API Coupling
As we know steel pipe coupling is a short pipe or tube that with threads on both ends, used to connect pipelines. So It is a kind of pipe fittings that with threaded connection, the advantage is easy for pipeline maintenance or to replace the broken pipe.
API Coupling refers to the steel couplings that used in connecting casing pipe and tubing. Also known by OCTG coupling, it is usually manufactured in seamless type, material grade same with the pipe body (API 5CT K55/J55, N80, L80, P110 etc), same PSL or providing higher grades than requested. Same heat treatment also applicable, except there is an special requirements.
Tubing coupling
Introduction
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 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.

Casing coupling
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:Round thread
• LTC/LC: Long
round thread casing
coupling
• STC/SC: Short round thread casing
couplingButtress thread • BTC/BC: Buttress thread casing couplingAll 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.
API Tubing and Casing Pup Joint
Tubing and Casing Pup Joints are machined according to the latest version of API Spec 5CT. It's used to connect two pipes of same diameter with the same types of thread on the two ends.
The Steel Grade includes J55,K55,N80-1, N80Q, L80-1, P110 etc.
There are two types of thread widely used in Tubing pup joint:Non-upset Thread(NUE) and External-upset Thread(EUE)
There are three types of thread widely used in Casing pup joint: Long-Round Thread(LTC), Short-Round Thread(STC),Buttress Thread(BTC)
There are two types of End thread: Pin*Pin, Pin*Box(Pin*Pin with coupling)
Remark: We can also produce Special Pup Joint of API 5CT/5B Thread. Thanks for share the drawing.
API Crossover
Crossover is also kind of pup joint, used to connect two pipes of different diameter with the same or different types of thread on the two ends.
The OD, Length and thread type etc. are customized.