Evaluation of Creep Crack Growth Rate of P92 Welds Using Fracture Mechanics Parameters

Abstract

High Cr ferritic heat resisting steels have been widely used for boiler components in ultrasupercritical thermal power plants operated at about 600°C. In the welded joint of these steels, type-IV crack initates in the fine-grained heat affected zone during long-term use at high temperatures and their creep strength decreases. In this paper, creep properties and creep crack growth (CCG) properties of P92 welds are presented. The CCG tests are carried out using cross-welded compact tension C(T) specimens at several temperatures. The crack front was located within the fine-grained HAZ region to simulate type-IV cracking. Finite element analysis was conducted to simulate multiaxiality in welded joints and to compare experimental results. The constitutive behavior for these materials is described by a power-law creep model. C∗ and Q∗ parameters are used to evaluate CCG rate of P92 welds for comparison. C∗ parameters can characterize approximately 20% of the total life of CCG in P92 welds, and Q∗ parameters can characterize approximately 80% of the total life. Q∗ parameter is one of the useful parameters to predict CCG life in P92 welds.