Annealing ridged tubes after forming and service
Can I be honest, copper tube is old world technology and I would not use it, at all, if it can be avoided. I know, factory planes have used it for years but don't think its popular anymore. Today you can use small -2 flex lines or ridged stainless steel lines.
The problem with ridged tubing, copper or aluminum, is it work hardens. As the engine vibrates, the tube becomes brittle and fails. When you flare it or bend it, it also gets harder. Every year or so you are suppose to anneal copper lines in the engine compartment. Copper lines typically use compression fittings or "solder on" fittings. Flaring copper is not typical like aluminum.
To anneal copper lines you need to make it soft first with high heat. Copper becomes soft between 1,200 to 1,650 F. You can heat it to 600-800F for a few an hour or so until evenly heated. Once the part is evenly heated or heat soaked, than allow it to air cool or water quench. Copper is not critical in the cooling phase like steel. Using a torch in the shop, probably the easiest method, get it to about 1000 F, when the copper glows a dull red in a dimly lighted work area. When you water quench, you need enough water to do the whole piece at one time.
Some say 2 hours on broil in your home oven will do it. I don't know about that. If it's big enough for the part and gets to +600F, than it will work. The idea is to heat the whole tube, not just one area, as well as cooling it all together.
BTW for you should anneal your copper spark plug washers, again torch to cherry red and quench. Spark plug washers get hard and will not seat.
Aluminum tubing is different. Some do it by using an acetylene torch, but it is easy to melt aluminum. It takes some skill. The difference between the annealing temp (650F-825F) and melting is small. One method uses a dirty acetylene flame to soot the tube up first, than a hot flame is used to burn the soot off, taking your time to remove the soot slowly and evenly. If you get too close you will melt aluminum fast. Let it air cool to 400-500F and than you can water cool. Tempilstik is a name brand of a product you paint on a surface to monitor temp, like when heating with a torch. Aluminum will not show heat (at all) like copper.
It cost more but flex lines are better. I avoid hard metal lines on things that shake.
To be fair of aluminum or copper line's, done with care work fine. I have a O-360 Lyc and I'm not going with primers. I want to avoid a bunch of 1/8" copper lines. If I end up adding them on later, I'll look for small stainless steel lines first. If I use copper, I'll solder the fittings on. The primer supply line from the gascolator and to the primer lines on the engine will be a flexible line.