DIYbanter - Corrosion on hot water heater pipes

On Monday, November 11, 2019 at 11:54:30 AM UTC-5, Fletcher wrote:
Is this hot water heater pipe corrosion normal?

I haven't seen it on any of my water heaters, but then they are copper
lines, soldered in. Looks like it's galvanic corrosion where
different metals meet. The new union is dielectric, was the old one too?
Looks like it could be, I see some red plastic at one end. If it was,
then using dielectric didn't help. I've read many explanations of
dielectric, how it's supposed to work, but I've never read an explanation
that actually made sense. And how much of a factor this is or isn't
probably depends on differences in small ground loop currents in one
installation compared to another. Me, I just solder in using copper
all the way to the water heater fitting, no dielectric unions, no flex
pipe, no problems. And water heaters went in that way for decades.
I think you'll find differences of opinion among plumbers too. Plus
I guess is if it lasts the life of the water heater that's all it needs
to do and if it looks bad before that, it's not hard to change out.
Worse would be it failing from the inside, where you can't see it.
I'd cut the old one apart and see what it looks like inside.

Another factor would be if the galvanic electrode in the tank is still
there or has it been used up? That's there to protect the tank, but
it likely helps protect the piping too. There are differing opinions on
that too. Some say to remove it from the tank and check every few years
If it's mostly gone, replace. Others say that the tanks have various
failure modes and that by the time the electrode is gone the tank likely
doesn't have much life left anyway, so don't bother.

(1) Needs to be connected by a nipple, only brass available
http://img4.imagetitan.com/img.php?i..._image6071.jpg

(2) Will the new brass nipple corrode just like the old did?
http://img4.imagetitan.com/img.php?i..._image6072.jpg

(3) Hot water outlet nipple seems to be steel?
http://img4.imagetitan.com/img.php?i..._image6074.jpg

(4) New & old nipples are both brass so why corrode?
http://img4.imagetitan.com/img.php?i..._image6075.jpg

(5) Cold water inlet has less corrosion it seems but why?
http://img4.imagetitan.com/img.php?i..._image6076.jpg