Abstract
In the present work, several specimens were obtained from microalloyed HP40Nb reformer tubes with the different serviced period. The creep tests were conducted at a temperature of 950 °C and under stress levels in the range 25–55 MPa. Results indicated that the degradation of the creep life was due to the increase of the serviced period. The microstructural degradation and creep voids were observed at the grain boundary regions, attributed to the main reason leading to the premature creep failure. The creep exponent started decreasing after the servicing and approached a constant value after 7.2 years. The creep coefficient was obtained to be a function of time when the creep exponent was constant. Norton’s creep power law equation was used to derive an equation describing the relationship between the diametrical expansion and serviced period of the reformer tubes. Larson-Miller curves were obtained from creep test data. Amount of carbides from the different serviced period was also calculated.
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Abbreviations
- A :
-
Creep coefficient
- C:
-
Larson-Miller constant
- n :
-
Creep exponent
- σ :
-
Applied stress
- \(\dot \varepsilon \) :
-
Minimum creep strain rate
- P :
-
Pressure
- P o :
-
External pressure
- P i :
-
Internal pressure
- r:
-
Radii of tube
- ro :
-
External radii of tube
- ri :
-
Internal radii of tube
- R 2 :
-
Coefficient of determination
- T:
-
Temperature
- tS :
-
Serviced period
- tr :
-
Rupture time
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Acknowledgments
This work was supported by the KETEP (No. 2013 2010 500060), granted financial resource from the Ministry of Trade, Industry & Energy (MOTIE), Republic of Korea. This work was also supported by the KETEP granted from MOTIE (No. 20141010101850). Authors deeply appreciate the company providing the serviced reformer tubes and relevant information.
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Van Hung Dao received his M.S degree in Mechanical Engineering from Chung-Ang University, Korea in 2016. He is currently a Ph.D. candidate at Chung-Ang University. His research interests are microstructural analysis and application of high temperature fracture mechanics to life assessment of structural material. He is extending research to behavior of additive manufactured materials.
Jung Soo Song received his Master degree in Mechanical Engineering from Chung-Ang University, Korea in 2002. He is currently a Ph.D. candidate at Chung-Ang University. And he is also a Senior Researcher in Energy Safety Research Institute at Chung-Ang University. His research interests are high temperature fracture mechanics, remaining life assessment and risk-based inspection for industrial facilities.
Joo Yong Kim received his M.S. degree in Mechanical Engineering from Chung-Ang University, Korea in 2016. He is now working on Korea Company. His research interests are microstructural analysis, reliability and life assessment of structural material such as reformer tube.
Kee Bong Yoon received his M.S. in Mechanical Engineering from KAIST and Ph.D. from Georgia Institute of Technology. He is currently a Professor at Chung-Ang University. His research interests are high temperature fracture mechanics, failure analysis and risk based management of facilities in semi-conductor industry as well as the conventional power and process plants. He is extending research to fracture of additive manufactured materials.
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Dao, V.H., Song, J.S., Kim, J.Y. et al. Creep deformation characteristics of microalloyed HP40Nb steel at 950 °C. J Mech Sci Technol 33, 4813–4821 (2019). https://doi.org/10.1007/s12206-019-0922-9
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DOI: https://doi.org/10.1007/s12206-019-0922-9