The scope of this research is to estimate the fatigue life of drill pipes subjected to multiaxial state of stress. Several approaches that model and estimate fatigue life under non-proportional multiaxial loading were investigated. The critical plane approach was chosen with Fatemi and Socie numerical model. A software program (Elrond) was constructed to estimate the fatigue life for non-proportional loading. The code was validated using previous researchers experimental fatigue data sets. The developed software was then applied to a real life drilling problem. The “Build and Hold” drilling job condition was analyzed using the developed software. Results were compared with the API RP7G fatigue design guidelines. Fatigue life charts were prepared using fatigue lives estimated by Elrond at several axial loading, dogleg severities and axial torque amplitudes. Also cumulative fatigue life charts using fatigue life values from Elrond were calculated according to the method of Hansford and Lubinski developed, and used in API RP7G. Elrond results were less conservative than the API results, especially for low values of axial torque.
Mechanical Engineering Department
MS in Mechanical Engineering
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(2016).Multiaxial fatigue in drill pipes under non-proportional loading [Master's Thesis, the American University in Cairo]. AUC Knowledge Fountain.
Helmy, Nahla. Multiaxial fatigue in drill pipes under non-proportional loading. 2016. American University in Cairo, Master's Thesis. AUC Knowledge Fountain.