The oil casing pipe is made of seamless steel tubes. The rules adopted at the time of delivery are irregular, but they must also meet certain rules.
1. The domestic casing is in accordance with SY/T6194-96, the length of the casing is not fixed, and its range is 8-13m. However, casings no shorter than 6m can be provided, and the number must not exceed 20%.
2. There are three lengths specified in the API: R-1 is 4.88～7.62m, R-2 is 7.62～10.36m, R-3 is 10.36m to longer.
3. There must be no folds, hair lines, delamination, cracks, folds and scars on the inner and outer surfaces of the casing. These defects shall be completely removed, and the removal depth shall not exceed 12.5% of the nominal wall thickness.
4. According to the provisions of SY/T6194-96, domestic casings should be tied with steel wire or steel tape. The protective ring should be screwed on the exposed part of each casing and coupling thread to protect the thread.