A sensor, system and method for online evaluation of coating life

Abstract

The present invention provides a sensor, system and method for online evaluation of coating life. The sensor adopts a flexible film substrate, a plurality of electrode grids are evaporated on the surface, and the sensor is mounted on the surface of a metal substrate at a certain inclination angle. The sensor is gradually buried in the coating slurry during the spraying process, and after the coating is cured, an electrode array with a gradient elevation from the outer surface is formed. In a harsh environment, moisture, salt spray and oxygen continuously penetrate into the tiny gaps in the coating, resulting in an increase in the dielectric constant and capacitance of the coating. Due to the difference in penetration distance, the capacitance between the outermost electrode pairs increases first; then, as the aging time increases, the capacitance of the lower electrode pairs also gradually increases. By monitoring the change curve of the coating capacitance of different gradient levels over time, the penetration depth and diffusion rate of water in the coating can be calculated. Based on the diffusion rate equation in the vertical direction, a coating aging kinetic model can be established. Through this model and the coating thickness value, the service life of the coating can be estimated.

Description

Technical Field

[0001] The present invention relates to the technical field of metal corrosion and protection, and in particular to the technical field of aging degree and service life prediction of anti-corrosion coatings, and more specifically to a sensor, system and method for online evaluation of coating life. Background Art

[0002] Marine engineering, petrochemical and shipbuilding industry equipment are prone to corrosion due to harsh environmental erosion during use. Severe corrosion can also cause huge economic losses and safety disasters. Organic coating is the most economical and widely used metal corrosion protection method. However, the coating will age and degrade in environments such as ultraviolet light, salt spray, high and low temperature alternation, and corrosive media (H2O, Cl - , H + , O2, etc.) diffuse into the metal matrix through the micropores and cracks in the coating, causing the coating to lose gloss and debond, and ultimately causing the corrosion resistance of the coating to decrease. To improve the durability of the coating, it is necessary to improve the diffusion resistance of the coating to corrosive media and study its aging mechanism.

[0003] At present, the failure of coatings is often judged by evaluating their own appearance (mainly gloss changes). For example, GB / T 1865-2009 stipulates test methods for evaluating the artificial weather resistance of paints, varnishes and related product coatings or evaluating their light resistance through artificial radiation exposure. However, coating failure usually occurs before visual defects appear. At this time, the coating may have debonded and the metal substrate has corroded. Therefore, if the failure process of the in-service coating can be quickly evaluated and its aging dynamics can be understood, preventive maintenance or replacement can be taken before the coating fails, it is possible to prevent serious corrosion of the metal substrate. In addition, the current service life assessment of coatings is mostly based on the results of accelerated corrosion tests, lacking real data support under field service conditions. Therefore, it is very necessary to study the failure dynamics of the coating from the outside to the inside. Summary of the invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a sensor, system and method for online evaluation of coating life. Micro-array electrodes with gradient arrangement are buried in the coating, and the multi-layer capacitance distribution of the coating from the outside to the inside can be measured. Through the changes of different layered capacitances with time and depth, the change curve of the coating aging depth with time can be monitored in real time, ultimately achieving the purpose of predicting the coating life.

[0005] According to a first aspect of the present invention, there is provided a sensor for online evaluation of coating life, comprising:

[0006] A flexible insulating substrate is solidified and encapsulated in a coating at a certain inclination angle; a plurality of parallel electrodes are arranged on the flexible insulating substrate, and the plurality of electrodes are arranged into an electrode array with a gradient elevation from the outer surface of the coating, and the spacing between adjacent electrodes is equal.

[0007] Based on the above technical solution, the present invention can also make the following improvements.

[0008] Optionally, each of the electrodes is led out through a printed lead, and all of the printed leads are gathered to form a multi-channel detection interface.

[0009] Optionally, the electrode is a grid electrode.

[0010] According to a second aspect of the present invention, there is provided a system for online evaluation of coating life, comprising the above-mentioned sensor, and further comprising:

[0011] A test module, the test module is communicatively connected to the sensor, and is used to output an excitation signal to each electrode of the sensor, and is also used to sample a response signal of each electrode, calculate the imaginary part of the impedance of each electrode pair in the coating according to the response signal, and calculate the capacitance value of each electrode pair in the coating according to the imaginary part of the impedance of the coating;

[0012] An evaluation module is communicatively connected with the test module and is used to compare the capacitance value of each electrode pair in the coating with a preset coating capacitance threshold value to determine the degree of aging of the coating.

[0013] Optionally, the evaluation module is further used to calculate the moisture content of the coating according to the capacitance value of each electrode pair in the coating, and evaluate the aging degree of the coating according to the moisture content of the coating.

[0014] Optionally, the test module includes an excitation signal storage module, an MCU, a DA converter, a voltage follower, an AD converter, a transconductance amplifier and a multi-channel signal switch.

[0015] The excitation signal storage module is connected to the MCU for outputting an excitation signal;

[0016] The input end of the DA converter is connected to the output end of the MCU, and is used to perform digital-to-analog conversion on the excitation signal to obtain a sinusoidal excitation signal;

[0017] The input end of the voltage follower is connected to the DA converter, and the output end is connected to the multi-channel signal switcher, so as to amplify the sinusoidal excitation signal;

[0018] The input end of the transconductance amplifier is connected to the multi-channel signal switch, and the output end is connected to the input end of the AD converter, so as to convert the received response signal from current to voltage;

[0019] The output end of the AD converter is connected to the input end of the MCU, and is used to perform analog-to-digital conversion on the response signal;

[0020] The MCU is communicatively connected to the multi-channel signal switcher for controlling channel switching of the multi-channel signal switcher, and is also used to calculate the imaginary part of the impedance of each electrode pair in the coating according to the received response signal, and calculate the capacitance value of each electrode pair in the coating according to the imaginary part of the impedance of each electrode pair in the coating.

[0021] According to a third aspect of the present invention, based on the above system, a method for online evaluation of coating life is provided, comprising:

[0022] sending a sinusoidal excitation signal to the array electrodes in the coating and receiving a response signal;

[0023] The imaginary part of the impedance of each electrode pair in the coating is calculated according to the sinusoidal excitation signal and the response signal, and the capacitance value of each electrode pair in the coating is calculated according to the imaginary part of the impedance of each electrode pair in the coating;

[0024] The degree of aging of the coating is determined by comparing the capacitance value of each electrode pair in the coating with a preset coating capacitance threshold.

[0025] Optionally, the method further includes:

[0026] The aging rate of the coating is evaluated based on the curve of the capacitance value of each electrode pair in the coating changing with time.

[0027] Optionally, the method further includes:

[0028] The water content at the corresponding depth of the coating is calculated based on the measured capacitance value of each electrode pair in the coating, the initial capacitance value of each electrode pair in the coating and the dielectric constant of water;

[0029] The aging rate and / or service life of the coating can be evaluated based on the curve of the moisture content at the corresponding depth of the coating versus time.

[0030] The present invention provides a sensor, system and method for online evaluation of coating life. The microarray electrodes arranged in a gradient manner can measure the multilayer capacitance distribution of the coating from the outside to the inside. The capacitance value of each electrode pair in the coating is measured by a high-frequency sine wave. The aging degree of the coating can be evaluated based on the variation law of the capacitance value; the moisture content and porosity of the coating can be calculated based on the capacitance value, so that the aging degree of the coating can also be evaluated; through the variation of different layered capacitances with time and depth, the variation curve of the aging depth of the coating with time can be monitored in real time, and finally the purpose of predicting the coating life can be achieved. The microarray electrodes of the present invention are buried in the coating surface of the on-site structural parts, combined with a multi-channel coating impedance test instrument, a low-power wireless transceiver and a cloud network server, to form an on-site coating aging online monitoring system. Authorized users can view the coating aging status and service life of any location in real time through the Internet without leaving home, providing an important basis for the precise maintenance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the sensor structure and installation scenario for online evaluation of coating life provided by the present invention;

[0032] Figure 2 A schematic diagram of electrode wiring of the flexible thin film array electrode sensor provided by the present invention;

[0033] Figure 3 Schematic diagram of the coating impedance monitoring circuit based on thin film array electrodes to monitor different depths;

[0034] Figure 4 Schematic diagram of the curve of coating capacitance changing with aging time and electrode depth;

[0035] Figure 5 The curves of coating impedance and capacitance changing with time;

[0036] Figure 6 This is the variation curve of coating water absorption with aging time. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0038] like Figure 1 As shown in the sensor structure and curing installation schematic diagram, the present embodiment provides a sensor for online evaluation of coating life, including:

[0039] A flexible insulating substrate is solidified and encapsulated in the coating at a certain inclination angle, and a plurality of parallel electrodes are arranged on the flexible insulating substrate. In order to increase the density of the electrodes and the detection accuracy, the electrodes can be grid electrodes. The plurality of electrodes are arranged into an electrode array with a gradient elevation from the outer surface of the coating, and the spacing between adjacent electrodes is equal.

[0040] It is understandable that, in view of the defects of the existing non-destructive monitoring technology for coating aging of large structural parts, the present invention proposes the following Figure 1 The flexible thin film array electrode sensor for online evaluation of coating life shown in the figure is attached to the surface of a metal structure (ship, bridge or pipeline) at an inclined angle, and is embedded and cured into the coating during the subsequent coating spraying process. A series of parallel and equidistant metal grid electrodes are etched or evaporated on the surface of the flexible sensor. During detection, the medium-frequency electrochemical impedance and capacitance values ​​between each adjacent electrode pair can be measured sequentially through the impedance test circuit, and the moisture content at different depths of the coating and the depth of the high moisture content front can be calculated. The service life of the coating under real field conditions can be predicted through the advancement curve of the high moisture content front over time.

[0041] More specifically, the sensor uses a flexible thin film printed electrode, on which a plurality of electrode grids are evaporated and attached to the surface coating of the metal substrate at a certain inclination angle. During the spraying process, the thin film printed electrode will gradually be buried in the coating slurry, and after the coating is cured, an electrode array with a gradient elevation from the outer surface is formed. In harsh environments, moisture, salt spray and oxygen continuously penetrate into the tiny gaps in the coating, resulting in an increase in the dielectric constant and capacitance of the coating. Due to the difference in penetration distance, the capacitance between the outermost electrode pairs increases first, and then the aging time increases, and the capacitance of the lower electrode pairs also gradually increases. By monitoring the change curve of the coating capacitance of different gradient levels over time, the penetration depth and diffusion rate of water in the coating can be calculated. Based on the diffusion rate equation in the vertical direction, a coating aging kinetic model can be established. By changing the model and the coating thickness value, the service life of the coating can be estimated. The coating aging rate monitoring sensor provided by the present invention is suitable for laboratory or on-site coating aging kinetic mechanism research and coating service life prediction.

[0042] In this embodiment, the sensor uses a polyethylene or nylon film with a thickness of about 50 μm to 100 μm as a flexible insulating substrate, and the surface of the flexible insulating film substrate is etched with 7 to 17 metal grids on its surface by printed circuit technology. Figure 2As shown, the width of the grid electrodes A, B, C, D…I is 20μm to 50μm, the length is 5 to 10mm, and the thickness is 10μm to 50μm. The spacing between any two metal grids is equal and between 100μm and 200μm. The material of the metal grid can be Cu, Ag or Au. Each grid electrode is led to the top of the flexible insulating film substrate through a printed lead, and a corresponding gold finger contact point is made on the film. All the printed leads are aggregated to form a multi-channel detection interface, which is convenient for connection with the multi-core electrode cable of the subsequent impedance test instrument. The length of the entire thin film electrode sensor is about 20 mm to 50 mm, and the width is 8 mm to 12 mm. The actual size needs to be determined according to the coating thickness of the on-site coating.

[0043] In the specific implementation process of sensor installation, one end of the thin film array electrode sensor can be bonded to the surface of the workpiece, and the other end can be led out at a certain horizontal angle and fixed by epoxy resin. The angle can be set at 1 to 10 degrees. The specific angle needs to be determined according to the thickness of the on-site coating, such as Figure 1 The middle inclination angle θ is shown. After the sensor is bonded and fastened, a coating of agreed thickness, such as 100μm to 1000μm, can be sprayed on the surface of the workpiece. After curing according to the process requirements, the lead wires AI of each electrode are connected to the impedance tester.

[0044] During the service life of the coating, water, salt and dissolved oxygen can penetrate into the coating through the micro-cracks or pores in the coating, and eventually reach the coating / metal substrate interface as the coating service time increases. Figure 1 As shown, 1 is a flexible thin film array electrode sensor, 12 is a metal pipeline surface coating, and 13 is an oil and gas metal pipeline. As the service time increases, moisture and salt successively reach the A, B, C, ... I electrodes on the array electrode sensor, and the resistance between two adjacent grid (metal foil) electrodes decreases, while the capacitance increases. Therefore, the depth of coating aging can be determined by monitoring the impedance between two adjacent metal grid electrodes, and the monitored impedance and capacitance value changes can be used to predict the coating service life and failure warning.

[0045] The flexible thin film array electrodes of the sensor can be connected to a multi-channel coating capacitance testing device to automatically measure the impedance value between each grid electrode in the array electrode, and calculate the coating aging rate and aging rate through the change in the capacitance value of the coating from top to bottom.

[0046] Based on the above sensor embodiment, this embodiment further provides a system for online evaluation of coating life, the system comprising the above sensor and further comprising:

[0047] A test module, the test module is communicatively connected to the sensor, and is used to output an excitation signal to each electrode of the sensor, and is also used to sample a response signal of each electrode, calculate the imaginary part of the impedance of each electrode pair in the coating according to the response signal, and calculate the capacitance value of each electrode pair in the coating according to the imaginary part of the impedance of the coating;

[0048] An evaluation module is communicatively connected with the test module and is used to compare the capacitance value of each electrode pair in the coating with a preset coating capacitance threshold value to determine the degree of aging of the coating.

[0049] As one of the preferred embodiments, the evaluation module is further used to calculate the moisture content of the coating according to the capacitance value of each electrode pair in the coating, and evaluate the aging degree of the coating according to the moisture content of the coating.

[0050] like Figure 3 As shown, the test module includes an excitation signal storage module, an MCU, a DA converter, a voltage follower, an AD converter, a transconductance amplifier and a multi-channel signal switch.

[0051] The excitation signal storage module is connected to the MCU for outputting an excitation signal;

[0052] The input end of the DA converter is connected to the output end of the MCU, and is used to perform digital-to-analog conversion on the excitation signal to obtain a sinusoidal excitation signal;

[0053] The input end of the voltage follower is connected to the DA converter, and the output end is connected to the multi-channel signal switcher, so as to amplify the sinusoidal excitation signal;

[0054] The input end of the transconductance amplifier is connected to the multi-channel signal switch, and the output end is connected to the input end of the AD converter, so as to convert the received response signal from current to voltage;

[0055] The output end of the AD converter is connected to the input end of the MCU, and is used to perform analog-to-digital conversion on the response signal;

[0056] The MCU is communicatively connected to the multi-channel signal switcher for controlling channel switching of the multi-channel signal switcher, and is also used to calculate the imaginary part of the impedance of each electrode pair in the coating according to the received response signal, and calculate the capacitance value of each electrode pair in the coating according to the imaginary part of the impedance of each electrode pair in the coating.

[0057] More specifically, the test module uses Figure 3The multi-channel coating impedance test circuit shown in the figure is implemented, wherein the flexible array electrode 1 is connected to a multiplexer 2 through a ribbon cable, and the multiplexer can connect any two (S0-S8)) grid electrodes to the D0 and D1 output terminals of the multiplexer 2 respectively under the control of the MCU8. The excitation signal storage module is implemented by Flash ROM7, and a sine wave waveform table is stored in the Flash ROM7. The MCU8 reads the waveform table data and then sends it to the D / A converter 6 to generate a sine wave signal of a certain frequency. The generated sine wave signal enters the voltage follower 4 through a high-pass filter composed of a capacitor C11 and a resistor R11, and the driving ability of the sine wave signal is improved by the voltage follower 4. Finally, the sine wave signal is loaded between any two grid electrodes in the flexible array electrode 1 through the output terminal (for example, the S1 and S2 output terminals) of the multiplexer 2, such as between the B and C electrodes of the electrode 1. Since there are resistor R2 and capacitor C2 in the coating between the electrodes, the sine wave will return to S2 of the multiplexer through the parallel circuit of R2||C2, and output to the transconductance amplifier 3 from the D1 terminal, converting the weak current signal into a voltage signal, and then input to the A / D converter 5 through the resistor R14, and the latter will perform analog-to-digital conversion on the feedback sine wave signal. Capacitor C12 is used to prevent the grid electrodes from being too high due to the impedance (10 11 Ω.cm 2 ) The signal self-excited oscillation problem caused by the MCU8 performs correlation integration on the output sine wave and the input sine wave, and uses the corresponding impedance calculation method to calculate the impedance value at different frequencies.

[0058] Figure 3 The evaluation module is an evaluation algorithm in the host computer 10, and the host computer 10 is connected to the MCU 8 of the test module through the RS485 port 9. The host computer 10 can be a terminal computer or a notebook computer.

[0059] Based on the above sensor embodiment and system embodiment, this embodiment further provides a method for online evaluation of coating life, the method comprising:

[0060] sending a sinusoidal excitation signal to the array electrodes in the coating and receiving a response signal;

[0061] The imaginary part of the impedance of each electrode pair in the coating is calculated according to the sinusoidal excitation signal and the response signal, and the capacitance value of each electrode pair in the coating is calculated according to the imaginary part of the impedance of each electrode pair in the coating;

[0062] The degree of aging of the coating is determined by comparing the capacitance value of each electrode pair in the coating with a preset coating capacitance threshold.

[0063] As a possible preferred embodiment, the method further includes: evaluating the aging rate of the coating according to a curve showing the change in capacitance of each electrode pair in the coating over time.

[0064] As a possible preferred embodiment, the method further includes: calculating the water content of the coating at a corresponding depth according to the measured capacitance value of each electrode pair in the coating, the initial capacitance value of each electrode pair in the coating and the dielectric constant of water;

[0065] The aging rate and / or aging degree of the coating is evaluated based on the curve of the moisture content at the corresponding depth of the coating changing with time.

[0066] Now combined Figure 3 The impedance measurement circuit in the embodiment is used to illustrate the calculation method of this embodiment. Assume that the output sinusoidal wave signal is v(t), as shown in the following formula (1), and the input sinusoidal wave signal is i (t), as shown in formula (2):

[0067] v(t)=V a sin(ωt-φ v )+N1 (1)

[0068] i(t)=I a R c sin(ωt-φ i )+N2 (2)

[0069] Where V a and I a is the signal amplitude, and φ v and φ i is the phase angle of the signal at the sampling moment, R c is the sampling resistor, ω is the signal frequency, N1 and N2 are random noise. The excitation signal is Figure 3 The D / A converter 6 generates ω, so ω is a known quantity, and φ v and φ i They are all unknown quantities. In order to calculate the phase difference and amplitude ratio between the two signals, a reference signal s(t) = sin(ωt) with unit amplitude is introduced as a standard reference signal.

[0070] First, calculate the amplitude V of v(t) relative to the signal s(t) a and phase difference φ v Expand equation (1) to get equation (3), multiply both sides by the reference signal sinωt of the same frequency to get equation (4), and integrate a signal period T from any time t0 to get equation (5):

[0071] v(t)=V a sinωtcosφ v +V a cosωtsinφ v+N1 (3)

[0072]

[0073]

[0074] make From formula (5), we can get:

[0075]

[0076] Multiply both sides of formula (3) by cosωt, and let It can be deduced that:

[0077]

[0078]

[0079] Depend on Available

[0080]

[0081] Similarly, for the current channel, let Then we have:

[0082]

[0083]

[0084] According to φ v and φ i and V a and I a R c Calculate the value and get the complex impedance of the measured system at frequency ω:

[0085]

[0086] φ=φ v -φ i (13)

[0087] Then the imaginary impedance value Z im = -Z × sin(φ) (14).

[0088] After the imaginary impedance value of the electrode pair under test is calculated, the capacitance value of the electrode pair under test in the coating can be calculated.

[0089] Considering that the coating resistance is generally large, and the coating resistance requires a lower sine wave frequency (≤0.01Hz) to be accurately measured, and the low-frequency signal is easily interfered by the environmental electromagnetic wave, the present invention only measures the capacitance value of the coating, and measures the imaginary part Z of the medium and high frequency impedance value (1kHz~100Hz) between two adjacent grid electrodes of the flexible array electrode sensor. im According to the following equations (15) and (16), the corresponding coating capacitance C can be calculated: c :

[0090]

[0091] Then the coating capacitance C can be calculated c ,

[0092] C C =1 / 2πfZ Im (16).

[0093] After the coating capacitance value is calculated, the coating moisture content (also called coating water absorption rate) can also be calculated based on the coating capacitance value.

[0094] When the thin film gate electrode is solidified on the surface of the metal structure together with the coating, the physical size and position of the electrode are completely fixed. At this time, the coating capacitance between the electrode pairs is mainly positively correlated with the relative dielectric constant of the coating, and the relative dielectric constant of the coating is positively correlated with its water absorption rate. The coating water absorption rate δ v It can be calculated by the following formula (17):

[0095]

[0096] Among them, C c (0) is the initial capacitance of the coating, C c (t) is the coating capacitance after the coating is immersed for t time, ε is the dielectric constant of water, which is 78F / m.

[0097] According to the calculated imaginary impedance value of the sensor, the moisture content in the coating and the change law of the moisture content with time and coating depth can be known, and then the coating failure mechanism can be analyzed and the coating failure dynamics process can be calculated. With the help of the change curve of the coating moisture content with time and depth, combined with the corresponding development trend prediction equation, the time of coating failure and the coating service life can be warned.

[0098] The present invention will now be described more intuitively in conjunction with several specific application scenarios.

[0099] Scenario 1:

[0100] See also Figure 1 and Figure 2, the coated gradient microarray electrode of the present invention is adhered to the surface of a carbon steel workpiece at a certain inclination angle, and then a 100μm to 1000μm polyurethane or epoxy coating is sprayed on the surface of the workpiece. After the coating is cured, the flexible terminal of the array electrode is led out to a multi-channel impedance tester. The surface of the flexible array electrode is engraved with 8 to 16 grid-shaped printed gold foils, each gold foil is a grid electrode, and the spacing between two adjacent grid electrodes is 50 to 100μm. The impedance tester adopts a two-electrode mode to connect two adjacent gold foils. The impedance tester outputs a sinusoidal wave excitation signal with a frequency of 100 to 1000Hz and an amplitude of 100 to 1000mV through a built-in DA converter and loads it between the two grid electrodes. At the same time, the corresponding potential and current sinusoidal waveforms are collected through the built-in AD converter of the impedance tester, and the imaginary impedance Z between any adjacent grid electrodes is calculated according to formulas (1) to (14) im Finally, the coating capacitance C between any grid electrodes is calculated by formulas (15) and (16): c .

[0101] The coating capacitance C between different electrode pairs c Plot the aging time, such as Figure 4 As shown, the capacitance C between all grid electrodes (such as A, B, C...I) can be seen. c Both gradually increase with the extension of aging time. However, as the electrode is buried deeper into the coating, the coating capacitance starts to increase later. The increase in coating capacitance indicates an increase in coating moisture content and coating defects. If the coating capacitance between a pair of grid electrodes exceeds the set critical aging point (critical capacity), that is, the preset coating capacitance threshold, such as 1μF / cm 2 , it can be considered that the coating aging has reached the depth of the corresponding grid electrode. According to the measured data, the coating aging depth D conforms to the kinetic equation shown in formula (18):

[0102] D=a×t n (18)

[0103] Where a is a coefficient, t represents the service time of the coating, and n is a power function, n=0 to 3. The n value can be obtained by fitting the capacitance-time curve of the flexible array grid electrode. The larger the n value, the faster the coating aging depth progresses.

[0104] Scenario 2:

[0105] In order to show the change process more directly, the change curve of the resistance and capacitance of the polyurethane coating over time is taken as an example, Figure 5As shown in the figure, the 300μm polyurethane coating gradually decreases in resistance under the two aging conditions of salt spray (SST) and ultraviolet radiation (UV), and drops to 106Ωcm at around 1500h. 2 , using 500Hz sine wave excitation, the coating capacitance gradually increases from 10 to 10 under different aging times by using formulas (1)-(16). -9 F / cm 2 Increase to 10 -4 F / cm 2 As the aging time continues, the coating resistance further decreases and the coating capacitance continues to increase. According to the definition in scenario 1, when the coating capacitance increases to 10 -6 F / cm 2 When the capacitance is above the preset coating capacitance threshold, it can be determined that the substrate protection function of the coating is lost, so this value can be used as the threshold for coating maintenance. Figure 5 The capacitance in is the capacitance between the coating base metal and the reference electrode, that is, the capacitance of the entire 300μm thick coating. According to the definition of a flat capacitor, if the coating thickness decreases, the coating capacitance increases. Assuming that the grid electrode spacing in the flexible array electrode in scenario 1 is 50um, which is only 1 / 6 of the coating thickness in this embodiment, the corresponding coating capacitance between each adjacent grid electrode should be 6μF / cm 2 Once the monitored coating capacitance is greater than this value, it can be considered that the coating aging has reached this depth.

[0106] Scenario 3:

[0107] According to formula (17), the aging rate of the coating can be calculated based on the logarithm of the ratio of the initial capacitance to the current capacitance of the coating. Still taking the aging curve of a 300μm thick polyurethane coating under salt spray (SST) and ultraviolet radiation (UV) as an example, Figure 6 The curve showing the change of moisture content of the coating over time. Figure 6 As shown in the figure, under the two aging conditions, the moisture content of the coating δ v It increases rapidly in the early stage of aging, but after aging for 900h, δ v Begins to stabilize, at this time, under UV aging conditions, δ v It increases to about 4.5%, and under salt spray aging conditions, the moisture content of the coating is even higher, reaching 5.1%.

[0108] The coating aging monitoring sensor, system and method for online evaluation of coating life of the present invention have the advantage of measuring the capacitance value of the coating by high-frequency sine waves, and the moisture content and porosity of the coating can be calculated based on the capacitance value, thereby evaluating the aging degree of the coating.

[0109] The present invention adopts gradient-arranged microarray electrodes to measure the multilayer capacitance distribution of the coating from the outside to the inside. Through the changes of different layered capacitances with time and depth, the aging depth change curve of the coating with time can be monitored in real time, ultimately achieving the purpose of predicting the coating life.

[0110] The microarray electrode of the present invention is embedded in the coating surface of the on-site structural parts, combined with a multi-channel coating impedance tester, a low-power wireless transceiver and a cloud network server, to form an on-site coating aging online monitoring system. Authorized users can view the coating aging status and service life at any location in real time through the Internet without leaving home, providing an important basis for accurate maintenance of the coating.

[0111] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0112] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A sensor for online evaluation of coating life, characterized in that: include: A flexible insulating substrate, wherein the flexible insulating substrate is cured and encapsulated in the coating at a certain inclination angle; A plurality of parallel electrodes are arranged on the flexible insulating substrate, wherein the plurality of electrodes are a series of parallel and equidistant metal grid electrodes etched or evaporated on the surface of the sensor, and the plurality of electrodes are arranged into an electrode array having a gradient elevation from the outer surface of the coating, and the spacing between adjacent electrodes is equal; The depth of coating aging is determined by monitoring the impedance between two adjacent metal grid electrodes, and the monitored impedance and capacitance value changes are used to predict coating service life and failure warning.

2. The sensor according to claim 1, characterized in that Each electrode is led out through a printed lead, and all the printed leads are gathered to form a multi-channel detection interface.

3. A system for online evaluation of coating life, characterized in that: The sensor according to any one of claims 1 to 2 further comprises: A test module, the test module is communicatively connected to the sensor, and is used to output an excitation signal to each electrode of the sensor, and is also used to sample a response signal of each electrode, calculate the imaginary part of the impedance of each electrode pair in the coating according to the response signal, and calculate the capacitance value of each electrode pair in the coating according to the imaginary part of the impedance of the coating; An evaluation module is communicatively connected with the test module and is used to compare the capacitance value of each electrode pair in the coating with a preset coating capacitance threshold value to determine the degree of aging of the coating.

4. The system according to claim 3, characterized in that The evaluation module is also used to calculate the moisture content of the coating according to the capacitance value of each electrode pair in the coating, and evaluate the aging degree of the coating according to the moisture content of the coating.

5. The system according to claim 4, characterized in that The test module includes an excitation signal storage module, an MCU, a DA converter, a voltage follower, an AD converter, a transconductance amplifier and a multi-channel signal switch. The excitation signal storage module is connected to the MCU for outputting an excitation signal; The input end of the DA converter is connected to the output end of the MCU, and is used to perform digital-to-analog conversion on the excitation signal to obtain a sinusoidal excitation signal; The input end of the voltage follower is connected to the DA converter, and the output end is connected to the multi-channel signal switcher, so as to amplify the sinusoidal excitation signal; The input end of the transconductance amplifier is connected to the multi-channel signal switch, and the output end is connected to the input end of the AD converter, so as to convert the received response signal from current to voltage; The output end of the AD converter is connected to the input end of the MCU, and is used to perform analog-to-digital conversion on the response signal; The MCU is communicatively connected to the multi-channel signal switcher for controlling channel switching of the multi-channel signal switcher, and is also used to calculate the imaginary part of the impedance of each electrode pair in the coating according to the received response signal, and calculate the capacitance value of each electrode pair in the coating according to the imaginary part of the impedance of each electrode pair in the coating.

6. A method for online evaluation of coating life based on the system according to any one of claims 3 to 5, characterized in that: include: sending a sinusoidal excitation signal to the array electrodes in the coating and receiving a response signal; The imaginary part of the impedance of each electrode pair in the coating is calculated according to the sinusoidal excitation signal and the response signal, and the capacitance value of each electrode pair in the coating is calculated according to the imaginary part of the impedance of each electrode pair in the coating; The degree of aging of the coating is determined by comparing the capacitance value of each electrode pair in the coating with a preset coating capacitance threshold.

7. The method according to claim 6, characterized in that Also includes: The aging rate of the coating is evaluated based on the curve of the capacitance value of each electrode pair in the coating changing with time.

8. The method according to claim 6, characterized in that Also includes: The water content at the corresponding depth of the coating is calculated based on the measured capacitance value of each electrode pair in the coating, the initial capacitance value of each electrode pair in the coating and the dielectric constant of water; The aging rate and / or service life of the coating can be evaluated based on the curve of the moisture content at the corresponding depth of the coating versus time.

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