'Super-rust' eats tankers 10 times quicker

Investigators lowered into the holds of the wrecked tanker Castor expected something unusual. The Castor's 16mm thick steel deck had sheared in half, nearly sinking the gasoline-laden ship in a New Year storm.

What they found was a virulent new form of corrosion, now dubbed "super-rust", which had devoured the ship from the inside out, 10 times faster than anyone had previously thought possible.

"The most startling find was that new deck plate put in in 1997 had wasted up to 5mm in three years. That's wastage 10 times what you'd expect," said Frank Iarossi, chairman of ABS, the surveying company responsible for the ship's annual health checks.

The news is yet another blow to an industry vigorously defending itself against government intervention after six major European tanker accidents in the last 18 months.

During a six week salvage drama starting on New Year's day, the Castor limped around the western Mediterranean in a desperate search for sheltered water in which to unload its 30,000 tonne gasoline cargo. Hurricane-force winds and eight metre waves swamped its decks, as country after country turned away the ship amid fears that the gasoline cargo might suddenly explode.

And while explosion tests commissioned by ABS showed that the fears of Morocco, Spain, Gibraltar, Algeria and Malta, Tunisia and Greece were misguided, the discovery of "hyper-accelerated corrosion" or "super-rust" as the cause of the ship's 20 metre crack is more serious.

The discovery has huge implications for an industry vital to the safe flow of energy around the globe. Nearly 2,000 tankers are involved in the lucrative international trade of petroleum products of over 500 million tonnes per year, and many of those could be affected. "There are possible implications for all coated tanks (on products tankers)...We need to reassess the rules," Iarossi said at the Seatrade safe shipping conference on Tuesday.

The discovery also casts doubt on the safety of double-hulled tankers, which will soon dominate the 1.5 billion tonne per year crude oil trade. "There are also an enormous amount of ballast spaces on double-hulled (crude) tankers. Are there any implications of what we found on the Castor with regard to them?" asked Iarossi.

Iarossi's frankness has stunned an industry usually better-known for its secrecy, and its zealous protection of client-confidentiality. ABS was responsible for checking the structure of the Castor during the three and a half years that "super-rust" was taking hold. But ABS is one of three surveying companies that are trying to move ahead of an industry beset by in-fighting, and increased honesty and transparency is one of the key goals that would set itself, Lloyd's Register and DNV apart.

Last month the trio published a list of "10 commandments" for ship safety that they would be pursuing and said they hoped the industry would follow. Iarossi said that though the investigation was still underway, it appeared the Castor's deck had buckled and sheared in two when a supporting steel girder had failed. An area of original steel from the 1977 built tanker had become sandwiched between two areas of new steel, and somehow it had become chemically "sacrificed" in an accelerated corrosion process.

The tanker's trading pattern from Romania to Nigeria had routinely exposed the deck to high temperatures, while saltwater pumped in and out of the tank had catalysed the disintegration of the girder. Once the Castor had found shelter and the 30,000 tonnes of gasoline had been pumped off, the owner, Athenian Sea Carriers had loaned it to ABS as a temporary laboratory.

"We had a laboratory for corrosion here," said Iarossi. "We had coated steel; we had exposed steel and we had new uncoated steel." He said sections had been cut from the deck and were now undergoing chemical and metallurgical tests.