Couplings are usually manufactured in accordance with API SPEC 5CT and API 5B specifications and can be divided into casing couplings and tubing couplings. Their functions are the same, but there are still some differences between the two.
Casing Coupling
Casing couplings are available for sizes over 4 1/2 inches. Casing couplings generally do not need to be thickened (non-thickened), that is, casing couplings are not thickened, so there are the following types:
- BTC: Buttress coupling
- LTC: Longbuttresscoupling
- STC: Short buttresscoupling
- Feature:
The manufacturing method of casing couplings is the same as that of seamless pipes. The end of the steel pipe has internal threads and is connected to the upper and lower casings. In order to ensure the sealing of the joint, there are strict requirements for the accuracy of the thread.
Tubing Coupling
Usually, the maximum outer diameter of tubing couplings is 4 1/2”. Since tubing is used for drilling activities, coupling types are more diverse and strict than casing. The most commonly used are thickened joints, referred to as EUE joint, which is the most advantageous in oil pipe connections. Pipes with EU end (EUE) coupling connections are also called UPTBG. Due to the thickening (upsetting) of the pipe end, the connection stress is better than that of buttress couplings.
Buttress couplings are another type used for pipe connections that have the same thickness as the pipe body and are called NU end (NUE) pipe or TBG.
- Feature:
Tubing couplings can solve the problem of fatigue fracture of existing couplings due to stress concentration. The end of the oil pipe is connected to the inner wall of the joint through a tapered thread. The end of the joint body and the oil pipe are connected with the same pitch flat thread. This coupling is not prone to fatigue fracture and has good connection effect. It can effectively prevent the occurrence of oil well pipe string fracture accidents.
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