Corrosion failure analysis of T2 copper tubes of a heat exchanger in the oilfield nitrogen production system

In a vertical shell-and-tube heat exchanger of the nitrogen production system in an oilfield, perforation failure of the internal heat exchange tubes occurred after only one year of service. The corrosion morphology and chemical composition of the failed tube were analyzed by visual examination, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The influence of temperatures ranging from 30 °C to 90 °C on the corrosion behavior of T2 copper was investigated through potentiodynamic polarization (PDP) testing. The uniform corrosion and pitting corrosion behaviors of T2 copper under static and dynamic conditions were separately studied using a circulating flow autoclave. The results indicate that the thicknesses of the corrosion product films are 10.12 μm in the splash zone and 105.8 μm in the dynamic waterline zone, respectively. No significant signs of corrosion or scaling were observed in the immersion zone. Corrosion intensity increases with rising temperature, and corrosion is more severe under dynamic conditions than under static conditions. Under dynamic conditions, the pitting corrosion rate in the dynamic waterline zone reached as high as 1.666 mm/y, whereas almost no pitting corrosion took place in the immersion zone. In the splash and dynamic waterline zones, liquid films experience continuous cycles of formation and evaporation, resulting in increased concentrations of Ca²⁺, CO3²⁻, and Cl⁻. These elevated ion concentrations promote the generation of loose and porous corrosion products such as CaCO₃, Cu₂(OH)₃Cl, and Cu₂(OH)₂CO₃, which facilitate under-deposit corrosion. Furthermore, circulating water disturbances in the dynamic waterline area cause frequent detachment of corrosion products, ultimately leading to perforation due to localized corrosion.