Feasibility of Using Oxide Thickness Measurements for Predicting Crack Growth Rates in P91 Steel Components

<p>There are only few methods available for predicting the age of cracks that are found in high</p> <p>temperature structural components during service; among the promising ones is the oxide</p> <p>thickness measurement technique. Oxide thickness profiles are taken from crack surfaces of</p> <p>components and used for predicting the rates of crack propagation. This technique is particularly</p> <p>suitable for high temperature components fabricated from ferritic steels commonly used in power</p> <p>plants that run on fossil fuels. To implement this technique, it is necessary to fully understand the</p> <p>kinetics of high temperature oxidation in these steels. In this study, the oxidation characteristics</p> <p>of an American Society of Testing and Materials (ASTM) Grade P91 ferritic steel used in high</p> <p>temperature piping is characterized.</p> <p>The literature shows that there are four primary mechanisms that influence the oxide thickness</p> <p>during high temperature exposure. Initially, the oxide thickness increases in a linear fashion with</p> <p>time and then as steady-state conditions are established, the parabolic relationship takes over.</p> <p>Multiple types of oxides with different rate characteristics can also form. Oxide degradation can</p> <p>occur by spallation due to porosity and formation of cracks. Evaporation or volatility can also</p> <p>occur and result in loss of oxide thickness. These factors must be considered in oxide thickness</p> <p>analysis to determine crack growth history.</p> <p>Two sets of laboratory experiments were conducted. The first consisted of measurement of oxide</p> <p>thicknesses after exposure to high temperature for various periods to determine the oxidation</p> <p>kinetics. The oxidized samples were subjected to SEM examination and measurements of</p> <p>physical properties such as density and porosity levels. The second set of experiments consisted</p> <p>of measuring the oxide layer thickness on the fracture surfaces of creep-fatigue crack growth</p> <p>samples tested as part of a previous study where the crack growth rates were measured. These</p> <p>reported measurements are used to compare with the predicted crack growth rates from the</p> <p>analytical models that are developed as part of this study. The success of the technique is</p> <p>measured by finding the correlation coefficient, which is within a factor of 2.58.</p>

Name thesis:degree_name

Master of Science in Mechanical Engineering (MSME)

Level thesis:degree_level

Thesis

Year dc:date.available

2017

Author dc:creator

• Huneycutt, Ralph Edward, IV

Advisor dc:contributor.advisor

• Saxena, Ashok

Contributors dc:contributor

• Couvillion, Rick J.
• Millett, Paul C.

• Fracture Mechanics
• Oxidation
• Oxidation Kinetics
• P91 Steel
• Predicting Crack Growth
• Engineering Mechanics
• Mechanical Engineering

Repository record dc:identifier

https://scholarworks.uark.edu/etd/2028

OAI identifier oai:identifier

oai:scholarworks.uark.edu:etd-3567