... by the load exceeding the collar strength or by high shock, vibration, or corrosion, but the primary cause of twistoff is fatigue failure. With fatigue failure, the drillstring fails downhole despite the stress being below the material-strength specification. This is caused by fatigue accumulated over time...

... in the literature, the complexity of such models can be difficult to implement in numerical-modeling strategies. Fatigue Failure. It is well known that a structure able to withstand initial loading without failure might fail if the loading is removed (or reversed) and reapplied repeat- edly. This phenomenon, known...

... 1978. Society of Petroleum Engineers joint specimen strain gauge load transfer loading Upstream Oil & Gas fatigue failure diagonal member weld defect deterioration chord wall wall adjacent column wall gauge fatigue life cyclic loading column member specimen branch member...

... the discussion on weight concentration, only fourteen 10-in.-OD collars are needed to supply as much wei~ht as twenty-five 7%- in.-OD collars. This means that the number of loca- tions where the stresses are high enough to cause fatigue failure is reduced 44 percent. Unfortunately. the use of large drill collars...

.... Introduction Fatigue is a strange and exceedingly dangerous problem. Fatigue failure occurs with little or no warning under repeated applications of a load which the metal would support indefinitely if the load were applied statically. The problem was first recognized in 1850, but it has become progressively...

... to learn more about the nature of stress in a tool joint due to bending caused a rather intensive experimental study to determine what actually happens to cause fatigue failure. It was known that a tool joint with insufficient make-up torque was subject to early fatigue failure. Therefore...

... failures of drill pipe, fatigue failures of drill-collar connections, worn tool joints and drill pipe, key seats, grooved casing, etc. Most of these detrimental effects greatly increase with the amount of tension to which drill pipe is subjected in the dog-leg. Therefore, the closer a dog-leg...