A method and device for evaluating cleaning parameters of a steam generator heat transfer tube

Abstract

This invention discloses a method and apparatus for evaluating cleaning parameters of heat transfer tubes in steam generators. The evaluation method involves: preparing an oxide layer on the surface of a pipe sample to form multiple pipe samples containing oxide layers of different and / or equal thicknesses; assembling the pipe samples into a cleaning test chamber and introducing deoxygenated and demineralized water into a demineralized water tank; heating the deoxygenated and demineralized water to the initial temperature and then introducing it into the cleaning test chamber; adding a cleaning agent to the cleaning test chamber for cleaning, while simultaneously cooling the demineralized water tank until the final temperature is reached to stop cleaning; collecting the cleaning waste liquid and testing the concentration of metal elements in it; rinsing the pipe sample and drying it, followed by morphological characterization; and evaluating the selected cleaning parameters based on the metal element concentration and morphological characterization results. The evaluation method and apparatus of this invention provide a good reference for selecting cleaning parameters for heat transfer tubes in steam generators, and can prevent corrosion of the heat transfer tubes due to excessively long chemical cleaning times or excessively high cleaning agent concentrations.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power plant steam generator cleaning technology, specifically relating to a method and apparatus for evaluating cleaning parameters of steam generator heat transfer tubes. Background Technology

[0002] In a pressurized water reactor nuclear power plant, approximately 50-80 kg of sludge accumulates on the secondary side of the steam generator during one fuel cycle. After several cycles of operation, this sludge forms scale on the heat transfer tubes, accumulates on the tube sheet, blocks the flow channels of the support plate, reduces the thermal performance of the heat transfer tubes, causes unstable water levels in the steam generator, and leads to problems such as flow-induced vibration and wear in the heat transfer tubes, as well as accelerated corrosion. Corrosion damage to the heat transfer tubes of the steam generator has always been a major factor contributing to unplanned shutdowns and capacity factor losses in nuclear power plants.

[0003] Chemical cleaning of steam generators not only boasts high deposit dissolution efficiency but also exhibits relatively low corrosion to metallic materials. Deposits in steam generators are unevenly distributed; the scale thickness on the surface of heat transfer tubes in nuclear power steam generators is far lower than the height of the sludge pile. Therefore, the scale dissolution rate on the heat transfer tubes is a critical parameter. Unlike thermal power plant boilers, nuclear power steam generators cannot be cut to determine process parameters such as cleaning agent concentration and deposit dissolution time during chemical cleaning. Therefore, simulation experiments before chemical cleaning of the steam generator are crucial. These simulations allow for the determination of relevant chemical cleaning parameters, thereby preventing corrosion of metal structural materials caused by excessively long chemical cleaning times or excessively high cleaning agent concentrations. Summary of the Invention

[0004] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method and apparatus for evaluating the cleaning parameters of heat transfer tubes in steam generators. This method simulates a shutdown and downlink operation to evaluate the selected cleaning parameters for the sludge and other fouling deposited on the heat transfer tubes of steam generators in actual nuclear power plants, thereby preventing corrosion of the heat transfer tubes due to excessively long chemical cleaning times or excessively high cleaning agent concentrations.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] One object of the present invention is to provide a method for evaluating the cleaning parameters of heat transfer tubes in a steam generator, comprising the following steps:

[0007] An oxide layer is prepared on the surface of the prepared pipe sample to form multiple pipe samples containing oxide layers of different thicknesses and / or the same thickness.

[0008] The pipe sample is assembled into a cleaning test chamber, which is connected to a demineralized water tank, and deoxygenated and demineralized water is introduced into the demineralized water tank.

[0009] After heating the deoxygenated and demineralized water in the demineralized water tank to the initial temperature, it is introduced into the cleaning test chamber, and the pipe sample is at least partially immersed in the deoxygenated and demineralized water;

[0010] Cleaning agent is added to the cleaning test chamber to clean the pipe sample. At the same time, the demineralized water tank begins to cool down until the end temperature is reached to stop the cleaning. The cleaning waste liquid is collected and the concentration of metal elements in the cleaning waste liquid is tested.

[0011] The pipe sample was rinsed with demineralized water and dried before its morphology was characterized.

[0012] The set cleaning parameters were evaluated based on the metal element concentration and morphology characterization results.

[0013] According to some preferred embodiments of the present invention, the method for preparing the oxide layer on the surface of the pipe sample is as follows: immersing the pipe sample in an alkaline solution at a temperature of 250-300°C, a concentration of 3-4 mg / kg, and an oxygen concentration of less than 100 mg / kg for 100-3000 hours. In some embodiments of the present invention, the alkaline solution is an ammonia solution.

[0014] According to some preferred embodiments of the present invention, the initial temperature is 120-140°C, the final temperature is 70-90°C, and the cooling rate is 5-40°C / h.

[0015] According to some preferred embodiments of the present invention, the cooling time of the demineralized water tank from the initial temperature to the final temperature is 3-10 hours.

[0016] Furthermore, this invention can evaluate the influence of factors such as oxide layer thickness, cooling rate within the same cooling range, and cleaning agent concentration through multiple sets of single-factor or multi-factor experiments. Based on the cleaning effect of each set of experiments, the rationality of the corresponding cleaning parameters can be evaluated. The cleaning parameters mainly include cleaning agent concentration and cooling rate within the same cooling range.

[0017] According to some preferred embodiments of the present invention, multiple pipe samples containing oxide layers of different thicknesses are selected for cleaning. During the cleaning of the multiple pipe samples, the starting temperature, ending temperature, and cooling rate of the deoxygenated and desalinated water in the corresponding demineralized water tank are the same, and the concentration of the cleaning agent is the same. Specifically, when evaluating the influence of oxide layer thickness on cleaning parameters, other factors in each group of experiments can be controlled to be the same: namely, the same cooling range, the same cooling rate, and the same cleaning agent concentration.

[0018] According to some preferred embodiments of the present invention, multiple pipe samples containing oxide layers of the same thickness are selected for cleaning. During the cleaning of multiple pipe samples, the initial and final temperatures of the deoxygenated and desalinated water in the demineralized water tank are the same, but the cooling rates are different, and the concentration of the cleaning agent is the same. Specifically, when evaluating the effect of the cooling rate on the cleaning parameters, other factors in each group of experiments can be controlled to be the same: namely, the same oxide layer thickness, the same cooling range, and the same cleaning agent concentration.

[0019] According to some preferred embodiments of the present invention, multiple pipe samples containing oxide layers of the same thickness are selected for cleaning. During the cleaning of multiple pipe samples, the initial temperature, final temperature, and cooling rate of the deoxygenated and desalinated water in the demineralized water tank are all the same, while the concentration of the cleaning agent is different. Specifically, when evaluating the effect of the cleaning agent concentration on the cleaning parameters, other factors in each group of experiments can be controlled to be the same: namely, the same oxide layer thickness, the same cooling range, and the same cooling rate.

[0020] According to some preferred embodiments of the invention, the concentration of the cleaning agent is 5%-10%.

[0021] According to some preferred embodiments of the present invention, the thickness of the oxide layer is 0-3 μm. Oxide layers of different thicknesses can be obtained by adjusting the immersion time of the pipe sample in the alkaline solution or the concentration of the alkaline solution. Furthermore, in some embodiments of the present invention, the oxide is iron(III) oxide (Fe3O4).

[0022] According to some preferred embodiments of the present invention, the method for characterizing the morphology of the pipe sample is as follows: a small sample of 1-2 cm * 1-2 cm in size is cut from the rinsed and dried pipe sample, and the morphology of the small sample is observed and photographed using a scanning electron microscope. Specifically, in the above evaluation method steps, after preparing an oxide layer on the prepared pipe sample surface, a small sample of 1-2 cm * 1-2 cm in size is also cut, and its morphology (morphology of the pipe sample before cleaning) is observed and photographed using a scanning electron microscope. This allows for a comparison of the microscopic morphology of the pipe sample before and after cleaning, thereby evaluating the cleaning effect and facilitating the evaluation of the selected cleaning parameters. By comparing the microscopic morphology of the pipe sample surface before and after cleaning: granular oxides are observed on the surface of the pipe sample before cleaning. After cleaning, the corrosion of the substrate can be judged based on whether the granular oxides are completely removed and whether microporous defects appear in the substrate of the pipe sample itself when the granular oxides are completely removed, thus comprehensively evaluating the cleaning effect.

[0023] According to some preferred embodiments of the present invention, the instrument for testing the concentration of metal elements in the cleaning waste liquid is an inductively coupled plasma atomic emission spectrometer, wherein the metal element is iron. By testing the concentration of metal elements in the cleaning waste liquid, the cleaning effect can be assessed based on the concentration of metal elements. Generally, the higher the concentration of metal elements, the more oxides are removed, and the better the cleaning effect.

[0024] According to some preferred embodiments of the present invention, during the cleaning process, the temperature of the deoxygenated and desalinated water in the cleaning test chamber is the same as the temperature of the deoxygenated and desalinated water in the desalinated water tank. That is, after the deoxygenated and desalinated water in the desalinated water tank is heated to the initial temperature and then introduced into the cleaning test chamber, the deoxygenated and desalinated water in the desalinated water tank and the deoxygenated and desalinated water in the cleaning test chamber are always kept in communication, so that when the deoxygenated and desalinated water in the desalinated water tank is subsequently cooled, the deoxygenated and desalinated water in the cleaning test chamber will also be cooled synchronously.

[0025] According to some preferred embodiments of the present invention, the cleaning agent is added to the cleaning test chamber from the dosing tank via a dosing pump, and an inert gas is introduced into the dosing tank to remove oxygen from the cleaning agent.

[0026] Another objective of this invention is to provide an evaluation device for the cleaning parameters of a steam generator heat transfer tube. The evaluation method described above uses the evaluation device to conduct a simulation experiment. The simulation experiment device includes a cleaning test chamber, a demineralized water tank, a chemical mixing tank, a waste liquid tank, an inert gas source, and a pipe sample with an oxide layer on its surface placed in the cleaning test chamber. The demineralized water tank has a heating module. The demineralized water tank, the chemical mixing tank, and the waste liquid tank are all connected to the cleaning test chamber. The inert gas source is connected to the chemical mixing tank. The bottom of the pipe sample is away from the bottom surface of the cleaning test chamber. A stirring rod is provided in the chemical mixing tank. The stirring rod has cavities extending through both ends, and the cavities extend along the length of the stirring rod.

[0027] According to some preferred embodiments of the present invention, a dosing pump is provided between the cleaning test chamber and the dosing tank, and an exhaust valve is provided on the top of the dosing tank; at least one set of filter components is provided between the cleaning test chamber and the waste liquid tank, and a valve is provided at the inlet end of each set of filter components.

[0028] Due to the adoption of the above technical solutions, compared with the prior art, the advantages of the present invention are as follows: The evaluation method and device for cleaning parameters of steam generator heat transfer tubes of the present invention are beneficial to evaluating the corrosion risk of metal materials in chemical cleaning processes, and have good reference and reference significance for the selection of cleaning parameters of steam generator heat transfer tubes in nuclear power plants, which helps to avoid corrosion of heat transfer tubes due to excessively long chemical cleaning time and excessively high cleaning agent concentration. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the evaluation device in a preferred embodiment of the present invention;

[0031] Figure 2 The image shown is an electron microscope image of the pipe sample before cleaning in Embodiment 1 of the present invention.

[0032] Figure 3 The image shown is an electron microscope image of the pipe sample after cleaning in Embodiment 1 of the present invention.

[0033] Figure 4 The image shown is an electron microscope image of the pipe sample before cleaning in Embodiment 2 of the present invention.

[0034] Figure 5 These are electron microscope images of the pipe sample after cleaning in Embodiment 2 of the present invention;

[0035] Figure 6 These are electron microscope images of the pipe sample before cleaning in Embodiment 3 of the present invention;

[0036] Figure 7 These are electron microscope images of the pipe sample after cleaning in Embodiment 3 of the present invention;

[0037] The attached diagrams are labeled as follows: Cleaning test chamber-1, Demineralized water tank-2, Dosing tank-3, Stirring rod-31, Exhaust valve-32, Waste liquid tank-4, Inert gas source-5, Pipe sample-6, Dosing pump-7, Waste liquid pump-8, Filter assembly-9, Valve-10, Water pipe-11. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0039] Reference Figure 1An evaluation device for cleaning parameters of a steam generator heat transfer tube in this embodiment includes a cleaning test chamber 1, a demineralized water tank 2, a dosing tank 3, a waste liquid tank 4, an inert gas source 5, and a pipe sample 6 with an oxide layer on its surface, which is placed in the cleaning test chamber 1. The bottom of the pipe sample 6 is far away from the bottom surface of the cleaning test chamber 1, that is, the pipe sample 6 does not contact the bottom surface of the cleaning test chamber 1 and does not contact the side wall of the cleaning test chamber 1, so as to ensure that the pipe sample 6 is thoroughly cleaned.

[0040] Specifically, the demineralized water tank 2 is used to store deoxygenated and demineralized water. The demineralized water tank 2 is equipped with a heating module for heating the stored deoxygenated and demineralized water. The demineralized water tank 2 is connected to the cleaning test chamber 1, and the deoxygenated and demineralized water in the demineralized water tank 2 can flow directly into the cleaning test chamber 1, with both chambers having the same temperature. The top of the preparation tank 3 is equipped with an exhaust valve 32. Inside the preparation tank 3 is a stirring rod 31, with cavities extending along its length from both ends. The preparation tank 3 is also connected to an inert gas source 5. When inert gas is introduced into the preparation tank 3, the hollow stirring rod 31 begins to stir, causing bubbles to rise from both ends of the stirring rod 31. This operation removes oxygen from the cleaning agent and improves the deoxygenation effect. The oxygen can be discharged through the exhaust valve 32. In addition, the dosing tank 3 and the cleaning test chamber 1 are connected by a water pipe 11 and a dosing pump 7 is installed between them. The cleaning agent is added to the dosing tank 3 and then the dosing pump 7 adds the cleaning agent to the cleaning test chamber 1 to complete the dosing.

[0041] Furthermore, the waste liquid tank 4 and the cleaning test chamber 1 are also connected by a water pipe 11, and a waste liquid pump 8 is installed between them. In this embodiment, two sets of filter components 9 are installed between the cleaning test chamber 1 and the waste liquid tank 4, and a valve 10 is installed at the inlet end of each filter component 9. The cleaning waste liquid from the cleaning test chamber 1 is discharged into the waste liquid tank 4 through the waste liquid pump 8, and the suspended solids are filtered by the filter components 9, which facilitates the observation of the particle size of oxides in the cleaning waste liquid after chemical cleaning.

[0042] This embodiment of a method for evaluating the cleaning parameters of a steam generator heat transfer tube includes the following steps:

[0043] Step 1: Prepare a clean and dry pipe sample 6, and immerse it in an alkaline solution at a temperature of 250-300℃, a concentration of 3-4 mg / kg, and an oxygen concentration of less than 100 mg / kg for 100-3000 hours to form multiple pipe samples 6 with oxide layers of different and / or the same thickness. Cut a small sample of 1-2 cm * 1-2 cm in size from the pipe sample 6, and observe its morphology (morphology of pipe sample 6 before cleaning) with a scanning electron microscope and take a picture to obtain an electron microscope image before cleaning; the thickness of the oxide layer is 0-3 μm.

[0044] By adjusting the immersion time of pipe sample 6 in alkaline solution or the concentration of alkaline solution, oxide layers of different thicknesses can be obtained.

[0045] Step 2: Assemble the pipe sample 6 into the cleaning test chamber 1, and introduce deoxygenated and demineralized water into the demineralized water tank 2.

[0046] Step 3: After heating the deoxygenated and demineralized water in the demineralized water tank 2 to the initial temperature of 120-140℃, the deoxygenated and demineralized water at the initial temperature is introduced into the cleaning test chamber 1 so that the pipe sample 6 is at least partially immersed in the deoxygenated and demineralized water.

[0047] Step 4: Add a 5%-10% cleaning agent to the mixing tank 3 and introduce inert gas into the mixing tank 3. Rotate the stirring rod 31, open the exhaust valve 32, and then turn on the dosing pump 7 to add the cleaning agent into the cleaning test chamber 1 to clean the pipeline sample 6. At the same time, the water temperature in the demineralized water tank 2 is reduced from the initial temperature at a rate of 5-40℃ / h until the final temperature of 70-90℃ is reached, at which point the cleaning is stopped. Turn on the waste liquid pump 8 to discharge the cleaning waste liquid in the cleaning test chamber 1 into the waste liquid tank 4. Use an inductively coupled plasma atomic emission spectrometer to test the metal element concentration of the cleaning waste liquid in the waste liquid tank 4.

[0048] Step 5: After rinsing the cleaned pipe sample 6 with clean deionized water and drying it, cut out a small sample with a size of 1-2cm*1-2cm from the pipe sample 6, observe its morphology with a scanning electron microscope and take a picture to obtain an electron microscope image after cleaning.

[0049] Step 6: Evaluate the selected cleaning parameters based on the metal element concentration and the morphological characterization results of pipe sample 6 before and after cleaning.

[0050] In the above evaluation method, the cooling time of the demineralized water tank 2 from the initial temperature to the final temperature is controlled within the range of 3-10 hours.

[0051] In other embodiments, the effects of factors such as oxide layer thickness, cooling rate within the same cooling range, and cleaning agent concentration can be evaluated through multiple sets of single-factor or multi-factor experiments. The rationality of the corresponding cleaning parameters can be assessed based on the cleaning effect of each set of experiments. Specifically, when evaluating the effect of oxide layer thickness on cleaning parameters, multiple pipe samples 6 containing oxide layers of different thicknesses can be selected for cleaning. The starting temperature, ending temperature, and cooling rate of the deoxygenated and desalinated water in the demineralized water tank 2 corresponding to the multiple pipe samples 6 are controlled to be the same, and the concentration of the cleaning agent is also the same. When evaluating the effect of cooling rate on cleaning parameters, multiple pipe samples 6 containing oxide layers of the same thickness can be selected for cleaning. The starting temperature and ending temperature of the deoxygenated and desalinated water in the demineralized water tank 2 are controlled to be the same, the concentration of the cleaning agent is the same, but the cooling rate is different. When evaluating the effect of cleaning agent concentration on cleaning parameters, multiple pipe samples 6 containing oxide layers of the same thickness can be selected for cleaning. The starting temperature, ending temperature, and cooling rate of the deoxygenated and desalinated water in the demineralized water tank 2 are controlled to be the same, but the concentration of the cleaning agent is different.

[0052] Example 1

[0053] This embodiment of a method for evaluating the cleaning parameters of a steam generator heat transfer tube includes the following steps:

[0054] Step 1: Prepare a clean and dry pipe sample 6. Immerse it in an ammonia solution at 290℃ with a concentration of 3.5 mg / kg and an oxygen concentration of 90 mg / kg for 1000 hours to form a pipe sample 6 containing a 1.5 μm thick layer of magnetite. Cut a 1 cm * 1 cm sample from the pipe sample 6 and observe its morphology (morphology of pipe sample 6 before cleaning) using a scanning electron microscope and take an electron microscope image before cleaning (e.g., ...). Figure 2 (As shown).

[0055] Step 2: Assemble the pipe sample 6 into the cleaning test chamber 1, and introduce deoxygenated and demineralized water into the demineralized water tank 2.

[0056] Step 3: After heating the deoxygenated and demineralized water in the demineralized water tank 2 to the initial temperature of 130°C, the 130°C deoxygenated and demineralized water is introduced into the cleaning test chamber 1, so that part of the pipe sample 6 is immersed in the deoxygenated and demineralized water.

[0057] Step 4: Add 10% EDTA to the dosing tank 3 and introduce nitrogen gas into the dosing tank 3. Rotate the stirring rod 31, open the exhaust valve 32, and then turn on the dosing pump 7 to add the cleaning agent into the cleaning test chamber 1 to clean the pipeline sample 6. At the same time, the water temperature of the demineralized water tank 2 is reduced from 130℃ at a rate of 5℃ / h until it reaches 80℃, at which point the cleaning is stopped. Turn on the waste liquid pump 8 to discharge the cleaning waste liquid in the cleaning test chamber 1 into the waste liquid tank 4. Use an inductively coupled plasma atomic emission spectrometer to test the iron concentration of the cleaning waste liquid in the waste liquid tank 4.

[0058] Step 5: After rinsing and drying the pipe sample 6 with clean deionized water, cut a small sample measuring 1cm*1cm from the pipe sample 6, observe its morphology using a scanning electron microscope, and take a picture to obtain an electron microscope image of the cleaned sample (e.g., ...). Figure 3 (As shown).

[0059] Step 6: Evaluate the selected cleaning parameters based on the iron concentration and the morphological characterization results of pipe sample 6 before and after cleaning.

[0060] In this embodiment, the final measured iron concentration was 3.1 g / kg. Before cleaning, the macroscopic surface of pipe sample 6 was observed to be black. Figure 2 It can be seen that its outer surface has well-crystallized granular iron oxide, and its inner layer has a dense layer of iron oxide; from Figure 3 It can be seen that after cleaning, the granular iron oxide on its surface was completely removed, and there are still a large number of micropores. This indicates that the oxide on the surface of pipe sample 6 was cleaned off, and the corresponding cleaning parameters have a good cleaning effect.

[0061] Example 2

[0062] The difference between the evaluation method for cleaning parameters of the heat transfer tube of the steam generator in this embodiment and that in embodiment 1 is that the cooling rate is 10℃ / h and the cleaning agent concentration is 5%.

[0063] In this embodiment, the final measured iron concentration was 2.8 g / kg. Before cleaning, the macroscopic surface of pipe sample 6 was observed to be black. Figure 4 It can be seen that its outer surface has well-crystallized granular iron oxide, and its inner layer has a dense layer of iron oxide; from Figure 5 It can be seen that the granular iron oxide on its surface was completely removed after cleaning, which indicates that the oxide on the surface of pipe sample 6 was cleaned off, and the corresponding cleaning parameters have a good cleaning effect.

[0064] Example 3

[0065] The difference between the evaluation method for cleaning parameters of the heat transfer tube of the steam generator in this embodiment and that in embodiment 1 is that the pipe sample 6 is soaked in ammonia solution for 300 hours, and the thickness of the iron oxide layer is 0.5 μm; the cooling rate is 10℃ / h.

[0066] In this embodiment, the final measured iron concentration was 0.9 g / kg. Before cleaning, the macroscopic surface of pipe sample 6 was observed to be black. Figure 6 It can be seen that its outer surface has granular magnetite, and its inner layer has a dense magnetite layer; from Figure 7 It can be seen that after cleaning, the granular iron oxide on its surface was completely removed and many micropore defects appeared on the surface. This indicates that the oxide on the surface of pipe sample 6 was cleaned off but the substrate was corroded, indicating that the cleaning was excessive. This suggests that for pipe sample 6 with a thin oxide layer, it may be necessary to reduce the concentration of the cleaning agent.

[0067] The present invention provides an evaluation method for cleaning parameters of heat transfer tubes in steam generators, which is helpful in assessing the corrosion risk of metal materials in chemical cleaning processes. It has good reference and guidance significance for the selection of cleaning parameters for heat transfer tubes in steam generators at nuclear power plants, and helps to avoid corrosion of heat transfer tubes due to excessively long chemical cleaning time and excessively high cleaning agent concentration.

[0068] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method of evaluating cleaning parameters for steam generator heat transfer tube cleaning, the method comprising: determining a plurality of tube cleaning parameters; determining a plurality of tube condition parameters; determining a plurality of tube failure parameters; and determining a plurality of tube performance parameters. Includes the following steps: An oxide layer is prepared on the surface of the prepared pipe sample to form multiple pipe samples containing oxide layers of different thicknesses and / or the same thickness. A small sample with a size of 1-2cm*1-2cm is cut out from the pipe sample, and the morphology of the pipe sample before cleaning is observed using a scanning electron microscope and an electron microscope image before cleaning is obtained. The thickness of the oxide layer is 0-3μm. The method for preparing the oxide layer on the surface of the pipe sample is as follows: the pipe sample is immersed in an alkaline solution with a temperature of 250-300℃, a concentration of 3-4mg / kg, and an oxygen concentration of less than 100mg / kg for 100-3000h. The pipe sample is assembled into a cleaning test chamber, which is connected to a demineralized water tank, and deoxygenated and demineralized water is introduced into the demineralized water tank. After heating the deoxygenated and demineralized water in the demineralized water tank to the initial temperature, it is introduced into the cleaning test chamber, and the pipe sample is at least partially immersed in the deoxygenated and demineralized water. Cleaning agent is added to the cleaning test chamber to clean the pipeline sample. Simultaneously, the demineralized water tank begins to cool down until the final temperature is reached, at which point the cleaning stops. The cleaning waste liquid is collected, and the concentration of metal elements in the waste liquid is tested. The initial temperature is 120-140℃, the final temperature is 70-90℃, and the cooling rate is 5-40℃ / h. During the cleaning process, the temperature of the deoxygenated and demineralized water in the cleaning test chamber is the same as the temperature of the deoxygenated and demineralized water in the demineralized water tank. After rinsing and drying the pipe sample with demineralized water, the pipe sample was characterized in morphology. The method for characterizing the morphology of the pipe sample was as follows: a small sample with a size of 1-2cm*1-2cm was cut out from the rinsed and dried pipe sample, and the morphology of the small sample was observed and photographed using a scanning electron microscope. The set cleaning parameters were evaluated based on the concentration and morphology characterization results of the metal element, wherein the metal element is iron.

2. The evaluation method according to claim 1, characterized in that The cooling time from the initial temperature to the final temperature in the demineralized water tank is 3-10 hours.

3. The evaluation method according to claim 2, characterized in that Multiple pipe samples containing oxide layers of different thicknesses were selected for cleaning. The starting temperature, ending temperature, and cooling rate of the deoxygenated and desalinated water in the corresponding demineralized water tanks were the same for all the pipe samples being cleaned, and the concentration of the cleaning agent was the same.

4. The evaluation method according to claim 2, characterized in that Multiple pipe samples containing oxide layers of the same thickness were selected and cleaned separately. During the cleaning of multiple pipe samples, the starting and ending temperatures of the deoxygenated and demineralized water in the demineralized water tank were the same, but the cooling rates were different, and the concentration of the cleaning agent was the same.

5. The evaluation method according to claim 2, characterized in that Multiple pipe samples containing oxide layers of the same thickness were selected and cleaned separately. During the cleaning of multiple pipe samples, the starting temperature, ending temperature and cooling rate of the deoxygenated and demineralized water in the demineralized water tank were the same, while the concentration of the cleaning agent was different.

6. The method of assessment according to any one of claims 3-5, wherein, The concentration of the cleaning agent is 5%-10%.

7. The evaluation method according to claim 1, characterized in that, The instrument used to test the concentration of metal elements in the cleaning waste liquid is an inductively coupled plasma atomic emission spectrometer.

8. The evaluation method according to claim 1, characterized in that, The cleaning agent is added to the cleaning test chamber from the dosing tank via a dosing pump, and an inert gas is introduced into the dosing tank to remove oxygen from the cleaning agent.

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