Abstract: Apparatus and methods are disclosed for maintaining drilling fluid circulation while attaching joints of pipe to a drill string during the operation of drilling a well borehole. A chamber is clamped over a thread joint connecting two joints of drill string pipe. An inlet valve is opened to flow drilling fluid into the chamber under pressure. The thread joint is then broken, the chamber is partitioned with a ram thereby forming an upper and lower sub chambers, and drilling fluid circulation is continued through the lower sub chamber and down the borehole through the drill string. The thread joint of another joint of drill string to be added is positioned in the upper sub chamber, pressure is equalized between the upper and lower sub chambers, the ram is opened, the thread joint is made, and drilling fluid is reestablished through the drill string without interruption.

Abstract: This disclosure is directed to an improved drill collar having pin and box connection in an elongate hollow member. In cross-section, the drill collar is formed of a square billet defining three rectangular corners. The fourth corner is rounded thereby reducing the weight in that area and thereby creating an eccentered center of mass and mass moment of inertia. A cutter is located along one of the edges so that the cutter scuffs against the well borehole during rotation to thereby enhance circular configuration and to reduce key seating or deviation.