A method for processing a large-diameter seamless steel pipe

Abstract

The application discloses a processing method for large-diameter seamless steel pipes, which comprises a phosphorus saponification treatment step for the steel pipes, and the phosphorus saponification treatment step comprises the following steps: steel pipe pretreatment, phosphating treatment, saponification treatment, and concentration control of saponification liquid in the saponification treatment process through an automatic monitoring system, which performs the following operations: extracting part of the saponification liquid sample from the saponification tank, detecting the pH value of the sample and comparing it with a preset pH threshold value, and automatically adding a predetermined amount of saponification agent concentrate into the saponification tank to improve the overall concentration of the saponification liquid when the pH value of the sample is lower than the preset pH threshold value. The application can monitor and adjust the saponification liquid concentration in real time, accurately and automatically, overcome the defects of the prior art, such as dependence on manual operation, large hysteresis and poor precision, and guarantee the stable cold-drawing production of the large-diameter seamless steel pipes and the continuous improvement of the surface quality of the products.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe production technology, and specifically to a processing method for large-diameter seamless steel pipes. Background Technology

[0002] Against the backdrop of accelerated global energy structure transformation and the continuous expansion of clean energy applications, the research and development of large-diameter seamless steel pipes for Type II cylinders carries the important mission of promoting technological innovation in the industry and ensuring energy security. With the continued deepening of natural gas resource development, compressed natural gas, as a highly efficient and clean energy carrier, places higher demands on container materials during its transportation and storage. Currently, gas cylinders for trailer-mounted applications are key equipment for energy transportation, and the performance of their core raw material—large-diameter seamless steel pipes—directly affects the stability and security of the energy supply chain.

[0003] Cold drawing (or cold rolling) is a key plastic processing technology for producing high-precision, high-strength, and high-surface-quality seamless steel pipes. In this process, to reduce friction between the die and the steel pipe, prevent surface scratches and breakage, and reduce drawing force, the steel pipe must be adequately lubricated before drawing. Phosphate saponification is currently the most effective and widely used lubrication pretreatment method.

[0004] Phosphating and saponification mainly consist of two key steps: phosphating and saponification. Saponification involves immersing the phosphated steel pipe in a saponification solution (usually an aqueous solution of metal soaps such as sodium stearate), causing a saponification film to adhere to its surface. This saponification film melts under the high temperature and pressure of the drawing deformation zone, forming a strong solid lubricating film that separates the steel pipe from the mold, thus achieving efficient lubrication.

[0005] The effective concentration of the saponification solution is a core process parameter that determines the quality of the saponification film, and consequently, the surface quality of the steel pipe and the success or failure of production. If the concentration is too low, a complete and effective lubricating film cannot be formed, leading to defects such as scratches, roughening, or even "steel sticking" on the inner and outer surfaces of the steel pipe. This significantly reduces the yield and accelerates mold wear, shortening its lifespan. If the concentration is too high, it not only wastes saponifying agent and increases production costs, but may also result in an excessively thick and porous saponification film that accumulates during drawing, similarly affecting the surface quality of the steel pipe and potentially clogging the circulation pipeline.

[0006] Currently, in industrial production, the control of saponification solution concentration mainly relies on manual operation. This involves operators periodically sampling the saponification tank, determining the concentration through laboratory titration or empirical observation, and then manually adding solid saponifying agent or pre-prepared saponification mother liquor based on the results. This manual control method has many drawbacks:

[0007] 1. Significant time lag: There is a significant time delay between the change in concentration, its detection, and the completion of replenishment. During this period, the concentration of the saponification solution may have been substandard for an extended period, leading to batch-wide product quality issues.

[0008] 2. Poor control precision: It relies on human experience to judge, so the accuracy cannot be guaranteed, and the amount of supplementation is difficult to control precisely, which can easily cause excessive concentration fluctuations and make it impossible to stabilize within the optimal process window.

[0009] 3. High labor intensity and low efficiency: Frequent sampling, testing and replenishment operations are required, which increases the labor burden of workers and is not conducive to continuous and automated production. Summary of the Invention

[0010] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a processing method for large-diameter seamless steel pipes. This method can monitor and adjust the concentration of saponification liquid in real time, accurately and automatically, overcoming the defects of existing technologies such as reliance on manual labor, large lag, and poor precision, and ensuring the stable production of large-diameter seamless steel pipes and the continuous improvement of product surface quality.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0012] A method for processing large-diameter seamless steel pipes, the method including a phosphating treatment step of the steel pipe, the phosphating treatment step comprising:

[0013] Steel pipe pretreatment: The surface of the steel pipe is subjected to degreasing, water washing, pickling, and secondary water washing in sequence;

[0014] Phosphating treatment: The pre-treated steel pipe is immersed in phosphating solution for phosphating treatment to generate phosphate crystals that adhere to the surface of the steel pipe, followed by water washing and drying.

[0015] Saponification treatment: The phosphated and dried steel pipe is immersed in the saponification liquid in the saponification tank for saponification treatment to generate a saponification film on the surface of the steel pipe.

[0016] During the saponification process, the concentration of the saponification solution is controlled by an automatic monitoring system, which performs the following operations:

[0017] A portion of the saponification liquid sample was extracted from the saponification tank.

[0018] The pH value of the sample is detected and compared with a preset pH threshold;

[0019] When the pH value of the sample is lower than the preset pH threshold, a predetermined amount of saponifying agent concentrate is automatically added to the saponification tank to increase the overall concentration of the saponification solution.

[0020] Preferably, the automatic monitoring system includes a controller, a detection unit, and a replenishment unit;

[0021] The detection unit includes a detection tank and a pH electrode disposed in the detection tank. The detection tank is connected to the saponification tank through a pipeline with a first valve. The pH electrode and the second valve are both communicatively connected to the controller.

[0022] The replenishment unit includes a pre-melting tank, which is connected to the saponification tank via a pipeline with a second valve. It is also equipped with a third valve for introducing solvent and a fourth valve for introducing saponifying agent. The second valve, the third valve, and the fourth valve are all communicatively connected to the controller.

[0023] The controller is configured to: control the first valve to open, allowing a portion of the saponification liquid to flow into the detection tank, and receive the detection signal from the pH electrode; when the detected pH value is lower than a preset pH threshold, first control the third and fourth valves to open, allowing a predetermined amount of solvent and saponifying agent to be introduced into the pre-melting tank to prepare a saponifying agent concentrate of a predetermined concentration in the pre-melting tank, and then control the second valve to open, replenishing the saponifying agent concentrate of the predetermined concentration into the saponification tank.

[0024] Preferably, the automatic monitoring system further includes a first stirring device and a second stirring device;

[0025] The first stirring device is located in the pre-melting tank and is used to mix the saponifying agent and the solvent. The first stirring device includes a first power component and a first stirrer. The first power component is communicatively connected to the controller, and the first stirrer extends into the pre-melting tank.

[0026] The second stirring device is located in the saponification tank and is used to mix the saponifying agent concentrate and the saponification liquid. The second stirring device includes a second power component and a second stirrer. The second power component is communicatively connected to the controller, and the second stirrer extends into the saponification tank.

[0027] The controller is further configured to:

[0028] When the third valve and the fourth valve are open, the controller controls the first power component to start, so as to drive the first stirrer to rotate and mix the saponifying agent and the solvent;

[0029] When the second valve is opened, the controller controls the second power component to start, so as to drive the second stirrer to rotate and mix the saponifying agent concentrate and the saponifying liquid.

[0030] Preferably, when the detected pH value is lower than a preset pH threshold, the third and fourth valves are first opened to introduce a predetermined amount of solvent and saponifying agent into the pre-melting tank. The amount of saponifying agent added is calculated using the following formula:

[0031] M = [(C target - C current ) / C stock ] × V tank × ρ

[0032] In the formula: M is the amount of saponifying agent added:

[0033] C target The target concentration of the saponification solution is 5% to 10%.

[0034] C current This represents the current concentration of the saponification solution.

[0035] C stock The concentration of the saponifying agent concentrate added to the saponification tank;

[0036] V tank The effective volume of the saponification tank is expressed in liters (L).

[0037] ρ is the density of the saponification solution (kg / L).

[0038] Preferably, the controller pre-stores data on the correspondence between the pH value and concentration of the saponification solution, and this correspondence data is pre-established in the following way:

[0039] Prepare multiple standard samples of saponification solution with different known concentrations;

[0040] The pH value of each standard sample was measured using a calibrated pH electrode.

[0041] Based on the measured relationship between the pH value and the concentration of each standard sample, a pH-concentration curve is established and stored in the controller.

[0042] The controller obtains the current concentration of the saponification solution by querying the relationship curve based on the pH value detected in real time by the pH electrode.

[0043] Preferably, the preset pH threshold is determined in the following way:

[0044] Based on the pH-concentration relationship curve, find the pH range corresponding to the target concentration of the saponification solution, and set the middle or lower limit of this pH range as the preset pH threshold.

[0045] Preferably, a filter is also provided on the pipeline with the first valve, and the filter is located at the connection between the pipeline and the saponification tank.

[0046] Preferably, the solvent introduced through the third valve is hot water at a temperature of 50°C to 70°C.

[0047] Preferably, during the saponification process, the temperature of the saponification liquid is also controlled by the automatic monitoring system.

[0048] The automatic monitoring system also includes a temperature sensor and a heating device. Both the temperature sensor and the heating device are communicatively connected to the controller. The temperature sensor is located in the detection tank and is used to detect the temperature of the saponification liquid in the detection tank. The heating device is located at the bottom of the saponification tank and is used to heat the saponification liquid in the saponification tank.

[0049] The controller is also configured to: when the temperature value detected by the temperature sensor is lower than a preset temperature threshold, control the heating device to heat the saponification liquid in the saponification tank until the temperature of the saponification liquid in the saponification tank is greater than the preset temperature threshold.

[0050] Preferably, the heating device is an electric heater, which is spirally wound around the bottom of the saponification tank, and the area of ​​the electric heater wound around the bottom of the saponification tank is greater than 80% of the total area of ​​the bottom of the saponification tank.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] 1. This invention achieves real-time, precise, and automated control of saponification solution concentration: Through an automatic monitoring system consisting of a controller, a detection unit, and a replenishment unit, it completely changes the outdated mode of relying on manual, intermittent sampling and testing. This system can automatically and frequently sample and test, and trigger replenishment actions in real time according to a preset pH threshold, ensuring that the saponification solution concentration remains stable within the optimal process range, fundamentally avoiding product quality problems caused by concentration fluctuations.

[0053] 2. By introducing a pre-melting tank and using a stirring device, this invention ensures that the added saponifying agent can be fully and uniformly mixed with the solvent (preferably hot water) to form a homogeneous concentrated saponifying agent solution before being injected into the saponification tank. This effectively prevents clumping, settling, and uneven concentration caused by directly adding solid saponifying agent into the saponification tank, ensuring that each batch of steel pipes can be processed under consistent and reliable saponification conditions, thereby significantly improving the lubrication quality and consistency of the inner and outer surfaces of large-diameter seamless steel pipes.

[0054] 3. This invention frees operators from the heavy and repetitive manual sampling, testing and solution preparation work, reduces labor intensity and the risk of human error. The entire concentration maintenance process does not require manual intervention, has a high degree of automation, and ensures the continuity and stability of production, laying a key technical foundation for building a fully automated intelligent cold drawing production line.

[0055] 4. This invention indirectly characterizes the concentration by detecting the pH value of the saponification solution and combines it with an independent detection tank for sampling and measurement. This structure avoids the pH electrode being immersed in the harsh saponification tank for a long time, reducing the risk of system inaccuracy and failure. It is easy to maintain, has a long service life, and is particularly suitable for the harsh conditions of continuous industrial production.

[0056] 5. This solution can monitor and adjust the concentration of saponification solution in real time, accurately and automatically, overcoming the shortcomings of existing technologies such as reliance on manual labor, large lag, and poor precision, thus ensuring the stable production of large-diameter seamless steel pipes and the continuous improvement of product surface quality. Attached Figure Description

[0057] Appendix Figure 1 This is a flowchart of the phosphating process of the present invention;

[0058] Appendix Figure 2 This is a control block diagram of the automatic monitoring system of the present invention. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0060] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0061] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation on the embodiments. Moreover, the method and / or process should not be limited to the steps performed in the written order; those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0062] Against the backdrop of accelerated global energy structure transformation and the continuous expansion of clean energy applications, the research and development of large-diameter seamless steel pipes for Type II cylinders carries the important mission of promoting technological innovation in the industry and ensuring energy security. With the continued deepening of natural gas resource development, compressed natural gas, as a highly efficient and clean energy carrier, places higher demands on container materials during its transportation and storage. Currently, gas cylinders for trailer-mounted applications are key equipment for energy transportation, and the performance of their core raw material—large-diameter seamless steel pipes—directly affects the stability and security of the energy supply chain.

[0063] Seamless steel pipe is a long strip of steel without any seams around its perimeter. Unlike welded pipe, it is not made by rolling and welding steel plates or strips. Its "seamless" characteristic gives it significant advantages in terms of pressure resistance, uniformity, and reliability.

[0064] The main production processes for seamless steel pipes are hot rolling and cold drawing, and the core idea is to start from a solid steel billet.

[0065] The production of seamless steel pipes using the cold drawing process mainly includes the following steps:

[0066] Raw materials: Hot-rolled pipes are usually used as billets.

[0067] Pickling: Removes iron oxide scale from the surface.

[0068] Cold drawing / cold rolling: At room temperature, steel pipes are drawn or rolled using dies to undergo plastic deformation, resulting in smaller diameters, thinner wall thicknesses, and higher precision.

[0069] Heat treatment: eliminates internal stress generated during cold working and restores the plasticity and toughness of the material.

[0070] Straightening and finishing: final shaping.

[0071] Features: High dimensional accuracy, excellent surface finish, and superior mechanical properties. However, production costs are high and production cycles are long. Primarily used in precision instruments, hydraulic systems, and other fields requiring high precision and surface finish.

[0072] In the cold drawing process, an outer mold and an inner mold (mandant) are typically used to simultaneously control the inner and outer walls of the steel pipe. The outer mold is usually an extremely hard die (typically made of tungsten carbide) responsible for sizing the outer diameter of the steel pipe and reducing the wall thickness. The inner mold (mandant) is usually a precise cylindrical or micro-conical tool inserted into the steel pipe, located in the deformation zone of the outer mold, responsible for sizing the inner diameter of the steel pipe and controlling the smoothness of the inner wall. This method of simultaneously controlling the inner and outer walls of the steel pipe with both molds allows for precise control of the outer diameter, inner diameter, and wall thickness of the steel pipe, with tolerances down to the micrometer level. It also solves the problem of the "air drawing" method's inability to control the quality of the inner wall, and can produce steel pipes with equally smooth inner and outer walls.

[0073] However, during the cold drawing process, a large amount of heat is generated at the contact surface between the mold and the steel pipe. This is because when the steel pipe is forcibly pulled through the mold, the metal undergoes enormous and rapid plastic deformation. The vast majority (over 90%) of the mechanical work driving this deformation is converted into internal energy (i.e., heat). On the other hand, under extremely high surface pressure (up to 1000 MPa or more), intense relative sliding friction occurs between the outer wall of the steel pipe and the working zone inside the mold hole. This friction is directly converted into heat.

[0074] Such concentrated heat generation can cause a series of problems:

[0075] For molds, the first consequence is a decrease in hardness (tempering). This is because the hardness of mold steel (or cemented carbide) decreases after exceeding its tempering temperature, leading to rapid wear, scratching, and a shortened lifespan. Secondly, repeated heating and cooling generate alternating thermal stress inside the mold, causing thermal cracks (crazing) and ultimately mold failure. Furthermore, thermal expansion of the mold changes its internal dimensions, affecting the dimensional accuracy of the cold-drawn steel pipe.

[0076] For steel pipes, high temperatures can cause oxidation, discoloration, or even "adhesion" or "welding" to the mold, resulting in severe surface scratches. Secondly, although it is called "cold drawing," if the temperature is too high (for example, exceeding the recrystallization temperature of certain steel grades), it may cause localized annealing of the steel pipe surface or the formation of unexpected metallographic structures, affecting its mechanical properties.

[0077] Therefore, in order to reduce the friction and braking force between the mold and the steel pipe during the cold drawing process, and thus reduce the heat generated during the cold drawing process, it is often necessary to perform phosphating treatment on the surface of the steel pipe before cold drawing. The main purpose of phosphating treatment is to form a special lubricating carrier film on the surface of the steel pipe, so as to greatly reduce the friction and drawing force during the cold drawing process, while avoiding damage to the steel pipe and the mold.

[0078] Phosphating is actually two consecutive chemical processes: phosphating and saponification.

[0079] Step 1: Phosphating

[0080] Objective: To generate a porous, dense phosphate crystal film (this film is called "phosphating film") on the surface of a clean steel pipe.

[0081] Process: The steel pipe that has been pickled and derusted is immersed in a phosphating solution containing zinc phosphate, manganese phosphate and other components. Through a chemical reaction, a phosphate layer that is insoluble in water is formed on the surface of the steel.

[0082] Key features:

[0083] Adsorption: This phosphating film has a large number of microporous structures and a huge specific surface area, just like a "sponge".

[0084] Adhesion: It bonds firmly to the metal substrate and will not easily fall off during deformation.

[0085] Lubrication: It also has a certain friction-reducing effect, but its main function is not direct lubrication.

[0086] Step 2: Saponification

[0087] Objective: To allow the phosphating film to "adsorb" the lubricant.

[0088] Process: The phosphated steel pipe is immersed in a saponification solution (usually sodium fatty acid, i.e., soap).

[0089] Key response:

[0090] Physical adsorption: The soap components in the saponification solution are drawn into the micropores of the phosphating film.

[0091] Chemical transformation: More importantly, the sodium stearate in the soap solution reacts chemically with the zinc phosphate on the surface of the phosphating film to produce zinc stearate.

[0092] Zn3(PO4)2 + 6C 17 H 35 COONa → 3Zn(C 17 H 35 COO)2 + 2Na3PO4

[0093] (Zinc phosphate + sodium stearate → zinc stearate + sodium phosphate)

[0094] Zinc stearate is a solid lubricant with extremely high performance.

[0095] The combined effects and benefits of phosphating treatment

[0096] After these two steps, a composite lubricating layer of "phosphating film + zinc stearate" is finally formed on the surface of the steel pipe. This film brings the following decisive benefits:

[0097] 1. Excellent lubrication and friction reduction effects:

[0098] During cold drawing, this solid lubricating film can effectively prevent direct contact between the workpiece (steel pipe) and the mold (drawing mold);

[0099] It greatly reduces friction, which can reduce the drawing force by 20% to 30%, which not only saves equipment energy consumption, but also allows for drawing with a larger amount of deformation;

[0100] To prevent the workpiece from "adhering" and "scratching" with the mold.

[0101] Without this lubricating film, under high pressure and intense friction, the metal surface of the steel pipe can easily "cold weld" or "stick" to the mold (usually hard alloy), resulting in deep grooves (i.e., "scratches" or "scratches") on the surface of the steel pipe, turning it into a scrap product.

[0102] 2. Extend the service life of the mold

[0103] Reduced friction means significantly less wear on the mold, which greatly extends the service life of the expensive tube-drawing mold and reduces production costs.

[0104] 3. Ensure product surface quality

[0105] Good lubrication allows the steel pipe to flow evenly during deformation, resulting in a smooth, defect-free inner and outer surface. This is crucial for cold-drawn pipes with high precision and high surface finish requirements.

[0106] 4. Assisting metal flow

[0107] This lubricating film helps the metal flow more evenly during deformation, reduces internal stress concentration, and improves the dimensional accuracy and mechanical properties of the product.

[0108] In the phosphating and saponification process of steel pipes, the effective concentration of the saponification solution is a core process parameter that determines the quality of the saponification film, and consequently, the surface quality of the steel pipe and the success or failure of production. If the saponification solution concentration is too low, a complete and effective lubricating film cannot be formed, leading to defects such as scratches, roughening, or even "steel sticking" on the inner and outer surfaces of the steel pipe, significantly reducing the yield rate, and simultaneously accelerating mold wear and shortening its lifespan. If the saponification solution concentration is too high, it not only wastes the saponifying agent and increases production costs, but may also result in an excessively thick and porous saponification film, which accumulates during drawing, similarly affecting the surface quality of the steel pipe and potentially clogging the circulation pipeline.

[0109] Currently, in industrial production, the control of saponification solution concentration mainly relies on manual operation. This involves operators periodically sampling the saponification tank, determining the concentration through laboratory titration or empirical observation, and then manually adding solid saponifying agent or pre-prepared saponification mother liquor based on the results. This manual control method has many drawbacks:

[0110] 1. Significant time lag: There is a significant time delay between the change in concentration, its detection, and the completion of replenishment. During this period, the concentration of the saponification solution may have been substandard for an extended period, leading to batch-wide product quality issues.

[0111] 2. Poor control precision: It relies on human experience to judge, so the accuracy cannot be guaranteed, and the amount of supplementation is difficult to control precisely, which can easily cause excessive concentration fluctuations and make it impossible to stabilize within the optimal process window.

[0112] 3. High labor intensity and low efficiency: Frequent sampling, testing and replenishment operations are required, which increases the labor burden of workers and is not conducive to continuous and automated production.

[0113] To address the aforementioned technical issues, this solution proposes a novel processing method for large-diameter seamless steel pipes. This method optimizes the phosphating and saponification process, enabling real-time, precise, and automatic monitoring and adjustment of the saponification solution concentration. This overcomes the shortcomings of existing technologies, such as reliance on manual labor, significant lag, and poor precision, ensuring the stable production of large-diameter seamless steel pipes in cold drawing and the continuous improvement of product surface quality.

[0114] The phosphating process steps of this scheme are described in detail below, as shown in the appendix. Figure 1 As shown:

[0115] Step S1) Steel pipe pretreatment: The surface of the steel pipe is sequentially degreased, washed with water, pickled, and washed a second time.

[0116] Phosphating requires extremely high surface cleanliness of the steel pipe. Any oil or rust will cause uneven or discontinuous phosphating film, ultimately leading to lubrication failure. Therefore, pretreatment of the steel pipe surface is necessary.

[0117] Degreasing: Use alkaline or neutral cleaning agents to thoroughly remove grease and dirt from the surface of the steel pipe.

[0118] Wash with water: Rinse with running water to remove any residual cleaning agent.

[0119] Pickling (rust removal): Hydrochloric acid or sulfuric acid solution is usually used to remove the iron oxide scale (rust) on the surface.

[0120] Second rinse: Rinse thoroughly again with running water to remove all acid and iron salts. This step is crucial; otherwise, residual acid will spoil the subsequent phosphating solution.

[0121] Step S2) Phosphating treatment: The pretreated steel pipe is immersed in phosphating solution for phosphating treatment to generate phosphate crystals that adhere to the surface of the steel pipe, followed by water washing and drying.

[0122] Phosphating mainly involves forming a porous, dense phosphate crystal film on the surface of a clean steel pipe (this film is called "phosphating film").

[0123] The specific steps of phosphating treatment are as follows:

[0124] Immersion or spraying: Immerse the pretreated clean steel pipe into the phosphating solution tank.

[0125] Chemical reaction: At a specific temperature (usually 40-60°C) and time, the iron on the surface of the steel pipe reacts with the free phosphoric acid and dihydrogen phosphate in the phosphating solution to generate water-insoluble phosphate crystals, which adhere firmly to the surface of the steel pipe.

[0126] The core reaction formula is: Fe + 2H3PO4 -> Fe(H2PO4)2 + H2↑

[0127] 3Fe(H2PO4)2 -> Fe3(PO4)2↓ + 4H3PO4 (deposition to form a film)

[0128] Appearance: The surface of the treated steel pipe has a uniform gray or dark gray coating.

[0129] Washing and drying: After phosphating, the film needs to be washed with water (to remove residual phosphating solution) and thoroughly dried. If the phosphating film is damp before entering the saponification tank, it will dilute the saponification solution and affect the results.

[0130] Step S3) Saponification treatment: The phosphated and dried steel pipe is immersed in the saponification liquid in the saponification tank for saponification treatment to generate a saponification film on the surface of the steel pipe.

[0131] During the saponification process, the concentration of the saponification solution is controlled by an automatic monitoring system. The automatic monitoring system performs the following operations:

[0132] A sample of the saponification solution was extracted from the saponification tank.

[0133] The pH value of the sample is detected and compared with a preset pH threshold;

[0134] When the pH value of the sample is lower than the preset pH threshold, a predetermined amount of saponifying agent concentrate is automatically added to the saponification tank to increase the overall concentration of the saponification solution.

[0135] For details, see attached. Figure 2 As shown, the automatic monitoring system includes a controller, a detection unit, a replenishment unit, a first stirring device, and a second stirring device.

[0136] The detection unit includes a detection tank and a pH electrode installed in the detection tank. The detection tank is connected to the saponification tank through a pipeline with a first valve. Both the pH electrode and the first valve are communicatively connected to the controller. A filter is also installed on the pipeline with the first valve, and the filter is located at the connection between the pipeline and the saponification tank.

[0137] In this way, the controller can control the first valve to open periodically, such as once per hour, according to the testing needs. After the first valve opens, the saponification liquid in the saponification tank will flow into the testing tank through the pipe with the first valve. The filter installed at the connection point with the saponification tank can filter the saponification liquid, preventing excessive impurities from flowing into the testing tank and contaminating the pH electrode, thereby greatly improving the service life of the pH electrode. When the saponification liquid flows into the testing tank, the pH electrode detects the pH value of the saponification liquid in real time and sends the detection result to the controller.

[0138] Specifically, the replenishment unit includes a pre-melting tank, which is connected to the saponification tank via a pipeline with a second valve, and is equipped with a third valve for introducing solvent and a fourth valve for introducing saponifying agent. The second, third, and fourth valves are all communicatively connected to the controller.

[0139] Thus, when the controller receives a pH value of the saponification solution detected by the pH electrode that is lower than the preset pH threshold, the controller will first control the opening of the third and fourth valves. When the third valve opens, solvent is introduced into the pre-melting tank. In this specific embodiment, the solvent is hot water at a temperature of 50°C to 70°C. When the fourth valve opens, saponifying agent is introduced into the pre-melting tank. When the saponifying agent and solvent meet in the pre-melting tank, a concentrated saponifying agent solution is formed (the concentration of the concentrated saponifying agent solution can be configured as needed). Then, the controller controls the opening of the second valve, allowing the concentrated saponifying agent solution in the pre-melting tank to flow into the saponification tank and mix with the saponification solution in the saponification tank. Because the concentration of the concentrated saponifying agent solution is high, when it mixes with the saponification solution in the saponification tank, the overall concentration of the saponification solution in the saponification tank will increase, thereby meeting the design requirements and ensuring the effectiveness of the saponification process.

[0140] Specifically, to ensure sufficient dissolution between the saponifying agent and the solvent in the pre-melting tank, a first stirring device is also provided in the pre-melting tank. This first stirring device includes a first power component and a first stirrer. The first power component is communicatively connected to the controller, and the first stirrer extends into the pre-melting tank. When the third and fourth valves are opened, the controller activates the first power component to drive the first stirrer to rotate and mix the saponifying agent and the solvent.

[0141] Furthermore, in order to ensure the thorough mixing of the saponifying agent concentrate and the saponifying liquid, a second stirring device is also provided in the saponification tank. The second stirring device includes a second power component and a second stirrer. The second power component is communicatively connected to the controller, and the second stirrer extends into the saponification tank. When the second valve is opened, the controller controls the second power component to start, so as to drive the second stirrer to rotate and mix the saponifying agent concentrate and the saponifying liquid.

[0142] Specifically, when the detected pH value is lower than the preset pH threshold, the third and fourth valves are opened first, allowing a predetermined amount of solvent and saponifying agent to be introduced into the pre-melting tank. The amount of saponifying agent added is calculated using the following formula:

[0143] M = [(C target - C current ) / C stock ] × V tank × ρ

[0144] In the formula: M is the amount of saponifying agent added:

[0145] C target The target concentration of the saponification solution is generally 5% to 10%.

[0146] C current This represents the current concentration of the saponification solution.

[0147] Cstock The concentration of the saponifying agent concentrate added to the saponification tank, for example, 0.20 represents 20%;

[0148] V tank The effective volume of the saponification tank is expressed in liters (L).

[0149] ρ is the density of the saponification solution (kg / L).

[0150] Based on the calculated amount of saponifying agent and the concentration of the saponifying agent concentrate, the required amount of solvent can be obtained.

[0151] Specifically, the controller pre-stores data on the correlation between the pH value and concentration of the saponification solution. This correlation data is pre-established in the following way:

[0152] Prepare multiple standard samples of saponification solution with different known concentrations;

[0153] The pH value of each standard sample was measured using a calibrated pH electrode.

[0154] Based on the measured relationship between the pH value and the concentration of each standard sample, a pH-concentration curve is established and stored in the controller.

[0155] The controller obtains the current concentration of the saponification solution by querying the relationship curve based on the real-time pH value detected by the pH electrode.

[0156] Specifically, the preset pH threshold is determined in the following way:

[0157] Based on the pH-concentration curve, find the pH range corresponding to the target concentration of the saponification solution, and set the midpoint or lower limit of this pH range as the preset pH threshold. For example, if the target concentration range of the saponification solution is 5%~10%, the corresponding pH range is generally between 9.5 and 11.5. In this case, 9.5 or 10.5 can be selected as the preset pH threshold. Of course, it can also be set according to actual needs in specific production.

[0158] In this specific embodiment, considering that the grease and insoluble soap scum in the saponification solution can easily cause the pH electrode to become clogged or fail, an automatic cleaning system for the pH electrode is also designed in this solution.

[0159] Systems for automatically cleaning pH electrodes include:

[0160] Mechanical scraping unit:

[0161] Scraper ring: This is the core component. It is a ring made of corrosion-resistant, flexible material (such as PTFE or PEEK) with an inner diameter precisely matched to the pH electrode rod, and contains soft yet tough bristles (such as nylon). This ring fits snugly onto the electrode.

[0162] Transmission mechanism: converts the rotational motion of the drive motor into the linear reciprocating motion of the scraper ring.

[0163] Drive motor: Usually a small stepper motor or servo motor is used to precisely control the rotation angle and stroke. The drive motor is connected to the controller, which controls the rotation of the drive motor, and then drives the scraper ring to reciprocate through the transmission mechanism to clean the pH electrode.

[0164] Spray cleaning unit:

[0165] Nozzle: One or more precision nozzles, aligned with the glass bulb and reference diaphragm of the pH electrode. The nozzles should produce a cone or fan-shaped water column with moderate impact force.

[0166] Solenoid valve: controls the opening and closing of the cleaning fluid pipeline. It is connected to the controller and the controller controls the opening and closing of the cleaning fluid pipeline through the solenoid valve.

[0167] Pump (optional): If the pressure in the cleaning fluid storage tank is insufficient, a pump is required to provide stable pressure and flow.

[0168] Cleaning solution storage tanks and piping: for storing and transporting cleaning solutions. The cleaning solution is typically deionized water or soft water to prevent minerals in the water from forming new scale. For stubborn stains, mild acidic or alkaline cleaning agents can be used periodically.

[0169] The automated cleaning system operates on an ordered, cyclical process, with the following specific steps and synergistic effects:

[0170] Triggering phase:

[0171] The controller automatically starts the cleaning program according to preset time intervals.

[0172] Execution phase:

[0173] Step 1: Spray pre-wetting / simultaneous rinsing

[0174] The controller first opens the solenoid valve (and starts the pump), and the cleaning solution is continuously sprayed through the nozzle onto the sensitive part of the pH electrode.

[0175] Function: Moisturizes and softens dried or semi-dried soap scum and grease, preparing it for mechanical scraping and reducing scraping resistance.

[0176] Step 2: Mechanical scraping (conducted simultaneously with spraying)

[0177] The controller simultaneously starts the drive motor. The drive motor, through the transmission mechanism, drives the scraper ring to reciprocate along the rod of the pH electrode from the upper limit to the lower limit (covering the entire bulb and diaphragm area).

[0178] Function: Under pressure and motion, the bristles physically scrape and sweep away all solid and sticky dirt adhering to the electrode surface. This is the most crucial step in removing soap scum.

[0179] End and Reset Phase:

[0180] After the set cleaning time or number of cycles is reached, the controller stops the drive motor and stops the scraper ring at the upper limit away from the measurement area (usually the upper part of the electrode rod) to avoid interfering with normal pH measurement.

[0181] The controller shuts off the solenoid valve, stopping the spraying.

[0182] The system enters standby mode, waiting for the next cleaning cycle.

[0183] Furthermore, since the temperature of the saponification solution also has a significant impact on the entire saponification process, an automatic monitoring system is used to control the temperature of the saponification solution during the saponification process.

[0184] The automatic monitoring system also includes a temperature sensor and a heating device. Both the temperature sensor and the heating device are connected to the controller. The temperature sensor is located in the detection tank to detect the temperature of the saponification liquid in the detection tank. The heating device is located at the bottom of the saponification tank to heat the saponification liquid in the saponification tank.

[0185] The controller is also configured to: when the temperature value detected by the temperature sensor is lower than the preset temperature threshold, control the heating device to heat the saponification liquid in the saponification tank until the temperature of the saponification liquid in the saponification tank is higher than the preset temperature threshold.

[0186] For example, the heating device is an electric heater, which is spirally wound around the bottom of the saponification tank, and the area of ​​the electric heater wound around the bottom of the saponification tank is greater than 80% of the total area of ​​the bottom of the saponification tank, so as to ensure the overall heating effect of the saponification liquid.

[0187] Compared with existing technologies, this invention achieves real-time, precise, and automated control of saponification solution concentration. Through an automatic monitoring system consisting of a controller, a detection unit, and a replenishment unit, it completely changes the outdated mode of relying on manual, intermittent sampling and testing. This system can automatically and frequently sample and test, and trigger replenishment actions in real time according to a preset pH threshold, ensuring that the saponification solution concentration remains stable within the optimal process range, fundamentally avoiding product quality problems caused by concentration fluctuations. By introducing a pre-melting tank and a stirring device, this invention ensures that the added saponifying agent can be fully and uniformly mixed with the solvent (preferably hot water) to form a homogeneous concentrated saponifying agent solution before being injected into the saponification tank. This effectively prevents clumping, settling, and localized uneven concentration caused by directly adding solid saponifying agent into the saponification tank, ensuring that each batch of steel pipes is processed under consistent and reliable saponification conditions, thereby significantly improving the lubrication quality and consistency of the inner and outer surfaces of large-diameter seamless steel pipes. This invention liberates operators from the heavy and repetitive manual sampling, testing, and solution preparation, reducing labor intensity and the risk of human error. The entire concentration maintenance process requires no manual intervention, achieving a high degree of automation and ensuring the continuity and stability of production. It lays a key technological foundation for building a fully automated intelligent cold-drawing production line. This invention indirectly characterizes the concentration by detecting the pH value of the saponification solution, combined with sampling and measurement in an independent detection tank. This structure avoids the pH electrode being immersed in the harsh saponification tank for extended periods, reducing the risk of system inaccuracy and malfunction. It is easy to maintain, has a long service life, and is particularly suitable for the demanding conditions of continuous industrial production. This solution can monitor and adjust the saponification solution concentration in real time, accurately, and automatically, overcoming the shortcomings of existing technologies such as reliance on manual labor, large lag, and poor accuracy. It ensures the stable operation of large-diameter seamless steel pipe cold-drawing production and the continuous improvement of product surface quality.

[0188] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for processing large-diameter seamless steel pipes, characterized in that, The processing method includes a phosphating treatment step for the steel pipe, the phosphating treatment step comprising: Steel pipe pretreatment: The surface of the steel pipe is subjected to degreasing, water washing, pickling, and secondary water washing in sequence; Phosphating treatment: The pre-treated steel pipe is immersed in phosphating solution for phosphating treatment to generate phosphate crystals that adhere to the surface of the steel pipe, followed by water washing and drying. Saponification treatment: The phosphated and dried steel pipe is immersed in the saponification liquid in the saponification tank for saponification treatment to generate a saponification film on the surface of the steel pipe. During the saponification process, the concentration of the saponification solution is controlled by an automatic monitoring system, which performs the following operations: A portion of the saponification liquid sample was extracted from the saponification tank. The pH value of the sample is detected and compared with a preset pH threshold; When the pH value of the sample is lower than the preset pH threshold, a predetermined amount of saponifying agent concentrate is automatically added to the saponification tank to increase the overall concentration of the saponification solution.

2. The processing method for large-diameter seamless steel pipes according to claim 1, characterized in that, The automatic monitoring system includes a controller, a detection unit, and a replenishment unit; The detection unit includes a detection tank and a pH electrode disposed in the detection tank. The detection tank is connected to the saponification tank through a pipeline with a first valve. Both the pH electrode and the first valve are communicatively connected to the controller. The replenishment unit includes a pre-melting tank, which is connected to the saponification tank via a pipeline with a second valve. It is also equipped with a third valve for introducing solvent and a fourth valve for introducing saponifying agent. The second valve, the third valve, and the fourth valve are all communicatively connected to the controller. The controller is configured to: control the first valve to open, allowing a portion of the saponification liquid to flow into the detection tank, and receive the detection signal from the pH electrode; when the detected pH value is lower than a preset pH threshold, first control the third and fourth valves to open, allowing a predetermined amount of solvent and saponifying agent to be introduced into the pre-melting tank to prepare a saponifying agent concentrate of a predetermined concentration in the pre-melting tank, and then control the second valve to open, replenishing the saponifying agent concentrate of the predetermined concentration into the saponification tank.

3. The processing method for large-diameter seamless steel pipes according to claim 2, characterized in that, The automatic monitoring system also includes a first stirring device and a second stirring device; The first stirring device is located in the pre-melting tank and is used to mix the saponifying agent and the solvent. The first stirring device includes a first power component and a first stirrer. The first power component is communicatively connected to the controller, and the first stirrer extends into the pre-melting tank. The second stirring device is located in the saponification tank and is used to mix the saponifying agent concentrate and the saponification liquid. The second stirring device includes a second power component and a second stirrer. The second power component is communicatively connected to the controller, and the second stirrer extends into the saponification tank. The controller is further configured to: When the third valve and the fourth valve are open, the controller controls the first power component to start, so as to drive the first stirrer to rotate and mix the saponifying agent and the solvent; When the second valve is opened, the controller controls the second power component to start, so as to drive the second stirrer to rotate and mix the saponifying agent concentrate and the saponifying liquid.

4. The processing method for large-diameter seamless steel pipes according to claim 3, characterized in that, When the detected pH value is lower than the preset pH threshold, the third and fourth valves are opened first, allowing a predetermined amount of solvent and saponifying agent to be introduced into the pre-melting tank. The amount of saponifying agent added is calculated using the following formula: M= [ (C target - C current ) / C stock ] × V tank × ρ In the formula: M is the amount of saponifying agent added: C target The target concentration of the saponification solution is 5% to 10%. C current This represents the current concentration of the saponification solution. C stock The concentration of the saponifying agent concentrate added to the saponification tank; V tank The effective volume of the saponification tank is expressed in liters (L). ρ is the density of the saponification solution (kg / L).

5. The processing method for large-diameter seamless steel pipes according to claim 4, characterized in that, The controller pre-stores data on the correspondence between the pH value and concentration of the saponification solution. This correspondence data is pre-established in the following way: Prepare multiple standard samples of saponification solution with different known concentrations; The pH value of each standard sample was measured using a calibrated pH electrode. Based on the measured relationship between the pH value and concentration of each standard sample, a curve showing the relationship between the pH value and concentration of the saponification solution is established and stored in the controller. The controller obtains the current concentration of the saponification solution by querying the relationship curve based on the pH value detected in real time by the pH electrode.

6. The processing method for large-diameter seamless steel pipes according to claim 5, characterized in that, The preset pH threshold is determined in the following way: Based on the pH-concentration relationship curve, find the pH range corresponding to the target concentration of the saponification solution, and set the middle or lower limit of this pH range as the preset pH threshold.

7. The processing method for large-diameter seamless steel pipes according to claim 6, characterized in that, A filter is also provided on the pipeline with the first valve, and the filter is located at the connection between the pipeline and the saponification tank.

8. The processing method for large-diameter seamless steel pipes according to claim 7, characterized in that, The solvent introduced through the third valve is hot water at a temperature of 50°C to 70°C.

9. The processing method for large-diameter seamless steel pipes according to claim 1, characterized in that, During the saponification process, the temperature of the saponification solution is also controlled by the aforementioned automatic monitoring system; The automatic monitoring system also includes a temperature sensor and a heating device. Both the temperature sensor and the heating device are communicatively connected to the controller. The temperature sensor is located in the detection tank and is used to detect the temperature of the saponification liquid in the detection tank. The heating device is located at the bottom of the saponification tank and is used to heat the saponification liquid in the saponification tank. The controller is also configured to: when the temperature value detected by the temperature sensor is lower than a preset temperature threshold, control the heating device to heat the saponification liquid in the saponification tank until the temperature of the saponification liquid in the saponification tank is greater than the preset temperature threshold.

10. The processing method for large-diameter seamless steel pipes according to claim 9, characterized in that, The heating device is an electric heater, which is spirally wound around the bottom of the saponification tank, and the area of ​​the electric heater wound around the bottom of the saponification tank is greater than 80% of the total area of ​​the bottom of the saponification tank.

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