Stress of API 5CT casings in oil wells: In order to ensure that the casings enter the wells continuously, without cracking or deformation, the casings should be strong enough to withstand the external forces they are subjected to. Therefore, it is necessary to analyze the stress on the inner casing.


1) Tension
2) Extrusion force
3) Internal pressure
4) Bending force


In short, the casing in the well bears the first three forces. The stress conditions of each part are different, the upper part is under tension, the lower part is under external force, and the middle part is under less stress. In the design of casing string, the steel grades and wall thickness of casing are selected based on the above safety factors. For API standard casing, the general safety factor of tension is 1.6-2.0, the safety factor of impact resistance is 1.00-1.50, 1.125, the safety factor of internal pressure is 1.0-1.33, and the safety factor of compressive strength is 0.85 at the cement injection site. It should be emphasized that the safety factor in casing string strength design is carefully selected according to the region, formation and later oil and gas production process. He is an experienced person.  Due to the different external forces applied to the upper, middle and lower parts of the casing string, the designed casing string is usually thicker or more steel grades on the upper and lower walls, while in the middle it is opposite, so it needs to be numbered. Enter the well. In most cases, the enclosure works in corrosive media. Therefore, in addition to requiring a certain degree of bonding strength, the shell is required to have good sealing performance and corrosion resistance.