Methods for fabricating pressure vessels

A method for fabricating a pressure vessel comprising:

• forming a frame comprising a plurality of curved metal sidewalls in a polygonal outline;
• forming metal sides for the frame including a top side and a bottom side;
• forming a plurality of metal internal support posts in a geometrical array comprising a center internal support post and a plurality of corner internal support posts formed at corners of the geometrical array, the corner internal support posts having a radial symmetry with respect to the center internal support post and a spacing(S) with respect to one another;
• attaching the metal sides to the curved metal sidewalls by welding or brazing the top side and the bottom side to the curved metal sidewalls to form a sealed pressure chamber and by forming a plurality of welded or brazed joints in the sealed pressure chamber between the internal support posts and the top side and between the internal support posts and the bottom side;
• and
• forming contoured surfaces with shaped features on at least one of the metal sides, the shaped features formed with plastic strain by applying a forming pressure to the sealed pressure chamber that is higher than an intended working pressure of the pressure vessel;
• wherein following the forming the contoured surfaces step, the shaped features comprise dome features and saddle features formed in the contoured surfaces with transitions therebetween, each of the dome features having a first cross section comprising a plurality of spaced domes with a first radius, each of the saddle features having a second cross section comprising a saddle point with a second radius;
• and
• wherein the forming the plurality of internal support posts step comprises selecting the spacing(S) of the corner internal support posts to determine the first radius and the second radius.