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Abstract. The corrosion behavior of mild steel in seawater was investigated using an immersion test and energy-dispersive X-ray spectroscopy in solutions from the sites of Muara Baru, Suramadu and Tol Mandara. As reference, solutions of 3.5% and 5% NaCl were prepared. Dissolved oxygen, salinity, conductivity, and total dissolved solids (TDS) were measured. It was found that uniform corrosion occurred on the mild steel during the immersion test. The corrosion resistance of the steel decreased with increasing exposure time. Since the magnitudes of conductivity, salinity and TDS of all test solutions were similar, it was concluded that dissolved oxygen (DO) and chloride ions play an essential role in inducing the corrosion risk of mild steel. Both parameters hinder the formation of a stable passive film on the surface of corroded mild steel.

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The pitting corrosion of Ni3(Si,Ti) intermetallic compound was investigated as function of chloride concentration by using electrochemical method and scanning electron microscope in sodium chloride solutions at 293 K. In addition, the pitting corrosion of type C276 alloy was also studied under the same experimental condition for comparison. The pitting potential obtained for the intermetallic compound decreased with increasing chloride concentration. The specific pitting potential and pitting potential of Ni3(Si,Ti) were lower than those of C276 alloy, which means that the pitting corrosion resistance of C276 alloy was higher than that of Ni3(Si,Ti).

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The pitting corrosion of Ni3(Si,Ti) with 4 at% Al consisting of two regions of a Ni3(Si,Ti) single-phase of L12 structure and two phases of L12 and fcc Niss was investigated as function of chloride concentrations by using electrochemical method, scanning electron microscope and energy dispersive X-Ray spectroscopy in neutral sodium chloride solutions at 293 K. In addition, the pitting corrosion of Ni3(Si,Ti) and type C276 alloy were also studied under the same experimental condition for comparison. The pitting potential obtained for the Ni3(Si,Ti) with 4 at%Al decreased with increasing chloride concentration. The specific pitting potential and pitting potential of Ni3(Si,Ti) with 4 at%, Ni3(Si,Ti) and C276 were the lowest, the moderate and the highest, respectively, which means that the pitting corrosion resistance of Ni3(Si,Ti) was higher than Ni3(Si,Ti) with 4 at% Al, but lower than that of C276. A critical chloride concentration of Ni3(Si,Ti) with 4 at% Al was found to be lower than that of Ni3(Si,Ti). The Pitting corrosion of Ni3(Si,Ti) with 4 at% Al occurred in the two phase mixture (L12 + Niss).

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