Dynamic Fracture Toughness and Charpy Transition Properties of a Service-Exposed 2.25Cr-1Mo Reheater Header Pipe

Abstract

Residual life analysis of power plant components like boiler tubes, superheater outlet headers, reheater headers, steam pipes, etc., is important for life extension and avoidance of catastrophic failure. In this context, fracture toughness is very important. The fracture characteristics after prolonged exposure to high temperatures and pressures are likely to be different from that of the virgin material. 2.25Cr-1Mo reheater header pipe exposed at 813 K for 120,000 h was studied by instrumented impact tests (IIT) to evaluate dynamic fracture toughness and Charpy transition properties. The methods presented in this paper for estimating dynamic fracture toughness from IIT of Charpy specimens give reliably conservative results without the need for precracking. For estimating fracture appearance transition temperature (FATT) from IIT load-time traces, the equation for percent shear fracture, PSF3, gives the best 1:1 correlation with measured values from fracture surfaces. The lower bound equation for variation of fracture toughness with temperature derived in the present study is higher than that obtained from the FATT master curve (FATT-MC) approach. Comparison of Charpy indices like FATT and upper-shelf energy for the service exposed steel to results for the virgin material reported in the literature and the compositional J-Factor estimates for temper-embrittlement susceptibility indicate that the present steel, even after 120,000 h exposure to high temperature service, has probably undergone only very little or nil degradation in toughness properties.