Slip Crushing
When drill pipe, casing or tubing are run in or pulled out of hole, they are set on slips at rotary bushing for connecting or disconnecting pipes. When pipe is sitting on slips, in addition to tensile load due to buoyed weight of string, the pipe also experiences radial load or hoop stress exerted by slip segments. The damage to the pipe that can be caused due to this additional stress by slip segments is called ‘Slip Crushing Effect’. Calculations and analysing tools help in determining the maximum load that can be placed on the slips without damaging tubulars subjected to a tensile load. Slip crushing is affected by the pipe diameter, slip angle, slip length and the coefficient of friction between slip and the master bushing.