On Wed, 15 Oct 2014 00:28:10 -0700, Jeff Liebermann
wrote:

On Wed, 15 Oct 2014 07:59:20 +0100, Charlie+ wrote:

What are these tanks made of that they need sacrificial anodes (of
magnesium etc. I assume)? As far as I know over here most/all these type
of tanks and cylinders are Cu sheet and have no anodes of this type.. !
Informative post tho! C+

Not copper. That would be far too expensive. The tank is made from
steel, which is either enamel or glass coated for protection. The
problem is that the glass or enamel can crack (or micro-crack)
allowing the water to contact the steel and eventually corrode a hole
in the tank.

Is this perhaps a gas water heater? When I took my electric water
heater apart, it had a steel shell but inside that was a flexible
plastic of some sort, milky clear/white, with maybe glass embedded in
the plastic. It was 1/4" thick or more and was never going to break,
because I pulled it away from the metal and bend it 60 degrees and there
was no cracking.

It was sold by Sears but seemed identical to the one that was first in
the house, by A.O.Smith. (I'm not positive it's labeled glass-lined
but people make it sound like all of the tanks are.)

When I brought it home I worried about dropping it, because I had heard
they were lined with glass, so I thought they would be fragile, but like
I say, it would have been impossible to break the glass.





The sacrificial anode corrodes instead of the steel
tank. It's exactly the same as the common zinc sacrificial anode used
to protect steel hulls on boats.

Note: I am not a plumber, expert on hot water tanks, or hydraulic
engineer. I just happen to have had some experience replacing my
water tank twice in 35 years and found it useful to first read the
available literature before making any more mistakes.