Effects of temperature on polarity reversal of under deposit corrosion of mild steel in oilfield produced water

Abstract

Under-deposit corrosion (UDC) is one of the main factors leading to perforation or leakage of gathering pipeline in the oilfield. In this paper, galvanic corrosion of mild steel under CaCO₃ deposit was investigated by using wire beam electrodes (WBE) in the oilfield-produced water. Potential and galvanic mappings indicated that the wire electrodes covered by CaCO₃ deposit mainly acted as anode while the rest bare wire electrodes acted as cathode at the beginning of corrosion, causing apparent UDC. However, the deposit-covered electrodes were finally transformed from anode to cathode along with the bare electrodes from cathode to anode, indicative of intensive galvanic polarity reversal. It is supposed that FeCO₃ corrosion products could fill into the deposit layer and form a physical diffusion barrier to block the transportation of aggressive ions from the bulk solution to the metal substrate.