Metallurgical failure analysis of twisted-off heavy weight drillpipe

•Metallurgical failure analysis of twisted-off heavy weight drillpipe was performed to identify the failure root causes.•The HWDP twist-off failure occurred at the end of the externally upset transition part of the pin tool joint.•The material characteristics of the alloys of HWDP tool joint and pipe body are conforming to AISI 4140H and AISI 4140.•The results of the present investigation indicate that the HWDP failed by Corrosion Fatigue mechanism. A heavy weight drill pipe (HWDP) was twisted-off and parted during drilling in an Egyptian oil well at depth of 1240 m. Failure investigation has been carried out to identify the root cause of the HWDP failure. Detailed failure investigation was performed including thorough visual examination, elemental chemical analysis, hardness testing, microstructural characterization using light optical microscope (LOM), scanning electron microscope (SEM) fractography and energy dispersive spectroscopy (EDS) of the failed specimens to reveal the nature of failure. The results showed that the failure mechanism of the HWDP was corrosion fatigue cracking initiating mainly at the carbon steel pipe inner surface. The failure was attributed to exposure to cyclic stresses caused by drillstring vibration; high stress concentration points in the HWDP body configuration at the upset transition area and the low toughness of the inhomogeneous microstructure at the interface of the friction welding thermomechanically affected zone and the carbon steel pipe.