Niobium containing steels for spiral and electric resistance welded line pipe production

Niobium containing thermomechanical treated steels have been used as line pipe materials for several decades. These steels combine high strength, high impact toughness and outstandingweldability. There are basically two different processes to produce pipes from hot strip. Both processes have specific needs that have to be considered during hot strip production. Thermomechanical rolling might cause anomalies called separations in the fracture behaviour. Separations might be distinguished in several categories. Cleavage fracture separations can be avoided by controlled rolling above Ar3 and grain boundary separations by coiling at low temperatures. (AU)