corrosion testing, materials selection and independent technical investigations

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ChemiCal investigation serviCes newsletter independent & objective DeCember 2009
Ballast water boost
Chemical Investigation Services together
with Prof Rob Knutsen at the University of Cape
Town have helped a Cape Town based
entrepreneur develop a novel ballast water
treatment system for ships.
Ballast water is pumped into vessels so as to
trim the vessel, keep the propeller at optimum
depth and ensure the draft matches the
prevailing sea conditions.
Ships pump ballast water on board during a
Accelerated corrosion test cell
voyage and then discharge the ballast water
when it is no longer needed. This transcontinental treated seawater they produce is corrosive to
movement of ballast water has lead to the the steel plate onboard ships or damaging to
transfer of marine species from one location to paint systems inside ballast tanks.
another including harmful species of organisms. Resource Ballast Technologies (Pty) Ltd
The International Maritime Organisation approached the Corrosion Team to assist them
(IMO) will make it mandatory for all ships to with the corrosion testing. The Corrosion Team
install ballast water treatment systems by 2014. set about designing an appropriate test
Cape Town based Resource Ballast pattern that would expose steel plate to both
Technologies (Pty) Ltd has been developing a treated seawater and untreated seawater.
unique ballast water treatment system for ships They proposed a laboratory based accelerated
since 2006. The IMO require that new ballast corrosion test program, as this approach would
water treatment systems be tested to see if the provide a rapid assessment of the impact of
seawater on steel.
Simon says... In addition the Corrosion Team also carried
out a literature review, so that together with
the accelerated test work a full and final
Talk to us about submission to the IMO could be made by early
corrosion 2009. The work was successfully completed in
mitigation & December 2008 and reported to the IMO.
materials selection Resource Ballast Technologies (Pty) Ltd
at the DESIGN received final approval for its ballast water
stage treatment system from the International
Maritime Organisation in October 2009.

2. Wire rope wizards
Premature corrosion of critically important First the team
wire ropes located in a severe marine carried out an
application became a major headache for accelerated corrosion
designers at a Cape firm of consulting test pattern for 1000
engineers. However a team of Cape Town hours, and then cut
based corrosion specialists solved the problem. open & mounted
A solution was developed as a joint venture sections of the wire
between Chemical Investigation Services, an rope test pieces for
independent technical investigation practice assessment.
and Prof Rob Knutsen of the University of Cape The sections were examined using high
Town. quality optical microscopy. This allowed the
The problem first appeared when Galfan team to report on the mechanism of corrosive
galvanized steel wire ropes installed in a marine attack that had so severely affected the wire
environment in 2003 and subject to very severe ropes.
in-service conditions, started showing signs of The next step in solving the problem was to
significant rusting. The corrosion began to subject specially coated pieces of wire rope to
appear within a relatively short period after a carefully designed cyclic accelerated
installation and this alarmed the design corrosion test. The objective of the test being to
engineers. select a suitable coating to protect the wire
At the centre of this investigation were wire ropes in the long term.
ropes galvanized with a special zinc alloy This successful test work lead to the selection
known as Galfan. This galvanizing alloy consists of an anti corrosion coating package which is
of zinc, aluminium and other special alloying easy to apply, cost effective and weathering
elements. resilient.
The corrosion team devised a 3-part program The proposed coating system of a thin gel
to get to the root of the problem including anti-rust first layer and a second highly adhesive
accelerated salt spray testing, a scientific grease layer is currently being applied to
literature review and a cyclic accelerated hundreds of metres of exposed wire ropes and
weathering test for 28 days. will ensure that the ropes can survive for a very
long period.
chemHelp what we offer
What is corrosion? z Failure investigations of all types
The deterioration of metal or alloy and its
z Corrosion & coatings assessments
properties resulting from a chemical or
electrochemical reaction with its z Petroleum product investigations
environment. z Special investigations for loss adjusters &
What is galvanic corrosion? lawyers
The form of corrosive attack that occurs z Refractory & ceramic product
when two dissimilar metals are electrically investigations
connected through physical contact or via
an electrolyte. z Independent technical investigations
We talk test techniques in our next newsletter...