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.
API Casing Coupling
|Size (Pipe OD) (in)||4-1/2, 5, 5-1/2, 6-5/8, 7, 7-5/8, 8-5/8, 9-5/8, 10-3/4, 11-3/4, 13-3/8, 16, 18-5/8, 20|
|Threading||Short Round-Thread Casing (STC)Long Round-Thread Casing (LC)Buttress Thread Casing (BC)|
|Grade||H-40, J-55, K-55, C-75, L-80, N-80, C-95, AS-95, P-110, L80-13CR|