Pioneering development by Sandvik Steel and by key customers in the offshore oil and gas industries has seen Sandvik’s duplex and super duplex stainless steels become the industry standard for hydraulic tubes in drilling risers, which provide the link between drilling platforms and equipment on the seabed. Replacing standard 316L stainless steels, Sandvik SAF 2205 and SAF 2507 duplex grades offer increased corrosion resistance but more especially high tensile and yield strength. The result is weight and cost savings in the hydraulic tubes used by drilling riser producers.
Drilling risers contain a package of tubes, comprising a heavy gauge, large diameter carbon steel central tube, through which the drill is lowered to the sea bed, and hydraulic tubes. Normally measuring between 38 mm and 127 mm outside diameter, the hydraulic tubes are secured around the central tube. Their function is to control valves, such as to exclude water during drilling, and operate at pressure, often at 300 bar or more. The risers, each of 20 or 30 metres in length, are joined together to achieve depths in excess of 2000 metres. The high strength benefits of duplex steels, compared to standard stainless steel grades, means that a much thinner hydraulic tube wall thickness can be used for the same pressure with a resultant weight saving.
