Methinks you speak from some experience. You kind of eluded to t in
your P.S., but there are different grades of SS. The stuff they would
make 4" pipe out of is most likely a lesser grade than they would use
in medical equipment and would probably start decaying a lot sooner.
My guess is that it would be cheaper to build a new amphitheater than
have 4" pipe and fittings made of surgical grade SS.
At 09:23 AM 4/20/2007, you wrote:
Stainless steel does rust, and corrode. Anyone who has owned a
sailboat can attest to that statement. Stainless steel works because
the chromium in the alloy combined with presence of oxygen in the
air forms a passivation layer of chromium (III) oxide. This layer is
too thin to be visible, which accounts for the nice shiny appearance
of stainless. Anything that disrupts that layer, or shields the
stainless from direct contact with oxygen (buried underground)
disrupts that reaction. This accounts for the rust stains that seep
out from under stainless steel cleats, and the corrosion in a nice
shiny new stainless steel turnbuckle that has spent a year or so
tightly wrapped in rigging tape. Stainless steel pipe would probably
last a lot longer than either black steel or galvanized pipe in this
application, but not forever.
Actually in the environment described, polyethylene sleeved, cement
lined ductile iron would last the longest. No exposed metal to rust
on the inside and no exposed metal to corrode on the outside. The
only question I would have since I haven't looked into it is the
sealing properties of the gaskets under air verses water pressure.
.Just random thoughts brought on from following this thread.
Richard L. Mote
Designer
Rowe Sprinkler Systems, Inc
P.S. Nickel, molybdenum and vanadium also contribute to passivation
and may be present in varying quantities some grades of stainless steel.
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Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, Connecticut
860-535-2080
www.fpdc.com
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