Experimental Research on Anti-corrosion Process of BG110-3Cr Casing Zinc Alloy

Abstract

In order to study the effect of processing technology of Radium zinc anode for direct casting corrosion protection on the outer surface of BG110-3Cr casing on the properties of casing matrix and anode material. The mechanical properties and SEM fracture morphology of two sets of tensile specimens of casing material obtained by heating and casting heat conduction of resistance furnace were tested by metal material tensile test method, and then metallographic specimens were prepared for observation of microstructure. According to the properties of cast anode material, the content of melting elements in alloy was detected by ICP method and direct reading spectroscopy method respectively, and the content of melting elements in alloy was determined by electrochemical method. The polarization curves of the alloys were measured at 20 °C, 40 °C, 60 °C and 80 °C respectively, and the electrochemical properties were evaluated by comparing the polarization curves with those of the national standard anodes. The experimental results show that: (1) Rm and Rp0.2 of BG110-3Cr steel decrease to 913.1 MPa and 799.4 MPa respectively after heating up to 600 °C, the equiaxed dimples with uniform fracture surface become pits, the yield strength decreases, the carbide particles in tempered sorbite aggregate, the strength decreases, but the toughness increases, which is higher than API standard; (2) Under the influence of heat transfer and heating up of casting, the white distribution in the metallographic structure of the casing is 1–3 μm. Carbide particles, measured Rm and Rp0.2 increased to 1015.1 MPa and 890.5 MPa, respectively. (3) No macrosegregation and microscopic segregation were observed in the metallographic structure of the cast anode material. The polarization curve showed that the corrosion potential decreased with the increase of temperature. The corresponding corrosion potential at 80 °C was −1.09 V. No passivation was observed and the electrochemical performance was stable. The results provide technical support and theoretical basis for the processing of temperature-resistant anodes for cast anticorrosive casing and their application in the field of cathodic protection of deep well casing.

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This paper was prepared for presentation at the 2019 International Petroleum and Petrochemical Technology Conference in Beijing, China, 27–29 March 2019.

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