“Twin-impact” double-blow drilling apparatus

A drilling apparatus comprising a spun-up outer pipe and a spun-up inner pipe, a rotary drive for driving the inner and the outer pipes, a rotary impact drive, shank ends on ends of the outer pipe engageable with the rotary drive and adapted for engaging a striker mounted on the inner pipe for axial movement together with the inner and the outer pipes, a compensation ring on the shank end on a same side as the rotary impact drive, the compensation ring having a hardness lower than a hardness of a material of the inner pipe, the outer pipe and the striker, and the compensation ring having a structure sufficient to compensate for applied forces.