Creep sagging analysis of pressure pipes II: Damage accumulation under variable temperature and pressure conditions

The problem of non-linear stress analysis of creeping reinforced pipes under constant pressure has been treated in a recent work [1]. In the present work, a damage accumulation analysis of the above problem is attempted taking into account the non-linear distribution of the stresses as well as non-linear damage accumulation under variable pressure and/or temperature conditions. For the stress analysis a non-linear differential equation is used to derive the stress concentration in critical locations of power pipes reinforced by rigid rings which are distributed along their axis. Due to step-wised temperature and internal pressure of the pipe, the damage accumulation is predicted by using a damage function specified with respect to damage parameter derived by the stress versus Larson–Miller coefficient curve. Advantages of the proposed methodology are:(a)the 2-D creep stress analysis incorporates mechanical behaviours of material derived by uniaxial tests,(b)the predicted damage accumulation due to the variable pressure takes into account the previous damage history as well as the loading order effect.