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Internal/External Corrosion In Galvanized-Copper Junction

Good Morning All,

My name is Mark and I am writing from an offshore platform in the Gulf of Mexico. We have a water line system for potable water that has been losing pressure. The system is mainly copper except where is penetrates bulk heads where it must be a harder metal. The metal in place now is simply galvanized pipe. There are insulated unions at each splice as well. We have experienced leaks lately, and when we open the pipe we find it clogged with what appears to be rust scale and there is also some external pitting close to the threads?! This is all up in ceiling rafters and is dry at all times. We have everything from 1.5" down to 1/2" copper in this system. Can someone shed light on what you feel we should do? I would really appreciate your help here!

Mark H. Olive
Oil Company - Gulf of Mexico
2006

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2006

Maybe I can offer some ideas about this problem. Just so you know, I'm not by any means an expert in the business ...just someone with some plumbing life-experiences.

A little more specific information may help:

(1) You say this system carries potable water. Is the line exhibiting the problems attached to an electric hot water heater?

(2) You can "...where is (sic) penetrates bulk heads where it must be a harder metal". What "harder metal" is the bulkhead? Steel or a steel alloy (which all contain iron...which in turn rusts)? Does the copper come directly into contact with the "harder metal"?

(3) You say that the pitting is found "close to the threads"...is the pitting found only where copper meets galvanized pipe or the bulkhead (I still don't know what the bulkhead metal is)?

(4) When you use the term "insulated unions", I'm assuming you mean a "dielectric union" that connects two lines without allowing one to come into direct contact with the other.

Your problems could be caused by different metals coming into direct contact with each other. When they touch each other, a "galvanic" reaction starts which causes corrosion of the less resistant metal (in this instance, the galvanized pipe) at that point.

The fact that you find rust scale at your clogs suggests that you may want to look at the all the unions along the system to see if/where copper meets the galvanized pipe...that may be the source of the problems. The galvanized pipe is probably your rust source...they tend to rust from the inside out and release the rust into the system. Symptoms of this happening include brown water (which can appear at the tap or in stained laundry, etc.) and rust clogs, which you say you have found.

I think the pitting could actually be caused by several different things, but since it is "close to the threads", I'm guessing that in this instance, it is found where the copper meets the galvanized pipe, again pointing to corrosion due to a galvanic reaction as the cause.

If the corrosion/pitting is found at the "insulated unions", then maybe the metal found in the specific union that was used was not appropriate in this instance. Brass is a good metal to use for unions since it doesn't react to either. You could use a brass union or a brass nipple with couplings on both ends to connect galvanized to copper.

I don't know if this next piece applies to you, since you are finding pitting at the joins, but here's another thought: If the line with the problems is attached to an electric water heater, then your water heater may need some attention instead of/as well as the plumbing lines. An electric water heater has a part in it that is designed to erode over time during normal use. This is called a "sacrificial anode" (in the normal course of use, this metal anode is consumed -- "sacrificed", if you will -- instead of the metal of the tank itself). When one anode is completely spent, then you need to replace it with a new one. While it doesn't happen very often, it is still considered regular maintenance (along with draining and refilling the tank once a year to help remove sediment, etc.) and should not be a big deal to do. Failing to do this maintenance contributes to the failure of electric water heaters due to the tanks rusting out. Some of the rust in your clogs could possibly be due to the tank itself being attacked in the absence of the anode.

Hope this helps. Good luck.

Gary Lieberman
- Silver City, New Mexico, USA