カソード電流に及ぼす海洋微生物とバイオフィルムの影響

鷲頭 直樹; 篠原 正; 元田 慎一; 酒井 潤一

doi:10.3323/jcorr.56.472

Research Paper

Effect of Marine Microorganisms and Biofilms on Cathodic Current

Naoki Washizu, Tadashi Shinohara, Shin-ichi Motoda, Jun’ichi Sakai

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Keywords: corrosion rate, type 329J4L, natural seawater, cathodic condition, open circuit condition, DNA base arrangement

JOURNAL FREE ACCESS

2007 Volume 56 Issue 10 Pages 472-479

DOI https://doi.org/10.3323/jcorr.56.472

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Published: October 15, 2007 Received: May 07, 2007 Available on J-STAGE: March 25, 2008 Accepted: June 26, 2007 Advance online publication: - Revised: -
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Date of correction: November 05, 2008 Reason for correction: - Correction: Abstract Details: Wrong : In order to explain the mechanism that works in microbiologically influenced enhancement of corrosion rates, cathodic currents were measured on type 329J4L stainless steel exposed to seawater, and a biological analysis on biofilms was conducted. The cathodic current densities measured at 0.1 V vs. SHE were ranging from 0.3 μA/cm² to 3 μA/cm², after the specimen had been held at 0.1 V vs. SHE in natural seawater. On the other hand, the cathodic current densities at 0.1 V vs. SHE after the exposure to natural seawater under an open circuit condition, were higher than 1 μA/cm² in the early stage of the measurement. However, they fell to values lower than 0.1 μA/cm² in 12 h. The current densities measured at 0.2 V vs. SHE were approximately 2 μA/cm² in the initial stages and the final stages of the measurement, after the beforehand exposure to natural seawater at 0.2 V vs. SHE. The current densities measured at 0.2 V vs. SHE after the beforehans of microorganisms selectively attach to steel surfaces under cathodic conditions, and that such microorganisms are the cause of large cathodic currents resulting in high corrosion rates.
Right : In order to explain the mechanism that works in microbiologically influenced enhancement of corrosion rates, cathodic currents were measured on type 329J4L stainless steel exposed to seawater, and a biological analysis on biofilms was conducted. The cathodic current densities measured at 0.1 V vs. SHE were ranging from 0.3 μA/cm² to 3 μA/cm², after the specimen had been held at 0.1 V vs. SHE in natural seawater. On the other hand, the cathodic current densities at 0.1 V vs. SHE after the exposure to natural seawater under an open circuit condition, were higher than 1 μA/cm² in the early stage of the measurement. However, they fell to values lower than 0.1 μA/cm² in 12 h. The current densities measured at 0.2 V vs. SHE were approximately 2 μA/cm² in the initial stages and the final stages of the measurement, after the beforehand exposure to natural seawater at 0.2 V vs. SHE. The current densities measured at 0.2 V vs. SHE after the beforehand exposure to natural seawater under an open circuit condition, were higher than 1 μA/cm² in the initial stages of the measurement and lower than 0.1 μA/cm² in the final stages. In the case of measurements at 0.3 V vs. SHE, the average values of cathodic current densities were approximately 0.2 μA/cm²afer the beforehand exposure to natural seawater at 0.3 V vs. SHE, and lower than 0.01 μA/cm² after the beforehand exposure to natural seawater in an open circuit state. The cathodic current densities after the exposure to synthetic seawater, were lower than 0.01 μA/cm² in the cases of measurement at 0.1 V vs. SHE, 0.2 V vs. SHE and 0.3 V vs. SHE. The data on DNA base arrangement detected by the denaturing gradient gel electrophoresis test in a biofilm formed at 0.2 V vs. SHE in natural seawater, was different from the data detected in a biofilm formed under an open circuit condition. It is, therefore, concluded that some specific types of microorganisms selectively attach to steel surfaces under cathodic conditions, and that such microorganisms are the cause of large cathodic currents resulting in high corrosion rates.

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Abstract

In order to explain the mechanism that works in microbiologically influenced enhancement of corrosion rates, cathodic currents were measured on type 329J4L stainless steel exposed to seawater, and a biological analysis on biofilms was conducted. The cathodic current densities measured at 0.1 V vs. SHE were ranging from 0.3 μA/cm² to 3 μA/cm², after the specimen had been held at 0.1 V vs. SHE in natural seawater. On the other hand, the cathodic current densities at 0.1 V vs. SHE after the exposure to natural seawater under an open circuit condition, were higher than 1 μA/cm² in the early stage of the measurement. However, they fell to values lower than 0.1 μA/cm² in 12 h. The current densities measured at 0.2 V vs. SHE were approximately 2 μA/cm² in the initial stages and the final stages of the measurement, after the beforehand exposure to natural seawater at 0.2 V vs. SHE. The current densities measured at 0.2 V vs. SHE after the beforehand exposure to natural seawater under an open circuit condition, were higher than 1 μA/cm² in the initial stages of the measurement and lower than 0.1 μA/cm² in the final stages. In the case of measurements at 0.3 V vs. SHE, the average values of cathodic current densities were approximately 0.2 μA/cm²afer the beforehand exposure to natural seawater at 0.3 V vs. SHE, and lower than 0.01 μA/cm² after the beforehand exposure to natural seawater in an open circuit state. The cathodic current densities after the exposure to synthetic seawater, were lower than 0.01 μA/cm² in the cases of measurement at 0.1 V vs. SHE, 0.2 V vs. SHE and 0.3 V vs. SHE. The data on DNA base arrangement detected by the denaturing gradient gel electrophoresis test in a biofilm formed at 0.2 V vs. SHE in natural seawater, was different from the data detected in a biofilm formed under an open circuit condition. It is, therefore, concluded that some specific types of microorganisms selectively attach to steel surfaces under cathodic conditions, and that such microorganisms are the cause of large cathodic currents resulting in high corrosion rates.

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