Study of Flow Accelerated Corrosion of Carbon Steel Pipeline in Oilfield Environment

Abstract

Flow accelerated corrosion (FAC) and erosion-corrosion (EC) are the major reasons for steel pipeline failure in the oil and gas industry. The present thesis focuses on the FAC and EC study of API X70 steel in a synthetic solution of oilfield water under a turbulent flow condition. The tests were carried out at a more critical location (90º pipe elbow) in a circulating loop system at a fixed flow velocity of 3 m s-1. Multiple electrodes were located at intrados (inner face) and extrados (outer face) of the 90º pipe elbow. The influence of flow on corrosion (FAC) and passivation was examined using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) tests. Corrosion rates of the electrodes located at the intrados are more than that at the extrados. Shear stresses are simulated using the CFD method and it is observed that the corrosion rate is inversely proportional to shear stresses. The effect of oleic acid hydrazide (OAH), a green inhibitor on X70 steel was investigated for the first time under flow condition. The maximum inhibition efficiency is found at 87.7% (extrados electrode E4) for 0.30 g/L OAH concentration. The studied inhibitor is good in the protection of the API X70 steel with higher efficiency in the dynamic corrosive environment. The laser surface melting (LSM) technique is used to examine the corrosion behavior of X70 steel using laser powers of 2, 2.5, and 3 kW. It is found that the resistance against FAC of the X70 steel is significantly improved by surface modification. LSM treated X70 steel exhibited higher corrosion resistance than untreated and inhibitor-used conditions. Slurry erosion-corrosion behavior by electrochemical and weight loss measurements for both untreated and laser melted samples located at the 90⁰ elbow test section was tested and compared. Laser surface melted samples exhibited improved hardness with enhanced EC resistance as compared to that of untreated counterparts due to alteration of surface metallurgy.