Research On The Numerical Simulation Of Weld Thermal Process In P91 Steel And The Effect On Joint Properties

P91 steel is recently developed heat-resisting steel. It possesses good processability, weldability, high-temperature stability and heat resistance. P91 steel thick-walled pipe has been widely used for power station construction and boiler pressure vessel in China.The joint of P91 steel has weakness of low impact toughness. Localized PWHT (Post Welded Heat Tempering) is often used to improve the joint impact. But the problem is the great dissemination of joint impact toughness. The min impact toughness in joint is only 5～8J,but according to the ASME(American Society of Mechanical Engineers), the steel impact in electric power must be more than 41J. So how to settle this problem is urgent.The paper combines the numerical simulation with theory to analyze this problem. FEM was employed to analyze welding and localized PWHT temperature field of P91 thick-walled pipe(Φ425×50mm) used in high-temperature and high-press(600℃,150atmospheric pressures), the result shows that the temperature field is non-uniform. The max temperature difference between int-and-ext wall is 80℃. The paper has proved that changing heating-way can improve the non-uniform of localized PWHT temperature field, make the temperature difference falling to 10℃, the whole joint meet the tempering temperature request(760±10℃),then increase the impact toughness and reduce the dissemination.Therefore, the result of the subject has considerable guiding signification for making the P91 thick-walled pipe localized PWHT technology.