Dealing with build up from galvanic corrosion in supply tees

Question

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:

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:

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.

Answer 1

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.

Answer 2

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).