What is the best simulation of atmospheric corosion?

ASTM B 117, "Method of Salt Spray (Fog) Testing"

AKA 1000-hour salt spray test. This will probably have to be sent out to do. Had this done on some aluminum samples coated with powder coat and various other flavors as well as a bare test piece. All that was left of the bare test piece after 50 hours or so was the part in the clamp. This involves hot salt water and UV light, probably a good simulation of driving conditions in parts of the snow belt and along the coast, accellerated, of course. The epoxy powder coat made it through with only a little nibbling at the edges where the stuff was thin. Polyester was worse, chewed the corners off and was working away at the edge centers. NONE of the conversion coatings lasted more than 100 hours..

Stan

Salt will make otherwise acceptable treatments fail. Cor-ten is the steel that is left unpainted.

I ran this test by surface-grinding steel scrap to get a clean oil- free surface, applying patches of several spray-on preservatives, then leaving it out under the gutter downspout. The roof concentrates at least some of the pollution in the air so I think that was an intensified but accurate test of rust in this area. The result was that LPS-3 lasted the longest, around 6 months, and I bought a few gallons. In less severe places it lasts 2-3 years for me, about as advertised. There are still a few unrusted spots on the bare machined steel of my front end loader, which has been outside (covered) for 4 years and used on snow that contains road salt. I use the other, cleaner sprays on my basement machines and tools.

If you have a lot to protect the pump spray bottle and bulk refills are much cheaper than spray cans and you can dilute the thick product with kerosine so it wicks into threads and cracks and rust pits better. I bought what the local MSC store had in stock; you might find something better where you are.

We ran a similar test in a materials science course in college. Strips of steel were left immersed in tap water, sodium hydroxide, and zinc chromate solutions. The water rusted its strip in a day, the lye in 2 weeks, the chromated strip stayed shiny all semester.

Military rifles were oxidized to iron oxide or phosphate and oiled. They are a very severe application because they have precision bearing surfaces that are exposed to salt water, rain and sand and a failure is fatal. The Springfield Armory test was to leave prototypes on the roof for a few weeks. The climate here is often very humid, currently

91%. In a drier climate phosphate + oil protects for a very long time. The oil was butter, not mentioned in this article: Supposedly the best protection for steel is an etching primer and automotive paint. I repainted the rusty bumpers on my truck that way about 10 years ago and haven't seen any rust. More recently I tried brush-on zinc paint on the bed fenders; the top coat didn't adhere well and some rust shows.

There are several anti-corrosion greases available for moving wear surfaces that you can't paint. LPS-3 dries to a thick wax rather than a good grease. LPS used to sell LPS-100 which was a better lube but I haven't seen it in years. I have enough and haven't tested the others.

I like the spray-can chain lube for motorcycles and garden equipment. The industrial stuff with graphite or moly is effective but hard to wash off clothing. Lubriplate marine trailer bearing grease works pretty well, too.

Jim Wilkins