Session: 10-06-01 Pipelines and Cables

Paper Number: 126583

126583 - Service Life Prediction for Free Spans of a Subsea Pipeline Undergoing Vortex Induced Vibrations 

Submarine pipelines have been widely employed for transporting offshore oil and gas from subsea wells to platforms or onshore processing facilities, thereby being regarded as the lifelines of offshore oil and gas industries. Free spans of a subsea pipeline may undergo vortex-induced vibrations (VIVs) and could be damaged by fatigue failure. The length of a pipeline span can alter its natural frequency and further influence the corresponding critical reduced velocity for the onset of VIVs. Flume tests indicated that the VIVs of a near-bed cylinder can be triggered effectively in a moderate shear flow. It is implied that the vibration cycles of a free span of subsea pipelines may be up to ten-millions and the very-high-cycle fatigue (VHCF) could be encountered during the engineering service. In this study, a prediction method is proposed for the service life of subsea pipeline free spanning by taking into account of VHCF mechanism. In the proposed method, the hydrodynamic loads and stress distributions along the free span are firstly  calculated theoretically. By performing a case study on the high-strength X70 steel pipelines, the fatigue assessment is then carried out on the basis of the S-N (Stress range – Number of cycles to failure) curve. The correlation of service life and the characteristic velocity of the flow can be finally established.

Presenting Author: Fu-Ping Gao Institute of Mechanics, Chinese Academy of Sciences

Presenting Author Biography: Fuping Gao is a full professor in offshore mechanics, deputy director of the Key Laboratory of Mechanics in Fluid Structure Coupling System at Chinese Academy of Sciences (CAS). Fuping obtained his PhD (2001) from CAS. He was a visiting scholar (2000) at the Hong Kong University of Science and Technology, then a post-doctoral research fellow (2001-2002) at Griffith University and the University of Western Australia. Fuping’s research interests are in offshore soil mechanics & geotechnical engineering, with focus on wave/current-structure-seabed interactions. Fuping has published over 150 journal and conference papers. He is currently serving as deputy editor of Ocean Engineering

Authors:

Qing-Yuan Song Institute of Mechanics, Chinese Academy of Sciences
Jun Liu Institute of Mechanics, Chinese Academy of Sciences
Fu-Ping Gao Institute of Mechanics, Chinese Academy of Sciences