Protecting Your Assets in Challenging Environments
November 2016 www.coatingsworld.com Coatings World | 47
physical stress; these factors present a unique set of challenges
for the coatings industry. Traditionally, inorganic zinc-rich coatings (IOZs) such as zinc silicates have been the preferred primers
for these environments because of their enhanced anti-corrosive properties, with zinc epoxy coatings taking a back seat.
However, while IOZs exhibit superior anti-corrosion properties,
they tend to suffer from low mechanical strength and require
specific conditions for application. Because of this, an increasing
number of offshore installation operators are choosing a zinc
epoxy instead. But the problem here is that zinc epoxies require
a more regular re-coat which usually means taking the asset out
of service. Each system, therefore, has its limitations.
In both zinc silicates and zinc epoxies, the zinc acts as the
sacrificial element and corrodes instead of the iron to leave the
steel intact. This process - known as the galvanic effect - only
works if the zinc primer is able to transfer galvanic current. In
general, a normal zinc coating is around 60-80 microns thick
but it is only the first 20-30 microns of a traditional zinc epoxy
coating that delivers the galvanic protection. The epoxy resin
insulates the zinc particles causing them to lose their galvanic
properties. Even at high zinc loads, around 80% of the zinc is
too far away from the point of corrosion for it to be of any use.
Activated Zinc
As a coatings specialist, our challenge has been to activate more
of the zinc to improve the galvanic effect of the coating without
increasing the actual zinc content itself. Doing this ensures that
the zinc throughout the film is delivering anti-corrosion protection. Our solution was to introduce two new substances into the
primer - hollow glass spheres and a proprietary activator. The
combination of these new items, together with the optimum mix
of binders, pigments, fillers and additives ensures that the zinc is
activated throughout the coating.
In general, traditional zinc coatings are porous and so offer
little resistance to water. But with our new coating, as well as
significantly enhancing the galvanic effect, we also found that
our new activated zinc primer had a lower water permeability.
Once the zinc becomes activated, the resistance to water is increased as it forms a layer of insoluble salts on the surface and
within the film – the barrier effect. The benefits of such a barrier
within the marine environment – where an installation is permanently immersed in water – are significant and can provide
additional protection over the lifespan of the installation.
It’s also important to note that water is not the only destructive force for installations operating offshore. In particularly
aggressive saltwater environments, chloride ions will penetrate
a protective coating to cause pitting corrosion. Our coating effectively captures these chloride ions by forming chloride-con-taining salts around the hollow glass spheres. This significantly
delays the corrosive process as the chloride ions are trapped
within the coating and prevented from reaching the steel surface
– the inhibitor effect.
Avantguard Technology
These innovations have been captured in a new Hempel coating
technology called Avantguard. This has, in our view, redefined
anti-corrosion coatings as Avantguard delivers a triple protec-
tion. It exhibits greater galvanic activity by increasing the ac-
tivation of the zinc; it creates an inorganic salt barrier against
water and other corrosive species; and it acts as a chloride scav-
enger by capturing chloride ions.
Offshore structures are often exposed to severe mechanical
stress and fluctuations in temperature which can cause a zinc
primer to crack as the steel contracts and expands. The new
Avantguard technology compensates for this through its unique
self-healing properties. The hollow glass spheres within the
primer absorb much of the energy from the cracking process
to prevent initial cracks from widening and developing. In addition, the sub products formed by the zinc activation process
will occupy the space left by micro-cracks and prevent them
from developing into something more serious. This significantly
reduces rust creep and ensures that the coating maintains its
anti-corrosive performance for much longer.
In terms of the application process, an Avantguard coating
may be applied at high temperatures and levels of humidity
without blistering. And, with a re-coat interval of one hour at
20 °C, it is 50 percent quicker to dry than most zinc-rich epoxy
primers at similar temperatures. Its high dry film thickness is not
susceptible to cracking which means that operators needn’t be
overly concerned when applying to welds or in corners where
over-application tends to occur.
Efficiency Gains
The advantages of utilizing this innovative technology in aggressive environments are significant. Owners of offshore structures
can increase the lifetime of their assets and reduce maintenance
requirements and costs. This is particularly relevant for hard-to-access areas that require a shut-down to maintain. For contractors, having confidence in their choice of coating allows them to
offer enhanced warranties for the equipment and structures they
supply. Avantguard’s wide tolerance allows contactors to touch-up and repair a coating on site. For fabricators, Avantguard is
easier to apply than other similar primers and enjoys a shorter re-coat interval which improves speed and efficiency. All in all, this
new technology has redefined anti-corrosion coatings by reducing
rust creep, enhancing resistance to corrosion, improving crack resistance and heightening tolerance to varying climatic conditions.
Below the Waterline
Ship owners are keen for their vessels to maintain a smooth
and foul-free hull. Fouling increases the drag of the hull which,
in turn, increases the fuel consumption and associated harmful
emission. The right coating keeps the hull smooth thus minimizing the need for cleaning operations or premature docking of
the ship.
The antifouling market is dominated by conventional antifouling coatings that rely on biocides to control hull fouling.
This is traditionally achieved by the addition of cuprous oxide as a pigment, combined with organic co-biocides, in order
to deliver the required biocide activity to fight off the entire
