DEVELOPMENT OF μ-PIXE/RBS/SEM SYSTEM FOR CORROSION LAYER ANALYSIS OF STEEL

Wall thinning of piping made of carbon steel when exposed to high temperature water flow and va-por is a common problem in all types of these plants. Oxide layer formation and dissolution should be related to the mechanism of corrosion. In order to understand the mechanism of corrosion, characterization of oxide layer including elemental concentration in the localized area is indispensable. In this study, simultaneous μ-PIXE/RBS/SEM analysis system was developed to obtain elemental characterization on oxide layer in localized area as well as to obtaining surface condition. Carbon steel samples were oxidized dynamically for 1100 hours and analyzed by the system. The oxide layer is not uniform even in the localized area of 30 × 30 μm2. In the chromium content of 0.003 wt%, oxide layer thickness varied from 0.71 to 1.2 mg/cm2. While accumulation of chromium is seen in the map, accumulation is not related to the iron distribution. Chromium and iron ratio in the accumulated region is more than five times higher than that of the other area. The higher chromium and iron ratio indicates that chromium migrate from substrate to oxide layer. In the chromium content of 1.01 wt%, oxide layer thickness varies from 1.4 to 3.9 mg/cm2. Oxide layer is thicker than that in the chromium content of 1.01 wt%, which is opposite to the result in the static condition. Large variation of X-ray yield of iron indicates that dissolution of the oxide layer might occur during long exposure to the water flow. These results of this experiment obviously show the simultaneous μ-PIXE/RBS and SEM analysis system to be useful for better understanding of the corrosion mechanism.