Corrosion investigation of the inlet section of REAC pipes in the refinery

• The corrosion thinning is localized at the inlet section of REAC tubes.
• Erosion corrosion failure mainly occurs in the first row of carbon steel base pipes.
• The water in oil emulsion could reduce the corrosion degree.

The corrosion failure causes of the inlet section of reactor effluent air cooler (REAC) in the refinery was investigated by using Aspen software, HTRI Xchanger Suite simulator (HTRI), Computational Fluid Dynamics (CFD) technology and erosion corrosion experiments. The result shows that the severe erosion corrosion failure mainly occurs in the first row of REAC pipelines, and the field with localized corrosion is mainly distributed in a range of 5.8 m away from the inlet of air coolers and reveals an inhomogeneous thinning. At the REAC inlet, the NH4HS concentration is about 12 wt% (> 10 wt%), the shear stress is high and oil phase is not appeared, thus the corrosion failure easily occurs at the inlet region. Meanwhile, the liquid phase fraction is larger at the bottom of the pipeline, forming corrosive solution and resulting in serious thinning. In the second and third passes, water and oil phase flow increases, i.e., both the NH4HS concentration and the shear stress greatly decrease. In addition, the water in oil emulsion can segregate the contact between the tube wall and the corrosive medium. Therefore, beyond the range of corrosion failure region and in the second/third passes, the risk of erosion corrosion is markedly reduced.