Depropanizer Towers with Additional Scaffolding Loads

During a certain period, scaffolding was required around three 30m tall depropanizer columns. Since the scaffolding was laterally supported from the columns, all wind loads generated by the scaffolding were transferred to the columns. As a consequence, various parts of the columns needed to be checked for additional loading.

All vessel components affected by the additional wind loading were checked for strength and stability according to the relevant engineering code.

During the project, it was required to work together with the scaffold designer to minimize scaffolding loadings and receive the relevant loading conditions for the analysis of the columns. Collaborating with the scaffolding supplier proved to be an efficient way to minimize lead time and reduce calculation costs to a minimum.


Multiple analyses were required to ensure code compliance in each column. Using linear elastic buckling analysis, the stability of the columns was assessed. For this purpose, FE models were built on the most critical part of the towers; the skirt section of the towers including the base ring and excess openings.

From the analysis, it was concluded that before linear buckling, yielding of the base skirt would occur; which indicated that the calculated (linear) buckling safety factor was not valid.

To determine the correct safety factor against instability, a plastic buckling analysis was required, which proved that instability would occur directly after reaching the yield point. As a consequence, an appropriate safety factor against yielding was selected to avoid instability.

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Next, a stress assessment was made of the skirt, base ring, anchor bolts, and supporting concrete. The analyses were performed following the Stoomwezen code and showed that all components satisfied the code limits.

In the final step of the project, all fixation points to the scaffolding were assessed for their strength and were compared to the local loadings calculated by the scaffolding designer.

“Collaborating with the scaffolding supplier turned out to be an efficient way to minimize lead time and reduce calculation costs to a minimum”, DRG Engineering Team


The analyses showed that in some cases local reinforcement was needed to avoid high local stress or a repositioning of the scaffolding fixation points.

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