Fitness-for-Service Evaluation of Pressure Vessel Using FEA
Challenge
An independent operator in the Gulf of Guinea
needed code compliance check (ASME VIII and
ASME B16.5) on a pressure vessel originally
designed to ASME BPVC Section VIII, Division 1.
The assessment was triggered by an incident
where a portion of the vessel was accidentally
ground into, reducing the wall thickness below
the minimum retirement thickness specified
for the vessel material.
A significant chunk of design information was not available. We focused on the following.
- Internal and external pressure design of the shell and heads.
- Nozzle reinforcement.
- Flange pressure-temperature rating.
Our approach
We assessed whether the pressure vessel
remains fit-for-purpose despite reduced wall
thickness, evaluating structural integrity under
the specified MAWP and temperature. A
survey was conducted to capture actual
thickness and material data (ASTM A516 Grade
70, 1480psig @ 200°F).
Using an FEA model with defined geometry, boundary conditions, material properties, and refined
meshing near critical areas, we analysed stress and deformation. An iterative analysis identified a new
MAWP ensuring stress remains below yield strength and compliant with ASME BPVC.
The original MAWP of 1480psig is unsafe due to local thinning. We advised de-rating, which preserves
structural integrity under current conditions. Nameplate updates were recommended. For continued
use at original MAWP, reinforcement and re-analysis are necessary. The process team also proposed a
lower-pressure scheme to keep the vessel in service.
