SPE and IADC Member

Abstract

Premature failures in drill pipe have plagued the drilling industry for a long time. These failures usually occur within two feet of the box and pin tool joints. Previous work has shown that most of these failures are the result of an abrupt internal taper (1/2" - 1-1/2" long) (12.7 - 38.1mm) and slip damage. New long taper upset designs have helped solve this fatigue problem. This paper discusses a new stress relief tool joint that greatly enhances the benefits of the new, long taper upset by almost doubling the fatigue life.

Introduction

Fatigue failures in drill pipe are caused by cyclic bending stresses. These stresses are concentrated in the thin wall section of the drill pipe where the thick upset blends into the tube. I believe drill pipe today is being subjected to higher and higher stresses with the advent of top drives, deeper wells and higher angle holes. This condition is further agitated by a more hostile environment with the increasing presence of H2S, CO2 and brine water. Therefore, I believe everything possible should be done to improve the fatigue life of drill pipe. Both the long taper upset and the new stress relief tool joint will help accomplish this.

REVIEW OF PROBLEMS AND PREVIOUS TEST WORK

I think the problem of drill pipe fatigue has been sufficiently defined. Many drilling contractors and oil operators along with the IADC and API have made studies of a vast number of failures, and most all of them pointed to an abrupt upset along with slip damage as being the problem. It has also been observed that rapid deterioration of the internal, plastic coating in this area compounds the problem.

P. 893^