Abstract: The improvement of the pressure-temperature (P-T) limit curve methodologies given by the ASME code Ver.2010 and the RCCM code Ver.2007 are presented, and a new P-T curve calculation procedure is proposed according to the RCCM code Ver.2007. The effect of crack size, cooling rate, stress intensity factor plasticity correction and cladding on the P-T curve are studied by performing 3D finite element analysis. The result indicates that crack size and cladding have significant impact on P-T curve, while stress intensity factor plasticity correction has limited influence; the cooling rate effect depends on which standard code is used.