Life assessment for creep and fatigue of steam turbine components

Abstract

Improvement of life assessment technologies for power plant materials and components is important in order to meet demands for economy and reliability. As for steam turbines, blade root and disc joints are one of the critical parts in turbines that experience the most severe creep and fatigue damage under high temperature or corrosive environment. In these parts, the structural stress concentration areas are close to the contact planes of blades and rotors, and this produces a complicated stress-strain field. Therefore, life assessment technologies based on precise stress analysis methods and damage mechanisms are necessary to ensure the reliability and economy of steam turbines. In this paper, creep and fatigue tests results by using component specimens simulating blade and rotor joint portions are described. Damage mechanisms of joint portions were investigated based on the observations of the micro-crack initiation and growth behaviors. Life assessment methodologies for joint structures are also discussed, based on the micro-damage, micro-crack or micro-cavity, and nonlinear finite element analyses of component specimens.