A microfluidic device and method for liquid ammonia corrosion testing

Abstract

The application provides a trace liquid adding device and method for liquid ammonia corrosion test, the trace liquid adding device for liquid ammonia corrosion test comprises a liquid container and a test kettle, the liquid container is used for containing a liquid medium and is connected with the test kettle through a capillary tube, a weighing sensor is arranged at the lower part of the liquid container and is used for measuring the mass change of the liquid medium in real time, a capillary tube plug is arranged at one end of the capillary tube close to the liquid container, the capillary tube plug is located in the liquid medium, and the flow rate of the liquid medium entering the test kettle is controlled by adjusting the relative position of the capillary tube plug and the capillary tube nozzle. The liquid medium is transported by virtue of the capillary vacuum siphon effect, the adding amount of the liquid medium is accurately measured by using the weighing sensor, and the measurement precision is higher than that of a traditional flow meter; meanwhile, the flow rate is adjusted by using a magnetic control coil, and the stable and accurate addition of trace liquid under the working condition of liquid ammonia is realized.

Description

Technical Field

[0001] This invention relates to the field of material corrosion performance testing technology, and more specifically, to a micro-liquid addition device and method for liquid ammonia corrosion testing. Background Technology

[0002] As the global energy system accelerates its transition to zero-carbon and clean energy, ammonia, with its excellent energy storage and transportation characteristics, has become a highly promising zero-carbon energy carrier and hydrogen storage medium, leading to a period of rapid development in related industries. With the large-scale application of ammonia energy, the demand for liquid ammonia storage and transportation continues to rise. As core storage and transportation equipment, the operational safety of liquid ammonia storage tanks directly determines the stable operation of the ammonia energy industry chain and is closely related to the safety of personnel and property. Multiple studies have confirmed that air contamination in liquid ammonia storage and transportation systems is one of the important causes of failure and damage to storage tanks and other equipment. Under the application requirements of LNG / ammonia dual-fuel ship transportation, the International Maritime Organization has explicitly required the testing of the stress corrosion resistance of low-temperature high-manganese austenitic steel in liquid ammonia storage and transportation environments, and has proposed six typical test environments, among which the addition of 0.1% water and 2.5 ppm oxygen to liquid ammonia is a key test environment. Simulating this test environment in the laboratory requires not only the safe and precise introduction of liquid ammonia and oxygen into the test vessel to construct a basic environment consistent with actual storage and transportation, but also the high-precision addition of trace amounts of liquid water. The concentration control level of the aforementioned trace impurities directly determines the realism and effectiveness of the simulated environment, and the precision of their addition will significantly affect the reliability and accuracy of the research results on the material corrosion failure mechanism. However, existing laboratories have significant shortcomings in the precise addition of trace liquid impurities.

[0003] Patent application number 202411023585.9 discloses a liquid ammonia corrosion testing system suitable for complex environments. It injects impurities under pressure using a liquid booster pump; however, the booster pump has low flow control accuracy, easily leading to overshoot and unstable flow rate when adding minute amounts, making it difficult to meet the milligram-level precision requirements. Furthermore, using the booster pump introduces additional pressure into the test vessel, interfering with the pressure balance of the simulated liquid ammonia environment. Patent application number 201820509138.8 discloses a vacuum feeding system for a reaction vessel, replacing traditional manual feeding with vacuum feeding. This allows the entire feeding process to be completed without opening the reaction vessel, and the amount of material added is accurately calculated using an electromagnetic flowmeter. However, high-precision electromagnetic flowmeters are expensive, resulting in extremely high equipment costs.

[0004] Therefore, there is an urgent need for a device and method that can accurately add trace amounts of liquid impurities to a liquid ammonia corrosion test vessel. Summary of the Invention

[0005] In view of this, the present invention aims to provide a micro-liquid addition device and method for liquid ammonia corrosion testing, so as to solve the problem in the prior art that it is difficult to accurately add micro-liquid impurities to the liquid ammonia corrosion test vessel.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] This invention provides a micro-liquid addition device for liquid ammonia corrosion testing, comprising a liquid container and a test vessel. The liquid container is used to contain a liquid medium and is connected to the test vessel via a capillary tube. A weighing sensor is installed at the bottom of the liquid container to measure the mass change of the liquid medium in real time. A capillary plug is installed at one end of the capillary tube near the liquid container. The capillary plug is located inside the liquid medium. The flow rate of the liquid medium entering the test vessel is controlled by adjusting the relative position of the capillary plug and the capillary tube opening.

[0008] This invention features a weighing sensor installed at the bottom of the liquid container, which can monitor the mass change of the liquid medium in real time and achieve accurate measurement of the amount of trace liquid added. At the same time, by adjusting the relative position of the capillary plug and the capillary tube opening, the flow rate of the liquid medium entering the test vessel can be directly controlled, avoiding the measurement error caused by uncontrolled flow rate in traditional addition methods.

[0009] In this invention, the liquid container is preferably a transparent open container with graduations, specifically a beaker with 50mL or 100mL specifications.

[0010] The invention also includes a magnetic control coil and a control system. The magnetic control coil is disposed on the side of the capillary tube near the liquid container. The control system is electrically connected to the magnetic control coil and is used to adjust the magnetic force of the magnetic control coil, thereby adjusting the insertion position of the capillary plug at the capillary tube opening.

[0011] This invention adjusts the insertion depth of the capillary plug within the capillary by controlling the magnetic force of the magnetic control coil. Compared to manual or mechanical adjustment, it offers faster response, higher adjustment precision, and remote automated control, avoiding the safety risks associated with manual operation and contact with toxic media such as liquid ammonia. Simultaneously, the magnetic drive method reduces mechanical wear, improves the stability and lifespan of the device, and ensures consistent adjustment of the flow rate of trace liquids.

[0012] In this invention, the magnetic control coil is preferably sleeved on the outer wall of the capillary tube, and the axial distance between the capillary tube plug and the magnetic control coil is ≤4cm, specifically 3cm or 4cm, to ensure that the magnetic field does not attenuate on the capillary tube plug and to avoid the problem of insufficient magnetic driving force and inaccurate displacement adjustment due to excessive distance.

[0013] In this invention, the capillary plug has magnetic response characteristics and can achieve precise axial displacement under the magnetic field of the magnetic control coil; the relative permeability of the capillary plug is preferably ≥100, and there are no dissolved or detached substances in pure water medium.

[0014] This setup ensures that the capillary plug is precisely driven by the magnetic control coil without hysteresis or delay, guaranteeing the accuracy of flow rate regulation. On the other hand, it completely eliminates the risk of media contamination, preventing the contamination of the test medium by leaching or shedding from the plug, which could lead to distorted corrosion test results.

[0015] In this invention, the capillary plug is preferably made of one or more of magnetically modified polyetheretherketone and 430 stainless steel.

[0016] In this invention, the capillary plug is nail-shaped and includes a cap-shaped sealing part. The sealing part has an annular groove on the side facing the capillary opening, and the annular groove abuts against the capillary opening.

[0017] The invention features an annular groove that forms a tight seal with the capillary tube opening, effectively preventing air leakage during vacuuming and ensuring stable vacuum levels in the test vessel and pipeline, thus avoiding air contamination that could interfere with the test medium. The positioning function of the annular groove limits the radial displacement of the capillary plug, ensuring the accuracy of subsequent flow rate adjustments. It also improves the stability of the fit between the plug and the capillary tube, reducing the risk of seal failure due to vibration or other factors during testing.

[0018] In this invention, the capillary plug further includes a tapered insertion part fixedly connected to the sealing mating part. The tapered insertion part extends into the inside of the capillary tube opening, and the size of the flow gap between the capillary plug and the inner wall of the capillary is adjusted by changing its insertion depth.

[0019] The formula for volumetric flow rate in a capillary tube is as follows:

[0020]

[0021] In the formula, Q is the volumetric flow rate, ∆P is the pressure difference across the capillary, r is the effective flow radius of the capillary, η is the liquid viscosity, and L is the capillary length. Under the current conditions, ∆P is constant at one atmosphere, and η and L are also constant. During the descent of the plug, the flow radius r gradually increases, and Q increases significantly; conversely, during the ascent of the plug, the flow radius r gradually decreases, and Q decreases significantly. By adjusting the position of the plug, the rate of liquid inflow can be adjusted, thereby achieving precise control of the added liquid quality.

[0022] In this invention, the inner diameter of the capillary is preferably 0.5 mm to 1.0 mm, the axial length of the capillary plug is 10 mm to 15 mm, and it includes a tapered insertion part and a sealing mating part. The axial length ratio of the tapered insertion part to the sealing mating part is 3 to 8: 1 to 2. The tapered insertion part is a tapered variable diameter structure with a taper of 1: 8 to 1: 16, more preferably 1: 10 to 1: 12.

[0023] This invention employs a tapered variable-diameter structure with a taper of 1:8 to 1:16 and an axial length of 10mm to 15mm. This allows the annular flow gap formed between the plug and the inner wall of the capillary to change linearly when the plug undergoes slight axial displacement, thereby achieving continuous and precise adjustment of the liquid flow rate and effectively improving the accuracy of adding trace amounts of liquid. By setting the axial length ratio of the tapered insertion part to the sealing mating part to 3 to 8: 1 to 2, the sealing reliability of the device and the flow rate adjustment stroke can be considered simultaneously. This ensures the sealing effect during the vacuum pumping and discharging stage while accurately controlling the flow rate, ultimately achieving stable and precise addition of trace amounts of liquid.

[0024] In this invention, the axial length of the capillary plug 3 is preferably 12 mm, the axial length ratio of the tapered insertion part to the sealing part is 5:1, and the taper of the tapered insertion part is preferably 1:10 or 1:12.

[0025] The invention also includes a solenoid valve and a control system. The solenoid valve is located on the side of the capillary tube away from the liquid container. The control system is electrically connected to the solenoid valve and the weighing sensor, respectively, and is used to control the solenoid valve to open or close the liquid medium transport path between the capillary tube and the test vessel according to the mass measurement signal of the weighing sensor.

[0026] This invention electrically connects the solenoid valve, the weighing sensor, and the control system, and can automatically control the opening and closing of the liquid delivery path based on the real-time mass signal from the weighing sensor, avoiding excessive or insufficient addition caused by manual judgment of when to close.

[0027] In this invention, a three-way pipe A and a liquid ammonia inlet pipe are also included. One end of the three-way pipe A extends into the test vessel, and the other two ends are respectively connected to the capillary tube and the liquid ammonia inlet pipe.

[0028] This setup effectively reduces the number of interfaces, lowers the risk of leakage, and ensures that liquid ammonia delivery and trace liquid addition do not interfere with each other, maintaining their respective delivery stability and accuracy.

[0029] The invention also includes a vacuum pump, a vacuum pipe, and a control system. The vacuum pump is connected to the test vessel through the vacuum pipe, and the control system is electrically connected to the vacuum pump to control the start and stop of the vacuum pump and the duration of vacuuming, thereby adjusting the vacuum level inside the test vessel and the capillary tube.

[0030] This invention provides a stable negative pressure condition for transporting trace amounts of liquid using the vacuum siphon effect by adding a vacuum pump to the device. The vacuum pump can completely evacuate the pipeline, completely expelling internal air and preventing air from mixing into the liquid ammonia medium and interfering with the accuracy of impurity proportions. This ensures the consistency between the simulated experimental environment and the actual liquid ammonia storage and transportation environment, thereby significantly improving the reliability of the experimental results.

[0031] In this invention, a three-way pipe B and an exhaust pipe are also included. One end of the three-way pipe B extends into the test vessel, and the other two ends are connected to the extraction pipe and the exhaust pipe, respectively.

[0032] The present invention features an exhaust pipe that allows for the rapid release of the medium inside the test vessel after the test, facilitating the opening of the vessel, removal of the sample, and cleaning of the equipment, thus improving the convenience of the test operation. At the same time, the use of a three-way pipe B for flow diversion avoids mutual interference between vacuuming and depressurization operations.

[0033] This invention also provides a liquid ammonia corrosion test method, including a trace liquid addition step, implemented using the trace liquid addition device for liquid ammonia corrosion testing described above, specifically including the following steps:

[0034] (1) By controlling the magnetic control coil through the control system, the capillary plug is inserted into the capillary tube opening to seal the liquid medium flow channel;

[0035] (2) Open the solenoid valve, start the vacuum pump, and evacuate the test vessel, capillary tube, three-way tube A and liquid ammonia inlet pipeline. When the pressure drops to the set value, turn off the vacuum pump and close the solenoid valve.

[0036] (3) Inject the liquid medium to be added into the liquid container, ensuring that the end of the capillary tube that extends into the liquid container is submerged in the liquid medium;

[0037] (4) By controlling the magnetic force of the magnetic control coil through the control system, the insertion depth of the capillary plug is adjusted so that the liquid medium fills the capillary under atmospheric pressure.

[0038] (5) Zero the weighing value of the weighing sensor and set the target mass of the liquid medium to be added through the control system;

[0039] (6) Open the solenoid valve, and at the same time adjust the magnetic control coil according to the real-time mass measurement signal of the weighing sensor to adjust the size of the flow gap and control the flow rate of the liquid medium.

[0040] (7) When the mass change detected by the weighing sensor reaches the target mass, the control system controls the solenoid valve to close and adjusts the magnetic control coil to seal the capillary tube opening with the capillary plug, thus completing the addition of a small amount of liquid.

[0041] In this invention, the amount of the trace liquid added is 0.01g to 20g.

[0042] In this invention, the average absolute error during the addition of trace amounts of liquid is ≤2mg, and the relative standard deviation (RSD) is ≤0.4%.

[0043] Compared with existing technologies, the micro-liquid addition device and method for liquid ammonia corrosion testing described in this invention have the following advantages:

[0044] (1) The present invention adds a capillary tube between the liquid container and the test vessel as a dedicated transport channel for micro-liquids. It relies on the vacuum siphon effect to drive the liquid medium to be accurately transported to the test vessel along the capillary tube. The structure is simple and highly reliable, which fundamentally avoids the problems of medium leakage and accuracy drift caused by sealing failure and component wear in traditional devices.

[0045] (2) The present invention sets a weighing sensor at the bottom of the liquid container to capture the mass change data of the liquid medium in real time. Compared with traditional volume measurement, flow measurement and other methods, weighing measurement directly reflects the actual added mass of liquid, avoids the measurement deviation caused by the change in medium volume due to temperature change, and has higher measurement accuracy. In addition, the control system can realize the quantitative addition of trace liquid through the data transmitted in real time by the weighing sensor.

[0046] (3) In this invention, the capillary plug is configured as a nail shape, including a cap-shaped sealing part and a conical insertion part. The sealing part has an annular groove that abuts against the capillary tube opening. The conical insertion part extends into the inside of the capillary. By changing its insertion depth, the size of the annular flow gap between the plug and the inner wall of the capillary is adjusted, thereby precisely controlling the liquid delivery flow rate. In addition, this invention sets a magnetic control coil on the capillary. The capillary plug is made of a material with magnetic response characteristics. By controlling the magnetic force of the magnetic control coil through the control system, non-contact axial precise displacement of the plug insertion depth is achieved. Attached Figure Description

[0047] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0048] Figure 1 This is a schematic diagram of the micro-liquid addition device for liquid ammonia corrosion testing according to the present invention;

[0049] Figure 2 This is a cross-sectional view of the capillary plug inserted into the capillary tube according to the present invention.

[0050] Explanation of reference numerals in the attached figures:

[0051] 1. Control system; 2. Weighing sensor; 3. Capillary plug; 4. Liquid container; 5. Magnetically controlled coil; 6. Capillary tube; 7. Solenoid valve; 8. Liquid ammonia inlet pipe; 9. T-connector A; 10. Reactor lid; 11. Test reactor; 12. Exhaust pipe; 13. T-connector B; 14. Vacuum pipe; 15. Vacuum pump; 16. Annular groove. Detailed Implementation

[0052] The present invention will be further described below with reference to specific embodiments. First, it should be noted that the data in the following experimental examples were obtained by the inventors through numerous experiments. Due to space limitations, only a portion of these data is shown in the specification, and those skilled in the art can understand and implement the present invention based on this data. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various modifications or alterations to the invention, and these modifications or alterations also fall within the scope of protection of this application.

[0053] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0054] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0055] Due to the unique physicochemical properties of liquid ammonia, including its low temperature (boiling point at atmospheric pressure -33.5℃), easy vaporization, and high toxicity, traditional manual addition methods not only pose extremely high safety risks but also cannot achieve closed-loop operation, making them completely unsuitable for adding trace amounts of liquid ammonia. Furthermore, to control experimental risks, laboratory liquid ammonia corrosion test vessels are generally small in volume (typically 3-5L). For example, in a 20L test vessel filled with 15L of liquid ammonia (approximately 9kg), the required water addition is only 9g (approximately 9mL), falling within the category of trace addition. Using conventional flow meters to add trace amounts of liquid presents two major drawbacks: First, it requires high-precision flow meters with extremely small flow rates, resulting in high equipment procurement costs and complex piping connections. Due to the large size of the flow meters, they are often located far from the liquid ammonia test vessel, which may cause liquid residue to remain in the pipe between the flow meter and the test vessel, leading to significant deviations in the addition quality. Second, to prevent air from entering and causing deviations in the test composition, the pipeline at the front end of the flow meter must be pre-filled with the liquid to be added or kept in a vacuum state, requiring complex degassing and sealed liquid storage structures, further increasing system cost and operational difficulty.

[0056] like Figure 1As shown, this embodiment provides a micro-liquid addition device for liquid ammonia corrosion testing, including a liquid container 4 and a test vessel 11. The liquid container 4 is used to contain the liquid medium and is connected to the test vessel 11 through a capillary tube 6. A weighing sensor 2 is installed at the lower part of the liquid container 4 to measure the mass change of the liquid medium in real time. A capillary plug 3 is installed at one end of the capillary tube 6 near the liquid container 4. The capillary plug 3 is located inside the liquid medium. The flow rate of the liquid medium entering the test vessel 11 is controlled by adjusting the relative position of the capillary plug 3 and the opening of the capillary tube 6.

[0057] In a preferred embodiment, the system further includes a three-way pipe A9 and a liquid ammonia inlet pipe 8. One end of the three-way pipe A9 extends into the test vessel 11, and the other two ends are connected to the capillary tube 6 and the liquid ammonia inlet pipe 8, respectively.

[0058] It should be noted that the liquid ammonia inlet pipeline 8 is a dedicated passage for liquid ammonia transportation, allowing the liquid medium transported by the capillary 6 to enter the test vessel 11 along with the liquid ammonia, thereby achieving uniform mixing of liquid ammonia and trace liquid impurities within the vessel.

[0059] In a preferred embodiment, the system further includes a magnetic control coil 5, a solenoid valve 7, and a control system 1. The magnetic control coil 5 is disposed on the side of the capillary tube 6 near the liquid container 4, and the solenoid valve 7 is disposed on the side of the three-way pipe A9 near the capillary tube 6. The control system 1 is electrically connected to the magnetic control coil 5, the solenoid valve 7, and the weighing sensor 2, respectively.

[0060] It should be noted that the magnetic control coil 5 can adjust its own magnetic force to change the insertion depth of the capillary plug 3 in the capillary tube 6, thereby precisely controlling the flow rate of the liquid medium; the solenoid valve 7 can quickly open and close and seal the liquid medium delivery path between the capillary tube 6 and the liquid ammonia test vessel 11; the control system 1 is electrically connected to the magnetic control coil 5, the solenoid valve 7, and the weighing sensor 2 respectively and realizes centralized control. According to the real-time feedback of the liquid medium mass change from the weighing sensor 2, the control system automatically controls the opening and closing of the solenoid valve 7 and the magnetic force of the magnetic control coil 5 to ensure that the liquid medium is accurately added into the test vessel 11 according to the preset mass.

[0061] In a preferred embodiment, the system further includes a vacuum pump 15, a suction pipe 14, a three-way pipe B13, and an exhaust pipe 12. One end of the three-way pipe B13 extends into the test vessel 11, and the other two ends are connected to the suction pipe 14 and the exhaust pipe 12, respectively. The other end of the suction pipe 14 is connected to the vacuum pump 15. The control system 1 is electrically connected to the vacuum pump 15 and is used to control the start and stop of the vacuum pump 15 and the duration of vacuuming, thereby adjusting the vacuum level inside the test vessel 11 and the capillary tube 6.

[0062] It should be noted that the vacuum pump 15, the extraction pipe 14, the three-way pipe B13, and the exhaust pipe 12 together constitute the vacuum pumping and depressurization passage of the device. The specific working method is as follows: the vacuum pump 15 is started and stopped and the vacuuming time is adjusted by the control system 1. The vacuum pump 15 simultaneously evacuates the inside of the test vessel 11 and the capillary tube 6 connected to it through the extraction pipe 14 and the three-way pipe B13, and the pressure in the test vessel 11 and the capillary tube 6 is precisely adjusted to the vacuum degree required for the test. This provides the necessary negative pressure conditions for the subsequent precise addition of trace liquids by utilizing the vacuum siphon effect. On the other hand, it can completely remove the air in the test vessel 11 and related pipes, avoid air mixing into the liquid ammonia test medium and interfering with the impurity ratio, and ensure the authenticity of the test environment. At the same time, the exhaust pipe 12 can depressurize the test vessel 11 after the test, which facilitates the subsequent opening of the vessel and cleaning of the equipment.

[0063] In a preferred embodiment, the test vessel 11 includes a lid 10 with an opening, and one end of each of the three-way pipes A9 and B13 extends into the test vessel 11 through the opening on the lid 10.

[0064] In a preferred embodiment, the capillary plug 3 is nail-shaped, including a cap-shaped sealing part and a tapered insertion part fixedly connected to the sealing part. The sealing part has an annular groove 16 on the side facing the capillary 6 opening, and the annular groove 16 abuts against the capillary 6 opening. The tapered insertion part extends into the capillary 6 opening, and the flow gap between the capillary plug 3 and the inner wall of the capillary 6 is adjusted by changing its insertion depth.

[0065] It should be noted that the tapered insertion part extends into the inside of the capillary tube 6, and the insertion depth of the tapered insertion part in the capillary tube 6 is changed by the magnetic control coil 5, thereby realizing the control of the flow rate of the liquid medium in the liquid container 4.

[0066] In this embodiment, the annular groove 16 abuts against the opening of the capillary tube 6. On the one hand, it can achieve a tight fit between the capillary plug 3 and the opening of the capillary tube 6. During the vacuum pump 15 evacuates the test vessel 11 and pipeline, it can effectively prevent air leakage, ensure the stability of the vacuum in the pipeline, and completely isolate the ingress of external air to prevent impurities from interfering with the test medium ratio. On the other hand, it can form a positioning fit, limit the radial offset between the capillary plug 3 and the opening of the capillary tube 6, and ensure that the tapered insertion part is always adjusted along the axial direction of the capillary tube 6 to adjust the insertion depth.

[0067] It should be explained that the shape design of the capillary plug 3 is a key structural factor for achieving precise addition of trace liquids. The shape of each part directly affects the sealing effect, the linearity of the liquid inlet speed adjustment, and the stability of the liquid flow, thus determining the addition accuracy.

[0068] Example 1

[0069] The micro-liquid addition device for liquid ammonia corrosion testing described above:

[0070] Using the test environment specified by the International Maritime Organization (IMO) of liquid ammonia + 0.1% water + 2.5ppm oxygen as the experimental background, 12.00 kg of liquid ammonia was selected as the base, and 12.0000 g of high-purity water was added. The experimental temperature was -33.5 ± 1℃, and the pressure inside the reactor was ≤ 1 Pa.

[0071] The minimum scale division of the weighing sensor 2 is 0.1 mg, and the measuring range is 200 g.

[0072] The inner diameter of capillary 6 is 0.8 mm, and the outer diameter is 3 mm;

[0073] The capillary plug 3 is made of magnetically modified polyetheretherketone with a relative magnetic permeability ≥100. The axial length of the capillary plug 3 is 12mm, including a tapered insertion part and a sealing part. The axial length ratio of the tapered insertion part to the sealing part is 5:1. The sealing part is cylindrical, and the tapered insertion part is a tapered variable diameter structure with a surface roughness Ra≤0.8μm.

[0074] The magnetron coil 5 is coaxially sleeved on the outer wall of the capillary tube 6, wherein the axial distance between the capillary tube plug 3 and the magnetron coil 5 is 3cm.

[0075] The taper of the capillary plug 3 tapered insertion part was set to 1:8, 1:10, 1:12, 1:14, and 1:16 respectively. Five sets of parallel tests were conducted for each taper range, and the addition accuracy, flow stability, and repeated addition error were recorded.

[0076] A liquid ammonia corrosion test method includes a trace liquid addition step, implemented using the trace liquid addition device for liquid ammonia corrosion testing described in the above technical solution, specifically including the following steps:

[0077] Step (1): Adjust the position of the capillary plug 3 in the capillary 6 through the control system 1 so that it fits tightly against the opening of the capillary 6;

[0078] Step (2): Vacuum the sealed test vessel 11 through the control system 1. During the vacuuming process, open the solenoid valve 7 at the front end of the capillary tube 6. When the pressure inside the test vessel 11 is below 1 Pa, turn off the vacuum pump 15.

[0079] Step (3): Close solenoid valve 7 through control system 1;

[0080] Step (4): Pour high-purity water into liquid container 4, place liquid container 4 on weighing sensor 2, adjust the position so that capillary tube 6 is inserted into high-purity water;

[0081] Step (5): Adjust the displacement of the capillary plug 3 in the capillary tube 6 by the control system 1. High-purity water enters and gradually fills the capillary tube 6 under atmospheric pressure until it reaches the solenoid valve 7.

[0082] Step (6): On the control system 1, the mass displayed by the weighing sensor 2 is zeroed, and the target added liquid mass is set to 12.0000g; the solenoid valve 7 is opened through the control system 1, so that the high-purity water enters the test vessel 11 through the solenoid valve 7 and the three-way pipe A9 in sequence, and the mass displayed by the weighing sensor 2 slowly decreases; initially, the position of the capillary plug 3 in the capillary tube 6 is lowered, such as making the liquid inlet speed about 10g / min, and later the position of the capillary plug 3 in the capillary tube 6 is raised, such as making the liquid inlet speed decrease to 2g / min; when the added liquid mass reaches 12.0000g, the solenoid valve 7 is closed, and the liquid medium addition is completed.

[0083] The actual added mass was collected and recorded in real time by the weighing sensor 2. The target added amount for each group was 12.0000g. Five parallel tests were conducted for each taper. The average added amount, absolute error and relative standard deviation (RSD) of each group were measured. The results are shown in Table 1 below.

[0084] Table 1. Accuracy and stability of adding trace amounts of liquid using capillary plugs with different tapers.

[0085] taper Average addition amount / g Mean absolute error / mg Relative Standard Deviation (RSD) / % Stability evaluation 1：8 12.0005 3.72 0.40 Difference 1：10 12.0000 0.12 0.03 excellent 1：12 12.0000 0.10 0.02 excellent 1：14 12.0002 0.42 0.10 good 1：16 11.9998 1.26 0.15 middle

[0086] As shown in Table 1, the taper directly affects the accuracy and stability of adding trace amounts of liquid. When the taper is too large (e.g., 1:8), the mean absolute error and relative standard deviation (RSD) are significantly higher, indicating poor stability. When the taper is too small (e.g., 1:16), both the error and RSD increase, resulting in only moderate stability. Only when the taper is between 1:10 and 1:12 are both the mean absolute error and RSD at relatively low levels, indicating good or excellent stability. This indicates that an excessively large taper will cause a rapid change in the flow gap when the capillary plug 3 undergoes a slight displacement, easily leading to sudden changes in flow rate, overshoot, and over-addition. An excessively small taper results in insufficient adjustment sensitivity, making it difficult to achieve precise micro-volume adjustment. This invention limits the taper to 1:10 to 1:12, which allows the flow gap to change smoothly, linearly, and controllably during slight axial displacement of the plug, ensuring continuous and precise flow adjustment and significantly improving the accuracy and repeatability of adding trace amounts of liquid.

[0087] Comparative Example 1

[0088] This comparative example is basically the same as the micro-liquid addition device for liquid ammonia corrosion test described in the above technical solution. The only difference is that the capillary plug 3, capillary 6, and magnetic control coil 5 in the example are replaced with a commercially available ultra-low flow high-precision flow meter (flow accuracy ±0.5%FS). The quantitative addition of trace amounts of water to the liquid ammonia corrosion test vessel is achieved through this flow meter. The composition of the remaining devices (control system, weighing sensor, liquid reagent container, solenoid valve, liquid ammonia inlet pipeline, three-way pipe, liquid ammonia test vessel, vacuum pump, etc.) remains the same.

[0089] Steps (1) to (5) are the same as in Example 1; Step (6): The flow rate and flow velocity are controlled by the flow meter. The actual added mass is collected and recorded in real time by the high-precision weighing sensor (2). The target added amount for each group is 12.0000g. A total of 5 parallel tests were conducted in Comparative Example 1. The average added amount, absolute error and relative standard deviation (RSD) of each group were measured respectively. The results are shown in Table 2 below.

[0090] Table 2. Accuracy and stability of adding trace amounts of liquid using a flow meter

[0091] Average addition amount / g Mean absolute error / mg Relative Standard Deviation (RSD) / % Comparative Example 1 12.05 50 0.42

[0092] As can be seen from Table 2, using a flow meter for adding trace amounts of liquid not only results in a large error, which can easily lead to deviations in the subsequent corrosion test results, but also in the high cost of high-precision flow meters, with the cost of a single unit typically reaching tens of thousands of yuan. Furthermore, during long-term use, the measurement accuracy will continue to decline and the stability will gradually decrease due to factors such as media erosion, component wear, scaling and contamination, and aging of electronic components. It is difficult to maintain the initial high-precision index for a long time, thereby increasing the operating cost and maintenance difficulty of the test system.

[0093] Trace amounts of water are a core control parameter affecting material corrosion in the liquid ammonia-oxygen corrosion system. Their content directly influences the characteristics of the corrosive medium and the corrosion rate of the sample. Under the standard requirement of 0.1%, any deviation in water content will distort corrosion test results and lead to inaccurate judgments about the material's corrosion mechanism—too high a water content will overestimate the corrosion rate, while too low a content will mask the actual corrosion failure characteristics of the material. Furthermore, test errors caused by insufficient water addition precision can also be transmitted to engineering applications. At best, this will significantly increase equipment manufacturing costs due to over-selection of materials; at worst, it will pose safety hazards to the operation of liquid ammonia storage tanks due to incorrect material selection. This invention, through precise control of the trace water addition process, significantly reduces addition errors and relative standard deviations, ensuring the stability and reliability of the corrosion test medium composition from the source, thereby significantly improving the accuracy, repeatability, and engineering guidance value of the test results.

[0094] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A micro-liquid addition device for liquid ammonia corrosion testing, comprising a liquid container (4) and a test vessel (11), characterized in that, The liquid container (4) is used to contain the liquid medium and is connected to the test vessel (11) through the capillary tube (6). A weighing sensor (2) is provided at the bottom of the liquid container (4) to measure the mass change of the liquid medium in real time. A capillary plug (3) is provided at one end of the capillary tube (6) near the liquid container (4). The capillary plug (3) is located inside the liquid medium. The flow rate of the liquid medium entering the test vessel (11) is controlled by adjusting the relative position of the capillary plug (3) and the opening of the capillary tube (6).

2. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 1, characterized in that, It also includes a magnetic control coil (5) and a control system (1). The magnetic control coil (5) is located on the side of the capillary tube (6) near the liquid container (4). The control system (1) is electrically connected to the magnetic control coil (5) and is used to adjust the magnetic force of the magnetic control coil (5) and thereby adjust the insertion position of the capillary plug (3) at the opening of the capillary tube (6).

3. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 1, characterized in that, The capillary plug (3) is nail-shaped and includes a cap-shaped sealing part. An annular groove (16) is provided on the side of the sealing part facing the capillary (6) opening. The annular groove (16) abuts against the capillary (6) opening.

4. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 3, characterized in that, The capillary plug (3) also includes a tapered insertion part that is fixedly connected to the sealing mating part. The tapered insertion part extends into the inside of the capillary (6) opening. By changing its insertion depth, the size of the flow gap between the capillary plug (3) and the inner wall of the capillary (6) can be adjusted.

5. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 1, characterized in that, It also includes a solenoid valve (7) and a control system (1). The solenoid valve (7) is located on the side of the capillary tube (6) away from the liquid container (4). The control system (1) is electrically connected to the solenoid valve (7) and the weighing sensor (2) respectively, and is used to control the solenoid valve (7) to open or close the liquid medium transport passage between the capillary tube (6) and the test vessel (11) according to the mass measurement signal of the weighing sensor (2).

6. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 1, characterized in that, It also includes a three-way pipe A (9) and a liquid ammonia inlet pipe (8). One end of the three-way pipe A (9) extends into the test vessel (11), and the other two ends are connected to the capillary tube (6) and the liquid ammonia inlet pipe (8), respectively.

7. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 1, characterized in that, It also includes a vacuum pump (15), a suction pipe (14) and a control system (1). The vacuum pump (15) is connected to the test vessel (11) through the suction pipe (14). The control system (1) is electrically connected to the vacuum pump (15) and is used to control the start and stop of the vacuum pump (15) and the duration of vacuuming, thereby adjusting the vacuum level inside the test vessel (11) and the capillary tube (6).

8. The micro-liquid addition device for liquid ammonia corrosion testing according to claim 7, characterized in that, It also includes a three-way pipe B (13) and an exhaust pipe (12). One end of the three-way pipe B (13) extends into the test vessel (11), and the other two ends are connected to the extraction pipe (14) and the exhaust pipe (12) respectively.

9. A method for adding trace amounts of liquid for a liquid ammonia corrosion testing, characterized in that, The micro-liquid addition device for liquid ammonia corrosion testing as described in any one of claims 1 to 8 is used, specifically including the following steps: (1) By controlling the magnetic control coil (5) through the control system (1), the capillary plug (3) is inserted into the capillary (6) opening to seal the liquid medium flow channel; (2) Open the solenoid valve (7), start the vacuum pump (15), and evacuate the test vessel (11), capillary tube (6), three-way pipe A (9) and liquid ammonia inlet pipe (8). When the pressure drops to the set value, turn off the vacuum pump (15) and close the solenoid valve (7). (3) Inject the liquid medium to be added into the liquid container (4), ensuring that the end of the capillary tube (6) that extends into the liquid container (4) is immersed in the liquid medium; (4) By controlling the magnetic force of the magnetic control coil (5) through the control system (1), the insertion depth of the capillary plug (3) is adjusted so that the liquid medium fills the capillary (6) under atmospheric pressure. (5) Zero the measurement value of the weighing sensor (2) and set the target mass of the liquid medium to be added through the control system (1); (6) Open the solenoid valve (7), and at the same time adjust the magnetic control coil (5) according to the real-time mass measurement signal of the weighing sensor (2) to adjust the size of the flow gap and control the flow rate of the liquid medium. (7) When the mass change detected by the weighing sensor (2) reaches the target mass, the control system (1) controls the solenoid valve (7) to close and adjusts the magnetic control coil (5) to make the capillary plug (3) seal the capillary (6) opening, thus completing the addition of a small amount of liquid.

10. The method for adding trace amounts of liquid for a liquid ammonia corrosion testing according to claim 9, characterized in that, The amount of the trace liquid added is 0.01g to 20g.

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