Abstract
The oil refining industry often relies on the use of easily available and cheaper crude oils rich in naphthenic acids (NAP) to improve its profit margins. However, the processing of these acidic crudes in distillation units can lead to severe corrosion issues in oil transfer lines. Moreover, it has been suggested that high flow velocities and multiphase flow conditions can enhance NAP corrosion in bends of transfer lines. To better understand the underlying phenomenon driving NAP corrosion, a flow loop was designed to mimic operating conditions encountered in the transfer lines of oil refineries. Experiments were performed to measure corrosion rates in single phase and multiphase flow conditions using metal samples with different piping geometries (straight and 90° elbow). The corrosion rates of carbon steel samples exposed to both single oil phase and gas-oil two-phase flow conditions (USL = 0.1-0.2 m/s; USG = 0-40 m/s) were determined using the weight loss method. This study demonstrates that the liquid refreshment rate was more important than the liquid velocity in controlling NAP corrosion in single phase flow conditions. In multiphase flow conditions, an annular-dispersed flow enhanced NAP corrosion in the pipe. In particular, the liquid film wetting the pipe proved to be more corrosive than a liquid phase transported as entrained droplets in the gas phase. The different piping geometry of the samples used to model the transfer lines did not show an effect on NAP corrosion as suggested by field observations.
