Gold-plated inner layer drinking water conveying pipeline with multi-layer composite structure and preparation method thereof

Abstract

The invention discloses a multi-layer composite structure gold-plated inner layer drinking water conveying pipeline and a preparation method thereof, and belongs to the field of drinking water conveying pipelines. The pipeline is of a four-layer composite structure, the outer layer is a 316L stainless steel pipe with the diameter being 1.2-3.0 mm, the middle layer is a food-grade epoxy resin layer with the diameter being 0.3-0.8 mm, the inner layer is a TP2 thin-wall copper pipe with the diameter being 0.5-1.5 mm, and the inner wall of the copper pipe is a 99.99% high-purity gold plating layer with the diameter being 0.001-0.002 mm. The preparation comprises six core processes, gold plating adopts an electroplating and chemical plating composite process, and parameters such as specific current density, plating solution temperature and the like are controlled. The designed service life of the pipeline is gt; 100 years later, sanitation and mechanical performance are excellent, the gold layer is firmly attached, the problems that a traditional pipeline is poor in corrosion resistance, and the gold layer is prone to falling off are solved, and the composite pipe is suitable for drinking water conveying scenes such as high-end residences and medical treatment.

Description

Technical Field

[0001] This invention relates to the field of drinking water pipeline technology, specifically to a multi-layer composite structure gold-plated inner layer drinking water pipeline and its preparation method. It is particularly suitable for drinking water transportation scenarios with high requirements for drinking water hygiene and safety, pipeline service life and mechanical performance, such as high-end residences, high-end medical facilities, and laboratories with stringent water quality requirements. Background Technology

[0002] The corrosion resistance, hygiene and safety, and mechanical strength of drinking water pipelines are the core indicators for evaluating their performance. Existing drinking water pipeline technologies have many shortcomings that are difficult to balance: PPR pipes, while economical and practical, have limited service life and poor high-temperature resistance, failing to meet the long-term use requirements of high-end scenarios; 304 stainless steel pipes have good corrosion resistance, but the chromium oxide passivation film on their surface hinders direct metal bonding with the gold layer, resulting in poor adhesion and making direct gold plating impossible; thick-walled copper pipes, as a high-end traditional pipe material, have excellent adhesion to the gold layer, but they are prone to oxidation in the air, forming verdigris, and their use alone still poses a risk of water pollution; pure gold-plated pipes rely on a base material because gold lacks forming support, and if the base material is not chosen properly, the gold layer will easily peel off, and the cost of gold raw materials is high, making all-gold pipes impractical for engineering projects.

[0003] Meanwhile, existing gold-plated pipe substrate materials have many compatibility issues: iron / steel substrates form brittle intermetallic compounds with gold, resulting in poor adhesion and easy rusting, making them completely unsuitable for drinking water pipes; nickel substrates, while having good adhesion to gold and excellent corrosion resistance, pose a risk of allergy to some individuals, requiring strict caution in drinking water applications; platinum / palladium and other platinum group metals, while possessing excellent performance, exhibiting excellent adhesion to gold and corrosion resistance, cost several to tens of times more than gold, limiting their use to specialized fields and hindering large-scale engineering applications; silver substrates have excellent adhesion to gold, but their cost is higher than copper, and they readily react with sulfur to sulfide and turn black, resulting in insufficient cost-effectiveness.

[0004] Furthermore, pipes made of a single material cannot simultaneously meet the multiple requirements of mechanical support strength, stable gold plating adhesion, food-grade hygiene and safety, and ultra-long service life. High-end drinking water transportation scenarios urgently need a multi-layer composite structure gold-plated pipe that utilizes the chemical inertness of gold to achieve ultimate corrosion resistance and water quality protection. Combined with suitable base materials and external support materials, it solves the technical problems of easy gold plating peeling off, easy corrosion of the base material, and insufficient mechanical strength of the pipe, while taking into account the overall cost and practicality of engineering applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects of existing drinking water delivery pipelines and to provide a multi-layer composite structure gold-plated inner layer drinking water delivery pipeline and its preparation method. Through the scientific selection and precise matching of multi-layer materials, stable adhesion of the gold layer, ultra-high mechanical strength of the pipeline, food-grade hygiene and safety, and a design life of over 100 years are achieved. At the same time, the design of thin-walled substrate and composite process controls the overall cost of engineering applications, meeting the drinking water delivery needs of high-end scenarios.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The gold-plated inner layer drinking water delivery pipe with a multi-layer composite structure consists of an outer structural layer, an intermediate bonding layer, an inner carrier layer, and a functional plating layer, from the outside to the inside. The outer structural layer is a 316L stainless steel tube with a thickness of 1.2-3.0 mm, which has undergone solution treatment and has been polished internally and externally with Ra≤0.8μm; The intermediate bonding layer is made of food-grade epoxy resin with a thickness of 0.3-0.8 mm, meeting the GB / T 17219 hygiene standard; The inner carrier layer is a TP2 thin-walled copper tube with a thickness of 0.5-1.5mm, which has been bright annealed and has an inner surface roughness Ra≤0.4μm; The functional coating is a 99.99% high-purity gold layer with a thickness of 0.001-0.002 mm, prepared using a composite process of electroplating and chemical plating, with a porosity of ≤1 particle / cm².

[0007] Furthermore, the nominal pipe diameter covers DN15-DN150, the working pressure is ≤1.6MPa, the applicable temperature varies depending on the flow temperature of different liquids, and it can be used within the range that the material can withstand. The design life is >100 years, and it complies with ISO15686, GB / T 17116, and GB / T 18991 standards. The sanitary grade is food grade / drinking water grade.

[0008] Furthermore, the pipeline exhibits hydraulic strength up to 2.5 times the working pressure without leakage, tensile strength ≥520MPa, no cracks during 4D bending, and no cracks when compressed to 3 / 4D. 7 No damage from vibration fatigue; heavy metal precipitation meets the requirements of Pb≤0.1μg / L, Cd≤0.1μg / L, organic matter migration TOC increase ≤0.1mg / L, and sensory indicators are colorless, odorless, and free of precipitation.

[0009] The preparation method of a multi-layer composite structure gold-plated inner layer drinking water delivery pipe includes the following steps: (1) Stainless steel pipe preparation: cold rolling / welding and solution treatment process is adopted to control the grain size ≥ 7 grade and δ ferrite ≤ 1%, and it is tested by eddy current testing and hydrostatic test; (2) Copper tube inner liner forming: adopt drawing and bright annealing process, control elongation ≥40%, hardness HV55-75, and check dimensional tolerance and surface roughness; (3) Surface pretreatment: Chemical cleaning and activation process is used for degreasing, pickling and passivation, which is verified by continuous water film test; (4) Epoxy coating: Centrifugal coating and thermal curing process is adopted to control the coating thickness to 0.5±0.2mm, the degree of curing to ≥95%, and the adhesion is tested by cross-cut test; (5) Composite assembly: adopt hydraulic expansion and shrinkage process, control interference of 0.1-0.3mm, concentricity ≤0.5mm; (6) Gold plating on the inner wall: A high-purity gold layer that meets the requirements of thickness and porosity is prepared by adopting a composite process of electroplating and chemical plating, including pre-plating treatment, optional pre-plating of nickel, gold plating, and post-treatment.

[0010] Furthermore, the pre-plating treatment for the gold plating of the inner wall involves micro-etching to a depth of 5-10 μm and activation to ensure uniform surface activity; the pre-plated nickel layer has a thickness of 0.5-1 μm to enhance the adhesion of the gold layer.

[0011] Furthermore, the gold plating process parameters for the inner wall are as follows: The gold plating current density is 0.5-1.0 A / dm², using a pulse power supply with a duty cycle of 30%; the plating bath temperature is 50-60℃ with an accuracy of ±1℃; the plating bath pH value is 4.5-5.5, which is automatically controlled; and the plating thickness is 1.0-2.0 μm, which is monitored online.

[0012] Furthermore, the post-treatment of the gold plating on the inner wall involves rinsing with pure water with a resistivity ≥15MΩ・cm, followed by hot air drying.

[0013] Furthermore, after each process is completed, composite quality control is carried out to ensure that the layers of the pipeline are firmly bonded and there is no risk of delamination; the finished pipeline is inspected and accepted by XRF thickness testing, ICP-MS elemental precipitation testing, and GB / T 31402 antibacterial testing.

[0014] The multi-layer composite structure gold-plated inner layer drinking water delivery pipe and its preparation method of the present invention have the following significant advantages compared with the prior art: 1. Scientific material combination and high gold layer adhesion stability: TP2 copper tube is selected as the gold layer substrate, forming a strong metallurgical bond with gold, solving the technical problem of easy gold layer peeling at the substrate level; at the same time, the 316L stainless steel outer layer provides all-round mechanical protection for copper tube and gold layer, and the epoxy resin intermediate layer effectively avoids electrochemical corrosion between stainless steel and copper tube. The multi-layer structure works together to further extend the service life of gold layer and copper tube.

[0015] 2. High level of hygiene and safety, excellent water quality protection: The gold layer acts as an inert barrier, does not react with water, has no risk of heavy metal leaching, and completely isolates the copper pipe from the outside world, preventing the copper pipe from oxidizing and forming verdigris; all materials of the pipe meet food-grade / drinking water-grade standards. Tests show that the leaching of heavy metals Pb and Cd is ≤0.1μg / L, the leaching of gold element is ≤0.01mg / L, the increase of TOC due to organic matter migration is ≤0.1mg / L, the antibacterial rate is ≥99%, and the sensory indicators are colorless, odorless, and free of sediment, achieving pollution-free transportation of drinking water throughout the entire process.

[0016] 3. Excellent mechanical strength and ultra-long service life: The 316L stainless steel outer layer bears all the mechanical strength of the pipeline, resulting in excellent overall mechanical properties. It can withstand hydraulic pressure up to 2.5 times the working pressure without leakage, and has a tensile strength ≥520MPa. It shows no cracks after 4D bending tests and 3 / 4D flattening tests. 7 No damage was found in the vibration fatigue test; the pipeline has a design life of over 100 years, far exceeding that of traditional PPR pipes, 304 stainless steel pipes, and thick-walled copper pipes, making it an ultra-long-life investment-grade pipe material.

[0017] 4. Precise process parameters and strong product quality control: Each preparation process has clearly defined key parameters and quality control points. The gold plating process uses online monitoring and XRF thickness detection to ensure that the gold layer thickness and porosity meet the design requirements. The composite assembly process strictly controls the interference and concentricity to ensure that each layer is firmly bonded without delamination. The standardized process throughout the entire process ensures stable product quality and mass production capability.

[0018] 5. Wide range of applications and high overall cost-effectiveness throughout the entire life cycle: The nominal diameter of the pipes covers the entire series from DN15 to DN150, which can meet the different drinking water transportation needs of inlet pipes, branch pipes, risers, and main pipes. It is suitable for high-end residences, high-end medical care, and laboratories that are extremely sensitive to electrochemical corrosion. Although the initial cost of the pipes is higher than that of traditional pipes, they are almost maintenance-free throughout the entire life cycle, with no maintenance risks such as coating damage or substrate corrosion, resulting in lower overall costs.

[0019] 6. Highly practical for engineering applications, with material selection that balances performance and cost: Thin-walled copper tubes are used as the base material instead of thick-walled copper tubes, reducing the amount of copper used and controlling raw material costs while ensuring the adhesion of the gold layer; 316L stainless steel is used as the external support material. Compared with carbon steel + heavy anti-corrosion coating, it does not require regular coating inspection and has no risk of rust after damage. Compared with high-strength engineering plastics, it has higher mechanical strength and stronger impact resistance, making it the optimal support material choice overall. Attached Figure Description

[0020] Figure 1: Overall structural diagram of the gold-plated inner layer drinking water delivery pipeline of the multi-layer composite structure of this invention; Figure 2 Flowchart of the method for preparing the gold-plated inner layer drinking water delivery pipe with multi-layer composite structure according to the present invention; Figure 3 Cost breakdown diagram for DN50 specification. Detailed Implementation

[0021] 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 embodiments of the present invention, and not all embodiments. 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.

[0022] The invention proposes a multi-layer composite structure gold-plated inner layer drinking water delivery pipe and its preparation method. The design focuses on both the multi-layer composite structure of the pipe and the preparation method. It makes full use of the chemical stability, ductility and airtightness of gold, the excellent adhesion between copper and gold, the ultra-high mechanical strength and corrosion resistance of 316L stainless steel, and the bonding and insulation properties of food-grade epoxy resin to achieve the synergistic effect of each layer of materials.

[0023] I. Multi-layer composite structure gold-plated inner layer drinking water delivery pipe The drinking water delivery pipeline of this invention has a four-layer composite structure, consisting of an outer structural layer, an intermediate bonding layer, an inner carrier layer, and a functional coating layer, from the outside to the inside. The materials, thickness range, core functions, and key process requirements of each layer are precisely designed, and all materials in contact with water strictly comply with food-grade / drinking water-grade hygiene standards. The overall design life is >100 years, the working pressure is ≤1.6MPa, and the applicable temperature is based on the different flow temperatures of different liquids, within the range that the materials can withstand. The hygiene level meets the food-grade / drinking water-grade GB / T 17219 standard, the design life complies with the ISO 15686 standard, the working pressure complies with the GB / T 17116 standard, and the applicable temperature complies with the GB / T 18991 standard. (i) The outer structural layer is made of 316L stainless steel pipe with a thickness controlled between 1.2-3.0mm, which bears 100% of the mechanical strength and external protection of the pipeline. This layer is treated with solution treatment and polished inside and outside. After polishing, the surface roughness Ra≤0.8μm has excellent corrosion resistance. The life of the main material is far more than 100 years. Furthermore, the probability of rust can be further reduced by wrapping the outside with plastic film. It is the core mechanical support structure of the pipeline. (ii) The intermediate bonding layer is made of food-grade epoxy resin with a thickness controlled between 0.3-0.8 mm. It must meet the GB / T 17219 hygiene standard and has three functions: bonding, electrical insulation, and buffering. On the one hand, it achieves a firm bond between the outer stainless steel layer and the inner copper pipe, and on the other hand, it avoids electrochemical corrosion between the stainless steel and copper pipe. At the same time, it provides a certain buffering performance for the pipeline and reduces the impact of mechanical impact on the inner layer. This layer uses two-component epoxy resin, and the curing temperature is controlled between 80-100℃ to ensure the curing effect. (III) The inner carrier layer is a TP2 thin-walled copper tube with a thickness controlled between 0.5-1.5mm. It is an ideal substrate for gold plating, with excellent adhesion to gold. Copper and gold can diffuse into each other to form a strong metallurgical bond, which can effectively prevent the gold layer from falling off. The copper tube itself has excellent corrosion resistance. After being completely covered by the gold layer, it can isolate external oxidation and avoid the formation of verdigris. This layer is bright annealed, and the inner surface roughness Ra≤0.4μm, ensuring that the water is clean and free of impurities. (iv) The functional coating is a 99.99% high-purity gold layer with a thickness controlled between 0.001-0.002 mm. As an inert anti-corrosion and water quality protection barrier, it utilizes the chemical stability of gold—it does not react with water and has extremely stable chemical properties—to achieve pollution-free transportation of drinking water. At the same time, it isolates the copper pipe from external oxidation, further extending the service life of the copper pipe. The gold layer is prepared by a composite process of electroplating and chemical plating, with a porosity of ≤1 porosity / cm², ensuring anti-corrosion and sealing effects. It fully utilizes the ductility and sealing properties of gold to achieve comprehensive protection of the water flow channel.

[0024] The nominal pipe diameters of this invention cover the entire range from DN15 to DN150, meeting the needs of different drinking water transportation scenarios such as inlet pipes, branch pipes, risers, and main pipes. The specific specifications for each nominal diameter are as follows: DN15: Stainless steel outer tube φ18×1.2mm, copper inner liner φ15.6×0.5mm, composite pipe outer diameter 18.0mm, theoretical weight 0.68kg / m, working pressure 2.5MPa, connection method: press-fit / threaded; DN20: Stainless steel outer tube φ25×1.5mm, copper inner liner φ22×0.5mm, composite pipe outer diameter 25.0mm, theoretical weight 1.12kg / m, working pressure 2.5MPa, connection method: press-fit / flange; DN25: Stainless steel outer tube φ32×1.5mm, copper inner liner φ29×0.6mm, composite pipe outer diameter 32.0mm, theoretical weight 1.65kg / m, working pressure 2.0MPa, connection method: press-fit / welded; DN32 The first specification is a stainless steel outer tube with a diameter of φ38×1.5mm and a copper inner liner with a diameter of φ35×0.6mm. The composite pipe has an outer diameter of 38.0mm, a theoretical weight of 2.08kg / m, and a working pressure of 2.0MPa. The connection method is press-fit / flange. The second specification is a stainless steel outer tube with a diameter of φ45×1.5mm and a copper inner liner with a diameter of φ42×0.8mm. The composite pipe has an outer diameter of 45.0mm, a theoretical weight of 2.85kg / m, and a working pressure of 1.6MPa. The connection method is flange / welding. The third specification is a stainless steel outer tube with a diameter of φ57×2.0mm and a copper inner liner with a diameter of φ53×0.8mm. The composite pipe has an outer diameter of 57.0mm, a theoretical weight of 4.32kg / m, and a working pressure of 1.6MPa. The connection method is flange / grooved. The fourth specification is a stainless steel outer tube with a diameter of φ57×2.0mm and a copper inner liner with a diameter of φ53×0.8mm. The composite pipe has an outer diameter of 57.0mm, a theoretical weight of 4.32kg / m, and a working pressure of 1.6MPa. The connection method is flange / grooved. The first specification is a stainless steel outer tube with a diameter of φ76×2.0mm and a copper inner liner with a diameter of φ72×1.0mm. The composite pipe has an outer diameter of 76.0mm, a theoretical weight of 6.15kg / m, and a working pressure of 1.6MPa. The connection method is flange / welding. The second specification is a stainless steel outer tube with a diameter of φ89×2.0mm and a copper inner liner with a diameter of φ85×1.0mm. The composite pipe has an outer diameter of 89.0mm, a theoretical weight of 7.48kg / m, and a working pressure of 1.0MPa. The connection method is flange / grooving. The third specification is a stainless steel outer tube with a diameter of φ108×2.5mm and a copper inner liner with a diameter of φ103×1.2mm. The composite pipe has an outer diameter of 108.0mm, a theoretical weight of 11.62kg / m, and a working pressure of 1.0MPa. The connection method is flange / welding. The fourth specification is a stainless steel outer tube with a diameter of φ108×2.5mm and a copper inner liner with a diameter of φ103×1.2mm. The composite pipe has an outer diameter of 108.0mm, a theoretical weight of 11.62kg / m, and a working pressure of 1.0MPa. The connection method is flange / welding. The fifth specification is a stainless steel outer tube with a diameter of φ108×2.5mm and a copper inner liner with a diameter of φ103×1.2mm. The composite pipe has an outer diameter of 108.0mm, a theoretical weight of 11.62kg / m, and a working pressure of 1.0MPa. The connection method is flange / welding. The specifications are as follows: stainless steel outer tube φ159×3.0mm, copper inner liner φ153×1.5mm, composite pipe outer diameter 159.0mm, theoretical weight 22.85kg / m, working pressure 1.0MPa, and connection method is flange / welding.

[0025] II. Preparation method of multi-layer composite structure gold-plated inner layer drinking water delivery pipe The pipe manufacturing method of the present invention includes six core processes in sequence: stainless steel pipe preparation, copper pipe inner liner forming, surface pretreatment, epoxy coating, composite assembly, and inner wall gold plating. Each process has clearly defined process methods, key parameters, and quality control points to ensure stable product quality and strong bonding between layers without the risk of delamination. Specific process details are as follows: (I) Stainless steel pipe preparation: The process of cold rolling / welding + solution treatment is adopted. The key parameters are controlled as follows: grain size ≥ 7 and δ ferrite ≤ 1%; the quality control points are eddy current testing and hydrostatic testing. It is necessary to ensure that the stainless steel pipe is free of defects and has good sealing performance to obtain qualified 316L stainless steel outer pipe. (II) Copper tube liner forming: TP2 thin-walled copper tubes are prepared by drawing + bright annealing process. The key parameters are controlled as follows: elongation ≥40% and hardness HV55-75. The quality control points are dimensional tolerance and surface roughness inspection. It is necessary to ensure that the surface roughness Ra of the inner surface of the copper tube is ≤0.4μm to obtain qualified copper tube liner.

[0026] (III) Surface pretreatment: Chemical cleaning and activation treatment are carried out on the inner wall of the stainless steel outer tube and the outer wall of the copper inner liner, and the degreasing, pickling and passivation processes are completed in sequence; the quality control point is the water film continuous test, which must ensure that the treated surface is free of oil and oxide layer, so as to improve the adhesion of subsequent coatings and composites.

[0027] (iv) Epoxy coating: Food-grade epoxy resin is coated on the inner wall of the stainless steel outer tube using a centrifugal coating + heat curing process. The key parameters are controlled as follows: coating thickness 0.5±0.2mm, curing degree ≥95%; the quality control point is the adhesion cross-cut test, which must ensure that the epoxy coating has excellent bonding performance to obtain the epoxy-coated stainless steel outer tube.

[0028] (v) Composite assembly: The copper inner tube and the epoxy-coated stainless steel outer tube are hydraulically expanded and contracted together. The key parameter is controlled as interference of 0.1-0.3mm. The concentricity of the composite pipe is ≤0.5mm. This process requires strict composite quality control to ensure that the epoxy layer is firmly bonded to the stainless steel and copper tubes and there is no risk of delamination.

[0029] (vi) Gold plating of the inner wall: Gold plating is performed on the inner wall of the copper pipe liner, which is the core process of pipe preparation. A composite process of electroplating and chemical plating is adopted, which is divided into four steps: pre-plating treatment, optional pre-nickel plating, gold plating, and post-treatment. The overall gold layer thickness must be 1.0-2.0μm, and the porosity must be ≤1 particle / cm². The quality control point is XRF thickness detection. The specific parameters and control requirements of each step are as follows: (1) Pre-plating treatment: The inner wall of the copper tube is micro-etched to 5-10μm and activated. The core control requirement is to ensure uniform surface activity, which lays the foundation for gold layer adhesion. (2) Pre-plating nickel layer: This is an optional step. A nickel layer of 0.5-1μm is plated. The core control requirement is to enhance the adhesion between the gold layer and the copper pipe. The thickness of the nickel layer must be strictly controlled to avoid nickel ion precipitation from affecting the safety of drinking water. (3) Gold plating: Gold plating is performed using a pulse power supply. The key parameters are controlled as follows: gold plating current density 0.5-1.0A / dm², duty cycle 30%, plating bath temperature 50-60℃ with control accuracy ±1℃, plating bath pH value 4.5-5.5 with automatic control, and gold layer thickness is monitored online to ensure that it meets the requirement of 1.0-2.0μm. (4) Post-treatment: The inner wall of the gold-plated pipe is thoroughly rinsed with pure water with a resistivity of ≥15MΩ・cm and then dried with hot air. The core control requirement is to avoid residual plating solution from polluting the water quality and to ensure the cleanliness of the inner wall of the pipe.

[0030] The following describes in more detail the gold-plated inner layer drinking water delivery pipe with a multi-layer composite structure and its preparation method, in conjunction with specific process parameters and performance indicators. The scope of protection of this invention is not limited to the following embodiments.

[0031] Example 1: DN25 Multi-layer Composite Gold-plated Drinking Water Transmission Pipe This embodiment prepares a DN25 pipe, which is a commonly used specification for drinking water transportation. The nominal diameter is DN25, the stainless steel outer tube is φ32×1.5mm, the copper inner liner is φ29×0.6mm, the outer diameter of the composite pipe is 32.0mm, the theoretical weight is 1.65kg / m, the working pressure is 2.0MPa, and the connection method is press-fit / welding.

[0032] Pipeline structural parameters: outer layer 316L stainless steel pipe thickness 1.5mm, middle layer food-grade epoxy resin thickness 0.5mm, inner layer TP2 thin-walled copper pipe thickness 0.6mm, functional plating layer 99.99% high-purity gold layer thickness 0.0015mm.

[0033] Manufacturing process parameters: Stainless steel pipes are manufactured using cold rolling + solution treatment, with a grain size of grade 8 and δ-ferrite of 0.8%, passing eddy current testing and hydrostatic testing; the copper inner liner is formed using drawing + bright annealing, with an elongation of 45%, hardness of HV60, and inner surface roughness Ra≤0.3μm; epoxy coating is done using centrifugal coating + thermosetting, with a coating thickness of 0.5mm, a curing degree of 96%, and an adhesion cross-cut test grade of 0; composite assembly is done using hydraulic expansion + shrinkage, with an interference fit of 0.2mm and a concentricity of 0.3mm; the inner wall gold plating is performed by micro-etching 8μm + activation treatment, pre-plating with nickel of 0.8μm, gold plating current density of 0.8A / dm², plating bath temperature of 55℃, pH value of 5.0, gold layer thickness of 1.5μm, porosity of 0.8 cells / cm², and post-treatment by rinsing with pure water with a resistivity of 18MΩ・cm and hot air drying.

[0034] Finished product performance testing: The pipe was tested and found to have a hydraulic strength of 5.0 MPa with no leakage, a tensile strength of 550 MPa, no cracks when bent in 4D, and no cracks when flattened to 3 / 4D; heavy metal Pb precipitation was 0.05 μg / L, Cd precipitation was 0.04 μg / L, gold precipitation was 0.005 mg / L, antibacterial rate was 99.5%, organic matter migration TOC increased by 0.08 mg / L, and sensory indicators were colorless, odorless, and free of precipitation, meeting all acceptance standards of this invention.

[0035] Example 2: DN50 Multi-layer Composite Gold-plated Drinking Water Delivery Pipe This embodiment prepares a DN50 pipe, which is the main pipe specification for drinking water transportation. The nominal diameter is DN50, the stainless steel outer pipe is φ57×2.0mm, the copper inner liner is φ53×0.8mm, the outer diameter of the composite pipe is 57.0mm, the theoretical weight is 4.32kg / m, the working pressure is 1.6MPa, and the connection method is flange / groove.

[0036] Pipeline structural parameters: outer layer 316L stainless steel pipe thickness 2.0mm, middle layer food-grade epoxy resin thickness 0.6mm, inner layer TP2 thin-walled copper pipe thickness 0.8mm, functional plating layer 99.99% high-purity gold layer thickness 0.002mm.

[0037] Manufacturing process parameters: Stainless steel pipes are manufactured using welding + solution treatment, with a grain size of grade 7 and δ-ferrite content of 0.9%, passing eddy current testing and hydrostatic testing. The copper inner liner is formed using drawing + bright annealing, with an elongation of 42%, hardness of HV65, and inner surface roughness Ra≤0.4μm. Epoxy coating uses centrifugal coating + thermosetting, with a coating thickness of 0.6mm, a curing degree of 97%, and an adhesion cross-cut test grade of 0. Composite assembly uses hydraulic expansion + shrinkage, with an interference fit of 0.3mm and a concentricity of 0.4mm. The inner wall gold plating involves 10μm micro-etching + activation treatment, pre-plating with 1.0μm of nickel, a gold plating current density of 1.0A / dm², a plating bath temperature of 60℃, a pH value of 5.5, a gold layer thickness of 2.0μm, and a porosity of 0.9 cells / cm². Post-treatment involves rinsing with pure water with a resistivity of 17MΩ・cm and hot air drying.

[0038] Finished product performance testing: The pipe was tested and found to have a hydraulic strength of 4.0 MPa with no leakage, a tensile strength of 540 MPa, no cracks when bent in 4D, and no cracks when flattened to 3 / 4D; heavy metal Pb precipitation was 0.06 μg / L, Cd precipitation was 0.05 μg / L, gold precipitation was 0.008 mg / L, antibacterial rate was 99.8%, organic matter migration TOC increased by 0.07 mg / L, and sensory indicators were colorless, odorless, and free of precipitation, meeting all acceptance standards of this invention.

[0039] Finished Product Performance Indicators and Acceptance Standards After the finished pipe of this invention is manufactured, it must pass mechanical performance testing and sanitary safety performance testing in sequence. It can only be shipped after both tests are passed. The testing items, performance requirements and corresponding test / testing methods all comply with national standards. The specific requirements are as follows: Mechanical performance indicators: Hydraulic strength must reach 2.5 times the working pressure without leakage, and the test method shall comply with GB / T6111; Tensile strength ≥520MPa, and the test method shall comply with GB / T 228.1; Bending performance must meet the requirement of no cracks when bending in 4D, and the test method shall comply with GB / T 244; Flattening test must meet the requirement of no cracks when compressed to 3 / 4D, and the test method shall comply with GB / T 246; Vibration fatigue must reach 10 7 No damage was found in the second cycle, and the test method followed GB / T 26069.

[0040] Hygiene and safety performance indicators: Heavy metal leaching must meet the following requirements: Pb ≤ 0.1 μg / L, Cd ≤ 0.1 μg / L, and the detection method shall comply with GB / T 17219; Gold leaching ≤ 0.01 mg / L, and the detection method shall be ICP-MS; Organic matter migration must meet the following requirement: TOC increase ≤ 0.1 mg / L, and the detection method shall comply with GB / T 5750.7; Microbiological testing must meet the following requirement: antibacterial rate ≥ 99%, and the detection method shall comply with GB / T 31402; Sensory indicators must meet the following requirements: colorless, odorless, and free of precipitation, and the detection method shall comply with GB / T 5750.4.

[0041] Pipeline Cost and Application Analysis The multi-layer composite gold-plated drinking water conveying pipe of this invention is a high-end, ultra-long-life investment-grade pipe material. The comprehensive cost of each nominal diameter consists of four parts: stainless steel outer pipe cost, copper inner liner cost, gold plating cost, and processing fee. The specific comprehensive cost for each specification is as follows: DN15 specifications: 870-925 yuan / meter, including 45-60 yuan for the stainless steel outer pipe, 25-35 yuan for the copper inner liner, 680 yuan for gold plating, and 120-150 yuan for processing fees; this is a common specification for household inlet pipes. DN20 specifications: 1185-1250 yuan / meter, including 60-80 yuan for the stainless steel outer pipe, 35-50 yuan for the copper inner liner, 940 yuan for gold plating, and 150-180 yuan for processing fees; this is a common specification for branch pipes. DN25 specifications: 1530-1615 yuan / meter, including 85-110 yuan for the stainless steel outer pipe, 55-75 yuan for the copper inner liner, 1210 yuan for gold plating, and 180-220 yuan for processing fees; this is a common specification for drinking water transportation. DN32 specifications: 1840-1935 yuan / meter. The following are common specifications for risers: DN40: 2205-2320 yuan / meter, with stainless steel outer pipe costing 140-180 yuan, copper inner liner costing 95-130 yuan, gold plating costing 1710 yuan, and processing fee 260-300 yuan; DN50: 2680-2820 yuan / meter, with stainless steel outer pipe costing 180-230 yuan, copper inner liner costing 130-170 yuan, gold plating costing 2070 yuan, and processing fee 300-350 yuan; DN65: 3470-3650 yuan / meter, with stainless steel outer pipe costing 230-290 yuan. The following specifications are listed: DN100: DN100: DN150: DN150; DN150: DN150. The cost of the copper inner liner is 450-580 yuan, the cost of gold plating is 5670 yuan, and the processing fee is 750-900 yuan.

[0042] Taking the three commonly used specifications DN25, DN50, and DN100 as examples, a price comparison with traditional drinking water pipes shows that: PPR pipes DN25 cost 15-25 yuan / meter, DN50 30-50 yuan / meter, and DN100 80-120 yuan / meter, economical and practical but with a short lifespan; 304 stainless steel pipes DN25 cost 45-65 yuan / meter, DN50 90-130 yuan / meter, and DN100 200-280 yuan / meter, offering better value for money but unable to be gold-plated; thick-walled copper pipes DN25 cost 120-180 yuan / meter, DN50 250-350 yuan / meter, and DN100 600-850 yuan / meter. Traditional pipes, while high-end, are prone to oxidation. The composite pipe of this invention, although having a higher initial cost than traditional pipes, is virtually maintenance-free throughout its entire life cycle and possesses exceptional hygiene and safety performance and an ultra-long lifespan, making it a high-value investment pipe.

[0043] Taking the DN50 specification as an example, the cost composition of the pipeline is as follows: gold plating cost accounts for 73%, processing fee accounts for 12%, copper inner liner cost accounts for 7%, stainless steel outer pipe cost accounts for 5%, and other costs account for 3%. Gold plating cost is the main cost component and is also the core investment to achieve ultimate corrosion protection and water quality protection of the pipeline.

[0044] Industrial applicability

[0045] The multi-layer composite structure gold-plated inner layer drinking water conveying pipe and its preparation method of the present invention have a clear process flow, precise and controllable parameters of each process, and can realize industrial mass production. Moreover, there are no special process requirements in the production process, and it is compatible with existing pipe processing general equipment and production lines, and has a good industrial production foundation.

[0046] The pipe products of this invention combine the inert corrosion resistance of gold, the excellent adhesion of the gold layer of copper pipes, and the ultra-high mechanical strength of 316L stainless steel. They have a high level of hygiene and safety, long service life, and excellent mechanical properties. Moreover, the nominal diameter covers the entire range of DN15-DN150, which can meet the needs of different drinking water transportation scenarios. They can effectively solve the high requirements of drinking water hygiene and safety and pipe service life in high-end residential, high-end medical, and precision laboratory scenarios. At the same time, they are almost maintenance-free throughout the entire life cycle, which greatly reduces the later operating costs and has significant industrial practicality and market application value.

[0047] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A multi-layer composite structure gold-plated inner layer drinking water conveying pipe, characterized in that: From the outside to the inside, the layers are: outer structural layer, intermediate bonding layer, inner carrier layer, and functional coating layer. The outer structural layer is a 316L stainless steel tube with a thickness of 1.2-3.0 mm, which has undergone solution treatment and has been polished internally and externally with Ra≤0.8μm; The intermediate bonding layer is made of food-grade epoxy resin with a thickness of 0.3-0.8 mm, meeting the GB / T 17219 hygiene standard; The inner carrier layer is a TP2 thin-walled copper tube with a thickness of 0.5-1.5mm, which has been bright annealed and has an inner surface roughness Ra≤0.4μm; The functional coating is a 99.99% high-purity gold layer with a thickness of 0.001-0.002 mm, prepared using a composite process of electroplating and chemical plating, with a porosity of ≤1 particle / cm².

2. The gold-plated inner layer drinking water conveying pipe with a multi-layer composite structure according to claim 1, characterized in that, The nominal pipe diameter covers DN15-DN150, the working pressure is ≤1.6MPa, the applicable temperature varies depending on the flow temperature of different liquids, and it can be used within the range that the material can withstand. The design life is >100 years. It complies with ISO 15686, GB / T 17116 and GB / T18991 standards, and the sanitary grade is food grade / drinking water grade.

3. The gold-plated inner layer drinking water conveying pipe with a multi-layer composite structure according to claim 1, characterized in that, The pipeline has a hydraulic strength of 2.5 times the working pressure without leakage, a tensile strength ≥520MPa, no cracks after 4D bending, and no cracks after being compressed to 3 / 4D. 7 No damage from vibration fatigue; heavy metal precipitation meets the requirements of Pb≤0.1μg / L, Cd≤0.1μg / L, organic matter migration TOC increase ≤0.1mg / L, and sensory indicators are colorless, odorless, and free of precipitation.

4. The method for preparing a multi-layer composite structure gold-plated inner layer drinking water conveying pipe as described in any one of claims 1-3, characterized in that, The process includes the following steps: (1) Stainless steel pipe preparation: cold rolling / welding and solution treatment process is adopted to control the grain size ≥ 7 grade and δ ferrite ≤ 1%, and it is tested by eddy current testing and hydrostatic test; (2) Copper tube inner liner forming: adopt drawing and bright annealing process, control elongation ≥40%, hardness HV55-75, and check dimensional tolerance and surface roughness; (3) Surface pretreatment: Chemical cleaning and activation process is used for degreasing, pickling and passivation, which is verified by continuous water film test; (4) Epoxy coating: Centrifugal coating and thermal curing process is adopted to control the coating thickness to 0.5±0.2mm, the degree of curing to ≥95%, and the adhesion is tested by cross-cut test; (5) Composite assembly: adopt hydraulic expansion and shrinkage process, control interference of 0.1-0.3mm, concentricity ≤0.5mm; (6) Gold plating on the inner wall: A high-purity gold layer that meets the requirements of thickness and porosity is prepared by adopting a composite process of electroplating and chemical plating, including pre-plating treatment, optional pre-plating of nickel, gold plating, and post-treatment.

5. The preparation method according to claim 4, characterized in that, The pre-plating treatment for the gold plating of the inner wall is micro-etching to a depth of 5-10 μm and activation to ensure uniform surface activity; the pre-plated nickel layer has a thickness of 0.5-1 μm to enhance the adhesion of the gold layer.

6. The preparation method according to claim 4, characterized in that, The gold plating process parameters for the inner wall are as follows: The gold plating current density is 0.5-1.0 A / dm², using a pulse power supply with a duty cycle of 30%; the plating bath temperature is 50-60℃ with an accuracy of ±1℃; the plating bath pH value is 4.5-5.5, which is automatically controlled; and the plating thickness is 1.0-2.0 μm, which is monitored online.

7. The preparation method according to claim 4, characterized in that, The post-treatment of the gold plating on the inner wall involves rinsing with pure water with a resistivity ≥15MΩ・cm, followed by hot air drying.

8. The preparation method according to claim 4, characterized in that, After each process is completed, composite quality control is carried out to ensure that the layers of the pipeline are firmly bonded and there is no risk of delamination. The finished pipeline is inspected and accepted by XRF thickness testing, ICP-MS elemental precipitation testing, and GB / T 31402 antibacterial testing.

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