Experimental Investigation of Drillpipe Loaded in Slips

Oilwell drillstrings are suspended in the rotary table using axisymmetric wedges in a restraining bowl structure. These wedges, are known as “slips”. Hardened dies on the inside surface of the slips grip the drillpipe. The string capacity to sustain axial loads is influenced by the slip-drillpipe interaction. When the design for a recent Gulf of Mexico (GOM) offshore well required the drillstring to support ∼4.5 kN, a test program to investigate slip-drillpipe interaction was initiated. The analysis of strain gage data revealed that drillpipe peak stresses are not confined to a single cross sectional plane on the drillpipe ID. Yielding is initiated on the ID along a line parallel to the drillpipe axis, and corresponds to the gap between slip segments. This paper presents test details and results of data analyses that are a prelude to an ongoing effort to determine a revised design basis for drillpipe loaded in slips.