There are couplings for casing and couplings for tubing, the function is the same that to connect the pipe to each other. On the other hand, still, there are some differences between the two.

Tubing coupling

Normally tubing coupling OD maximum is 4 1/2”, as the tubing pipe is applied for the drilling activities (Inside the tubing is the sucker rod to drill/pump the oil), couplings type is more various and rigorous than casing, mostly used is thicken type upset coupling (Internal upset and external upset), for short is EUE coupling, it is the most favorable in tubing connections. Tubing with EU end (EUE) coupling connection also called UPTBG. Because of the end of the tubing is thickened (upset), the connecting stress is better than buttress coupling.

Buttress coupling another type used for tubing connections, it has the same thickness of the pipe body, called NU end (NUE)tubing or TBG.

Features

The oil tubing coupling can solve the problem of a fatigue fracture in the existing coupling due to stress concentration. The oil tubing end is connected to the inside wall of the coupling in a tapered thread. The coupling body end and oil tubing are connected with the same thread pitch flat thread. The coupling is not easy to produce fatigue fracture and has a good connection effect. It can prevent the accident of oil well pipe string break effectively.

Casing coupling

Casing coupling is for the dimensions more than 4 1/2 inches. Differently, than tubing coupling is, casing coupling normally does not need to be thickened (Non-upset), which means no upset casing coupling, so it has the following types:

• BTC: Buttress coupling
• LTC: Long buttress coupling
• STC: Short buttress coupling

All three types have the same thickness of the casing pipe body, they just have different lengths.

The oil casing coupling is a necessary piece used to connect the two casing. The coupling manufacturing method is the same as a seamless pipe. The steel pipe ends with an internal thread to connect with the upper and lower casing. In order to ensure joint tightness, the precision of the screw thread is strictly required.