 is turned on and off with a period of T2. on and the power-off potential E off ; By integrating E of multiple dynamic DC power supply interference cycles during the measurement period off , get a dynamic DC power interference cycle E off A curve that changes with time, based on which the metal interface capacitance time constant is calculated; wherein T2 <T1 / (a+1),T1<T / 2,a> 1.

[0039] In this embodiment, the device is mainly composed of a metal sample 1 buried in a soil simulation medium 3, a reference electrode 2 and an auxiliary electrode 4, a dynamic DC power supply 6, a circuit breaker 7 and a data recorder 5. The connection relationship between the various parts is as follows: Figure 1As shown in the figure. The metal specimen 1, the reference electrode 2, and the auxiliary electrode 4 are all buried in the soil simulation medium 3. The soil simulation medium 3 is used to simulate the soil environment of buried pipelines. A soil simulation solution can be prepared from deionized water and chemically pure reagents according to experimental requirements. At the same time, quartz sand after cleaning and drying is prepared for standby. The corrosive medium is quartz sand plus the soil simulation solution. The metal specimen 1 is used to simulate the buried pipeline to be measured and is made into a cylindrical shape with a certain surface area (working surface). The non-buried end of the metal specimen 1 is connected to one end of the data recorder 5, and the other end of the data recorder 5 is connected to the reference electrode 2. The reference electrode 2 is used as a reference comparison electrode for measuring the potential of the metal specimen 1. The data recorder 5 is used to collect the potential of the metal specimen 1 in real time. The non-buried end of the metal specimen 1 is also connected to an output terminal of the dynamic DC power supply 6 through a circuit breaker 7, and the other output terminal of the dynamic DC power supply 6 is connected to the auxiliary electrode 4. The dynamic DC power supply 6 is used to simulate the dynamic DC stray interference current and provide the inflow and outflow current (density) for the metal specimen 1 through the auxiliary electrode 4. The dynamic DC power supply 6 outputs an interference voltage signal with a positive and negative voltage width ratio of 1:1 and a period of T. The interference period T is generally about 1 hour. The circuit breaker 7 also operates in a periodic on-off state, with an on-off ratio of a:1 and an on-off period of T1. T1 should be significantly less than T / 2, that is, to ensure that each half of the interference period T contains multiple on-off periods T1. A longer power-on time and a shorter power-off time are set in the on-off period T1, that is, a larger a value is set, which can avoid excessive disturbance to the surface state of the metal specimen 1 caused by the interruption of the loop current. To improve the measurement accuracy, the data acquisition period T2 of the data recorder 5 should be as small as possible to ensure that multiple potential data can be collected even in the power-off state of the circuit breaker 7, that is, T2 < T1 / (a + 1). The potential collected when the circuit breaker 7 is turned on is called the on-potential E on , and the potential collected when it is turned off is called the off-potential E off . In this embodiment, the measurement period is selected as multiple dynamic DC power supply interference periods (lasting for several days). By integrating the off-potentials E off collected during the multiple dynamic DC power supply interference periods, a curve of E off changing with time within one dynamic DC power supply interference period is obtained, and based on the off-potential-time curve within one period T obtained, the metal interface capacitance time constant is calculated according to the definition of the time constant.

[0040] In this embodiment, by measuring the metal interface capacitance time constant based on the real-time monitoring of the off-potential of the metal specimen 1, the corrosion behavior caused by dynamic DC stray interference can be evaluated in real time based on the time constant, solving the problems in the prior art that only the equivalent resistance, capacitance, inductance and other parameters can be obtained by measuring the electrochemical impedance spectrum of the metal in the laboratory, and studying the charge and discharge capacitance effect of the electric double layer at the metal interface, and the corrosion behavior of the metal specimen 1 during the alternation of positive and negative currents cannot be reflected in real time, etc.

[0041] As an optional embodiment, obtain E in a dynamic DC power supply interference cycle off Methods for time-varying curves include:

[0042] Get the E of N dynamic DC power supply interference cycles for integration during the measurement period off ,in,

[0043] N=[T,T1] / T

[0044] Where, [T, T1] represents the least common multiple of T and T1, [T, T1] ≠ T;

[0045] Only the last E is retained in a circuit breaker on-off cycle. off , the jth E of the ith dynamic DC power supply interference cycle off Indicated as E off (t i +(i-1)T+(j-1)T1), where t i For the first E off The collection time, t i =T1-mod((i-1)T,T1), mod(a,b) represents the remainder when a is divided by b;

[0046] The E of the ith dynamic DC power supply interference cycle off Shift left along the time axis by (i-1)T, the jth E off Changes to E off (t i +(j-1)T1), 0≤t i +(j-1)T1≤T;E off (t i +(j-1)T1) is the integrated dynamic DC power supply interference cycle E off Curve changing with time, 2 adjacent E off The time interval is T1 / N; where i=1,2,…,N, j=1,2,…,int(T / T1), and int() is the rounding function.

[0047] This embodiment provides a dynamic DC power supply interference cycle E obtained by integration off The technical solution of the curve changing with time. Real-time monitoring of E on 、E off Waveform diagram Figure 2 As shown, the waveform with larger amplitude is E on , the waveform with smaller amplitude is E off ; E in one cycle off Waveform Figure 3 shown.

[0048] In this embodiment, the E of N dynamic DC power supply interference cycles for integration is first obtained. off In this embodiment, the duration T of the dynamic DC power supply interference cycle is not an integer multiple of the duration T1 of the circuit breaker on-off cycle, that is, [T, T1]≠T. Therefore, taking N=[T, T1] / T, after N dynamic DC power supply interference cycles T, E off Repeat the change rule of T in the first N cycles. To simplify the scheme, only the last E is retained in a circuit breaker on-off cycle. off , that is, each E off The collection time is the last moment of each circuit breaker on-off cycle. off Indicated as E off (kT1), kT1 is the acquisition time. Then, starting from the second dynamic DC power supply interference cycle, make E off (kT1) is translated to the left along the time axis. The second period is translated by 1 T, the third period is translated by 2 T, and so on. The Nth period is translated by N-1 T. In this way, E of N periods can be off (kT1) are all translated to 0~T, and we can get E in one cycle off The curve changes with time. Because [T,T1]≠T, each cycle E off The initial acquisition time t i are all different, of course, each cycle E off The collection time of two adjacent E off The time interval is T1 / N.

[0049] As an optional embodiment, two E are collected during each circuit breaker on-off cycle. off , shielding the first E in each circuit breaker on-off cycle off , keep the second E off .

[0050] In this embodiment, E is collected during each circuit breaker on-off cycle. off Since the data recorder 5 and the circuit breaker 7 are not synchronously controlled by synchronous clocks, their respective clocks may not be synchronized. The first power-off potential data of each circuit breaker on-off cycle may be collected by the data recorder 5 during the execution of the disconnection action of the circuit breaker 7, making the first power-off data inaccurate. For this reason, this embodiment shields (clears) the first power-off potential value in each circuit breaker on-off cycle, and retains the first and subsequent power-off potentials.

[0051] As an optional embodiment, the metal interface capacitance time constant τ is equal to the time constant τ calculated based on the curve in the positive half cycle and the negative half cycle of the dynamic DC power supply interference cycle. + and τ - The sum.

[0052] This embodiment provides a technical solution for calculating the time constant of metal interface capacitance. This embodiment divides the time constant τ into two parts: one part is based on the curve E in the positive half cycle of the dynamic DC power supply interference cycle off (j) Calculated time constant τ + ; The other part is based on the curve E in the negative half cycle off (j) Calculated time constant τ - The time constant τ is equal to the sum of these two time constants, that is, τ = τ + +τ - .like Figure 4 This embodiment calculates τ according to the definition of the time constant. + and τ - In an electronic circuit, when a capacitor is charged with a constant voltage through a resistor, the time required for the terminal voltage of the capacitor to reach 1-1 / e (approximately equal to 0.63) of the maximum value is the time constant; and when the circuit is disconnected, the time constant is the time required for the terminal voltage of the capacitor to reach 1 / e (approximately equal to 0.37) of the maximum value.

[0053] As an optional embodiment, τ + The calculation methods include:

[0054] Calculate E in the positive half cycle off The maximum value E max+ ;

[0055] Calculate E from the positive half cycle off The initial value E 0+ The time required to change to E1 is τ + ; Where E1=E 0+ +0.63(E max+ -E 0+ ).

[0056] This embodiment gives τ + The calculation method of Figure 4 As shown, this embodiment uses the curve E of the positive half cycle (0 to 30 minutes). off (j), calculate τ according to the definition of time constant + The specific method and the formula involved will not be described in detail. It is worth noting that based on the curve, a certain E off When the time corresponding to the value (such as E1) is reached, if the data point of the curve does not exist,off , can be based on the E off The interpolation method is used to calculate the E between two adjacent data points. off The corresponding time value.

[0057] As an optional embodiment, τ - The calculation methods include:

[0058] Calculate E in the negative half cycle off The minimum value of E min- ;

[0059] Calculate E from the negative half cycle off The initial value E 0- The time required to change to E2 is τ - ; Where E2 = E min- +0.37(E 0- -E min- ).

[0060] This embodiment gives τ - The calculation method of Figure 4 As shown, this embodiment uses the curve E of the negative half cycle (30 to 60 minutes). off (j), calculate τ according to the definition of time constant - , the specific methods and formulas involved will not be repeated here.

[0061] As an optional embodiment, a method for analyzing corrosion risk according to the relative size of the dynamic DC power supply interference period T and the metal interface capacitance time constant τ includes:

[0062] When T≤τ, most of the current is charged and discharged through the metal interface capacitor, and the current is not a non-Faraday current; only a small part of the current flows through the reaction resistor to cause corrosion, and the corrosion risk is relatively small;

[0063] When T>τ, most of the current flows through the interface reaction resistance, which is a Faraday current and has a greater corrosion risk.

[0064] This embodiment provides a method for analyzing corrosion risk based on the relative size of the dynamic DC power supply interference period T and the metal interface capacitance time constant τ. When the dynamic DC interference period is less than its time constant, it indicates that most of the current will be charged and discharged through the interface double-layer capacitance, which is a non-Faraday current, and only a small part of the current flows through the reaction resistor to cause corrosion, and the corrosion risk is relatively small; when the interference period is greater than its time constant, it indicates that the capacitance effect of the interface double layer is reduced, and most of the current will flow through the interface reaction resistor, which is a Faraday current, which will lead to increased corrosion.

[0065] As an optional embodiment, the duration of the measurement period is 13 hours, T=1 hour, T1=130 seconds, T2=1 second, and a=64.

[0066] This embodiment provides a set of specific experimental parameters. In this embodiment, the duration of the measurement period is 72h, i.e. 3 days; the dynamic DC power supply interference period T = 1h = 3600s, and the positive and negative half-periods are both 30min; the number of dynamic DC power supply interference periods included in the measurement period N = [T, T1] / T = [3600, 130] / 3600 = 13; the on-off period of the circuit breaker 7 T1 = 130s, the on-off ratio is 64:1, and the on and off times are 128s and 2s respectively; the collection period of the data recorder 5 T2 = 1s.

[0067] The time constant is calculated based on the above parameters, and the calculation results are shown in Table 1.

[0068] Table 1 Time constant calculation results

[0069]

[0070] As an optional embodiment, the metal sample 1 is made of X70 pipeline steel pipe, processed into a cylindrical shape with a diameter of 11.3 mm and a length of 5 mm, and the working surface is an area of ​​1 cm 2 The back of the circular metal surface is electrically connected to the copper wire, and the current density flowing out and into the surface of the metal sample 1 is 10mA / cm 2 .

[0071] This embodiment provides a specific structural parameter of the metal sample 1. It is worth noting that this embodiment provides a preferred implementation method, and does not deny or exclude other feasible implementation methods, such as metal samples 1 made of different sizes and materials.

[0072] Figure 5 The present invention is a flowchart of a method for measuring the metal interface capacitance time constant using the device according to an embodiment of the present invention, comprising the following steps:

[0073] Step 101, the dynamic DC power supply 6 outputs an interference signal according to the set interference cycle and positive and negative voltage width ratio, and provides an experimental current flowing into and out of the metal sample 1; the circuit breaker 7 works according to the set on-off cycle and on-off ratio;

[0074] Step 102: During the measurement period, the data recorder 5 collects the energized potential E of the metal sample 1 in real time according to the set period when the circuit breaker 7 is turned on and off. on and the power-off potential E off ;

[0075] Step 103: E of multiple dynamic DC power supply interference cycles within the measurement period offIntegrate to get a dynamic DC power interference cycle E off A curve varying with time, based on which the metal interface capacitance time constant is calculated.

[0076] The method of this embodiment, Figure 1 Compared with the technical solution of the device embodiment shown in the figure, its implementation principle and technical effect are similar and will not be repeated here.

[0077] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A device for measuring the time constant of metal interface capacitance under dynamic DC interference, characterized in that: include: A metal sample, a reference electrode and an auxiliary electrode buried in a soil simulation medium, a dynamic DC power supply, a circuit breaker, and a data recorder; one output end of the dynamic DC power supply is electrically connected to the metal sample through the circuit breaker, and the other output end is electrically connected to the auxiliary electrode, and is used to provide an experimental current flowing into and out of the metal sample by outputting a voltage signal with a positive-negative voltage width ratio of 1:1 and an interference period of T; the on-off ratio of the circuit breaker is a:1, and the on-off period is T1; the data recorder is connected in parallel between the metal sample and the reference electrode, and is used to collect the on-potential E of the metal sample in real time when the circuit breaker is turned on and off with a period of T2. on and the power-off potential E off ; By integrating E of multiple dynamic DC power supply interference cycles during the measurement period off , get a dynamic DC power interference cycle E off A curve that changes with time, based on which the metal interface capacitance time constant is calculated; wherein T2 <T1 / (a+1),T1<T / 2,a> 1; The metal interface capacitance time constant τ is equal to the time constant τ calculated based on the curve in the positive half cycle and the negative half cycle of the dynamic DC power supply interference cycle + and τ - of and; τ + The calculation methods include: Calculate E in the positive half cycle off The maximum value E max+ ; Calculate E from the positive half cycle off The initial value E 0+ The time required to change to E1 is τ + ; Where E1=E 0+ +0.63(E max+ -E 0+ ); τ - The calculation methods include: Calculate E in the negative half cycle off The minimum value of E min- ; Calculate E from the negative half cycle off The initial value E 0- The time required to change to E2 is τ - ; Where E2 = E min- +0.37(E 0- -E min- ).

2. The device for measuring the metal interface capacitance time constant under dynamic DC interference according to claim 1, characterized in that: Get a dynamic DC power interference cycle E off Methods for time-varying curves include: Get the E of N dynamic DC power supply interference cycles for integration during the measurement period off ,in, N=[T,T1] / T Where, [T, T1] represents the least common multiple of T and T1, [T, T1] ≠ T; Only the last E is retained in a circuit breaker on-off cycle. off , the jth E of the ith dynamic DC power supply interference cycle off Indicated as E off (t i +(i-1)T+(j-1)T1), where t i For the first E off The collection time, t i =T1-mod((i-1)T,T1), mod(a,b) represents the remainder when a is divided by b; The E of the ith dynamic DC power supply interference cycle off Shift left along the time axis by (i-1)T, the jth E off Changes to E off (t i +(j-1)T1), 0≤t i +(j-1)T1≤T;E off (t i +(j-1)T1) is the integrated dynamic DC power supply interference cycle E off Curve changing with time, 2 adjacent E off The time interval is T1 / N; where i=1,2,…,N, j=1,2,…,int(T / T1), and int() is the rounding function.

3. The device for measuring the metal interface capacitance time constant under dynamic DC interference according to claim 2, characterized in that: Collect 2 E in each circuit breaker on-off cycle off , shielding the first E in each circuit breaker on-off cycle off , keep the second E off .

4. The device for measuring the metal interface capacitance time constant under dynamic DC interference according to claim 1, characterized in that: Corrosion risk is analyzed based on the relative size of the dynamic DC power supply interference period T and the metal interface capacitance time constant τ, including: When T≤τ, most of the current is charged and discharged through the metal interface capacitor, and the current is not a non-Faraday current; only a small part of the current flows through the reaction resistor to cause corrosion, and the corrosion risk is relatively small; When T>τ, most of the current flows through the interface reaction resistance, which is a Faraday current and has a greater corrosion risk.

5. The device for measuring the metal interface capacitance time constant under dynamic DC interference according to claim 1, characterized in that: The duration of the measurement period is 13 hours, T=1 hour, T1=130 seconds, T2=1 second, and a=64.

6. The device for measuring the metal interface capacitance time constant under dynamic DC interference according to claim 1, characterized in that: The metal sample is made of X70 pipeline steel pipe, processed into a cylindrical shape with a diameter of 11.3 mm and a length of 5 mm, and the working surface is an area of ​​1 cm 2 The circular metal surface is connected to the copper wire on the back, and the current density flowing out and into the metal sample surface is 10mA / cm 2 .

7. A method for measuring the time constant of metal interface capacitance using the device of claim 1, comprising the following steps: The dynamic DC power supply outputs interference signals according to the set interference cycle and positive and negative voltage width ratio, and provides experimental current flowing into and out of the metal sample; the circuit breaker works according to the set on-off cycle and on-off ratio; During the measurement period, the data recorder collects the energized potential E of the metal sample in real time according to the set period when the circuit breaker is connected and disconnected. on and the power-off potential E off ; E of multiple dynamic DC power supply interference cycles during the measurement period off Integrate to get a dynamic DC power interference cycle E off A curve varying with time, based on which the metal interface capacitance time constant is calculated.

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