DN40 UV-resistant plastic-coated seamless steel pipe implementation standard quality requirements

Among many steel pipe materials, DN40 UV-resistant plastic-coated seamless steel pipe has emerged in various projects with its excellent performance. Whether it is the water supply and drainage system of municipal engineering, the transportation of corrosive media in the chemical industry, or the laying of various pipelines in construction projects, it can do the job well. However, to ensure that it performs at its best in practical applications, it is crucial to have a deep understanding of its implementation standards and quality requirements.

First, the interpretation of the domestic authoritative standards for DN40 UV-resistant plastic-coated seamless steel pipe.

CJ/T120-2008 "Plastic-coated composite steel pipe for water supply": This standard can be called the "quality bible" of plastic-coated steel pipes in the water supply field. For DN40 UV-resistant plastic-coated seamless steel pipes, in the selection of base pipes, if seamless steel pipes are used, they must strictly meet the various requirements of GB/T8163 for seamless steel pipes, from the chemical composition to the mechanical properties of the steel pipe, there are detailed and precise regulations. In terms of coating materials, if polyethylene coating is selected, its density must exceed 0.91g/m³ (tested according to GB/T1033), tensile strength must be greater than 9.80mpa (tested according to GB/T1040), elongation at break must reach more than 300% (tested according to GB/T1040), Vicat softening point must be higher than 85℃ (determined by GB/T1633), non-volatile content must not be less than 99.5% (tested according to GB/T2914), and hygienic performance must meet the requirements of GB/T17219 to ensure the safety and sanitation of drinking water transportation.

GB/T23257-2017 "Polyethylene Anticorrosion Layer for Buried Steel Pipe": When DN40 UV-resistant plastic-coated seamless steel pipe is used in buried scenes, this standard is the "tightening curse" of its quality. There are clear and strict regulations on coating thickness, which need to be accurately controlled according to different use environments and design requirements. In general, the coating thickness should be thick enough to resist various corrosive media in the soil. At the same time, there are also detailed requirements for key indicators such as the impact resistance and peeling resistance of the coating to ensure that the coating can always be closely attached to the surface of the steel pipe during long-term burial, providing reliable protection for the steel pipe.

Related construction industry standards: In the field of construction engineering, standards such as JG/T3091-1998 "Insulating electrical conduits and accessories for construction" put forward requirements for the application of plastic-coated steel pipes in building electrical wiring and other aspects. For example, when DN40 anti-UV plastic-coated seamless steel pipes are used as building electrical threading pipes, their insulation performance must meet the corresponding standards to ensure the safe and stable operation of the electrical system and prevent safety hazards such as leakage.

Second, the appearance and dimensional accuracy of DN40 anti-UV plastic-coated seamless steel pipes.

- Appearance quality: The inner and outer walls of high-quality DN40 anti-UV plastic-coated seamless steel pipes should be as smooth as carefully polished works of art, with uniform color and no trace of scratches, pinholes, or foreign matter. The steel pipe should be straight and upright as a whole, and the curvature should be strictly controlled. If DN≥150, the curvature shall not be greater than 0.2% of the total length to ensure that the medium delivery will not be affected by the bending problem during installation and use. Its end face should be perpendicular to the pipe axis, as accurately as a precision instrument, laying a good foundation for subsequent connection operations.

- Dimensional accuracy: In terms of size, the outer diameter, wall thickness, and length of the DN40 UV-resistant plastic-coated seamless steel pipe must meet precise standard requirements. The outer diameter dimension deviation is usually controlled within a very small range, such as ±0.5mm, to ensure perfect fit with various pipe fittings; the wall thickness deviation is also strict, generally not more than ±10% of the nominal wall thickness, to ensure the strength and pressure resistance of the steel pipe; the length can be customized according to actual engineering needs, but the tolerance range must also be strictly controlled, such as ±5mm, to avoid inconvenience in construction due to length error.

Coating performance

- Thickness requirements: Coating thickness is a key factor affecting the performance of DN40 UV-resistant plastic-coated seamless steel pipe. Generally, the coating thickness should not be less than 150 microns. In some special environments with extremely high requirements for anti-corrosion and anti-UV performance, the coating thickness must even reach more than 200 microns. Using professional 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, and accurate measurements are performed at any four points that are orthogonal to the circumference of each cross section. During the measurement, the instrument probe must be perpendicular to the surface of the steel pipe, and avoid the weld of the steel pipe and other parts that may interfere with the measurement results. Finally, the average value of the measured value is taken as the coating thickness at that point to ensure that the coating thickness is uniform and meets the standard.

- Adhesion: The adhesion between the coating and the steel pipe substrate is as important as a strong adhesive. For polyethylene coatings, the adhesion should not be less than 30N/cm; the adhesion level of epoxy resin coatings should be between 1-3. The test is carried out by professional testing methods such as the cross-cutting method or the pulling method. When the surface of the plastic-coated pipe is cross-cut, a special tool must be used to ensure that the depth of the cross-cut is uniform; when applying tension after pasting the test piece, the direction of the tension application must be perpendicular to the surface of the plastic-coated pipe, and the shedding of the plastic coating layer must be closely observed to determine whether the adhesion meets the standard.

- Anti-UV performance: As the core performance of the anti-UV plastic-coated seamless steel pipe, its coating must have excellent anti-ultraviolet ability. By simulating the actual outdoor environment, the test is carried out in an artificial accelerated aging test chamber. After a certain period of ultraviolet irradiation, the coating should not show obvious discoloration, powdering, cracking, and other phenomena. For example, after 1000 hours of ultraviolet irradiation test in accordance with relevant standards, the tensile strength, elongation at break, and other performance indicators of the coating shall not decrease by more than 10%, ensuring that the coating can continue to provide reliable protection for the steel pipe during long-term outdoor use.

- Corrosion resistance: Whether facing strong corrosive media such as acids and alkalis, or humid and harsh environments, the coating of DN40 anti-UV plastic-coated seamless steel pipe should show strong corrosion resistance. Salt spray test, immersion test, and other methods can be used for testing. In the salt spray test, the steel pipe is placed in a salt spray environment of a specific concentration. After a specified time, observe whether there are signs of corrosion on the coating surface; the immersion test immerses the steel pipe in different corrosive medium solutions, and regularly checks the integrity and adhesion of the coating to ensure that the coating can effectively protect the steel pipe matrix and extend the service life of the steel pipe in various corrosive environments.

Third, the matrix performance of DN40 anti-UV plastic coated seamless steel pipe

- Material requirements: The matrix of DN40 anti-UV plastic coated seamless steel pipe is usually made of high-quality carbon structural steel or low-alloy high-strength structural steel, such as 20# steel, Q345 steel, etc. The chemical composition of these steels must strictly comply with the corresponding national standards, and the contents of elements such as carbon, silicon, manganese, phosphorus, and sulfur have clear range limits to ensure that the steel has good comprehensive performance. At the same time, the smelting quality of steel is also crucial, and advanced smelting processes must be used to ensure that the internal structure of the steel is uniform and there are no obvious defects such as pores and inclusions.

- Mechanical properties: The steel pipe matrix should have excellent mechanical properties to cope with various complex usage scenarios. Its tensile strength, yield strength, elongation, and other indicators must meet the requirements of relevant standards. For example, for DN40 UV-resistant plastic-coated seamless steel pipes made of 20# steel, their tensile strength should generally be no less than 390MPa, their yield strength should be no less than 245MPa, and their elongation after fracture should be no less than 25%. Through mechanical property testing methods such as tensile tests and impact tests, the mechanical properties of steel pipes are accurately evaluated to ensure that they will not fail when subjected to external forces such as pressure, tension, and impact.

- Process performance: During the manufacturing process, the matrix of DN40 UV-resistant plastic-coated seamless steel pipes must have good process performance. The cold bending performance, expansion performance, and flattening performance of the steel pipe must meet the standards. For example, during the cold bending test, at the specified bending radius and bending angle, cracks, wrinkles and other defects should not appear in the bending part of the steel pipe; in the expansion test, after the steel pipe port is expanded to a certain proportion, there should be no abnormal conditions such as rupture, so as to ensure the smooth operation of the steel pipe during processing and installation.

When actually purchasing and using DN40 UV-resistant plastic-coated seamless steel pipes, the majority of engineering personnel must strictly screen and inspect according to the above-mentioned implementation standards and quality requirements. Carefully check the quality certification documents of the product, including raw material inspection reports, factory inspection reports, etc., to ensure that each indicator meets the standards. If conditions permit, a professional third-party testing agency can be entrusted to conduct a comprehensive inspection of the steel pipe to lay a solid foundation for the quality of the project.