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Galvanic Corrosion

hr Member Posts: 6,106
brass is an alloy of copper and zinc, and a good match for galvanized steel. Remember the "relative area effect" has a lot to do with galvanic corrosion.

When you look at a galvanic series table to compare metals remember they use seawater as the electrolyte. Fresh potable water is weak electrolyte, distilled water is extremely weak.

I suspect this is why copper coils with aluminum fins (ac condensors)fare so poorly on the seashore;)

hot rod

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  • ALH_4
    ALH_4 Member Posts: 1,790
    Galvanized and Brass

    Galvanic corrosion between copper and iron has been a recurring topic on The Wall, but I do not remember anyone sharing experiences of galvanized steel to brass connections that caused galvanic corrosion in plumbing.

    I know the theory behind galvanic corrosion, but the only time I have seen a problem in piping I could definitely say was galvanic corrosion is when copper has been connected to aluminum.

    In what situations have people seen the worse galvanic corrosion problems?
  • radioconnection_2
    radioconnection_2 Member Posts: 70

    With galvanizing being a sacrificial element for these applications, I'd guess the electrolysis should be horrendous when going between galvanized and brass or copper. Cast iron to brass, brass to copper... IMHO!
  • Phil_15
    Phil_15 Member Posts: 13
    Electrolysis,Grounding and pressure reducing valves

    We are required to have a heavy copper grounding wire to connect across the potable water pressure reducing valves that contain plastic. I assume that the plastic somehow restricts electron flow and thus prevents a good gound connection?

    I recently saw a home that had the copper wire across the platstic component pressure reducing valve but then, upstream of the main shutoff valve, the copper pipe transitioned to plastic piping before exiting the house underground to the meter 100 ft away from the house. The house was built in 1983, has type S copper and has experieiced some pin hole leaks and green corrosion is apparent at many of the copper-to-cpper sweat fittings.

    I was wondering, could the plastic pipe not allow proper grounding or is the water in the pipe a sufficient conductor? Could improper grounding be a cause of the degrading copper? I know degrading copper has been discussed here on Dan's wall and water pH has been identified as the major culprut but could improper grounding (and thus electrolysis) also be contributing to the problem?


  • Larry C_11
    Larry C_11 Member Posts: 3

    Electricians use the metallic cold water line as a grounding electrode, if the pipe extends at least 10 feet out into the soil.

    In an (sub)urban environment, many things are tied to the earth, including electrical distribution, cable TV, phone system, gas, water, and sewer lines. Often installers will assume that the water piping is a "good" ground. If (or when) a house electrical ground is disconnected, the current that normally flows on this wire will take a parrallel path thru the plumbing, cable TV cable shield, the gas line, or whatever, to get back to where it wants to go.

    Since potable water is usually not a very good conductor, the copper pipes are a common path. The cause of the pinhole leaks might be the disolving of the copper electrode (pipe) as the electric current is flowing thru the water. I believe that if the water pipe can not be used as an grounding electrode, there should be at least two ground rods connected to the Service Entrance panel.

    I would recommend that a qualified Electrician look at the installation.
  • Rich Kontny_4
    Rich Kontny_4 Member Posts: 73
    Type \"S\" ?

    Type "S" copper is a new one to me.I have worked in four states and I am only aware of types K,L,M, DWV and the short lived "B" alloy.

    The green at the joints is residue flux corroding the copper. This is due to a poor soldering job. Pin holes can be caused by a ph problem with the water from the inside or the soil surrounding the copper on the outside.

    Brass eventually will destroy galvanized theads on very old water and waste systems. I have had many old brass trap connectors fall off in my hand when I went to change them.

    Last winter we had a homeowner who was told o shock his well (disinfect it) with believe it or not five gallons of Pool Shok.

    After lab analysis of the pin holed copper distribution system it was conclusive that the high concentration of chlorine (15-18 times the recommended concentration) scoured the normal green layer that forms on the interior walls of the pipe. This scouring left bare the copper and subjected it to the high concentrated chlorine, the result was a trashed water distribution system in a 9 year old home.We replaced the entire system from well to furthest fixture with Aquapex.

    I am told by my brother who is a mechanical contractor in Florida that galvanized piping is used underground there instead of copper due to alkalinity problems. The recent introduction of plastics has most likely given them a better option.

    As Hot Rod stated you have lots of variables at play and usually the trial and error method is used instead of pro-active soil and water analysis before materials are used.

    Rich K.
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