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Corrosion Special Topical Papers

ASTM D5894-96 Practice for Cyclic Salt Fog/UV Exposure of Painted Metal

Extensive research work on the effect of condensation and UV radiation led to the incorporation of UV radiation and condensation cycles into the cyclic salt spray test. The improved simulation of natural atmospheric conditions is found in the ASTM D5894. Basically, the procedure involves the following:

• One week's fluorescent UV-condensation cycle (168 hours) as per ASTM G53 with 4 hours of UV exposure at 60^oC using UVA-340 fluorescent lamps and another 4 hours of condensation (pure water) at 50^oC
• After one week, transfer the samples to a cyclic salt fog chamber and expose for another week  as per ASTM G85 Annex 5.
• After one week, transfer the samples back to the fluorescent UV chamber and repeat for a total of four or twelve 2-week cycles, giving a total test duration of 1344 to 4030 hours.

Although this test is currently the most "realistic" laboratory test available for evaluating the coating performance, there does not exist a magic conversion factor where X hours of laboratory exposure is equivalent to Y years of actual weathering in service condition. If one considers the fact that the duration for a full scale test requires over 4000 hours (about 6 months) and two sets of salt spray equipment, not many companies may be able to justify the high cost and the long wait for running such an "accelerated test". This is particularly true for in-house quality control/assurance applications where rapid response to a process change is required.

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