For investigation of the corrosion behavior of low alloy steels for large-diameter pipes for application in CO2 containing aqueous media, two alloy variations were produced as laboratory heats of 100 kg each, which contained 0.78 and 0.96 % Cr, respectively. Plates were rolled with a thickness of 20 mm and welded by use of two different chromium-free wires in order to investigate the corrosion behavior of the weld seam area. Furthermore, a segment of a large-diameter pipe with a chromium content of 0.59 % in the base material was included in the investigations. Laboratory tests were performed to determine the CO2 corrosion resistance in 0.1 % sodium chloride solution on flat specimens in the rotating cage under 1 bar (0.1 MPa) CO2 at 40, 70 and 90 °C and 1 m/s average flow velocity. The influence of an increased CO2 partial pressure of 30 bar (3.0 MPa) was investigated by use of rotating discs at 40 and 90 °C and 850 Rpm. The investigations revealed only a minor influence of the chromium content on the corrosion resistance. All specimens showed an improved resistance of the weld seams to CO2 corrosion compared to the base metals. The chromium contents added did not decisively improve the corrosion resistance of the steels.
Key Words: CO2 corrosion, low alloy steel, chromium, large-diameter pipe, flow, rotating cage, rotating disc, weld seam, corrosion rate