As offshore activities expand into ever deeper waters in which floating facilities are the order of the day, tanker owner and manager Stena Bulk is offering a series of good quality tankers for use as floating units.
The company has seven Concordia Class VLCCs which it reckons are well suited for offshore use. The vessels, built in the early-1970s to mid-1970s, are each of around 273,000 deadweight tons, giving them a storage capacity of some 2 million bbl.
One of the Concordia Class vessels, the Stena Contender, has already made the transition to the offshore sector, being employed since 1995 as a floating storage unit on Elf's N'Kossa field off the Congo.
As they approach the 30-year sailing limit for tankers, the remaining vessels in the class will have to leave Stena Bulk's fleet over the next few years. "They are in very good condition," says Ulf Ryder, the company's president. "We don't want to see them beached."
The vessels were all built to a high standard and have large crews. Constant maintenance means that their repair needs have been minimal over their lifetime. In terms of the condition assessment program (CAP) operated by the ABS, DNV and LR classification societies, all have qualified for the top grade.
According to a study of 25-year inspection and repair needs carried out for Stena Bulk by Fearnleys, the Concordia class vessels required on average 11 days in drydock and an outlay of $400,000, compared with 50 days and $4 million for the typical VLCC.
30+ years to go
"We're looking for 25-year contracts," says Ryder. "We see our main markets as Brazil, West Africa, the Persian Gulf, the South China Sea, and if the American authorities change their regulations, the Gulf of Mexico. The North Sea is not a core area for us.
"To verify our claims, we asked ABS to assess how long one of the Concordia Class ships - the Stena Congress - would last in one of our core areas without any special work being done on it. They decided it had in excess of 30 years' remaining life."
Stena Bulk now has its sights set firmly on Brazil, where Petrobras is in the process of bringing three major floating production projects onstream, for the Barracuda, Caratinga and Marlim fields. The main contract for Bar racuda is already out to bid. While production will be through a wellhead platform, processing will take place on a floating production, storage and offloading (FPSO) vessel. The vessel will be outfitted with 12,000 tons of processing equipment, providing a production capacity of 200,000 b/d of oil and 3.5 MMcf/d of gas, plus facilities for injecting 200,000 b/d of water. Storage of 2 million bbl is required.
35 mm plate
The company claims its ships will have a much longer lifetime for an offshore owner than other tankers. They are constructed of mild steel only, with 35 mm plate in the deck and bottoms. The insides of the tanks are coated. They are the only VLCCs which have this, says Ryder.
Other tankers being offered for offshore duty are built mainly of 18-25 mm steel plate, using high-tensile steel. High-tensile steel has a higher yield strength, which makes it possible to reduce the thickness.
But from a long-term perspective, this approach can cause problems, according to Stena Bulk's contract manager Per Palludan. As the scantlings are reduced, movements in the structure are accentuated, which can cause higher fatigue stress at the joints. The greater degree of movement can also cause micro-cracks, which are vulnerable to corrosion.
Because of the high standards to which they were built, none of the seven vessels has encountered any corrosion problems. This is a usual problem in aging tankers built with thinner plate. Problems can also arise with the weld between areas of old and new steel, says Palludan.
There would be no unpleasant surprises in converting one of the Concordia Class vessels for offshore work, whereas the delays which have arisen in projects involving other second-hand tankers due to the uncovering of poor structural conditions are well known. "You need to be sure of your hull," says Palludan. "If you're trying to bring a high-cost project onstream on schedule, you can't afford delays." The conversion of the Stena Contender for N'Kossa went very smoothly, he says.
Engineering capacity
"We also go a step further than other owners - we're prepared to become involved in the conversion work," he says. "Last year, when we bid for a couple of conversion contracts in the Persian Gulf, we did all the engineering for the storage units." Conversion to a storage unit could moreover be carried out by Universe Tankships, the Stena Group company which built the ships and crews them. "We're prepared to keep the marine crews on the vessels during the test period as well," says Palludan "We have a flexible attitude on these matters."
The Concordia Class vessels are also highly competitive, when the alternative would be a newbuild. This is partly because of the shorter lead time to prepare the vessel for an offshore role. "We've also done our own price checks," Palludan says. "A newbuilding unit for a project not requiring an engine and rudder would cost around $60 million, whereas ours would come much cheaper.";
For more information contact Per Palludan, Stena Bulk, telephone +46 31 85 50 11, fax +46 31 12 06 51 or e-mail:[email protected].
