Risk-Based Operations Assessment of a Multilayered Vessel Under Cyclic Loading Conditions

Operational risks have been evaluated for a multilayered vessel through the fitness-for-service (FFS) assessment. The vessel has been in service for more than four decades and is subjected to cyclic mechanical and thermal loads during normal operations. Leakage has been found over the years by inspections, which led to safety concerns for continued operation. FFS assessment was used to evaluate the condition of the vessel to determine if the vessel was fit for continued operation and the associated risks for a catastrophic type failure or burst of all layers of the vessel. Finite element analysis and fatigue evaluation, with associated partial probability, were conducted for the assessment per API 579. The operational risks were evaluated on the combined basis of FFS assessment results, failure modes, and field inspection findings. It was concluded that, despite of the problems found during inspections, risks for the catastrophic type failure of the multilayered vessel are very low and continued operation with appropriate monitoring and maintenance is recommended.