[lotechman]

Edge welds are primarily used on materials less then 3mm thick. With sheet metal the rigidity is obtained by the formed 90 degree bends done before the flanges of the bends are clamped together to be welded. If you are doing finite element analysis your approach will be much different than other people dealing with fillet and groove welds on plate. The bends really add to the rigidity of the structure.
Automotive gas tanks commonly use a flanged joint with edge welding or some type of resistance welded seam.
Something else is the flanged part can be spot welded if a sealing weld is not required. Another trap that I have fallen into is that with aluminum alloys if you just fuse the edges together using the parent metal alloy alone the joint will be less than desired. Aluminum welds require the addition of filler metal alloy to make a strong joint. It is very tempting for an aluminum welder when presented with an edge joint to just do an autogenous weld.
In my career I did a lot of work with heavy plate ranging from half inch to one inch (25mm) sometimes as heavy as 3 inch ( 75mm) I never ran across any edge joints on plate.