Development of Grade X80 Heavy Gauge Linepipe for Extremely Low Temperature Service

摘要

Grade X80 with 29.6mm thick linepipe with excellent low-temperaturetoughness down to -45 degrees C or less was developed. Good balanceof Drop Weight Tear Test (DWTT) properties applicable to the designtemperature of -45 degrees C and high Charpy V-Notched (CVN)absorbed energy of approximately 250J were achieved by amicrostructure control. DWTT 85% transition temperature of thisdeveloped pipe was -65 degrees C or less and CVN absorbed energy at-85 degrees C remained high. In the developed pipe, substantialseparation was not formed, although slight separation was observedafter DWTT. It can be considered that the excellent properties wereobtained due to the suppression of separation. The suppression ofseparation was achieved by a microstructure control. Fine ferritebainitemicrostructure including few deformed ferrite grains wasformed in the developed pipe by the optimized TMCP condition.