The objective of the paper is to assess the local damage of long tubular members and pipes caused by the impact of a rigid mass. The formulation is general and covers a wide range of events: low velocity-large mass impacts, as encountered in collisions; medium velocity impacts caused by dropped objects; and projectile and missile impacts. By making assumptions on the cross-sectional deformed shape of the cylinder, the two-dimensional shell problem was reduced to a one-dimensional problem of a plastic string resting on a rigid-plastic foundation. It was shown that the deformation propagates away from the point of disturbance with a constant plastic wave speed and diminishing amplitude. Calculated were the instantaneous velocity and deflection profiles, the final deformed shape of the shell, and the maximum deflection attainable under impact. A parametric study was performed by changing the mass and velocity of the impacting object over several orders of magnitude. An approximation to the dynamic solution was also obtained by using the static solution of the shell under "knife" loading and comparing the plastic work of the deformation process to the kinetic energy of the impacting mass. This approximation was compared to the dynamic solution and good agreement was shown for a range of masses and impact velocities encountered in offshore applications. Finally, use of the proposed methodology was illustrated by predicting the local damage caused by a drill collar accidentally falling on one of the brace tubular members of an offshore platform.
Structural impact is of relatively frequent occurrence in offshore construction, drilling and production activities. Collisions of offshore platforms with supply vessels, for example, can be classified as large mass and low velocity impacts. An intermediate range of impact scenarios is covered by dropped objects hitting parts of the protective or load-carrying structure.