I don't think that you can do this. I know that sometimes copper is used for the final connection to the equipment, but when it is used, it is connected with flare fittings, not sweated joints. I believe that the odor used in the natural gas to make it easier to detect small leaks is corrosive to copper. A long time ago when I was in high school, I worked part time at the local hardware store. On a very cold winter day a customer came in and bought a 50' length of garden hose and some adapter fitting from hose thread to pipe thread. As he was going out the door, I just had to ask why garden hose in the winter? His reply, "My hose is cold and I'm going to hook up a gas space heater on the other side of the basement". Don(resqcapt19)
#8029 - 03/05/0206:48 PMRe: Natural Gas thru Copper Pipe
In the UPC the only approved material for gas is: std. weight wrought iron or steel (galvanized or black), yellow brass (containing not more than 75% copper). Approved PE pipe may be used in exterior buried piping systems. (UPC 1210.1) - I believe similar provisions exist in the IPC
#8031 - 03/09/0206:06 PMRe: Natural Gas thru Copper Pipe
In the 2000 edition of UPC, 1210.1 changed to allow Types K, L, and ACR copper. The gas must contain less than 0.3 grains of hydrogen sulfide per ft³ (1210.1.1). The joints must be brazed, flared or screwed (1211.2). So the joints can not be sweated with typical plumbing solder and the code requires the brazer to be certified. Also, there are requirements for labeling, supporting and protecting the copper.
#8032 - 03/09/0209:08 PMRe: Natural Gas thru Copper Pipe
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.
#8034 - 03/11/0202:56 PMRe: Natural Gas thru Copper Pipe