Coated steel pipes with DN>50 mm are subjected to flattening test. The length of the pipe section test piece is (50±10) mm.
Under the 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, and apply plastic when flattening. Fire pipe welds are perpendicular to the direction of load application. After the test, check the inner coating, and the test results should meet the requirements of 5.8.
