Written on: January 1, 2025 by W. Stephen Tait
Hello, everyone. One of the most frequent questions that I’m asked is, “When is corrosion testing required for spray packaging?”
Spray packaging corrosion risk without corrosion testing or a comprehensive company corrosion database is approximately 62% for aerosol containers and approximately 20% for laminated metal foil packaging.
Therefore, high risk comes with no corrosion testing. Consequently, your best defense against spray product failures and litigation from unexpected corrosion is a complete and robust corrosion testing program. I recommend that corrosion tests be conducted on:
1. New products: Corrosion science is not advanced enough at this time to use first principles to determine if a formula’s chemical composition is or is not corrosive toward various types of spray packages and how fast corrosion penetrates and degrades package materials. Consequently, corrosion testing is needed to avoid a high risk of in-market failures.
2. Derivatives of existing products (line extensions): Small changes to the chemical composition of a formula could transform a benign formula into a spray package-eater. Thus, derivative formulas (or line extensions) should be tested for corrosion compatibility with the chosen spray package, no matter how small the changes to the formula.
3. All new and derivative insecticide formulas: Insecticide chemicals are often electrochemically active and thus corrosive toward spray packaging. Insecticide formulas also typically need a corrosion inhibitor to prevent or control spray package corrosion.
4. When developing a corrosion inhibitor: Corrosion testing is needed to develop a suitable inhibitor for a corrosive formula. Corrosion inhibitors typically have an effective concentration range, so corrosion testing is also needed to determine the effective inhibitor concentration range.
5. Anhydrous formulas and derivative anhydrous formulas: Anhydrous formulas are typically contaminated with small amounts of water, which is electrochemically active toward package metals; plus, water degrades polymer coatings and laminate films. Consequently, corrosion testing on anhydrous formulas is needed to determine if the formula is corrosive and if there is contaminant water concentration, below which package corrosion does not occur.
6. New and derivative low pH formulas: pH is the negative log of hydrogen ion concentration in moles per liter. Hydrogen ions are electrochemically active and cause corrosion of spray package metals and metal foils. Consequently, low pH formulas should be tested for corrosion with all types of spray packages.
7. New and derivative high pH formulas: High pH formulas can also cause spray package corrosion. Thus, high pH formulas should also be tested for their corrosivity toward packaging.
8. Changes to an existing formula’s chemical composition: Small changes to the chemical composition of a formula could transform a benign formula into a spray package-eater. Thus, any change to the chemical composition—no matter how small the change—should be tested for corrosion.
9. Changing package materials for existing formulas: Changes to package materials could include different types of polymer coatings or laminate films, different coating thicknesses and different package metals. The chemical composition of a formula determines if a given type of package material is resistant to corrosion. Thus, corrosion tests should also be conducted when switching package materials.
10. Changes to raw material suppliers for existing formulas: The chemical composition of raw materials from different suppliers might be different. Consequently, corrosion testing should also be conducted when changing raw material suppliers.
11. Changing surfactant suppliers, types and concentrations for existing formulas: Surfactants make a surface more or less susceptible to wetting by formula ingredients, formula-water and contaminant-water. Thus, corrosion testing should be conducted when changing the type of surfactant, its concentration or a surfactant supplier.
12. Changing fragrance types, fragrance suppliers and fragrance concentrations: Many fragrances offer some modicum of corrosion inhibition. There are also a few types of fragrances, such as those incorporating vanilla, that often cause corrosion. Consequently, changes to the type of fragrance, fragrance suppler and fragrance concentration in a formula should be tested for changes in corrosion.
Unexpected spray package corrosion can be very costly and disruptive of product development programs. It is also extremely costly when in-market corrosion failures disrupt product manufacturing. Indeed, the cost of unexpected corrosion typically significantly exceeds the cost for corrosion testing. Consequently, the answer to the “when-to-test-question” is—formula-package corrosion compatibility tests should be conducted on virtually every:
• New and derivative formulas
• Substitution of formula ingredients
• New formula ingredient supplier
• Change of ingredient concentration
• New package materials
• New package component supplier
Thanks for your interest and I’ll see you in February. Contact me at 608-831-2076; rustdr@pairodocspro.com or from our two websites: pairodocspro.com and aristartec.com. SPRAY
