Written on: April 1, 2019 by W. Stephen Tait
Hello, everyone. Spray package corrosion is typically not at the forefront of most people’s thinking. However, everyone on a metal spray package development team should tacitly know there is always a risk of spray package corrosion and that corrosion could wreak havoc on product introduction timetables or cause an expensive product recall.
I’m going to share some guidelines on how to minimize spray package corrosion risk when formulating new spray products or derivative line extensions from existing products and qualifying packaging for spray products. The guidelines are categorized:
1. Formula chemistry
2. Corrosion inhibitors
3. Spray packaging components
4. Good corrosion test practices
5. Company corrosion knowledge
1) Formula chemistry
Corrosion is a synergistic relationship between all of your formula ingredients, the type of spray package and the physical form of the formula (e.g., water-out or oil-out emulsion, single phase product, etc.). Hence, don’t assume:
• That a given formula is not corrosive just because individual ingredients by themselves are not typically corrosive;
• That small changes in the chemical composition of your formula won’t affect spray package corrosion;
• That formula raw materials from different vendors have the same corrosivity or non-corrosivity;
• That packaging components from different vendors have the same corrosion resistance
Raising pH is not a sure-fire way to reduce spray package corrosion. It is important to note that some propellants might contribute to or cause spray package corrosion and the amount of contaminant water determines if an anhydrous formula is or is not corrosive.
2) Corrosion inhibitors
Corrosion inhibitors are often the most effective and cost-effective way to control and prevent spray package corrosion. However:
• No single type of corrosion inhibitor is effective with all formula chemical compositions;
• Corrosion inhibitors have effective concentration ranges;
• Corrosion inhibitor concentrations outside of the effective range often cause severe spray package corrosion
Raising pH is not a sure-fire way to reduce spray package
corrosion…
3) Spray packaging components
• Spray package components from different vendors might not have the same corrosion resistances to a given formula;
• No individual type of spray package will resist corrosion by all possible types of formula chemical compositions—aluminum containers are not universally more corrosion- resistant than steel containers, and vice-versa;
• Internal polymer coatings for aluminum and steel aerosol containers won’t prevent container corrosion by a corrosive formula;
• Laminate films on metal foils and aerosol valves also won’t prevent container corrosion by a corrosive formula;
• Thicker internal polymer coatings typically don’t prevent container corrosion by a corrosive formula
4) Good corrosion testing practices
There are two generic types of corrosion tests: constant temperature storage tests and electrochemical corrosion tests. Corrosion testing on spray packaging is essential with new products and derivative line extensions for existing products. Not conducting corrosion testing has the following approximate risks:
• 62% corrosion risk for metal packaging, such as aerosol containers and laminated aerosol valves;
• 20% corrosion risk for laminated metal foil bags with attached aerosol valves
My guidelines for good corrosion testing practices are:
• Don’t rely on temperature to accelerate spray package corrosion;
• Low time storage test data has a high risk, for example:
o Three months of testing has an approximately 31% risk
o Six months of testing has an approximately 16% risk;
• One year of constant temperature storage corrosion testing provides lower risks of approximately 3% and 7% for laminated foil bags and aerosol containers, respectively;
• The number of samples for corrosion tests and periodic storage test container examinations also determines the magnitude of risk—in other words, testing and examining more samples reduces risk. For example:
o Examining one or two containers has essentially no statistical confidence and a very high risk
o Examining three containers has an approximately 50% statistical risk;
• The length of a corrosion test can be significantly reduced (less than three months) with a high level of empirical confidence (greater than 99%) with the Aristartec electro- chemical test technology;
• Electrochemical corrosion testing can also be used to significantly reduce corrosion test times with low risk for derivative line extensions of existing products;
• Electrochemical tests can be integrated with corresponding storage tests to increase statistical confidence, reduce the testing time needed for commercial introductions of new products and line extensions and reduce the number of storage test samples
5) Company corrosion knowledge
• An extensive company corrosion database typically reduces risk, particularly when the database is actively maintained and used;
• A company corrosion database could also reduce corrosion test times, particularly for line extension derivatives to existing products;
• An extensive company corrosion database can also be integrated with storage testing and electrochemical corrosion testing to provide a high level of confidence with a corresponding low risk
These guidelines evolved from decades of corrosion R&D. The guidelines are dynamic, so they will improve and their numbers will increase with advances in corrosion engineering and science.
Please visit both pairodocspro.com and aristartec.com to view a Vision Video that explains our advanced Aristartec technology for measuring and preventing spray package corrosion, respectively, and developing corrosion inhibitors. Thanks for reading and I’ll see you May. SPRAY
