Metal finishing Q&As since 1989

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Accelerated corrosion testing via saltwater immersion

I have a 50 GAL tank heated to 120 Deg What is the Acceleration rate? time wise (ie) One month in my tank = how many month's, years in normal condition's? I have 30 lbs of Sea Salt to 50 Gal water, and a prop that circulates the water around?

Is there some kind of online chart or conversion table available?

Jerry Hall
instruments - San Diego, California
2005

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First of two simultaneous responses --

As has been stated hundreds of times at this site, NO!

James Watts
- Navarre, Florida
2005

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Second of two simultaneous responses -- 2005

Sorry Jerry, it doesn't work that way.

There is no way an accelerated test can accurately predict real-world results; there are too many factors, and the very nature of the accelerated test requires that some of those factors (such as time) are artificially changed in the hope that compensating factors (salinity, pH, etc.) will make up for them.

Accelerate testing is best used as an indication of process stability and/or whether or not a new process is set up correctly (for example: if coating x normally lasts 96 hours in salt spray and yours lasts 10 hours, something isn't quite right). Trying to say x months = y years would be a sketchy proposition at best, and even if you correlated your test results to real-world results and developed such a formula it would only hold true in the specific environment you were in (including location; sea water at one port is not identical to sea water at a different port).

Probably your best bet would be to find out what tests your competitors are doing and how well their products seem to hold up; benchmark off that and go with it.

Good luck.

Jim Gorsich
Compton, California, USA

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You might want to refer to letter #3010.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2005

Thanks guys I think I'll just let them go and see which one fails first.

Jerry Hall
instruments - San Diego, California
2005

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September 2009

Hi, Jerry. That's fine, but it's not the heart of the problem -- because the one that fails first in your test may be the one that would last longest in real life :-(

An example is galvanized coatings: over time, in real life, they form exceptionally corrosion-resistant complex carbonate coatings, and galvanizing is known to last 60 years and even more in actual service. But galvanized coatings perform poorly in accelerated tests where there is no opportunity for these products to form. On the other hand, a paint might last thousands of hours in accelerated testing, and not last even that long in real life where scratches can occur on the first day.

As Jim Gorsich noted, accelerated corrosion testing is a quality control measure: if a particular coating lasts about xxxx hours each time it's tested, and then suddenly it lasts only one third that long, something went wrong in the process. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey