Corrosion behavior of low-nickel alloy steels in a simulated oilfield environment containing carbon dioxide

Abstract

The microstructures and mechanical properties (tension strength Rm, yield strength Rt0.5 and impact energy Akv) of the low-nickel alloy steels 08Ni, 12CrNi and 20CrNi with and without heat treatment were measured and analyzed, as well as the common gathering pipeline steels (X60 and 16Mn). The results indicate that the mechanical properties of the low-nickel alloy steels with heat treatment are superior compared with other test materials, in the sequence as follows: (20CrNi) > (12CrNi) > (08Ni) > 20CrNi > 12CrNi > X60 > 08Ni > 16Mn (“(steel)” indicates the material with heat treatment, and “steel” means without). The weight-loss method was used to test the corrosion rates of the test materials exposed to a simulated oilfield environment for 168 h at 90 °C with the CO2 partial pressure and total pressure 2 MPa and 10 MPa, respectively. The systematical characterization with scanning electron microscope and X-ray diffraction displayed the different micro-morphology of corrosion scales formed on the surface of the test materials with FeCO3 as the only detected composition of corrosion product. That the low-nickel alloy steels with heat treatment showed a higher corrosion resistance than those without, mainly resulted from the different microstructures of the matrix, the characteristics of corrosion scale and the composition of elements.