How to avoid re-coating ballast water tanks, even after they have been corroded by chemically treated ballast water
The cost of installing a ballast water management system (BWMS) on a large tanker can be significant (some estimates put it in the region of US$5M), but it is a necessary investment. Following the entry into force of IMO’s International Convention for the Control and Management of Ships’ Ballast Water and Sediments (Ballast Water Management Convention) in September 2017, all vessels are required to manage their ballast water using an approved treatment system.
When approximately 5 billion tonnes of ballast water are transferred internationally every year, investing in the right pre-approved ballast tank coating is key to mitigating the corrosion effects of ballast water, and reducing the risk of a coating failure. Active chemicals in the BWMS – particularly hypochlorite, chlorine and ozone – are highly corrosive. With ballast tanks being the largest area of structural steel on a vessel, a high-performing coating must be ensured from the outset. Recoating ballast water tanks outside of a planned maintenance period is both costly and disruptive to the shipowner.
With more than 70 different systems for ballast water management currently available, or in development, leading coating manufacturers such as Hempel are developing robust solutions to meet all industry needs.
Shipowners take into account several factors when choosing a coating: versatility and ease of application; excellent corrosion and abrasion resistance; fully certified to conform with IMO’s and PSPC (the Performance Standard for Protective Coatings) rules; and a minimal environmental impact. One such solution is Hempel’s Hempadur Quattro XO range.
Certified to the highest standards, Hempadur Quattro XO is a universal anticorrosive primer range that ensures superior corrosion protection and reduced maintenance costs for owners and operators. These two-component pure epoxy, PSPC-compliant coatings have been developed for water ballast tanks in new vessels to ensure long-term corrosion protection over the ship’s lifetime and to minimise maintenance costs, but also fit well with the working methods of shipbuilders. Versatile, with high productivity for shipyards and reduced maintenance costs for shipowners, Hempel’s Hempadur Quattro XO range has a proven track record.
Hempel has carried out testing of its ballast tank coatings against seawater treated with hypochlorite, a commonly used active chemical in ballast water treatment systems. This treated water can be highly corrosive – a challenge for any coating. The results have been good and verified by an independent test house.
During this testing, which involved constant immersion in hypochlorite-treated seawater at 30°C (including a constant addition of freshly prepared hypochlorite), rust, blister formation, discoloration or a decrease in hardness was not seen. Even up to four times the concentration ppm (parts per million) of free chlorine delivered by a BWMS (recommended concentration has a maximum of 10 ppm) these effects were not seen. Hempel’s more stringent test also took into account temporary or locally higher concentrations of free chlorine in the ballast tanks.
It is understandable that IMO’s testing procedures (and those of other industry bodies) for ballast water tank coatings are very robust. A coating failure is not only costly to an owner but can also have an adverse environmental impact. IMO- and PSPC-approved ballast tank coatings, such as the Hempadur Quattro XO range, not only offer long-term corrosion protection from the inside out, but also peace of mind to owners.