E N V I R O N M E N T
Areas of naval vessels subject
to continuous water immersion,
such as the underwater hull, bilges
and tanks, are considered critical
as these areas are more prone
to coating failures and corrosion.
Corrosion and loss of metal
in tankage is a major factor in
determining the life of commercial
vessels. Freeboard areas, which are
subject to continuous water spray
while underway, and ship decks are
also considered critical.
Research in to the development of
specialised protective coatings for
military applications is supported
by the Australasian Corrosion
Association (ACA). The organisation
works with private companies,
not-for-profit bodies and academia
to research all aspects of corrosion
prevention and mitigations.
The ACA provides an extensive
knowledge base that supports best
practice in corrosion management,
thus ensuring all impacts of
corrosion are responsibly managed,
the environment is protected, public
safety enhanced and economies
improved.
Several ACA members are currently
engaged in a range of Defence
related projects. The Chair in
Electromaterials and Corrosion
Sciences at Deakin University,
Professor.Maria Forsyth, and Senior
Research Fellows, Dr Katerina
Lepkova and Dr Laura Machuca
Suarez, at Curtin University's
Western Australian School of Mines:
Minerals, Energy and Chemical
Engineering are investigating
anti-corrosives such as lanthanidebased
ones to mitigate microbially
induced corrosion and special anticorrosive
pigments.
A related anti-corrosive pigment
project is being undertaken by
researchers Dr Sam Yang and
Dr Tony Hughes at the CSIRO's
Materials Science and Engineering
division, specifically looking at ways
to transport these pigments to
defect sites.
Swinburne University's Associate
Professor Scott Wade from the
Faculty of Science, Engineering
and Technology, is researching
microbiologically influenced
corrosion of piping materials and
mitigation options, and high velocity
oxygen fuelled (HVOF) coatings for
marine hydraulic applications.
For many decades, the RAN
employed solvent-based gloss
alkyds as the topside coating
for vessels but these were not
very durable, often failing in as
few as six months. In the 1990s,
a polyurethane coating was
introduced but this has since
been replaced by a Low Solar
Absorbing (LSA) Polysiloxane
coating which has a colour-stable
pigment which provides improved
visible camouflage in the waters
around northern Australia. The
polysiloxane also has improved
thermal protection reducing the
cost of cooling ships, where trials
of patrol boats in norther Australian
waters showed that the surface
temperature of the polysiloxane
coating could be as much as 15ºC
cooler than traditional coatings.
The development of rapid-cure,
ultra-high solids, two-pack epoxy
amine coatings technology
offers potential advantages for
the RAN, especially when dealing
with complex internal surface
geometries found inside sea
water ballast tanks which feature
baffles with cut outs between bays
and numerous longitudinal and
transverse stiffeners to provide
requisite rigidity and strength.
Historically, corrosion on these
edges would appear after a period
in service, largely as a result of the
poor edge retention of conventional
coatings that were used.
The latest epoxy amine coatings
are applied using specialised
plural component high pressure
spray equipment where the two
components are mixed at, or close
to, the tip of the spray gun and
generally require each component
to be pre-heated to reduce flow
viscosity. The coatings can be
spray applied at high film build
without sagging, have improved
edge retention and produce very
low emissions of volatile organic
compounds. These coatings cure
very quickly and can be walked on
within a few hours, promising a fast
return to service.
The specification of high
performance coatings for RAN ships
must be supported by rigorous
quality assurance inspections.
It is imperative that coatings are
applied as per specification or
manufacturer’s recommendations,
which is best achieved through the
use of independent inspectors who
are required to witness the condition
of the substrate and undertake
measurements, such as dry film
thickness at key ‘hold points’,
during the surface preparation and
painting processes to ensure that
the environmental conditions are
suitable for painting. These include
weather conditions, substrate
temperatures, and dew point.
Other corrosion management
technologies applicable to naval
vessels and infrastructure includes
research into anti-corrosive
coatings, for superstructure,
underwater hull, tanks and bilges as
well as cathodic protection of hulls,
bilges, ballast tanks, seawater piping
systems.
44 September 2019