Further, in this stage of time, the arc starts to slowly rotate along the peripheral edges of the tube ends. During this stage of time, I1 current of (280–300 A) is employed. In stage T3 (20–30 s), arc accelerates and rotates with a high speed of about 250 m/s (linear) along the peripheral edges of the tubes while heating up the faying surfaces to the point of solidus (red hot condition). A current of 200–220 A (I2 current) and is provided during the T3 stage. Finally, upsetting action takes place in T4 (0.3 s) by supplying a current of 1100 A (as per I3 stage).