Can you explain ASTM B 117-90 salt spray (fog) testing?

First of three simultaneous responses --

A. Hi Sandy,

ASTM B117 is a standard that describes all of the details on how to conduct a salt spray test. I suggest to obtain a copy of the standard; you will find the answers to your questions there.

Second of three simultaneous responses --

A. Hi Sandy,
ASTM B117 is a document that describes how to run a salt spray cabinet. It describes pH, specific gravity, collection rate, flow rates, temperatures, pressures, etc. -all of which are associated with the proper maintenance of a salt spray cabinet.

What it does NOT tell how long any part should last in salt spray, nor does is tell what is considered a passing test. Those parameters are set by you, if you are the company whose products are to be tested.

Third of three simultaneous responses --

A. Hi Sandy!

ASTM B117 is a document, available from ASTM International, (formerly the American Society for Testing and Materials) that gives 10 pages of instructions on "How To Run A Salt Spray Test". Ten pages is a lot to try to fit into a paragraph answer, so the best I can do for you is urge you to buy the document from ASTM, who can be found on the web at www.astm.org.

Now, B117 does NOT give accept/reject criteria: it merely tells how to do the testing. Hence it won't say how long to test for, nor how thick your zinc plating must be to pass, nor whether it needs to be chromated or not, etc. It is just "How To Run A Salt Spray Test", nothing more.

Good luck!

First of two simultaneous responses --

A. "-90" indicates that it was last revised in 1990.

Second of two simultaneous responses --

A. Hi Sandy,

The "-90" indicates the year that the standard was revised. In this case, it would have been 1990.

A. Hi Rodney,

There really aren't many visual aids to help with this fog test (not that I know of at least). However, visual inspection is often more than enough. The end-point of the test is often user-driven. Some examples are:
a) first sign of white rust (when testing effectiveness of zinc coatings)
b) first sign of red rust (lets you know that the iron in the product is corroding which can be used as a failure limit)
c) 5% red rust which often can be considered to compromise the strength of the material in question.
It depends really.

Hi Sunil. I would expect 10 hours per day to be more severe because the parts will be in the test chamber for 2.4X as many days.

But regardless of what you think or I think, tests don't have any merit if they include uncontrolled variables. This is just food for thought, not a scenario I fully embrace, but consider:

We already know that salt spray testing is a poor way of comparing one type of coating against another type of coating because it doesn't take real world corrosion mechanisms into account. For example, galvanizing is the most proven of all finishes, with real-world structures that have been protected for a hundred years in bad conditions ... yet galvanizing performs poorly in salt spray testing. It performs poorly because real world protection by galvanizing depends upon the formation of tough zinc carbonate corrosion products which develop in the open air as the result of interaction with carbon dioxide, but cannot develop in a closed chamber. If we now open the chamber every day, letting carbon dioxide laced air in, what has happened? Have we given galvanized finishes the fresh air they need? Probably not, but who knows?

Regards,