[en] The problem of modelling a pipe and its restraining units during the pipe whip accident is discussed; the following main points (which are available in the FRUSTA program) are considered: (a) A complete dynamic model of the pipe is considered only for the part between the postulated rupture and the first elbow, the remaining part is considered only to simulate its stiffness. (b) Both a circumferential (pipe only on one side of the rupture) and a longitudinal (pipe on both the sides of the rupture) breakage can be considered. (c) The pipe mass is lumped in each node (max.20) (d) The pipe stiffness is simulated by means of a particular element, which can account for the elastic, plastic, ovalization, instability and unloading behaviour of the pipe. (e) The restraint is simulated by a proper element with a bilinear characteristic after a 'no load' phase. (f) A damper can be simulated by means of an element, whose reaction force is proportional to the velocity of the application point. (g) A dummy (fully indefinitely elastic) element can be introduced in order to simulate end conditions, rigid motions, etc. (h) The crushing behaviour of the pipe when hitting a restraining surface can be approximately simulated by introducing a proper restraint, which accounts for the pipe elasticity and reduction of moment capability. (i) A step by step integration procedure is followed: a Gauss-Euler algorithm is used. (j) Maxima of the kinematics, stress and strain characteristics are given. (Auth.)