Chemical Engineering August 2020 - 36

applied haphazardly to a poorly prepared
surface will compromise the durability
of the coating much earlier than
necessary. Proper surface preparation
is vital to creating a coatings system
that will last. Other important factors
are proper mixing, thickness and
weather conditions. Coatings users
must ensure that they have the mix ratios
correct and that they are applied
at the proper thicknesses. Weather
conditions also play a role in impacting
coating application. For instance, in
cold weather, water-based coatings are
not going to experience optimal application
and curing. Following the manufacturer's
recommendations will help to
guide users in planning how and when
to best apply certain coatings [5].
An important and convenient aspect
of many VCI coatings is that
they can be applied directly to the
metal. Some VCI coatings are primers,
some are topcoats and some
can flexibly serve in either category.
Using good primers is an important
part of a successful coatings system,
because it helps the coatings bond
better to the metal surface. While it
may not always be practical due to
time and budget considerations, the
ideal coatings system will include two
coats of a primer with a heavy-duty
topcoat to finish it. Two-component
primers and topcoats are even better,
although they require extra mixing to
allow the advantages of cross-linking
to occur. In these cases, maintenance
engineers will need to weigh
time, convenience and cost against
desired performance.
Dealing with pre-rusted surfaces
Surfaces must be free of rust and contaminants
if coatings users want the
coating to last as long as possible. For
surfaces that have already rusted, this
could involve chemical rust removal or
some type of blasting. Sandblasting is
common, but not always convenient,
and sometimes is not even allowed or
feasible in certain environments. A convenient
alternative is to apply a waterbased
rust-converting primer that uses
polyvinylidene dichloride (PVDC) resins
and a chelating agent to turn the rust
into a passive layer that seals it off and
protects it from further rusting. For situ34
ations
where either water-based or solvent-based
topcoats may be applied,
it is ideal to choose a rust-converting
primer that is compatible with either
coatings system and exhibits adhesion
behavior according to ASTM Class 5B.
Rust-converting primer is also a good
option for structural repairs where concrete
has delaminated to reveal rusty
rebar. Such a coating can be applied
to passivate the rebar before continuing
the concrete repair process.
Following this guidance will help
maintenance engineers to tackle the
challenging corrosion scenarios encountered
in CPI facilities and get the
best performance possible out of their
protective coatings.
■
Edited by Mary Page Bailey
References
1. Koch, G.H., et. al., Corrosion Costs and Preventive Strategies in the
United States, Supplement, USDOT, CC Technologies and NACE International,
Publication No. FHWA-RD-01-156. U.S., 2002.
2. CODEMET, " Triple Metal Protection, " https://youtu.be/Es72rcpmOx4.
3. Miksic, B.A., Kharshan, M. and Camp, R., Water-Based Coatings Powered
by NANO-VpCI, Technical paper presented at international conference
in Sosnowiec, Poland, October 2014.
4.
Cortec Laboratories, " Evaluating Performance of VpCI-396 and
VpCI-395 in Buried, Humid Conditions, " Project #16-168-1525,
October 6, 2016.
5. Bieber, M., Personal Interview, April 7, 2020.
Authors
Ana Juraga (Email:
ana.juraga@
ecocortec.hr) is corporate communications
manager at Cortec Corp. She has
been a content writer at Cortec for 10
years. Besides dealing with media relations,
she collaborates with Cortec's
engineers and chemists in creating informative
technical content. She is passionate
about educating the engineering
community about green
corrosion-inhibiting technologies and the numerous advances
in this field.
Julie Holmquist (Email: jholmquist@
cortecvci.com)
has
been
a
content
writer at Cortec Corp. for more than
four years. She specializes in writing
about corrosion-inhibiting technology
for concrete, electronics, manufacturing,
oil and gas, and many other industries.
Her articles have been published
in dozens of industry magazines.
Markus Bieber (Email:
mbieber@
cortecvci.com) is currently the vice
president of integrated solutions at Cortec
Corp. He has spent more than 20
years in product and sales management
in the coatings industry working
for Cortec Corp., The Sherwin Williams
Co. and Hydrite Chemical. Bieber has
authored numerous papers for NACE
International and The Society for Protective
Coatings (SSPC) focused on coating technologies, as
well as VCI corrosion-inhibitor technologies.
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