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In practice, large diameter, thin wall shells of revolution are never fabricated with constant diameters and thicknesses over the entire length of the assembly. These initial geometric imperfections have significant effect on the load carrying capacity of cylindrical shells. The cylindrical shell in the study is flue gas desulphurization (FGD) "vessel" which is a large hybrid tank-vessel-stack assembly in a major Canadian refinery. The function of the FGD vessel is to contain and support a proprietary process that utilizes an ammonium sulphate scrubbing system to produce environmentally friendly air emissions. FGD vessel stack has internal diameter of 6.1m, height of 45.34m and wall thickness of 9.525mm. Initial imperfections in FGD vessel is in the form of wall thickness variations. FGD wall thickness at 144 points along the circumference and elevation are measured. Monte Carlo method is employed to generate the measured data again. Test of significance is carried out to see the accuracy of the data generated. This Monte Carlo algorithm can be used to create data for any type of shell without spending time in actual measurements. Next, load carrying capacity of shell is determined considering imperfections to be axisymmetric and then asymmetric. Fourier decomposition is used to interpret imperfections as structural features can be easily related to the different components of imperfections. Further, double Fourier series is used to represent asymmetric initial geometric imperfections. The ultimate objective of these representations is to achieve a quantitative assessment of the critical buckling load considering the small axisymmetric and asymmetric deviations from the nominal cylindrical shell wall thickness. Analysis of cylindrical shells when used as pressure vessels and are under external pressure is also carried out. Comparison of reliability techniques that employ Fourier series representations of random axisymmetric and asymmetric imperfections in axially compressed cylindrical shells and shells under external pressure with evaluations prescribed by ASME Boiler and Pressure Vessel Code, Section VIII, Division 1 and 2 is also carried out.
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