ORAL REFERENCE: FT588 FATIGUE ON DRILL STRING CONICAL THREADED CONNECTIONS, TEST RESULTS AND SIMULATIONS L. Bertini 1 , M. Beghini 1 , C. Santus 1 , and A. Baryshnikov 2 1 DIMNP - Dipartimento di Ingegneria Meccanica Nucleare e della Produzione - Universit` a di Pisa. Via Diotisalvi n.2, Pisa. 56100 - Italy. 2 ENI S.p.A. - San Donato Milanese (MI) - Italy. ABSTRACT The paper is concerned with fatigue life of drill string threaded connections used in Oil drilling technology. Full scale tests, finite element simulations and discussion of fatigue models are reported. Full scale fatigue tests were performed at the University of Pisa. Two kinds of not standard fatigue test rigs are proposed for different geometry and connection constructions, both exploiting near resonance conditions induced in the specimens to get the overall structure not loaded and test time reduced. Finite element analyses were performed to get an interpretation of tests and particular care was devoted to model the connection presetting and the following fatigue loading. Prediction of the specimen fatigue life was performed to reproduce test results and different approaches are proposed. Basic material resistance properties were previously produced to apply fatigue models. Some limitations in prediction were observed, in particular due to high mean stress generated at notched nucleation sites and also not clear demarcation between nucleation and propagation in full scale tests. KEYWORDS: full scale tests, fatigue life prediction, drill string threaded connections, finite element simulations. 1 INTRODUCTION Oil drilling typically employs long hollow drill string to reach the production area [1]. Fatigue damage in drill string is a well known issue in oil drilling technology, recording more than 50% failures [2]. Since failures entails the lost of the drilling site, drill string failures are time consuming and very costly. Failure usually results from material fatigue aggravated by the corrosive environment, improper equipment handling, excessive rotational speeds or loading. Coupling of various damage conditions reduces dramatically the fatigue life of the string. In particular, corrosion effect is a key factor [3, 4] primarily related to hydrogen sulfide (H 2 S) which can drastically reduce or eliminate the endurance limit. Full Scale fatigue tests (i.e. tests on real components) are therefore strategic for oil drilling companies. Indeed devices for drilling elements fatigue tests have been recently proposed based on four points bending scheme [5]. Connections between elements working for long periods in deviated wells or experiencing buckling tilting plus bending lateral vibration [6] are the drill string typical locations of fatigue damage. To connect drill string elements in situ conical shouldered threaded connections are used (briefly named as Copyright (c) 2006 Elsevier Ltd. All Rights Reserved.