Micro-area Electrochemical Behavior Research Of Typical Local Corrosion Of Pressure Vessel Steel

Simulating the harsh corrosive environment of Tahe oilfield,this paper proposed the special corrosion phenomenon of carbon steel covered with oil droplet and confirmed it by using advanced scanning vibration electrode technology,high resolution transmission X-ray 3d imaging and so on.(1)At early stage,oil droplets can protect the steel from corrosion by electrolyte and the naked steel is corroded uniformly.(2)Afterwards,electrolyte ions will penetrate the thinner oil edges and reach the surface of the metal.At the same time,the oil will diffuse into the solution in the form of tiny droplets.As a result,the protected area by oil is shrinking inward as time goes by.At this stage,there are some pits nucleating on the naked steel and growing rapidly.The pits are distributed intensively near the oil droplets.And the pits near the oil are deeper compared with those off the oil droplets.(3)If the corrosion time is long enough,the whole droplets will dissolve into the solution and the surface of the steel returns to uniform corrosion.(4)Through the analysis,a conclusion has been drawn that the pitting reason is likely the sedimenting of carbon-contained impurity in the oil.The sedimentation will destroy the continuity of product film which will be attacked by pits.The conclusion of this paper can provides theoretical basis to avoid corrosion of pressure vessel by oil droplets.