1) According to the domestic casing of SY/T6194-96, the length of the casing is not fixed, and its range is 8-13m. However, it can provide shells not less than 6 meters in quantity, not more than 20%.
(2) The inner and outer surfaces of the casing shall be free from folding, striation, separation, cracking, rolling and crushing. These defects should be thoroughly removed and the removal depth should not exceed 12.5% of the nominal wall thickness.
(3) There should be no creases, wrinkles, separation, cracks, rolling, crusts and other defects on the outer surface of the coupling.
(4) The surface of the shell and the connecting thread shall be smooth, without burrs, tearing and other defects sufficient to break the strength and close connection of the thread.