Metal Finishing Guide Book

2013

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similar variation of this Mass Loss Corrosion Coupon procedure is described in Paragraph 8.7 of ASTM B368, using nickel coupons for the "CASS" test. CRITERIA FOR CYCLIC TESTS The American Iron and Steel Institute, in cooperation with the Automotive Corrosion and Prevention Committee of the SAE, conducted a study of existing cyclic corrosion tests (completed in 2003, revised in 2007) in order to develop tests that could be used to rank performance of materials used in automotive "cosmetic" applications. Approximately 20 existing corrosion tests were selected for study. These included "static" exposure condition tests (tests where the exposure conditions do not vary over the duration of the test), such as ASTM B117, and "cyclic" exposure condition tests such as ASTM G85 Annex 5 and GMW14872 (formerly GM9540P), (tests which subject test pieces to a variety of different exposure atmospheres and conditions over the duration of the test). Ten different test materials were exposed in each test. The results of the tests were compared to real-world exposure results from 10 sites around the globe utilizing duplicates of the same materials. It was concluded from results that an acceptable corrosion test must: (1) simulate the rank order of performance of coatings in actual service; (2) produce the same type (character) of failure as found in real-world experience (example: blistering); (3) be reproducible; (4) be of relatively short duration; and (5) be feasible and cost effective. The test established as a result of this effort is the SAE J2334 Laboratory Cyclic Corrosion Test. The SAE J2334, GMW14872 (formerly GM9540P), and ASTM G85, Annex 5 meet the above criteria and are some of the more commonly used cyclic corrosion tests in the U.S. and around the Fig. 1. Schematic drawing of a typical salt fog test chamber. world. The SAE J2334 and the GMW14872 were originally developed for testing cosmetic finishes on automotive components. Fortuitously, they have been shown to produce more "realistic" corrosion results and, therefore, are used to test a much wider variety of materials, finishes, and applications. ASTM G85, Annex 5, is known to be particularly useful for testing both: architectural coatings and industrial maintenance paints as well as other applications. TYPES OF TESTS For the purposes of this discussion ASTM B117 is described first. The other ASTM Corrosion Test Standards discussed are described in terms of how they vary from the basic B117 Standard. Only those aspects of these standards, which are different from the B117 standard, will be discussed. 537

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