A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed in front of the orifice. This paper deals with UT thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.
Cite this paper
K. Hwang, C. Lee and C. Choi, "A Study on the Cause Analysis for the Wall Thinning and Leakage in Small Bore Piping Downstream of Orifice," World Journal of Nuclear Science and Technology, Vol. 4 No. 1, 2014, pp. 1-6. doi: 10.4236/wjnst.2014.41001.
 J. Horowitz, “Recommendations for Controlling Cavitation, Flashing, Liquid Droplet Impingement Erosion, and Solid Particle Erosion in Nuclear Power Plant Piping Systems,” EPRI 1011231, Final Report, November 2004.
 K. M. Hwang, “Investigation on the Evaluation for Liquid Droplet Impingement Erosion through Prediction Model and Experiment,” The Journal of Mechanical Science and Technology (Korean), Vol. 35, No. 10, 2011, pp. 1105-1110.
 Y. S. Lee, S. G. Park and J. S. Lim, “Extraction Steam Line Drain Failure,” KHNP-FAC-2009-EPRI-01, Rev. 1, 2009.
 C. Crowe, M. Sommerfield and Y. Tsuji, “Multiphase Flows with Droplets and Particles,” CRC Press, Boca Raton, 1998.
 R. Morita and Y. Chiyama, “Development of a Wall Thinning Rate Model for Liquid Droplet Impingement Erosion,” ASME 2012 Pressure Vessels and Piping Conference, Vol. 6, 2012.
 J. H. Brunton and M. C. Rochester, “Erosion of Solid Surfaces by the Impact of Liquid Drops,” Erosion Treatise on Materials Science and Technology, Vol. 16, Edited by C. M. Preece, Academic Press, New York, 1979.