Akinobu Nishikawa

Elimination of Error from Nonuniform Current Distribution in Polarization Measurement by Boundary Element Inverse Analysis

Abstract A method was proposed for eliminating error in measuring polarization curves from nonuniform current density distribution on an electrode. Boundary element direct analysis showed the current density distribution on a steel plate specimen on soil was considerably nonuniform and that the nonuniform current density distribution caused significant error if no correction was made in measurement of polarization curves. An inverse analysis using the boundary element method (BEM) was used to eliminate the error resulting from the nonuniform current distribution. BEM was shown to be applicable to an arbitrarily shaped specimen with no restriction on location of the reference electrode.

Evaluation of Cathodic Protection Under Disbonded Coating on Buried Steel Structures by Laboratory and Field Tests

Cathodic protection (CP) inside a long crevice, such as a disbonded coating area beneath a long insulating sheet covering buried steel pipe, was studied in the laboratory and in field tests for up to 7.2 y. Exposed steel inside a long crevice under an insulating sheet was simulated using a crevice model, a multi-electrode block that consists of 64 steel specimens arranged as a plane and a covering acrylic plate to form a crevice with a small or large gap to characterize the potential and current distribution on the steel inside the crevice. In laboratory tests, CP was effective for specimens inside the crevice with a depth more than 600 times larger than the crevice gap, even when both crevice ends were opened in a stagnant water. In a flowing water, sufficient CP was attained inside the crevice with a small gap; however, the CP was insufficient for that with a larger gap. In the field tests, CP was achieved on specimens with and without crevices. Without CP, the corrosion rate of the specimens inside the...

Stochastic Corrosion Analysis of Underground Structures Using Boundary Element Method.

A new stochastic boundary element method for analyzing the corrosion of underground structure was developed. In case of analyzing the corrosion of underground structure buried in soil which electric conductivity and polarization characteristics are changing along time, it Is necessary to consider about the stochastic character of these unstable condition (conductivity and polarization characteristics) . The non-linear relationship between unknown variables and these unstable condition was linearized by Taylor series and, the mean and covariance of unknown variables are estimated. In order to demonstrate the effectiveness of the method, the simulation was performed and the result was compared with conventional Monte Carlo method and the field experimental result. A computer simulation of the identification is performed at first with a measured potential by using the Kalman filter which stochastic model was considered with the proposed method.