Investigations on the oxygen corrosion behaviors of P110 steel in a dynamic experiment simulating nitrogen injection

Abstract

AbstractNitrogen injection is widely applied to enhance oil recovery, but the corrosion failure risk of tubing and casing is increased by residual oxygen in nitrogen. In this study, the corrosion behaviors of P110 steel under dynamic conditions with different oxygen partial pressures (2.5–0.003 MPa) simulating high‐pressure (30 MPa) nitrogen injection were studied. The morphology and composition of corrosion products were characterized by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and energy‐dispersive X‐ray analysis methods; furthermore, the localized corrosion rate and three‐dimensional surface morphologies were analyzed. The results show that the general corrosion rate decreased significantly with decreasing O2 partial pressure, especially when O2 partial pressure was below 0.5 MPa, and there is a corrosion morphology change from general corrosion to localized corrosion (pitting). Besides, the localized corrosion rates are about 20 times the general corrosion rates. The corrosion products are mainly FeOOH and Fe3O4. In addition, the scales in the intact area are relatively flat and dense, whereas the damaged scales are porous and brittle. Fluid flows not only changed the morphologies and microstructures, resulting in a more protective product layer but also promoted the transfer of the corrosive mediators and affected the development of localized corrosion.