NONLINEAR CYCLING ANALYIS OF PIPE BENDS WITH INITIAL OVALITY

The paper presents the nonlinear shakedown analysis using finite element method for piping bends taking account of the maximum ovality tolerance. In the ASME Code, Section III NB-4223.2, it is required that the ovality tolerance of piping after bending shall be considered when the pipe structure is subjected to any combination of cyclic thermal and pressure loads. Parametric studies are carried out to assess the progressive strain accumulation induced by various finite element analyses employing different types of boundary conditions and cycling loading. The resulting strain state of the stabilized cycle for the pipe bend including the maximum ovality tolerance is compared with the strain state for the perfectly round pipe bend. This paper also discusses the choice of the global shakedown related to the global in-plane strain and the local shakedown defined as the radial strain on the side of the elbows. Furthermore, the strain range is taken as the representative parameter for fatigue calculations.