Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Volume 65 , Issue 11
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  • Tatsushi Iwamoto, Yasunobu Suzuki, Masataka Yatomi, Tomohiro Nakajima, ...
    2016 Volume 65 Issue 11 Pages 450-453
    Published: November 15, 2016
    Released: June 30, 2017

    As one of anti-corrosion system for marine steel structures, there is a method using calcareous deposits from mineral ions in seawater. In this process, chemical compositions and temperature of seawater around the structures have influence on the process, quality of deposits coating in principle. So we had some experiments under actual environment in Singapore, then we investigated relationship between the applicability, anti-corrosive performance and environmental factors by comparing the results with ones in Japan. Consequently, in Singapore, chemical composition of calcareous deposits coating was different from one in Japan. But the growth rate and anti-corrosive performance of calcareous deposits coating were the same as ones in Japan, although the concentration of mineral ions and pH of seawater around test site were lower than ones in Japan. Moreover with cathodic protection, the anti-corrosive performance was maintained during experiments. These results mean that anti-corrosion system using calcareous deposits coating is effective in low tidal current speed even if water quality around structure is changed in some extent.

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  • Yasuo Shino, Toshio Suzuki, Kenichi Kubo, Akio Motoi
    2016 Volume 65 Issue 11 Pages 454-457
    Published: November 15, 2016
    Released: June 30, 2017

    Boiler steam conditions of MSW incinerators have recently been shifting to higher temperature and pressure to attain more efficient energy recovery from the waste. Consequently, boiler tubes are now exposed to more harmful environment than before. Flyash comprising particulate matters in the hot gas stream, part of which finally accumulates on the surface of boiler tubes, plays a crucial role in erosion and corrosion mechanism of boiler materials. However, the thermophysical properties of these substances at actual gas temperatures are not well reported. Test samples were collected from several MSW incinerators in order to clarify high temperature thermal conductivities of flyash adhered to boiler tubes, outer surface scale formed on riser tubes, and incinerated ash. Results from the measurement showed flyash adhered to riser tubes and that to superheater have respective high- temperature thermal conductivities and the thermal conductivity of outer surface scale on riser tubes has a decreasing tendency with increasing temperature. Besides, two thermal conductivity values obtained from laser flash and hot wire measurements of the identical powdered test sample presented a fairly good agreement if the difference in bulk density was taken into consideration.

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  • Ryota Miyahara, Nobue Fujibayashi, Tsutomu Komori, Takumi Ujiro
    2016 Volume 65 Issue 11 Pages 458-461
    Published: November 15, 2016
    Released: June 30, 2017

    Recently, cyclic corrosion test containing acetic acid or nitric acid has been carried out to investigate the corrosion by acid rain and the corrosion behavior of Al alloys. The effects of solution condensation on the corrosion behavior of an Al alloy and a stainless steel in these tests were investigated. The change of pH and ion concentration of Cl, NO3, CH3COO with solution condensation were investigated. The polarization measurements were carried out in condensed solutions and the correspondence between the result of the CCT and that of polarization measurements was analyzed.

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  • Masahiro Sakai, Junya Watanabe
    2016 Volume 65 Issue 11 Pages 462-466
    Published: November 15, 2016
    Released: June 30, 2017

    Ant nest corrosion of copper occurs in organic carboxylic acid such as formic and acetic acid. Hence, it is predicted that organic carboxylic acid anions coexist with dissolved copper ions inside the pit of ant nest corrosion. In this paper, we present the results of immersion tests of phosphorous deoxidized copper tubes in copper(Ⅱ) formate and copper(Ⅱ) acetate aqueous solutions to investigate the corrosion behavior of copper in the solution containing both copper and carboxylate ions. Ant nest corrosion with irregularly branched tunnels developed for copper tubes immersed in copper formate solution, while a semispherical pit developed for copper tubes immersed in copper acetate solution. Especially, rapid progress of the corrosion in copper formate solution led to perforation of the copper tube with 0.28mm thickness in 26 days. The propagation of this corrosion corresponds to the corrosion rate of 3.9mm/y. Moreover, anodic polarization curves of the copper tube in copper formate and copper acetate solutions were measured. The anodic current density in copper formate solution increased monotonically with applied potential, while the anodic polarization curves in aerated copper acetate solution showed a drop-off in current density originating from the formation of an oxide film.

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Research Paper
  • Tomohiko Omura, Koji Akioka, Kenji Kobayashi
    2016 Volume 65 Issue 11 Pages 467-475
    Published: November 15, 2016
    Released: June 30, 2017

    Effects of several types of surface films on hydrogen entry in low alloy steels were investigated using a hydrogen permeation technique. Effects of Zn plating under cathodic hydrogen charge, additions of alloying elements such as Ni, Cu and Mo in an acidic solution, and sulfide film formed in wet H2S environments were evaluated, and classified into the following two types.

    Zn plating drastically suppressed hydrogen entry into low alloy steel. The mechanism was considered to be a resistance against hydrogen permeation, due to small hydrogen diffusivity in Zn or small hydrogen evolution rate on Zn surface. Formation of sulfide film in a wet H2S environment was also effective for suppressing hydrogen entry according to the similar mechanism. Zn plating and sulfide film were classified into the “surface resistance type”

    Additions of Ni, Cu and Mo were also effective for suppressing hydrogen entry in the acidic solution. The mechanism was considered to be a change in hydrogen overpotential, not a resistance to hydrogen permeation. The decrease in hydrogen overpotential would lead to a decrease in hydrogen surface coverage. These alloying elements were considered to work as the “small hydrogen overpotential type”.

    In the case of the “resistance” type surface films such as Zn or sulfide, thickness of the steel plate affects the hydrogen concentration just beneath the surface film because it was determined by the balance of the diffusion of hydrogen through the surface film and the base steel.

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