Development of Modern Steels for Strain Based Design Pipe Lines and Simulation Results

Due to the exploration of gas and oil sources in remote regions with harsh environment, the pipe line designers are faced with the challenging conditions. Especially in the cases where displacement-controlled loads are the predominant design condition, such as ground movement, strain-based design is applied instead of stress-based design to build safer pipelines and to assure the integrity of the lines along their lifetimes. It requires steels to have a large strain hardening capacity, long uniform elongation, and good toughness to achieve a well-defined and sufficient plastic deformation. In order to fulfil the requirements, all the processing steps are supposed to be well designed, for example, the chemical composition, microstructural design, thermo-mechanical controlled process (TMCP) and heat treatment, etc. In general pipe line steel has a low carbon, high manganese content combined with a certain amount of micro-alloying elements as Nb, Ti and sometimes B. Using Thermo-mechanical rolling and cooling schedules excellent combinations of strength and toughness can be established. To successfully produce steel plates for strain based design pipe lines the actual heating rolling and cooling technologies must be developed further as well as the equipment to produce such steel. The paper gives an overview about modern plate mill equipment and new setup strategies for the production of heavy plates X70 to X100 as well as thethermo-dynamic simulations used during the development.