Plastic-coated steel pipes, also known as plastic-coated pipes, steel-plastic composite pipes and plastic-coated composite pipes, are steel-plastic composite pipes based on steel pipes. After spraying, rolling, immersion and suction processes, a plastic anti-corrosion layer is welded on the inner surface of steel pipes (bottom pipes) or a plastic anti-corrosion layer is welded on the inner and outer surface of steel-plastic composite pipes. Plastic coated steel pipe has excellent corrosion resistance and relatively small friction resistance. Epoxy resin coated steel pipe is suitable for water supply and drainage, sea water, warm water, oil, gas and other media delivery. PVC coated steel pipe is suitable for water drainage, sea water, oil, gas and other media delivery.
1. Visual inspection of the appearance quality of coated steel pipes. The experimental results should conform to the rule of 5.1.
2. Thickness measurement takes two cross sections of different lengths from both ends of the coated steel pipe. In each cross section, the thickness of the coatings at four arbitrary points on the circumference is measured by an electromagnetic thickness gauge. The experimental results should conform to the rule of 5.4.
3. Pinhole experiment
The length of the tube section is about 1000mm. The inspection of the steel tube coating is discontinued under the regular experimental voltage by EDM leak detector. The thickness of the coating is not more than 0.4mm, the experimental voltage is 1500V, the thickness of the coating is more than 0.4mm and the experimental voltage is 2000 V. Check whether the spark is produced or not. The experimental results should conform to the rule of 5.5.
4. The adhesion experiment is terminated according to 7.4.2 in CJ/T 120-2008. The experimental results should conform to the rule of 5.6.
5. Bending experiment DN < 50mm for coated steel tube to stop bending. The length of the tube section is (1200 + 100) mm. In the environment of temperature (20 +5)degrees C, the bending is stopped on the bending machine or die with 8 times the nominal diameter of the steel pipe as the radius of curvature and the bending angle of 30 degrees. In bending test, there is no filler in the pipe, and the weld is located on the side of the main bending surface. After the experiment, the specimen is cut off from the middle of the curved arc and the inner coating is checked. The experimental results should conform to the rule of 5.7.
6. Flattening experiment DN > 50 mm coated steel tube stop flattening experiment. The length of the tube section specimen is (50 + 10) mm.
When the temperature is (20 +5) C, the specimen is placed between the two plates, and the distance between the two plates is four fifths of the outer diameter of the specimen. The weld of the coated steel pipe is perpendicular to the direction of loading when it is flattened. After the experiment, the inner coating should be checked and the experimental results should conform to the rule of 5.8.
7. Flattening experiment
8. The impact test is to cut the specimen about 100 mm in length from the arbitrary position of the coated steel tube, and stop the impact test according to the rules under the environment of (20 +5)degrees Celsius. The damage of the inner coating is observed. In the experiment, the weld should be in the opposite direction of the impact surface, and the experimental results should conform to the rule of 5.9.
9. The length of the specimen in the vacuum test section is (500 +50) mm. Appropriate measures are taken to block the inlet and outlet of the pipeline. The negative pressure is gradually increased from the inlet to 660 mm mercury column. The inner coating is inspected after one minute. The experimental results should conform to the rule of 5.10.
10. The length of the high temperature test tube is (100 + 10) mm. The specimen is placed in a thermostat and heated to (300 + 5). The temperature is kept constant for 1 hour. Then the natural temperature is taken out and cooled to room temperature. After the experiment, take out the specimen and check the inner coating (allowing the appearance to darken and darken). The experimental results should conform to the rule of 5.11.
11. The length of the specimen in the cryogenic test section is (100 +10) mm. The specimen is placed in a cryogenic chamber and cooled to (-30 +2). The temperature is kept constant for 1 hour. Then the specimen is taken out and placed in the environment of (20 +5). (4-7) H.
12. Pressure cycle experiment is connected with water pressure supply system, water is filled to clean air, and then 3000 alternating water pressure experiments from (0.4 +0.1) MPa to MPa are stopped. The period of each experiment is not more than 2 seconds. After the experiment, the inner coating was checked and the adhesion experiment was terminated according to the 6.4 rule. The experimental results should conform to the 5.13 rule.
13. Temperature Cycle Experiments
The length of the tube section is (500 +50) mm. The specimen is placed for 24 hours at each temperature according to the following order: after the experiment, the specimen is placed in the environment of (20 +5)degrees Celsius for 24 hours, the inner coating is checked, and the adhesion test is terminated according to the rule of 6.4. The experimental results should conform to the rule of 5.14.
14. The length of the specimen in the warm water aging test section is about 100 mm. The exposed parts at both ends of the section should stop the corresponding anti-corrosion treatment. The section should be immersed in distilled water at (70 (+2)degrees centigrade for 30 days. After the experiment, the tube is cooled naturally to room temperature, and the inner coating of the specimen should be checked. The experimental results should conform to the rule of 5.15.
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