Survival assessment of die-marked drill pipes:: integrated static and fatigue analysis

Abstract

Drill pipes under operational loads may fail in static or fatigue mode. Static failures are evaluated at two critical levels: the rotary table level (surface level) and the dogleg level, whereas fatigue failure occurs in a pipe section at the dogleg level due to the cumulative effect of fatigue damage in a number of drilling events. The current practice of static and fatigue failure analyses is based on a smooth pipe surface condition. In practice, however, dies of gripping systems mark the pipe surface during making and breaking operations (screwed and unscrewed to connect and disconnect two pipes). These marks on the pipe surface cause stress concentrations, which make a pipe more susceptible to both failure modes. This paper presents an integrated approach for static and fatigue failure analysis, considering the effects of stress concentrations due to die-marks from different gripping systems. Thus, the approach is intended to assist engineers in assessing the overall survivability of drill pipes through a detailed failure evaluation considering the effect of die-mark related stress concentrations in representative field conditions.