Accurate evaluation of the corrosion behaviour of metallic biomaterials is necessary for the reliability not only because dissolved metal ions may cause toxicity but also because the corrosion may accelerate wear and fatigue. Corrosion test is generally carried out in a saline solution, simulated body fluids and medium and so on. However, the in vitro corrosion behaviour does not always coincide with the in vivo behaviour observed in animal tests or in the human body. Understanding of the interaction between metallic materials and tissues (cells) is necessary to connect the results in vitro and in vivo. We then investigated the corrosion behaviour of metallic biomaterials under cell culture environments to elucidate the corrosion factor originating from the presence of cells (tissues). Here, the author explains the in vivo environment where metal surface is subjected and presents the results of electrochemical tests and the pH measurement under cell culture environments. It was revealed that the presence of cells causes the retardation of mass diffusion on the metal surface with cell bodies and extracellular matrices, and then it appears that quasi-crevice corrosion proceeds. Cell response to the anodic or cathodic polarization of metal substrate is also presented.
Corrosion Under Insulation(CUI) of carbon steel and low alloy steel in oil refinery and petrochemical plants is the most important degradation phenomena of equipment materials. Since the characteristics of CUI have not been fully understood the accurate prediction and estimation of CUI is difficult actually. In this study, data collection of CUI was carried out in actual plants. This information is analyzed for clarifying the controlling factors of CUI. The modification of CUI Technical Module published by API is examined based on this analysis. From this study, it become obvious that the corrosion rates of CUI may follow Gumbel distribution, and CUI are controlled by types of equipments, temperature and structure design. In particular, corrosion rate of CUI is accelerated at impediment to drainage area such as stiffening ring of tower. Based on the present results, the modification of CUI technical module was established for the more accurate prediction and estimation of CUI.
Iron corrosion under enrichment culture of anaerobic microorganisms utilizing metallic iron as an electron donor was investigated. Enrichment culture from residual water on bottom of a crude oil storage tank in Kyushu region caused severe iron corrosion. But the other two enrichment cultures from drain water of an oil field in Tohoku region and sediment at mouth of the Edogawa river did not corrode iron severely. Black ferrous sulfide film was detected in the corrosion products under the enrichment cultures from the drain water of the oil field in Tohoku region and the sediment at mouth of the Edogawa river. Therefore, sulfate reducing bacteria (SRB) were considered to be causative microorganisms to iron corrosion. But the ferrous sulfide film was not detected in the corrosion products under the enrichment culture from the crude oil storage tank in Kyushu region. Ferrous carbonate (FeCO3) was a main component of the corrosion products by the enrichment culture from the crude oil storage tank in Kyushu region. Therefore, iron corrosion under the enrichment culture from the crude oil storage tank in Kyushu region was considered to be not simply caused by the SRB. Open circuit potential of a carbon steel (SS400) coupon with corrosion products under the enrichment culture from the crude oil storage tank in Kyushu region was about 120 to 140 mV higher than that by the other two enrichment cultures or abiotic control in anaerobic artificial seawater deaerated by Ar gas. Therefore, Galvanic coupling between corrosion products layer and base metal was considered to be possible mechanism of iron corrosion under the enrichment culture of the crude oil storage tank in Kyushu region.