Managing spray package corrosion risks

Written on: January 1, 2021 by W. Stephen Tait

Happy New Year—I hope everyone is healthy and safe and that this year will see the end of the COVID-19 pandemic with a restart and stabilization of the global economy.

All enterprises involve risk; the challenge is to manage risk by reducing it to a level that allows the enterprise to perform its function in a safe and efficacious manner. Products that use spray packaging are no exception.

Both metal and polymer package components have a risk of corrosion. Hence, corrosion risk should be at the front of the R&D process as the economy begins to recover from the pandemic with resumption of paused programs for new/derivative (line extension) spray product development. Indeed, corrosion testing should be an integral part of the suite of tests used to qualify new/derivative products, such as microbial challenge tests, toxicology tests, consumer preference tests, etc.

One or more risk factors could either cause package corrosion or be caused by package corrosion. Hence, spray package corrosion testing is a tool to manage and minimize risk.  The actual risk for each product should be evaluated by personnel who specialize in risk assessment.

How much risk is acceptable?
There are no standards for risk levels, hence each company determines what level of risk is manageable/acceptable for its products, including consideration for the complexity/diversity and the range of uses for a given product.

Figure 1 provides estimation for risk of both traditional metal aerosol containers and metal containers with internal bags. The graphs in Figure 1 are based on corrosion found in commercial spray packaging for aluminum, tinplated steel (ETP), tin free steel (TFS), stainless steel (used in spray valves) and metal packages with internal laminated foil bags.














Notice in Figure 1 that the risk of corrosion is high with no corrosion testing (approximately 62% for traditional aerosol containers and 20% for metal packages with internal bags) and decreases with time. In other words, as the knowledge increases on how a given formula affects the corrosion of its package, the risk decreases.

Notice also that the risk for traditional spray containers and those with internal bags is not zero after one year of storage stability testing. Indeed, the risk after one year of stability testing is approximately 7% and 2% for traditional aerosol containers and containers with internal bags, respectively. Please note that the actual one-year risks in Figure 1 would be significantly higher if the wrong test parameters are used, such as insufficient number of replicate samples for each examination or using a higher temperature to accelerate package corrosion.

Notice also in Figure 1 that an electrochemical corrosion test can produce risks below 1% in a significantly shorter time than a traditional storage stability test. However, as with a storage test, the actual risks could be significantly higher if the wrong test parameters are used.

Consequently, one should start corrosion tests at least one year prior to the target commercial manufacturing date for a new spray product or a derivative of a base product when storage stability testing is used to assess the corrosion risk for a spray product with its package. Electrochemical corrosion tests that use the appropriate test parameters and data analysis protocols significantly reduce the time for corrosion risk assessment.

Assuming package corrosion will not occur in a new or a derivative spray product means one accepts a high risk, leading to package corrosion that could cause one or more of the following:
• Spray packages that leak and cause property damage or personal injury
• Spray packages that cease to spray
• Spray products that are no longer efficacious
• Spray products that are discolored by metal corrosion
• Microbial product degradation

In other words, ignoring corrosion risk or assuming there will be no risk might lead to surprise corrosion that results in an expensive recall (most likely with government involvement), litigation and souring the market for a specific type of spray product.

Thanks for reading Corrosion Corner and I’ll see you in February. You can contact me at 608-831-2076 or; or from one of our two websites and SPRAY