With SUSAN WHITWORTH Tait, Ph.D.
Executive Director & CFO,
Pair O Docs Professionals, LLC
Hello, Everyone. We again have a paradox—both docs from Pair O Docs Professionals LLC. are authoring this month’s edition of Corrosion Corner.
Last month, we discussed the structural and cosmetic failure modes possible with refillable multi-use (RMu) packaging. This month we’ll finish the discussion with corrosion, one cause of package failures.
The various news articles on RMu packaging gave Steve a strong sense of Déjà vu. Multiple decades ago, he investigated replacing disposable single-use aerosol containers with RMu aerosol containers. The concept was ultimately not commercially successful due to issues with de-crimping aerosol valves, incompatible cleaning processes and extensive corrosion issues.
As mentioned last month, glass, coated aluminum and stainless steel are the most likely materials for RMu packaging. All three of these materials will corrode. As always, corrosion issues are whether the corrosion rate is low enough for the package to have the desired service life and whether the corrosion rate is low enough that metal ions from corrosion will not adversely affect product performance and efficacy.
Materials research & corrosion testing needed
Glass is brittle and some annual loss is unavoidable from chipping, cracking and breaking. However, glass packages could have longer service lifetimes with proper handling, cleaning procedures and selection of cleaning detergents. For example, our Aristartec FlexiCell electrochemical test cell has both glass and metal components and both types of components are designed to be re-usable. The cells have undergone storage jostling, assembly handling, high temperature washing and interactions with hundreds of different test fluids, such as consumer spray products.
We do lose some of the glass-components each year from chipping and breakage, but none of them experience etching (glass corrosion). Most of our glass-components have been in use for nearly two decades as a result of extensive research and testing on different types of glass and selecting detergents that do not etch glass while cleaning.
All of the FlexiCell metal components have been in use for nearly two decades as a result of extensive research to find metal alloys that are resistant to corrosion by a wide range of liquids and by developing a cleaning process that doesn’t corrode the metal components (which includes non-corrosive detergents).
Common materials in spray & RMu packages
Disposable single use spray packaging and RMu packaging both use stainless steel and aluminum. For example, stainless steel (SS) springs are used in both package platforms for aerosol valves, pumps and sprayers and coated aluminum is also used for both package platforms.
A common myth is that stainless steel alloys (SS-alloys) are corrosion-proof. However, SS-alloys do corrode under various conditions. A common household example is the iridescent blue color inside SS cookware. General corrosion, pitting corrosion, crevice corrosion, weld corrosion, vapor phase corrosion and interfacial corrosion can all affect SS-alloy RMu packaging as well as aluminum RMu packaging.
Consequently, RMu packages need to undergo similar corrosion testing as is conducted on traditional spray packaging. However, the multiple cycles needed for RMu packages requires specific testing protocols expanded beyond those used for disposable single-use packaging to reflect the new conditions of use and the longer service lifetimes.
Corrosion prevention & control for metal RMu packages
Last month, we also mentioned that thicker metals would increase the denting resistance of metal RMu packages. However, thicker metals and thicker internal coatings do not increase stainless steel and aluminum corrosion resistances. The important concept to remember is corrosion compatibility of the metal RMu packages with the:
• Residual product inside the package during storage prior to cleaning and refilling
• Cleaning process (temperature and detergents)
It has been Pair O Docs’ experience that completely different corrosion test protocols are needed when service lifetimes are expected to be significantly greater than the traditional two to five years for disposable single-use packages. In other words, a completely new set of protocols are needed to reduce the risk of corrosion failures when packages are expected to have service lifetimes around a decade or more.
Also, storage stability tests for RMu packages should be conducted for longer times using different protocols. Electrochemical corrosion tests significantly reduce the testing time when the appropriate protocols are used to account for repeated package usage and can be used to screen products for quality control throughout container lifetime.
Corrosion testing should also integrate all the long-term facets of RMu packages, including:
• Revised formulas over the service lifetime of the packages
• New vendors and supply chains during that time
• New cleaning processes over the service lifetime and
• Monitoring for internal coating degradation
New ideas always have new risks. The challenges facing RMu packaging can be overcome with research and properly designed corrosion tests for stainless steel packages and aluminum packages with internal coatings.
Please visit www.pairodocspro.com for more information. Thanks for reading and we will see you in August. SPRAY