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Engineering Specialties Used:
Finite Element Analysis
Inelastic Buckling Analysis
Risk Analysis

A facility planned significant welding work on several sections of a 100 foot tall vertical pressure vessel shell. This welding work would require a hydro-test of the tower after the field work was completed. Filling the vessel with water for the hydro-test produces significant live loads which are not normally experienced by the vessel support structure and which were not part of the original design. Buckling of the skirt was a risk. Buckling is a non-ductile phenomenon; once it started, the vessel skirt would collapse. Several large openings in the skirt compounded this concern.

Finite Element Model of a
Pressure Vessel Skirt


Argos Engineers built a three-dimensional finite element model (FEM) for the skirt including material post yield properties. We applied appropriate boundary conditions and then added an incremental vertical static load to the model until the onset of plastic collapse. Margins were calculated and compared to traditional Code margins. Closed-form calculations were completed for a simplified geometry and compared to the FEM methodology employed to validate the FEM approach. Careful evaluation revealed that sufficient margins remained to hydro-test the tower in place.

Representative Petro-Chemical
Plant Towers

Based upon these findings, the client continued with the planned plant turnaround with confidence. Risks were reduced since the pressure vessel did not need to be moved. Also, because the pressure vessel could be hydro-tested in place, the turnaround schedule was minimized. Argos Engineers is ready to partner with your turnaround team to analyze critical equipment. We can perform the detailed analysis needed to evaluate risk and to ensure there is a sufficient margin for safety.

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