Oil well casing is seamless or welded tubing made of high quality steel with tapered threads machined on both ends. Most casing is connected with casing clamps to form a casing column. The casing column is used to seal the exposed rock in the well wall. Oil well tubing has its own special standards, and each type should meet them.
The casing connection threads are all tapered, and there are four types of API standard casing connection threads: Short Circular Thread (STC), Long Circular Thread (LTC), Trapezoidal Thread (BTC), and Straight Connection Thread (XL). In addition, there are non-standard threads. Round threads have a taper of 1:16 and a pitch of 3.175mm (8 buttons/in). Trapezoidal threads are 1:16 (OD < 16in) and 1:12 (OD ≥ 16in) with a pitch of 5.08mm (5 buckets/in). Casing column (casing string) is usually the same outer diameter, the same or different steel grade and different wall thickness of the casing with the joint hoop connected to form, should meet the requirements of strength and production.
