W. Stephen Tait, Ph.D.
Chief Science Officer & Principal Consultant,
Pair O Docs Professionals, LLC
Corrosion Corner
Managing spray
package corrosion risks
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
rustdr@pairodocspro.com; or from one of our two websites
www.pairodocspro.com and www.aristartec.com. Spray
Figure 1: Estimation of the corrosion risks for spray packaging.
28 Spray January 2021