New Development of High Grade X80 to X120 Pipeline Steels

Abstract

An overview of the manufacturing technology for high-strength pipeline steels was introduced. The microstructure and mechanical properties of X80, X100, and X120 grade steel plates and pipes were analyzed and discussed. Through the UOE simulator, the changes of mechanical properties after pipe-forming from plate to pipe were evaluated. 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 drop weight tear test (DWTT) property. DWTT 85% SATT of X80 steel was about −40°C in pipe. The deformation capacity of X80 pipeline was evaluated by large-scale deforming machine operating under the loading of bending and axial compression force. It was found that the developed X80 pipeline 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 were 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 X00 steel pipe was shown below −40°C. Also, the development of X120 grade pipeline steel was tried. The microstructure of X120 steel was composed of bainitic ferrite and acicular ferrite. The tensile properties of developed X120 steel plate and pipe fully satisfied the property target required in the current research. DWTT 75% SATT of the developed X120 steel plate and pipe was below −30°C.