The pressure to temperature (
P-
T) curve is significant to ensure the vessel integrity and deal with the reactor pressure vessel(RPV) ageing. The traditional method using the material near static facture limit value (
KIc) by
t-
RTNDT curve to plot the
P-
T curve cannot obtain the appropriate
RTNDT for an irradiated material and is overly conservative. With the surveillance data of a reactor pressure vessel, this paper calculates the Master Curve index temperature,
RTT0, at the ending of the RPV 50 years life. The ASME Code Case N629 effort to utilize the Master Curve Method is used to plot the
P-
T curve , compared with results of traditional method, the
P-
T operating window is extended and the RPV economy is improved.