Joint efficiency is defined as a ratio of joint tensile strength to pipe body tensile strength.
The connection strength of premium connection is high and can be equal to that of pipe body.A premium connection is defined by :
Most premium connections have a double shoulder. (top of the pin , bottom of the box).
The length of premium connection coupling is longer than that of API coupling.
connections have trapezoidal
threads for multiple sealing effect.
API threads are sealed by the intermeshing of internal and external threads
For standard premium OCTG connections with the loads expected in drilling with casing applications the Stress Concentration Factors (SCF) is normally higher than 2.0, however from a fatigue perspective it is desirable that the SCF value be as low as possible.
Premium connection has good anti-sticking performance (can be repeatedly lifted and unloaded without damaging the threads)
Example of premium connections compatible with API connections are Vam Eis, DSTJ, GPDS
Hope this is useful for you.