Corrosion behaviour of carbon and stainless steels in biodiesel, B5 blend and S500 diesel under storage conditions

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In this study the corrosion behavior and physic and chemical properties of pure soy methyl biodiesel (b100), B5 blend and Diesel S-500 fuel were monitored in carbon steel storage horizontal tanks with a capacity of 25 liters kept under unsheltered conditions for 120 days. Corrosion immersion tests using standardized coupons of AISI 1020 and AISI 316L were conducted under these conditions. On every 30 days samples of the fuels were also taken so that water content, oxidative stability index, density, viscosity and acidity were monitored in accordance to EN ISO 12937, EN ISO 14112, EN ISO 15557, EN ISO 3675, EN ISO 3104 and ASTM 664 standardized procedures. At the end of the experiment corrosion rates of the coupons were determined according to ASTM G1-03 and G31-04 standardized methodologies. Water contamination increased with storage time turning the fuels potentially more aggressive. Reduction on the oxidation induction period was found to increase with time of storage, particularly for the pure biodiesel and B5 blend, turning the pure biodiesel out of specification by 30 days of storage. The oxidation stability of the B100 samples monthly taken decreased faster than the B5 blend and Diesel S-500 samples. Irrespective of the above mentioned alterations no evidence of localized attack was noted for both AISI 1020 steel and AISI 316L coupons surfaces. Density, viscosity and acidity were however found within accepted specification limits all over the 120 days period. On top of that results in corrosion rates were found to be insignificant (<0.02 mm / year). These results demonstrated the excellent corrosion resistance of carbon steel and stainless steel, within the experimental conditions used, suggesting the suitability of these two alloys for use in biodiesel and B5 blend storage tanks.