The increasing demand for natural gas will further influence the type of its transportation in the future, both from the strategic and economic point of view. Long-distance pipelines are a safe and economic means to transport the gas from production sites to end users. High-strength steels in grade X80 are nowadays state of the art. Grade X100 was recently developed but not yet utilised. The present-day technical limitations on the production of X120 line pipe namely the steel composition, the pipe forming and the welding are addressed in this paper. Production test results on X120 pipes are presented to describe the materials properties. A low carbon and low PCM steel with VNbTiB microalloying concept is used. In the plate rolling the main attention is turned to the heavy accelerated cooling. The large spring back that occurs during the U-forming step of the UOE process is one of the most complex aspects in forming X120. To handle this aspect FEM calculations were used to modify the forming parameters and to optimise the shape of the U-press tool. For optimising the existing welding procedure with respect to an avoidance of HAZ softening, a low heat input welding technology and new welding consumables were developed.

The present paper deals with the development of low carbon (, 0 . 04%) microalloyed steel plates for high grade (> X80, yield strength > 550 MPa) longitudinally welded large diameter pipes for gas transmission. The interest in increasing the grade level of steels for linepipe is to improve transportation efficiency by an increase in operation pressure. In addition, increasing the grade allows thinner wall pipes to be used, reducing costs and improving the rate of field joint welding. A general requirement for linepipe steels is a simultaneous increase in fracture toughness as the strength increases. However, it is remarkably difficult to achieve a combination of high strength and good low temperature toughness. Bainitic microstructures have shown the capability to attain such requirements.

This paper deals with the development of low carbon NbTiB micro-alloyed high strength low alloy steel for heavy plates with high wall thickness. In the production of heavy plate it is remarkably difficult to achieve a combination of high strength and good low-temperature toughness. Bainitic microstructures have shown the capability to attain such requirements. To achieve a bainitic microstructure even for heavy wall products the formation of bainite can be promoted and supported by the use of small amounts of boron as a micro-alloying element. This industrial research project is based on the addition of small amounts of boron to promote the desired bainitic structure. Mill rolling trials were carried out to determine the optimum process parameters. The results of experimental mill rolling trials on 35 mm plates will be presented in this paper.

Plate fracture is a defective fracture structure in nodular cast iron that can be found especially in the transition area of feeder, feeder neck and the cast part itself. It occurs rather spontaneously due to the fact that the exact reason for it is still unknown. The microstructure of the casting in the area of plate fracture comprises aligned graphite nodules in combination with a pronounced dendritic microstructure as characteristical features. A series of casting trials was performed in which plate like samples were produced. It could be shown by means of metallographic investigation of these samples in combination with the simulation of the solidification that specific local conditions during the solidification are the metallurgical reasons for the appearance of plate fracture. These specific conditions were the local temperature gradient and the velocity of the liquid/solid interface.