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Korean Journal of Metals and Materials > Volume 54(11); 2016 > Article
Korean Journal of Metals and Materials 2016;54(11): 817-825. doi: https://doi.org/10.3365/KJMM.2016.54.11.817
Effects of Induction Heat Bending and Heat Treatment on the Boric Acid Corrosion of Low Alloy Steel Pipe for Nuclear Power Plants
Ki-Tae Kim1, Min-Chul Shin3, Hyun-Young Chang2, Heung-Bae Park2, Gi-Ho Sung3, Young-Sik Kim1,*
1Materials Research Center for Clean and Energy Technology, School of Materials Science and Engineering, Andong National University, Gyeongbuk 36729, Republic of Korea
2Power Engineering Research Institute, KEPCO E&C, Gyeongbuk 39660, Republic of Korea
3Sungil SIM Co. Ltd, Busan 46753, Republic of Korea
Correspondence  Young-Sik Kim ,Tel: +82-54-820-5504, Email: yikim@anu.ac.kr
Received: 19 October 2015;  Accepted: 19 May 2016.  Published online: 5 November 2016.
ABSTRACT
In many plants, including nuclear power plants, pipelines are composed of numerous fittings such as elbows. When plants use these fittings, welding points need to be increased, and the number of inspections also then increases. As an alternative to welding, the pipe bending process forms bent pipe by applying strain at low or high temperatures. This work investigates how heat treatment affects on the boric acid corrosion of ASME SA335 Gr. P22 caused by the induction heat bending process. Microstructure analysis and immersion corrosion tests were performed. It was shown that every area of the induction heat bent pipe exhibited a high corrosion rate in the boric acid corrosion test. This behavior was due to the enrichment of phosphorous in the ferrite phase, which occurred during the induction heat bending process. This caused the ferrite phase to act as a corrosion initiation site. However, when re-heat treatment was applied after the bending process, it enhanced corrosion resistance. It was proved that this resistance was closely related to the degree of the phosphorus segregation in the ferrite phase.
Keywords: low alloy steel, induction heat bending, boric acid corrosion, phosphorus
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