Frequency Domain Fatigue Evaluation on SCR Girth-Weld Based on Structural Stress

The Steel Catenary Riser (SCR) is a vital component for transporting oil and gas from the seabed to the floating platform. The harsh environmental conditions and complex platform motion make the SCR’s girth-weld prone to fatigue failure. The structural stress fatigue theory and Master S–N curve method provide accurate predictions for the fatigue damage on the welded joints, which demonstrate significant potential and compatibility in multi-axial and random fatigue evaluation. Here, we propose a new frequency fatigue model subjected to welded joints of SCR under multi-axial stress, which fully integrates the mesh-insensitive structural stress and frequency domain random process and transforms the conventional welding fatigue technique of SCR into a spectrum analysis technique utilizing structural stress. Besides, a full-scale FE model of SCR with welds is established to obtain the modal structural stress of the girth weld and the frequency response function (FRF) of modal coordinate, and a biaxial fatigue evaluation about the girth weld of the SCR can be achieved by taking the effects of multi-load correlation and pipe-soil interaction into account. The research results indicate that the frequency-domain fatigue results are aligned with the time-domain results, meeting the fatigue evaluation requirements of the SCR.