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topic 17163

Corrosion resistance of zinc-dichromate in marine environment


Does anyone here have a good idea on the equivalency between neutral salt spray test (ASTM ASTM B117 [link by ed. to spec at TechStreet] ) and ocean shipping (unwrapped in box) for zinc-dichromate coating on steel substrate? How many hours to white rust is equal to, say 10 weeks on ocean?


Haidong Z [last name deleted for privacy by Editor]
Caterpillar - Peoria, Illinois


There is no real correlation between salt spray hours and hours in shipment on the seas. So the only sure correlation you have to go by is that 10 weeks at sea will be no worse than 10 x 7 x 24 = 1680 hours of salt spray. But that is far more time than a zinc plus dichromate finish is expected to endure in a salt spray cabinet. So, I believe the real answer is that the parts should not be exposed to the environment during transit.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever


There is no direct correlation between the number of hours in salt spray and length of service in the field. ASTM B117 attempts to clarify this in several paragraphs at the both the beginning and end of the standard. The best use of salt spray is as a process control tool. (If a given process lasts x number of hours in salt spray, then doesn't..something is wrong with the process.) Cindy

Cynthia L. Meade
- Sylvania, Ohio, USA

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