The cracking in the deck of Castor, a 600-foot tanker, sent an alarm through the industry. The rapid corrosion that caused the crack has come to be known as super-rust.
The 600-foot Castor developed multiple cracks in its deck plating on Dec. 30, 2000, while carrying nearly 30,000 tons of unleaded gasoline in the western Mediterranean Sea. The largest of the cracks extended about 72 feet – almost the full width of the ship.
A 41-page technical report by the ABS blames the near catastrophe on highly accelerated corrosion, dubbed ‘super-rust,’ that was devouring the ship from the inside out. While the corrosion was limited in area, the extent of the corrosion was excessive, the report says. The findings raise many questions about corrosion rates, ship inspections and the seaworthiness of older tankers.
The ABS said the conclusions have implications for how ships are inspected and wider implications for how the new generation of double-hulled tankers should be built and maintained. At the least, the ABS said, rules should be amended regarding how and when ships are inspected and what surveyors should look for.
The report’s recommendations include:
– Amending international surveying standards to reflect that exposed steel following a breakdown of coating could realistically experience corrosion rates of five to seven times the normal 0.10 mm a year.
– Changing the ABS rules and the standards of the International Association of Classification Societies to strongly encourage tanker owners to repair or replace damaged coatings. For owners who choose not to repair damaged coatings or coat replacement steel, those tanks or hold spaces should be subject to annual review.
– Redefining the location of gauging points to make sure that gauging includes areas of bare steel exposed after a coating breakdown.
– Giving surveyors more control over where gauging samples are taken and shifting the selection of the gauging company from the ship’s owner to the class society.
– Requiring annual examinations of ballast and cargo/ballast tanks on tankers 15 years and older.
– Creating an action plan so that excessive corrosion in older tankers is detected before a catastrophe strikes.
‘Furthermore, ABS is investigating requirements for cargo tank coatings in tankers at time of new construction, results of which will be shared with other IACS members,’ the report said.
Castor, built in South Korea in 1977, was sailing from Romania to Nigeria when the crew discovered the cracks following four days of poor weather with gale-force winds. The damage was just forward of amidships in way of three tanks. Small plumes of cargo could be seen escaping from the tanks through the damaged plating.
The ship set sail to find a port of refuge and in the process, set off an international brouhaha. Castor became a leper of the sea as it was towed around the Mediterranean for more than a month in search of a haven where it could unload its cargo.
Authorities in Morocco, Gibraltar and Spain prohibited the ship from entering their waters. A gunboat escorted the vessel from Algerian waters. Malta, Tunisia and Greece announced they would also bar the ship entry to their coasts.
With no port to take the ship, salvagers on Jan. 22, 2001, were forced to complete an open-water, ship-to-ship transfer of the gasoline from the three damaged tanks. The remaining cargo was discharged in another open-water, ship-to-ship transfer on Feb. 9. Not until Feb. 19 was Castor – now empty of its cargo – able to find an open port when it was towed to Pireas, Greece, where it was examined by ABS inspectors.
The incident set off an uproar about the responsibilities of individual countries to provide ports of refuge to ships in distress. The International Maritime Organization and the ABS called for new international rules to allow ships in need to find a safe berth. IMO Secretary-General William O’Neil said the IMO would take up the issue as a ‘matter of priority.’
‘One can very well understand the reluctance of coastal states to put their citizens and their coastlines at risk,’ O’Neil said shortly after the incident. ‘At the same time, for the international community not to have some form of structured arrangements in place to cope with a ship in distress like the Castor is clearly not satisfactory and is a matter which we must address.’
The inspection of the ship, though, has raised even more serious questions about super-rust and the problems it may cause.
One of the key findings was that the underside of Castor’s plating and longitudinals had previously been coated. The coating, however, had deteriorated over time to expose bare steel to the corrosive atmosphere in the ullage space. The corrosion rates in this area were up to 0.71 mm per year, or seven times the normal rate assumed by the Tanker Structure Cooperative Forum.
In some places, more than 65 percent of the deck plating and longitudinal members had corroded away, causing the longitudinals to detach from the deck plating. The unsupported deck plating then buckled and cracked across the deck through the corroded area.
Even though portions of the tanker were corroding to the point of nearly sinking the vessel, the ship had been inspected several times in the months prior to the incident.
Castor had undergone its annual survey in Greece just four months before the cracks appeared and had gone through three separate port inspections in Ukraine, Russia, and Malta in the two months before the casualty. Neither the survey nor the inspections detected the corrosion problems, and the ship was carrying the necessary permits.
Because the inspections failed to detect the areas of excessive corrosion, they ‘therefore failed to adequately represent the condition of the vessel’s structure,’ the report concluded. ‘While the area of corrosion was limited, the extent of the corrosion was excessive.’