Testing methods for plastic-coated steel pipes

Plastic-coated steel pipes not only have the advantages of steel pipes such as high strength, easy connection, and resistance to water flow impact, but also overcome the shortcomings of steel pipes that are prone to corrosion, pollution, and scaling when exposed to water, as well as the low strength and poor fire-fighting performance of plastic pipes. The design life can reach 50 Years. The main disadvantage is that bending is not allowed during installation. During thermal processing, electric welding, and cutting, the cutting surface should be painted with non-toxic room-temperature curing glue provided by the manufacturer.

1. Appearance inspection:
Visually inspect the appearance quality of plastic-coated steel pipes, and the test results should comply with the provisions of 5.1.

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 orthogonal points on the circumference of each cross-section. The test results shall comply with the provisions of 5.4.

3. Pinhole test:
The length of the pipe section test piece 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, and the test voltage is 1500 V. The coating thickness is greater than 0.4mm. The test voltage is 2000V. Check whether there is any spark generated. The test results should comply with the provisions of 5.5.

4. Adhesion test:
The adhesion test shall be carried out by 7.4.2 in CJ/T 120-2008, and the test results shall comply with the provisions of 5.6.

5. Bending test:
Coated steel pipes with DN≤50mm are subjected to bending tests. 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:
Coated steel pipes with DN>50 mm are subjected to flattening tests. 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 approximately 100 mm in length from any position of the coated steel pipe, conduct an impact test by the provisions of Table 2 in an environment with a temperature of (20±5) °C, and observe the damage to the inner coating. During the test, the weld should be in the opposite direction to the impact surface, and the test results should comply with the provisions of 5.9.

8. Vacuum test:
The length of the pipe section test piece is (500±50) mm. Use appropriate measures to block the inlet and outlet of the pipe. Gradually increase the negative pressure from the inlet to 660 mm mercury and maintain it for 1 minute. After the test, check the inner coating. The test results should comply with 5.10 Provisions.

9. High temperature test:
The length of the pipe section specimen is (100±10) mm. Place the specimen in a constant temperature box, raise the temperature to (300±5) ℃, and keep the temperature constant for 1 hour. Then take it out and cool it to normal temperature naturally. After the test, take out the test piece and inspect the inner coating (the appearance is allowed to become darker or darker). The test results should comply with the provisions of 5.11.

10. Low temperature test:
The length of the pipe section test piece is (100±10) mm. Place the test piece in a low-temperature box, cool it to (-30±2) ℃, and keep it constant for 1 hour. Then take it out and place it at a temperature of (20±5) ℃. environment (4~7) h. After the test period, take out the test piece to check its inner coating, and conduct an adhesion test according to the provisions of 6.4. The test results shall comply with the provisions of 5.12.

11. Pressure cycle test:
The length of the pipe section test piece is (500±50) mm. Use appropriate measures to block the pipe inlet and outlet, connect it to the hydraulic supply system, fill it with water remove the air, and then perform 3000 times from (0.4±0.1) MPa to MPa. For alternating hydraulic pressure tests, the period of each test shall not be greater than 2 seconds. After the test, check the inner coating and conduct an adhesion test according to the provisions of 6.4. The test results shall comply with the provisions of 5.13.
    
12. Temperature cycle test:
The length of the pipe section specimen is (500±50) mm. The specimen is placed in each temperature condition for 24 hours in the following order: (50±2)℃; (-10±2)℃; (50±2)℃; (-10±2)℃; (50±2)℃; (-10±2)℃. After the test, the specimen is placed in an environment with a temperature of (20±5) ℃ for 24 hours. The condition of the inner coating is checked, and the adhesion test is performed according to the provisions of 6.4. The test results shall comply with the provisions of 5.14.
                            
13. Warm water aging test:
The length of the pipe section test piece is about 100 mm. The exposed ends of the pipe section should be treated accordingly. The pipe section should be soaked in distilled water at (70±2) ℃ for 30 days. After the test, take it out and cool it to normal temperature naturally. Check the test piece. For inner coating, the test results shall comply with the provisions of 5.15.