Galvanized pipe is a variety of steel piping that is coated in a layer of zinc. If you have a home that is more than 30 years old, your water pipes may be made up of galvanized piping. A working knowledge of galvanized pipe is needed for the do-it-yourselfer who lives in an older home or does repair work for people.
While the layer of zinc over the steel was originally helpful to increase the lifespan of your plumbing and avoid corrosion, it's since been discovered that it has a tendency to react with the minerals in the water it carries, producing scale and lowering pressure levels.
As such, galvanized pipe is only used in modern homes for hand rails and replacement of existing pipe. Galvanized nipples are still used to penetrate fire rated walls for sinks and urinals.
Galvanized pipe should only be used in systems that carry water. Gas lines are not suitable for this kind of piping as the zinc flakes off and clogs the flow of gas.
Check with the local department of public works to find out the pH level of the water in your locale. If you have a well on your property, have a sample of water tested. Low pH, below 6.5, is hard on copper. This is a good reason for using galvanized pipe.
Installing Galvanized Pipe
Step 1 - Cut
Galvanized is installed in much the same way as black iron pipe. The pipe comes in standard lengths of 21 feet. Hold the pipe for cutting in a pipe vise or a solid bench vise.
Put on a pair of safety gloves and googles, then cut the pipe to length using a pipe cutter with rotary cutting wheels. Use quality cutting oil in this process. Always wear gloves when working with pipe.
- Tip: Place cardboard or plywood under your cutting and threading area. This will save you a lot of cleaning later.
Step 2 - Deburr
Once it is cut to length, deburr the interior of the pipe to remove the sharp ridge caused by the cutting process. With the pipe still held in the vise, thread the end of the pipe with a die cutter, ensuring you have the correct size for the diameter of the pipe. Once again, use a good cutting oil to prevent damage to the die and ease the process. Turn the die on in half-turn strokes, backing off every turn to dislodge shavings from the die.
Cut the thread to the width of the die. Because the thread is tapered, going farther will remove too much of the pipe, causing possible leakage. Tap out shavings from the pipe and clean the threads. Be careful that you do not cut yourself on the threads - they are very sharp.
You can buy a ratchet type threader for around $30 at discount tool places that will handle pipe up to 1 inch. As most places charge $5 or more to cut one thread, this might be more economical in the end.
Step 3 - Fittings
Galvanized pipe is joined using fittings made of malleable cast iron. They are threaded onto the pipe to make the connection. Use Teflon tape and a good quality pipe joint compound when attaching. Once the pipe is installed, turn on the water supply and check for leaks. If leaks are present, re-tighten any joints.
Be aware that while galvanized pipe can be attached to existing systems, certain plumbing pieces like black iron can accelerate corrosion when in contact with the zinc. If this is something you have to contend with, use a dielectric fitting in between the two metals.
Make sure you are wrapping the Teflon tape in the right direction. Facing the end of the pipe, you go in a clockwise direction with at least four wraps, but no more than six or seven. Then apply some pipe dope in the same direction. Tighten at least two turns past hand tight. If the pipe is still loose, you may have to re-cut the pipe.
Step 4 - Hanging the Pipe
Undue stress on connections from the weight can lead to leakage. Support the pipe at least every 6 feet if it runs along a floor joist. You can use pipe hanging straps or use regular pipe hangers if the pipe is close to the support. Vertical runs should be supported at every floor level.
A good rule of thumb for placing supports is every 6-8 feet on horizontal piping. If you do have a leak, you may have to take some things apart to fix the leak.
- Warning: Do not try to tighten a joint in the middle of a run, as you are also loosening the joint on the other end.
Step 5 - Joining with Copper
In case of leakage, galvanized pipe can be joined with copper. This is done with a dielectric union. The reaction between copper and galvanized leads to corrosion very quickly, and the dielectric union eliminates this. The two metals are effectively separated by a rubber washer.
Remove the old leaking joint. Cut the pipe with a hacksaw near the joint. Using pipe wrenches, work back to the next nearest joint, working in both directions. Check the galvanized to see if it is badly clogged with mineral buildup. If so, keep working backward until you find pipe that is not clogged.
Next, thread the galvanized pipe into the dielectric union, using pipe joint compound. Uncouple the union, and solder the copper replacement pipe onto the union. Reattach, tightening well to avoid leakage.
The down side to this situation is if you find one clogged pipe and a leaking joint, the chances are good that the entire system needs replacing. However, using a dielectric union will often fix the issue for a long period of time.