Simplified Primary Stress Evaluation Procedure for Thinned Class 1 Piping Elbow

Inelastic finite element analysis offers an alternate procedure to evaluate damaged piping components for their fitness-for-service purposes. Redistribution of stress resultants beyond yield taken into account in a typical inelastic analysis becomes significant as a damaged piping component may not satisfy code stress criteria based on elastic analysis. A complete inelastic analysis to estimate the limit load of the component may be a numerically intensive and cumbersome process. This paper involves a two step analytical process — unloading a component to satisfy code stress categories after a prior plastic distribution of stress resultants is setup in the component. Linearization of stresses in the thinned section has shown reduction in the general membrane and membrane plus bending stress intensities when analyzed using this simplified method. To illustrate the method, an analysis is performed on both thick and thin pipe with local thinning.