Metal finishing Q&As since 1989

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ASTM B117 24 hour salt spray test = 10-15 years in environment?

 

Is there documented transference rate in regards to: 24 hours salt spray test ASTM B117 is equivalent to 10-15 years for 304 Stainless Steel? Where do I find this information?

Teresa Burnine
- Shelbyville, Indiana

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Unfortunately, you'll find that information in the graveyard of discarded ideas, Teresa :-)

There is no correlation at all because the corrosion mechanism is fundamentally different. Salt spray testing is merely a "screening" test to help indicate that a process has not gone south. It's best used as an ongoing QA test.

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

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I concur with Ted. Should you want a published reference, check out almost any volume of NACE's journal "Corrosion", which often has articles lamenting the lack of good correlation between test data and reality. Yet another is ASTM Cyclic Corrosion Cabinet Testing [affil link on Amazon], ASTM STP 1238, 1995. Good luck!

Lee Gearhart
metallurgist - E. Aurora, New York
 

Teresa - If you refer back to ASTM B117, there are several paragraphs which indicate that there is no direct correlation between salt spray and real world performance. New tests are being developed within the automotive industry that provide some correlation to outdoor exposure but they are relatively new and the correlation is still limited.

Cynthia L. Meade
- Sylvania, Ohio, USA
 

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As everyone else said, that correlation does not exist. Many have tried to come up with better tests, but not a one correlates. GM, Chrysler, and Ford use long 6-month vehicle durability tests and claim that they correlate to real life, but I am still skeptical.

However, you should try and pick a salt spray standard that is in the ballpark. 24 hours to red rust seems a bit weak if you want your part to last 10-15 years. I'd at least expect 150-500 hours if you seriously expect that type of part life. The environment around the part also matters. If the part will see physical damage, heat, water, and/or salt, you may want to beef up your finish and your salt spray requirements.

Tim Neveau
Rochester Hills, Michigan