How to detect plastic-coated steel pipes

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

It has the advantages of good pressure strength, stable insulation performance, no burrs, and high pressure up to 6Mpa. Therefore, it is used as a protective tube for wires or cables, and no leakage will occur when used as a protective tube for wires or cables.

1. Appearance inspection: Check the appearance quality of plastic-coated steel pipes.
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 on each cross-section to measure the coating thickness at any four orthogonal points on the circumference.
3. Pinhole test: The length of the pipe section specimen is about 1000mm. Use an electric spark leak detector to check the steel pipe coating under the specified test voltage. The coating thickness is not greater than 0.4mm. The test voltage is 1500 V. The coating thickness is greater than 0.4mm, test voltage is 2000 V. Check whether there is any electric spark.
4. Adhesion test: The adhesion test is carried out by 7.4.2 in CJ/T 120-2008, and the test results should comply with the provisions of 5.6.
5. Bending test: Bending test is conducted on coated steel pipes with DN≤50mm. The length of the pipe section specimen is (1200±100) mm. In an environment where the temperature is (20±5) ℃, the radius of curvature is 8 times the nominal diameter of the steel pipe, the bending angle is 30o, and the pipe is bent 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, cut the specimen open from the middle of the bending arc and check the inner coating. The test results shall comply with the provisions of 5.7.
6. Flattening test: Flattening test is conducted on coated steel pipes with DN>50 mm. The length of the pipe section specimen is (50±10) mm. In an environment with a temperature of (20±5) ℃, place the specimen between two flat plates, and gradually compress it on the pressure testing machine until the distance between the two flat plates is four-fifths of the outer diameter of the specimen. Apply coating when flattened. The steel pipe welds are 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.
7. Impact test: Cut a sample of about 100 mm in length from any position of the coated steel pipe. In an environment with 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.