Abstract
The features of unusual wall thinning of carbon steel piping used in the transport of pure water at elevated temperatures are described. The case of Mihama nuclear power plant is used as a typical example, since the results of investigations conducted by the investigation committee of the Nuclear and Industrial Safety Agency are already available at their web site, and detailed information, such as data on residual wall thickness distribution and clear photographs of the thinned pipe wall surface etc. are readily available. Two models for illustrating the generation mechanism were examined : the FAC (flow accelerated corrosion) model and the macro-cell corrosion model. The latter explained the mechanism reasonably well, and methods for preventing wall thinning, based on this model, are given. Procedures for detecting the progress of wall thinning were also described.
