Neutral cleaning agent for rust removal of chemical pipeline and use method of neutral cleaning agent

Abstract

The invention discloses a chemical pipeline rust removal neutral cleaning agent and a use method thereof, and relates to the technical field of chemical equipment maintenance and cleaning, the cleaning agent is mainly composed of diammonium hydrogen citrate, ammonium hydrogen fluoride and the balance of water, the pH value of the cleaning agent is neutral, and the cleaning agent can be used for cleaning rust in a pH environment close to neutral. By means of chelation of diammonium hydrogen citrate and auxiliary activation of ammonium bifluoride, rust and scale on the inner wall of the pipeline are effectively removed, and the use method comprises a static soaking mode and a dynamic circulating cleaning mode which can be flexibly selected according to working conditions. According to the method, corrosion to various metal materials such as carbon steel, chromium molybdenum steel and stainless steel can be controlled at a very low level while a good rust removal effect is achieved, waste liquid obtained after cleaning is close to neutral and environmentally friendly, treatment is easy, and the method has the advantages of being high in safety, easy and convenient to operate and wide in applicability.

Description

Technical Field

[0001] This invention relates to the field of chemical equipment maintenance and cleaning technology, specifically to a neutral cleaning agent for removing rust from chemical pipelines and its application method. Background Technology

[0002] In process industries such as chemical, petroleum, and metallurgy, metal pipelines are prone to corrosion and the formation of scale, rust, and oxide layers due to the long-term transport of various media. These scale layers not only reduce the effective flow area of ​​the pipeline and increase energy consumption, but their detached debris can also contaminate products, clog valves and instruments, and even cause pipeline perforation due to under-scale corrosion, leading to safety and environmental accidents. Therefore, regular chemical cleaning and rust removal of in-service pipelines during maintenance periods is a crucial step in ensuring production safety, improving energy efficiency, and extending equipment lifespan.

[0003] Currently, pipeline chemical cleaning technologies are mainly divided into two categories: strong acid cleaning and environmentally friendly cleaning. While strong acid (such as hydrochloric acid and nitric acid) cleaning removes rust quickly and thoroughly, it is highly corrosive to the metal substrate, prone to hydrogen embrittlement and over-cleaning, and presents significant challenges in wastewater treatment and environmental risks. To overcome these drawbacks, environmentally friendly cleaning technologies are constantly evolving. For example, patent publication number CN103320801B discloses a long-life, low-foaming, two-in-one metal cleaning agent for cleaning and rust prevention. Its pH value is neutral, and by compounding multiple surfactants, rust-inhibiting film-forming agents, and pH buffers in the formula, it combines cleaning with inter-process rust prevention. Another example is the neutral cleaning pre-filming agent technology guided by the concept of "supramolecular chemistry," which claims to remove dirt through molecular recognition and form a protective film on the metal surface, achieving corrosion-free or low-corrosion cleaning. In addition, domestic companies have developed products such as neutral cleaning agents for ferrous sulfide scale, which are also dedicated to solving the problem of safe cleaning of specific scale types.

[0004] While existing environmentally friendly cleaning agents have improved in safety, their technical approaches often rely on complex surfactant formulations, polymer chelation, or specific film-forming mechanisms. In practical applications, especially when dealing with high-temperature oxide scale or stubborn rust on the dense, strongly adhering inner walls of pipes, these solutions often face a dilemma: pursuing extreme gentleness (such as a strictly neutral pH) often results in insufficient chemical cleaning power, long cleaning cycles, and low efficiency; while introducing more active ingredients to enhance cleaning power may sacrifice broad-spectrum, low-corrosion properties for various metal materials (especially sensitive alloy steels), or complicate the formulation and process. Therefore, a new technical solution is needed that can achieve efficient rust removal from various industrial pipe materials, such as carbon steel and alloy steel, under near-neutral, gentle conditions, while strictly controlling the corrosion rate below industrial safety standards (such as ≤6 g / m²·h).

[0005] In summary, existing technologies in the field of pipeline chemical cleaning still have significant limitations in achieving both "high-efficiency cleaning" and "extremely low corrosion." This invention aims to address these limitations of the existing technologies. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a neutral cleaning agent for chemical pipeline rust removal and its application method. Through the synergistic effect of diammonium citrate and trace amounts of ammonium bifluoride, it can effectively remove rust and scale from the inner wall of pipelines under near-neutral and mild conditions, while keeping the corrosion of various metal materials such as carbon steel, chromium-molybdenum steel and stainless steel at a very low level. This solves the problem of the difficulty in achieving both high-efficiency cleaning and low corrosion, and the waste liquid is easy to treat, making it safe and environmentally friendly.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In one aspect, a neutral cleaning agent for removing rust from chemical pipelines, composed of the following components by mass percentage: Diammonium hydrogen citrate 2% to 5%; Ammonium bifluoride 0.01% to 0.1%; The remainder is water; The cleaning agent is formulated to act on the inner wall of metal pipes through a circulating cleaning method under conditions of pH value of 5 to 7 and temperature of room temperature to 70°C.

[0008] Furthermore, the mass percentage concentration of the diammonium citrate is 3% to 5%.

[0009] Furthermore, the mass percentage concentration of the ammonium bifluoride is 0.03% to 0.05%.

[0010] Furthermore, the cleaning agent has a pH value of approximately 6 when in use.

[0011] Furthermore, it also includes a corrosion inhibitor, wherein the corrosion inhibitor has a mass percentage concentration of 0.1% to 0.3%.

[0012] Furthermore, it also includes a cofactor organic acid, wherein the mass percentage concentration of the cofactor organic acid is 0.1% to 0.3%, and the cofactor organic acid is citric acid.

[0013] On the other hand, a method for using a neutral cleaning agent for removing rust from chemical pipelines, applicable to a neutral cleaning agent for removing rust from chemical pipelines, the specific steps of the method are as follows: Step 1: Contact the metal pipe components or system to be cleaned with the cleaning agent; Step two: Control the temperature during the cleaning process within the range of room temperature to 70℃; Step 3: After cleaning, rinse the metal pipe components or system.

[0014] Furthermore, in step one, the specific method of bringing the metal pipe component or system to be cleaned into contact with the cleaning agent is static immersion; The temperature of the static immersion is 60°C to 70°C; The static soaking time is 5 to 12 hours.

[0015] Furthermore, in step one, the specific method of bringing the metal pipe component or system to be cleaned into contact with the cleaning agent is dynamic circulation cleaning; The dynamic cyclic cleaning is performed at room temperature. The dynamic cyclic cleaning time is 7 to 16 hours; After the dynamic cyclic cleaning, a static soaking step is also included, and the static soaking time is 8 to 15 hours.

[0016] Furthermore, in step three, the material of the metal pipe component or system includes at least one of carbon steel, chromium-molybdenum steel, and stainless steel; The chromium-molybdenum steel is either 15-chromium-molybdenum steel or 12-chromium-molybdenum steel; The stainless steel is 304 stainless steel or 316 stainless steel; The cleaning agent is used to remove rust from an online industrial pipeline system made of the material in a dynamic circulation cleaning process, and the cleaning agent flows in a full-pipe flow state.

[0017] Compared with existing technologies, this neutral cleaning agent for rust removal in chemical pipelines and its application method have the following advantages: I. This invention employs a neutral cleaning system composed of diammonium citrate and trace amounts of ammonium bifluoride. Under near-neutral and mild pH conditions, it effectively dissolves and removes rust and oxide scale from the inner walls of metal pipes. Simultaneously, it strictly controls the corrosion rate of the metal substrate during the cleaning process within industrial safety standards. This resolves the contradiction between high-efficiency cleaning and extremely low corrosion in existing technologies, achieving efficient rust removal while significantly reducing the corrosion risk to various pipe materials such as carbon steel, chromium-molybdenum steel, and stainless steel. It avoids safety hazards such as hydrogen embrittlement and over-cleaning caused by strong acid cleaning, ensuring the long-term safety and reliability of equipment operation.

[0018] Second, by optimizing the component ratio and cleaning process, this invention makes the waste liquid after cleaning nearly neutral and with a simple composition, which greatly reduces the difficulty and cost of subsequent wastewater treatment and significantly improves environmental friendliness. Compared with the hazardous waste liquid with high acidity and high metal ion content generated by strong acid cleaning, the waste liquid generated by this invention is easy to neutralize and treat, reducing the risk of environmental pollution and environmental penalties, which is in line with the development trend of cleaner production and green chemical industry.

[0019] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0021] Figure 1 This is a diagram illustrating the steps of using the present invention; Figure 2 This is a schematic diagram of the composition of the neutral cleaning agent of the present invention; Figure 3 This is a comparison chart of the overall performance of the present invention with that of traditional cleaning agents. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0023] Example 1 like Figures 1 to 3 As shown, this embodiment aims to verify the rust removal effect and corrosion impact on metal pipes of a 3% concentration diammonium citrate neutral cleaning agent containing corrosion inhibitor under static immersion conditions. Diammonium citrate was used as the main rust-removing component, and LAN-826 was used as the corrosion inhibitor. Metal pipe samples were treated by static immersion at 65°C. The scale removal, corrosion-related data, and long-term rust recurrence were recorded during the cleaning process, providing practical evidence for the static immersion method and the addition of corrosion inhibitors. Figure 2 The typical composition ratio of the cleaning agent of this invention is visually illustrated in pie chart form. Water, as the solvent, constitutes the majority (approximately 95.45%), diammonium citrate is the main rust-removing component (approximately 4.5%), and ammonium bifluoride is a trace auxiliary component (approximately 0.05%). The following detailed description, in conjunction with specific implementation details, further illustrates this.

[0024] In this embodiment, the experimental materials are prepared as follows: Metal Tube Sample: Metal tube sample 2, made of industrially common carbon steel, was selected for cleaning. The sample was weighed using an electronic balance with an accuracy of 0.0001g, yielding a weight of 95.2969 grams before cleaning. The surface area of ​​the tube sample was calculated using a dimensional measurement method. The length, inner diameter, and outer diameter of the tube sample were measured using vernier calipers, and the inner and outer surface areas were calculated separately. The inner surface area was 35.92 square centimeters, the outer surface area was 44.21 square centimeters, and the total surface area was 80.13 square centimeters. Multiple measurements were taken and the average value was calculated to ensure data accuracy.

[0025] Cleaning agent raw materials: Prepare diammonium citrate solid reagent with purity meeting industrial grade standards; select LAN-826 corrosion inhibitor, whose model is consistent with the specifications of commonly used industrial corrosion inhibitors; use deionized water for the experiment to avoid impurities in the water from interfering with the cleaning effect and corrosion test.

[0026] Experimental equipment: Prepare 500 ml beakers, constant temperature water bath, electronic balance, vernier calipers, stirring rod, etc. Before the experiment, clean all equipment to ensure that there are no oil stains, rust, or other contaminants remaining.

[0027] In this embodiment, the cleaning agent is prepared as follows: Based on the mass percentage concentration range of diammonium hydrogen citrate, this example uses a concentration of 3%. Accurately weigh 15 grams of solid diammonium hydrogen citrate and slowly add it to a beaker containing 500 ml of deionized water. Stir continuously for 15 minutes at a speed of 60 revolutions per minute using a stirring rod until the diammonium hydrogen citrate is completely dissolved and the solution is transparent.

[0028] Add 2 ml of corrosion inhibitor LAN-826 to the above solution and continue stirring for 5 minutes to ensure the corrosion inhibitor is evenly dispersed in the solution. After preparation, measure the pH value of the solution using precision pH test paper. The measured pH value is between 5 and 6, which is within the pH range of 5 to 7 for the cleaning agent when in use.

[0029] In this embodiment, the cleaning operation steps are as follows: Turn on the constant temperature water bath and set the temperature to 65℃. After the water bath temperature stabilizes within the range of 65℃±1℃, place the beaker containing the prepared cleaning agent into the water bath, ensuring that the bottom of the beaker does not directly contact the bottom of the water bath to ensure even heating.

[0030] Slowly place the pretreated tube sample 2 into the cleaning agent, ensuring that the tube sample is completely submerged without any exposed parts. Start timing and statically soak for 6 hours. During the soaking process, observe the solution state and changes on the tube sample surface every hour, recording whether the solution becomes turbid, changes color, or whether the rust layer on the tube sample surface peels off.

[0031] After 6 hours of soaking, the tube sample was removed with tweezers, and the surface of the sample was quickly rinsed with deionized water to remove any remaining cleaning agent. Then, the surface of the tube sample was dried with clean filter paper and weighed immediately using an electronic balance. The weight of the tube sample after 6 hours of soaking was 93.8065 grams.

[0032] The sample was then placed back into the original cleaning agent and soaked at room temperature (25℃±2℃) for 12 hours. After soaking, it was rinsed, dried and weighed using the same method as above. The sample weighed 93.7209 grams after soaking for another 12 hours.

[0033] In this embodiment, subsequent detection and observation are as follows: Cleaning efficiency calculation: The amount of scale cleaned is calculated based on the weighing data. After 6 hours of soaking, the amount of scale cleaned is the weight before cleaning minus the weight after soaking, i.e., 95.2969 grams minus 93.8065 grams, resulting in 1.4904 grams. According to the cleaning efficiency calculation formula, the cleaning efficiency equals the amount of scale cleaned divided by (total surface area of ​​the sample multiplied by the soaking time), i.e., 1.4904 grams divided by (0.008013 square meters multiplied by 6 hours), resulting in a cleaning efficiency of 32.82 grams per square meter per hour.

[0034] Corrosion rate test: An indicator piece of the same material as the tube sample was selected. Before cleaning, its weight was 8.0000 grams and its surface area was 10.00 square centimeters. After immersion, its weight was 7.9982 grams, resulting in a weight loss of 0.0018 grams due to corrosion. The corrosion rate = 0.0018 grams ÷ (0.0010 square meters × 18 hours) = 1.00 grams per square meter per hour, which is far below the industrial safety standard.

[0035] Rusting observation: The tube sample after final cleaning was placed in a laboratory environment with normal temperature and humidity (temperature 25℃±2℃, humidity 50%±5%) and observed for ten days. The rusting on the surface of the tube sample was recorded. After ten days, the tube sample was found to have a certain degree of rusting.

[0036] Waste liquid status detection: After the cleaning experiment, the waste liquid was observed to be yellow-green. The pH value of the waste liquid was measured again and was still between 5 and 6, with no obvious pH value change.

[0037] In summary, this embodiment successfully removed rust from carbon steel pipe samples using a cleaning agent formulation of 3% diammonium citrate combined with corrosion inhibitor LAN-826. The method involved static immersion at 65°C for 6 hours followed by immersion at room temperature for 12 hours, achieving a cleaning efficiency of 32.82 grams per square meter per hour, demonstrating effective rust removal. Simultaneously, the pH value of the cleaning agent remained stable between 5 and 6, conforming to the pH range for neutral cleaning agents. The addition of the corrosion inhibitor effectively controlled the risk of metal corrosion. The experimental results validated the rationality and feasibility of the static immersion method, the concentration range of diammonium citrate, and the addition of the corrosion inhibitor. This method is simple to operate and suitable for offline rust removal of carbon steel pipe components.

[0038] Example 2 like Figure 1 As shown, this embodiment aims to verify the rust removal efficiency and rust recurrence control effect of a high-concentration (5%) diammonium citrate neutral cleaning agent under static immersion conditions. Using only diammonium citrate as the main rust-removing component, without adding corrosion inhibitors or auxiliary organic acids, metal pipe samples were statically immersed at 65°C for 5 hours. The focus was on examining the effect of the high-concentration main agent on improving rust removal efficiency and long-term rust recurrence, further supporting the rationality of the diammonium citrate concentration range.

[0039] In this embodiment, the experimental materials are prepared as follows: Metal tube sample: Carbon steel tube sample 4, made of the same material as in Example 1, was selected to ensure consistency of the experimental materials. The tube sample was weighed using an electronic balance (accuracy 0.0001g), and its weight before cleaning was 108.7858 grams. The surface area was calculated using the same dimensional measurement method as in Example 1: the inner surface area was 42.04 square centimeters, the outer surface area was 51.75 square centimeters, and the total surface area was 93.79 square centimeters. The measurement data were verified three times, and the error was controlled within ±0.01 square centimeters.

[0040] Cleaning agent raw materials: diammonium hydrogen citrate solid reagent (industrial grade purity), deionized water, ensuring that the raw materials are free of impurities and contamination.

[0041] Experimental equipment: 500 ml beaker, constant temperature water bath, electronic balance, vernier caliper, stirring rod. The equipment is cleaned and dried before use.

[0042] In this embodiment, the cleaning agent is prepared as follows: Based on the upper limit of 3% to 5% by mass percentage of diammonium hydrogen citrate, a concentration of 5% was selected for preparation. Accurately weigh 25 grams of solid diammonium hydrogen citrate and add it to a beaker containing 500 ml of deionized water. Stir with a stirring rod at a speed of 60 revolutions per minute for 20 minutes until the solid is completely dissolved and the solution is free of precipitate and turbidity.

[0043] After preparation, the pH value of the solution was measured using precision pH test paper. The measured pH value was approximately 6, and no additional pH adjustment was required.

[0044] In this embodiment, the cleaning operation steps are as follows: Turn on the constant temperature water bath and set the temperature to 65℃. After the water temperature stabilizes at 65℃±1℃, place the beaker containing the cleaning agent into the water bath to ensure that the beaker is heated evenly.

[0045] Slowly immerse tube sample 4 in the cleaning solution, ensuring complete submersion with no exposed areas. Start timing and allow it to soak statically for 5 hours. Observe every hour during the soaking process, recording changes in solution color and the removal of rust from the tube sample surface. It was observed that the solution gradually turned yellowish-green, and the rust layer on the tube sample surface gradually loosened and fell off.

[0046] After 5 hours of soaking, the tube sample was removed with tweezers, and the surface residual cleaning agent was quickly rinsed with deionized water. The surface moisture was then absorbed with filter paper, and the sample was immediately weighed using an electronic balance. The weight of the tube sample after 5 hours of soaking was 107.1626 grams.

[0047] In this embodiment, subsequent detection and observation are as follows: Cleaning efficiency calculation: The amount of dirt cleaned is the weight before cleaning minus the weight after soaking, i.e., 108.7858 grams minus 107.1626 grams, which gives 1.6235 grams. The cleaning efficiency is 1.6235 grams divided by (0.009379 square meters multiplied by 5 hours), which gives 34.62 grams per square meter per hour.

[0048] Rusting observation: The cleaned tube sample was placed in a laboratory environment with normal temperature and humidity (temperature 25℃±2℃, humidity 50%±5%) and observed for nine days. After nine days, it was found that the tube sample had only a little rusting, and the degree of rusting was lighter than that in Example 1.

[0049] Waste liquid status detection: After the experiment, the waste liquid was observed to be yellow-green with a pH of about 6. The solution was stable and there was no stratification or precipitation.

[0050] In summary, this embodiment, using a 5% concentration of diammonium citrate cleaning agent, achieved a cleaning efficiency of 34.62 grams per square meter per hour on carbon steel pipe samples under static immersion conditions at 65°C for 5 hours. Compared to the 3% concentration in Example 1, this represents a significant improvement in cleaning efficiency. Furthermore, after nine days, only a small amount of rust reappeared on the pipe samples, indicating that the high concentration of diammonium citrate not only improves rust removal efficiency but also helps control rust reappearance to some extent. The experimental results verify the feasibility of the 5% upper limit for diammonium citrate concentration. This method achieves good rust removal and rust reappearance control without the need for corrosion inhibitors, reducing formulation complexity and making it suitable for offline cleaning of heavily rusted carbon steel pipes.

[0051] Example 3 like Figure 1 As shown, this embodiment aims to verify the rust removal effect and corrosion rate of 20 steel using a low-concentration (2.5%) diammonium citrate neutral cleaning agent under dynamic circulation cleaning. Without the addition of corrosion inhibitors, auxiliary organic acids, or ammonium bifluoride, rusted DN50 pipes and screws were circulated and cleaned for 7 hours at room temperature. The cleaning effect, corrosion control, and rust re-emergence of the dynamic circulation method were examined. The following detailed description of the specific implementation process is provided.

[0052] In this embodiment, the experimental materials are prepared as follows: Rusty pipes and screws: Select carbon steel pipes with a diameter of DN50 and a length of about 1.8 meters. Both the inner and outer walls of the pipes have obvious rust layers. At the same time, select several rusty carbon steel screws of the same material as the pipes to ensure the representativeness of the experimental subjects.

[0053] Indicator Plate: 20 steel was selected as the indicator plate, a material similar to that of carbon steel pipes, and it is used to detect the corrosion rate of the cleaning agent. The indicator plate measures 12 mm × 40 mm × 3 mm and has two 4 mm diameter holes. Its surface area was calculated to be 13.22 square centimeters using dimensional measurements. Weighing it using an electronic balance (accuracy 0.0001 g) yielded a weight of 8.0106 grams for the indicator plate before cleaning (using 2200 cleaning agent).

[0054] Cleaning agent ingredients: diammonium hydrogen citrate solid reagent (industrial grade purity), deionized water.

[0055] Experimental equipment: two circulating pumps of similar specifications, pipe fittings, seals, a 20 kg capacity liquid storage tank, an electronic balance, vernier calipers, and a stirring rod. Before the experiment, the circulating pumps, pipes, and liquid storage tank were cleaned to remove internal impurities and oil stains.

[0056] In this embodiment, the cleaning agent is prepared as follows: Based on a diammonium citrate concentration ranging from 2% to 5% by mass, a concentration of 2.5% was selected for preparation. Accurately weigh 500 grams of solid diammonium citrate and add it to a storage tank containing 20 kilograms of deionized water. Turn on the built-in stirrer in the storage tank and stir at a speed of 50 revolutions per minute for 30 minutes until the solid is completely dissolved and the solution is transparent.

[0057] The pH value of the solution was measured and found to be between 5 and 6.

[0058] In this embodiment, the cleaning operation steps are as follows: Circulation loop setup: Connect the two circulation pumps, the storage tank, and the DN50 rusted pipe using pipe fittings to form a closed circulation loop, ensuring that all connections are well-sealed and leak-free. Insert the rusted screws inside the pipe, and simultaneously fix the 20mm steel indicator plate (2200mm) in the middle of the pipe, ensuring that the indicator plate is in full contact with the flowing cleaning agent.

[0059] Dynamic circulation cleaning: The circulation pump was turned on and the flow rate was adjusted to allow the cleaning agent to circulate in the loop. The experiment was conducted at room temperature (25℃±2℃) without additional heating. Due to the pipe placement angle, the cleaning solution did not achieve full pipe flow, and some pipe inner walls were not completely covered by the cleaning agent.

[0060] Cleaning time control: The circulating cleaning lasted for 7 hours. During this period, the operating status of the circulating pump, the color change of the solution, and the internal condition of the pipeline were observed every hour. It was found that the solution gradually turned light yellow and some floating rust flowed with the solution.

[0061] Post-cleaning treatment: After 7 hours of circulating cleaning, turn off the circulating pump, disassemble the pipes, remove the screws and indicator plates, rinse the surface with deionized water to remove residual cleaning agent, absorb the moisture with filter paper, and weigh and observe the condition.

[0062] In this embodiment, subsequent detection and observation are as follows: Cleaning effect observation: The removed screws still had some loose rust. The rust layer in the area where the cleaning agent flowed through the pipe wall was reduced, but there was still residual rust. The rust layer in the area where the agent did not flow through remained basically unchanged. Overall, the cleaning effect was average.

[0063] Corrosion rate calculation: The indicator plate 2200 weighs 7.9943 grams after cleaning. The weight loss due to corrosion is 8.0106 grams. Subtracting 7.9943 grams gives 0.0163 grams. The corrosion rate is 1.80 grams per square meter per hour, which meets the industrial safety standard requirement of ≤6 grams per square meter per hour.

[0064] Rusting observation: After cleaning, the screws, pipes and indicator plates were placed in a laboratory environment with normal temperature and humidity. After two days, a lot of rusting was observed.

[0065] Waste liquid status detection: After the experiment, the waste liquid was light yellow and the pH value was still between 5 and 6.

[0066] In summary, this embodiment used a 2.5% concentration of diammonium hydrogen citrate cleaning agent to remove rust from DN50 carbon steel pipes and screws under dynamic circulation cleaning conditions at room temperature for 7 hours. Although the cleaning effect was only moderate due to the incomplete full-pipe flow of the cleaning solution, the corrosion rate was controlled at 5.72 grams per square meter per hour, which meets industrial safety standards, verifying the feasibility of the dynamic circulation cleaning method. The experimental results show that under the dynamic circulation cleaning method, the flow state of the cleaning agent has a significant impact on the cleaning effect. Full-pipe flow ensures that the inner wall of the pipe is fully in contact with the cleaning agent, improving the rust removal effect. It also indicates that without the addition of corrosion inhibitors and ammonium hydrogen fluoride, the rust return phenomenon is relatively obvious, providing a reference for subsequent formulation optimization.

[0067] Example 4 like Figure 1 As shown, this embodiment aims to verify the rust removal effect and corrosion impact on 20 steel of a 3% concentration diammonium hydrogen citrate neutral cleaning agent containing ammonium bifluoride under a combined dynamic circulation and static soaking treatment. Ammonium bifluoride was added as an auxiliary component. After 7 hours of circulating cleaning of DN50 pipes and screws at room temperature, they were then statically soaked for 15 hours. The focus was on examining the effect of ammonium bifluoride in improving the rust removal effect and the change in corrosion rate. The following detailed description is provided in conjunction with the specific implementation details.

[0068] In this embodiment, the experimental materials are prepared as follows: Rusty pipes and screws: A carbon steel pipe with a diameter of DN50 and a length of about 2.08 meters was selected. The inner wall of the pipe had a thick rust layer. At the same time, several rusty carbon steel screws of the same material were selected to ensure that the experimental object was similar to the rust condition of the actual industrial pipe.

[0069] Indicator plate: A 20 steel indicator plate with dimensions of 13 mm × 40 mm × 2 mm is selected. It has two round holes with a diameter of 4 mm. The calculated surface area is 12.77 square centimeters. The indicator plate 2169 weighs 8.0408 grams before cleaning when weighed by an electronic balance (accuracy 0.0001g).

[0070] Cleaning agent ingredients: diammonium hydrogen citrate solid reagent (industrial grade purity), ammonium hydrogen fluoride solid reagent (industrial grade purity), deionized water.

[0071] Experimental equipment: two identical circulating pumps, pipe fittings, seals, a 50 kg capacity liquid storage tank, an electronic balance, vernier calipers, and a stirring rod. The equipment was cleaned and ready for use.

[0072] In this embodiment, the cleaning agent is prepared as follows: According to the formula, accurately weigh 1500g of diammonium hydrogen citrate solid and 7.5g of ammonium hydrogen fluoride solid, and add them simultaneously to a storage tank containing 50kg of deionized water. Turn on the stirring device of the storage tank and stir at a speed of 50 revolutions per minute for 40 minutes to ensure that the two solids are completely dissolved, the solution is uniformly mixed, and there is no precipitation or stratification.

[0073] The pH value of the solution was measured and found to be between 6 and 7.

[0074] In this embodiment, the cleaning operation steps are as follows: Establishing the circulation loop: Connect the two circulation pumps, the storage tank, and the DN50 rusted pipe using pipe fittings to form a closed circulation loop, ensuring a leak-free connection. Insert the rusted screw into the pipe, and fix the indicator plate 2169 in the middle of the pipe to ensure it is in full contact with the cleaning agent.

[0075] Dynamic circulation cleaning: Turn on the circulation pump and adjust the flow rate to ensure the cleaning agent flows throughout the pipe. Perform circulation cleaning at room temperature (25℃±2℃) for 7 hours. Observe every 1.5 hours during this period. The solution gradually turns dark green, and the rust layer peeling off is more obvious than in Example 3.

[0076] Soaking procedure: After 7 hours of circulating cleaning, turn off the circulation pump, keep the cleaning agent in the pipeline submerged in the pipeline, screws, and indicator plates, and let it stand for 15 hours.

[0077] Post-cleaning treatment: After the static soaking is completed, disassemble the pipe, remove the screws and indicator plates, rinse them with deionized water, absorb the moisture with filter paper, and weigh and observe the condition.

[0078] In this embodiment, subsequent detection and observation are as follows: Cleaning effect observation: After 7 hours of circulation, the screws had a small amount of surface rust, the pipe cleaning effect was average, and there was still a lot of residual rust; after 15 hours of standing soaking, the screws no longer had surface rust, but there was still a lot of residual rust on the inner wall of the pipe. Although the cleaning effect was improved, it did not reach the ideal state.

[0079] Corrosion rate calculation: The indicator plate 2169 weighs 7.9850 grams after cleaning. The weight loss due to corrosion is 8.0408 grams. Subtracting 7.9850 grams from this gives 0.0558 grams. The corrosion rate is 2.50 grams per square meter per hour, which meets the industrial safety standard requirement of ≤6 grams per square meter per hour.

[0080] Waste liquid status detection: After the experiment, the waste liquid was dark green, the pH value was around 7, and the solution was stable.

[0081] In summary, this embodiment uses a cleaning agent formulation of 3% diammonium citrate and 7.5 grams of ammonium bifluoride. A combined treatment method of 7 hours of dynamic circulation at room temperature followed by 15 hours of static soaking was used to remove rust from DN50 carbon steel pipes and screws. The addition of ammonium bifluoride improved the rust removal effect to some extent, but it led to a significantly excessive corrosion rate on the 20 steel, indicating that the amount of ammonium bifluoride added needs to be strictly controlled; excessive addition will exacerbate metal corrosion. Experimental results verified the effectiveness of ammonium bifluoride concentrations in the range of 0.01% to 0.1%. Further optimization of the formulation within this concentration range is needed, and the use of corrosion inhibitors could be considered to control corrosion risks.

[0082] Example 5 like Figure 1 As shown, this embodiment aims to verify the rust removal effect and corrosion control of 15CrMo steel by a neutral cleaning agent composed of high-concentration (4%) diammonium citrate and an appropriate ratio of ammonium bifluoride under dynamic circulation and static immersion conditions. Appropriate dosages of ammonium bifluoride were selected according to the ammonium bifluoride concentration range, and DN80 pipes and screws were treated at room temperature. The focus was on examining the adaptability of this formulation to alloy steel materials and its corrosion rate control effect, further demonstrating the rationality of the formulation composition.

[0083] In this embodiment, the experimental materials are prepared as follows: Rusty pipes and screws: Select DN80 15 chromium-molybdenum steel pipes with a length of about 3 meters. This material is one of the chromium-molybdenum steel types. The inner wall of the pipe has obvious rust and oxide scale. At the same time, select several rusty screws of the same material.

[0084] Indicator plate: 15CrMo steel indicator plate 1530 is selected, with dimensions of 10 mm × 50 mm × 2 mm. It has two round holes with a diameter of 4 mm. The calculated surface area is 12.65 square centimeters. The weight before cleaning is 8.3450 grams when weighed by an electronic balance (accuracy 0.0001g).

[0085] Cleaning agent ingredients: diammonium hydrogen citrate solid reagent (industrial grade purity), ammonium hydrogen fluoride solid reagent (industrial grade purity), deionized water.

[0086] Experimental equipment: two identical circulating pumps, pipe fittings, seals, a 70 kg capacity liquid storage tank, an electronic balance, vernier calipers, and a stirring rod. The equipment was cleaned and dried.

[0087] In this embodiment, the cleaning agent is prepared as follows: According to the formula, accurately weigh 2800 grams of diammonium hydrogen citrate solid and 28 grams of ammonium hydrogen fluoride solid, and add them to a storage tank containing 70 kilograms of deionized water. Turn on the stirring device and stir at a speed of 55 revolutions per minute for 40 minutes until both solids are completely dissolved, the solution is uniformly mixed, and it is transparent.

[0088] The pH value of the solution was measured and found to be approximately 6.

[0089] In this embodiment, the cleaning operation steps are as follows: Circulation loop setup: Use pipe fittings to connect the circulation pump, storage tank, and DN80 rusted pipe to form a closed circulation loop, ensuring that all connections are well-sealed and leak-free. Insert the rusted screws inside the pipe, and fix the 15CrMo steel indicator plate 1530 in the middle position between the pipe inlet and outlet, ensuring that the indicator plate is in full contact with the flowing cleaning agent.

[0090] Dynamic circulation cleaning: The circulation pump was turned on, and the flow rate was adjusted to ensure that the cleaning agent flowed fully in the pipeline. The experiment was conducted at room temperature (25℃±2℃) and the circulation cleaning was carried out continuously for 7 hours. During this period, the solution was observed every hour. The solution gradually turned light yellow, and the rust and oxide scale gradually fell off.

[0091] Soaking procedure: After 7 hours of circulating cleaning, turn off the circulating pump, keep the cleaning agent in the pipeline submerged in the pipeline, screws, and indicator plates, and let it soak for 15 hours.

[0092] Post-cleaning treatment: After the static soaking is completed, disassemble the pipe, remove the screws and indicator plates, rinse the surface with deionized water to remove residual cleaning agent, absorb the moisture with filter paper, and weigh and observe the condition.

[0093] In this embodiment, subsequent detection and observation are as follows: Cleaning effect observation: After 7 hours of circulation, there was little rust on the screws, the pipe cleaning effect was very good, and there was basically no rust; after 15 hours of static soaking, the cleaning effect of the pipe inlet and outlet parts was good, there was no obvious rust layer and oxide scale residue on the inner wall, and the screw surface was clean and rust-free.

[0094] Corrosion rate calculation: The indicator plate 1530 weighs 8.3181 grams after cleaning, with a corrosion weight loss of 0.0200 grams. The corrosion rate is 1.00 grams per square meter per hour, which meets the industrial safety standard requirement of ≤6 grams per square meter per hour.

[0095] Waste liquid status detection: After the experiment, the waste liquid was light yellow, with a pH value of about 6 and no obvious impurities precipitated.

[0096] In summary, this embodiment utilizes a cleaning agent formulation of 4% diammonium citrate and 28 grams of ammonium bifluoride. Through a combined treatment method of 7 hours of dynamic circulation at room temperature followed by 15 hours of static soaking, excellent rust removal was achieved on DN8015 chromium-molybdenum steel pipes and screws. The corrosion rate was controlled at 3.54 grams per square meter per hour, far below industrial safety standards, verifying the good adaptability of this formulation to chromium-molybdenum steel and demonstrating the rationality of the 0.03% to 0.05% concentration range of ammonium bifluoride. This method effectively removes rust and scale from the inner wall of pipes with minimal corrosion to the metal substrate, making it suitable for online rust removal of 15 chromium-molybdenum steel industrial pipes.

[0097] Example 6 like Figure 1 As shown, this embodiment aims to verify the rust removal effect and corrosion impact on stainless steel of a 3% concentration diammonium hydrogen citrate neutral cleaning agent containing auxiliary organic acid (citric acid) and ammonium hydrogen fluoride under dynamic circulation and static immersion conditions. Citric acid was added as an auxiliary component according to the range of auxiliary organic acid addition, and DN80 pipes and screws were treated at room temperature. The adaptability of this formula to 304 and 316 stainless steel was examined to ensure its effectiveness in applying to various metal materials.

[0098] In this embodiment, the experimental materials are prepared as follows: Rusty pipes and screws: A carbon steel pipe with a diameter of DN80 and a length of about 6 meters was selected, with a thick rust layer on the inner wall of the pipe; at the same time, several rusty carbon steel screws of the same material were selected to ensure that the rust state of the experimental objects was representative.

[0099] Indicator plates: 304 stainless steel indicator plates 5030 and 316 stainless steel indicator plates 6012 are used. Both indicator plates measure 10 mm × 50 mm × 2 mm, with two 4 mm diameter holes, and a calculated surface area of ​​12.65 square centimeters for each. Weighing was performed using an electronic balance (accuracy 0.0001 g). Before cleaning, indicator plate 5030 weighed 9.5148 grams, and indicator plate 6012 weighed 7.9430 grams.

[0100] Cleaning agent ingredients: diammonium hydrogen citrate solid reagent (industrial grade purity), citric acid solid reagent (industrial grade purity, used as an auxiliary organic acid), ammonium hydrogen fluoride solid reagent (industrial grade purity), and deionized water.

[0101] Experimental equipment: two identical circulating pumps, pipe fittings, seals, a 100 kg capacity liquid storage tank, an electronic balance, vernier calipers, and a stirring rod. The equipment was cleaned and ready for use.

[0102] In this embodiment, the cleaning agent is prepared as follows: According to the formula, accurately weigh 2850 grams of diammonium hydrogen citrate solid, 150 grams of citric acid solid, and 30 grams of ammonium hydrogen fluoride solid, and add them simultaneously to a storage tank containing 100 kilograms of deionized water. Turn on the stirring device of the storage tank and stir at a speed of 50 revolutions per minute for 45 minutes to ensure that the three solids are completely dissolved, the solution is uniformly mixed, and there is no precipitation or stratification.

[0103] The pH value of the solution was measured and found to be approximately 6.

[0104] In this embodiment, the cleaning operation steps are as follows: Circulation loop setup: Use pipe fittings to connect the circulation pump, storage tank, and DN80 rusted pipe to form a closed circulation loop, ensuring a leak-free connection. Place the rusted screws inside the pipe, and fix 304 stainless steel indicator plates (5030) and 316 stainless steel indicator plates (6012) at both ends inside the pipe, ensuring that the indicator plates are in full contact with the flowing cleaning agent.

[0105] Dynamic circulation cleaning: The circulation pump was turned on, and the flow rate was adjusted to ensure that the cleaning agent flowed fully in the pipeline. The experiment was conducted at room temperature (25℃±2℃) and the circulation cleaning was carried out continuously for 7 hours. During this period, the solution was observed every 1.5 hours. The solution gradually turned yellow-green, and the rust layer continued to peel off.

[0106] Soaking procedure: After 7 hours of circulating cleaning, turn off the circulating pump, keep the cleaning agent in the pipeline submerged in the pipeline, screws, and indicator plates, and let it soak for 15 hours.

[0107] Post-cleaning treatment: After the static soaking is completed, disassemble the pipe, remove the screws and two indicator plates, rinse them with deionized water, absorb the moisture with filter paper, and weigh and observe the condition.

[0108] In this embodiment, subsequent detection and observation are as follows: Cleaning effect observation: After 7 hours of circulation, there was still a small amount of surface rust on the screws and a large amount of rust inside the pipes; after 15 hours of standing soaking, the pipe cleaning effect was acceptable, most of the rust layer on the inner wall was removed, a small amount of stubborn rust remained, and the surface rust on the screws was basically removed.

[0109] Corrosion rate calculation: Indicator 5030 weighed 9.5145 grams after cleaning, with a corrosion weight loss of 0.0003 grams; Indicator 6012 weighed 7.9429 grams after cleaning, with a corrosion weight loss of 0.0001 grams. The corrosion rates of both indicators were negligible, proving that the cleaning agent has no significant corrosive effect on 304 and 316 stainless steel.

[0110] Waste liquid status detection: After the experiment, the waste liquid was yellow-green, with a pH of about 6. The solution was stable and there was no impurity precipitation.

[0111] In summary, this embodiment employs a cleaning agent formulation consisting of 3% diammonium citrate, 150 grams of citric acid-assisted organic acid, and 30 grams of ammonium bifluoride. Through a combined treatment method of 7 hours of dynamic circulation at room temperature followed by 15 hours of static soaking, a good rust removal effect was achieved on DN80 carbon steel pipes and screws. Simultaneously, the corrosion rate of this formulation on 304 and 316 stainless steel is negligible, verifying the cleaning agent's suitability for stainless steel pipes and demonstrating broad applicability to various metal materials such as carbon steel and stainless steel. The addition of the auxiliary organic acid further optimizes the rust removal effect and does not corrode sensitive metal materials, expanding the application range of the cleaning agent.

[0112] Example 7 like Figure 1 As shown, this embodiment aims to verify the rust removal effect and corrosion control of 12CrMo steel using a 3% concentration diammonium hydrogen citrate neutral cleaning agent containing auxiliary organic acid (citric acid) and an appropriate proportion of ammonium hydrogen fluoride under dynamic circulation and static immersion conditions. The components were compounded according to the formula ratio and treated on DN80 pipes and screws at room temperature. The focus was on examining the adaptability of this formula to 12CrMo steel and its corrosion rate control. The following detailed description of the specific implementation process is provided.

[0113] In this embodiment, the experimental materials are prepared as follows: Rusty pipes and screws: Select a DN80 12CrMo steel pipe with a length of about 3 meters. This material is one of the chromium-molybdenum steel types. The inner wall of the pipe has a rust layer and a small amount of oxide scale. At the same time, select several rusty screws of the same material to ensure that the experimental materials meet the requirements.

[0114] Indicator plate: 12CrMo steel indicator plate 1230 is selected, with dimensions of 10 mm × 50 mm × 2 mm. It has two round holes with a diameter of 4 mm. The calculated surface area is 12.65 square centimeters. The weight before cleaning is 8.0735 grams when weighed by an electronic balance (accuracy 0.0001g).

[0115] Cleaning agent ingredients: diammonium hydrogen citrate solid reagent (industrial grade purity), citric acid solid reagent (industrial grade purity, with auxiliary organic acid), ammonium hydrogen fluoride solid reagent (industrial grade purity), and deionized water.

[0116] Experimental equipment: two identical circulating pumps, pipe fittings, seals, a 70 kg capacity liquid storage tank, an electronic balance, vernier calipers, and a stirring rod. The equipment was cleaned and dried.

[0117] In this embodiment, the cleaning agent is prepared as follows: According to the formula, accurately weigh 1995 grams of diammonium hydrogen citrate solid, 105 grams of citric acid solid, and 21 grams of ammonium hydrogen fluoride solid, and add them to a storage tank containing 70 kilograms of deionized water. Turn on the stirring device and stir at a speed of 55 revolutions per minute for 40 minutes until the three solids are completely dissolved, the solution is uniformly mixed, and it is transparent and pale yellow.

[0118] The pH value of the solution was measured and found to be approximately 6.

[0119] In this embodiment, the cleaning operation steps are as follows: Circulation loop setup: Connect the circulation pump, storage tank, and DN80 rusted pipe using pipe fittings to form a closed circulation loop, ensuring good sealing at all connections and no leakage. Insert the rusted screws inside the pipe, and fix the 12CrMo steel indicator 1230 in the middle of the pipe, ensuring that the indicator is in full contact with the flowing cleaning agent.

[0120] Dynamic circulation cleaning: The circulation pump was turned on, and the flow rate was adjusted to ensure that the cleaning agent flowed fully in the pipeline. The experiment was conducted at room temperature (25℃±2℃) and the circulation cleaning was carried out continuously for 7 hours. During this period, the solution was observed every hour. The solution gradually turned yellow-green, and the rust layer gradually loosened and fell off.

[0121] Soaking procedure: After 7 hours of circulating cleaning, turn off the circulating pump, keep the cleaning agent in the pipeline submerged in the pipeline, screws, and indicator plates, and let it soak for 15 hours.

[0122] Post-cleaning treatment: After the static soaking is completed, disassemble the pipe, remove the screws and indicator plates, rinse the surface with deionized water to remove residual cleaning agent, absorb the moisture with filter paper, and weigh and observe the condition.

[0123] In this embodiment, subsequent detection and observation are as follows: Cleaning effect observation: After 7 hours of circulation, there was very little rust on the screws, but there was still a lot of rust inside the pipe; after 15 hours of standing soaking, the cleaning effect inside the pipe was good, and there was basically no rust, and the screw surface was clean and rust-free.

[0124] Corrosion rate calculation: The indicator plate 1230 weighs 8.0670 grams after cleaning. The weight loss due to corrosion is 8.0735 grams minus 8.0670 grams, resulting in 0.0065 grams. The corrosion rate is 0.80 grams per square meter per hour, which is far below the industrial safety standard and causes minimal corrosion to 12CrMo steel.

[0125] Waste liquid status detection: After the experiment, the waste liquid was yellow-green with a pH of about 6 and no obvious precipitation or stratification.

[0126] In summary, this embodiment employs a cleaning agent formulation consisting of 3% diammonium citrate, 105 grams of citric acid-assisted organic acid, and 21 grams of ammonium bifluoride. Through a combined treatment method of 7 hours of dynamic circulation at room temperature followed by 15 hours of static soaking, excellent rust removal was achieved on DN8012 chromium-molybdenum steel pipes and screws, leaving virtually no rust residue on the pipe's inner wall. Although the corrosion rate on 12 chromium-molybdenum steel is slightly higher than industrial safety standards, this rate can be effectively controlled by adding corrosion inhibitors, validating the suitability of this material for 12 chromium-molybdenum steel. This solution enhances the rust removal effect through the synergistic effect of the auxiliary organic acid and ammonium bifluoride, and the formulation is mild with environmentally friendly waste liquid, demonstrating promising practical application prospects.

[0127] Comparative Example like Figure 3 As shown, this comparative example uses a commonly used strong acid cleaning solution (hydrochloric acid cleaning agent) in the prior art, and compares it with the neutral cleaning agent of the present invention to examine the rust removal efficiency, corrosion rate, rust recurrence and environmental friendliness of the waste liquid of the strong acid cleaning agent, highlighting the advantages of the neutral cleaning agent of the present invention in terms of safety, environmental protection and corrosion control. The following is a detailed description in conjunction with the specific implementation content.

[0128] In this comparative example, the experimental materials were prepared as follows: Metal tube sample: A carbon steel tube sample of the same material and specifications as in Example 2 was selected to ensure fairness in the comparison. The tube sample weighed 108.7632 grams before cleaning, and the total surface area was 93.78 square centimeters. The measurement method was the same as in Example 2.

[0129] Cleaning agent ingredients: hydrochloric acid (industrial grade, concentration 37%), deionized water, and a 5% concentration hydrochloric acid cleaning agent is prepared according to the commonly used ratios in existing technology.

[0130] Experimental equipment: 500 ml beaker, constant temperature water bath, electronic balance, vernier caliper, stirring rod, acid-resistant gloves, safety glasses and other safety protection equipment. The equipment should be cleaned and ready for use.

[0131] In this comparative example, the cleaning agent was prepared as follows: Accurately measure 50 ml of 37% hydrochloric acid and slowly add it to a beaker containing 450 ml of deionized water while stirring at a speed of 40 revolutions per minute to prevent the gas produced by the evaporation of hydrochloric acid from accumulating. This will prepare a 5% hydrochloric acid cleaning solution that is transparent and colorless.

[0132] The pH value of the solution was measured and found to be less than 1, indicating that it is strongly acidic.

[0133] In this comparative example, the cleaning operation steps are as follows: Turn on the constant temperature water bath and set the temperature to 65℃. After the water temperature stabilizes at 65℃±1℃, place the beaker containing hydrochloric acid cleaning agent into the water bath.

[0134] Wearing acid-resistant gloves and protective goggles, the carbon steel tube sample was slowly placed into the hydrochloric acid cleaning solution, ensuring complete immersion. Timing was started, and the sample was statically immersed for 5 hours, consistent with the immersion time in Example 2. During the immersion process, the solution rapidly turned yellowish-brown, and numerous bubbles were observed to be generated; the rust layer on the tube sample surface quickly peeled off.

[0135] After 5 hours of soaking, the tube sample was immediately removed with tweezers and rinsed with plenty of deionized water to remove any remaining hydrochloric acid cleaning agent until the pH of the rinsing solution was close to neutral. Then, the surface moisture of the tube sample was dried with filter paper and weighed using an electronic balance. The weight of the tube sample after 5 hours of soaking was 106.9875 grams.

[0136] In this comparative example, the subsequent tests and observations are as follows: Cleaning efficiency calculation: The amount of dirt cleaned is 108.7632 grams minus 106.9875 grams, resulting in 1.7757 grams. The cleaning efficiency is 1.7757 grams divided by (0.009378 square meters multiplied by 5 hours), which yields 38.25 grams per square meter per hour. This rust removal efficiency is higher than that of Example 2 of this invention.

[0137] Corrosion rate test: A 20 steel indicator sheet of the same specifications as in Example 3 was selected. Before cleaning, its weight was 8.0095 grams and its surface area was 13.21 square centimeters. It was immersed in the aforementioned hydrochloric acid cleaning agent at 65°C for 5 hours, then removed, rinsed, and dried. The weight was 7.8231 grams, with a corrosion weight loss of 0.3000 grams. The corrosion rate was 45.00 grams per square meter per hour, far exceeding the industrial safety standard requirement of ≤6 grams per square meter per hour, indicating extremely severe corrosion of the metal substrate.

[0138] Rusting observation: After cleaning, the tube sample was placed in a laboratory environment with normal temperature and humidity. After 2 days, severe rusting was observed on the surface of the tube sample, and the rust layer thickness was much greater than that of the embodiment of the present invention.

[0139] Waste liquid status and treatment: After the experiment, the waste liquid is yellowish-brown, contains a large amount of iron ions, has a pH value of less than 1, and is highly corrosive and polluting. It needs to be treated in a complex manner such as neutralization and precipitation before it can be discharged. The treatment cost is high and there are environmental risks.

[0140] Impact of the metal matrix: Observation of the tube sample surface revealed overwashing in some areas, uneven gloss of the metal matrix, and a risk of hydrogen embrittlement. Long-term use may lead to a decrease in pipe strength and cause safety accidents.

[0141] In summary, while the rust removal efficiency of this comparative example, using a 5% concentration hydrochloric acid cleaning agent from the prior art, was higher than that of Example 2 of this invention under static immersion at 65°C for 5 hours, the corrosion rate far exceeded industrial safety standards. Furthermore, the pipe sample experienced rapid rust re-rusting, posing a risk of over-washing and hydrogen embrittlement to the metal substrate. The waste liquid also caused severe pollution and was difficult to treat. Compared to the neutral cleaning agent of this invention, the existing strong acid cleaning methods have significant disadvantages in terms of safety, environmental friendliness, and protection of the metal substrate. This further highlights the technical advantages of the neutral cleaning agent of this invention in balancing highly efficient rust removal with extremely low corrosion, environmental friendliness, and ease of treatment.

[0142] To more clearly illustrate the key parameters and core effects of each embodiment and comparative example, the following table summarizes and explains them:

[0143] As shown in the table above, the embodiments of the present invention, by rationally adjusting the proportions of diammonium citrate, ammonium bifluoride, auxiliary organic acid, and corrosion inhibitor, and combining static immersion or dynamic circulation methods, effectively remove rust from various metal pipes such as carbon steel, chromium-molybdenum steel, and stainless steel under mild pH conditions. In most embodiments, the corrosion rate is controlled within industrial safety standards; while in some embodiments the corrosion rate slightly exceeds these standards, it can be optimized by adding corrosion inhibitors. The waste liquid is neutral or near-neutral, with stable color, and is environmentally friendly and easy to treat. Compared to the strong acid cleaning agent in the comparative examples, the neutral cleaning agent of the present invention has significant advantages in corrosion control, rust inhibition, and environmental friendliness, and its rust removal efficiency meets actual industrial needs, fully verifying the rationality and feasibility of the technical solution of the present invention.

[0144] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A neutral cleaning agent for removing rust from chemical pipelines, characterized in that, It consists of the following components by mass percentage: Diammonium hydrogen citrate 2% to 5%; Ammonium bifluoride 0.01% to 0.1%; The remainder is water; The cleaning agent is formulated to act on the inner wall of metal pipes through a circulating cleaning method under conditions of pH value of 5 to 7 and temperature of room temperature to 70°C.

2. The neutral cleaning agent for removing rust from chemical pipelines according to claim 1, characterized in that, The mass percentage concentration of the diammonium citrate is 3% to 5%.

3. The neutral cleaning agent for rust removal from chemical pipelines according to claim 1, characterized in that, The mass percentage concentration of the ammonium bifluoride is 0.03% to 0.05%.

4. The neutral cleaning agent for rust removal from chemical pipelines according to claim 1, characterized in that, The cleaning agent has a pH of approximately 6 when in use.

5. The neutral cleaning agent for rust removal from chemical pipelines according to claim 1, characterized in that, It also includes a corrosion inhibitor, wherein the corrosion inhibitor has a mass percentage concentration of 0.1% to 0.3%.

6. The neutral cleaning agent for removing rust from chemical pipelines according to claim 1, characterized in that, It also includes an auxiliary organic acid, wherein the auxiliary organic acid has a mass percentage concentration of 0.1% to 0.3%, and the auxiliary organic acid is citric acid.

7. A method of using a neutral rust-removing cleaning agent for chemical pipelines, applicable to the neutral rust-removing cleaning agent for chemical pipelines as described in any one of claims 1 to 6, characterized in that, The specific steps of this method are as follows: Step 1: Contact the metal pipe components or system to be cleaned with the cleaning agent; Step two: Control the temperature during the cleaning process within the range of room temperature to 70℃; Step 3: After cleaning, rinse the metal pipe components or system.

8. The method of using a neutral cleaning agent for rust removal in chemical pipelines according to claim 7, characterized in that, In step one, the specific method of bringing the metal pipe component or system to be cleaned into contact with the cleaning agent is static immersion. The temperature of the static immersion is 60°C to 70°C; The static soaking time is 5 to 12 hours.

9. The method of using a neutral cleaning agent for rust removal in chemical pipelines according to claim 7, characterized in that, In step one, the specific method of bringing the metal pipe component or system to be cleaned into contact with the cleaning agent is dynamic circulation cleaning. The dynamic cyclic cleaning is performed at room temperature. The dynamic cyclic cleaning time is 7 to 16 hours; After the dynamic cyclic cleaning, a static soaking step is also included, and the static soaking time is 8 to 15 hours.

10. The method of using a neutral cleaning agent for rust removal in chemical pipelines according to claim 7, characterized in that, In step three, the material of the metal pipe component or system includes at least one of carbon steel, chromium-molybdenum steel, and stainless steel. The chromium-molybdenum steel is either 15-chromium-molybdenum steel or 12-chromium-molybdenum steel; The stainless steel is 304 stainless steel or 316 stainless steel; The cleaning agent is used to remove rust from an online industrial pipeline system made of the material in a dynamic circulation cleaning process, and the cleaning agent flows in a full-pipe flow state.

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