On Fri, 3 Jul 2015 21:29:52 -0400, "Jim Wilkins"
wrote:

"John B." wrote in message
.. .
On Fri, 3 Jul 2015 18:00:57 -0400, "Jim Wilkins"
wrote:


"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in
message
68.4.170...
fired this volley in
:

Pebbles in streams are round because they roll around against
each
other in the running water. Water itself is a lubricant, not an
abrasive

What I said, Clare. But the "Well Guys" (who just MIGHT have a
financial
interest in the results... nah...) said "No way -- WATER is an
abrasive!".
So it MUST be true! G

L

This claims that water becomes more corrosive where it mixes with
oxygen:
http://inspectapedia.com/water/Well_Casing_Leaks.php

Differing oxygen levels are said to be the reason why stainless
corrodes in some areas under a boat. The concentration gradient
creates a weak battery.

-jsw

Nope. Stainless corrodes because of a lack of oxygen in the water,
while the article seemed to say that water near the surface
contained
more oxygen.

http://www.boatus.com/boattech/artic...-corrosion.asp
(crevice corrosion)
or
http://www.passagemaker.com/channels...and-corrosion/

But as water is made up of oxygen, in part, I suspect that the term
should be "free oxygen".
--
cheers,

John B.

Here is the relevant corrosion mechanism those articles omitted:
https://en.wikipedia.org/wiki/Concentration_cell
"Concentration cell corrosion occurs when two or more areas of a metal
surface are in contact with different concentrations of the same
solution."

-jsw


Yes, Yes. But the common "crevice corrosion" that effects stainless
stuff below the water line on a boat is something different. It is a
dissolving of the protective coating on the surface of the
"stainless". See: https://en.wikipedia.org/wiki/Crevice_corrosion

I suspect that finding a body of water that varied in concentration of
the same solution within the length of a boat might be difficult.
Certainly the ocean is never still :-)

--
cheers,

John B.