Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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testing ACCELERATED CORROSION TESTING BY RAYMUND SINGLETON SINGLETON CORP., CLEVELAND Accelerated corrosion testing of metals and coatings was first developed in the late 1890s and early 1900s for testing products to increase their useful performance and service life. This method of testing the corrodibility of ferrous and nonfer- rous metals and organic and inorganic coatings has since been improved and vari- ations added to better test new materials and how they may with stand a wider range of real world environments. Accelerated corrosion testing has also evolved from providing information to help determine durability of products and qual- ity assurance to use in product research and development. Professional trade, industry, and standards organizations, such ASTM Inter- national, the Society of Automotive Engineers (SAE), the Federation of Soci- eties for Coatings Technologies (FSCT), and others, have developed a number of accelerated corrosion tests to meet the demands of changes in technology, ma- terials, and other performance requirements and environmental regulations. For instance, water-based coatings have been developed as a response to envi- ronmental concerns. Some powder coatings and their application methods re- duce the use of solvents and ease application. In addition, the automotive industry has improved coatings and increased the number of surfaces coated as part of the response to market pressures for longer warranties. Some of the more widely used tests are the ASTM Standards detailed in this article, General Motors GM9540P, and SAE J-2334. There are many other tests in use; however, those mentioned also exhibit wider applicability and versatility and are, therefore, some of the more popular procedures. No single test is dom- inant because of the wide variety of industries and specific issues such as various materials, applications methods, properties, and varying surfaces. Other con- siderations include the multitude of environments and customer demands faced by a product and industry. A variety of standard tests has been developed to ad- dress these issues. One of the first ASTM accelerated corrosion tests developed was ASTM B117 Operating Salt Spray (Fog) Apparatus. Early development was initiated in order to evaluate the corrodibility of metals and coatings in a marine or "near shore" environment. As corrosion testing was increasingly used to evaluate product quality and materials used in product development, variations on the basic stan- dard have been added to increase its usefulness for a wider range of environ- ments and materials. This process has resulted in the development of the accel- erated corrosion tests to be discussed in this article. The usefulness of testing coatings for resistance to water as a good indicator of their service life resulted in the ASTM D 1735 Standard Testing Water Resis- tance of Coatings Using Water Fog Apparatus and the ASTM D 2247 Standard Testing Water Resistance of Coatings in 100% Relative Humidity. Demand for im- proved evaluation of decorative copper/nickel/chromium or nickel/chromium coatings on steel, zinc alloys, aluminum alloys, and plastics designed for severe service resulted in the ASTM B 368 Standard The Copper Accelerated Acetic Acid-Salt Spray (Fog) Test. Additional needs for testing of product resistance to harsh industrial environments led to the development of the ASTM G 85 291

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