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In order to evaluate the effect of chromium content in carbon steel on the corrosion resistance of carbon steel materials, the corrosion behavior of 1Cr and N80 steels was investigated in this study by immersion weight loss method under three different CO2 partial pressure and temperature conditions in formation water for 72, 168 and 336 h. Detailed material surface morphological characterization was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser scanning microscopy (CLSM). The results show that the pitting corrosion of N80 carbon steel is serious at medium temperature and low CO2 partial pressure (50 °C, 0.30 MPa), and the corrosion rate is significantly higher than that of 1Cr steel. However, at high-temperature and high CO2 partial pressure (100 °C/0.63 MPa and 114 °C/0.73 MPa), 1Cr steel is more inclined to the mesa corrosion dominated by local corrosion characteristics, and the corrosion rate is seriously higher than that of N80 steel with uniform corrosion. From the experimental results, we can know the corrosion resistance of carbon steel and 1Cr steel is not only affected by the corrosion environment, but also depends on the formation process of the product film, as well as its compactness and integrity characteristics. At low-temperature and low CO2 partial pressure, 1 wt.% chromium content can provide a certain degree of corrosion resistance, while high temperature and high partial pressure can broaden the application window of carbon steel N80 and weaken the corrosion inhibition effect of chromium. [ABSTRACT FROM AUTHOR]

The role of BN, AlN and MnS particles on the degradation in creep life and rupture ductility has been investigated for 9 to 12Cr martensitic steels and 1Cr bainitic steel mainly at 550 to 650 oC. The BN particles form in Gr.92 and Gr.122 during normalising at around 1100 oC. The BN particles have nothing to do with the degradation in creep life. The AlN particles precipitate in the high-Al heats of 12Cr-1Mo-1 W-0.3 V steel during creep, reducing dissolved nitrogen and fine nitrides beneficial for the creep strength and degrading the creep life. The MnS particles have nothing to do with the degradation in creep life of 1Cr-1Mo-0.25 V steel. The BN, AlN and MnS particles are responsible for the degradation in reduction of area of the steels by accelerating the formation of creep voids at interfaces between the particles and alloy matrix. [ABSTRACT FROM AUTHOR]

The effect of silty sand on the pre-passivation behaviour of 1Cr steel in a CO2 aqueous environment was investigated by electrochemical measurements and immersion tests. The results indicated that the cathodic reaction was accelerated by silty sand at the initial corrosion stage, but it was inhibited during the late corrosion stage. The corrosion film presenting as one single layer structure under silty sand condition was mainly composed of Cr(OH)3, amorphous FeCO3, and silty sand. The content of Cr(OH)3 in the film with silty sand was lower and then higher than that without silty sand with increasing corrosion time. The film was separated by silty sand at the early stage and it was filled with silty sand during the late stage. In addition, the pre-passivation behaviour of 1Cr steel under silty sand condition was weakened and then strengthened compared to sand-free condition. [ABSTRACT FROM AUTHOR]