What are the execution standards and quality requirements for DN40 UV-resistant coated seamless steel pipes

Among numerous pipe materials, DN40 UV-resistant coated seamless steel pipes have distinguished themselves in various projects due to their superior performance. Whether it's water supply and drainage systems in municipal engineering, the transportation of corrosive media in the chemical industry, or the laying of various pipelines in building projects, they perform admirably. However, to ensure their optimal performance in practical applications, a thorough understanding of their execution standards and quality requirements is crucial.

First, a comprehensive overview of the execution standards for DN40 UV-resistant coated seamless steel pipes:

- CJ/T120-2008 "Water Supply Coated Composite Steel Pipes": This standard can be considered a "quality bible" for coated steel pipes in the water supply field. For DN40 UV-resistant coated seamless steel pipes, in the selection of the base pipe, if a seamless steel pipe is used, it must strictly comply with the various requirements of GB/T8163 for seamless steel pipes, with detailed and precise regulations on everything from the chemical composition to the mechanical properties of the steel pipe. Regarding coating materials, if polyethylene coating is selected, its density must exceed 0.91 g/m³, tensile strength must be greater than 9.80 MPa, elongation at break must reach over 300%, Vicat softening point must be higher than 85℃, non-volatile content must not be less than 99.5%, and hygiene performance must meet the requirements of GB/T17219 to ensure the safety and hygiene of drinking water transportation.

- GB/T23257-2017 "Polyethylene Anti-corrosion Coating for Buried Steel Pipelines": When DN40 UV-resistant coated seamless steel pipes are used in buried applications, this standard serves as a strict quality control measure. It has clear and strict regulations on coating thickness, requiring precise control based on different usage environments and design requirements. Generally, the coating thickness must be sufficiently thick to resist various corrosive media in the soil. Simultaneously, detailed requirements are set for key indicators such as impact resistance and peel resistance of the coating to ensure that the coating remains tightly adhered to the steel pipe surface during long-term burial, providing reliable protection for the steel pipe.

- Relevant Building Industry Standards: In the field of building engineering, standards such as JG/T3091-1998 "Insulating Electrical Conduit and Fittings for Buildings" set forth requirements for the application of plastic-coated steel pipes in building electrical wiring and other aspects.

- ASTM Standards: The relevant standards developed by the American Society for Testing and Materials (ASTM) are highly influential internationally. Taking ASTM A849/A849M-20a as an example, this standard has comprehensive and detailed requirements for steel pipes with an external anti-corrosion coating. From the quality control of raw materials to key performance indicators such as the thickness, adhesion, and chemical corrosion resistance of the coating, there are clear quantitative regulations, providing an important reference for the application of DN40 UV-resistant plastic-coated seamless steel pipes in international projects.

- EN Standards: European standards (EN) also occupy an important position in the piping field. For example, EN10287 covers the requirements for steel pipes coated with plastic, providing strict and unified standards for dimensional accuracy, mechanical properties, and the quality of the plastic coating. This standard guides the use of DN40 UV-resistant coated seamless steel pipes in the European market and related international cooperation projects.

Second, Appearance and Dimensional Accuracy of DN40 UV-resistant Coated Seamless Steel Pipes.

- Appearance Quality: High-quality DN40 UV-resistant coated seamless steel pipes should have smooth, even inner and outer walls, resembling a meticulously crafted work of art, with uniform color and no traces of scratches, pinholes, or foreign matter. The pipe should be straight and upright, with strict control over bending. For DN≥150, the bending degree should not exceed 0.2% of the total length to ensure that bending does not affect media transport during installation and use. Its end face should be perpendicular to the pipe axis, as precise as a precision instrument, laying a good foundation for subsequent connection operations.

- Dimensional Accuracy: Regarding dimensions, the outer diameter, wall thickness, and length of DN40 UV-resistant coated seamless steel pipes must meet precise standard requirements. Outer diameter deviations must typically be controlled within a very small range, such as ±0.5mm, to ensure a perfect fit with various pipe fittings. Wall thickness deviations are equally stringent, generally not exceeding ±10% of the nominal wall thickness to guarantee the strength and pressure resistance of the steel pipe. Length can be customized according to actual project needs, but the tolerance range must also be strictly controlled, such as ±5mm, to avoid inconvenience caused by length errors during construction.

Third, Coating Performance of DN40 UV-resistant Coated Seamless Steel Pipes.

- Thickness Requirements: Coating thickness is a key factor affecting the performance of DN40 UV-resistant coated seamless steel pipes. Generally, the coating thickness should not be less than 150 micrometers. In some special environments with extremely high requirements for corrosion resistance and UV resistance, the coating thickness may even need to reach over 200 micrometers. Using specialized equipment such as electromagnetic thickness gauges and ultrasonic thickness gauges, two cross-sections of different lengths are selected at both ends of the steel pipe. Precise measurements are taken at any four orthogonal points on the circumference of each cross-section. During measurement, the instrument probe must be perpendicular to the steel pipe surface and avoid weld seams and other areas that may interfere with the measurement results. The average of the measured values is taken as the coating thickness at that point, ensuring uniform and compliant coating thickness.

- Adhesion: The adhesion between the coating and the steel pipe substrate is crucial, acting like a strong adhesive. For polyethylene coatings, the adhesion should not be less than 30 N/cm; for epoxy resin coatings, the adhesion grade should be between 1 and 3. Testing is conducted using professional methods such as the cross-cut test or pull-out test. When crisscrossing the surface of the coated pipe, a special tool must be used to ensure uniform crisscross depth. When applying tension after attaching the test piece, the direction of the tension must be perpendicular to the surface of the coated pipe. Close observation of the coating peeling is necessary to determine if the adhesion meets the standard.

- UV Resistance: As a core performance characteristic of UV-resistant coated seamless steel pipes, the coating must possess excellent UV resistance. By simulating actual outdoor environments and conducting tests in an artificial accelerated aging test chamber, the coating should not show obvious discoloration, chalking, or cracking after a certain period of ultraviolet irradiation.

- Corrosion Resistance: Whether facing highly corrosive media such as acids and alkalis, or harsh, humid environments, the coating of DN40 UV-resistant coated seamless steel pipe should exhibit strong corrosion resistance. This can be tested using methods such as salt spray testing and immersion testing. In the salt spray test, the steel pipe is placed in a salt spray environment of a specific concentration, and after a specified time, the surface of the coating is observed for any corrosion marks. The immersion test involves immersing the steel pipe in different corrosive media solutions, and the integrity and adhesion of the coating are checked periodically to ensure that the coating can effectively protect the steel pipe substrate and extend the service life of the steel pipe under various corrosive environments.

Fourth, Performance of the Steel Pipe Substrate for DN40 UV-resistant Coated Seamless Steel Pipe.

- Material Requirements: The substrate of DN40 UV-resistant coated seamless steel pipe is typically made of high-quality carbon structural steel or low-alloy high-strength structural steel, such as 20# steel or Q345 steel. The chemical composition of these steels must strictly comply with relevant national standards. The content of elements such as carbon, silicon, manganese, phosphorus, and sulfur is subject to specific range limitations to ensure the steel possesses excellent comprehensive performance. Simultaneously, the smelting quality of the steel is also crucial, requiring advanced smelting processes to ensure a uniform internal structure and the absence of obvious defects such as porosity and inclusions.

- Mechanical Properties: The steel pipe matrix should possess excellent mechanical properties to withstand various complex usage scenarios. Its tensile strength, yield strength, elongation, and other indicators must meet relevant standard requirements. For example, for a DN40 UV-resistant coated seamless steel pipe made of 20# steel, its tensile strength should generally be no less than 390MPa, its yield strength no less than 245MPa, and its elongation after fracture no less than 25%. Through tensile tests, impact tests, and other mechanical property testing methods, the mechanical properties of the steel pipe are accurately evaluated to ensure that it will not crack, deform, or fail under external forces such as pressure, tension, and impact.

- Process Performance: During manufacturing, the substrate of DN40 UV-resistant coated seamless steel pipe must possess excellent process performance. The cold bending performance, flaring performance, and flattening performance of the steel pipe must all meet standards. When actually purchasing and using DN40 UV-resistant coated seamless steel pipe, engineering personnel must strictly adhere to the above-mentioned standards and quality requirements for screening and inspection. Carefully verify the product's quality certification documents, including raw material inspection reports and factory inspection reports, to ensure that every indicator meets the standards. Where conditions permit, a professional third-party testing agency can be commissioned to conduct comprehensive testing of the steel pipe, laying a solid foundation for project quality.