Overview of New Development for X80/X100 Grade Linepipe Steels

An overview of the manufacturing technology for X80/X100 grade linepipe steel at POSCO was introduced. The microstructure and mechanical properties of X80/X100 steel plates and pipes were analyzed and discussed. Microstructure of plate steel was observed with optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and electron back scattered diffraction (EBSD). Through the UOE simulator, the changes of mechanical properties after pipe forming from plate to pipe were tested and understood. The microstructure of X80 steel was composed of acicular ferrite containing M/A (Martensite/Austenite Constituent) phase. Tested X80 steel plate and pipe were found to have excellent DWTT property. DWTT 85% SATT of X80 steel was about -60℃ in plate and -40℃ in pipe. The deformation capacity of X80 linepipe was evaluated by large scale deforming machine operating under the loading of bending and axial compression force. The compressive axial force had a little effect on the peak moment but changed the deformation pattern and state of critical compressive strain of linepipe. It was found that the developed X80 linepipe was within the specification of DNV and API codes in terms of buckling capacity. In case of X100 steel, bainitic ferrite exhibiting lath and granular type morphology was major phase and M/A existed as second phase. It was shown that the developed X100 steel can be realized to have appropriate properties for UOE pipe. DWTT 85% SATT of the tested 19mm thick X00 steel pipe was below -40 oC.

کلیدواژه ها:

Linepipe ، X80 ، X100 ، plate ، pipe ، UOE Simulator ، bending capacity