Physicochemical Characteristics of Soil Moisture and Their Effects on the Corrosion Behavior of Buried Mild Steel in Calabar Metropolis, Nigeria

Soil moisture collected from three locations, namely University of Calabar (UNICAL), Calabar municipal solid waste dumpsite (MSWD) and a mechanic workshop (MW) all within Calabar metropolis, Nigeria, were analyzed quarterly in a one year study at different depths (0.5 m and 1 m) for some physicochemical parameters. UV-visible spectrophotometer, titration and atomic absorption spectrophotometer (AAS) were the employed analytical techniques. With the exception of chloride, all other parameters showed higher values with depth. Higher values for the analyzed parameters were generally reported for MSWD and this was largely the result of the presence of a variety of contaminants in this location. Microbial analysis of soil samples from the locations revealed the presence of SRB in MW, which could have possibly influenced the soil moisture chemistry of the location. Corrosion rate was calculated from weight loss measurements and the quarterly results were all for follow the trend: UNICAL < MW < MSWD. At the end of the 4th quarter, the corrosion rates at 0.5 m depth were 0.0057, 0.0070, and 0.0101 mm/hour for UNICAL, MW, and MSWD, respectively, while their corresponding values at 1 m depth were 0.0087, 0.0114, and 0.0128 μm/hour. The values were shown to increase with depth. R-mode factor analysis identified some important factors which could have been responsible for the variation in the chemistry of the soil moisture.

Evolution of the Corrosion Product Film and Its Effect on the Erosion–Corrosion Behavior of Two Commercial 90Cu–10Ni Tubes in Seawater

The composition and structural evolution of the corrosion product film of two commercial 90Cu-10Ni tubes, namely TubeA and Tube B, after being immersed in natural seawater for 1, 3, and 6 months were characterized by scanning electronmicroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and its effecton the erosion--corrosion behavior of the tubes was determined through a rotating cylinder electrode system using variouselectrochemical techniques. For the freshly polished samples used as contrast samples, the flow velocity mainly enhancedthe cathodic reaction at low flow velocities while both the anodic and the cathodic reactions were remarkably accelerated athigher flow velocities. The corrosion product films formed on the two commercial 90Cu-10Ni tubes after being immersedin seawater for up to 6 months are of a complex three-layer or multilayer structure. The structural evolution of the films isout of sync for the two tubes. A continuous residual substrate layer depleted of Ni was observed in the inner layer of thefilms on Tube B after 30, 90, and 180 days＇ immersion, while it was observed in the film on Tube A only after 180 days＇immersion. The nature of the inner layer plays a crucial role in the erosion-corrosion resistance of the 90Cu-10Ni tubes athigher flow velocity. The film with a compact and continuous inner layer of Cu20 doped with Ni2＋ and Ni3＋ which bondsfirmly with the substrate could survive and even get repaired with the increased flow velocity. The film on Tube Bpossessing a hollow and discontinuous inner layer composed of the residual substrate was degraded rapidly with increasingrotation speed in spite of its quite good resistance at the stagnant or lower speed conditions.