Own or have access to porta power spreading jaws? Me neither, You could fashion a piece of solid square stock with a grinder, taper to square/rectangle what ever it is. chuck the flange in a vise, tack one side of pipe to flg. or 2 sides if it fits tight, heating with torch may assist. and pound the die in. don`t wana make a die? try various specialty hammers to streach tube to flange:-D what ever ya try, let us know what ya did and how it turned out:clock: