This paper explains the electrochemical corrosion control method. This method is an improvement technology for durability of concrete structure, and attracts attention in recent years. The electrochemical corrosion control method is classified into 4 methods, such as cathodic protection method, desalination method, re-alkalization method and electrodeposition method. This paper also shows the principle of these methods, the sphere of applications and construction illustrations.
The anodic reactions of carbon steel in fresh water containing bicarbonate ions or silica were investigated by the measurements of polarization curves, the surface observation and element analysis of the surface. The polarization curves of the carbon steel in the solution with low conductivity were determined by the iR compensation, where the solution resistance was obtained by using in-situ electrochemical impedance spectroscopy. The stable passive film was formed on the carbon steel surface in the solution containing 100ppm bicarbonate ions. On the other hand, though the passive film was formed on carbon steel surface in the solution containing silica, the pitting occurred during the measurement of polarization curve. The observation by laser microscope indicated that the pits were covered with the mound. The element analyses by Glow Discharge Optical Emission Spectroscopy (GD-OES) gave that the passive film and the rust, which were formed on the carbon steel in the solution containing silica, involved a large amount of Si.
Wall thinning to the inside surfaces of T's, elbows and straight tubes which were located at just downstream of elbows occurred, when a 1% CuCl2 (II) solution was allowed to flow through a pure copper piping with a nominal dimension of 15A at the flow velocity of 1-2m/s. Flow velocity difference corrosion was presumed to be the cause of the damage, since it occurred at the surface of inner curvature of the elbow where the flow velocity was lower than that at the outer curvature. This assumption was proved to be valid, as evidenced by measurement of the macro cell current which was directed from the higher flow velocity area to the lower velocity area, as well by the polarization behavior of these areas. Based on the corrosion mechanism, preventative action was taken, resulting in a reduction in wall thinning of the inner curvature surface of the elbow down to the level of that at outer curvature surface of higher velocity area. Finally, the issue of how closely the 1% CuCl2 accelerating test solution simulated the corrosion of pure copper piping in a system that carries brine or tap water was discussed.
ID blade of meta-stable austenitic stainless steel shows an elastic anisotropy and potential susceptibility to delayed fracture due to the strain-induced martensite. Authors first estimated the five elastic stiffness coefficients of the ID blade from the orientation dependency of the laser-excited Lamb waves. Rayleigh wave velocity decreased with a maximum difference of 400m/s with angles from the rolling direction, while the sheet velocity varied with a maximum increase of 500m/s. Hydrogen pre-charged ID blade showed the wave velocities higher than that of the as-received one. Fracture strength of hydrogen pre-charged ID blade decreased to 43% and 73% of those of the as-received one in the rolling and transverse direction, respectively. The blade suffered brittle fracture after 4.17ks hydrogen charging at the radial fastening stress level. Both the acoustic emission source location and fractographic observation suggested the delayed fracture assisted by the strain-induced martensite.
Hot corrosion behavior of Ni-10mass%Cr alloys having several Mo content under a molten NaCl-KCl-Na2SO4 mixture in 75vol%O2-N2 atmosphere containing 0.1vol%HCl was examined by thermogravimetry, chemical analyses of scale formed on the alloys and electrochemical technique. Especially, the effect of Mo addition and the influence of HCl in atmosphere on the hot corrosion behavior were considered. In the atmosphere with HCl, corrosion resistance of the Ni-Cr-Mo alloy increased with an increase in the amount of Mo in the alloy. In this case, it was found that a protective Cr2O3 layer was formed as an inner scale on the alloy. The analyses of the scale formed in the initial stage showed that for Ni-Cr-Mo alloy exposed at the gas mixture with HCl, in the initial stage less than 6ks, MoO2 was formed at the scale/alloy interface, followed by a growth of Cr2O3 layer. The electrochemical measurement showed that the anodic current with increasing polarization potential measured in the atmosphere containing HCl rose less than that in the atmosphere without HCl. Moreover, the inhibition of the rise in the anodic current was also observed when H2O vapor was introduced into the atmosphere. Consequently, the mechanism, that the protective Cr2O3 layer was formed by the anodic oxidation reaction of the alloy with H2O vapor produced by the reaction of HCl and O2- in the molten salt, was proposed.