Electrochemical Noise L450 Steel Hydrogen Sulfide Stress Corrosion Cracking

The gathering pipeline’s safe and reliable operation was important for the production in oil and gas field.So the study of corrosion phenomena of gathering pipe and the evaluation of the adaptability of the pipe in the operating mode condition are of great importance in corrosion protection and selecting suitable material for reforming and enlarging gathering pipeline system. In this thesis, the sensitivity of the anti-SSCC of the L450steel and the corrosion phenomena of this steel in the operating mode condition were studied. The main research contents and conclusions were as follows.1) The sensitivity of anti-SSCC of the L450steel in the saturated aqueous solution of hydrogen sulfide was evaluated. The experimental results show that the weld zone of this steels has a higher sensitivity than the base metal and the specimens from the base metal in different way of cutting off have little difference in sensitivity.2) The mechanism of SSCC of different specimens of L450steel, the specimens from the weld zone, the specimens from base metel which was cutting off along with axial direction and along with hoop, in the saturated aqueous solution of hydrogen sulfide was studied, using the SEM and EDS. The experimental results show that the mechanism of cracking of L450steel in this environment are mixed mechanism of anodic dissolution and hydrogen-induced cracking.3) The electrochemical behavior of SSCC of L450steel, the specimens from base metel be cutted off along with hoop, was studied using the techniques of AC impedance spectroscopy, electrochemical noise, SEM and EDS. The experimental results show that the techniques of AC impedance spectroscopy does that characterizing the changes of the solution/sample interface impedance and cannot distinguish the different stages of SSCC, however the electrochemical noise can achieve the objective, the characteristics of the electrochemical noise in different SSCC stage was summarized.4) The electrochemical behavior of SSCC of L450steel, the specimens from base metel be cutted off along with hoop, was studied using the SEM and EDS in the operating mode condition. The experimental results show that on the surface of L450steel, the uniform corrosion was occurring mainly and the pitting and other localized corrosion was relatively slight. The occurrence of pitting depends on the rupture-repair of the passivation film.5) The electrochemical behavior of SSCC of L450steel was studied using the techniques of electrochemical noise, SEM and EDS and the applicability of the electrochemical noise on the on-line monitoring was studied. The results show that the technique of electrochemical noise can be used for on-line monitoring of localized corrosion.