Level 3 Assessment for Geometric Imperfections

Problem

Following extensive weld repairs during a turnaround, a refinery fractionation column experienced measurable geometric distortion, including a global lean and localized out-of-roundness beyond original fabrication tolerances. The owner needed to understand whether this distortion—combined with existing damage mechanisms and historical modifications—compromised the structural integrity of the vessel under operating loads.

Solution

A Level 3 fitness-for-service (FFS) assessment was performed using detailed finite element analysis (FEA) based on actual measured geometry from laser scan data. The distorted shape, including vessel lean and local deviations, was explicitly incorporated into the model. The assessment evaluated multiple failure modes—plastic collapse, local strain, and buckling—under combined loading conditions including pressure, weight, wind, and seismic effects, in accordance with API 579 and ASME Section VIII, Division 2 methodologies.

Value

Demonstrated that the vessel remained fit-for-service despite significant geometric distortion, with a remaining strength factor above code requirements. Avoided unnecessary repair or replacement of a critical asset now, and provided confidence to continue safe operation while identifying practical follow-ups (monitoring vessel lean, etc.), enabling risk-informed decision-making.