Conference Proceedings Paper
Flow-Accelerated Corrosion Entrance Effect in Feeders
9th International Conference on CANDU® Maintenance - 2011 December 04-06
Lan Sun (AECL Nuclear Laboratories)
John Pietralik (AECL Nuclear Laboratories)
Chris Schefski (AECL Nuclear Laboratories)
Yuqing Ding (Atomic Energy of Canada Limited)
Flow‑Accelerated Corrosion (FAC) is a major degradation mechanism in carbon steel piping systems in nuclear power plants. Although FAC has been studied for more than 25 years, not all of the effects are known. One particular controlling factor is the entrance effect or leading‑edge effect, which refers to an accelerated wear immediately downstream of a weld if the weld connects resistant upstream material with non-resistant downstream material. This type of degradation has been observed at a number of nuclear and fossil power plants, and has raised concern related to plant FAC monitoring programs.
The chromium content has been understood to play a critical role in the prediction and control of FAC in power piping systems. The entrance effect enhances the FAC thinning rate of the downstream material and it is associated with the effect of chromium content on FAC, because even small contents of chromium (in the order of 0.1%) can effectively eliminate FAC in single-phase systems, and greatly reduce the FAC thinning rate in two-phase systems.
This paper analyzes the FAC entrance effect in CANDU feeders and presents a few nuclear power plant cases. The plant data and degradation mechanism is explained by a numerical model which simulated the flow and the related mass transfer, and the obtained enhancement ratios for several feeder cases agree with the plant data very well. The development of inspection plans and replacement strategy should benefit through the increase in utility awareness and understanding of this effect.
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