“Low Temperature” FAC

Flow-acceleration corrosion (FAC) is a degradation mechanism that impacts carbon steel under conditions often found in both nuclear and fossil power plants. FAC damage is normally found between about 90 – 230°C. However, damage at higher temperatures and occasionally lower temperatures has been reported. Although not common, low temperature degradation can result in shutdowns and costly maintenance activities. Described are reports of damage to piping and equipment in the condensate system and downstream of a blowdown demineralizer at several Pressurized Water Reactors (PWR). In all cases, the piping contained flowing deoxygenated, neutral water at about 120°F (∼ 50°C). Also, experience with non-FAC degradation was reported at one unit. This paper also describes damage to systems in two Boiling Water Reactors (BWR). In these cases, there was a low concentration of dissolved oxygen in neutral water. Damage to BWRs may be less common, but damage rates similar to those found in PWRs have been observed. Based on this work, it is recommended that plant operators perform susceptibility analyses and if necessary inspections in areas where there is neutral water with a low concentration of dissolved oxygen. PWR units that run their polishers full-time are especially vulnerable. Implications to system re-design will also be presented.