(1) Domestic tubing is in accordance with SY / T6194-96. The length of the tubing
is variable, and the range is 8-13m. But no less than 6m sleeves can be provided, and the number must not exceed20%.
(2) The inner and outer surfaces of the casing must be free of folds, hairlines, delaminations, cracks, folds and scars. These defects shall be completely removed, and the removal depth shall not exceed 12.5% of the nominal wall thickness.
(3) The outer surface of the coupling must be free from defects such as folds, hairline, delamination, cracks, folds, and scarring.
(4) The surface of the tubing and coupling threads should be smooth, without burrs, tears, and other defects sufficient to interrupt the threads and affect strength and tight connection.