Abstract

The corrosion behavior of a C1018 carbon steel in supercritical CO2 environment with different amount of H2S (5 ppm-200 ppm) was investigated in both ex-situ morphological analysis and in-situ electrochemical methods. The corrosion rates were measured using both linear polarization resistance (LPR), weight loss method and electrochemical impedance spectroscopy (EIS), at temperatures from 60°C up to 120°C with an interval of 20°C, the experiments were performed at 400 psi (sub-critical) and 1600 psi (supercritical) of CO2 partial pressure. The corroded surfaces and the corrosion products were analyzed using various techniques, including scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), and X-ray Diffraction (XRD). The results show that the slight presence of H2S in a supercritical CO2 environment plays an insignificant role in terms of the observed corrosion rates. The types and the thickness of corrosion products changed as temperature increased. Under the effect of time, the corrosion rates decreased with exposure time gradually due to the formation of corrosion products.

Introduction

Supercritical CO2 storage has been gaining more attention due to its wider application. It is one of the desirable solutions for reducing CO2 emission, which is an important contributor to the global climate crisis. In other cases, some of the early applications were focused on the oil and gas industry, by using supercritical CO2 to sequence the mature wells for better production[1],[2]. In those environments, C1018 carbon steel was extensively used, due to its good balance of toughness, strength, and ductility as well as its excellent weldability. However, C1018 is not known to be rather corrosion resistant. Moreover, corrosion can be severe in a supercritical CO2 system, which can reach high temperature (up to 150°C) and high pressure (1000MPa) range and sometimes contain H2S. Therefore, the corrosion behavior can be the biggest challenge to the fitness of C1018 steel in the oil and gas supercritical CO2 environment.

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