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Weight-Saving Plastic Design of Pressure Vessels

“Weight-Saving Plastic Design of Pressure Vessels” by J.S. Porowski, William J. O’Donnell and R.H. Reid, ASME Transactions, Journal of Pressure Vessel Technology, Vol. 119, Feb. 1997.

Within the last two decades, the use of elastic finite element analyses to demonstrate design compliance with the rules of the ASME Code has become a generally accepted engineering practice. Linearized stresses from these analyses are commonly used to evaluate Primary stresses. For redundant structures or complex structural details, the use of such analyses, instead of simple equilibrium models, often results in significant over-conservatism. Direct use of finite element analyses is often preferred because solutions are not unique, and effective equilibrium models are not easily constructed for complex three-dimensional structures. However, finite element analyses include Secondary stresses even for pressure, mechanical and shock loading. The use of finite element inelastic analysis to partition mechanically induced stresses into the Primary and Secondary categories was introduced in Ref. (1). The authors have since used this approach to design more efficient structures. The practical application of this method to reduce the weight of complex redundant structures designed to meet Primary stress limits is described herein. Plastic design utilizes the ability of actual materials to find the most efficient load distribution. A heat exchanger subjected to pressure, accelerations, and nozzle external loads is evaluated as a practical example. The results of elastic analyses are compared with those obtained by inelastic analyses. It is shown that inelastic analyses can be used to reduce the weight of structures using only PC’s for the engineering computations.