Effect of hydrodynamics on the flow accelerated corrosion (FAC) and electrochemical impedance behavior of line pipe steel for petroleum industry

Abstract

The present work focuses on the flow accelerated corrosion (FAC) study of API X70 steel in a synthetic solution of oilfield water under a turbulent flow with 3 m/s velocity in a loop system. Multiple electrodes are located at intrados and extrados of the 90° pipe elbow. The influence of flow on corrosion and passivation were examined using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) tests. Corrosion current density for all the located specimens at intrados and extrados of the elbow are found to be increased however charge transfer resistances were significantly decreased along the fluid flow path. Corrosion rates of the electrodes located at the intrados are more than that at the extrados. Shear stresses are simulated using computational fluid dynamics (CFD) method and it is observed that the corrosion rate is inversely promotional to shear stresses. Surface morphology and corrosion products were examined using SEM and Raman spectroscopy. Raman spectroscopy indicates that the compositions of corrosion compounds formed by FAC are FeCO3, α-Fe2O3, γ-Fe2O3, α – FeOOH, and β – FeOOH.