Short answer: if it's non-magnetic use a grinding wheel, angle grinder, rotary tool or similar device. Stainless steel will spark, aluminum will not.
Basically, a modern pot or pan is:
1) Aluminum. Non-magnetic. Scratches easily with a knife. Does not spark. Usual classifications are sheet aluminum, utensil aluminum, or cast aluminum. Some yards buy all aluminum for the same price.
2) Steel. Strongly magnetic. Much harder to scratch. Sparks when put to a grinder. Thinner pots go as light iron, thick cast iron as steel.
3) Stainless steel. Non-magnetic.* Hard to scratch like steel. Sparks when put to a grinder.
*Some types of stainless steel are semi-magnetic. However, many yards will only buy it as normal steel if it's magnetic, especially if you only have a few pounds.
davycoppitt wrote:what scrap yards would classify pans with teflon coating on them as?
Depends on the yard. Some yards would consider that dirty or painted aluminum, which goes for a slightly lower price. Others don't care.