Sensor and method for monitoring corrosion behavior of metal in chloride molten salt

Abstract

The invention belongs to the technical field of material performance monitoring, and particularly relates to a sensor and a method for monitoring the corrosion behavior of metal in chloride molten salt, and the sensor and the method are used for monitoring the corrosion characteristics of the metal in a chloride molten salt environment for solar photo-thermal power generation. The corrosion rate and corrosion behavior are monitored in multiple dimensions, data are mutually verified, the reliability of the result is ensured, the temperature control module is cooled through real-time air, it is ensured that the temperature of the probe head is consistent with the actual working condition temperature, and the monitoring accuracy is further improved. In addition, the electrochemical noise signal fluctuation characteristics can help to preliminarily distinguish local corrosion and uniform corrosion behaviors, and deep analysis of the corrosion behaviors is realized. The method can also be widely used for corrosion monitoring and early warning of a photo-thermal power station using various heat storage media except chloride molten salt, and solving the problem of molten salt corrosion has indispensable strategic significance for guaranteeing the equipment stability, reducing the operation cost and improving the international competitiveness.

Description

Technical Field

[0001] The present invention relates to the technical field of material property monitoring, and particularly to a sensor and method for monitoring the corrosion behavior of metals in chloride molten salts. Background Art

[0002] At present, the mainstream solar power generation technologies mainly include solar photovoltaic power generation technology and solar thermal power generation technology. Among them, solar thermal power generation technology is more environmentally friendly than solar photovoltaic power generation technology. The tower-type solar thermal power station is the most widely used design form. A solar thermal power station is a renewable energy technology that uses solar heat collection technology to convert solar energy into heat energy and drives a generator to generate electricity through heat energy. Molten salt is usually used as the heat transfer and storage medium. The corrosion and damage of structural materials by high-temperature molten salt as the heat transfer and storage medium are major technical challenges faced in solar thermal power stations. In the past few decades, researchers have systematically studied the corrosion behavior of various structural materials in molten salts. These studies can be roughly divided into three categories: carbon steel and low-alloy steel, stainless steel, and nickel-based alloys. Chloride molten salt is one of the most important candidate molten salts for concentrating solar power plants. So far, a large number of studies have shown that nickel-based alloys will suffer severe corrosion in chloride molten salts. And considering cost issues, stainless steel with low cost has to be used as the construction material in commercial applications. Therefore, in order to extend the equipment life and improve system reliability, it is crucial to monitor the corrosion of stainless steel in the application of solar thermal power stations.

[0003] Corrosion monitoring and detection technology is an important part in the operation of modern industrial equipment. Through the combination of electrochemistry monitoring, resistance probes, non-destructive testing and sensor technology, real-time monitoring, accurate prediction and efficient detection of corrosion behavior can be achieved, which is an important means to ensure the safe operation of industrial equipment, extend the equipment life and reduce the maintenance cost. With the development of industrial technology, corrosion monitoring has shifted from traditional periodic inspection to real-time online monitoring. Especially in high-temperature, high-pressure, complex chemical environments and new energy fields (such as solar thermal power generation, wind power, nuclear power, etc.), the application of corrosion monitoring is more critical. Molten salt, as a heat transfer and energy storage medium widely used in solar thermal power generation, will corrode metal materials such as pipelines, storage tanks and heat exchange equipment under high-temperature conditions, seriously affecting the safety and service life of the equipment. The difficulties in corrosion monitoring are as follows: First, there are various forms of corrosion, and mechanisms such as high-temperature oxidation, pitting corrosion, stress corrosion, etc. may exist simultaneously, and the corrosion behavior is complex and difficult to separate and analyze. Second, molten salt corrosion occurs at high temperatures, usually above 500 °C, and conventional monitoring equipment is difficult to work stably for a long time, resulting in increased monitoring difficulty. Third, the detection of pitting corrosion and crevice corrosion requires high-precision monitoring means, and traditional methods (such as weight loss method) are difficult to achieve. Generally, electrochemistry methods are the most commonly used technologies in corrosion monitoring. Based on the characteristics of electrochemical reactions during the corrosion process, they can be divided into: linear polarization resistance method (LPR), electrochemical impedance spectroscopy (EIS), potentiostat monitoring and electrochemical noise (EN). Among them, the resistance probe is a commonly used technology for monitoring the corrosion rate based on the resistance change caused by metal corrosion. By measuring the resistance change of the metal probe, it reflects the reduction of the metal cross-sectional area and can quickly obtain the corrosion rate. Summary of the Invention

[0004] To solve the problems existing in the prior art, the main object of the present invention is to propose a sensor and method for monitoring the corrosion behavior of metals in chloride molten salts.

[0005] According to one aspect of the present invention, the present invention provides the following technical solutions:

[0006] A sensor for monitoring the corrosion behavior of metals in chloride molten salts, comprising:

[0007] A probe part, a temperature control part, and a data acquisition and processing part;

[0008] The probe part integrates an electrochemical noise module, a resistance module and a temperature control module.

[0009] As a preferred solution of the sensor for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, wherein: the electrochemical noise module includes a working electrode WE1, a working electrode WE2 and a reference electrode RE, and WE1 and WE2 are made of the same metal.

[0010] As a preferred embodiment of the sensor for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, among which: the resistance module uses a flat coil as the resistance ER.

[0011] As a preferred embodiment of the sensor for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, among which: the temperature control module includes an air inlet pipe, an air outlet hole, a thermocouple TC and a thermocouple cap TC cap.

[0012] As a preferred embodiment of the sensor for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, among which: the probe head is connected to the probe body through a flange. The thermocouple TC and the thermocouple cap TC cap are placed in the middle of the probe head. WE1, WE2 and RE are placed in a triangle around the thermocouple, and the ER flat coil is placed outside; after all the components of the probe head are fixed, the head cavity is cast with alumina ceramic sealing filler, and after solidification, high-temperature curing treatment is carried out.

[0013] As a preferred embodiment of the sensor for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, among which: the temperature control part includes a flow controller and a compressed air buffer chamber. The flow controller can monitor the temperature of the probe head in real time and adjust it in real time according to the actual temperature of the molten salt heat exchange part; the temperature control part must be externally connected to an air compressor to blow cold high-speed air into the blow pipe inside the probe to cool the probe head, so as to provide a sufficient cooling rate and cooperate with the temperature control part to realize the real-time control of the probe temperature to simulate the actual temperature of the molten salt heat exchange part; in addition, ensuring that the temperature of the probe head is consistent with the actual working condition temperature can further improve the accuracy of monitoring.

[0014] As a preferred embodiment of the sensor for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, among which: the insulating ceramic sleeve of the data signal line of the data acquisition and processing part uses a four-hole ceramic tube, and a NiCr alloy wire is passed through each hole to ensure the insulation between the NiCr alloy wires and delay their oxidation. The NiCr alloy wires are respectively connected to the functional modules of the probe head.

[0015] According to another aspect of the present invention, the present invention provides the following technical solution:

[0016] A method for monitoring the corrosion behavior of metals in chloride molten salts, which places the above-mentioned sensor for monitoring the corrosion behavior of metals in chloride molten salts in the chloride molten salt for monitoring, and is realized through the resistance module and the electrochemical noise module. The data of the two are mutually verified to ensure the reliability of the results.

[0017] The noise resistance R is calculated from the noise signal of the electrochemical noise module n , and V is obtained by conversion corr , and then Vcorr Integrate with respect to time to obtain the relationship curve between corrosion depth and time;

[0018] The resistance signal monitored by the resistance module is converted into the cross-section of the metal. Since the width of the metal flat coil used in the resistance module is constant, the resistance signal can be converted into the remaining thickness of the metal flat coil.

[0019] As a preferred solution of the method for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, wherein: the data acquisition and processing part monitors the current signals (i.e., noise current) of WE1 and WE2 in real time, as well as the voltage signals (i.e., noise voltage) between RE and WE1 and WE2. The noise signal is collected once every 1 h, the monitoring window time of the noise signal is 1024 s, and the monitoring frequency is 2 Hz. The noise resistance R per 1 h is calculated by Equation (1) n , and V is obtained through conversion corr ; then integrate V corr with respect to time to obtain the relationship curve between corrosion depth and time. The calculation method of V corr can be expressed by Equation (2):

[0020]

[0021]

[0022] wherein, S E is the standard deviation of the noise voltage; S I is the standard deviation of the noise current; M is the molar mass of the element participating in the corrosion reaction, n is the number of electrons transferred during the corrosion reaction process, R n is the noise resistance, K α is the anodic Tafel slope, K β is the cathodic Tafel slope..

[0023] As a preferred solution of the method for monitoring the corrosion behavior of metals in chloride molten salts according to the present invention, wherein: adopt the linear relationship between the resistance ER and the cross-section, and convert the monitored resistance signal into the cross-section of the flat coil. Since the width of the flat coil used in the resistance module is constant, the resistance signal can be converted into the remaining thickness of the flat coil. The remaining thickness D R should have a negative linear relationship with the resistance ER, and can be expressed by Equation (3):

[0024] D R = aER + b (3)

[0025] wherein, a and b are calibration coefficients, and their values can be calibrated according to the different resistances of flat coils with different thicknesses.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention provides a sensor and method for monitoring the corrosion behavior of metals in chloride molten salts, mainly used for monitoring the corrosion characteristics of metals in high-temperature chloride molten salts for solar thermal power generation. By integrating a resistance probe module, an electrochemical noise module, and a temperature control module, the corrosion behavior is monitored in multiple dimensions, and the data are mutually verified to ensure the reliability of the results. The temperature control module ensures that the temperature of the probe head is consistent with the actual working condition temperature through real-time air cooling, further improving the accuracy of monitoring. In addition, the fluctuation characteristics of the electrochemical noise signal can help to preliminarily distinguish local corrosion and uniform corrosion behaviors, realizing in-depth analysis of the corrosion behavior. It can also be widely used for corrosion monitoring and early warning of solar thermal power plants using various heat storage media other than chloride molten salts. With the rapid development of solar thermal power plant projects and the accumulation of technology, solving the problem of molten salt corrosion is of indispensable strategic significance for ensuring equipment stability, reducing operating costs, and enhancing international competitiveness. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0029] Figure 1 It is a partial cross-sectional view of the probe of the sensor.

[0030] Figure 2 It is Figure 1 The cross-sectional view along A-A in

[0031] Figure 3 It is Figure 1 The cross-sectional view along B-B in

[0032] Figure 4 It is the side view of the probe part of the sensor.

[0033] Figure 5 It is some test results obtained using a reference electrode, including potential stability test, open circuit potential test, and potentiodynamic polarization test.

[0034] Figure 6 It is the test result of the electrochemical noise module.

[0035] Figure 7 It is the monitoring result of the sensor placed in chloride molten salt.

[0036] The realization, functional features, and advantages of the present invention will be further described in conjunction with embodiments and with reference to the accompanying drawings. Specific Embodiments

[0037] The technical solutions in the embodiments will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] The present invention provides a sensor and method for monitoring the corrosion behavior of metals in chloride molten salts, which has the following advantages:

[0039] (1) The present invention integrates a resistance module, an electrochemical noise module, and a temperature control module, monitors the corrosion behavior in multiple dimensions, and the data is mutually verified to ensure the reliability of the results. The temperature control module ensures that the temperature of the probe head is consistent with the actual working condition temperature through real-time air cooling, further improving the monitoring accuracy. At the same time, in the high-temperature chloride molten salt environment, alumina ceramic glue is used to cast all voids, improving the corrosion resistance of the overall structure of the sensor.

[0040] (2) The monitoring method of the present invention is realized through the resistance module and the electrochemical noise module. The noise resistance Rn is calculated from the noise signal of the electrochemical noise module, and Vcorr is obtained through conversion; then Vcorr is integrated with respect to time to obtain the relationship curve between corrosion depth and time. The resistance signal monitored by the resistance probe module is converted into the cross-section of the metal. Since the width of the metal flat coil used in the resistance module is constant, the resistance signal can be converted into the remaining thickness of the metal flat coil.

[0041] The present invention provides a sensor for monitoring the corrosion behavior of metals in chloride molten salts, including:

[0042] A probe part, a temperature control part, and a data acquisition and processing part;

[0043] The probe part integrates an electrochemical noise module, a resistance module, and a temperature control module.

[0044] Preferably, the electrochemical noise module includes a working electrode WE1, a working electrode WE2, and a reference electrode RE. WE1 and WE2 are made of the same metal, and RE uses a Pt reference electrode.

[0045] Preferably, the resistance module uses a metal flat coil as the resistance ER, with a thickness of 1 mm, and both sides of the flat coil are polished to 1000# sandpaper.

[0046] Preferably, the temperature control module includes an air inlet pipe, an air outlet hole, a thermocouple TC, and a thermocouple cap TC cap.

[0047] Preferably, Figures 1-4 As shown in the figure, the probe head is connected to the probe body through a flange, a thermocouple TC and a thermocouple cap TC cap are placed in the middle of the probe head, WE1, WE2 and RE are placed in a triangle around the thermocouple, and an ER flat coil is placed on the outside; after all the parts of the probe head are fixed, an alumina ceramic sealing filler is used to cast the head cavity, and a high-temperature curing treatment is performed after solidification; all signals are marked accordingly to facilitate connection with data acquisition and processors and temperature controllers; the probe part adopts a round tube structure, the diameter and length of which meet the requirements of on-site installation, and the inner sleeve is an insulating ceramic sleeve of the air blowing pipe and the data signal line.

[0048] Preferably, the temperature control part includes a flow controller and a compressed air buffer chamber. The flow controller can monitor the temperature of the probe head in real time and make real-time adjustments according to the actual temperature of the molten salt heat exchange part. The temperature control part must be connected to an external air compressor to blow cold high-speed air into the air pipe inside the probe to cool the probe head, so as to provide sufficient cooling speed, and cooperate with the temperature control part to realize real-time control of the probe temperature to simulate the actual temperature of the molten salt heat exchange part. In addition, ensuring that the temperature of the probe head is consistent with the actual operating temperature can further improve the accuracy of monitoring.

[0049] Preferably, the data signal line insulating ceramic sleeve of the data acquisition and processing part adopts a four-hole ceramic tube, and a NiCr alloy wire is passed through each hole to ensure the insulation between the NiCr alloy wires and delay their oxidation. The NiCr alloy wires are respectively connected to the probe head functional module. The data acquisition and processing part can collect the temperature signal, electrochemical noise signal and resistance signal of the probe head in real time, and convert them into the relationship curve of corrosion rate and corrosion depth over time. Combined with the wireless signal transmitting device, remote display and monitoring can be realized.

[0050] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0051] Example

[0052] In order to verify the potential stability of the reference electrode RE, the present invention provides a reference electrode stability test of the sensor, using 347 stainless steel as the experimental working electrode to perform open circuit potential and potentiodynamic polarization tests, so as to obtain the Tafel anode and cathode slopes and calculate the corrosion rate, such as Figure 5 As shown, Figure 5 (a) and (b) are the reference electrode potential stability tests. Figure 5 (a) It can be seen that the short-term test potential fluctuation of the reference electrode is within 6mV; Figure 5As can be seen from (b), the potential fluctuation of the reference electrode during long-term testing is within 5 mV, and the potential fluctuations of the two tests are both less than 10 mV, indicating that the potential stability of the reference electrode is acceptable. (c) shows the open-circuit potential test of stainless steel using the reference electrode. It can be seen that the open-circuit potential of this stainless steel is between 440 and 470 mV in a specific environment. (d) shows the potentiodynamic polarization test of stainless steel using the reference electrode. It can be seen that the corrosion potential of this stainless steel is 0.39 V and the corrosion current density is 2.51×10 -6 A·cm -2 .

[0053] Provide the short-term noise potential signal and noise current signal obtained by the electrochemical noise module test. The test time is 80 h and the test temperature is 800 °C. As Figure 6 shown, Figure 6 in which (a) is the noise potential and (b) is the noise current. The occurrence of corrosion events can be inferred based on the noise resistance and the time nodes of the pulse peaks.

[0054] Place the sensor in the actual KNM chloride molten salt heat exchanger of a CSP power plant for continuous monitoring for 90 days to verify the effectiveness and stability of the in-situ monitoring probe for chloride molten salt corrosion under actual working conditions. The fluctuation range of the actual chloride molten salt temperature is about 700 - 800 °C. The results are as Figure 7 shown. It can be analyzed that around the tenth day, serious corrosion began to occur, and there were a large number of pulse peaks in the noise current; around the fiftieth day, the corrosion situation tended to be stable.

[0055] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent structural transformations made using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A sensor for monitoring the corrosion behavior of metals in chloride molten salts, characterized in that: include: Probe part, temperature control part, data acquisition and processing part; The probe part integrates the electrochemical noise module, resistance module and temperature control module.

2. The sensor for monitoring the corrosion behavior of metals in chloride molten salts according to claim 1, characterized in that: The electrochemical noise module includes a working electrode WE1, a working electrode WE2 and a reference electrode RE, and WE1 and WE2 are made of the same metal.

3. The sensor for monitoring the corrosion behavior of metals in chloride molten salts according to claim 2, characterized in that: The resistance module uses a flat coil as the resistor ER.

4. The sensor for monitoring the corrosion behavior of metals in chloride molten salts according to claim 3, characterized in that: The temperature control module includes an air inlet pipe, an air outlet, a thermocouple TC and a thermocouple cap TC cap.

5. The sensor for monitoring the corrosion behavior of metal in chloride molten salt according to claim 4, characterized in that: The probe head is connected to the probe body through a flange. A thermocouple TC and a thermocouple cap TC cap are placed in the middle of the probe head. WE1, WE2 and RE are placed in a triangle around the thermocouple, and an ER flat coil is placed on the outside. After all parts of the probe head are fixed, an alumina ceramic sealing filler is used to cast the head cavity, and high-temperature curing treatment is performed after solidification.

6. The sensor for monitoring the corrosion behavior of metals in chloride molten salts according to claim 1, characterized in that: The temperature control part includes a flow controller and a compressed air buffer chamber. The flow controller monitors the temperature of the probe head in real time and makes real-time adjustments according to the actual temperature of the molten salt heat exchange part. The temperature control part is connected to an external air compressor to blow cold high-speed air into the air blowing pipe inside the probe to cool the probe head, and cooperates with the temperature control part to realize real-time control of the probe temperature to simulate the actual temperature of the molten salt heat exchange part. In addition, the temperature of the probe head is ensured to be consistent with the actual working temperature.

7. The sensor for monitoring the corrosion behavior of metals in chloride molten salts according to claim 1, characterized in that: A NiCr alloy wire is passed through each hole of the insulating ceramic sleeve of the data signal line of the data acquisition and processing part, and the NiCr alloy wires are respectively connected to the functional modules of the probe head.

8. A method for monitoring the corrosion behavior of metals in chloride molten salts, characterized in that: The sensor for monitoring the corrosion behavior of metal in chloride molten salt according to any one of claims 1 to 7 is placed in chloride molten salt for monitoring, which is achieved through a resistance module and an electrochemical noise module, and the data of the two are mutually verified to ensure the reliability of the results.

9. The method for monitoring the corrosion behavior of metal in chloride molten salt according to claim 8, characterized in that: The data acquisition and processing part monitors the current signals of WE1 and WE2 and the voltage signals between RE and WE1 and WE2 in real time; the noise resistance R per 1h is calculated by formula (1): n , converted to V corr ; Then V corr Integrate the time to obtain the relationship curve between corrosion depth and time; V corr The calculation method can be expressed by formula (2): Among them, S E is the standard deviation of the noise voltage; S I is the standard deviation of the noise current; M is the molar mass of the element involved in the corrosion reaction, n is the number of electrons transferred during the corrosion reaction, and R n is the noise resistance, K α is the anode Tafel slope, K β is the cathode Tafel slope.

10. The method for monitoring the corrosion behavior of metal in chloride molten salt according to claim 8, characterized in that: The linear relationship between resistance ER and cross section is used to convert the monitored resistance signal into the cross section of the flat coil. Since the width of the flat coil used in the resistance module is constant, the resistance signal can be converted into the remaining thickness of the flat coil. The remaining thickness D R It should have a negative linear relationship with the resistance ER, which can be expressed by formula (3): D R =aER+b (3) Among them, a and b are calibration coefficients, and their values ​​can be calibrated according to the different resistances of flat coils of different thicknesses.

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