Analysis of Corrosion Process of the Steel for Gas Pipeline with in-situ Raman Spectroscopy

The change in the chemical composition of the corrosion product on steel can be identified with in-situ Raman spectroscopy while the steel is polarized in a solution. In this paper, we tried to clarify the corrosion process of the steel for gas pipelines.γ-FeOOH and Fe3O4 were detected with the Raman spectra measured in the 100mg/dm3Cl− solution holding at −0.3V vs.Ag/AgCl. The coexistence of γ-FeOOH and Fe3O4 was confirmed from the Raman spectrum measured in the corrosion test. It is considered that Fe3O4 was formed via the reduction as follows:Fe2+ + 8FeOOH + 2e− → 3Fe3O4 + 4H2OIn the early stage of corrosion, γ-FeOOH was detected from Raman spectra measured in the 1000mg/dm3HCO3− solution holding at 0.5V vs. Ag/AgCl. However, the peak of γ-FeOOH disappeared from the Raman spectra measured in the corrosion test after the middle stage of corrosion. It is conceivable that the γ-FeOOH disappeared or that the surface was covered with corrosion products inert to Raman measurement.We were able to investigate the corrosion process of the steel for gas pipelines with in-situ Raman spectroscopy while it was polarized in a solution.