Session: 14-06-01: Developments in Design Theory for Component and System Safety and Reliability

Paper Number: 109395

109395 - Effects of Thermal Mechanical Fatigue on a 2.2Cr-1Mo Steam Header 

Remaining life estimates are an essential tool used with many high-temperature components. Understanding the remaining life of a component is critical to maintaining safe operation and is necessary for budgeting repairs. However, the life expectancy of many high-temperature components is often limited due to thermo-mechanical fatigue. This fatigue results from the high stresses that occur during the cyclic loading at elevated temperatures and pressures. Finite Element Analysis, FEA, is often used to predict the performance of these components.
In this study, the predicted lifetime of a 2.25Cr-1Mo power plant header was evaluated using FEA. The material was represented using the Chaboche non-linear kinematic hardening (NLKH) model. The Chaboche NLKH model coefficients were established for temperatures up to 600°C using data from virgin machined samples. The material was then applied to a realistic power plant header using the commercial software Abaqus. A pressure and temperature profile representative of the system is applied to evaluate the header under normal operating conditions. The temperature and pressure profiles are uniform, with separate temperatures applied to the header and the tube. Specifically, the header temperature ranges from 480 to 505 °C, while the tube temperature ranges from 480 to 525 °C. The pressure within the header varies from 4 to 8 MPa.
The header did not predict damage likely to cause LCF in response to the common transient. The results suggest that failure will be considered high cycle fatigue in response to the applied transient. However, these results were in conflict with industrial experience, indicating that other factors may be contributing to the material failure. To address these conflicting results, future work will evaluate the material condition of service-exposed units to account for material deterioration. It is important to note that the material response was approximated from virgin machined samples, and there may be variations in material behavior due to exposure to service conditions. As such, further research is necessary to fully understand the effects of exposure to service conditions on material behavior and lifetime estimates. Additionally, additional transients will be considered, as it is possible that infrequent transients are damaging transients.
In conclusion, the use of remaining life estimates is necessary for maintaining safe operation and budgeting for repairs of high-temperature components. However, predicting the life expectancy of these components often requires in-depth reviews to evaluate the thermo-mechanical fatigue. Incorporating material models such as the Chaboche NLKH model used in this study into FEA is a widely used tool for predicting the performance of these components. Further research is necessary to fully understand the effects of exposure to service conditions on material behavior and lifetime estimates.

Presenting Author: Michael Zimnoch UNCC

Presenting Author Biography: Graduate Student at the University of North Carolina Charlotte.

Authors:

Michael Zimnoch UNCC
Elnaz Haddadi UNC Charlotte
Ian Perrin UNC Charlotte
Alireza Tabarraei UNC Charlotte