Chemical Engineering August 2020 - 35

Cortec
ures 2 and 3 can be applied directly to
the metal as a one-coat or two-coat
system. They can be top-coated with
either a VCI water-based acrylic system
(Figure 4) or, for higher durability,
covered with a one-component VCI
solvent-based moisture-cure urethane
(Figure 5) or two-component VCI solvent-based
urethane coating. For the
more
extreme conditions, such
as
FIGURE 4. A VCI water-based acrylic topcoat covers this
industrial smokestack
ing environment, this will often require
users to lean toward solvent-based
coatings, but often water-based epoxy
and acrylic VCI coatings find their
place, as well, improving the overall
environmental profile of the application
and reducing exposure to VOCs - although
solvent-based VCI coatings
are typically also compliant with VOCcontent
regulations.
Choosing a coating
There are many basic areas to coat
around a chemical plant - railings,
walkways and structural steel - and
an additional benefit when using VCI
coatings for these areas is that they
can be tinted to match the desired
color-scheme - whether safety yellow,
red, green or blue - to serve the
purpose of both corrosion protection
and aesthetics. Certainly, the main
functionality is to protect the metal
from rusting, but a secondary function
is to improve appearance.
Depending on the severity of the
conditions encountered in a chemical
plant, different coatings may be
better suited for each application, as
the coatings may need to be durable
and chemically resistant against varying
process media, including fumes
and liquids. Often, in these situations,
epoxy-based coatings (Figures 2 and
3) are chosen.
Coatings like those illustrated in Figthose
encountered by splash zones,
floors or internals of a tank that will be
filled with an acid or caustic liquid, it
is recommended to simply use a basic
100% solids two-component novolac
(special phenol- or formaldehydebased
polymer) epoxy coating that is
chemically resistant.
Epoxies and urethanes are among
the more durable resin systems and
can be fortified with micro-corrosioninhibiting
VCIs. Rust-converting primers
for pre-rusted surfaces and novolac
epoxies for floors or chemical splash
zones are also good options for extreme
surface-prep needs and harsh chemical-exposure
applications, respectively.
For the best performance, application
crews should employ best practices
to prepare a clean surface and closely
follow manufacturer's instructions for
coatings application.
Ensuring coating integrity
As important as it is to choose a proper
coating, it is also important to take precautions
that will help to ensure the
best coating integrity. A good coating
Cortec
FIGURE 5. Steel panels coated with VCI solvent-based
moisture-cure urethane showed corrosion resistance
after over 1,000 hours buried in dirt and clay in a humidity
test chamber
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Chemical Engineering August 2020

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