Metal Finishing Guide Book

2012-2013

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in which they may be used, manufacturers and product development personnel now can select an accelerated corrosion test that best suits their particular product and applicable environmental conditions. Table I is provided to give a guide to which ASTM test standard can be used for the representative situations listed. Along with the development of new accelerated corrosion tests ASTM Standards have been developed to give direction and resources for the preparation of test pieces prior to testing and evaluation of post test results. A good example is ASTM D609 Standard Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint Varnish, Conversion Coatings and Related Coating Products. This standard provides guidelines for the preparation of test pieces before they are introduced into the accelerated corrosion test. ASTM Standards: D1654 Standard Test Method for Evaluation of Painted or Coated Specimen Subjected to Corrosive Environments; D610 Standard Practice for Evaluating Degree of Rusting on Painted Steel Surfaces, and; D714 Standard Test Method for Evaluating Degree of Blistering of Paints were developed to provide common standards for analyzing and reporting the results obtained from the corrosion tests and observed on the tested specimens. These standards are summarized below. ISSUES Primary issues that arise when discussing the usefulness of accelerated corrosion tests are comparison to real-world exposures and the consistency of test results. Accelerated corrosion tests are performed under controlled conditions with a limited number of variables, which generally do not duplicate the vast variety of variables that occur in any one location in a real- world environment. Comparison standards can be used to compensate for this. Comparison standards are properly prepared, representative test pieces from a product with a known ���track record��� of exhibiting acceptable performance from exposure in applicable real-world environments and/or also acceptable corrosion resistance after being exposed to the specified accelerated corrosion test(s). They then can be used as standards against which other tested pieces are compared. This process helps especially product developers and also quality professionals predict how a new product or production run of an existing product will perform when used. It is usually not possible, unless additional ���long-term, real-time���, comparative outdoor or ���in-service��� exposure data is available, to directly compare any given number of hours in an accelerated corrosion test with a given number of years exposure in real-world environments. The development of additional variations on basic accelerated corrosion tests have allowed engineers, technicians, and quality professionals to better evaluate durability of products to be used in a wider variety of environments, under multiple corrosive influences, and under constantly changing service conditions. The issues are: consistency in the accuracy of test results from subsequent runs of the same test in a single test chamber; and consistency for comparison of test results obtained from the same test run in other chambers. These issues have been addressed with the development of ASTM methods for evaluating this necessary consistency. This verification is called repeatability of results from subsequent runs of the same test in a single test chamber and reproducibility of results from subsequent runs of the same test in other test chambers (regardless of how many other corrosion test chambers are involved). These important verification procedures are covered in Section X3 of the Appendix of the ASTM B117 test standard and incorporate ���Mass Loss��� Corrosion Coupons described in that section. A sim591

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