During well construction, a hole is drilled using a drilling tool connected to a long string of drill pipes. To avoid the well from collapsing, casing pipes are inserted into the well. In the offshore wells, a riser pipeline connects the wellhead at the bottom of the sea to a production vessel. The risers, casing and drill pipes are connected using threaded connections. There are lots of failure modes in casings but one of the most important one is fatigue failure in threaded connections. When dynamic loads act on the connections, their fatigue resistance becomes important. These loads can be caused by operational and environmental conditions. Offshore risers, tendons and columns are usually subjected to dynamic loads because of waves and currents. Also wind acting on a platform can cause the structure to move and creating fluctuating loads. Because of connection’s geometry stresses are multiaxial in this area. Threads act as stress riser and high stress concentration cause fatigue crack initiation. This thesis has been focused on fatigue life prediction of threaded connections and also studying the effect of different design features on a connection’s fatigue life. In this study the API line pipe connection is used as a reference. There are lots of different fatigue life prediction methods but in a general justify; TEXT-INDENT: 0.25in; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr; mso-pagination: widow-orphan" Axial tensile tests were performed on 42crmo4 steel which is a usual material for risers and also axial fatigue tests were done at room temperature on standard simple specimens and S-N diagram was established. Based on established diagram and use of weakest-link theory which is a statistical method, fatigue life of threaded connections was predicted. The predicted fatigue life for the evaluated threaded connection was compared with experimental results in literature. Besides the effects of geometry change on the fatigue life were evaluated. The results show that connection fatigue size has a considerable effect on its fatigue life. Keywords: Weakest-link theory, Critical distance theory, Fatigue life prediction, Casing connection
