Creep Ratcheting Bounds for Piping Systems with Seismic Loading
J. S. Porowski and W. J. O’Donnell, presented at ASME Pressure Vessels and Piping Conference, San Francisco, California, June 1979.
Keywords: creep ratcheting; piping systems; earthquake motions; seismic loading; thru-the-wall bending; axial bending; elastic core stresses; residual stresses
Cyclic histories of piping systems and components often include multiple earthquake motions. In piping components such as elbows, the seismic loading may include significant thru-the-wall bending, as well as the membrane stresses in the wall resulting from overall axial bending in the piping system. Incremental plastic growth of the structure may occur when severe seismic stresses are superposed on existing stresses in the system.
Moreover, for elevated temperatures, the residual stresses introduced by the seismic event may cause enhancement of the creep strains during subsequent operation of the equipment. The concept of elastic core stresses, partial relaxation of residual stresses, and maximum energy dissipation strains are used to derive upper bound solutions for the total accumulated plastic and creep strains. These bounds are given in a form suitable for evaluating very complex loading conditions.
Company President, Bill, Sr. began his career in the Naval Nuclear Program at Westinghouse/ Bettis. He is active on the ASME Subcommittee on Design, and serves as a Contributing Member of the ASME (BPV III) Working Group on Fatigue Strength. He has also co-authored numerous papers on various topics including elevated temperature, fatigue and creep.