Abstract
The effect of high temperature on corrosion behavior and passive film composition of Ni-based alloy 825 in H2S-containing environment was investigated by Confocal Laser Microscope (CLM), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), and X-ray Photoelectron Spectroscopy (XPS). The experiment was carried out at 150 and 230°C in NaCl solution. The partial pressure of H2S was set to 1.2 MPa and CO2 was set to 3.2 MPa. The results showed that Ni-based alloy 825 presented good general corrosion resistance. Pitting corrosion was likely to occur at 230°C because of Cr depleted in the passive film. NiS appeared at high temperature and is damaging to protectiveness of passive film.
Highlights
With the increase in energy demand and development in oil field exploitation methods, ultra-deep oil and gas fields have gradually increased
The conclusion is listed as follows: 1) The general corrosion of Alloy 825 is relatively slow in environment with 3.2 MPa CO2, 1.2 MPa H2S
2) No pitting corrosion occurred at 150°C
Summary
With the increase in energy demand and development in oil field exploitation methods, ultra-deep oil and gas fields have gradually increased. Downhole equipment is facing temperatures above 100°C. Because of the high H2S, high Cl−, and high CO2 that exist in the downhole environment, materials usually used in production suffer from decreasing corrosion resistance. Carbon steel will face high corrosion risk in the harsh corrosive environment (Javidi and Bekhrad, 2018). Nickel-based alloys with better corrosion resistance are used in production equipment. There was plenty of research about the corrosion behavior at temperature lower than 200°C. There are few reports on the passive film composition of alloy 825 under extreme environments. The relation between passive film composition and corrosion resistance still needs to be studied. Its high content of Cr and Ni makes for great passivation performance and good corrosion resistance. Mo is a typical additive to improve the stability of passive film and prevent occurrence of localized corrosion (Laszczyńska et al, 2017; Hendersona et al, 2018)
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