Inspection of coating appearance: Check if the coating is smooth with no burrs, if there is any exposed steel, and if the color matches the customer's requirements.
Check if the coating thickness meets the customer's specifications.
Conduct pinhole testing.
Adhesion test: The adhesion test is conducted according to Appendices A and B in CJ/T 120-2016.
Bend test: Cut a specimen approximately 50mm long from any position on the tested plastic-coated steel pipe. Place it between two flat plates at room temperature and gradually compress it on a tensile testing machine. For polyethylene coatings, the distance between the two plates should be controlled to 2/3 of the outer diameter of the specimen; for epoxy resin coatings, the distance should be controlled to 4/5 of the outer diameter. During compression, the weld seam of the plastic-coated steel pipe should be perpendicular to the compression direction. After compression, observe the inner coating for any cracks or peeling. For plastic-coated steel pipes with nominal sizes larger than DN200, DN150 pipes can be used as substitutes.
Flattening test: Plastic-coated steel pipes with outer diameters greater than 50mm undergo a flattening test. The specimen length is (50±10)mm. Place the specimen between two flat plates at a temperature of (20±5)°C. Gradually compress it on a pressure testing machine until the distance between the two plates is 4/5 of the specimen's outer diameter for epoxy resin coatings and 2/3 for polyethylene coatings. During compression, the weld seam of the coated steel pipe should be perpendicular to the load application direction. After the test, inspect the inner coating for any cracks or peeling. If there are no such defects, the test is passed. For plastic-coated steel pipes with nominal sizes larger than DN200, DN150 pipes can be used as substitutes.
Impact test: Cut a specimen approximately 100mm long from any position on the tested plastic-coated steel pipe. Conduct the impact test as specified at room temperature, with the weld seam positioned opposite to the impact surface, as shown in the diagram below. After the test, inspect the inner coating for any cracks or peeling. If there are no such defects, the test is passed. For plastic-coated steel pipes with nominal sizes larger than DN200, DN150 pipes can be used as substitutes.
Hygiene performance testing: Hygiene performance tests should be conducted according to GB/T 17219.
Vacuum test: The specimen length for the pipe segment is (500±50)mm. Use appropriate measures to block the pipe inlet and outlet. Gradually increase the negative pressure from the inlet to 660mmHg and maintain it for 1 minute. After the test, inspect the inner coating for any peeling.
High-temperature resistance test, low-temperature resistance test, pressure cycle test, temperature cycle test, warm water aging test, etc.
