Let's be clear. These are NOT pie cuts! Pie cuts are made using straight tubing. A series of pie cuts welded together are geometric in shape, not exactly smooth flowing.
These tight bends are NOT mandrel bends, either! What are they? A special process that uses special tooling to get a perfectly round 3 inch OD.
What you're buying is THREE of these bends, each 30 degrees, to total a 90 degree bend. These can be clocked for a quick jog over so larger mandrel bends are not wasted, and less cutting!
They are made from 321 stainless, which can be welded easily to any grade of stainless (304/409 for example) or mild steel.