Feasibility of Using Oxide Thickness Measurements for Predicting Crack Growth Rates in P91 Steel Components
Date of Graduation
Master of Science in Mechanical Engineering (MSME)
Rick J. Couvillion
Second Committee Member
Paul C. Millett
Fracture Mechanics, Oxidation, Oxidation Kinetics, P91 Steel, Predicting Crack Growth
There are only few methods available for predicting the age of cracks that are found in high
temperature structural components during service; among the promising ones is the oxide
thickness measurement technique. Oxide thickness profiles are taken from crack surfaces of
components and used for predicting the rates of crack propagation. This technique is particularly
suitable for high temperature components fabricated from ferritic steels commonly used in power
plants that run on fossil fuels. To implement this technique, it is necessary to fully understand the
kinetics of high temperature oxidation in these steels. In this study, the oxidation characteristics
of an American Society of Testing and Materials (ASTM) Grade P91 ferritic steel used in high
temperature piping is characterized.
The literature shows that there are four primary mechanisms that influence the oxide thickness
during high temperature exposure. Initially, the oxide thickness increases in a linear fashion with
time and then as steady-state conditions are established, the parabolic relationship takes over.
Multiple types of oxides with different rate characteristics can also form. Oxide degradation can
occur by spallation due to porosity and formation of cracks. Evaporation or volatility can also
occur and result in loss of oxide thickness. These factors must be considered in oxide thickness
analysis to determine crack growth history.
Two sets of laboratory experiments were conducted. The first consisted of measurement of oxide
thicknesses after exposure to high temperature for various periods to determine the oxidation
kinetics. The oxidized samples were subjected to SEM examination and measurements of
physical properties such as density and porosity levels. The second set of experiments consisted
of measuring the oxide layer thickness on the fracture surfaces of creep-fatigue crack growth
samples tested as part of a previous study where the crack growth rates were measured. These
reported measurements are used to compare with the predicted crack growth rates from the
analytical models that are developed as part of this study. The success of the technique is
measured by finding the correlation coefficient, which is within a factor of 2.58.
Huneycutt, R. E. (2017). Feasibility of Using Oxide Thickness Measurements for Predicting Crack Growth Rates in P91 Steel Components. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/2028