Corrosion Reason and Protection Methods of the Degreasing Sedimentation Tank in Produced Water Treatment System

In view of the serious corrosion problem of the water treatment system in Heshui oilfield, the produced water, the morphology and composition of corrosion products on the surface of internal components were tested and analyzed by ion chromatography, chemical titration, dissolved oxygen detection tube, scanning electron microscope (SEM), energy spectrometer (EDS). Meanwhile, corrosion prevention measures were put forward and field tests were carried out. The results show that the main reasons for the corrosion of the oil removal sedimentation tank were under-scaling corrosion and oxygen corrosion. Due to the different sources of produced water entering the station, poor compatibility, and high content of Ba²⁺, Ca²⁺, SO₄^2- and other scale-forming ions, it was easy to scale after mixing. After the fouling material was deposited in the oil removal sedimentation tank, due to uneven distribution, the ion diffusion and medium transfer in the fouling area were blocked, forming a closed environment. Under the action of acidification autocatalysis, corrosion in the fouling area were accelerated, causing localized corrosion. In this regard, the water quality could be improved by adding chemicals (corrosion inhibitors, scale inhibitors, fungicides and deoxidizers) to control the uniform corrosion rate within 0.15 mm/a, so the corrosion of water treatment system equipment and pipelines could be controlled.