Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr
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CORROSION New Technologies Combat Corrosion With a vast selection of coatings and other protective products available in the market and new, higher-tech solutions on the way, mine operators can choose from many effective weapons to blunt the attack of a relentless chemical enemy By Russell A. Carter, Managing Editor Given the nature of the business, the twin forces of corrosion and abrasion are almost constant companions in mining operations. The typical extraction sequence of blasting, loading, hauling, crushing and grinding chunks of raw dirt and rock—often under harsh environmental conditions— basically constitutes an informal demonstration laboratory for the mechanisms of material destruction at thousands of mines around the world. And, since few locations have exactly the same geological, environmental, structural or operational characteristics, the struggle to combat damage to infrastructure and equipment from corrosion is generally a localized battle. The site-specific nature of corrosion problems and solutions may be the reason why estimates of the annual cost of corrosion in the mining industry vary widely. The actual cost figure may not be critically important, but it's high; a 2001 report from the U.S. Federal Highway Administration, for example, estimated that the overall annual cost of corrosion to critical sectors of U.S. infrastructure was more than $150 billion. More recently, a study by the National Association of Corrosion Engineers (NACE) pegs the total annual cost for organic and metallic protective coatings in the U.S. alone at $108.6 billion. The NACE's technical literature suggests that no material is resistant to all corrosive situations but materials selection is critical to preventing many types of failures. Factors that influence materials selection are corrosion resistance in the environment, availability of design and test data, mechanical properties, cost, availability, maintainability, compatibility with other system components, life expectancy, reliability and appearance. Appropriate system design is also important for effective corrosion control, and includes the consideration of many factors such as materials selection, process and construction parameters, geometry for drainage, avoidance or electrical separation of dissimilar metals, avoiding or sealing of crevices, corrosion allowance, operating lifetime, and maintenance and inspection requirements. The bottom line: Experts believe 50% of all corrosion costs are preventable, and Proper surface preparation is probably the most important factor affecting the total success of surface treatments for corrosion protection. 50 E&MJ; • FEBRUARY 2013 approximately 85% of these fall within the area of coatings. Industry vendors such as Sherwin Williams Protective & Marine Coatings, Akzo Nobel's International Paint, Dulux Protective Coatings and others supply a steady stream of new and improved anti-corrosion coating products each year, and many of these can be remarkably effective and long-lasting—if they are applied correctly, on a surface that has been properly prepared. Test, Treat and Finish Phoenix, Arizona, USA-based ChlorRid International points out that protective coatings designed for steel, for example, perform best when applied to a salt-free, clean surface. If the steel is coated before any one of a number of harmful soluble salts is removed from the surface, corrosion and premature failure of the coating are likely. Left unchecked, salt contamination corrodes deep into the substrate, making future decontamination even more challenging. For this reason, a number of industrial and military organizations have established tighter limits for acceptable soluble salt content on surfaces prepared for coating. ChlorRid has developed two salt testing kits: its ChlorIon Meter is a hand-held digital testing device that electronically measures chloride with an internal ion-specific electrode; ChlorTest is a complete system that the company said will allow even inexperienced inspectors to obtain accurate results. Once tested, surfaces can be cleaned by applying ChlorRid's salt removal product. Products and methods to test and remove salt contaminants are available from a variety of sources. However, not every coating installation can take place under ideal conditions, and for that reason Sherwin-Williams added a new product to its Macropoxy family of high performance coatings—Macropoxy 80, a high-build HAPs-free epoxy formulated for application over marginally prepared steel substrates and damp surfaces. The coating, according to the company, comwww.e-mj.com