Method for controlling organic dissolved substances of polyurea anticorrosive coating on inner wall of desalted water tank

Abstract

The invention discloses a control method for organic dissolved substances of a polyurea anti-corrosion coating on the inner wall of a desalting water tank, and belongs to the technical field of dissolved substance control of anti-corrosion coatings. The method comprises the following steps: determining a relation model between the organic matter dissolution amount and the soaking time in the soaking process of a polyurea anticorrosive coating test piece in demineralized water; solving the reciprocal of the soaking time of the model to obtain a relation model of the organic matter dissolution rate and the soaking time; controlling the content of organic matters which are easy to dissolve out in the test piece according to the total dissolving-out amount of the organic matters obtained by soaking the polyurea anticorrosive coating test piece in the demineralized water for the first time for 4 days; the influence degree of dissolution of the organic matters in the test piece on the water quality is controlled through the average dissolution rate of the organic matters after the polyurea anticorrosive coating test piece is primarily soaked in the demineralized water for 4-7 days. According to the invention, the control index of the organic dissolved substance of the polyurea anticorrosive coating on the inner wall of the desalted water tank is provided, and the dissolved substance can be effectively controlled.

Description

Technical Field

[0001] This invention relates to a method for controlling organic leachates from a polyurea anti-corrosion coating on the inner wall of a demineralized water tank, belonging to the technical field of leachate control for anti-corrosion coatings. Background Technology

[0002] The application of polyurea in the corrosion protection of demineralized water tank interiors in nuclear power plants and thermal power plants is becoming increasingly widespread. The leaching of this high-molecular-weight organic coating in the demineralized water medium directly impacts the quality of the water supplied to the tanks. Currently, several power plants have experienced persistently high levels of conductivity and total organic carbon (TOC) in their demineralized water tanks (exceeding standards for more than six months) after polyurea corrosion protection was completed and put into operation. This has severely affected the normal operation of the demineralized water tank interiors during the generator unit's normal production phase, resulting in significant economic losses. The main reason for these problems is the leaching of the anti-corrosion coating after prolonged immersion in demineralized water.

[0003] The leaching of the anti-corrosion coating on the inner wall of the demineralized water tank in power plants is an important technical indicator that must be considered in addition to the conventional performance of the coating, such as anti-corrosion, waterproofing, and anti-aging. Literature such as "Experimental Study and Application of Leaching Characteristics of Anti-corrosion Coating on the Inner Wall of Power Plant Demineralized Water Tank" (Xing Chengxia, Li Yongli, et al., Coating Industry, 2016, 46(1):63-68.) and "Detection of Leachate from Polyurea Anti-corrosion Coating in Demineralized Water Tank and Its Impact on Water Quality" (Xing Chengxia, Chen Weiwei, Hu Yuanxiang, et al., Electroplating & Finishing, 2022, 41(18):1333-1337.) have studied the leaching characteristics, leaching detection, and impact on water quality of the anti-corrosion coating on the inner wall of the demineralized water tank.

[0004] In the aforementioned prior art, a method for detecting the dissolution rate of polyurea anti-corrosion coatings in demineralized water, using total organic carbon (TOC) as a characteristic indicator, was established. Polyurea anti-corrosion coating samples from several representative manufacturers were selected, and the TOC dissolution patterns of the samples from each manufacturer in demineralized water were investigated. The dissolution rates were measured and compared. Based on the TOC control values ​​for the demineralized water supply from power plant tanks, the impact of TOC dissolution from polyurea anti-corrosion coatings from various manufacturers on the water quality of the tank supply was analyzed. The results showed that all polyurea anti-corrosion coatings exhibited a certain degree of organic matter dissolution in demineralized water, mainly occurring during the rapid growth period of the initial dissolution stage (1-2 weeks). When the dissolution rate exceeded 10 μg / (cm³), the dissolution rate increased significantly. 2 At point d), the water quality in the tank is significantly affected. After this period, the TOC leaching rate decreases significantly, falling below 2.0 μg / (cm³). 2 ·d) has little impact on the water quality of the water tank.

[0005] However, the aforementioned existing technologies have too long a cycle for measuring the organic leaching rate of the anti-corrosion coating on the inner wall of the demineralized water tank, lacking operability and practicality. Furthermore, the existing technologies do not provide separate measurement indicators, methods, and control requirements for both the level of organic leaching from the coating and its impact on water quality. Summary of the Invention

[0006] To address at least one of the aforementioned technical problems, the present invention aims to provide a method for controlling organic leaching from the polyurea anti-corrosion coating on the inner wall of a demineralized water tank. The present invention proposes control indicators for the organic leaching from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank, enabling effective control of the leaching.

[0007] To achieve the above objectives, the present invention provides a method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of a demineralized water tank, comprising the following steps:

[0008] (1) The model for determining the relationship between the amount of organic matter leaching from polyurea anticorrosive coating test pieces and the immersion time in demineralized water is shown in Equation I below:

[0009] Formula I

[0010] Where Q is the amount of organic matter dissolved, in μg / cm³. 2 t represents the soaking time in days; k and b are both coefficients, k > 0, and b is the intercept.

[0011] (2) Taking the reciprocal of the soaking time from Equation I, we obtain the relationship model between the organic matter dissolution rate and the soaking time, as shown in Equation II below:

[0012] Formula II

[0013] Where v is the organic matter dissolution rate, in μg / (cm²) 2 ·d); t is the soaking time in days; k is a coefficient, k > 0;

[0014] (3) According to Formula I, the amount of easily soluble organic matter in the polyurea anticorrosive coating test piece is controlled by the total amount of organic matter dissolved (initial dissolution amount) after the polyurea anticorrosive coating test piece is initially soaked in demineralized water for 4 days; according to Formula II, the degree of influence of organic matter dissolution on water quality in the polyurea anticorrosive coating test piece is controlled by the average dissolution rate of organic matter after the polyurea anticorrosive coating test piece is initially soaked in demineralized water for 4 to 7 days.

[0015] According to a specific embodiment of the present invention, preferably, the preparation steps of the polyurea anti-corrosion coating test piece include: spraying polyurea anti-corrosion coating onto the surface of a template to form a coating; curing the coating for 12 to 24 hours after its formation, then demolding it without using a release agent to obtain the demolded coating; and curing the demolded coating for more than 7 days to obtain the polyurea anti-corrosion coating test piece.

[0016] According to a specific embodiment of the present invention, preferably, the demineralized water is ultrapure water with a resistivity of 18.2~18.3 MΩ and a TOC content of <50 μg / L.

[0017] According to a specific embodiment of the present invention, preferably, the ratio of the surface area of ​​the polyurea anti-corrosion coating test piece to the volume of the demineralized water is (0.1~0.3) cm². -1 .

[0018] According to a specific embodiment of the present invention, preferably, the temperature during the immersion process of the polyurea anti-corrosion coating test piece in demineralized water is 20~30℃.

[0019] According to a specific embodiment of the present invention, preferably, in step (1), the amount of organic matter leached in Formula I is obtained by the TOC content of the immersion solution of the polyurea anticorrosive coating test piece.

[0020] According to a specific embodiment of the present invention, preferably, in step (3), the total amount of organic matter leached from the polyurea anticorrosive coating sample after initial immersion in demineralized water for 4 days is 200 mg / m³. 2 The following conditions indicate that the content of easily soluble organic matter in the polyurea anti-corrosion coating test piece is low.

[0021] According to a specific embodiment of the present invention, preferably, in step (3), the average dissolution rate of organic matter in the polyurea anticorrosive coating sample after initial immersion in demineralized water for 4-7 days is 10 mg / (m³). 2 When ·d), the leaching of organic matter from the polyurea anti-corrosion coating test piece has a small impact on water quality.

[0022] The present invention has at least the following beneficial effects:

[0023] This invention proposes control indicators for organic leaching from the polyurea anti-corrosion coating on the inner wall of a demineralized water tank, along with methods for determining and setting control values ​​for these indicators. This enables effective control of the leached substances. By utilizing the relationship models between the amount of organic matter leaching and soaking time, and the relationship model between the rate of organic matter leaching and soaking time proposed in this invention, and based on the determination of the amount and rate of organic matter leaching from the polyurea anti-corrosion coating on the inner wall of a power plant demineralized water tank, an accurate evaluation of the level of organic matter leaching from the coating and its impact on the water quality of the tank can be achieved. Attached Figure Description

[0024] Figure 1 The curve shows the change in the initial dissolution amount of the coated sample with immersion time.

[0025] Figure 2 The curves show the dissolution rate of two power plant coating samples as a function of immersion time.

[0026] Figure 3 The curves show the dissolution rate of three special-purpose coating samples as a function of immersion time.

[0027] Figure 4 The curves show the leaching amount of the B1 coated specimen after immersion in water for four times, as a function of immersion time.

[0028] Figure 5 The curves show the dissolution rate of the B1 coated specimen after immersion in water for four times, as a function of immersion time.

[0029] Figure 6 The curve shows the dissolution rate of the S3 sample as a function of temperature.

[0030] Figure 7 The curve shows the dissolution rate of the S5 sample as a function of temperature.

[0031] Figure 8 The curve shows the dissolution rate of the B3 sample as a function of temperature.

[0032] Figure 9 The curve shows the dissolution rate of the B1 sample as a function of temperature. Detailed Implementation

[0033] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0034] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0037] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0038] According to a specific embodiment of the present invention, the present invention provides a method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of a demineralized water tank, which includes the following steps:

[0039] (1) The model for determining the relationship between the amount of organic matter leaching from polyurea anticorrosive coating test pieces and the immersion time in demineralized water is shown in Equation I below:

[0040] Formula I

[0041] Where Q is the amount of organic matter dissolved, in μg / cm³. 2 ; t is the soaking time in days; k and b are both coefficients, k > 0, b is the intercept; k is mainly affected by the total amount of soluble matter in the coating, that is, the greater the content of easily soluble substances added to the coating raw material, the larger k is, and the longer the period of influence on the water quality of the demineralized water tank.

[0042] (2) Taking the reciprocal of the soaking time from Equation I, we obtain the relationship model between the organic matter dissolution rate and the soaking time, as shown in Equation II below:

[0043] Formula II

[0044] Where v is the organic matter dissolution rate, in μg / (cm²) 2 ·d); t is the soaking time in days; k is a coefficient, k > 0;

[0045] (3) According to Formula I, the amount of easily soluble organic matter in the polyurea anticorrosive coating test piece is controlled by the total amount of organic matter dissolved (initial dissolution amount) after the polyurea anticorrosive coating test piece is initially soaked in demineralized water for 4 days; according to Formula II, the degree of influence of organic matter dissolution on water quality in the polyurea anticorrosive coating test piece is controlled by the average dissolution rate of organic matter after the polyurea anticorrosive coating test piece is initially soaked in demineralized water for 4 to 7 days.

[0046] In some embodiments, the preparation steps of the polyurea anti-corrosion coating test piece include: spraying polyurea anti-corrosion coating onto the surface of a template to form a coating; curing the coating for 12 to 24 hours after its formation, then demolding it without using a release agent to obtain the demolded coating; and curing the demolded coating for more than 7 days to obtain the polyurea anti-corrosion coating test piece.

[0047] In some embodiments, the demineralized water is ultrapure water with a resistivity of 18.2~18.3 MΩ and a TOC content of <50 μg / L.

[0048] In some embodiments, the surface area ratio (i.e., surface-to-volume ratio) of the polyurea anti-corrosion coating sample to the volume of the demineralized water is (0.1~0.3) cm². -1 Based on this surface-to-volume ratio, the number, size, and volume of demineralized water of the test pieces can be adjusted, as long as the surface-to-volume ratio range is met. Furthermore, if multiple test pieces are used, the surface area of ​​each test piece is equal to the total surface area of ​​all test pieces.

[0049] In some embodiments, the temperature during the immersion process of the polyurea anti-corrosion coating test piece in demineralized water is 20~30°C.

[0050] In some embodiments, in step (1), the amount of organic matter leached in Formula I is determined by the TOC content of the immersion solution of the polyurea anti-corrosion coating test piece.

[0051] In some embodiments, in step (3), the total amount of organic matter leached from the polyurea anti-corrosion coating sample after initial immersion in demineralized water for 4 days is 200 mg / m³. 2 The following conditions indicate that the content of easily soluble organic matter in the polyurea anti-corrosion coating test piece is low.

[0052] In some embodiments, in step (3), the average organic matter dissolution rate of the polyurea anticorrosive coating test piece after initial immersion in demineralized water for 4-7 days is 10 mg / (m³). 2 When ·d), the leaching of organic matter from the polyurea anti-corrosion coating test piece has a small impact on water quality.

[0053] The technical solutions of the present invention are specifically illustrated below through embodiments, but the present invention is not limited to these embodiments. Of course, various modifications can be made within the scope of the key points of the present invention.

[0054] 1. Determination of control indicators for organic leaching substances in the anti-corrosion coating of the inner wall of the demineralized water tank.

[0055] (1) Overview of test methods

[0056] A coated sample with a certain surface area was immersed in a certain volume of pure water (resistivity 18.2 MΩ, TOC < 50 μg / L) and left to stand at room temperature (25 ± 2 ℃). Samples were taken at specific immersion intervals to determine the total organic carbon (TOC) content in the immersion solution. The testing interval was adjusted appropriately based on the TOC content and its trend in the immersion solution (i.e., demineralized water). The total immersion time was 1 to 3 months.

[0057] This experiment is divided into an initial dissolution stage and a deep dissolution stage. The initial dissolution stage involves immersing the sample from the start until TOC dissolution equilibrium is reached, examining the basic changes in dissolution. The deep dissolution stage involves immersing the sample, which has reached dissolution equilibrium, again in pure water to examine the deep dissolution characteristics. The deep dissolution experiment can be conducted 1 to 3 times depending on the dissolution results.

[0058] (2) Instruments and equipment

[0059] Total organic carbon analyzer: Sievers T900, GE, USA.

[0060] (3) Test pieces and soaking solution

[0061] This experiment selected three representative polyurea anti-corrosion coating samples (numbered S3, S5, and B3) for the inner walls of demineralized water tanks and two typical case samples (numbered B1 and C1) for the inner walls of demineralized water tanks used in power plants as test samples. Considering factors such as the surface volume ratio of the anti-corrosion coating on the inner walls of power plant demineralized water tanks, the amount of immersion water, the detection range of the testing method, and operability, the test pieces were 10 mm wide, and the length varied from 60 to 100 mm depending on the specifications of the samples. After the test pieces were made, surface contaminants were removed, and the pieces were repeatedly rinsed to ensure they were thoroughly cleaned, then dried and weighed.

[0062] The water used for soaking the test pieces was ultrapure water that had undergone secondary demineralization and further purification using a laboratory high-purity water system, with a resistivity of 18.2 MΩ. The soaking container was a chromatographic grade sampling bottle made of PE plastic, which was repeatedly washed and soaked to ensure that the sampling bottle was clean and free of contamination.

[0063] (4) Determination of the amount of organic matter leached from the coating

[0064] Calculate the organic matter leaching amount of each sample of the polyurea anti-corrosion coating specimen using the following formula (III):

[0065] Formula III

[0066] in:

[0067] i: Number of sampling measurements taken when the TOC of the immersion solution for the polyurea anti-corrosion coating specimen reaches equilibrium;

[0068] Q i : The amount of organic matter dissolved when the coating dissolution reaches equilibrium, expressed in μg / cm³. 2 ;

[0069] C1, C2, ..., C i-1 C i : TOC content of the soaking solution for each sample test, in mg / L;

[0070] V t : This refers to the sample volume taken for each test, in mL;

[0071] V p : This represents the total volume of demineralized water, in mL;

[0072] S: Surface area of ​​the polyurea anti-corrosion coating sample, in cm². 2 ;

[0073] Plot the total organic carbon leaching of the coated specimen as a function of soaking time (days) on the x-axis and the amount of TOC leached from the soaking solution on the y-axis.

[0074] The initial dissolution test results of the 5 coated samples are as follows: Figure 1 As shown. From Figure 1 It can be seen that there are significant differences in the initial leaching amount of organic matter among the different types of coating samples. The leaching amounts of samples B1 and C1 are significantly higher than those of the other three samples. Looking at the trend of leaching amount with soaking time, the increase in leaching amount gradually slows down after a certain soaking time.

[0075] The amount of organic matter leached from polyurea anticorrosive coating specimens during immersion in demineralized water showed a good logarithmic relationship with the immersion time. The relationship model is shown in Equation I below:

[0076] Formula I

[0077] Where Q is the amount of organic matter dissolved, in μg / cm³. 2 t represents the soaking time in days; k and b are coefficients. The coefficient k is mainly affected by the total amount of soluble matter in the coating. That is, the higher the content of easily soluble substances added to the coating raw materials, the larger k is, and the longer the period of influence on the water quality of the demineralized water tank.

[0078] The relationship between the organic matter leaching amount Q and immersion time for the coated specimens numbered B1, C1, S3, S5, and B3 is shown in the following formula:

[0079] Test piece B1: f(Q) = 107.31lnt + 22.721

[0080] C1 test piece: f(Q) = 38.214lnt + 10.748

[0081] Test piece B3: f(Q) = 3.373lnt + 20.201

[0082] S5 test piece: f(Q) = 7.8618lnt + 0.8796

[0083] S3 test piece: f(Q) = 4.4886lnt - 1.214

[0084] Taking the reciprocal of the soaking time from Equation I yields the relationship model between the organic matter dissolution rate and the soaking time, as shown in Equation II below:

[0085] Formula II

[0086] Where v is the organic matter dissolution rate, in μg / (cm²) 2 ·d); t is the soaking time in days; k is a coefficient;

[0087] The relationship between the organic matter leaching rate v and immersion time for the coated specimens numbered B1, C1, S3, S5, and B3 is shown in the following formula:

[0088] Test piece B1: f(v) = 107.31 / t

[0089] C1 test piece: f(Q) = 38.214 / t

[0090] Test piece B3: f(Q) = 3.373 / t

[0091] S5 test piece: f(Q) = 7.8618 / t

[0092] S3 test piece: f(Q) = 4.4886 / t

[0093] The relationship curve between the dissolution rate of organic matter in the sample and the soaking time is shown in the figure. Figure 2 and Figure 3 As shown.

[0094] It can be seen that the dissolution rate of the test piece decreases and tends to reach equilibrium as the soaking time increases. When the soaking time of the test piece reaches 4 days, the dissolution rate gradually tends to reach equilibrium, and the time to reach dissolution equilibrium is 7 to 10 days.

[0095] After initial dissolution reaches equilibrium, the water is changed, and the deep dissolution test begins. Taking the B1 sample, which showed the highest initial dissolution, as an example, the relationship between deep dissolution and soaking time is as follows: Figure 4 and Figure 5 As shown.

[0096] from Figure 4 , Figure 5 It can be seen that after the initial 4-7 days of immersion, the easily soluble substances in the coated test pieces dissolve rapidly. After changing the water and entering the second, third, and third deep leaching immersion tests, the amount and rate of dissolution are significantly reduced, and the time to reach leaching equilibrium is shorter than the initial leaching equilibrium time. The easily soluble organic matter in the test pieces is slowly released and dissolved at a lower leaching rate.

[0097] By comparing the dissolution levels of different test pieces, the greater the initial dissolution amount after 4 days of soaking, the higher the dissolution rate when reaching dissolution equilibrium, and the longer it takes to reach a lower dissolution rate through slow release dissolution, resulting in a more lasting effect.

[0098] Based on the above experimental study on the leaching characteristics of organic matter in the coated test pieces, the total amount of organic matter leached out of the coated test pieces after the first 4-day immersion (initial leaching amount) can be used to control the content of easily soluble organic matter in the test pieces, and the average leaching rate after the first 4-7 days of immersion can be used to control the degree of impact of organic matter leaching from the test pieces on water quality.

[0099] 2. Methods for determining the initial leaching amount and leaching rate of organic matter in the coating.

[0100] Sample preparation:

[0101] (1) Preparation of coating sample

[0102] According to the raw material component ratios required by the paint manufacturer and the ratios of various auxiliary materials to be added to the raw materials for on-site spraying of the water tank, a special spraying equipment was used to spray the raw material sample onto an HDPE board (high-density polyethylene, 60cm×100cm) under specified spraying process parameters and environmental conditions. The coating was applied evenly in one coat, and the coating thickness should meet the design requirements of the inner wall coating of the water tank. The coating was cured at (23±2)℃ for 12 hours, then demolded and cured for another 7 days. After curing, a 30cm×30cm section of the coating was cut as a sample. The material conveying pipes of the spraying equipment and the PE board must be cleaned beforehand. During spraying, no release agent should be applied to the PE board to minimize possible contamination of the coating during the spraying process.

[0103] (2) Preparation of test pieces

[0104] Cut two 80mm × 20mm test pieces from the coating sample, ensuring the cut surfaces are smooth and burr-free. Accurately measure the length and width of the test pieces, and measure the thickness using calipers. Gently wipe the surface of the test pieces with slightly damp cotton wool to remove any adhering substances, then allow them to dry and weigh them.

[0105] Selection of test conditions:

[0106] (1) Effect of soaking solution temperature on dissolution

[0107] This experiment investigated the effect of immersion solution temperature within the range of room temperature (23℃±2℃) to 80℃ on the dissolution of organic matter from the test specimens. The experimental results are shown in […]. Figure 6 , Figure 7 , Figure 8 and Figure 9 .

[0108] from Figures 6 to 9It can be seen that as the temperature of the soaking solution increases, the amount of organic matter dissolved from the sample increases significantly compared to room temperature. However, the trend of the dissolution rate is consistent with that at room temperature, and the dissolution equilibrium point does not advance with increasing temperature. That is, as the temperature increases, the total amount of dissolved substances increases, but the trend of the dissolution rate does not change significantly, and it does not have the effect of accelerating dissolution.

[0109] It is necessary to control the immersion solution temperature for the coating dissolution test. Considering that the water temperature in the demineralized water tank is usually between 20℃ and 30℃, this test selects room temperature of 23℃±2℃. If the room temperature is low, a constant temperature water bath or constant temperature chamber can be used for temperature control.

[0110] (2) Selection of soaking time

[0111] Based on the relationship between the amount and rate of organic matter leaching from the coating and the soaking time, the total soaking time for the coating test pieces was 7 days. Among them, the amount of organic matter leaching measured after 4 days of soaking was the initial leaching amount of the test piece, which was used to evaluate the total amount of easily leached organic matter in the coating. The average leaching rate from the 4th to the 7th day of soaking was used to evaluate the degree of impact of coating leaching on water quality.

[0112] (3) Selection of test piece size

[0113] The size of the test piece determines its surface area, which must be compatible with the volume of the immersion solution. The ratio of the test piece surface area to the volume of the immersion solution (i.e., the surface-to-volume ratio) must consider both the actual surface-to-volume ratio of the water tank and the quantitative accuracy range of the TOC determination method used. If we consider the surface-to-volume ratio of a 3600t demineralized water tank (0.3m³),... -1 When the immersion solution volume is 250 mL, the surface area of ​​the sample is only 0.75 cm². 2 Less than 1.0cm 2 If the sample area is too small, the dissolution rate will be too low, the sample will lack representativeness, and it will not be conducive to the accurate determination of TOC.

[0114] Therefore, by measuring the organic leachate from various types of coated test pieces, the surface volume ratio of the test pieces was found to be between 0.1 and 0.3 cm³. -1 The range is sufficient for accurate determination of TOC dissolution concentration in the test specimens within the range of (0~50) mg / L. The test specimens used in this experiment were 80mm × 20mm in size, with a thickness between 0.1 and 0.3mm according to the water tank design values. The immersion liquid volume was 250mL, and the surface volume ratio was (0.15±0.03)cm³. -1 (See Table 1 below).

[0115] (4) Selection of soaking liquid volume

[0116] The volume of the immersion solution should be appropriate for the surface area of ​​the test piece; 250 mL was chosen for this experiment. Considering the need for temperature control via a constant-temperature water bath in winter when room temperature is low, a 250 mL stoppered conical flask is suitable. Furthermore, the 80 mm × 20 mm test piece can be completely submerged in the 250 mL immersion solution and lean against the inner wall of the flask, preventing the less dense test piece from floating on the surface.

[0117] Operating instructions:

[0118] (1) Preparation of soaking solution for test pieces: At room temperature (25±1)℃, add 250mL of soaking water to each of two conical flasks and determine the blank value C0 (mg / L), which should be less than 50μg / L. Then add the amount of soaking water consumed in the test to the flasks so that the volume of soaking water in the flasks is 250mL. Place one test piece in each flask, cover and start the standing time. During the standing process, maintain the temperature at room temperature (25±1)℃, and shake the flasks moderately 1~2 times a day.

[0119] (2) When the solution has been left to stand for 96 hours, shake the bottle gently until the solution is uniform, accurately transfer an appropriate volume (V, mL) of the soaking solution, measure the TOC value, then add V mL of soaking water to the bottle, cover the bottle and continue to stand.

[0120] (3) When the solution has been left to stand for 168 hours, shake the bottle gently until the solution is uniform, take an appropriate amount of the soaking solution and measure the TOC value.

[0121] Note: If the TOC measurement value exceeds the linear measurement range of the instrument, the oxidant can be appropriately diluted or the dosage of the instrument added can be increased before measurement.

[0122] Result processing:

[0123] Calculate the initial dissolution amount Q of the sample according to Formula IV:

[0124] Formula IV

[0125] In Equation IV:

[0126] Q — Initial dissolution rate of the sample, mg / m³ 2 ;

[0127] C1 – TOC value measured after 96 hours of standing, mg / L;

[0128] S — Surface area of ​​the test piece, cm² 2 ;

[0129] 250 — Volume of the immersion solution for the test piece, in mL.

[0130] 10 — Unit conversion factor.

[0131] Calculate the average initial dissolution amount of the two samples.

[0132] Calculate the organic leaching rate v of the sample according to formula V:

[0133] Formula V

[0134] In formula V:

[0135] v — the rate of organic leaching from the sample, mg / (m 2 ·d);

[0136] C1 – TOC value measured after 96 hours of standing, mg / L;

[0137] C2 – TOC value measured after 168 hours of standing, mg / L;

[0138] S — Surface area of ​​the test piece, cm² 2 ;

[0139] 3 — Soaking time: 3 days;

[0140] V — The volume of soaking solution measured when C1 is determined, in mL;

[0141] 250 — Volume of the immersion solution for the test piece, mL;

[0142] 10 — Unit conversion factor.

[0143] Calculate the average dissolution rate of the two samples.

[0144] Allowable difference:

[0145] The key factor affecting the accuracy of the two indicators is the TOC value of the test solution. The TOC of the test solution should be measured at least three times, and the relative standard deviation of the effective measured value should be less than 1.0%.

[0146] 3. Actual sample determination

[0147] To further verify the feasibility and reliability of the test method, the organic matter leaching amount and leaching rate of three special polyurea anti-corrosion coating samples for the inner wall of demineralized water tanks (numbered S3, S5 and B3) and two polyurea coating samples for the inner wall of power plant demineralized water tanks (numbered B5 and B1) were measured. The results are shown in Table 1.

[0148] Table 1. Results of the first immersion leaching rate determination of polyurea-coated test pieces on the inner wall of the demineralized water tank.

[0149]

[0150] As shown in Table 1, the results of the first 10-day immersion test of the test pieces indicate that the easily soluble substances in the test pieces mainly dissolve within 4 days after immersion, with the TOC concentration of the immersion solution ranging from 1.22 to 12.00 mg / L. Test piece B1 showed the highest dissolution concentration, while test piece B5 showed the lowest. The TOC concentration increased slightly on the 7th and 10th days of immersion. Regarding the dissolution rate, the average dissolution rate from the 7th to the 10th day decreased compared to the average dissolution rate from the 4th to the 7th day, as the immersion time increased.

[0151] As shown in Table 1, the higher the initial dissolution amount, the higher the dissolution rate. Sample B5, with its polyurea coating on the inner wall of the demineralized water tank, exhibited the lowest initial dissolution amount and dissolution rate, at 84 mg / m³. 2 and 5.5 mg / (m 2 •d). An investigation revealed that the plant's water tanks were flushed for three days before being put into normal operation, and no abnormal water quality issues occurred. The initial leaching amount and leaching rate of the polyurea coating sample on the inner wall of the demineralized water tank, numbered B1, were the highest, at 704 mg / m³. 2 and 146.4 mg / (m 2 ·d) After the water tank of the plant was put into operation, the TOC content of the effluent often exceeded the standard for as long as 2 years.

[0152] To further verify the rationality of the soaking time selection, after the first (10-day) soaking of the test pieces in Table 1, a second (7-day) soaking was performed with changed water. The test results are shown in Table 2.

[0153] Table 2. Results of the second immersion dissolution rate determination of polyurea-coated test pieces on the inner wall of the demineralized water tank.

[0154]

[0155] As shown in Table 2, after the second soaking with fresh water, the TOC concentration of the soaking solution decreased significantly, and the dissolution rate and amount also decreased accordingly. Samples with high dissolution amounts and rates during the first soaking maintained high dissolution amounts and rates during the second soaking. Therefore, the soaking time selected for this experiment was 7 days, and the average dissolution rate from day 4 to day 7 can be used to evaluate the organic matter dissolution level of the sample.

[0156] 4. Control value for organic matter leaching from coating

[0157] Based on the current leaching levels of the special polyurea coating on the inner wall of demineralized water tanks and actual engineering applications, the total organic matter leaching of the polyurea anti-corrosion coating sample after the initial 4-day immersion in demineralized water, as determined by this method, was 200 mg / m³. 2The following conditions indicate that the content of easily soluble organic matter in the polyurea anticorrosive coating test piece is low; the average organic matter dissolution rate of the polyurea anticorrosive coating test piece after initial immersion in demineralized water for 4-7 days, as determined by this method, is 10 mg / (m²). 2 In case ·d), the leaching of organic matter from the polyurea anti-corrosion coating test piece has a small impact on water quality; in both cases, the impact of organic matter leaching from the coating on the organic matter content of the water tank supply is within a controllable range.

[0158] As can be seen from the above embodiments, the present invention proposes control indicators for organic leaching from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank, as well as methods for determining and controlling the control indicators. Through the relationship models between the amount of organic leaching and soaking time and the relationship models between the rate of organic leaching and soaking time proposed in the present invention, based on the determination of the amount and rate of organic leaching from the polyurea anti-corrosion coating on the inner wall of the power plant demineralized water tank, the level of organic leaching from the coating and its impact on the water quality of the tank can be accurately evaluated.

[0159] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling organic leachates from a polyurea anti-corrosion coating on the inner wall of a demineralized water tank, comprising the following steps: (1) The model for determining the relationship between the amount of organic matter leaching from polyurea anticorrosive coating test pieces and the immersion time in demineralized water is shown in Equation I below: Equation I Where Q is the amount of organic matter dissolved, in μg / cm³. 2 t represents the soaking time in days; k and b are both coefficients, k > 0, and b is the intercept. (2) Taking the reciprocal of the soaking time from Equation I, we obtain the relationship model between the organic matter dissolution rate and the soaking time, as shown in Equation II below: Formula II Where v is the organic matter dissolution rate, in μg / (cm²) 2 ·d); t is the soaking time in days; k is a coefficient, k > 0; (3) According to Formula I, the content of easily soluble organic matter in the polyurea anticorrosive coating test piece is controlled by the total amount of organic matter leached out by the polyurea anticorrosive coating test piece after initial immersion in demineralized water for 4 days; according to Formula II, the degree of influence of organic matter leaching in the polyurea anticorrosive coating test piece on water quality is controlled by the average dissolution rate of organic matter in the polyurea anticorrosive coating test piece after initial immersion in demineralized water for 4 to 7 days.

2. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, The preparation steps of the polyurea anti-corrosion coating test piece include: spraying polyurea anti-corrosion coating onto the surface of a template to form a coating; curing the coating for 12-24 hours after its formation, then demolding it without using a release agent to obtain the demolded coating; and curing the demolded coating for more than 7 days to obtain the polyurea anti-corrosion coating test piece.

3. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, The demineralized water is ultrapure water with a resistivity of 18.2~18.3 MΩ and a TOC content of <50 μg / L.

4. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, The ratio of the surface area of ​​the polyurea anti-corrosion coating sample to the volume of the demineralized water is (0.1~0.3) cm². -1 .

5. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, The temperature during the immersion of the polyurea anti-corrosion coating test piece in demineralized water is 20~30℃.

6. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, In step (1), the amount of organic matter leached in Formula I is obtained by the TOC content of the immersion solution of the polyurea anti-corrosion coating test piece.

7. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, In step (3), the total amount of organic matter leached from the polyurea anti-corrosion coating sample after initial immersion in demineralized water for 4 days was 200 mg / m³. 2 The following conditions indicate that the content of easily soluble organic matter in the polyurea anti-corrosion coating test piece is low.

8. The method for controlling organic leachates from the polyurea anti-corrosion coating on the inner wall of the demineralized water tank according to claim 1, wherein, In step (3), the average organic matter dissolution rate of the polyurea anti-corrosion coating test piece after initial immersion in demineralized water for 4-7 days is 10 mg / (m³). 2 When ·d), the leaching of organic matter from the polyurea anti-corrosion coating test piece has a small impact on water quality.

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