W. Stephen Tait, Ph.D. Chief Science Officer & Principal Consultant, Pair O Docs Professionals, LLC Corrosion Corner Is corrosion testing needed for derivative products and packaging? 32 Spray June 2016 package/component service life below the target time. Consequently, the corrosion risk associated with hidden/ known formula and package derivatives is the same as the corresponding risk for new formulas and packages. Figure 1 provides the risk associated with pitting corrosion as a function of test length. It demonstrates that risk decreases with time, risk is high at low test times (incomplete tests) and electrochemical tests provide lower risk results after shorter times. Let’s return to the various rationalizations for not conducting corrosion tests on derivative formulas/packages and discuss why these rationalizations are often technically incorrect. The base formula is not corrosive—therefore the derivative won’t be corrosive Whether or not corrosion occurs and how fast it proceeds through a package is determined by the 1) chemical composition of the environment (your formula), 2) the type of package materials and 3) the type of surface treatment on the package metal, such as a coating or laminate film. Changing any of these three factors could transform a noncorrosive formula into a voracious package/component eater. For example, fragrances are often metal corrosion inhibitors. In other words, the base, unfragranced formula is corrosive and the fragrance is actually controlling or Hello everyone. It’s a common marketing strategy to modify a base formula to increase sales for a product or line of products. Formula modifications and line extensions are derivatives. Formula derivatives could include changing or adding new fragrances, surfactants, dyes or pigments, thickening agents and so on. Derivatives also include substituting ingredients with more cost effective ones or ingredients that modify the formula’s performance, plus altering one or more formula ingredient concentrations. Package derivatives include modifying packages and package components, such as changing to an entirely different package material—e.g., going from tinplated steel aerosol containers to aluminum aerosol containers, package/component vendors and package materials—internal container coatings, laminate films and valve coatings. Variability produces hidden derivatives that include varying concentrations of contaminant water in anhydrous formulas, the normal manufacturing variability of formula ingredient concentrations—particularly corrosion inhibitors and fragrances, formula ingredient chemistry variability, and packaging materials variability. Corrosion testing is often skipped when implementing a formula and package derivative. The rationale is typically: • The base formula is not corrosive, therefore the derivative won’t be corrosive • The current and new package/components have identical specifications, therefore the derivatives are also corrosion-resistant • The new or substitute formula ingredients are not corrosive • The changes are small • There’s not enough time for corrosion testing All of these skipping-corrosion-test rationales often lead to unexpected corrosion failures. The May 2016 edition of Corrosion Corner discussed corrosion risk and how the cost for corrosion failures is significantly higher than corrosion testing. Corrosion science is not at the point where first principals can be substituted for corrosion testing to predict if corrosion will occur, where it will occur in the spray package, which package materials will corrode and if corrosion will reduce Figure 1: The estimated risk of pitting corrosion as a function of test length.
Spray June 2016
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