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dialectric unions

Herb_2 Member Posts: 6
I live in an area where plumbers often run copper pipe directly into galvanized pipe, without using dialectric unions. I have been monitoring such joints for the past twenty years, and have found little or no evidence of corrosion. Questions: 1. Should I still use dialectric unions (in this case, for radiator piping)? 2. If I used brass nipples betweeen the galvanized and copper material, would this retard corrosion?


  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    What you don't see...

    will kill your pipes. In the case of potable water, disimilar metal mixies WILL cause an early death for the lesser of the two noble metals. It's happening from the inside out. You are correct in your assesment in the use of brass as a neutral connection, however, it should be a high grade of YELLOW brass, NOT red brass. Brass is not brass anymore. Never has been. It's a mixture of many different, but similar compounds.

    As it pertains to a good tight closed loop heating system, di-electrics are not necessary because one of the key critical components to electrolytic corrosion is missing (oxygen). If there's ANY chance that the system will see a high content of oxygen from any of the potential sites of availability you have a potential for corrosion. It's just a matter of how much. And in the case of a true metallic barrier, the sources of oxygen quickly disappear, the residual 02 content IS lessened, but it too can rebalance over time with no water movement. It's mother natures way. She despises imbalances in EVERYTHING. Heat, Temperature, pressure, humidity. EVERYTHING! Even oxygen content. But it's not there for long when you start heating it up and running it through systems designed to control and eliminate air.

    For the life of me, I don't understand why people would use galvanized in ANY piping system. I've never seen it hold up to any of the rigors of the real world.

    In short, I generally don't do anything in the way of dielectric connections. With all the new bronze isolatioon flanges out today, true disimilar metal mixes are athing of the past...

    With ProPress it's even less of an issue.


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  • curiousity kills
    curiousity kills Member Posts: 118

    I have been in the plumbing and heating trade for 8 years and all we do is residential service. I have NEVER seen corrosin when a copper male adapter is fitted to the water heater and I have replaced some of these tanks that have been like this for 15 years.I have seen many cases where a dielectric nipple was installed to PREVENT corrosion' rusted and formed a leak' and in worse case causing the customer somtimes to replace the water heater if the corroded dielectric nipple cannot be succesfully removed.
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    In the case of a tank...

    the electrolytic corrosion is spread out over the tanks exposed surface. You also have an anode in the tank which is sacrificing itself for the tank. Once it's gone, the oxygen turns its attention to the remaining exposed mild steel. Water pH and other factors have an influence on the time factors to failure..

    So, have you discoved the right way to do things wrong???

    Just curious...

    Also curious why you find it necessary to use an alias. I don't use my actual e-mail address, but it's written out so anyone who wants to contact me can.


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  • curiousity kills
    curiousity kills Member Posts: 118
    Regarding your curiousity

    My name is Eric Roy and Im not hiding anything and Im not
    making this a personal attack Im just giving info on what I have seen over my time in the field. You cannot pass an inspection without a dielectric connection to a water heater I understand this however you can give me all the personal technical info you have on this matter and I will show you more water heaters in my metal scrap pile 12 + years old that are directly connected with copper male adapters and not leaking and replaced for preventive reasons versus water heaters leaking less than this with dielecric connections.Ask any service plumber in residential field service what a diectric nipple looks like after 6yrs. I have however seen connections to a water heater with black malible piping and the damage it will do. I have seen homedepot install hydronic expansion tanks versus potible tanks and totally agree this is wrong.
    I wouldnt never install a dielectric nipple to anything I would connect with a quality brass nipple instead.
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Thanks for the response Roy...

    And I too am not trying to attack you... What's the water like in your area? Hard, soft medium?

    I too used to do a direct connection between the tank and the service lines, until I saw pictures of what was happening to the INSIDE of the tank, and I agree with your assesment of dielectric unions create more problems than they avoid. That is why I prefer the use of yellow brass nipples. They're neutral to all metals concerned.

    Thanks for taking up the discussion. We can all learn something from each other.


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  • curiousity kills
    curiousity kills Member Posts: 118

    We do have hard and acidic water in some areas of NH and if the water was treated properly before it reached the tank this could stretch the life of the water heater and in most cases pay for itself. What I tell my customers to help prolong their tanks is to flush once a year and change the anode rod after 6 years.Most customers dont do either.I do enjoy responding to people and having discussions on this site and learn something new every time I read responses.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,232
    It all depends...

    on the water. The cleaner and less aggressive the water the less it matters how things are plumbed. In my area, (central coastal California) we get all sorts of different water from 40 ppm total dissolved solids to over 1000... from mildly acid to basic. The only combination I've found that seems to work well long term and in all waters is a plastic lined steel nipple in the tank with a copper flex line to the plumbing. The steel nipple has no conflict with the tank and the lining puts distance between different metals, (use the lined nipples wrapped at the ends so that there is little or no exposed steel). The dielectric available on flex lines can be a true dielectric and has no steel in it to cause trouble. The combination agrees with what the National Assn. of Corrosion Engineers has written and has helped to keep me out of hot water trouble for about twenty years. Now there's all those other types of trouble to deal with... ;~)
  • hr
    hr Member Posts: 6,106
    I'll kick your brass, partner :)

    I'm not sure what they heck we get these days from the fitting companies.

    Brass is copper and zinc. Or maybe some iron, nickel, silicone or aluminum thrown in. Color varies with the amount of copper in the mix. Alpha brass has a copper content generally above 64% Beta brass at 60% or less copper.

    Lead can be added for better workability although the Clean Water Act, or whatever has "supposedly removed lead from plumbing brass and fixtures. Not sure what is used as a replacement :)

    Then you have bronzes which are copper and tin, usually. Sometimes aluminum, silicone, or manganese are blended in specfic bronzes.

    The copper itself can be modified with sulpher and tellurium. Some US copper ores have silver in them.

    Copper nickel is another common alloy in the HX industry.

    My concern is virtually all the brass or bronze fittings I see these days are stamped China, Thailand, or Taiwan. Even though they are sold as as American brands.

    I'm not sure who, if anyone, is keeping an eye on the alloy %s or quality of ingredients used in these fittings. They sure do seem awful soft these days. Doesn't take much wrenching to "egg" them :) Don't even think about dropping them!

    I'm not sure what alloy is used in the sweat flanges we use these days either. Maybe it is good for DHW use? Maybe not. Are the Taco flanges, for example, approved for DHW use? Could they be leaded brass which is desired for easy machine-ability. Or casting brass with lead?

    Alloys with more than 15% zinc are susceptible to dezinicification. Often dismissed as casting pinholes, the water can actually cause this dezincification, and leaks. It's not uncommon in "budget priced" imported valves with thin, low quality brass used.

    Anyways a copper to iron connection at a boiler will be fine as the area ratio of the iron to copper will be in your favor, and oxygen is not being constantly added. You hope!

    In theory a water heater tank is glass lined and the same should be true. I suppose the threads however present a small area for the corrosion to start, then the area ratio works against you, lots of copper pipe to a small steel area.

    To be safe use dissimilar metals that are close to one another on the galvanic series. We all have those charts on our wall I'm sure :)

    Brass nipples of any color or alloy will be a good idea on WHs. Better than a direct copper connection.

    Avoid coupling small anodes to large cathodes. Copper rivets last better in steel sheets than steel rivets in copper sheets :)

    And maintain the anode rods in water heater tanks. Some top quality 10 year tanks come with 2 anode rods. Although an anode removal and replacement could run as much as a new heater. In some cases you may have to disconnect the tank and lean it over to even remove the rod for inspection and replacement. Segemented, bendable rods are handy for replacements if this is you bag, baby.

    hot rod

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