The detection method of plastic-coated steel pipe

plastic-coated steel pipe not only has the advantages of high strength, easy connection, and water impact resistance, but also overcomes the shortcomings of steel pipes such as easy corrosion, pollution, scaling, low-strength plastic pipes, and poor fire performance. the design life can reach 50 years. the main disadvantage is that it is not allowed to bend during installation, and when performing operations such as thermal processing and 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 meet the requirements 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 points perpendicular to the circumference of each cross-section. the test results should meet the requirements of 5.4.

3. pinhole test

the length of the pipe section test piece is about 1000mm. use the electric spark leak detector to check the coating of the steel pipe under the specified test voltage. the thickness of the coating is not more than 0.4mm. the test voltage is 1500v. 2000v. check whether there is any electric spark, and the test result should meet the requirements of 5.5.

4. adhesion test

the adhesion test shall be carried out according to 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 the bending test. the length of the pipe section test piece is (1200±100) mm. in an environment with a temperature of (20±5) ℃, take 8 times the nominal diameter of the steel pipe as the radius of curvature, and the bending angle is 30o, and bend it on a pipe bender or mold. during the bending test, there is no filler in the tube, and the weld is located on the side of the main bending surface. after the test, cut the test piece from the middle of the curved arc to check the inner coating. the test results should meet the requirements in 5.7.

6. flattening test

the coated steel pipe with dn>50 mm was subjected to the flattening test. the length of the pipe section test piece is (50±10) mm. in an environment with a temperature of (20±5) ℃, place the test piece 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 test piece. the steel pipe weld is perpendicular to the direction of load application. after the test, check the inner coating, and the test result should meet the requirements in 5.8.

7. impact test

cut a sample with a length of about 100 mm from any position of the coated steel pipe, and in an environment with a temperature of (20±5) °c, as shown in figure 2, conduct an impact test according to the provisions of table 2, and observe the damage of the inner coating condition. during the test, the weld seam should be in the direction opposite to the impact surface, and the test results should meet the requirements 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 hg, and keep it for 1 min. after the test, check the inner coating. the test result should comply with 5.10 provisions.

9. high-temperature test

the length of the pipe section test piece is (100 ± 10) mm. the test piece is placed in a constant temperature box, heated to (300 ± 5) ℃, and kept at a constant temperature for 1 h, then taken out and naturally cooled to room temperature. after the test, take out the test piece and check the inner coating (allow the appearance to become darker and darker), and the test result should meet the requirements of 5.11.

10. low-temperature test

the size and length of the pipe section test piece are (100±10) mm. place the test piece in a low-temperature box, cool it down to (-30±2) ℃, and keep it at a constant temperature for 1 h, then take it out and place it in a refrigerator at a temperature of (20±5) ℃. environment (4～7) h. after the test period is over, take out the test piece to check its inner coating, and carry out the adhesion test according to provisions 6.4, and the test results should meet provisions 5.12.

11. pressure cycle 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, connect it to the hydraulic supply system, fill it with water and remove the air, and then carry out 3000 times from (0.4±0.1) mpa to mpa for the alternating water pressure test, the period of each test shall not be greater than 2 s. after the test, check the inner coating, and carry out the adhesion test according to the provisions of 6.4. the test results should meet the provisions of 5.13.

12. temperature cycle test

the length of the pipe section test piece is (500±50) mm, and the test piece is placed in the following order for 24 hours under each temperature condition: (50±2)°c; (-10±2)°c; (50±2)°c; (-10±2)°c; (50±2)°c; (-10±2)°c. after the test, place the specimen in an environment with a temperature of (20±5)°c for 24 hours, check the condition of the inner coating, and conduct an adhesion test according to the provisions of 6.4. the test results should meet the provisions of 5.14.

13. warm water aging test

the size and length of the pipe section test piece are about 100 mm. corresponding anti-corrosion treatment should be carried out at both ends of the pipe section. place the pipe section in (70±2) ℃ distilled water and soak for 30 days. for the inner coating, the test results shall comply with the provisions of 5.15.