There are couplings for casing pipe
and couplings for tubing, the function is the same that to connect the pipe each other. On the other hand, still there are some differences between the two.
Casing coupling is for the dimensions more than 4 1/2 inch. 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 following types:
• BTC: Buttress coupling
• LTC: Long buttress coupling
• STC: Short buttress coupling
All three types has same thickness of the casing pipe body, 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 seamless pipe. The steel pipe ends with internal thread to connect with the upper and lower casing. In order to ensure the joint tightness, the precision of screw thread is strictly required.
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.
The oil tubing coupling can solve the problem of fatigue fracture in the existing coupling due to stress concentration. 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 same thread pitch flat thread. The coupling is not easy to produce fatigue fracture, and has good connection effect. It can prevent the accident of oil well pipe string break effectively.