Sorry for the delay, see you actually got an answer. The "International Residential Code" section G2413.5.2 says K and L type coppers are allowed, same restriction for Hydroden Sulfide. G2413.10.2 says joints are made with an approved gas type fitting or brazed, that's where your 'overheated' type joint would come from.
Let's face it guys, were talking about 3 lbs max here, the only real worry is probably piercing the pipe with something.
