Hello Johnyutah, I suppose I'll yank your chain just a bit (I really am funnin' ya though). I really don't know of too many schools that can afford to run on brand new metal, maybe some of the privates, but even then I don't know that I would believe that either. At our school the local shops and industries are very generous with their donations of metal, sometimes we get fairly new scrap, other times we get the take-outs from a plant modification or re-vamp. In either case, the students will weld on what we have to work with. I totally agree with your take on welding on the junk iron right along with some of the new stuff. You aren't going to have the choice very often when you get out there in the working world.
As to any of the students out there who are reading parts of this thread: be prepared to break out the torch, plasma, and carbon arc, cut pieces and parts to make your various welds with and get used to working with the cruddy stuff as well as the new. Take the time to make welds on new metal without doing any prep.(grinding, descaling, etc.) and then make some that you have meticulously cleaned and prepped. Take note of the differences. Do the same with metals that are being referred to as "junk iron", pay close attention to the differences that you see with the arc, puddle, slag, bead profiles, undercut, and any other inconsistencies that you notice. If you get the chance, make a weld and then take it out with the carbon arc. After you have removed it weld it back up without doing any grinding or clean-up, then do it again, only this time take the time to do some grinding to get rid of any extra slag or oxidation on the gouged faces. Weld this up and make note of the differences.
The various types, grades, and thicknesses of metals all have their own idiosyncrasies and will display slightly different traits when you weld them. Thick plate and beams of substantial weight will generally have a thick layer of mill scale and will impede proper fusion at the toes of welds, they generally require a slight bit of grinding and if they are over 1" in thickness might also require a preheat. Rectangular and square tubing will react differently when being welded due to their metallurgical make-up, they are generally cold-worked to attain their shape and as such they react differently to an arc compared to beams, channels, and other structurals. If you really wish to see these differences find a piece of 3/8" wall A500 rectangular tubing, 3/8" A-36 plate, and an A36 structural such as a channel, beam, or angle with a 3/8" thickness, try to use pieces that are in a similar condition with regard to rust and surface condition. Now set each one of these up and run a few vertical stringers on them. I believe you will come to find out that they react slightly differently from one another. Hey Johny, I'll be waiting to see the others come after you! Me, I'm not worried, I can generally hold my own. Best regards, Allan