황산염 환원 박테리아에 의한 철강의 미생물 부식의 전기화학적 분석

Abstract

Although microbiologically influenced corrosion researches were started about 100 years ago, most microbial corrosion studies were carried out in 1980s because the significance of corrosion damages was known recently. For the first time, Gaines, however, suggested that corrosion at the inner and outer sides of a water pipe be influenced with sulfide-oxidizing bacteria and iron-oxidizing bacteria.

Recently, with a rapid development of industries, many structural steels were exposed to severe corrosive environments, so that development of corrosion resistant steels was necessary in terms of both economical and industrial safety viewpoints. Unexpected accidents caused by a structural corrosion often happened. For examples, water pipe line leaked due to the corrosion of welded area of stainless steel pipe inspected safe and unexpected severe pitting corrosions in cargo oil tank bottom plating were also observed. Corrosion damages of fuel oil tank in aircraft as well as the abnormal corrosion of weld metal area of stainless steels were reported.

A series of corrosion accidents mentioned above were not significant compared with conventional corrosion based on that the electrochemical theory is a simple concept. Eventually it was, however, thought that the origin of corrosion was attributed to microorganism existing in various corrosive environments. Furthermore it was reported that the corrosion damage associated with bacteria in some places such as a petroleum chemical industry, a nuclear power generating plant and concrete structures frequently happened and the amounts of damage were estimated to be over several billion dollars.

In this study, the susceptibility of TMCP (Thermo Mechanical Control Process) steel, Normalized steel and conventional Mild steel to MIC caused by SRB was investigated based on the electrochemical aspects.

The results of this research in absence of SRB, corrosion potential shifted to a low level in the beginning and then maintained a stable level later on. However the corrosion potential shifted to lower range in the beginning with the SRB presence, but after 14 to 20 days incubation, the corrosion potential changed to a noble level again, indicating MIC caused by the SRB.

Corrosion current density in the presence of SRB was higher than that in absence of SRB. Furthermore, a pitting corrosion was observed in the SRB growing medium while the control did not show any such phenomenon. Normalized steel had a better corrosion resistance than the TMCP steel. It appeared that there were some differences between polarization curves depending on the presence or absence of SRB in the corrosion test cell.