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Increasingly, modern accelerated atmospheric corrosion tests are based on cyclic exposure conditions rather than the continually wet ("constant exposure") conditions of the more simplistic, traditional salt fog tests.

Simplistic salt fog exposure tests, such as the ASTM B117 procedures, have been criticized on the basis of issues such as:

1. Unrealistic test conditions leading to poor correlation with in-service (real world) performance and the question: "How meaningful is the test data ?".
   
   
2. Sample to sample variations, and also variations from cabinet to cabinet.

However, it has also been pointed out that simplistic salt fog testing has proven to be of value in the sense of:

1. It has highlighted shortcomings and advantages of certain corrosion protection schemes - for example, the advantages of increasing the thickness of sacrificial zinc coatings on steel and the beneficial effect of "duplex coating systems" (galvanized steel with an additional paint coating system).
   
   
2. It is widely used and specified in numerous industries.
   
   
3. It has an extensive track record as a quality control tool.

Traditional Salt Fog Tests:

ASTM B117: Standard Practice for Operating Salt Spray (Fog) Apparatus

ASTM B368: Standard Test Method for Copper-Accelerated Acetic Acid-Salt Spray (Fog) Testing (CASS Test)

ISO 7253: Paints and varnishes - Determination of resistance to neutral salt spray (fog)

Cyclic Exposure Tests:

ASTM D5894: Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal, (Alternating Exposures in a Fog/Dry
Cabinet and a UV/Condensation Cabinet)

ASTM G85: Standard Practice for Modified Salt Spray (Fog) Testing - Annex A5, dilute electrolyte cyclic fog dry test

GM 9540P: Accelerated Corrosion Test

SAE J2334: Cosmetic Corrosion Lab Test

References/Literature:

GalvInfo Note #15: "The Salt Spray Test and Its Vagaries.", published at galvinfo.com

J. Guthrie, B. Battat and C. Grethlein: "Accelerated Corrosion Testing", The AMPTIAC Quarterly, Volume 6, No.3., Fall 2002.

"Which Accelerated Test is Best", Problem Solving Forum, JPCL, August 2000, pp.17-28. (comments by various experts)

Links:

ASTM International
www.astm.org

ISO - International Organization for Standardization
www.iso.ch

SAE International
www.sae.org