ABSTRACT
Steel catenary risers (SCRs) are preferred solution for deepwater application, however their fatigue design at touch down zone (TDZ) is challenging. With uncertainties of SCRs fatigue usually a larger safety factor is used in practice. In this work, the significance of relevant parameters on the SCR fatigue in TDZ is investigated with Morris method. By ranking the parameters in order of significance, the results show that the undrained shear strength of mudline has more influence on SCR fatigue in TDZ. Moreover, the probability of fatigue life of SCR in TDZ is presented as an alternative to deterministic fatigue life.
Steel catenary risers (SCRs) are recognized as a preferred solution in exploring the deep-water oil and gas, since it is cheap and easy to produce and install. However, fatigue performance in touchdown zone (TDZ) is still a challenge in the design due to the uncertainty with respect of design parameters, which are generally related to riser itself, the connected floater and the seabed soil characteristic. The uncertainty related to the seabed soil mainly comes from the complex nature of riser-seabed interaction in the TDZ.
During the past two decades, many researchers have focused on elaborating the riser-seabed interaction (Elosta et al. 2013, Katifeoglou an Chatjigeorgiou, 2012, Wang et al. 2013, Shiri, 2014) given that the uncertainty of riser-seabed interaction affects the fatigue design of SCRs in the TDZ. They investigated the riser-soil interactions in terms of vertical embedment and large lateral movements of SCR in the TDZ by developing numerical model or using commercial finite element software. The advanced model can reflect the riser-seabed interaction more realistically; however the soil property at a specific site for SCR TDZ generally cannot be measured accurately, especially in deep water. In addition to the uncertainty of the soil property, there is uncertainty associated with the motion of floater connected with SCRs. For one thing, the floater neutral position may be relocated a few times during design life. Moreover, the SCRs property may also have uncertainty.
