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 My wife and I love the television ads with the E-Trade Baby.
A line from one ad in particular, where somebody says something exceedingly
obvious and the baby responds, "Let me see your shocked face", has
become a standard around our house. Whenever we come to an obvious conclusion
or see something on TV or in the newspaper that states the obvious, one of us
will say, "Let me see your shocked face." Well, get ready, LET ME SEE
YOUR SHOCKED FACES - air conditioning machines corrode!!
If you wanted to
create a single laboratory device to study multiple types of corrosion you
might start by designing an air conditioning machine - a mechanical device made
from a variety of dissimilar metals, subject to changing moisture and
temperature conditions, frequently located in hostile environments and often
subject to minimal maintenance, cleaning or inspection. In my 30 years of
materials engineering experience in the HVAC industry I've seen general
corrosion, pitting corrosion, galvanic corrosion, fretting corrosion, crevice
corrosion, corrosive wear, erosion/corrosion, stress corrosion, thermal
oxidation and biological corrosion in HVAC equipment. I've seen exotic
materials such as super ferritic stainless steels, titanium, superalloys and
high-nickel alloys fail due to corrosion in a few weeks or even a few days and
I've seen common materials such as plain carbon steel and pure copper survive
for many, many years without any trace of corrosion damage in similar
applications.
Though solving corrosion problems is often viewed more as a
black art than as an engineering discipline, there are excellent tools and
techniques available to address corrosion issues and to solve corrosion
problems. Step wise the process is clear cut:
 Identify the corrosion mechanism.- Understand the environment, both external and internal.
- Understand the equipment - materials of construction,
operating cycles, hours.....
- Identify alternatives - materials, coatings, limiting
operating envelope, changing the environment (water treatment, alternative
lubricants/refrigerants, filter the air, etc.), redesign the machine (better
drainage, eliminate contact of dissimilar metals, .....)
- Implement change.
- Monitor results.
Pragmatically, the process can be difficult. Identifying the
corrosion mechanism is not always easy, gaining knowledge of the environment
takes time and a lot of tedious work, understanding the equipment requires
cooperation from the OEM, identifying alternatives to solve the problem depends
on where/who you are - if you're the OEM you may be able to implement material
or other redesign changes, if you're the user you may be able to influence the
environment, etc., etc.. Regardless of the problems and pitfalls of the
process, corrosion problems can be addressed successfully. Engaging an expert
in corrosion engineering/science can help to make the process go more smoothly and help eliminate those shocked faces.
Editor's Note: CR4 would like to thank PJ Sikorsky of GEA Consulting for contributing this blog entry.
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Re: Say It Isn't True!! - A Real Corrosion Story
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