Aluminum tops or bottoms are used with tinplated steel bodies The corrosion potential of aluminum is often significantly different from the corrosion potential for steel, making galvanic corrosion between these two metals a higher probability. However, the chemical composition of your formula could make the corrosion potential differences insignificant, cause galvanic corrosion of either the aluminum or the steel or inhibit corrosion of both metals such that package service life is not significantly reduced by galvanic corrosion. One might get the impression that galvanic corrosion can be predicted by simply measuring the corrosion potential of the different metals. However, measuring the corrosion potential of the two metals is not sufficient to determine if galvanic corrosion will reduce package service life below the target length. The rate of galvanic corrosion is determined by the chemical composition of the formula and the ratio of the areas for the different metals. Consequently, you need to do corrosion testing to determine if galvanic will occur and the rate of galvanic corrosion is large enough to reduce package service life below the desired target length. We would be happy to teach our Elements of Spray Package (Aerosol Container) Corrosion short course at your R&D facility. We have also introduced the Corrosion Partnership Program, which makes our electrochemical corrosion laboratory, corrosion consulting and anti-corrosion technology conveniently available for your R&D program. Contact: rustdr@pairodocspro.com; 608-831-2076; www.pairodocspro. com. Back articles of Corrosion Corner are available from Spray. Thanks for your interest and I’ll see you in November. Spray October 2016 Spray 25 Galvanic corrosion
Spray October 2016
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