Slip engaging portion of drill string formed of increased wall thickness and reduced hardness

Claim 1

A TUBULAR DRILL PIPE SECTION TO BE USED IN A WELL BORE COMPRISING UPPER AND LOWER TOOL JOINTS, A MAIN STEEL TUBULAR PORTION EXTENDING UPWARDLY FROM SAID LOWER JOINT AND TERMINATING NEAR SAID UPPER TOOL JOINT, AND AN ELONGATE STEEL PROTECTOR TUBE EXTENDING DOWNWARDLY FROM SAID UPPER TOOL JOINT AND SECURED TO THE UPPER END OF SAID MAIN PORTION, SAID MAIN PORTION HAVING A MUCH LESSER WALL THICKNESS THROUGHOUT SUBSTANTIALLY ITS ENTIRE LENGTH THAN SAID PROTECTOR TUBE AND BEING MADE OF A STEEL HAVING SUBSTANTIALLY GREATER HARDNESS AND UNIT TENSILE AND TORSIONAL STRENGTH THAN THE STEEL OF SAID PROTECTOR TUBE, THE LENGTH OF SAID PROTECTOR TUBE BEING ABOUT AT LEAST FOUR TIMES THE OUTSIDE DIAMETER OF SAID MAIN PORTION AND SAID PROTECTOR TUBE BEING DISPOSED IN SAID DRILL PIPE SECTION AT A LOCATION FOR ENGAGEMENT BY SUPPORTING SLIPS AT THE TOP OF THE WELL BORE, THE CROSS-SECTIONAL AREA OF SAID PROTECTOR TUBE BEING SUCH THAT THE TOTAL TENSILE AND TORSIONAL STRENGTH OF SAID PROTECTOR TUBE IS NO LESS THAN THE TOTAL TENSILE AND TORSIONAL STRENGTH OF SAID MAIN PORTION, WHEREBY SAID PROTECTOR TUBE HAS LESS NOTCH SENSITIVITY AND GREATER RESISTANCE TO INWARD CRUSHING THAN SAID MAIN PORTION TO THE ACTION OF THE SLIPS.