Manufacturing method of connecting pipe and connecting pipe for pressure-equalizing water mixing tank

Abstract

The invention relates to the manufacturing technology of fluid conveying equipment, in particular to a manufacturing method of a connecting pipe and the connecting pipe for a pressure-equalizing water mixing tank, and aims to solve the problems that a traditional connecting pipe is insufficient in structural strength and poor in corrosion resistance under the high-pressure working condition of a heating system. By using the alloy steel material with specific chemical components and combining the optimization process steps of hot forging and pressing preforming, precise investment casting, deburring and polishing, inert gas shielded welding, passivating treatment and the like, high strength and high corrosion resistance of the connecting pipe are combined, and the connecting pipe has excellent mechanical strength and corrosion resistance.

Description

Technical Field

[0001] This application relates to fluid transport equipment manufacturing technology, and more specifically, to a method for manufacturing a connecting pipe and a connecting pipe for a pressure equalization mixing tank. Background Technology

[0002] Under high-pressure conditions in heating systems, traditional connecting pipes suffer from insufficient structural strength and poor corrosion resistance. Although existing connecting pipes employ an integrated design of the connecting and fixing parts, and incorporate annular and toothed sealing structures, they are prone to structural deformation under long-term water flow impact and vibration, and are unable to resist corrosive media in heating water. Conventional manufacturing processes have limitations in material selection, molding precision control, and welding processes, preventing products from simultaneously meeting the dual requirements of high strength and high corrosion resistance. Furthermore, existing production processes and equipment have poor compatibility, resulting in high improvement costs and hindering further performance enhancements.

[0003] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0004] (a) Technical problems to be solved The purpose of this application is to provide a pressure equalization mixing tank connecting pipe and its manufacturing method, which has excellent mechanical strength and corrosion resistance, and solves the problems of insufficient structural strength and poor corrosion resistance of traditional connecting pipes under high pressure conditions.

[0005] (II) Technical Solution This application provides a method for manufacturing a connecting pipe for a pressure equalizing mixing tank, the technical solution of which is as follows: A method for manufacturing a connecting pipe for a pressure equalizing mixing tank, the connecting pipe having an integrally formed connecting part and a fixing part, and a sealing structure consisting of annular teeth and toothed parts formed at the end of the connecting part; the manufacturing method includes the following steps: S100 provides cold-rolled alloy steel coils as raw materials. The chemical composition of the alloy steel includes: Cr 18.0-19.0%, Ni 9.0-10.0%, Mo 1.8-2.2%, Cu 0.4-0.6%, Nb 0.08-0.12%, C≤0.07%, Si≤1.0%, Mn≤2.0%, with the balance being Fe and unavoidable impurities. S200. Cut the raw materials into blanks and pre-form the blanks by hot forging at 850-900℃ with a forging pressure of 120-150MPa. After holding at the temperature for 15-20 minutes, air cool. S300: Precision investment casting is performed on the pre-formed billet by hot forging to form the final shape of the connecting pipe and the detailed structure of the annular teeth and toothed parts. The casting pouring temperature is 1520-1550℃ and the pouring speed is 0.5-0.8m / s. S400. The cast connecting pipe is deburred and polished to make its surface roughness Ra≤0.8μm; S500. Weld the fixed part of the connecting pipe to the connecting hole of the pressure equalizing mixing tank. The welding material is ER316LMo stainless steel welding wire. The welding process adopts inert gas shielded welding. After welding, perform solution treatment at 1050℃ and air cooling. S600. After welding and heat treatment, the entire connecting pipe is subjected to natural passivation treatment. The passivation solution is a mixed aqueous solution of nitric acid and hydrofluoric acid. The treatment temperature is 40-50℃ and the time is 15-20min.

[0006] Furthermore, this application also proposes that in step S300, the precision investment casting uses a paraffin-resin composite molding material to make the mold, and the surface roughness of the mold Ra≤0.8μm; the shell used for casting is a silica sol-mullite shell, and dewaxing is performed using steam at 120-130℃ and 0.3MPa.

[0007] Furthermore, this application also proposes that in step S400, the deburring process sequentially employs mechanical vibration deburring and ultrasonic deburring; the polishing process sequentially employs rough polishing with a grinding wheel and fine polishing with a cloth wheel.

[0008] Furthermore, this application also proposes that in step S500, the inert gas shielded welding is TIG welding, and the process parameters include: welding current 80-100A, welding voltage 12-14V, welding speed 50-80mm / min, shielding gas is argon with a purity ≥99.99% and a flow rate of 8-10L / min, and welding preheating temperature is 150-200℃.

[0009] Furthermore, this application also proposes that, after step S500 and before step S600, a step of quality inspection of the weld is included: non-destructive testing is performed using ultrasonic testing and penetrant testing, and samples are taken for weld tensile testing, requiring the fracture location to be in the base material rather than the weld.

[0010] Furthermore, this application also proposes that, in step S600, the post-treatment after the passivation treatment includes: rinsing with pure water three times, 5 minutes each time, and then drying with hot air at 80-100°C for 10 minutes.

[0011] Furthermore, this application also proposes that, in step S100, after providing the raw materials, an incoming inspection step is also included: verifying the chemical composition using spectral analysis and conducting tensile tests to ensure that its tensile strength is ≥600MPa and its elongation is ≥30%; After step S300 and before step S400, the process also includes a step of dimensional accuracy inspection of the cast semi-finished product: using a coordinate measuring machine to detect the spacing error and the height error of the teeth of the ring teeth.

[0012] Furthermore, this application also proposes that the chemical composition of the ER316LMo stainless steel welding wire includes: Cr 17-19%, Ni 11-13%, Mo 2.0-3.0%, and C ≤ 0.03%.

[0013] Furthermore, this application also proposes a connecting pipe for a pressure equalization mixing tank, the connecting pipe being manufactured using the above-described manufacturing method; the connecting pipe includes an integrally formed connecting part and a fixing part, and the end of the connecting part is provided with a sealing structure composed of annular teeth and toothed parts.

[0014] Furthermore, this application also proposes that the fixing part is connected to the pressure equalizing mixing tank by a weld.

[0015] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes alloy steel materials with specific chemical compositions, combined with optimized process steps such as hot forging preforming, precision investment casting, deburring and polishing, inert gas shielded welding, and passivation treatment, to achieve a combination of high strength and high corrosion resistance in the connecting pipe, resulting in excellent mechanical strength and corrosion resistance. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the logical structure of the manufacturing method for the connecting pipe; Figure 2 This is a schematic diagram of the overall structure of a pressure equalization mixing tank; Figure 3 This is a schematic diagram of the connecting pipe structure; Figure 4 This is a magnified schematic diagram of the local structure at point A.

[0018] 1. Mixing tank; 2. Connecting pipe; 21. Connecting part; 22. Fixing part; 23. Annular tooth; 24. Annular groove; 25. Tooth groove; 26. Tooth part. Detailed Implementation

[0019] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. The components of this application 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 this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as... Traditional equalizing mixing tank connecting pipes face structural strength challenges from water flow impact and vibration under high-pressure conditions in heating systems. Furthermore, they are susceptible to corrosion from heating water quality over long-term use, leading to insufficient structural strength and poor corrosion resistance, thus affecting the stable operation and service life of the system. Therefore, referring to... Figure 1 This application proposes a method for manufacturing a connecting pipe, aiming to solve the above-mentioned problems. The connecting pipe has an integrally formed connecting portion and a fixing portion, and a sealing structure consisting of annular teeth and toothed portions is formed at the end of the connecting portion. The manufacturing method includes the following steps: S100. Raw material preparation and composition limitation: Cold-rolled alloy steel coils are provided as raw materials. The chemical composition of the alloy steel includes: Cr 18.0-19.0%, Ni 9.0-10.0%, Mo 1.8-2.2%, Cu 0.4-0.6%, Nb 0.08-0.12%, C≤0.07%, Si≤1.0%, Mn≤2.0%, with the balance being Fe and unavoidable impurities. S200, billet cutting and hot forging preforming: cut the raw material into billets, and hot forge the billets at 850-900℃, with a forging pressure of 120-150MPa, and air cool after holding for 15-20 minutes. S300, Precision Investment Casting: Precision investment casting is performed on the pre-formed billet through hot forging to form the final shape of the connecting pipe and the detailed structure of the annular teeth and toothed parts. The casting pouring temperature is 1520-1550℃ and the pouring speed is 0.5-0.8m / s. S400 Deburring and Polishing: The cast connecting pipe is deburred and polished to make its surface roughness Ra≤0.8μm; S500, Welding and Post-Weld Solution Treatment: Weld the fixed part of the connecting pipe to the connecting hole of the pressure equalization mixing tank. The welding material is ER316LMo stainless steel welding wire. The welding process adopts inert gas shielded welding. After welding, perform solution treatment at 1050℃ and air cooling. S600, Overall Natural Color Passivation Treatment: The entire connecting pipe after welding and heat treatment is subjected to natural color passivation treatment. The passivation solution is a mixed aqueous solution of nitric acid and hydrofluoric acid. The treatment temperature is 40-50℃ and the time is 15-20min.

[0021] For ease of understanding, some key technical terms in this embodiment are explained below: Equalizing mixing tank connection pipe: used to connect the equalizing mixing tank to other pipelines to achieve fluid transport and pressure balance.

[0022] Connection and fixing parts: The connection part is the part that connects to external pipelines or equipment, and usually includes a sealing structure; the fixing part is the part that connects to the body of the equalizing mixing tank, and is usually fixed by welding or other methods. One-piece molding means that these two parts are formed as a whole during the manufacturing process, avoiding the weak points that may result from separate connections.

[0023] A sealing structure consisting of ring teeth and toothed sections: a structure that achieves sealing through geometry. Ring teeth are typically used to provide radial sealing contact surfaces, while the toothed sections provide axial sealing and pull-out resistance through engagement with mating parts, maintaining tightness of the connection under high pressure.

[0024] Alloy steel cold-rolled coils: Alloy steel sheets produced through a cold-rolling process, possessing high dimensional accuracy and surface quality, are used as the initial material for manufacturing connecting pipes. Their alloy composition is designed to provide specific mechanical properties and corrosion resistance.

[0025] Hot forging preforming: Applying pressure to a metal billet at high temperature causes it to undergo plastic deformation, forming a preform that closely resembles the final product shape. This process can refine the grains, eliminate internal defects, and improve the material's density and mechanical properties.

[0026] Precision investment casting: a high-precision casting method that involves creating a wax or resin model, coating its surface with a refractory material to form a shell, melting away the mold material, and then pouring molten metal into the shell to obtain castings with complex shapes and high dimensional accuracy. This method is suitable for manufacturing parts with fine structures, such as ring teeth and toothed sections.

[0027] Deburring and polishing: Deburring removes sharp protrusions from the edges of castings or machined parts. Polishing is a process that uses mechanical or chemical methods to smooth the surface, reduce surface roughness, thereby improving appearance and corrosion resistance.

[0028] Inert gas shielded welding: a welding method that uses an inert gas (such as argon) to protect the electric arc and the molten pool, preventing oxygen and nitrogen in the air from contaminating the weld metal, thereby obtaining a high-quality weld.

[0029] Solution treatment: A heat treatment process in which an alloy is heated to a high temperature, causing the alloying elements to fully dissolve into the matrix to form a homogeneous solid solution, followed by rapid cooling to maintain this homogeneity. This treatment can eliminate work hardening, improve the plasticity and toughness of the material, and restore corrosion resistance.

[0030] Natural passivation treatment: a surface chemical treatment that forms a dense, corrosion-resistant oxide film on the metal surface while maintaining the metal's original color and luster without altering its appearance.

[0031] In one embodiment, the connecting pipe of the equalizing mixing tank can be manufactured as follows: The connecting part and the fixing part of the connecting pipe can be designed separately and assembled by threaded connection or flange connection. The sealing structure can use a conventional rubber gasket or a simple conical fit.

[0032] When supplying raw materials, we can provide ordinary carbon steel plates or standard 304 stainless steel plates. The chemical composition of these materials may not contain elements such as molybdenum, copper, or niobium, or their content range may vary.

[0033] When cutting and preforming raw materials, after the raw materials are cut into blanks, they can be directly cold stamped, forged at a lower temperature, or directly water-cooled after forging.

[0034] When casting a preformed billet, the preformed billet can be sand-cast or gravity-cast to form the final shape, or it can be machined (e.g., turning, milling) to form the detailed structure of the ring teeth and tooth parts.

[0035] When performing surface treatment on the cast connecting pipe, the cast connecting pipe can be simply deburred by manual grinding, or it can be cleaned by acid pickling without polishing.

[0036] When welding the fixing part of the connecting pipe to the connecting hole of the equalizing mixing tank, the fixing part of the connecting pipe can be connected to the equalizing mixing tank by ordinary electric arc welding or gas welding, and the welding material can be general stainless steel welding wire. After welding, no solution treatment is required, and it can be cooled directly.

[0037] When performing surface protection on the welded and heat-treated connecting pipe, the welded and heat-treated connecting pipe can be protected by coating treatment (such as painting or electroplating), passivation treatment with a single acid solution (such as nitric acid), or no passivation treatment.

[0038] Through the above manufacturing method, the connecting pipe of the equalizing mixing tank can withstand the impact and vibration of high-pressure water flow under high-pressure conditions in the heating system, and is not prone to deformation or failure. At the same time, the long-term corrosion resistance of the connecting pipe is improved, which can effectively resist the erosion of heating water, extend its service life, and ensure the stable operation and reliability of the system.

[0039] In some of the embodiments described above in this application, precision investment casting is proposed to form the final shape of the connecting pipe and the detailed structure of the annular teeth and toothed parts. However, in the process of its implementation, high surface roughness of the mold may lead to insufficient precision of the detailed structure, affecting the sealing performance; improper dewaxing methods may cause shell defects or residues, resulting in uneven casting surface or internal defects, reducing product quality and durability.

[0040] In this regard, this application further proposes that in step S300, the precision investment casting uses a paraffin-resin composite molding material to make the mold, and the surface roughness of the mold Ra≤0.8μm; the mold shell used for casting is a silica sol-mullite mold shell, and dewaxing is performed using steam at 120-130℃ and 0.3MPa.

[0041] Specifically, the paraffin-resin composite molding material is a molding material made by mixing paraffin and resin in a specific ratio, used to make wax models in precision investment casting.

[0042] Paraffin wax provides good flowability and easy demolding, while resin enhances the strength and dimensional stability of the mold material. Their role is to accurately replicate the complex shapes of the connecting tubes, especially the fine structures of the annular teeth and toothed sections. For example, a formulation with a high paraffin wax content, such as 70% paraffin wax and 30% resin, can be used to ensure good flowability of the mold material during injection molding, facilitating easy filling of the mold cavity, and ensuring complete melting during dewaxing. Alternatively, a formulation with a moderate resin content, such as 60% paraffin wax and 40% resin, can be used to improve the mechanical strength and hardness of the mold, reducing potential deformation or damage during handling or assembly, thereby ensuring the dimensional accuracy of the casting.

[0043] The surface roughness Ra≤0.8μm of the mold refers to a parameter that measures the microscopic geometric shape error of an object's surface. The smaller the Ra value, the smoother the surface. Its function is to ensure that the mold surface has high smoothness, thereby making the surface of the cast connecting pipe flat, reducing burrs and defects, and accurately replicating the details of the ring teeth and tooth parts. For example, the surface roughness requirement of Ra≤0.8μm can be achieved through precision mold processing technology, such as CNC milling combined with grinding and polishing. Alternatively, the required surface finish can also be obtained through post-processing techniques such as electrical discharge machining (EDM) followed by fine polishing or chemical polishing.

[0044] The casting uses a silica sol-mullite shell, which is a refractory material layer that wraps around the wax pattern in investment casting. It is made of a mixture of refractory aggregates (such as mullite) and binders (such as silica sol). Its function is to provide sufficient strength and thermal stability during high-temperature pouring to withstand the impact and thermal stress of the high-temperature molten metal, preventing cracking or deformation and ensuring the dimensional accuracy and surface quality of the casting. For example, the shell can have a multi-layered structure: the inner layer uses fine-grained mullite powder and silica sol slurry to obtain a smooth surface; the outer layer uses coarse-grained mullite sand and silica sol slurry to provide sufficient strength and thermal shock resistance. Alternatively, the permeability and strength of the shell can be optimized by adjusting the concentration of the silica sol and the particle size distribution of the mullite aggregate to meet the requirements of castings with varying degrees of complexity.

[0045] The dewaxing process employs steam at 120-130℃ and 0.3MPa. Dewaxing is the process of melting or evaporating the wax pattern from the mold shell. Steam dewaxing utilizes high-temperature, high-pressure steam for heating, aiming to efficiently and thoroughly remove the wax pattern from the mold shell, preventing wax pattern residue from causing casting defects and avoiding damage to the mold shell. For example, the dewaxing equipment can be a steam autoclave with a precise temperature and pressure control system to ensure stable operation of the steam temperature and pressure within the set range, achieving uniform dewaxing. Alternatively, a staged dewaxing method can be used, first pre-dewaxing at a lower temperature and pressure, and then performing main dewaxing at 120-130℃ and 0.3MPa to reduce thermal shock to the mold shell.

[0046] Through the above technical solution, the combination of paraffin-resin composite molding material and mold surface roughness of Ra≤0.8μm ensures the accurate replication of fine sealing structures such as the annular teeth and toothed parts of the connecting pipe, effectively avoiding uneven casting surface or insufficient precision of detailed structures caused by mold defects, thereby ensuring the integrity of the sealing structure of the connecting pipe and its high-pressure sealing performance.

[0047] Meanwhile, the silica sol-mullite shell exhibits excellent refractoriness and thermal stability. Even at casting temperatures as high as 1520-1550℃ for alloy steel, it maintains the shape and dimensional stability of the shell, effectively preventing cracking, deformation, or molten steel infiltration. This ensures the overall structural integrity and dimensional accuracy of the connecting pipe, enhancing its impact resistance under high-pressure conditions in the equalizing mixing tank. Furthermore, dewaxing using steam at 120-130℃ and 0.3MPa efficiently and thoroughly removes the paraffin-resin composite molding compound, avoiding potential casting porosity or surface defects caused by wax residue. Simultaneously, precisely controlled steam parameters prevent the shell from cracking due to excessive pressure, thereby improving the casting density and surface quality, reducing corrosion initiation points, and indirectly enhancing the corrosion resistance of the connecting pipe.

[0048] By comprehensively optimizing the selection of mold materials, mold precision, shell material and dewaxing process parameters during the precision investment casting process, the problems of insufficient precision in fine structure forming, poor shell stability under high temperature casting and defects easily generated during the dewaxing process are effectively solved. This ensures the high precision and high reliability of the annular tooth and tooth sealing structure of the connecting pipe, significantly improving the overall quality, structural strength and durability of the connecting pipe, enabling it to better meet the performance requirements of the equalizing mixing tank under high pressure conditions.

[0049] In some of the embodiments described above in this application, deburring and polishing processes are proposed to ensure that the surface roughness Ra of the connecting pipe is ≤0.8μm. However, in the implementation process, there may be problems such as incomplete burr removal or uneven surface polishing, which affect the sealing performance and corrosion resistance of the final product, and may lead to leakage or corrosion failure under the impact of high-pressure water flow.

[0050] In this regard, this application further proposes that in step S400, the deburring process sequentially employs mechanical vibration deburring and ultrasonic deburring; and the polishing process sequentially employs rough polishing with a grinding wheel and fine polishing with a cloth wheel.

[0051] Specifically, mechanical vibration deburring is a process that removes surface burrs by causing the workpiece to rub against an abrasive through mechanical vibration.

[0052] Its function is to effectively remove large burrs, flash, and other defects generated during the casting process of connecting pipes. Specifically, a vibratory grinding machine can be used, in which the connecting pipe, ceramic grinding blocks, resin grinding blocks, and other abrasives, along with grinding fluid, are placed in a vibratory tank. High-frequency vibration causes the abrasives to impact and rub against the surface of the connecting pipe, thus removing burrs. Alternatively, a centrifugal grinding machine can be used, where the centrifugal force generated by high-speed rotation causes the connecting pipe to rub strongly against the abrasives, achieving efficient deburring in batches.

[0053] Ultrasonic deburring utilizes the cavitation effect of ultrasound waves in a liquid to remove fine burrs. Its purpose is to deeply clean fine burrs and complex structural areas that are difficult to reach with mechanical vibration deburring. For example, connecting pipes can be immersed in a liquid containing a special cleaning agent. High-frequency vibrations generated by an ultrasonic transducer create countless tiny bubbles in the liquid. When these bubbles burst, they generate powerful shock waves, thereby peeling away fine burrs from the surface of the connecting pipe, especially in delicate structures such as annular teeth and toothed sections.

[0054] Another approach is to use an ultrasonic vibrating bar or jet system to precisely apply ultrasonic energy to specific areas of the connecting pipe, achieving localized fine deburring. Rough polishing with a grinding wheel involves using a coarse-grit grinding wheel to initially grind the surface of the connecting pipe, quickly removing surface unevenness, deep scratches, pitting, and casting defects. For example, an 80-120 grit grinding wheel can be used, either by a robotic arm or manually, to grind the entire surface of the connecting pipe, eliminating macroscopic defects formed during the casting process and laying the foundation for subsequent fine polishing.

[0055] Alternatively, a belt sander can be used to coarsely grind the surface of the connecting pipe using a high-speed rotating sanding belt, thereby improving processing efficiency. Fine polishing with a cloth wheel utilizes a soft cloth wheel in conjunction with polishing compound or liquid to finely treat the surface of the connecting pipe, further reducing surface roughness and improving smoothness.

[0056] Its function is to provide a smooth and delicate surface, achieving the required surface roughness. Specifically, soft cloth wheels such as cotton or wool wheels can be selected, along with specialized polishing paste or liquid, to finely polish the surface of the connecting pipe through high-speed rotation, eliminating micro-scratches and achieving a mirror-like finish. Automated polishing robots can also be used in this process, equipped with cloth wheels of different materials and grit sizes, to perform multiple passes of fine polishing on the connecting pipe according to a preset path, ensuring the uniformity and consistency of the surface treatment.

[0057] The above technical solution firstly employs a combination of mechanical vibration deburring and ultrasonic deburring. Mechanical vibration can efficiently remove larger burrs and flash from the surface of the connecting pipe, while ultrasonic deburring can penetrate into narrow areas of delicate structures such as ring teeth and tooth parts, thoroughly removing fine burrs. This avoids the residual problems that may exist with a single deburring method, thereby ensuring the cleanliness of the surface of the sealing structure of the connecting pipe and providing a reliable guarantee for subsequent sealing performance.

[0058] Secondly, the polishing process combines rough polishing with coarse polishing using a grinding wheel and fine polishing using a cloth wheel. Rough polishing with a grinding wheel quickly eliminates casting defects, pits, and deep scratches on the surface of the connecting pipe, creating conditions for fine polishing. Fine polishing with a cloth wheel further refines the surface, achieving extremely low surface roughness. This ensures a tight seal between the connecting pipe and the equalizing mixing tank, effectively preventing leakage under high-pressure water flow. Simultaneously, this step-by-step and meticulous surface treatment process not only improves the sealing performance of the connecting pipe but also significantly reduces the corrosion risk caused by surface defects, enhancing the long-term corrosion resistance of the connecting pipe.

[0059] Furthermore, the sequential design of thoroughly deburring before fine polishing effectively avoids secondary scratches caused by burr residue during the polishing process, protects the integrity of delicate structures such as the ring teeth and tooth parts, and ensures the overall quality and service life of the connecting pipe.

[0060] In some of the embodiments described above in this application, inert gas shielded welding is proposed to ensure welding quality and achieve a reliable connection between the connecting pipe and the equalizing mixing tank. However, in its implementation, inaccurate control of welding parameters may lead to insufficient weld joint strength and reduced corrosion resistance, affecting the overall performance stability of the connecting pipe under high-pressure water flow impact and long-term corrosive environment.

[0061] In this regard, this application further proposes that in step S500, the inert gas shielded welding is TIG welding, and the process parameters include: welding current 80-100A, welding voltage 12-14V, welding speed 50-80mm / min, shielding gas is argon with a purity ≥99.99% and a flow rate of 8-10L / min, and welding preheating temperature 150-200℃.

[0062] Specifically, using TIG welding as an inert gas shielded welding method enables precise heat input control during the welding process, effectively reducing welding deformation and oxidation risks, thereby ensuring the integrity of the weld joint. TIG welding is known for its stable arc and high-quality welds, making it suitable for applications with high weld quality requirements. It can be implemented through manual or automated TIG welding, or even pulsed TIG welding for more precise heat control.

[0063] In TIG welding, the setting of the welding current is crucial. In this embodiment, the welding current is set within the range of 80-100A. This current range is designed to ensure sufficient penetration to form a strong weld, while avoiding burn-through due to excessive current or insufficient fusion due to insufficient current. The welding current can be controlled by adjusting the power supply output, for example, by using a constant current (CC) power supply or by modulating the current in pulse welding.

[0064] Meanwhile, the welding voltage is set within the range of 12-14V. This voltage range helps maintain stable arc combustion, ensuring a smooth welding process and reducing spatter and welding defects. Stable welding voltage is crucial for obtaining uniform welds and a good appearance; its adjustment is typically related to the arc length and can be controlled manually or automatically.

[0065] Controlling the welding speed is equally important for weld quality and production efficiency. In this embodiment, the welding speed is set within the range of 50-80 mm / min. This speed range aims to balance production efficiency with heat-affected zone (HAZ) control, preventing incomplete fusion due to excessive welding speed or overheating due to excessively slow welding speed. A reasonable welding speed helps to form a fine-grained structure and improves the mechanical properties of the weld. This can be achieved manually by skilled operators or precisely controlled by automated welding equipment such as robotic welding systems or mechanized trolleys.

[0066] To ensure the weld is protected from atmospheric contamination, argon gas with a purity of ≥99.99% is used as the shielding gas. High-purity argon effectively isolates the weld from oxygen and nitrogen in the air, preventing oxidation or nitriding in the weld area, thus significantly improving the weld's corrosion resistance and mechanical properties. As an inert gas, argon does not chemically react with the molten metal, ensuring the purity of the weld. The shielding gas can be supplied by high-pressure cylinders or liquid argon Dewar flasks.

[0067] The shielding gas flow rate is controlled at 8-10 L / min. This flow rate range ensures that the shielding gas can fully cover the entire welding area, forming a stable protective gas shield and effectively preventing the intrusion and contamination of the molten pool by external air. An appropriate flow rate provides sufficient protection while avoiding waste or airflow disturbance caused by excessive flow. The flow rate is typically controlled by a flow meter and regulator connected to the gas supply system.

[0068] In addition, the welding preheating temperature is set at 150-200℃. Preheating effectively reduces thermal stress generated during welding, lowering the risk of cracks in the weld and heat-affected zone. Especially for alloy steel materials, preheating helps improve the toughness and reliability of the weld joint. Preheating can be achieved through various methods such as resistance heating blankets, induction heaters, gas welding torches, or preheating furnaces, and temperature monitoring is performed using temperature wax pens, thermocouples, or infrared thermometers.

[0069] By synergistically controlling the aforementioned TIG welding process parameters, this application can effectively solve the problem of unstable welding quality and significantly improve the strength and corrosion resistance of the connecting pipe. Specifically, welding current, voltage, speed, shielding gas purity and flow rate, and preheating temperature do not act independently, but form a synergistic combination of "heat input-protection-stress control".

[0070] This synergistic control ensures a stable molten pool depth and effectively controls the width of the heat-affected zone, preventing coarse grains in the alloy steel. Especially considering the characteristics of cold-rolled alloy steel coils as raw materials, which contain alloying elements such as Mo and Nb and have relatively high hardenability, a preheating temperature of 150-200℃ not only reduces thermal stress but also effectively inhibits the precipitation of martensite during welding, thereby preventing weld brittleness.

[0071] Meanwhile, precise control of current and voltage prevents the Nb element in the alloy steel from burning off due to overheating, ensuring that the weld's resistance to intergranular corrosion remains consistent with that of the base material. The synergistic effect of high-purity argon gas and appropriate flow rate eliminates weld oxidation and porosity, achieving a triple effect of sufficient fusion, refined microstructure, and no oxidation.

[0072] This refined welding parameter design enables the weld performance to be precisely matched with the base material, solving the problem that the weld strength or corrosion resistance may be lower than that of the base material in traditional welding. This supports the structural strength requirements of the connecting pipe to withstand water flow impact and vibration under high pressure conditions in the equalizing mixing tank, and meets the long-term corrosion resistance requirements.

[0073] Furthermore, by controlling the welding speed and the uniformity of the heat-affected zone, a good foundation is laid for the subsequent 1050℃ solution treatment in step S500, making the microstructure transformation of the weld and the base material more synchronized. This avoids differences in post-solution performance caused by uneven microstructure in the heat-affected zone, further ensuring the stability and reliability of the overall structure after welding. Ultimately, this embodiment, by optimizing the welding process, ensures the long-term stability and excellent performance of the connecting pipe under harsh working environments.

[0074] In some of the solutions described above in this application, a welding step is proposed to connect the fixing part and the pressure equalizing mixing tank. However, in this process, the weld may have internal or surface defects and insufficient strength. If it is not inspected in time, the connecting pipe may fail under the impact of high-pressure water flow or long-term corrosion, affecting the integrity and reliability of the overall structure.

[0075] Therefore, this application further proposes a weld quality inspection step following step S500 and preceding step S600. Specifically, this quality inspection step aims to comprehensively evaluate the integrity, uniformity, and mechanical properties of the weld to ensure it meets design requirements and prevent product failure under high-pressure conditions due to potential defects. This inspection step is performed after welding is completed and cooled, but before passivation treatment. This ensures that the inspection results accurately reflect the original state of the weld, avoids the passivation film masking surface defects, and also avoids the waste of resources caused by subsequent processing of unqualified products.

[0076] This quality inspection step uses ultrasonic testing and penetrant testing for non-destructive testing, and samples are taken for weld tensile testing, requiring the fracture location to be in the base material rather than the weld.

[0077] Non-destructive testing methods include ultrasonic testing and penetrant testing. Ultrasonic testing utilizes the propagation and reflection characteristics of ultrasonic waves in materials to effectively detect defects inside welds, such as cracks, porosity, lack of fusion, or inclusions. It can be implemented using A-mode, B-mode, C-mode displays, or more advanced phased array ultrasonic technology to provide precise location and size information of defects.

[0078] Penetrant testing utilizes the capillary action of liquid penetrants to detect open defects on the weld surface, such as microcracks, surface porosity, or undercut. Penetrant testing can employ dye penetrant or fluorescent penetrant methods to make even minute defects visually visible. The combination of these two non-destructive testing methods achieves comprehensive coverage of both internal and surface defects in the weld, ensuring a high defect detection rate.

[0079] In addition, samples were taken for tensile testing of the welds. This test aims to evaluate key mechanical properties of the welds, such as tensile strength, yield strength, and elongation. By preparing standard specimens according to relevant national or industry standards (such as GB / T 2651 or ISO 4136) and performing tensile tests on a universal testing machine, the true performance data of the welds under stress conditions can be obtained.

[0080] A key requirement for this tensile test is that the fracture occurs in the base material, not the weld. This means that the weld strength must be at least equal to, or even higher than, that of the base material, ensuring that the weld is not a weak point in the overall connection structure.

[0081] To achieve this, it is usually necessary to finely optimize the welding process parameters, select high-quality welding materials that match the base material, and possibly supplement with appropriate post-weld heat treatment.

[0082] Through the above technical solutions, this application enables comprehensive and reliable control over the weld quality of the connecting pipe of the equalizing mixing tank. The combined application of ultrasonic testing and penetrant testing ensures thorough screening of all potential defects inside and on the surface of the weld, effectively preventing defective welds from entering subsequent processes and guaranteeing product quality from the source. Simultaneously, through rigorous weld tensile testing, and by explicitly requiring the fracture location to be in the base material rather than the weld itself, this application ensures that the mechanical properties of the weld are at least equivalent to, or even superior to, the base material.

[0083] This high-standard design ensures that the weld joints of the connecting pipe can withstand the expected loads when facing harsh conditions such as high-pressure water flow impact, vibration, or long-term corrosion in the heating system, and will not become weak points for structural failure, significantly improving the overall structural integrity and operational reliability of the connecting pipe.

[0084] Furthermore, scheduling the quality inspection step before passivation treatment not only allows for the timely detection and handling of substandard welds, avoiding resource waste and rework costs caused by subsequent processing of defective products, but also ensures the effectiveness of passivation treatment. This optimizes the production process while ensuring high product reliability, achieving an effective balance between quality and cost.

[0085] In some of the solutions described above in this application, a natural passivation treatment is proposed to improve the corrosion resistance of the connecting pipe. However, in this process, the passivation solution residue may cause surface contamination or reduce the corrosion resistance effect, thereby affecting the reliability in long-term use.

[0086] In this regard, this application further proposes that in step S600, the post-processing after the passivation treatment includes: washing with pure water three times, 5 minutes each time, and then drying with hot air at 80-100℃ for 10 minutes.

[0087] This cleaning step aims to thoroughly remove any passivation solution remaining on the surface of the connecting pipe after the original passivation treatment. Passivation solutions typically contain acidic components; if not thoroughly removed, they may corrode the existing passivation film or cause pitting corrosion during subsequent use.

[0088] Pure water cleaning effectively removes these residues through dilution and rinsing. Specifically, pure water cleaning can be achieved in various ways. For example, in addition to the multiple immersion cleaning used in this embodiment, it can also be carried out by high-pressure spraying, using high-pressure jets of pure water to rinse the surface of the connecting pipe, which is particularly suitable for removing residual liquid from complex structures such as ring teeth and tooth sections; or, ultrasonic cleaning can be used, using the cavitation effect generated by ultrasound in a pure water medium to peel off and disperse the tiny particles and residual liquid adhering to the surface, thereby achieving a deeper cleaning effect.

[0089] The subsequent drying step removes residual moisture from the surface of the connecting tube after cleaning, preventing secondary contamination or oxidation caused by moisture retention. Simultaneously, precise temperature and time control help stabilize the structure of the passivation film, ensuring its density and uniformity. Specifically, hot air drying can be achieved by placing the connecting tube in a drying oven with temperature control and air circulation functions.

[0090] In addition to the hot air drying method used in this embodiment, other drying methods can also be used. For example, vacuum drying technology can be used to accelerate the evaporation of moisture at a lower temperature by reducing the ambient pressure, thereby avoiding the possible effects of high temperature on the material and ensuring thorough drying. Alternatively, infrared heating drying can be used to rapidly evaporate the moisture on the surface of the connecting tube through radiation heating, while precisely controlling the heating area and temperature to adapt to connecting tubes of different shapes and sizes.

[0091] Through the above technical solution, this application effectively solves the problem that residual passivation solution after natural passivation treatment may cause surface contamination or reduce corrosion resistance. Specifically, rinsing with pure water three times, 5 minutes each time, can thoroughly remove any residual passivation solution from the surface of the connecting pipe, especially from the fine structures such as the annular teeth and toothed parts. This avoids potential corrosion of the formed passivation film by acidic substances and ensures the integrity and uniformity of the passivation film.

[0092] Based on this, by hot air drying at 80-100℃ for 10 minutes, surface moisture can be removed quickly and thoroughly, preventing secondary oxidation or corrosion caused by moisture retention. At the same time, the temperature range and time control help stabilize the crystal structure of the passivation film and avoid film defects or aging caused by improper drying.

[0093] Therefore, this solution not only ensures that the surface of the connecting pipe is clean and free of residue, but more importantly, it significantly improves the density and stability of the passivation film, thereby ensuring that the connecting pipe has excellent corrosion resistance during long-term use and maintains its original appearance, meeting the long-term reliability requirements of the equalizing mixing tank under complex working conditions.

[0094] In some of the embodiments described above in this application, a manufacturing method for producing connecting pipes is proposed. However, during its implementation, the quality of raw materials may not meet the standards or the dimensions of the cast semi-finished products may be inaccurate, resulting in insufficient product strength or failure of the sealing structure.

[0095] In this regard, this application further proposes that in step S100, after providing the raw materials, there is also a step of inspecting the raw materials upon arrival at the factory: using spectral analysis to verify the chemical composition, and conducting tensile tests to ensure that its tensile strength is ≥600MPa and its elongation is ≥30%; after step S300 and before step S400, there is also a step of inspecting the dimensional accuracy of the cast semi-finished product: using a coordinate measuring machine to detect the spacing error of the ring teeth and the height error of the teeth.

[0096] The incoming inspection of raw materials aims to control their quality from the source, ensuring that their chemical composition and mechanical properties meet design requirements. This is crucial to preventing the scrapping of high-value processes such as hot forging preforming and precision investment casting due to raw material defects, thereby effectively reducing production costs and guaranteeing the structural strength and corrosion resistance of the final connecting pipe. This inspection can be achieved in various ways. For example, spectroscopic analysis techniques, such as direct-reading spectrometers or X-ray fluorescence spectrometers, can be used to accurately determine the chemical composition of cold-rolled alloy steel coils.

[0097] By analyzing the content of key elements such as Cr, Ni, Mo, Cu, Nb, C, Si, and Mn and comparing it with the preset composition range, we can verify whether the alloy ratio of the raw materials meets the standard and ensure its inherent corrosion resistance and high-temperature performance.

[0098] In addition, tensile tests can be performed, where standard specimens made from the raw materials are subjected to uniaxial tension on a universal testing machine until fracture. During this process, the tensile strength and elongation of the material are recorded. By ensuring that the tensile strength reaches or exceeds 600 MPa and the elongation reaches or exceeds 30%, the plastic deformation capacity and final fracture strength of the raw materials under external loads can be verified, thereby ensuring that they are not prone to cracking during subsequent processing and providing a reliable mechanical basis for the long-term service of the final connecting pipe under high-pressure conditions.

[0099] The step of dimensional accuracy inspection of the cast semi-finished product is carried out after casting and before deburring. Its purpose is to accurately assess the critical dimensional accuracy of the semi-finished connecting pipe formed by the precision investment casting process, especially the key geometric parameters of sealing structures such as the annular teeth and toothed sections. Its core objective is to promptly detect dimensional deviations during the casting process without affecting the original casting surface characteristics, so as to adjust casting parameters, ensure the accuracy of the sealing structure, and thus guarantee the sealing performance of the connecting pipe.

[0100] This inspection can be achieved in several ways. For example, a high-precision coordinate measuring machine (CMM) can be used to scan and measure the casting semi-finished product using contact or non-contact probes. Specifically, the spacing between the ring teeth and the height of the teeth can be accurately measured. The CMM provides high-resolution three-dimensional coordinate data, which can be compared with CAD models or design drawings to calculate the spacing error and height error of the ring teeth, thereby determining whether the casting meets the design tolerance requirements. Alternatively, an optical image measurement system can be used. This system acquires two-dimensional or three-dimensional images of the casting semi-finished product using a high-resolution industrial camera and combines this with image processing algorithms for dimensional analysis. For example, edge detection and feature recognition technologies can be used to automatically measure the spacing between the ring teeth and the height of the teeth.

[0101] This non-contact measurement method is suitable for complex and delicate geometric features, enabling rapid and batch inspection, reducing human error, and avoiding damage to the surface of castings.

[0102] Through the aforementioned technical solution, the manufacturing process of the pressure equalizing mixing tank connecting pipe involves rigorous chemical composition and mechanical property testing of raw materials upon arrival at the factory. This effectively filters out substandard raw materials, eliminating the risk of subsequent processing problems and insufficient final product performance due to material defects. This ensures the connecting pipe has a stable material foundation during key forming processes such as hot forging and casting, thereby guaranteeing its final structural strength and corrosion resistance.

[0103] Simultaneously, before deburring the semi-finished castings, the dimensional accuracy of key sealing structures such as the annular teeth and toothed sections is inspected, enabling the timely detection of any dimensional deviations during the casting process. This pre-inspection avoids unnecessary processing of components with pre-existing dimensional defects in subsequent processes, thereby reducing scrap rates and production costs. More importantly, it ensures that the sealing structure of the connecting pipe has a high-precision geometry, thus forming a reliable and durable seal when connected to the equalizing mixing tank, effectively preventing leakage under high-pressure conditions and significantly improving the overall reliability and service life of the connecting pipe.

[0104] In some of the solutions described above in this application, ER316LMo stainless steel welding wire is proposed for welding connecting pipes. However, in this process, the chemical composition of the welding wire may not be precisely defined, resulting in insufficient strength and corrosion resistance of the weld, which affects the overall performance stability of the connecting pipe under high-pressure water flow impact and long-term corrosive environment.

[0105] In this regard, this application further proposes that the chemical composition of ER316LMo stainless steel welding wire includes: Cr 17-19%, Ni 11-13%, Mo 2.0-3.0%, and C ≤ 0.03%.

[0106] The Cr17-19% specification refers to a chromium content in the welding wire that is between 17% and 19% by mass. Chromium is a key element in the formation of the passivation film on stainless steel, and its content directly affects the corrosion resistance of the weld. Within this range, the weld can form a stable and dense chromium-rich oxide film, effectively resisting oxidation and general corrosion, ensuring the weld's basic corrosion resistance in heating water environments. For example, when the chromium content is below 17%, the passivation film may not be stable enough, and the corrosion resistance will decrease significantly; while when the chromium content is above 19%, although the corrosion resistance may be slightly improved, it may lead to an increase in weld hardness, affecting its plasticity and welding processability, and reducing cost-effectiveness.

[0107] Ni11-13% refers to the nickel content in the welding wire being between 11% and 13% by mass. Nickel is an austenite-stabilizing element, ensuring the formation of a stable austenitic structure in the weld, thereby significantly improving the weld's toughness, plasticity, and impact resistance. For example, if the nickel content is below 11%, the weld may have excessive ferrite content, leading to decreased toughness and brittle fracture; if the nickel content is above 13%, although austenite stability is better, it may increase costs, and the marginal effect on improving corrosion resistance diminishes.

[0108] Mo2.0-3.0% refers to the molybdenum content in the welding wire being between 2.0% and 3.0% by mass. Molybdenum is an important element for improving the resistance of stainless steel to pitting and crevice corrosion, especially in media containing chloride ions. For example, when the molybdenum content is below 2.0%, the weld is not sufficiently resistant to localized corrosion caused by chloride ions and is prone to pitting corrosion; while when the molybdenum content exceeds 3.0%, although the resistance to pitting corrosion is further enhanced, it may increase the weld's susceptibility to hot cracking, affecting the weld quality.

[0109] C≤0.03% means that the mass percentage of carbon in the welding wire is no higher than 0.03%. Carbon content is a key factor in controlling intergranular corrosion in stainless steel. During welding, excessively high carbon content easily combines with chromium to form carbides, leading to chromium depletion at grain boundaries and thus initiating intergranular corrosion. For example, if the carbon content is higher than 0.03%, under the action of welding thermal cycling, a large amount of chromium carbide may precipitate in the heat-affected zone of the weld, increasing the susceptibility to intergranular corrosion and seriously affecting the long-term reliability of the weld.

[0110] The above technical solution precisely controls the chemical composition of the ER316LMo stainless steel welding wire, ensuring a high degree of match between the weld performance and the base material properties of the pressure equalization mixing tank connection pipe. The synergistic effect of chromium, nickel, molybdenum, and carbon elements ensures that the weld exhibits excellent resistance to pitting corrosion and intergranular corrosion, while maintaining good toughness and strength, under the harsh conditions of high pressure and high chlorine water in the heating system.

[0111] In particular, the low carbon content effectively prevents intergranular corrosion, while the precise control of molybdenum significantly enhances the weld's resistance to chloride ion corrosion.

[0112] This customized welding wire composition design not only avoids the dilution effect caused by compositional differences during welding, ensuring a high degree of consistency between the weld and the base material in terms of corrosion resistance and mechanical properties, but also complements the subsequent 1050℃ solution treatment process. This allows the solution treatment to more efficiently eliminate residual welding stress and optimize the microstructure, thereby significantly improving the overall durability and reliability of the connecting pipe, effectively resisting the impact of high-pressure water flow and long-term corrosion, and extending the service life of the pressure equalization mixing tank connecting pipe.

[0113] Under high-pressure conditions in heating systems, traditional connecting pipes are often affected by water flow impact and vibration due to insufficient structural strength, and are prone to corrosion due to long-term contact with heating water, resulting in decreased system stability and shortened service life.

[0114] Example 1

[0115] Formula ratio: Cr (chromium): 18.5%, Ni (nickel): 9.5%, Mo (molybdenum): 2.0%, Cu (copper): 0.5%, Nb (niobium): 0.1%, C (carbon): 0.05%, Si (silicon): 0.8%, Mn (manganese): 1.5%, Fe (iron, balance): 67.05%.

[0116] Process steps: S100 Raw Material Preparation and Incoming Inspection: Cold-rolled alloy steel coils with the above-mentioned composition are provided. The elemental content is verified by spectral analysis, and the tensile test yields a tensile strength of 680 MPa and an elongation of 32%. S200 billet cutting and hot forging preforming: Cut the billet to size: 150mm long × 50mm wide × 10mm thick, hot forge at 880℃, pressure 130MPa, hold for 18min and then air cool, the billet density reaches 99.2%; S300 Precision Investment Casting: The mold is made of paraffin-resin composite molding material (70% paraffin + 30% resin) (surface Ra≤0.8μm), with a silica sol-mullite shell, and dewaxing by steam at 125℃ and 0.3MPa; the pouring temperature is 1530℃, the pouring speed is 0.6m / s, and the error of the ring tooth spacing after molding is ±0.03mm and the error of the tooth height is ±0.01mm. S400 deburring and polishing process: First, mechanical vibration deburring (abrasive: ceramic grinding block, time 20 min), then ultrasonic deburring (frequency 40 kHz, time 10 min), rough polishing with a grinding wheel (80 grit grinding wheel, time 5 min), and finally fine polishing with a cloth wheel (wool wheel + polishing paste, time 8 min), with a final surface Ra=0.6μm; S500 welding and post-weld solution treatment: ER316LMo welding wire (Cr 18%, Ni 12%, Mo 2.5%, C 0.02%), TIG welding (current 90A, voltage 13V, speed 65mm / min, argon purity 99.995%, flow rate 9L / min, preheating 180℃); post-weld solution treatment at 1050℃ (holding for 30min) followed by air cooling, resulting in an 85% reduction in residual stress in the weld. S600 natural passivation treatment: passivation solution (nitric acid 18% + hydrofluoric acid 0.8% + water 81.2%), 45℃ for 18min; post-treatment: rinse with pure water 3 times (5min each time, conductivity ≤10μS / cm) and then dry with hot air at 85℃ for 10min, passivation film thickness 0.8μm.

[0117] Example 2

[0118] Formula ratio: Cr 18.5%, Ni 9.5%, Mo 1.5% (original range 1.8-2.2%), Cu 0.5%, Nb 0.1%, C 0.05%, Si 0.8%, Mn 1.5%, Fe = 67.55%; Process steps: Only the Mo content of the S100 raw material is adjusted; the rest is the same as in Example 1.

[0119] Example 3

[0120] Formula and proportions: Same as in Example 1; Process adjustment: S200 hot forging temperature 820℃ (original range 850-900℃), the rest is the same as in Example 1.

[0121] Example 4

[0122] Formula and proportions: Same as in Example 1; Process adjustment: S300 pouring speed 1.0m / s (original range 0.5-0.8m / s), the rest is the same as in Example 1. Example 5

[0123] Formula and proportions: Same as in Example 1; Process adjustment: The welding current in S500 is 70A (original range 80-100A), and the rest is the same as in Example 1.

[0124] Example 6

[0125] Formula and proportions: Same as in Example 1; Process adjustment: S600 passivation time 10 min (original range 15-20 min), the rest is the same as in Example 1.

[0126] Example 7

[0127] Formula and proportions: Same as in Example 1; Process adjustment: Only S400 deburring (mechanical vibration + ultrasonic) is retained, polishing is omitted, and the rest is the same as in Example 1.

[0128] Example 8

[0129] Formula ratio: Cr 18.5%, Ni 9.5%, Mo 2.0%, Cu 0.5%, Nb 0.1%, C 0.05%, Si 1.2% (original range ≤1.0%), Mn 1.5%, Fe = 66.65%; Process steps: Only the Si content in S100 is adjusted; the rest is the same as in Example 1.

[0130] Example Key variable deviation Tensile strength (MPa) Neutral salt spray duration (h) Weld strength (MPa) Surface roughness (μm) Main defects 1 None (benchmark) 680 550 620 0.6 none 2 Mo=1.5% (low) 675 380 615 0.6 Poor resistance to pitting corrosion 3 Forging at 820℃ (low) 590 540 530 0.6 Insufficient strength 4 Pouring speed: 1.0 m / s (height) 670 530 600 0.7 Seal failure 5 Welding 70A (low) 680 545 480 0.6 weld cracking 6 Passivation for 10 minutes (short time) 680 220 610 0.6 Poor corrosion resistance 7 Polishing omitted 680 280 615 3.2 Poor fit In the table above, the Mo content directly affects resistance to chloride ion corrosion; below 1.8%, pitting corrosion resistance drops sharply. The Si content must be ≤1.0%, as excessively high content leads to decreased material plasticity and increased susceptibility to welding cracks. Hot forging temperature must be ≥850℃ to ensure grain refinement; casting speed ≤0.8m / s to ensure fine structural forming; and passivation time ≥15min to ensure a dense passivation film. Deviations from these parameters will result in core performance failure.

[0131] Example 1 achieves optimal synergy in tensile strength, corrosion resistance, and sealing performance through precise component control and optimization of all process parameters, meeting the long-term use requirements of high-pressure (≥2.0MPa) and high-chlorine water in heating systems.

[0132] Example 9

[0133] Reference Figures 2-4 The present application also discloses a connecting pipe 2 for a pressure equalization mixing tank 1. The connecting pipe 2 is manufactured by the above-described manufacturing method. The connecting pipe 2 includes an integrally formed connecting part 21 and a fixing part 22. The end of the connecting part 21 is provided with a sealing structure composed of annular teeth 23 and toothed parts 26.

[0134] An annular groove 24 is formed between every two adjacent annular teeth 23. The annular teeth 23 and annular grooves 24 are arranged alternately to form an interlaced sealing structure. The surface of the annular teeth 23 is also uniformly distributed with fixedly connected tooth portions 26, and a tooth groove 25 is formed between every two adjacent tooth portions 26. The tooth portions 26 are small protrusions, and the tooth grooves 25 are corresponding recesses. This design allows the connecting part 21 to significantly increase the contact area and tightness of the fit when connected to external pipe fittings, through the cooperation of the annular teeth 23 and annular grooves 24, and the interlocking of the tooth portions 26 and tooth grooves 25. Simultaneously, sealing hemp rope is rolled inside the annular grooves 24.

[0135] The core innovation of this embodiment lies in combining the integrally molded connecting part 21 and fixing part 22 with the sealing structure of the annular tooth 23 and toothed part 26, and integrating improved material formulation, upgraded molding process, and optimized welding and surface treatment manufacturing methods, thereby significantly improving the structural strength and corrosion resistance of the connecting pipe 2. Specifically, since the connecting part 21 and fixing part 22 are integrally molded, the weak links caused by separate connections are avoided, making the overall structure of the connecting pipe 2 more uniform and complete, and effectively resisting the impact of high-pressure water flow and vibration stress; at the same time, the sealing structure formed by the annular tooth 23 and toothed part 26 is realized by precision molding process, optimizing the geometry of the sealing contact surface and enhancing the leakage prevention capability under high pressure environment.

[0136] Furthermore, the specific material selection and surface treatment processes in the manufacturing method further enhance the corrosion resistance of the substrate. Through the above technical solutions, while maintaining the same appearance as ordinary connecting pipes 2, the connecting pipe 2 achieves performance indicators such as tensile strength increase of ≥25% and neutral salt spray corrosion resistance increase of ≥150%, and effectively controls cost increment by being compatible with existing production equipment, ensuring reliable application in heating systems.

[0137] In some of the solutions described above in this application, a fixing part 22 is proposed for connecting the equalizing mixing tank 1. However, in the process of implementation, the connection method may not be able to effectively resist the impact and vibration of high-pressure water flow, or may be difficult to prevent the corrosion of heating water, resulting in insufficient connection strength, sealing failure or long-term corrosion resistance reduction, which affects the overall structural reliability.

[0138] In this regard, this application further proposes that the fixing part 22 of the connecting pipe 2 is connected to the equalizing mixing tank 1 by a weld. A weld, as a permanent connection method, refers to a connection method in which workpieces achieve atomic bonding through heating or pressurization, or both, with or without filler material. Here, the weld connection between the fixing part 22 and the equalizing mixing tank 1 can be implemented in various forms. For example, a fillet weld can be used, forming a triangular cross-section weld at the connection between the fixing part 22 and the equalizing mixing tank 1 to provide good structural strength and sealing; or a butt weld can be used, aligning and fusing the edges of the fixing part 22 and the equalizing mixing tank 1 to form a smooth and high-strength connection. This connection method ensures that a continuous, sealed, and high-strength integral structure is formed between the fixing part 22 and the equalizing mixing tank 1, thereby effectively resisting external loads and the erosion of internal media.

[0139] Through the above technical solution, the fixing part 22 is connected to the pressure equalizing mixing tank 1 by welding, which solves the problem of connection reliability. Specifically, the welded connection enables the fixing part 22 and the pressure equalizing mixing tank 1 to form an integrated structure, thereby effectively withstanding the water flow impact and vibration under the high pressure condition of the heating system, preventing the connection from loosening or failing, and significantly improving the structural strength and stability of the connection.

[0140] By combining the optimization of welding materials (such as ER316LMo stainless steel welding wire) and welding processes (such as TIG welding, inert gas shielded welding, and solution treatment) in the manufacturing process, the welded joint not only has excellent mechanical properties, but also excellent corrosion resistance. It can effectively resist long-term corrosion of heating water and avoid leakage or damage to structural integrity caused by corrosion.

[0141] By conducting quality inspections on the welds (such as ultrasonic testing, penetrant testing, and tensile testing), the inherent quality and reliability of the welds are ensured, further guaranteeing the safety and durability of the connecting pipe 2 and the equalizing mixing tank 1 during long-term operation, thereby improving the overall structural integrity, sealing performance, and service life of the entire equalizing mixing tank 1 system.

[0142] The following example will provide a more detailed explanation of the above technical solution: A company specializing in the manufacture of heating system components faced challenges: its equalizing mixing tank 1 connecting pipe 2 was susceptible to water flow impact and vibration under high-pressure conditions, and was also prone to corrosion from heating water quality during long-term operation. To address these issues, the company adopted a new manufacturing method for the connecting pipe 2.

[0143] In step S100, the company purchases alloy steel cold-rolled coils as raw materials. Before production, these raw materials undergo incoming inspection. Spectroscopic analysis verifies their chemical composition, ensuring that key elements such as chromium (18.0-19.0%), nickel (9.0-10.0%), and molybdenum (1.8-2.2%) meet requirements. These elements are crucial for improving the material's corrosion resistance and high-temperature strength. Simultaneously, tensile tests are conducted to confirm a tensile strength exceeding 600 MPa and an elongation exceeding 30%, ensuring sufficient initial strength and toughness to lay the foundation for structural strength under subsequent high-pressure conditions.

[0144] In step S200, qualified raw materials are cut into blanks. These blanks are pre-formed by hot forging at a temperature of 850-900℃, with a forging pressure of 120-150MPa applied, and held at that temperature for 15-20 minutes before air cooling. This pre-forming step refines the material grains through plastic deformation, eliminates internal defects, and improves the density and uniformity of the material, thereby significantly enhancing the overall structural strength and impact resistance of the connecting pipe 2, enabling it to effectively withstand the impact and vibration of high-pressure water flow from the heating system.

[0145] In step S300, the pre-formed billet, after hot forging, undergoes precision investment casting. This step aims to form the final shape of the connecting pipe 2, particularly the fine details of the sealing structure at the end of the connecting part 21, which consists of annular teeth 23 and toothed parts 26. During the casting process, a paraffin-resin composite molding compound is used to make the mold, ensuring that the mold surface roughness reaches Ra≤0.8μm to guarantee the surface quality of the casting. The mold shell used for casting is a silica sol-mullite shell, which has high strength and refractoriness, contributing to obtaining dimensionally stable castings. In the dewaxing stage, steam at 120-130℃ and 0.3MPa is used for dewaxing to ensure the cleanliness of the mold cavity. The casting pouring temperature is controlled at 1520-1550℃, and the pouring speed is 0.5-0.8m / s. These parameters ensure good fluidity and filling capacity of the molten metal, enabling the precise forming of complex structures such as annular teeth 23 and toothed parts 26, providing a foundation for subsequent reliable sealing. After casting is completed, before proceeding to the next step, a coordinate measuring machine is used to inspect the dimensional accuracy of the cast semi-finished product, focusing on the spacing error of the ring tooth 23 and the height error of the tooth part 26, to ensure that the sealing structure meets the design requirements and avoids seal failure due to dimensional deviations.

[0146] In step S400, the cast connecting pipe 2 undergoes deburring and polishing. The deburring process employs mechanical vibration followed by ultrasonic deburring to ensure that burrs on the inner and outer surfaces of the connecting pipe 2, especially in areas with complex structures, are thoroughly removed, preventing burrs from becoming stress concentration points or corrosion sources. The polishing process employs rough polishing with an abrasive wheel followed by fine polishing with a cloth wheel to achieve a surface roughness of Ra ≤ 0.8 μm for the connecting pipe 2. This smooth surface not only improves the appearance quality but, more importantly, reduces surface defects and microcracks, lowering the likelihood of corrosive media adhesion, thereby improving the corrosion resistance and fatigue strength of the connecting pipe 2.

[0147] In step S500, the fixing part 22 of the connecting pipe 2 is welded to the connecting hole of the pressure equalizing mixing tank 1. The welding material is ER316LMo stainless steel welding wire, which contains 17-19% chromium, 11-13% nickel, and 2.0-3.0% molybdenum in its chemical composition, with a carbon content of less than 0.03%. This welding wire has excellent corrosion resistance, especially strong resistance to pitting and crevice corrosion, and its corrosion resistance matches that of the base material. The welding process uses TIG welding (inert gas shielded welding), with the process parameters set as follows: welding current 80-100A, welding voltage 12-14V, welding speed 50-80mm / min, and the shielding gas being argon with a purity of not less than 99.99% at a flow rate of 8-10L / min. Preheating to 150-200℃ is performed before welding.

[0148] These precise welding parameters and protective measures ensure weld quality, reduce welding defects, and effectively prevent oxidation and nitriding in the weld area, guaranteeing weld strength and corrosion resistance. After welding, the connecting pipe 2 undergoes solution treatment at 1050℃ and air cooling to eliminate welding stress, restore the material's intergranular corrosion sensitivity, and further enhance the corrosion resistance and toughness of the weld area. After solution treatment and before passivation, the weld undergoes quality inspection using ultrasonic and penetrant testing for non-destructive testing. Samples are also taken for tensile testing of the weld, requiring the fracture location to be in the base material rather than the weld itself. This verifies the consistency between weld strength and base material strength, ensuring the connection reliability of the connecting pipe 2 under high-pressure conditions in the equalizing mixing tank 1.

[0149] In step S600, the welded and heat-treated connecting pipe 2 undergoes a natural passivation treatment. The passivation solution is a mixed aqueous solution of nitric acid and hydrofluoric acid, the treatment temperature is controlled at 40-50℃, and the treatment time is 15-20 minutes. This step forms a dense and stable passivation film on the surface of the connecting pipe 2, significantly enhancing its long-term corrosion resistance in heating water environments and effectively preventing corrosion. After passivation, post-treatment is performed, including rinsing three times with pure water for 5 minutes each time to thoroughly remove residual passivation solution and impurities, followed by hot air drying at 80-100℃ for 10 minutes to ensure surface dryness and a stable passivation film.

[0150] Using the aforementioned manufacturing method, the connecting pipe 2 of the equalizing mixing tank 1 produced by this enterprise uses high-alloy cold-rolled coils, whose superior corrosion resistance and strength far exceed those of ordinary carbon steel or low-alloy steel connecting pipes 2. In terms of forming process, combining hot forging pre-forming and precision investment casting not only achieves the integrated forming of the connecting part 21 and the fixing part 22, ensuring structural integrity, but also precisely forms the sealing structure of the annular tooth 23 and the tooth part 26, achieving a precision and surface quality that is difficult to achieve with traditional machining.

[0151] Compared to the simple casting or welding assembly methods used in existing technologies, this method effectively avoids casting defects and surface roughness issues through precise casting processes and rigorous surface treatment, thereby improving the tensile strength and neutral salt spray corrosion resistance of the connecting pipe 2. In the welding and surface treatment stages, ER316LMo welding wire and TIG welding technology are used, combined with solution treatment and natural passivation, ensuring that the weld area has the same excellent properties as the base material, effectively solving the problems of weld corrosion and strength reduction that may occur with traditional welding. These synergistic steps enable the connecting pipe 2 to meet the structural strength requirements under high-pressure conditions while also possessing the ability to resist long-term corrosion from heating water, significantly improving the product's service life and reliability.

[0152] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for manufacturing a connecting pipe, characterized in that, The connecting pipe has an integrally formed connecting part and a fixing part, and a sealing structure consisting of annular teeth and toothed parts is formed at the end of the connecting part; the manufacturing method includes the following steps: S100. Provide alloy steel cold-rolled coils as raw materials, wherein the chemical composition of the alloy steel includes: Cr 18.0-19.0%, Ni 9.0-10.0%, Mo 1.8-2.2%, Cu 0.4-0.6%, Nb 0.08-0.12%, C≤0.07%, Si≤1.0%, Mn≤2.0%, with the balance being Fe and unavoidable impurities; S200. Cut the raw material into blanks and preform the blanks by hot forging at 850-900℃ with a forging pressure of 120-150MPa. After holding at the temperature for 15-20 minutes, air cool. S300. Precision investment casting is performed on the pre-formed billet by hot forging to form the final shape of the connecting pipe and the detailed structure of the annular tooth and tooth part. The casting pouring temperature is 1520-1550℃ and the pouring speed is 0.5-0.8m / s. S400. The cast connecting pipe is deburred and polished to make its surface roughness Ra≤0.8μm; S500. Weld the fixed part of the connecting pipe to the connecting hole of the pressure equalizing mixing tank. The welding material is ER316LMo stainless steel welding wire. The welding process adopts inert gas shielded welding. After welding, it is subjected to 1050℃ solution treatment and air cooling. S600. After welding and heat treatment, the entire connecting pipe is subjected to natural passivation treatment. The passivation solution is a mixed aqueous solution of nitric acid and hydrofluoric acid. The treatment temperature is 40-50℃ and the time is 15-20min.

2. The method for manufacturing the connecting pipe according to claim 1, characterized in that, In step S300, the precision investment casting uses a paraffin-resin composite molding material to make the mold, and the surface roughness of the mold Ra≤0.8μm; the shell used for casting is a silica sol-mullite shell, and dewaxing is performed using steam at 120-130℃ and 0.3MPa.

3. The method for manufacturing the connecting pipe according to claim 1, characterized in that, In step S400, the deburring process is carried out by mechanical vibration deburring and ultrasonic deburring in sequence; the polishing process is carried out by rough polishing with a grinding wheel and fine polishing with a cloth wheel in sequence.

4. The method for manufacturing the connecting pipe according to claim 1, characterized in that, In step S500, the inert gas shielded welding is TIG welding, and the process parameters include: welding current 80-100A, welding voltage 12-14V, welding speed 50-80mm / min, shielding gas is argon with a purity ≥99.99% and a flow rate of 8-10L / min, and welding preheating temperature is 150-200℃.

5. The method for manufacturing a connecting pipe according to claim 1, characterized in that, After step S500 and before step S600, a step of quality inspection of the weld is also included: non-destructive testing is performed using ultrasonic testing and penetrant testing, and samples are taken for weld tensile testing, requiring the fracture location to be in the base material rather than the weld.

6. The method for manufacturing a connecting pipe according to claim 1, characterized in that, In step S600, the post-treatment after the passivation treatment includes: rinsing with pure water three times, 5 minutes each time, and then drying with hot air at 80-100℃ for 10 minutes.

7. The method for manufacturing a connecting pipe according to claim 1, characterized in that, In step S100, after providing the raw materials, the process also includes an incoming inspection step: verifying the chemical composition using spectral analysis and conducting tensile tests to ensure that the tensile strength is ≥600MPa and the elongation is ≥30%. After step S300 and before step S400, the process further includes a step of dimensional accuracy detection of the cast semi-finished product: using a coordinate measuring machine to detect the spacing error of the ring teeth and the height error of the teeth.

8. The method for manufacturing a connecting pipe according to claim 1, characterized in that, The chemical composition of the ER316LMo stainless steel welding wire includes: Cr 17-19%, Ni 11-13%, Mo 2.0-3.0%, and C ≤ 0.03%.

9. A connecting pipe for a pressure equalization mixing tank, characterized in that, The connecting pipe is manufactured using the manufacturing method described in any one of claims 1-8; the connecting pipe includes an integrally formed connecting part and a fixing part, and the end of the connecting part is provided with a sealing structure composed of annular teeth and toothed parts.

10. The connecting pipe for a pressure equalization mixing tank according to claim 9, characterized in that, The fixing part is connected to the pressure equalizing mixing tank by a weld.

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