Cut out the old pipe and solder in a new coupling
Photo 1: Cut out the damaged pipe
Shut off the main water supply valve, drain the damaged water line and use a pipe cutter to cut out a section of pipe that extends about 1 in. to each side of the leak. Start by gripping the pipe firmly in the cutter's jaws and tightening the cutter's screw. Rotate the cutter in the direction shown—as you tighten the screw handle—until the pipe snaps.
When a copper water pipe corrodes and leaks, or bursts from freezing, you have to fix it fast. If the leak is pinhole-sized and less than 1/2 in. of pipe must be removed, you can make the repair by cutting the pipe and soldering (“sweating”) on an ordinary pipe coupling.
But to repair longer sections, use a “sweat” coupling, which you can find at home centers and well-stocked hardware stores. You can buy a sweat coupling sized to repair 1/2-in. or 3/4-in. copper pipe. Mark the leak, shut off the main water valve and drain (or thaw and drain) the affected pipe. Cut out the damaged section (Photo 1), then measure the gap and, from the sweat coupling, cut a repair piece that’s 1 in. longer than the damaged section.
The key to a good solder joint is to keep the inside of the pipes dry, so keep a cotton rag stuffed in each pipe end to absorb dribbles of water until just before you solder. Open a faucet above that level to keep pressure from building up and dribbling more water into your repair. Then complete the steps shown in Photos 2 - 4 for a leak-proof repair. Once finished, turn the main supply valve on and check for leaks.
Sweat coupling and tubing cutter
Cut the repair sleeve from the 12-in. repair coupling stock. Smooth the rough-cut inside edges of the sleeve by inserting the blade of the pipe cutter into the cut ends and turning the cutter until the sleeve will slide over the pipe ends without snagging. Clean the sleeve's inside edges for soldering with a 3/4-in. dia. wire fitting brush.