Page 44: of Maritime Reporter Magazine (March 2001)

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Maritime Reporter Magazine, page 43, Mar 2001

Maritime Reporter Magazine, page 44, Mar 2001

Maritime Reporter Magazine, page 45, Mar 2001

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Circle 320 on Reader Service Card

Coatings & Corrosion Control specialist marine consultancy firm.

This came as a shock to the system to an industry that had been used to doing major corrosion repair work around the time of the second special survey.

Suddenly, owners found that they were footing hefty repair bills on very young ships. But why were double-hulled tankers rusting away so quick- ly? The answer was provided only recently, thanks to work done by Sigma Coatings, for whom Jansen acts as a consultant. "Research done by Rodney Towers at Sigma sug- gests that the corrosion problems caused on board double-hulled tankers can be attributed to the ther- mos-flask effect of the design. Crude oil is usually loaded in locations where temperatures can reach as high as 45 to 50 degrees Celsius. It is then shipped to locations that are much cooler. If it is carried on board single-hulled ships, the oil cools down comparatively quickly under the influence of the ambient sea temperature, reaching sea tempera- ture between 36 and 48 hours after being loaded, depending on the volume of oil and other factors.

On board double-hulled vessels, cooling down times are much longer, taking days rather than hours," Jansen explains. Oil in double-hulled tanks takes an average of 20 days to reach sea tempera- ture, he adds.

The significance of the longer cooling down peri- od is found in the lifecycle of corrosion inducing bacteria. The bacteria survive longer in the warmer oil in double-hulled ships, lengthening the electro- chemical corrosion process that naturally occurs at the bottom of cargo tanks on board oil carriers.

Not only do the bottom of tanks on board double- hulled vessels rust more rapidly, under-deck plating and ullage areas are more prone to corrosion as well. The reason for this is a different one, howev- er. Here, it is the choice of construction material that is significant. To offset the increase in weight due to the extra steel required for double-hulled newbuilds, shipyards incorporated higher levels of high-tensile steel into their designs. "High-tensile

Circle 233 on Reader Service Card j^Lobelt has been a leader in high quality marine controls and steering systems for over 35 years. Our international reputation for tough, quali- ty-built, precision controls covers 23 countries. We are the only company to use die-cast bronze components and stainless steel hardware exclusively. We back every one of our products with a 5 year warranty, along with worldwide sales and support. All of these factors combined make

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At Cascade General, our dedication to craftsmanship is matched only by our dedication to efficiency. Everything hinges on teamwork. When your vessel enters our shipyard, you're met by specialized teams, some three generations strong, that quickly and flawlessly tackle every issue at hand with the passion of a world-class pit crew.

The teams at Cascade General have been honing this kind of precision planning to a science over the last 50 years. It's what allows us to complete repairs in record time—even accomplish projects previously considered impossible. It's why when you think of the most capable shipyard in the western hemisphere that consistently delivers pit stop performance, you'll think

Cascade General.

CASCADE GENERAL

PORTLAND SHIPYARD