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There is corrosion forming on the inlet and TP valve connections to my water heater; the outlet seems to be fine. More specifically, the nipples are what is corroding. I have read the copper pipe and galvanized steel will cause this, and I assumed this was the issue. Upon further investigation, "Dielectric" is clearly readable on the nipple labels so they are not steel I guess.

I thought that these nipples were produced to avoid this exact problem. Why are they still corroding? The inlet nipple has corroded to the point that there is now a tiny drip present.

Edited for adding pics below. I am suspecting that maybe the nipple is corroding from the outside?

Click any image for full size (8Mpixels)

enter image description here enter image description here

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Are there any metal clad electrical cables coming into contact with the pipe? That is a very common cause of accelerated ferrous oxidation. –  Tim Post May 15 '12 at 15:19
    
Not that I am aware of in immediate view, but I will check when I get home tonight. I don't think I have any of that in the home though; just sheathed wiring I think. –  Evil Elf May 15 '12 at 15:26
    
Well, worth a check, but if your whole house is wired with non metallic cable .. probably just a shot in the dark :) –  Tim Post May 15 '12 at 15:28
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So you've got two different types of metal touching each other? That'll trigger a reaction right there. –  The Evil Greebo May 15 '12 at 16:45
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Can you post some pictures? Somebody might see something you missed. –  Tester101 May 16 '12 at 13:54

4 Answers 4

up vote 2 down vote accepted
+50

On second review of the photos, I don't think that the corrosion is due to electrolysis. The dielectric nipples should be adequate to prevent that and there is no sign of issues with the hot connection. As for the T&P connection, if the copper drain pipe does not come into contact with anything then there is no closed circuit for electrolysis to take place.

It looks more like corrosion due to a small leak over a long period of time. A leak that would not have always been noticeable, but would slowly get worse over time. You can see where the water has been dripping and there is signs of calcium buildup.

Like I mentioned in a previous comment, I would inspect the sacrificial anode rod and replace it if needed. As for the cold connection, you could:

  • cut the copper line and unscrew the copper section from the nipple
  • brush the nipple with a steel wire brush to remove the buildup
  • reinstall the copper section using teflon tape and a joint compound on the nipple
  • reconnect the copper line that you cut with a shark bite coupling or a solder coupling if you know how

You could do the same with the T&P connection, just cut the vertical down pipe so that you can remove the copper pipe from the T&P and then remove the T&P, clean and reinstall.

You mentioned that the tank was installed in 2006, so it would be nearing the end of its life expectancy (most residential warranties are for 5 to 6 years) so I would keep an eye on the tank for any leaks.

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I think this is the case. I will be checking the anode rod and replacing the nipple and copper on the inlet in the next week or two. I will check back in with pics and results. I suspect that the corrosion is just on the outside of the nipple, although I wouldn't be surprised if the nipple threads have started to corrode away as well. –  Evil Elf May 21 '12 at 12:56

I'm thinking that the installation is missing this dialectic union. Your "dialectric" nipple has an ABS plastic coating inside a galvanized steel pipe. If the dialectic union were used in conjunction with this nipple it would provide electrical isolation from the copper - galvanize connection. This document explains this in better detail.

enter image description hereenter image description here

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So, two devices for the same purpose? I am amazed at how little standardization there seems to be on this topic. Plumbers in forums everywhere saying they do different things. There has to be a correct method I would think. –  Evil Elf May 18 '12 at 19:36
    
Not two devices for the same thing, they both are used together. The nipple is a dialectic on the inside only. You need the union to isolate the currents from the galvanized to copper connection. –  SteveR May 18 '12 at 19:42
    
That makes sense. I am comfortable doing these repairs myself, but how do I know if the inside of the heater is good shape? Check the anode rod? –  Evil Elf May 18 '12 at 20:00
    
Yes, check the anode rod. –  pdd May 18 '12 at 20:42
    
You say the heater is 6yrs old, you should get another 6yrs out of it. Maybe more if you check, replace the anode rod and drain it once a year. –  SteveR May 19 '12 at 16:32

Leave it alone. The inlet and outlet threads on your water heater are plastic. It's a one time deal, you've got to do it right the first time. Wait until you need to replace the water heater. Use all copper next time. Mineral deposits can be sign of leakage, but sometimes the deposits seal the leak.

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It is electrolysis from two dissimilar metals. You have copper pipe in contact with galvanized steel pipe. A small electrical current is created (Google "thermocouple"). There is no dielectric union between these two metals.

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-1 This is the same as SteveR's answer. –  BMitch May 29 '13 at 19:59

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