Airbags are by far the worst way to lift tanks. They cause excessive stress to the rafter and floor to shell connections and also causes racking of the roof columns and racking.
Racking is the condition of differential rotation between the columns and shell caused by uneven lifting of the tank. Airbags are incapable of lifting a tank evenly or perpendicularly and are one of the leading causes of racking.
Tank wander is another problem caused by airbags. since airbags are unstable and flexible platforms, the tank moves as it is lifted and lowered so that the tank does not return back to its original footprint requiring refitting of piping and attachments like walkways or ladders etc.
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