Plastic-coated steel pipes, also known as plastic-coated pipes, steel-plastic composite pipes, and plastic-coated composite steel pipes, are steel-plastic composite steel pipes that use steel pipes as the base and weld a layer of plastic anti-corrosion layer on the inner surface of the steel pipe (bottom pipe) or weld a plastic anti-corrosion layer on the inner and outer surfaces through spraying, rolling, dipping, and suction processes.

1. Appearance inspection: Check the appearance quality of the plastic-coated steel pipe.
2. Thickness measurement: Take two cross-sections of different lengths from both ends of the plastic-coated steel pipe, and use an electromagnetic thickness gauge to measure the coating thickness at any four points orthogonal to the circumference in each cross-section.
3. Pinhole test: The length of the pipe section specimen is about 1000mm. Use an electric spark leak detector to inspect the steel pipe coating under the specified test voltage. The coating thickness is not more than 0.4mm, the test voltage is 1500 V, and the coating thickness is greater than 0.4mm, and the test voltage is 2000 V. Check whether there is electric spark generation.
4. Adhesion test: The adhesion test is carried out by 7.4.2 of CJ/T 120-2008, and the test results shall comply with the provisions of 5.6.
5. Bending test: The coated steel pipe with DN≤50mm is subjected to a bending test. The length of the pipe section specimen is (1200±100) mm. Under the environment of a temperature of (20±5) ℃, the curvature radius is 8 times the nominal diameter of the steel pipe, the bending angle is 30o, and the bending is carried out on a pipe bending machine or mold. During the bending test, there is no filler in the pipe, and the weld is located on the side of the main bending surface. After the test, the specimen is cut open from the middle of the bending arc to check the inner coating. The test results shall comply with the provisions of 5.7.
6. Flattening test: The coated steel pipe with DN>50 mm is subjected to a flattening test. The length of the pipe section specimen is (50±10) mm. At a temperature of (20±5) ℃, place the specimen between two plates and gradually compress it on a pressure testing machine until the distance between the two plates is four-fifths of the outer diameter of the specimen. When flattened, the weld of the coated steel pipe is perpendicular to the direction of load application. After the test, check the inner coating, and the test results should comply with the provisions of 5.8.
VII. Impact test: Cut a specimen of about 100 mm in length from any position of the coated steel pipe. At a temperature of (20±5) ℃, during the test, the weld should be in the opposite direction of the impact surface, and the test results should comply with the provisions of 5.9. Plastic-coated steel pipes have excellent corrosion resistance and relatively small friction resistance. Epoxy resin-coated steel pipes are suitable for the transportation of water supply and drainage, seawater, warm water, oil, gas, and other media, and polyvinyl chloride-coated steel pipes are suitable for the transportation of drainage, seawater, oil, gas, and other media. Plastic-coated steel pipes not only have the advantages of steel pipes such as high strength, easy connection, and resistance to water impact, but also overcome the shortcomings of steel pipes such as easy corrosion, pollution, and scaling when exposed to water, and the low strength and poor fire-fighting performance of plastic pipes. The design life can reach 50 years.