Flow accelerated corrosion (FAC) is a major issue for aging of carbon steel piping system such as secondary sides of NPPs. An equipotential switching direct current potential drop (ES-DCPD) method was developed to monitor the thickness of piping that covers area instead of points unlike ultrasonic technique (UT). Hence it covers wide range of piping at one time and takes less monitoring time. In this paper, two accelerated FAC phenomenon; 23.7% thinning in 216.7 hrs and 51.4% thinning in 795 hrs are discussed. These were monitored by both ES-DCPD as well as UT. To accelerate FAC process water chemistry parameters were controlled and monitored. As sensitive factors on FAC, temperature and pH were changed during the test, the wall loss monitored results successfully reflected these changes. These results were also found in agreement with predication model.

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