API RP 7G pdf download.Recommended Practice for Drill Stem Design and Operating Limits 14 Special Processes 14.1 DRILL STEM SPECIAL PROCESSES 14.1.1 Usually the materials used in the manufacture of down hole drilling equipment (tool joints, drill collars, stabilizers and subs) are AISI–4135, 4137, 4140, or 4145 steels. 14.1.2 These are alloy steels and are normally in the heat treated...