The bottom section of the scrubbing tower on the 250,000 ton tanker "KULU" is fabricated entirely in Ferralium® 255 (UNS S32550, Alloy 255, DIN 1.4507, ASTM F61) super duplex stainless steel. It has withstood some 18 months of continuous service without any sign of corrosion, so an almost indefinite service life can reasonably be expected.
The inert gas system
The "KULU", owned by the Kulu Tanker Corporation of Panama, uses an inert gas system to blanket its oil tanks and greatly reduce the risk of explosion. The system uses waste exhaust gases from the boilers, which are inert after combustion but carry various corrosive products in gaseous form. In the scrubbing tower these gases are cooled and washed with seawater, producing an extremely corrosive solution, which is why the bottom section is built in Ferralium® 255. The fan impellers that draw the inert gas over the oil storage tanks are also cast and fabricated in Ferralium® 255.
Manufacture
The system was made by Airscrew Fans Ltd of Weybridge, who now have an agreement for it to be manufactured by Wilson Walton International of Croydon. Over the following five years at least £100m is expected to be spent installing inert gas systems in tankers already in service.
