If you want to solder copper pipes you’ll need to be prepared. Although it isn’t especially difficult, soldering pipes is typically more elaborate than soldering electronics, and you’ll need different equipment. People usually solder pipes to seal joints between sections of pipe (e.g. elbow joints). You’ll want to use a soldering torch rather than a soldering iron when working with copper pipes, but you can also find specialized soldering irons that will work for soldering pipes.
You need to use the appropriate solder. In this case you need to look for specialized solder wire designed specifically for pipe soldering; this type of solder is much thicker than standard solder and has acid flux instead of rosin as well as a higher concentration of silver than electronics solder. Never use leaded solder when soldering pipes. Also, ensure you have an abrasive item — such as sandpaper or steel wool — on hand so that you can clean and scour your pipes before soldering, thus improving the likelihood that you’ll end up with quality solder joints.
First you’ll cut off the water to your plumbing before beginning, which will enable you to work without fear of flooding the room. Then, if you’re installing new pipes, use a tube cutter to cut pipes up to an inch in diameter — you’ll need a hacksaw for larger pipes — and cut slowly so you don’t dent the pipe. After turning off the water and cutting your pipes you need to clean up the pipes with your abrasive material of choice. Abrade the part of the pipe where you’ll be soldering so that it is clean and smooth.
Next you’ll solder the pipe. Fire up your propane torch or soldering iron and apply heat to the pipe you’re working on. You can maintain even heat by moving the flame around the work area. After the pipe is evenly and thoroughly hot you’ll apply the tip of your solder wire to the area you’re sealing; it should melt immediately. Be sure to hold the solder on the opposite side of the pipe as your torch. The solder should flow easily around the joint. After you’ve finished soldering let the joint cool (it shouldn’t take long). If you have more than one joint to solder, move on to the next pipe when the previous one has cooled.
After you’re done wait a few minutes, turn the water back on, and check for leaks. You’ll need to repeat the process if your solder joints are leaking.