Fracture toughness of stainless steel casting (duplex stainless steel) is reduced under the condition about 300℃ by the thermal aging. For the flaw evaluation on thermal aged duplex stainless steel pipes, Fracture Assessment Curve (FAC) of R6 Option2 method is calculated using the stress-strain curve and J-resistance curve of thermal aged duplex stainless steel. To evaluate the fracture load on thermal aged duplex stainless steel in simple method, corrective factor is prepared in order to convert limit load based on net section criteria to fracture load based on R6 method.