You can repair or replace almost any copper tubing in your mobile home. For some joints, you must know how to flare the ends of the tubing properly. The photos and instructions here are for water lines, but they apply for copper gas lines too. Gather a tubing cutter, a flare block and punch, a roll of copper tubing, carpenter’s rule, and brass fittings for the connections you need to make. NOTE: Use only new tubing of the same diameter and wall thickness as the old. Measure the damaged area and assess what materials you need. To replace a length between two joints, you’ll want two brass flare
nuts and a threaded union for each new joint you have to make. Shut off the main water valve and open the faucet nearest the damage to bleed water from the line. Block up the line to prevent
misalignment when you cut out the damaged section.
Use two wrenches for taking loose the old joints—one to hold the union steady, the other to loosen the nut on the tubing to be removed. To take out small lengths within a section, put a tubing cutter to work.
Measure and cut the replacement tubing. Deburr all cut ends with the pointed tool on the tubing cutter. Slip a flare nut onto the tubing end before you make the flare. Insert the tubing into the right-size slot in the flaring block, and tighten the block clamps. Center the punch over the tubing end in the flaring block. Twist the punch downward until it presses tightly into the lips of the tubing and the block. The pressure forms the tubing into the flared shape. Don’t overtighten the punch, or you’ll fracture the soft copper, leaving a crack in the flare. A little practice will acquaint you with the feel of a proper flare.
When all the ends have been flared, screw the flare nuts onto the threaded union. Again, use two wrenches—one for the nut and one to steady the union. Tighten the nuts firmly. If you spot a leak at the joint after the water (or gas) is turned back on, tighten the nuts some more. Do not ever use pipe dope on these joints. Reflare the tubing if you have to. Flared fittings seal tighter and cleaner than joints using sealants.