Oxide-scale thickness measurement for predicting crack growth history in elevated temperature components

Structural components from ferritic steels are known to oxidize in air when exposed to high temperatures and can develop cracks during service. Oxide thicknessxon the surface of the crack is related to the exposure time, and temperature and can be used to determine the history of cracks. A model for describing the kinetics of oxide formation in ASTM grade P91 piping steel is developed using flat, polished specimens of the steel and exposing them to high temperatures. Oxide thickness measurements were made and an oxidation kinetics model was developed. Oxide thickness profiles on the creep-fatigue crack surfaces of compact type specimens with a known crack growth history were also characterized using scanning electron microscopy. The oxidation model is then used to predict drack growth rates in compact type specimens. Good agreement between the measured and predicted crack growth rates were found.