Propagation behaviour of general and localised corrosion of carbon steel in simulated groundwater under aerobic conditions

Abstract

Carbon steel is one of the candidate overpack materials for geological disposal of high-level radioactive waste in Japan. Corrosion of carbon steel is classified into two types: general corrosion and localised corrosion. In this study, propagation of general and localised corrosion (pitting corrosion and crevice corrosion) were investigated by immersion tests of carbon steel under the aerobic conditions. The results of the immersion tests showed that the corrosion growth rate was strongly dependent on the environmental conditions and type of steel. However, the upper limit of the pitting factor, the ratio between the maximum corrosion depth and the average corrosion depth, was determined approximately using only average corrosion depth. Based on the experimental and literature data, an empirical model that predicts the maximum corrosion depth of an overpack from average corrosion depth was developed by applying the extreme value statistical analysis using the Gumbel distribution function.

Re-evaluation of the required thickness of the carbon steel overpack for high-level radioactive waste disposal in Japan based on the latest scientific and engineering knowledge

“…It was found for all synthetic and natural samples that the degree of roughness diminishes with increasing mean corrosion depth. In order to estimate the maximum corrosion depth for an overpack, Taniguchi et al [5] applied the extreme value statistical analysis technique to the pitting factor data of Data (1) and Data (2) in Figure 2. The upper of the extreme value statistical analysis result is expressed by the following equation (see Taniguchi et al [5] for details due to limitations of Figure 1.…”

“…where P is the estimated maximum corrosion depth, α is the scale parameter, λ is the location parameter, S is the area of an overpack, s is the area of a sample used for the corrosion test and a is the confidence ratio [5]. Figure 4 shows relationships between mean corrosion depth, α and λ which are derived by the extreme value statistical analysis of pitting factor data obtained by constant-current acceleration tests and immersion tests [13].…”

Atmospheric Corrosion Estimation of Welded Low Alloy Steel in Wet and Dry Condition Containing Chloride Ions

“…In order to ascertain the corrosion of welded steels, statistical analysis was introduced. To evaluate the corrosion depth of steels, Gumbel distribution method has been used in previous papers [12][13][14] . In this study, the Gumbel distribution analysis was applied after removing the rust from the welded steel.…”

“…The corrosion depth can be measured quantitatively using micro laser microscopy and estimated statistically by Gumbel distribution analysis [12][13][14] . In the corrosion of steel, the maximum depth determines the lifetime of the material, because the rst crack originates from that location.…”

Long term integrity of overpack closure weld for HLW geological disposal Part 1 - prediction and evaluation method for structural integrity of weld joint

“…It was also pointed out that the maximum corrosion depth of the weld zone did not exceed the depths of the base metal estimated in this study (see LongTermCor2010-08). 12…”