Introduction
Lifting a damaged pressure vessel is already a challenging task, but doing so while keeping a plant fully operational adds another level of complexity. Recently, we faced this exact situation when a jacketed pressure vessel in a brewery suffered severe buckling and tearing due to a vacuum breaker failure. The challenge was not only to lift the damaged vessel safely but also to ensure plant operations continued without interruption.
In this blog, we’ll discuss how we tackled this challenge, leveraging Finite Element Analysis (FEA) to optimize the lifting strategy and mitigate risks.
Understanding the Damage
The damaged vessel was a 5-meter diameter, 20-meter tall jacketed pressure vessel used in a brewery, making it a critical component of the plant. The failure occurred in areas without support rings and where the shell was thinner, leading to severe buckling and tearing. A major concern was that the shell might tear further during the lift, making it essential to secure the vessel before moving it.
Engineering the Lift: Safety and Structural Considerations
- Securing the Damaged Shell
Since the vessel’s structural integrity was compromised, we implemented extra safety measures:
- Strapping the shell from the bottom support ring to the lifting bracket to ensure that if further tearing occurred, the vessel would remain secured.
- Strategic placement of the tailing lug along a neutral axis to prevent additional compression or tensile stresses in the already buckled areas.
- FEA Analysis for Risk Reduction
To anticipate and manage potential failure modes, we performed:
- Linear Static Analysis to evaluate general stress distributions during the lift.
- Eigenvalue Bifurcation Buckling Analysis to identify weak points and possible instability scenarios.
- A mixed-element FEA model (solid & shell elements) to ensure both local and global deformations were accurately captured.
These analyses were instrumental in refining the lifting plan and ensuring that the most critical risks were addressed before execution.
Executing the Lift: Challenges and Real-Time Adjustments
With the lifting strategy in place, we needed to ensure that the actual lift adhered to strict safety and operational constraints:
- Wind Speed Limitations: A maximum wind speed threshold was set to prevent instability.
- Slow, Controlled Lift: The rigging team was instructed to lift slowly to minimize dynamic loads, reducing the risk of sudden stress increases.
- Weekend Execution: The lift was scheduled over a weekend when fewer personnel were in the area, minimizing exposure to hazards.
- NDT and Wall Thickness Verification: Non-destructive testing (NDT) and wall thickness measurements were taken to validate the accuracy of the FEA model, ensuring that the predicted behavior matched reality.
Key Takeaways and Lessons Learned
- FEA is Essential for Planning Complex Lifts
Using FEA to model different scenarios before execution significantly reduces risks. It allows engineers to identify weak points, refine lifting strategies, and make data-driven decisions.
- Sensitivity Analysis Improves Decision-Making
By performing a sensitivity analysis, we gained a clearer understanding of which factors had the greatest impact on the structural stability of the vessel. This enabled us to prioritize critical reinforcements and refine our safety measures.
- Accurate Modeling Reflects Reality
Ensuring that the FEA model closely represents actual conditions is crucial. Field validation, such as wall thickness measurements and NDT, helps confirm assumptions and avoids surprises during execution.
- Communication and Coordination are Critical
A successful lift in an operational plant requires seamless coordination between:
- Engineering teams (for stress analysis and risk assessment)
- Rigging crews (for execution and safety compliance)
- Plant personnel (to ensure operations continue smoothly)
Conclusion
Lifting a damaged vessel without disrupting plant operations is a complex task that requires careful engineering, risk assessment, and precise execution. By integrating FEA, safety reinforcements, and controlled lifting procedures, we successfully removed the damaged vessel while keeping the plant running smoothly.