Abstract
Each of the 700 or more drilling rigs operating in West Texas has an investment of $30,000 to $70,000 in drill stem and one one drilling company there estimates drill stem costs on each rig to be $137 a day. A large part of the cost is attributed to rapid depreciation of drill stem from corrosion and corrosion fatigue, heavy corrosion from underlying salt strata being the principal culprit. Deeper wells drilled recently have faced an increasing corrosion problem as a result of reduction in salt content of well fluids.
The very costly results of corrosion fatigue failures of drill collar joints is cited, including the numerous operational difficulties resulting from mitigation measures.
Hughes Tool Company first placed cast zine rings in boxes before the pin was screwed in, thus forcing the ring into place and intimately engaging the unengaged threads at the bottom of the box. These proved unsatisfactory, so magnesium strip was pressed in place in the, drill collarbox. Tests of the rings are described. Recent changes in drilling practice have made magnesium rings unsuitable and aluminum rings are being tested.
