Apparatus and methods for improving contact stress distribution within collet-type mechanisms

An internally-gripping tubular running tool comprising:

• (a) an elongate mandrel defining an outer mandrel surface configured to define one or more mandrel contact surfaces each corresponding to a curved surface of a truncated circular cone, each said mandrel contact surface having a taper angle;
• and
• (b) a plurality of slips elements each having:
• an outer workpiece engagement surface configured for radially-compressive gripping engagement with an internal surface of a tubular workpiece;
• and
• one or more inner surface regions each configured for contacting engagement with a corresponding one of the one or more mandrel contact surfaces, with at least part of each inner surface region defining a first surface region having a curvature which, as viewed in section transversely perpendicular to a longitudinal axis of the internally-gripping tubular running tool, is invariant along the axial length of the first surface region.

An externally-gripping tubular running tool comprising:

• (a) an elongate, generally cylindrical mandrel having an inner bore defining one or more mandrel contact surfaces each corresponding to a curved surface of a truncated circular cone, each said mandrel contact surface having a taper angle;
• and
• (b) a plurality of slips elements each having:
• an inner workpiece engagement surface configured for radially-compressive gripping engagement with an external surface of a tubular workpiece;
• and
• one or more outer contact surface regions each configured for contacting engagement with a corresponding one of the one or more mandrel contact surfaces, with at least part of each outer surface region defining a first surface region having a curvature which, as viewed in section transversely perpendicular to a longitudinal axis of the externally-gripping tubular running tool, is invariant along the axial length of the first surface region.