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plumbing qn: brass valve with galv pipe?

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ALH_4
ALH_4 Member Posts: 1,790
in THE MAIN WALL
My understanding is that there is no "neutral". What is important is how far apart the metals are on the galvanic series. You subtract the materials' anodic indices to determine whether galvanic corrosion will be a problem. There should be no more than .15 to .25 difference at the most. Of common metals, copper is almost on the opposite end of the spectrum from aluminum for instance. Aluminum is a .35 and Copper is a .95 giving a .60 difference. This is not a good combination. The magnitude of the problem also depends on the quantity of material present. If you have a ton of aluminum with a copper washer, you have nothing to worry about. If you have a ton of copper with an aluminum washer, that washer will be gone quickly in the presence of an electrolyte.

I patched some 12-ft long aluminum shell and tube heat exchangers for honey a while ago. They were connected directly to copper pipe with copper Raypak boilers. In spots the shells were like swiss cheese. Almost every tube was deeply pitted when we took one of them apart. However, the heat exchangers were somewhere between 20 and 30 years old, so that does seem a reasonable life. One of the heat exchangers had stainless steel tubes with an aluminum shell. It was beyond repair. I assume that even though the anodic indices of copper and stainless are relatively close, there was sufficient ratio of steel to aluminum to speed the process.

-Andrew

Comments

  • John Ketterman
    John Ketterman Member Posts: 187


    I know this is not a heating question...my apologies...

    I have some 80-year-old shutoff valves in galvanized cold and hot water supply lines that have jammed in an open position. There are unions nearby so they are easy to replace. But local hardware stores have only brass (bronze?) valves. They swear up and down that while copper is not OK with galvanized, brass is OK. Should I believe them?

    If, as I suspect, the answer is no, where do I get galv-compatible valves? (I searched the web but may not have used the right search terms.)

    I don't want to try the "lots of teflon tape" route, I can't guarantee that I'll achieve full electrical insulation.
  • [Deleted User]
    [Deleted User] Posts: 1,160
    Brass...

    is an accepted method of dissimilar metal protection. It is neutral to dissimilar metals.

    Go for it.

    ME
  • LarryC
    LarryC Member Posts: 330
    Is copper - galvanized OK?

    Is copper + galvanized OK? How about copper + black iron?
    Stainless + copper?

    Where would I find a chart of compatable metals? Is any of this a problem when used with nonconductive liquids?

    Thanks,

    LarryC
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    Here's a galvanic chart. Note how "brasses" occupy the center region.

    This is probably a WAY over-simplification, but if you need to connect metals on either side of the chart, do so with brass and everything will corrode at essentially its' "natural" rate.
  • Ron Schroeder
    Ron Schroeder Member Posts: 995
    Just don't be surprized

    if you end up replacing more of that pipe than you want to. Those threaded ends may not be in as good shape as you would like.

    Good Luck

    Bruce
  • Weezbo
    Weezbo Member Posts: 6,231
    put some heat to the valves with the bonnet open...if you hear

    a crack sound then tighten the bonnet nut a bit and see if the valve will open .sometimes it does. old galvy once opened reveals what you thought was going on ..aint..:)

    every valve you heat first will have a better chance of comming off without tearing the threads off the galvy or worse holding onto it until one of the fittings deeper in the wall cracks and you may end up repiping your home by default as it were.brass valves work fine. dont worry. remember though that it may be that there are buildups inside the pipe that may make you wonder how you ever got water out of it....that might be more info than you needed buh at least i figure knowing about the possibilities going into it might help you maintain a cool head:)

    i bought a new book the other day Marks standard handbook for mechanical engineers *~/:) it has a chapter on galvanic action....so i think you can get a pretty good grip on the subject with a quick read of a few pages in an engineers hand book at the local library.
  • R. Kalia_4
    R. Kalia_4 Member Posts: 18


    Thanks to all for the advice! I bought new brass valves already but I'll start with a propane torch.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,895
    I'll add one...

    ... more idea. Screw a plastic lined steel nipple into the galvanized pipe, then your brass valve, then back to lined steel and then galvanized. This puts distance between the different metals, greatly reducing what they "see" of each other.

    Yours, Larry
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