Development of Structural Evaluation Criteria for Elbows
For the Westinghouse Electric Corporation, Advanced Reactors Division, a method of bounding the accumulated plastic and creep strains in austenitic stainless steel elbows subjected to mechanical and thermal loads at elevated temperatures was derived. The concept of an elastic core in the wall of the elbow was employed. The analysis included the effect of primary bending and additional secondary elliptical deformation modes characteristic of the complex behavior of elbows.
Bounds were obtained based on the results of elastic analyses alone. The elastic membrane and bending stresses were normalized and used in modified isostrain diagrams to obtain representative core stress. Isochronous curves were then used to determine the upper bound membrane strains. Bounds for bending strains were also obtained. These bounds were used along with appropriate strain limits and creep fatigue analysis to evaluate the acceptability of various designs.