A casing includes an inner shell and an outer shell that surrounds the inner shell and comprises a plurality of inflection points. An annular flange is between the inner shell and the outer shell, and a plurality of joints attach the inner shell to the annular flange. A connector is between the annular flange and the outer shell at each of the plurality of inflection points. A method for assembling a casing includes joining a plurality of curved sections to one another to generally define an arcuate inner shell and surrounding the arcuate inner shell with an outer shell. The method further includes attaching the arcuate inner shell to an annular flange at first attachment points and connecting the annular flange to the outer shell at second attachment points spaced approximately equidistantly from the first attachment points.