An investigation is made into the dynamic stability of a pipe with a postulated circumferential through-crack. The dynamic deformation of the pipe is found to control the ensuing jet force in such a manner that positive or negative damping results, depending on the local mode shape geometry. The leak is governed by quasi-steady fluid dynamics, which permits a simple closed-form evaluation of the damping energy for a crack geometry idealized from existing LEFM solutions. Energy losses develop via structural damping and plastic dissipation at the crack tip; the latter is estimated using the Irwin’s plastic zone correction approach. Application to a PWR plant primary circuit piping suggests that structural damping in practice rules out the instability.

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