Galvanized pipe is actually steel pipe that has been coated with a layer of zinc to help prohibit corrosion. Almost all galvanized pipe is connected with the use of threaded fittings.
Corrosion and chemical deposits accumulate inside galvanized and reduce the flow capacity. This worsens with age and can jeopardize the integrity of the sprinkler system. Rust and flaking is another problem with galvanized sprinkler pipe that can plug sprinkler heads. I have seen systems where rusts flakes will get stuck in a sprinkler valve and prevent the valve from closing. The valve then has to be disassembled to remove the flakes.
I still see galvanized piping in a lot of the sprinkler systems I work on. It is usually installed in yards and houses that were built 30-40 years ago. The image you see above is nothing what galvanized pipe looks like after it has been in the ground a number of years (see photos below). The pipe I usually see has rust bumps both internally and externally and the pipe tends to flatten out and become almost paper thin in extreme cases. When it reaches this point, you can’t thread it or even use dresser couplings with gaskets to repair it because the pipe isn’t round anymore.
If your planning to work on galvanized sprinkler lines, my suggestion is to get a big pipe wrench, lots of W-D 40, and a sawzall to cut the pipe with. You can use a hacksaw, but it takes forever.
Pros – When new galvanized pipe is very strong.
Cons – Reduced flow. Repairs are very difficult. Use of a pipe threader is often necessary to repair the pipe. Internal flaking which affects other components in the sprinkler system. The only reason I didn’t give it one star is because it is much stronger than Poly pipe. Can be and often is miserable to work on.
As you can see, old galvanized sprinkler pipe looks nothing like the image at the top of the page. When removing fittings from old galvanized piping, it is easy to break the pipe off in the fitting (see the image above). It is often times easier to cut out the bad sections and start over like I did on the photo below.
So is Galvanized Sprinkler pipe the best option usually. I’d imagine that since it’s basically steel, coated in zinc, it’ll be a lot more than PVC, but is it worth it?
I would go with PVC Schedule 40 pipe for underground sprinkler piping. It is much cheaper and easier to work with than galvanized pipe. I only use galvanized nipples when I come out of the ground to install faucets or backflow preventers.
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What kind of paint can you use on exterior of galvanized piping to prevent rusting and scaling or also to make the pipe last longer.
I use Rustoleum paint that I buy at Home Depot. I usually do 2 or 3 coats.