Oil casing is the core point of maintaining the operation of oil and gas wells. Due to different geological conditions and complex underground stress conditions, tensile, compressive, bending and torsional stresses act on the pipe body as a whole, which places higher requirements on the quality of the oil casing itself. If the oil casing itself is damaged due to various reasons, it is likely to cause the production of the entire well to decrease or even be destroyed. Oil casing has the following characteristics:

Domestic oil casing is stipulated in SY/T6194-96. The length of oil casing is not fixed, and its range is 8-13m. However, oil casing no shorter than 6m can be provided, and the total amount cannot be higher than 20%. The inner and outer surfaces of petroleum casing must not be disassembled, hairline, separated, cracked, folded or scabbed. Such defects should be completely eliminated, and the depth of elimination should not be greater than 12.5% of the nominal wall thickness.

The surface layer of the coupling must not have defects such as disassembly, hair lines, separation layers, cracks, folds, and scabs. The thread surface of petroleum casing and couplings should be smooth, and no burrs, tears, or other defects that can cause thread termination to interfere with strength and tight connections are allowed.