Numerical analysis of impacts of pressurized pipe onto surrounding structures induced by pipe whipping

In civil and military nuclear industry, the safety analysis requires to identify the damage induced by a pipe whipping. Due to the complexity of the phenomena and the pipe geometry and characteristics, the analyses are based on simplifying assumptions. For example, the pipe rupture which is assumed to occur at several predetermined positions along the pipe is usually considered as quasi-instantaneous and complete (double-ended guillotine break). The loading induced by the fluid in the pipe is also represented by an axial force at the pipe extremity. The analysis aims at determining the most vulnerable structures and equipment in the vicinity of the pipe. For this purpose, complete dynamic analyses can be performed but the complexity of the phenomena may require a too large modeling effort: important calculation time due to the geometric, material and contact non linearities, number of cases to be studied, large amount of numerical results to be analyzed... Non linear modeling may also be insufficient to verify the state of the impacted structures since empirical formulae are often preferred for perforation analysis because of their validity verified on experimental campaigns. The present paper focuses on a particular point and shows an analysis of numerical modeling of a pipe elbow impacting a metallic plate using the EUROPLEXUS fast transient dynamic software. Local and global results have been extensively analyzed in order to construct simplified models constituted by a limited number of masses and stiffnesses. The identification of the simplified model parameters -specially the masses- is based on the analysis of the local and average velocities, deformation and kinetic energies and impact forces between the impacting tube and the impacted plate. A parametrical study has been performed in order to identify the effect of the initial velocity of the projectile and the dimensions of the impacted plate (thickness and length). It has been confirmed the ratio between the pipe and plate thicknesses may be a good indicator to determine which structure may concentrate the main part of plasticity and so damage. Another dimensionless number proposed in the literature gives also reliable information to determine the pipe limit velocity corresponding to the onset of material plasticity in one of the structures.