Other published literature discusses collapse pressure (CP) for round tubing,1  and proposes one collapse pressure (CP) expression for any OD-to-wall (D/t) ratio. This expression is easily solved and can be used with all units: US, metric, etc. CP for oval tubing was a subject of another paper.2 

This paper presents available corrections of CP formulas including loading when external pressure is combined with internal pressure and axial force.

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