Appearance quality requirements of casing

(1) Domestic casing according to SY/T6194-96, the length of the casing is not fixed, and its range is 8-13m. However, casings not shorter than 6 m can be supplied, and the number must not exceed 20%.
(2) The inner and outer surfaces of the casing shall be free from folding, hairline, separation, cracking, rolling and crusting. These defects should be completely removed and the depth of removal should not exceed 12.5% of the nominal wall thickness.
(3) The outer surface of the coupling shall not have defects such as folding, hairline, separation, crack, rolling, crusting and so on.
(4) The surface of the casing and coupling threads shall be smooth and shall not be allowed to be burred, torn, and other defects sufficient to cause the thread to interrupt the strength and tight connection.