A support grid for a chemical reactor fixed bed catalyst. The support grid is formed of (i) a center support cylinder, made in areas of a vertical cylinder, that is assembled within the vessel on the bottom closure head; (ii) a peripheral support skirt located at the outer circumference of the grid, assembled in sections inside the reactor pressure vessel, that sets without welding to bottom closure head of the reactor vessel; (iii) a set of radial support arms that extend from the center support structure to the support skirt to tie these sections into a rigid frame to support the catalyst bed support grid wedges; and (iv) a grid or disc formed of a plurality of catalyst bed support grid wedges or sections that are radial in orientation and are assembled inside the reactor pressure vessel to form a disc that is about 80% of the reactor vessel in outside diameter.