Creep sagging analysis of pressure pipes

A new concept is developed to predict the mechanical behavior of pipes under the combination of internal pressure and elevated temperature. A non-linear differential equation is formulated to approximate the stress/displacement distribution in these pipes, which are reinforced by rigid rings uniformly distributed along their axis. The proposed model incorporates a non-linear time-dependent stress–strain material behavior rule derived by uniaxial tests. Taking into account equilibrium equations and boundary conditions, a general analytical expression for the case of biaxial creep loading is formulated. Numerical solution and results of a typical example are included.