Corrosion Basics. January 21 st , 2009 Robert J. Sinko. Corrosion Experts!. “An expert is someone who carries a briefcase and comes from more than 50 miles away” (anonymous) “An expert is a man who has made all the mistakes which can be made in a very narrow field” (Niels Bohr).
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January 21st, 2009
Robert J. Sinko
Left out in the rain
Note that atomic hydrogen forms on surface and becomes diatomic in solution.
Hydrogen atoms can be absorbed into
materials (Ti and carbon steel couple)
Figure 2.6 – Electrochemical reactions occurring during the corrosion of zinc in air-free hydrochloric acid.
Used by permission, NACE, Corrosion Basics An Introduction, NACE, 1984, pg 28.
Severe crevice attack as well as general
Soot blower metallographic sample
Knife line attack
Transgranular chloride SCC in 316 stainless steel
If your sink at home is a nice shiny chromium plated brass, do not pour your ammonia down this drain and let it sit overnight. It will stress corrosion crack!
PVC/galvanized steel trap drains– go ahead – no problem with ammonia.
Corrosion fatigue, cracks can be oriented the other direction depending on stress state of shaft.
Valve trim diffuser with cavitation
Centrifuge feed nozzle
Look for “comet tails”! Water was flowing from right to left in copper water pipe.
Weld wires as coupons
Electrical resistance probe
R = ρ*l/A
Honeywell’s SmartCET® uses a sensor for background electrochemical noise to detect pitting along with LPR probe and a sophisticated computer program.