On 19 Apr 2007 at 13:46, Warren Wolfe wrote:
On Navy ships, a large chunk of zinc is connected
to the steel hull
at some point. Then, when oxidation, and other electro-chemical
degradation takes place, this "sacrificial anode" is where essentially
all the corrosion takes place. Every now and then, the remnants of the
zinc are removed, and a new block is attached. (It's VERY easy and
cheap to replace a block of zinc - repairing a thinning, corroding hull
is quite another matter.)
You've probably got the same type of anode in the tank your home
water heater, except that it's most likely magnesium. It's
surprising how few homeowners know about this and allow the anode to
corrode away to nothing (eventually resulting in a leaking tank)--
it's usually very easy to replace one.
Another approach used in buried pipelines is to impart a small
current between the pipe and earth.
Cheers,
Chuck