Level 3 Assessment for Volumetric Damage

Problem

A large column experienced widespread corrosion under insulation (CUI), with damage distributed across multiple shell courses and localized regions. Traditional inspection methods were insufficient to fully characterize the extent of damage, and the owner required confirmation that the vessel remained fit for service under combined pressure, weight, and wind loading.

Solution

A full Level 3 fitness-for-service (FFS) assessment was performed using finite element analysis (FEA). A three-dimensional shell model was developed incorporating spatially varying thickness data derived from laser scanning. The vessel was evaluated against multiple failure modes including plastic collapse, local strain, and buckling under realistic combined loading scenarios. Joint efficiency effects and uncertainty in thickness measurements were explicitly accounted for in the model.

Value

Demonstrated that the vessel remains fit for service at original design conditions despite widespread CUI damage, with a remaining strength factor exceeding code requirements. Eliminated the need for immediate repair or replacement of a critical asset. Established a defensible basis for continued operation with quantified margins, along with clear guidance for monitoring and future inspection planning.