Corrosion Corner
A plethora of spray package
corrosion opportunities—
Part 1
Hello everyone. How a spray package is constructed, its
materials of construction and the chemical composition
of a formula all interact to determine if corrosion
will occur and how fast the corrosion will proceed to degrade the
package materials. The rate of corrosion, in turn, determines if
corrosion will cause package failure and the length of spray package
lifetimes.
Spray packages are typically multi-component systems that have
multiple microenvironments inside each type of package. The
type of corrosion in each microenvironment is often significantly
different from the corrosion in the other microenvironments
because the:
• chemical composition of the microenvironment is often
different from the chemical composition of your formula
• different types of microenvironments often have different
chemical compositions from other microenvironments
W. Stephen tait, ph.D.
Chief Science Officer & principal Consultant,
pair O Docs professionals, LLC
• probability of corrosion in a microenvironment is different
for each different type of microenvironment
• corrosion rate in each microenvironment is governed by the
chemical composition of the microenvironment
Figures 1–3 illustrate the different microenvironments in aerosol
containers, bag-on-valve (BOV) packages and aerosol valves,
respectively.
Figure 1 illustrates the type of microenvironments that are
inside traditional aerosol containers. A cut-away for aluminum
containers is on the left photograph and a cut-away for steel containers
is on the right.
Aluminum refillable, multiple use (RMu) packages are similar
to the aluminum aerosol container on the left of Figure 1 (sans
the aerosol valve) and steel RMu packaging is similar to the steel
aerosol container on the right (also sans the aerosol valve, plus the
top and bottom double seams are sometimes replaced with welds).
Figure 1: A diagram of aerosol container microenvironments
28 Spray October 2019