Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 304 of 331

EVALUATION OF RESULTS Some primary ASTM Standards that have been developed to assist in the evalua- tion of corrosion test results are ASTM D 1654 — Standard Test Method for Eval- uation of Painted or Coated Specimen Subjected to Corrosive Environments; ASTM D 610 — Standard Test Method for Evaluating Degree of Rusting on Paint- ed Steel Surfaces; and ASTM D 714 — Standard Test Method for Evaluating De- gree of Blistering of Paints. Other standards are also available for evaluation of spe- cific materials and finishes. ASTM D 1654 is used for the evaluation of substrates, pretreatments, coating systems, or a combination thereof. This standard is used when the coating has been scribed prior to exposure to the corrosive environment. ASTM D 1654 rec- ommends a straight-shank tungsten carbide tip or equivalent scribing tool to pro- duce a cut through the coating to the substrate of the test piece. The scribe serves as a deliberate failure of the coating system prior to corrosion testing. Once the test piece has been through the selected accelerated corrosion test it is then cleaned by rinsing with a gentle stream of water at 45°C (110°F). Loose coat- ing is then removed using compressed air to blow it off or a scraper to scrape it off. The creep back (distance of failure) of the coating is measured and the rat- ing system applied described in the standard applied. ASTM D 610 provides a series of photographic reference standards that demonstrate degrees of rust on the surface of a test piece. The test pieces are first gently cleaned then the amount of rust observed is compared to the pho- tographic standards. It is important to compare only rust and not surfaces stained by rust. ASTM D 714 is used to evaluate coating adhesion by observing the amount of blistering that has occurred. The test pieces are first gently cleaned then com- pared to a series of photographic references. They are graded first by the size of the blisters that appear on the surface and then the number of blisters that ap- pear. CONCLUSION The corrosion tests discussed in this article demonstrate some of the advance- ments in accelerated corrosion testing and complexity of the subject. They also provide a solid basis for evaluating the performance of a wide variety of products and materials. These standards were developed through a cooperative effort be- tween the ASTM International, industry, government, and other trade organi- zations worldwide. BIBLIOGRAPHY ASTM "Technical & Professional Training" manual, version 1.4, Corrosion Testing. Organic Finishing Guidebook and Directory Issue, 99(6A);596–602; 2001 303

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