Plastic Limit Analysis of Modified 9Cr-1Mo Steel Pressure Vessel Containing Volume Defect with Creep Damage Law

Abstract

A numerical method for evaluating the plastic limit load of modified 9Cr-1Mo steel pressure vessel structures containing volume defect at [Formula: see text]C is proposed based on the plastic limit load concept under high temperature. Firstly, the creep analysis of the defected pressure vessel is conducted with the Liu–Murakami creep model to obtain the creep damage after a prescribed service time. Secondly, the obtained creep damage is introduced into Ramberg–Osgood model through the hardness ratio to characterize the material deterioration during the creep process. Thirdly, the plastic limit load of the defected pressure vessel under high temperature is obtained through the classic zero curvature criterion with the modified Ramberg–Osgood model. The numerical examples for the pressure vessels with different sizes of volume defects are performed, and the failure modes of pressure vessel structures at the limit state are revealed and the fitting formulae between the plastic limit load ratio and the dimensionless defect factor are established based on the numerical results. Results show that the plastic limit load and the service time of pressure vessel structures under high temperature are sensitive to the volume defect ratio and can be determined easily through the fitting formulae which are convenient for engineering applications.