Page 18: of Maritime Reporter Magazine (May 2001)

Hilksi o m Control

Castor's Downfall: Hyper-Accelerated Corrosion

Few marine incidents have vexed the collective international marine commu- nity as much as the recent situation with the damaged product tanker Castor, a ship, which experienced a near fatal deckplate crack in mid-voyage and then was denied safe harbor for fear of the ship splitting open and spewing its gaso- line cargo. Though the ship was eventu- ally docked safely without environmen- tal incident, the name Castor will serve as a lightning^ rod in the IMO to more firmly establish rules and procedures for ships in distress at sea.

As the political wrangling and finger pointing start to subside, attention is now turned on the ship itself, and more accurately finding out the reason that an

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Frank larossi assumed healthy ship developed a near fatal deck- plate crack. Fol- lowing an exhaustive inspection and analysis of the damaged prod- uct tanker Cas- tor, the Cyprus Department of Merchant

Shipping and ABS have jointly announced preliminary findings that point to hyper-accelerated corrosion as the probable principal cause behind the structural failure. "The Castor has become a floating laboratory, which is providing us with some surprising findings," said ABS chairman and CEO Frank J. larossi. "If these initial conclusions hold up, there will be significant implications for class and possibly wider implications for the manner in which the new generation of double hulled tankers should be con- structed and maintained."

A formal report into the casualty will not be issued by the Cypriot authorities and by ABS until the conclusion of detailed laboratory testing of steel sam- ples cut from the damaged section of the tanker. "It will take some time to scien- tifically verify that our interpretation of events is correct," said larossi. "The Castor represents an unprece- dented level of cooperation between the class society and the Flag State involved in a casualty," said Captain Andreas

Constantinou, senior marine surveyor for the Cyprus Department of Merchant

Shipping.

The 600 tons of steel, primarily in the deck plating and underdeck longitudi- nals, that was renewed on the Castor at

Special Survey in late 1997 has provid- ed the key to understanding what tran-

The underdeck and remains of an underdeck lon- gitudinal in the affected section. You can see the original coating and where there has been coat- ing breakdown. The longitudinal shown had the flange replaced at the last special survey in 1997. This was welded to a web that, at that time met class requirements and had wasted less than 18 percent from its original 15mm dimension. What has happened in the interim is that the adjacent deck coating and the new steel on the flange were both more resistant to cor- rosion than the partly wasted web. The galvanic action attacked the weakest component, the web, which became the sacrificial anode. Obvi- ously it did not waste to zero but it did waste suf- ficiently to be unable to sustain the buckling load and fractured. The deformed but intact web is an indication of the residual strength that remained in the structure.