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Dielectric unions

Knots
Knots Member Posts: 11
in Oil Heating
I am considering replacing all the near boiler piping with same size copper. Present pipe is 1 1/2 in. Black iron. Will I need dielectric unions where the new copper joins the steel pipe? Some, who are supposed to know, say yes and some say no. Any help would be greatly appreciated.

Comments

  • NY_Rob
    NY_Rob Member Posts: 1,370
    As I understand it- dielectric unions are used where oxygen will be present in the system, like in the fresh water supply and output for your domestic hot water heater tank.
    In a closed system like hydronic baseboard that is not leaking and /or constantly using make-up water- there is little to no oxygen in the system after the first few firings- so no oxygen = no corrosion = no need for dielectric unions.

    You can go with brass unions for your copper-black iron connections to cover all the bases just in case.


  • ChrisJ
    ChrisJ Member Posts: 16,240
    NY_Rob said:

    As I understand it- dielectric unions are used where oxygen will be present in the system, like in the fresh water supply and output for your domestic hot water heater tank.
    In a closed system like hydronic baseboard that is not leaking and /or constantly using make-up water- there is little to no oxygen in the system after the first few firings- so no oxygen = no corrosion = no need for dielectric unions.

    You can go with brass unions for your copper-black iron connections to cover all the bases just in case.



    https://en.wikipedia.org/wiki/Galvanic_corrosion


    "Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. This same galvanic reaction is exploited in primary batteries to generate an electrical voltage."

    Has nothing to do with oxidation.


    To the OP, I would try to use brass fittings where possible. I'd never use dielectric unions as they are generally considered junk.

    Brass nipples into brass couplers and use copper male adapters into those. You'll have all good heavy connectors and brass into iron isn't terrible.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • JUGHNE
    JUGHNE Member Posts: 11,262
    Why do you want to change it?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    http://www.copper.org/applications/plumbing/techcorner/pdf/galvanic_corrosion.pdf

    There was an error rendering this rich post.

    ChrisJ
  • Tinman
    Tinman Member Posts: 2,808
    No, not in a leak free closed system.
    Steve Minnich
  • JUGHNE
    JUGHNE Member Posts: 11,262
    Someone in the past commented that they just use a brass valve for the transition from copper to iron. That also gives you isolation valves from the system piping for maintaining the boiler and accessories.
  • ChrisJ
    ChrisJ Member Posts: 16,240
    edited April 2016
    Stephen Minnich said:

    No, not in a leak free closed system.

    Please see my response as well as Mark's response above.
    Oxygen is not required for galvanic corrosion, this is why batteries work without vents.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Tinman
    Tinman Member Posts: 2,808
    I saw them. The only problems I've ever seen with copper to black iron connections in closed, leak free systems is the leaking dielectric unions when they're used. I've never used them in that application and I never will.
    Steve Minnich
    SWEIjonny88rick in AlaskaSolid_Fuel_Man
  • ChrisJ
    ChrisJ Member Posts: 16,240
    edited April 2016
    Stephen Minnich said:

    I saw them. The only problems I've ever seen with copper to black iron connections in closed, leak free systems is the leaking dielectric unions when they're used. I've never used them in that application and I never will.

    That's because it's rarely a problem in plumbing. Just use brass to transition when possible and everyone is happy.

    I have a big heavy 2" copper adapter screwed into a cast iron fitting on my steamer because I wasn't going to use a dielectric. Chances are that cast iron fitting will out last all of us.


    That's my opinion anyway for what it's worth (about $0.123 USD)
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Knots
    Knots Member Posts: 11
    Thank you guys very much.....will not use dielectric unions. Changing to copper due to many leaks and poor near boiler piping design in present setup.
  • SWEI
    SWEI Member Posts: 7,356
    Make sure your water pH is high enough, chlorides are low enough, and keep the air out. Should last 50-100 years under those conditions.
  • mars_6
    mars_6 Member Posts: 107
    Would not waste the time or the money on them. Have seen plumbers put them on SS tank domestic outlets and seen them fail for all the reasons spoken to above. I have the never had an issue with brass to CI fittings on a closed boiler system. and I have many of them out there. just my opinion as per this question.

    There was an error rendering this rich post.

  • mars_6
    mars_6 Member Posts: 107
    Mark E thanks for the link it will be good info for my field crews to understand why we do not need these POS on boiler systems. I still remember the system in Aurora Co that the Code required we install them. Matt funny that.

    There was an error rendering this rich post.

    Mark Eatherton
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    Matt, Our job of education of the building inspectors will never end. They are basically good guys with the best of intentions, but lack common sense and experience. And most of them are willing to admit that, so long as its not in public :smile:

    We should do lunch again some day soon.

    ME

    There was an error rendering this rich post.

  • rick in Alaska
    rick in Alaska Member Posts: 1,463
    I had an engineer spec a dielectric union on the black iron fuel line coming in to the building because it went to a copper flex line before the burner. That and a couple of other things they spec'd, that I wouldn't do, kept me from getting the job.
    Turns out this was a civil engineer ( so I was told) designing the system for the Coast Guard housing.
    Can't argue with some engineers.
    Rick
  • jumper
    jumper Member Posts: 2,384
    May not be necessary but why not?
  • rick in Alaska
    rick in Alaska Member Posts: 1,463
    Mostly because I didn't want to have a rubber gasket in the line that I don't know if it is fuel rated. I like solid connections as much as I can, and just not a fan of dielectric unions. Also, didn't see the need for it in this application. I figure a brass adapter to flare should work just as good (or better) than a dielectric union.
    Might be all wrong, but it just didn't seem right at the time.
    Rick
    SWEI
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    His (CE) recommendation would also violate the NEC, which requires all connected appurtenances be "bonded".

    ME

    There was an error rendering this rich post.

  • jumper
    jumper Member Posts: 2,384
    NEC deals with fuel lines?
  • SWEI
    SWEI Member Posts: 7,356
    NEC deals with bonding, which includes fuel lines, tanks, etc.
    From the 2014 edition:

    250.104 Bonding of Piping Systems and Exposed Structural Metal.

    (B) Other Metal Piping. If installed in, or attached to, a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:
    1. Equipment grounding conductor for the circuit that is likely to energize the piping system
    2. Service equipment enclosure
    3. Grounded conductor at the service
    4. Grounding electrode conductor, if of sufficient size
    5. One or more grounding electrodes used
    The bonding conductor(s) or jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The points of attachment of the bonding jumper(s) shall be accessible.

    Informational Note No.1: Bonding all piping and metal air ducts within the premises will provide additional safety.

    Informational Note No.2: Additional information for gas piping systems can be found in Section 7.13 of NFPA 54-2012, National Fuel Gas Code.
    Mark Eatherton

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