Inspection Interval Guidelines To Reduce Drillstring Failures

Summary Inspection interval guidelines were developed to reduce the occurrence of costly drillstring fatigue failures. The guidelines are based on a state-of-the-art fracture mechanics model and incorporate reliability data of commercial inspection services using conventional nondestructive testing techniques. On the basis of extensive full-scale testing, the model was found to predict fatigue-crack-growth behavior reliably. By establishing inspection intervals on the basis of fatigue-crack growth, inspection services are systematically and cost-effectively specified to achieve acceptable reliability (or risk). Simple equations and charts are presented in terms of practical drilling parameters to reduce typical downhole fatigue failures.