Furnaces, casting machinery upgraded
Rautaruukki Steel has supplied over 3,500 tons of steel plates for suction anchors for the Schiehallion, Troll C and Åsgard A, B and C platforms. These anchors for Åsgard B were delivered to Norway at the end of 1998.Rautaruukki Steel in Raahe has undergone an intensive program of modernization, totalling some FIM 2 billion, recently. Improve ments have involved completely rebuilding two blast furnaces and installing new steelmaking equipment, a ladle furnace and vacuum degassing.
One of the most up-to-date continuous casting machines has also been added, which enables Rautaruukki to make cleaner and more homogeneous products. This, together with the other investments, has placed the company is in a better position to produce more demanding steel grades for offshore and arctic projects.
The Europe-wide Rautaruukki Group makes a wide range of flat steel products such as plates, coils and sheets, while its subsidiary, Fundia, makes long products, including steel bars and wire. The Group's manufacture of flat and tubular products forms an integrated production chain in which the steel manufactured at the Raahe works - which amounted to about 2.5 million tons in 1998 - is upgraded in different stages of production into value added products.
TMCP specialty steels
One product which is seeing increased demand for the offshore market is TMCP (thermomechanically controlled process) steels. Production of TMCP steel started at Raahe in 1991 and has now overtaken the demand for normalized steel. The process involves a period of accelerated cooling (after the plate is milled and before the hot leveling stage) which results in very small grain sizes in the finished product. The result is a very low level of alloy elements in the steel which makes TMCP extremely strong, tough, easy to work and with a good quality finished surface."A major benefit of TMCP steel is that it has excellent weldability over a wide range of heat inputs," says offshore product development manager, Jorma Saralampi. "Since the steel has better hydrogen cracking resistance, it can be welded without preheating which reduces costs. There is also a reduced risk of brittle fractures and lamellar tearing."
Total deliveries of TMCP steel in 1998 amounted to almost 45,000 tons of which nearly 27,000 tons were used for offshore structures. Rautaruukki has supplied TMCP steel for all the spar projects made by Aker Rauma since 1995, including the Neptune and Genesis spars, and most recently the Diana spar - its largest offshore delivery to date at 30,000 tons - which was delivered from 1997-8.
FPV and suction anchors
Much of the company's TMCP plate production is increasingly pre-formed prior to delivery, either bevelled, bent or welded. For example, 5,000 tons of pre-fabricated steel plate were supplied for the Bingo 8000 FPV, and Rautaruukki has also supplied pre-fabricated sections of suction anchors for the Troll C and Åsgard A, B and C semisubmersibles.For the Åsgard suction anchors, Rautaruukki delivered the steel in 10-20 sections, depending on the number of anchors, straight from its own harbour at Raahe to Fabricon in Norway where they were welded together.
Over the last 18 years, Rautaruukki has spent considerable effort in reducing its lead times. For domestic deliveries, this factor has been shortened from around 10 weeks for steel plate and coils to only two weeks from the date of order to dispatch. "We believe that there is margin to reduce this time still further, now that all the production enhancements are in place, but we are currently already one of the best in the world in this respect," says Saralampi.
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