15% HCl溶液中における高合金油井管の耐食性に与える合金成分の影響

抄録

Corrosion behavior of high Ni alloys (Ni: 25-60%, Cr: 22-25%, Mo: 3-6%) and duplex sainless steels used for oil country tubular goods in 15% HCl solution are evaluated by means of immersion tests and polarization measurements. Effects of alloying elements (Ni, Mo, Cu, W) in Fe-Cr-Ni alloys are also discussed. Corrosion rate of Fe-Cr-Ni-Mo alloys at 60°C decreased from 6 to 2g/m²h when Ni content was increased from 25 to 50%. Corrosion rate of Fe-Cr-Ni alloys without Mo in 15% HCl solution is independent from Ni content because increase of Ni content lowers anodic dissolution rate and also enhances cathodic reaction. Addition of W or Cu into Fe-Cr-Ni alloys without Mo has beneficial effects decreasing corrosion rate in 15% HCl solution although only small effects of addition of W or Cu are observed in Mo bearing high Ni alloys, Duplex stainless steels showed much higher corrosion rate (above 100g/m²h) than those of high Ni alloys. The role of alloying elements in high Ni alloys determined by polarization measurements are described as follows; 1) inhibit anodic dissolution: Mo, Ni, 2) enhance cathodic reaction: Ni, 3) lowering passivating potential: Mo, W. It is determined by Auger electron spectroscopy that oxides or hydro-oxides of Mo and Ni precipitate on the surface of high Ni alloys during immersion in 15% HCl solution and that enrichment of Mo observed in outer layer and Ni consentration observed in inner layer.