Abstract: Aiming at the serious corrosion and perforation of surface gathering and transportation pipelines in Nanmazhuang oilfield, the composition of produced water transported by four gathering and transportation pipelines was analyzed.The average corrosion rate of 20 carbon steel was measured by weight loss method, and the corrosion product film and pitting pits were characterized.The results show that the produced water of Nanmazhuang oilfield is neutral or weakly alkaline, and the content of Cl^-and HCO₃^-is high, which may cause corrosion and carbonate scaling.The average corrosion rate of produced water to 20^#steel is low (< 0.076 mm/a), but there is serious pitting corrosion.The maximum pitting depth is 66 μm-97 μm, and the pitting coefficient is more than 50.The main causes of pitting corrosion are incomplete corrosion product film, Cl^- and CO₂ corrosion.Combined with the surface pipeline corrosion morphology, the corrosion mechanism model of surface gathering pipeline in Nanmazhuang oilfield is established, and its mechanism is described.