W. Stephen Tait, Ph.D.
Chief Science Officer & Principal Consultant,
Pair O Docs Professionals, LLC
Corrosion Corner
Different types of
Spray Package Corrosion
December 2020 SPRAY 21
Hello, everyone. The internal environment in spray
packages (i.e. your formula) typically consists of multiple
microenvironments and they, plus the package materials,
determine if corrosion will occur and how fast it occurs.
Consequently, spray package corrosion comes in numerous forms,
as illustrated in Figures 1–3 for traditional metal aerosol containers,
spray valves and bag-on-valve (BOV) packages, respectively.
Figure 1: Types of corrosion found in metal aerosol containers.
Figure 2: Types of corrosion typically found on spray valves.
The approximate percentages on the right side of Figure 1 are
the probabilities for corrosion occurring in traditional aerosol
containers. Notice that the percentages add up to more than
100%—this means that multiple types of corrosion are possible
for any given formula/package system.
Figure 3: Types of bag-on-valve (BOV) corrosion.
The types of corrosion are classified under one of two
umbrella classifications:
1. General corrosion, sometimes referred to as
uniform corrosion
2. Localized corrosion such as metal pitting and
coating/laminate film blisters
Corrosion can reduce package service lifetime in one of three ways:
1. Packages leak product or propellant
2. A package ceases to spray when metal corrosion occurs;
loose pieces of coating or laminate film clog the valve
3. Metal ion contamination from corrosion diminishes
product efficacy
Thus, package service lifetime is defined as the filled-package age
when corrosion causes one or more of these failures.
Last month’s Corrosion Corner provided a graph that estimated
the risk of corrosion versus time for different types of both spray
packages and types of corrosion tests. The no-corrosion-data risk
typically ranges from approximately 20%–60% depending on the
type of package.
The old adage “A picture is worth a thousand words” rings
true, so I’m going to provide photos of actual general and localized
corrosion that caused reduced package service life (Note: A.
Caridad, SPRAY Editorial Director, told me this writing style is
referred to as “Zen Writing”).
The graph in last month’s Corrosion Corner also demonstrated
that the corrosion risk from a one-year storage test is approximately
7% for aerosol containers and approximately 4% for BOV