Testing method of plastic-coated steel pipe

Plastic-coated steel pipe not only has the advantages of high strength, easy connection, and water flow impact resistance of steel pipe, but also overcomes the disadvantages of easy corrosion, pollution, and scaling of steel pipe in water, low strength, and poor fire protection performance of plastic pipe, and has a design life of 50 years. The main disadvantage is that it must not be bent during installation. During hot processing and electric welding cutting, the cutting surface should be coated with non-toxic room-temperature curing glue provided by the manufacturer.

First, appearance inspection
Visually inspect the appearance quality of plastic-coated steel pipe, and the test results should comply with the provisions of 5.1.

Second, 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 on the circumference that is orthogonal in each cross-section. The test results should comply with the provisions of 5.4.

Third, pinhole test
The length of the pipe section specimen is about 1000mm. The steel pipe coating is inspected with an electric spark leak detector under the specified test voltage. If the coating thickness is not more than 0.4mm, the test voltage is 1500 V. If the coating thickness is greater than 0.4mm, the test voltage is 2000 V. Check whether there is spark generation. The test results should comply with the provisions of 5.5.

Fourth, adhesion test
The adhesion test is carried out by 7.4.2 of CJ/T 120-2008, and the test results should comply with the provisions of 5.6.

Fifth, 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 it 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, the specimen is cut open from the middle of the curved arc, and the inner coating is checked. The test results shall comply with the provisions of 5.7.

Sixth, flattening test
A flattening test is conducted on coated steel pipes with a DN>50 mm. The pipe section specimen is (50±10) mm long. Under a temperature of (20±5) ℃, the specimen is placed between two flat plates and gradually compressed on a pressure testing machine until the distance between the two flat plates is four-fifths of the outer diameter of the specimen. During flattening, the weld of the coated steel pipe is perpendicular to the direction of load application. After the test, the inner coating is checked and the test results shall comply with the provisions of 5.8.

Seventh, impact test
A specimen of about 100 mm in length is cut from any position of the coated steel pipe. Under a temperature of (20±5) ℃, as shown in Figure 2, an impact test is conducted according to the provisions of Table 2 to observe the damage to the inner coating. During the test, the weld should be in the opposite direction of the impact surface, and the test results shall comply with the provisions of 5.9.

Eighth, vacuum test
The length of the pipe section specimen is (500±50) mm. Use appropriate measures to block the inlet and outlet of the pipeline, gradually increase the negative pressure from the inlet to 660 mm Hg, and maintain it for 1 min. After the test, check the inner coating. The test results should comply with the provisions of 5.10.

Ninth, high temperature test
The length of the pipe section specimen is (100±10) mm. Place the specimen in a constant temperature box, heat it to (300±5) ℃, and keep it constant for 1 hour, then take it out and cool it naturally to room temperature. After the test, take out the specimen and check the inner coating (the appearance color is allowed to darken and darken), and the test results should comply with the provisions of 5.11.

Tenth, low temperature test
The length of the pipe section specimen is (100±10) mm. Place the specimen in a low temperature box, cool it to (-30±2) ℃, and keep it constant for 1 hour, then take it out and place it in an environment with a temperature of (20±5) ℃ for (4~7) hours. After the test cycle, 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.

Eleventh, 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 water pressure supply system, fill it with water to exclude air, and then conduct 3000 alternating water pressure tests from (0.4±0.1) MPa to MPa. The cycle of each test is not more 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.

Twelfth, temperature cycle test
The length of the pipe section test piece is (500±50) mm. Place the test piece under each temperature condition for 24 h 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 inner coating is checked, and the adhesion test is carried out according to the provisions of 6.4. The test results shall comply with the provisions of 5.14.

Thirteenth. Warm water aging test
The length of the pipe section specimen is about 100 mm. The exposed parts at both ends of the pipe section shall be subjected to corresponding anti-corrosion treatment. The pipe section is placed in distilled water at (70±2) ℃ and soaked for 30 days. After the test, it is taken out and naturally cooled to room temperature. The inner coating of the specimen is checked. The test results shall comply with the provisions of 5.15.