SOLUTION

WJE performed an FFS evaluation based on API 579-1/ASME FFS-1 to determine whether the Flare KO Drum was safe to continue operating using Part 4, Assessment of General Metal Loss, and Part 5, Assessment of Local Metal Loss. The assessment used Level 3 methods based on the proximity to and interaction of the local thin area with structural discontinuities, including stiffening rings, nozzles, and saddle supports.

To establish protection against global plastic collapse and other relevant failure mechanisms, a nonlinear elastic-plastic finite element (FE) model of the drum was created with representative geometry, boundary conditions, and design loading. The model incorporated remaining wall thickness readings from the PAUT inspection by mapping the high-fidelity grid-style measurements directly onto the FE mesh to capture the as-inspected state of the vessel. To address the remaining life and establish inspection intervals, iterative analyses were performed to identify a future corrosion allowance based on short- and long-term corrosion rates for the drum.

Based on the applicable design loading and acceptance criteria listed in API 579-1, the FFS evaluation demonstrated that the Flare KO Drum had sufficient remaining strength to satisfy the minimum required design margins for in-service equipment and was fit for continued service with periodic monitoring.