W. Stephen Tait, Ph.D.
Chief Science Officer & Principal Consultant,
Pair O Docs Professionals, LLC
Corrosion Corner
Is corrosion testing
cost-effective?
Hello everyone. In February, I started a two-part discussion
on whether or not corrosion testing is cost-effective.
The objectives for corrosion tests—corrosion risks as a
function of test time/completion—were discussed. I also mentioned
that storage tests and electrochemical tests have several
common parameters and that using inappropriate parameters
invalidate results from both of these tests.
In this issue, I’ll complete the discussion with a few details on
electrochemical corrosion testing and an example of how much
an unexpected corrosion incidence might cost.
Not all types of electrochemical
corrosion tests are the same
One can conclude that skipping corrosion tests and abbreviated
corrosion tests are risky based on Figure 1.
Electrochemical corrosion tests are completed in 1/4 of the
time or less than the time needed to complete a corrosion storage
test. Electrochemical tests are shorter because sensitive instruments
are used to detect and measure corrosion instead of the
human eye.
The risk associated for electrochemical corrosion tests in
Figure 1 is less than 1%. This risk is based on the correlation for
the proprietary Aristartec system, developed from two decades of
direct comparisons between almost 1,000 tests and the corresponding
36 Spray March 2020
actual corrosion for commercial spray packages.
I’m not aware of any correlations for other types of electrochemical
corrosion tests. For example, the American Society
for Testing & Materials (ASTM) procedures for electrochemical
corrosion tests provide information about variability, but not
correlations between predictions from the procedures and actual
corrosion. Hence, the risk associated with other types of electrochemical
tests is most likely higher than the Aristartec system,
particularly when other tests use inappropriate test parameters
and procedures.
What typically happens when unexpected corrosion results in
spray package failure or significant product degradation, and how
much does the unexpected corrosion cost? Spray package failures
typically trigger an internal company investigation into the failure.
The objectives for an investigation typically include:
• Determining the root cause of the failures
• What to do with existing inventory
• Continuing or halting manufacturing
• Developing recommendations to avoid future failures
Failure investigations typically last from at
least six months to one or more years, depending
on the number of manufacturing batches
involved and how widely the product was
distributed. The investigation team typically
includes people from all R&D disciplines
and all levels of corporate management, as
well as personnel from manufacturing, quality
assurance, legal, marketing, sales and customer
service. Internal investigations typically involve
numerous employees during the investigation
lifetime—not usually all are involved at the
same time.
Is skipping corrosion tests
and/or abbreviated
corrosion tests cost-effective?
The cumulative hours for a corrosion investigation
typically add up to a significant amount
of time and cost. For example, an investigation
might cost $180,000 if the investigation
lasts one year and accumulates 1,200 hours of
personnel time at a cost $150 per hour.
However, the loss of sales during the year,
the cost of scrapped goods and consulting fees
are not included in this example. In addition, an investigation
also diverts resources from other projects, causing delays in the
commercialization of other products. Thus, the $180,000 in this
example is probably significantly lower than actual the cost.
Part 2
Figure 1: The estimated risk of corrosion versus the percent test completion.