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I opened up the wall behind my kitchen sink during a major remodel to find iron nipples in threaded brass fittings. Here is an image with labels:

Exposed pipes with labels identifying copper supply lines, galvanized and cast iron waste lines, and fittings. A vertical cold water supply line on the left side has two in-line brass tee fittings where iron threaded nipples were removed. A vertical hot water supply line on the right side has one in-line brass tee fitting with an iron nipple (1/2" MIPS) terminating in a brass shut-off valve. Cast iron DWV continues below subfloor. Both copper supply lines are topped with surge arrestor sections.

I removed the iron nipples from both cold water supply tees on the left side. Here's a picture of the condition of the lower-left nipple after removal, which was feeding a brass 1/2" FIPS x 3/8 comp shut off valve that supplied a dishwasher:

Clogged iron nipple

I was planning to plug the lower left tee and run both the dishwasher and sink off the top left tee, using a 1/2" FIP x 3/8 comp x 3/8 comp valve, because the lower tee intrudes into the rear frame of the sink base cabinet and would require cutting the cabinet, which I want to avoid.

However, after discovering the brass-to-iron connections I decided to sweat off that lower left tee entirely and replace it with a soldered couple. I wasn't able to remove the iron nipple from the hot supply tee on the upper right so I am going to cut that out and replace it with new brass tee, brass nipple, and valve.

My question is about the remaining cold water supply tee on the top left. Is it reasonable to clean the remains of the corroded iron nipple out of the female threads of the brass tee and install a new brass nipple and fitting, without replacing the tee itself? I'd like this area to be leak-free for the long term.

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  • looks like grease to me, not corrosion, never connect brass to steel. use plastic or steel nipples in those steel tees.
    – Jasen
    Sep 6, 2021 at 7:21
  • It looks to me that the water supply piping is copper and the drains are cast iron fittings and galvanized piping. Is my observation correct?
    – d.george
    Sep 6, 2021 at 9:33
  • @d.george Yes, the supply lines are 1/2" copper with brass tees and the waste lines are as you say (mainly cast iron under the house). That third iron nipple on the hot line to the right never did budge so late last night I gave up, sweated off the lower left cold tee and replaced it with a new couple, cut the upper left tee out and will replace in kind with a new fitting. I would like to keep the upper left tee as it's currently pressurized with no leaks, and since brass is the anode here it should be OK... but I'm operating on theory, not experience, to make that call...
    – Air
    Sep 6, 2021 at 15:38
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    Note: Having explored this problem a bit more, I am self-answering on behalf of the "replace everything" camp.
    – Air
    Sep 6, 2021 at 20:18

2 Answers 2

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The best solution, as long as the area is already exposed, is to replace all brass fittings that had been mated to iron nipples.

I did try cleaning out the female threads of the upper left brass tee using toothpicks and a wire brush, and installing a new brass nipple with PTFE tape. After adding a new shut-off valve and pressurizing the line, the work seemed to be water-tight but developed a very slow leak after about 12 to 15 hours.

I could certainly try to finesse that connection with pipe dope, try it a bit looser or tighter, and likely get it to remain water-tight for days. But given that I will install kitchen cabinets in front of this section of wall, and my goal is not to have to open that area up again for the lifetime of the cabinets, it doesn't make sense to save a few hours and a little money by re-using an old fitting that might still fail a month or a year later. Especially if that failure might start as a slow leak and end up putting significant amounts of water into my walls and cabinets before being discovered.

As for the analytical side, while the brass anode is protected in theory, I would speculate that the close mating of the brass and iron threads plus any added friction when removing the corroded nipple may still result in significantly more damage the tee's female threads than a normal brass-to-brass connection. Depending on the extent of this damage, tape or dope may not be sufficient to produce a seal that lasts for 20+ years.

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  • It never hurts to rip it all out and replace it, especially when it will be buried behind not just a wall but cabinets, too. I do agree that what you were seeing in that pipe didn't look like corrosion, but grease or some sort of other gloop. Was it hard or soft? Also, be sure to click the check mark so others know this has a resolution.
    – FreeMan
    Sep 7, 2021 at 12:43
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    @FreeMan I like to leave self-answers unaccepted for a while so people still have incentive to provide competing answers and vote. The build up was hard and slightly crumbly, I feel silly not having thought to test it with a magnet but it was very characteristic of rust; I think it also had a bit of scum built up on top, probably from the reduced flow/scouring action.
    – Air
    Sep 7, 2021 at 18:01
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The photo shows copper supply and galvanized pipe with cast iron fittings for sewer. I am not certain what the plugged fitting in the second photo is. You need to clean it and determine if there is metal loss, also, if possible, what the blockage is. Rust would be magnetic , but carbonate scale mixed with rust will also be relatively magnetic. There is no galvanic corrosion between your copper supply and galvanized sewer. If copper is connected directly to galvanized steel, the galvanic corrosion will extend no more than roughly one pipe diameter of distance into the galvanized ( call it one inch in round numbers).

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  • Second photo shows the 1/2" IPS x 2 1/2" nipple that I removed from the lower left cold supply valve. Each of the three supply tees pictured had a similar nipple and the threads of those two that I was able to remove from their fittings were severely damaged/crumbling. I suspect these nipples were installed between 2015 and 2018 and I have not found scale to be a problem elsewhere in the home.
    – Air
    Sep 6, 2021 at 19:46
  • You are correct; installing steel nipples between copper pipe and brass fittings is a mistake. I think basically you have an inch of galvanic corrosion on each end of the nipples. The brass and copper components should be good. Sep 7, 2021 at 16:55

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