Flow-Assisted (or Accelerated) Corrosion (FAC) process is a widespread problem within the steam water circuits of power plants. In some cases, in the past or without an adapted prediction program, the occurred damages have been extensive and have required unscheduled shutdowns and costly repairs. Several catastrophic failures have also caused human injuries or deaths. This phenomenon mainly affects the carbon steel pipings and components with low chromium contents.

On a temperature point of view, there is no low or high threshold but significant damages occur between 75 °C and 300°C, with a kinetics that is maximum around 150°C – 180 °C. The FAC degradation can lead to wall thinning of piping from 0.1 to 10 mm/year. The phenomenon depends critically of a couple of variables:

                         1) Water chemistry.
                         2) Temperature of water.
                         3) Hydrodynamic (flow rate and pipe design).
                         4) Moisture contents for wet steam lines.
                         5) Oxygen contents.
                         6) Alloys impurities in the steel.

The influence of these variable has been studied on the CIROCO loop in FRANCE at EDF R&D department called MMC. The results obtained have been used to develop a basic theoretical model and a software, BRT-CICERO™, whose algorithms have been written by EDF SEPTEN. This software is now used in all French Nuclear Power Plants, in South Africa (Koeberg NPP) and China (DNMC) as well, to achieve predictions concerning the thinning of secondary pipings. A cooperative R&D program between EDF and EPRI (US research Institute for the Utilities) has been carried out during several years on this subject.

EDF continues its tests to improve its knowledge of the phenomena and to make the software answers closer to physical reality.

The main goal of this paper is to provide information necessary to have a good comprehension of the FAC phenomenon and to review the main hypothesis used for the FAC modelling of carbon steels, in pure or demineralized, deoxygenated and alkaline buffered (light or strong buffer) water.

Precisely, we focus on the algorithms which model the effects of the temperature, of the carbon steel composition, of the chemistry and of the impurities in the water (i.e. oxygen).

Finally, the calculated and measured thicknesses on components are analyzed according to the grid pattern in order to confirm the accuracy of such a software based on R&D experiments and NPP's feedback.