Metallurgical Failure Analysis of Hydraulic Drilling Jar

Hydraulic drilling jar (HDJ) was twisted off (fractured) at the end of the female-threaded box connection with upper lock housing during drilling operation in Egyptian oil company. The failed HDJ was used in drilling in two section holes 16″ and 12 ¼″. The jar was rotated under compression cyclic bending and fatigue stresses. The failure investigation included visual examination, chemical analysis and microstructure characterization performed by light microscopy, micro-hardness testing, scanning electron microscopy and energy-dispersive spectroscopy analysis. The experienced failure was identified as multiple fatigue cracking, washout and twisting off. The root cause of failure is the exposure of the jar to severe combined stresses caused by axial and lateral vibrations and rotation bending during drilling through the 16″ hole followed by the 12 ¼″ hole sections employing the same jar along string high deflections. Corrosion appears to be a contributing factor in both the initiation and propagation of fatigue cracks. The fatigue cracks are propagated and connected under the exerted severe loads reaching the housing outer wall and forming perforations. The pressurized mud flushes out and enlarges the perforations leading to wash out condition with sudden drop of mud pressure. Eventual jar twist-off occurrs when drilling is further continued.