رسائل دكتوراة
English
2015
Analytical and Numerical Analysis of Cylindrical and Spherical Pressure Vessels with Small-Diameter Nozzles
Husain J. Al-Gahtani, فيصل محمد مختار
كلية الهندسة-جامعة الملك فهد للبترول والمعادن · السعودية
In most cases, shell theory is used in analyzing pressure vessel-nozzle junctures as regions that constitute potential sources of weakness as a result of the high stress concentrations developed. Exact analytical methods are available for spherical vessel-nozzle intersections. However, they are unfit for practical design purposes unless when approximated. The problem is compounded in the case of cylindrical vessel-nozzle junctures because, coupled with the high level of complexity and non-readiness for handy analysis of practical design problems, the available analytical shell solutions are not exact. Furthermore, for both the spherical and cylindrical vessels, these solutions seize to hold when the nozzle configuration violates the thin shell assumption. This raises a concern when a need arises to analyze spherical and cylindrical vessels intersected by small-diameter nozzles. Again, most of the analyses available in the literature concentrate on evaluating the vessel stresses, paying little or no attention to the nozzle. Many researchers have pointed out the shortcoming of such approach, yet no studies have been dedicated to report, simultaneously, a comprehensive behavior of both the vessel’s and nozzle’s stresses in their analyses.This research work develops and studies FEM solution models (valid for any nozzle diameter) of discontinuity stresses in spherical and cylindrical vessels. Two different theories, the shell and the elasticity theories, are used to solve the vessel problem intersected by moderate-to-large-diameter nozzles and small-diameter nozzles, respectively. Adequacy of the approximate analytical solutions for the spherical shells relative to the exact and FEM solutions is also studied in the analysis. Illustrations are made on how the developed models perform better than many existing ones in terms of consideration of the possibility of critical stresses existing in the nozzles rather than only in the main vessel. Design charts are developed for the vessels with moderate-to-large-diameter nozzles and augmented by those with small-diameter nozzles to yield the overall design charts valid for any possible nozzle dimension. Contrary to the common practice in the literature, the developed charts are presented in such a way to depict the location of maximum stresses on the juncture. In addition, they provide an alternative presentation of the SCF values that are believed to be more accurate and all-encompassing than the conventional ρ-SCF plots. Finally, handier analytical and empirical closed-form SCF models for regions around the vessel-nozzle intersections are developed. The results generated in this study form a large database that has been missing in the previous collection of literature. Hence, it becomes handy for possible usage by any other interested researcher for future studies.