Galvanized iron water supply piping (C) Daniel FriedmanGalvanized Iron Water Supply Piping, & Galvanized Drain Piping

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Galvanized supply or drain pipe troubleshooting: galvanized iron pipes in buildings: clogs, leaks, repair, replacement advice.

Our page top photo illustrates galvanized iron (or some say "galvanized steel") water supply piping in home. This article lists in-depth references on inspecting, testing, and repairing problems with galvanized iron building plumbing: water supply and drain waste vent piping, piping materials, clogged or noisy pipes, and types of pipe hazards or product defects.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Galvanized Steel Water Supply Piping in buildings

Galvanized steel pipe rust and clog (C) Carson Dunlop Associates

This article discusses

The articles at this website will answer most questions about water supply & drain piping, wells, & water tanks as well as many other building plumbing system inspection or defect topics. New York State License # 16000005303 (inception to 2008).

Galvanized steel (iron) is not commonly used as a water entry service pipe, although galvanized steel fittings may be found at the point of entry into the house.

Where galvanized service piping is used, it is typically at least 1 1/4-inch diameter. The word galvanized means zinc-coated. The coating helps prevent the steel from rusting.

Galvanized steel (iron) piping was common until roughly 1950. This piping typically lasts 40 to 60 years. Some lower-quality pipes do not last as long and there are some oversized pipes still in use after 60 years. Where it is found today in single-family homes, it is usually near the end of its life.

"Galvanized" refers to a metal plating process that coated iron or steel water pipe surfaces with a corrosion-resistant zinc surface.

Galvanized iron water supply piping (C) Daniel Friedman

Life expectancy of galvanized steel piping: Galvanized steel supply pipes are typically 1/2-inch diameter. The connections are threaded. When the pipe corrodes, the rust accumulation inside the pipe chokes down the diameter of the pipe, resulting in poor water pressure.

Rust also attacks the pipe walls, making the walls thinner. Eventually, the pipe will rust through, usually at the joints first, resulting in leakage.

Galvanized iron water supply pipe can also burst from freezing, and may split at seams depending on how the pipe was manufactured.

Galvanized iron water supply (or drains) are more likely to burst by splitting or fracturing if pipe sections are corroded from an external cause such as corrosive water or by contact with materials or surfaces that increase the pipe corrosion rate.

Our photo (above left) illustrates a galvanized iron pipe failure (and replacement) at a spa in Lourdes, Mexico.

Black Iron Piping in buildings

Uncommon for water supply piping but found as gas piping, oil piping, and some other uses, is black iron pipe - essentially the same material as galvanized iron piping, but without the protective galvanized zinc coating.

Diagnosing rusty galvanized steel piping

Galvanized supply pipes (C) Daniel Friedman

As rust builds up inside the pipe, a brownish color is often noted in the water when a faucet is turned on, especially after several days of inactivity. This rust in the water usually dissipates after a few seconds.

As we mentioned in our discussion of lead water entry mains piping, many of the old lead service lines were connected to a galvanized nipple – a short piece of steel pipe that was often in contact with the soil. This pipe rusts on the outside and inside, and may be close to the end of its life. It is often wise to replace this as a precautionary measure.

Galvanized steel piping will often leak first at the joints. Steel pipe has threads cut into it where it joins a fitting. The pipe wall is thinner at the threaded connections. As the piping rusts from the inside, the pipe rusts through first at the threaded connections, where the pipe wall is thinner.

- Home Reference Book, used with permission.

Our photo (above-left) shows silver-colored water supply piping that is probably galvanized iron. But this pipe looks a little too good. We suspect from the photo that the pipe has been painted.

Watch out: because it's easy to spray-paint silver or aluminum paint on metal pipes in buildings, you may need to check closely or use a magnet to be sure that the silver-colored water supply piping you are examining is really galvanized iron (magnetic) and not painted brass (not magnetic) or painted black iron pipe (magnetic, paint scrapes off).

Also, as our photo above demonstrates, don't miss nearby visually obvious safety hazards like the missing discharge tube on the pressure relief valve on that water heater! If someone spray painted brass water supply piping with aluminum paint you could be fooled.


Galvanized Steel Pipe to Copper Pipe Connections - Dielectric Fittings

Water supply piping connection: copper to galvanize (C) Daniel Friedman

In most jurisdictions plumbing codes require the use of a dielectric fitting when joining steel piping to copper or other metals; some plumbing jurisdictions permit use of a 6-inch brass nipple in this location as an alternative to diaelectric fittings. Why?

When connecting iron or galvanized iron pipes to copper in buildings, often galvanic corrosion and ultimately plumbing leaks will occur at the meeting of these two dissimilar metals.

Using a dielectric fitting (misspelled as diaelectric or dieelectric) or an approved brass fitting to connect these two metals, or more commonly, using plastic or bronze fittings at the joint between these two metals will avoid future corrosion and leaks.

Details about the requirement for dielectric fittings at copper to steel pipe connetions are at DIELECTRIC FITTING CODES.

More about the galvanic scale and corrosion between dissimilar metals is at GALVANIC SCALE & METAL CORROSION.

At ELECTRICAL GROUND SYSTEM INSPECTION we discuss the need for a jumper wire around interruptions in the metal piping system, such as where a diaelect4ric fitting is installed or where a water meter interrupts continuity.

Galvanized Steel Drain Piping in buildings

Our photographs (below) show galvanized drain piping in use in buildings. At below left, the cleanout in a galvanized drain line has been lost, plugged with who-knows-what, and is an odor and leak source. At below-right, the rope trying to secure the galvanized drain line to the cast iron sewer piping confirm a history of leak troubles and improper plumbing connections.

Galvanized plumbing drain (C) Daniel Friedman

Clogged Galvanized Steel Plumbing Drains

When diagnosing clogged drain piping in a building, an important distinction is between a specific point of clogging and piping that really needs total replacement. If a point-clog exists it can generally be cleared successfully. When mineral deposits or rust have decreased the interior diameter of galvanized iron pipe drains so that drainage is poor, plumbers use two methods to try to clear the lines:

  1. Snaking the galvanized drain pipe, sometimes euphemistically "running a wire" through the drains. We paid Plass the Plumber a stiff fee to provide this ineffective service in Poughkeepsie, leading to a big bill and no improvement in the piping. Eventually we opened the walls and cut open the drain line to see that only a very tiny internal diameter of drainage was left in a rust and mineral-clogged pipe.
  2. Using acid drain cleaners. This process might work if the drain pipes are not too badly clogged and if the steel or iron is otherwise in good condition. Beware of running acid into septic systems.

Galvanized plumbing drain (C) Daniel Friedman


Continue reading at DIELECTRIC FITTINGS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see DRAIN & SEWER PIPING - home



Or see SUPPLY PIPING - home

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