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Send  Share  RSS  Twitter  18 Jun 2009

MARINE: Sector Taps Corrosion Brains


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A consortium of Chemical Investigation Services (CIS ) and the Centre for Materials Engineering (CME) at the University of Cape Town (UCT) have assisted a Cape Town based entrepreneur to develop a novel ship ballast water treatment system.

Ballast water is pumped into vessels during a voyage so as to trim the vessel, keep the propeller at optimum depth and ensure the draft matches the prevailing sea conditions. Ballast water is carried in the double bottom space, between cargo holds and in the port and starboard trim tanks.

Ships uplift ballast water from various ports during a voyage and then discharge the ballast water at the cargo loading port when the ballast is no longer needed. This transcontinental movement of ballast water has lead to the transfer of marine species from one location to another including harmful species such as toxic dino flagellate algae, macroalgae, vibrio cholerae and varieties of zooplankton.

The International Maritime Organisation (IMO) has set out a program for certain vessels to install ballast water treatment systems by 2010 and all other vessels by 2014. Intensive development work is currently in progress worldwide to develop ballast water treatment systems and get final systems approval from the IMO prior to commercialization.

Resource ballast technologies, based in Cape Town, has been working for the past five years on their own patented ballast water treatment system and have basic approval from the IMO and should have final approval by November this year.

The IMO now require that prospective ballast water treatment systems be assessed to see if the treated seawater they produce is corrosive to the steel plate onboard ships or damaging to coating systems inside ballast tanks.

Says Simon Norton of Chemical Investigation Services: “RBT approached our consortium to assist them with the necessary corrosion assessments to quantify the impact of treated sea water on steel plate inside ships ballast tanks. The consortium of CIS and CME then set about designing an appropriate test process that would expose marine steel plate to both treated and untreated seawater.”

The IMO requires long term corrosion testing to assess the impact of treated seawater on steel plate and this usually involves weight loss testing of metal coupons in immersion tanks.

We opted to do a six month immersion test using both coated and uncoated metal coupons and evaluate both weight loss with time, damage to coatings and water uptake in the coatings. Together with this we also proposed a laboratory based accelerated corrosion test programme to examine both coated and bare steel, as this approach would provide a rapid assessment of the nature of the treated ballast water,” says professor Knutsen from CME.

With the ballast water system development the client required that we switch the project around and complete the accelerated corrosion test work first before the six month weight loss testing. Additionally, the client also asked us to carry out a literature review in a very short period of time so that together with the accelerated test work they could make a submission to the IMO by December 2008. This we successfully completed within deadline,” Knutsen says.

Modern electrochemical test equipment is now so powerful that this apparatus now allows scientists to carry out rapid corrosion testing on a variety of metal materials and to report a corrosion loss rate in mm per annum.

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