November 2013 Spray 23 Variability in manufacturing processes could alter corrosivity or corrosion resistance Variability of your formula compositions and the materials used for your spray packages always occurs. Some of the more common sources of formula and package variability are: • Formula ingredient concentrations • Sporadic contamination • Laminate film and internal coating variability • Container and valve metal chemical composition variability (rare) • Sporadic physical defects in container and valves (rare) Different metals have significantly different corrosion resistances with the same environment Spray package metals could be tinplated steel, tin-free steel and aluminum. The number of polymer materials for spray packages is larger and many of these package materials are changing to address environment and regulatory issues. None of these materials is corrosion resistant to all types of spray formulas. For example, aluminum generally is more corrosion resistant to corrosion by low pH formulas than steel. The opposite is generally true for high pH formulas. In summary, spray package corrosion complexity is caused by a large number of factors and makes it difficult to predict a) if corrosion will occur, b) where corrosion will occur and c) how fast corrosion penetrates the package metals and grows through a laminate film or internal coating. Consequently, corrosion testing is needed to determine when corrosion will be an issue for a given spray packageformula system. SPRAY Please send your questions/comments/suggestions to rustdr@ pairodocspro.com. Back issues of Corrosion Corner are available on CD from ST&M. Thanks for your interest and I’ll see you in December.
Spray November 2013
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