Abstract

Obtaining a realistic prediction of the fatigue damage of pipelines employed in the subsea industry is vital for safe operations, as they are permanently subjected to wind-sea waves, swell and marine currents. Considering pipeline fatigue damage due to vortex-induced vibration (VIV) over its life cycle is critical in the design phase. Several VIV fatigue damage prediction models have been and are being developed by oil companies and research institutes. Uncertainties in the input data, such as in the effective axial tension, wall thickness, structural damping, water depth, and others, can influence the selection of materials, welding procedures, fulfilment of safety criteria, and other important decisions; therefore, on the total cost of the project. Reliable predictions of VIV fatigue damage are vital to controlling the degradation and ensuring the integrity of the operation at an optimized cost.

This paper aims to evaluate the variability of VIV fatigue damage prediction when uncertain inputs in wall thickness, water depth, structural damping, gap height, effective axial force, and Hi-Lo weld cap are considered. To this, a sensitivity analysis is conducted and an in-house software used for estimating VIV fatigue damage over the pipeline life cycle is employed combined with a Monte Carlo simulation. A case study based on a synthetic Norwegian offshore oil field is used. The information can support oil and gas companies in focusing on the most critical input parameters and uncertainties when carrying out a VIV fatigue damage analysis in new projects, and to help visualize the uncertainties in free span analysis.

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