Niobium bearing steels in pipeline projects

Niobium is the primary strengthener and toughening agent in modern linepipe steels. Consumption of FeNb in these products has grown from virtually zero in 1957 to over fourteen million pounds (6000 tonnes) of contained niobium in 2001. During this period there has been a steady increase in strength levels from 42 ksi to 100 ksi and above, as well as requirements for improved toughness at temperatures down to -50°F (-46°C). Pipeline pressures have increased and installation has been accomplished in water depths greater than 9,000 ft. (2,592 m). The required combinations of mechanical properties coupled with ease of field weldability, and resistance to corrosive media such as natural gas containing H2S and CO2, are achieved through the use of low carbon contents, alloying with elements such as molybdenum, chromium, copper, nickel and the like and utilizing the beneficial effect of niobium in retarding austenite recrystallization during hot rolling. The latter technologies are collectively described as Thermal Mechanical Controlled Processing (TMCP) practices. A brief history and chronology of the developments are presented and current niobium usage is illustrated with examples for Double Submerged Arc Welded (DSAW), seamless and Electric Resistance Welded (ERW) linepipe. Technical data for recent projects is presented. (AU)