Corrosion Corner ello, everyone. There are essentially up to two phases in a spray package: a liquid phase (could be your product plus the propellant) and a gas phase. Spray packages that use liquid propellants have both phases, while spray packages with internal bags typically only have a liquid phase. Spray package corrosion could be one of three general types: general corrosion (sometimes referred to as uniform corrosion), localized corrosion and vapor phase corrosion. The different types of corrosion are often referred to as different corrosion mechanisms. I’m going to provide an overview for each of the three mechanisms. General corrosion General corrosion could occur in either the liquid area of the spray package or in the vapor area. In some instances, general corrosion could be in both areas. General corrosion covers a large area of the spray package interior and removes package metal, coating or laminate film at more or less a uniform rate. General corrosion is typically very slow and does not significantly reduce container and container component service lifetime. However, general corrosion does contaminate the product with metal ions and these ions could adversely affect product efficacy, such as smell and color. General corrosion could also cause large areas of coating or laminate delamination from the package 28 Spray October 2014 W. Stephen Tait, Ph.D. Chief Science Officer & Principal Consultant, Pair O Docs Professionals, LLC What are package cothrer osvaiorin omues chsapnraisym s? H base metal. Pieces of free coating could clog spray valves, thus preventing the package from spraying and reducing package service lifetime. Service lifetimes are defined as the length of time before a spray package leaks product or propellant, valves leak propellant or partially full containers no longer spray. In other words, service lifetime is the amount of time during which spray packages and valves function properly. Localized corrosion Localized corrosion occurs in very small areas and in occluded areas that restrict diffusion into and out of the area. Localized corrosion is different from general corrosion in the following ways: • Localized corrosion is significantly faster than general corrosion and often reduces service lifetime • Localized corrosion is in a very small area • Localized corrosion occurs in occluded areas such as container seams and laminated bag welds—diffusion into occluded areas is restricted and significantly lower than bulk diffusion • Localized corrosion often needs a large amount of surrounding surface area to support the high rate of this type of corrosion
Spray Oct 2014
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