The coupling is a short length of pipe used to connect two joints of casing pipes or tubings. Unlike ordinary coupling, it effectively solves the problem of fatigue fracture that is easily caused by the stress concentration and protect the threads.The coupling is normally made of the same steel grade as the casing pipe or tubing.
Mostly the couplings are required to be given a kind of color as an identification..
Such as Green (J55), White ( P110), Blue(C75), Red ( N80)
All of the couplings are produced strictly according to API 5CT and 5B specifications.