Corrosion behavior of X70 pipeline steel in acidic and near neutral simulated seawater solution

Abstract

In order to compare the corrosion characteristics of X70 pipeline steel in acidic (pH=3) and near neutral (pH=77) simulated seawater solutions, the corrosion behaviors of X70 pipeline steel in simulated seawater solutions were studied by polarization curve, electrochemical impedance spectroscopy (EIS) and corrosion weight loss experiment. The results show that the corrosion weight loss of X70 pipeline steel immersed in acidic solution for 168 h is about 16 times as much as that in near neutral simulated seawater solution. Most of the surfaces are uniformly corroded, and corrosion circles centered on inclusions are formed locally. With the prolongation of immersion time, the radius of capacitive reactance arc and |Z|[BFQB] are both increased with adsorption first and then weak diffusion occuring. Rct increases and the corrosion rate decreases. A thick corrosion product film is formed in the near neutral simulated seawater solution. The chloride ions are aggregated and destroyed the corrosion product film. Tiny corrosion pits form and locally aggregate to induce large pits. The charge transfer resistance decreases, the corrosion rate increases and then tends to be stable. X70 pipeline steel is active in the simulated seawater solution. Compared with that in the acidic seawater solution, the Ecorr of the steel in the near neutral simulated solution moves positively by 137 mV, and icorr is about 0047 times of that in the acidic seawater solution. The corrosion laws of X70 pipeline steel in acidic and neutral simulated seawater solutions can provide theoretical support for its application in corrosion control of submarine pipelines, which is of great significance for its safe service.

Keywords

• metal materials engineering; x70 pipeline steel; simulated seawater solution; corrosion weight loss; eis