Carbon Dioxide Corrosion Of Oil And Gas Pipe Behavioral Research

This subject mainly discussed the immersing corrosion behaviors of seven different kinds of steel in the NACE aqueous solution without CO2 and saturated CO2, the dynamic corrosion behaviors was discussed in the saturated CO2 NACE aqueous solution as well. The seven kinds of steel were Wu steel X60,Bao steel X60,Zhu steel X60,Wu steel X65,Bao steel X70,316L and 16Mn steel. The experiment was carried out at 60C and 90C its time was 24h 48h 96h 120h and 240h.Results showed that immersing corrosion rate at 90 C was greatly higher than the one at 60C.The pitting corrosion was found on the part of surface of sample, the other part was uniform corrosion. Corrosion products was mainly FeCO3.While the reaction was happen at 90 C,that was 3Fe+4H2O- Fe3O4+4H2 ,the mesa corrosion was appeared at 90 C, the sample was corroded severely not only at location part but the whole one. The corrosion rate was higher in the saturated CO2 NACE aqueous solution than the NACE aqueous solution without CO2.Because the CO2 was reacted at aqueous solution, its products was H2CO3. H2CO3 is a kind of weak acid ,its corrosive quality was greater than the HC1 at the same pH.The dynamic corrosion rate was higher than the immersing corrosion rate at 60 C. It showed that corrosion was decided on the diffusion to imparting medium. Along the experiment time was prolonged, the corrosion products was appeared on the surface of sample. Then the runoff effect became more aggravated, so the dynamic corrosion rate was elevated.The supreme depth of pitting corrosion of every kind of materials would became bigger when the experiment time was prolonged. The pitting corrosion would be developed to the deeper part of the sample and could induce the perforation in short time because the pitting corrosion rate was high. The pitting corrosion was mainly found on the surface of the sample under the condition of 60 C,while the other part of the sample was uniform corrosion. From the figure of the EDS, Cl was checked, the result showed that Cl- was the main factor to induce pitting corrosion.The coefficient of pitting corrosion: Wu steel X65>Bao steel X70>Wu steel X60>Bao steel X60>Zhu steel X60.It show that the Wu steel X65 was susceptible to the perforation of corrosion under the condition of NACE aqueous solution saturated CO2 at 60C,while the slightly pitting corrosion or uniform corrosion was appeared on the surface of the Zhu steel X60, pitting corrosion was appeared and developed in the band structure, so the band structure was the susceptible part to induce pitting corrosion.Pitting corrosion was appeared and developed on the surface of sample when the experiment time was prolonged at 60C,at the same time the amount of the pitting was augmented because the corrosion battery which is the small anode and big cathode came into being. Thus the location part of the sample was smelt and developed to the deeper part. The transformation tendency of the corrosion rate is different along the experiment time was prolonged at the different conditions of experiment. It mainly depended on the protective quality of the corrosion product scale.