Condition assessment of corroded spanning subsea pipelines under vortex-induced vibration

Vortex-induced vibration (VIV) is a critical failure form of spanning subsea pipelines. The presence of corrosion defect may accelerate the degradation of spanning pipelines. This paper presents a condition assessment of corroded subsea pipelines under VIV using acoustic-structure coupling method and simulation of flow around a cylinder. First, the acoustic-structure coupling method is used to perform the modal analysis of pipeline with the corrosion defects, and the wet modal frequencies across pipelines with the varying ovality corrosion levels are compared. Subsequently, a 3D transient simulation of flowing around the pipeline containing corrosion defect were performed, in which the vortex shedding patterns, temporal variations in lift and drag coefficients, and frequency-domain characteristics of lift coefficients after Fast Fourier Transform (FFT) are obtained. Eventually, condition of corroded spanning pipelines is estimated based on the resonance theory, which is implemented through comparing the vortex shedding frequency with the first-order natural frequency. It is observed that ovality and the presence of corrosion defects significantly reduce the overall structure stiffness, influencing vibration mode characteristics and vortex shedding frequency of pipeline. In essence, the outcomes of this study can support the integrity assessment of subsea pipelines.