The corrosion behavior of 3Cr steel in simulated oilfield CO2 and formation water environment at different temperature and partial pressure of CO2 were investigated using dynamic immersion tests, scanning electron microscopy inspection and X-ray diffraction analysis. The result demonstrated that with an increasing of temperature, the corrosion rate of 3Cr steel decreased, and reached the maximum corrosion rate when the partial pressure of CO2 was 0.5MPa. The high content of Ca2+ in the formation water had also played an important role in the corrosion behavior of the 3Cr steel for it can lead to a deposition of the CaCO3 on the surface of the specimen.
There was an oil pipeline fracture found in the unlock process of Z well in western oilfield.The reason that made the oil tube fracturewassystematically studied usingmacroscopic analysis,physical and chemical property test,scanning electron microscope with an energy dispersive X-ray spectrometer and X-ray diffraction analysis.The results suggested that the requirement of relevant standard for C110 steel grade was satisfied with the chemical component and mechanical property of oil tube.The perforation of oil tube made H2S in the fluid medium enter the oil set of connected rings. In addition, the high-pressure gas left by gas contained certain H2S and O2 so that the tubewould fracture and be invalid under the combined action of sulfide stress corrosion and oxygen corrosion.
In this paper, with the observing corrosion morphology of the inner cavity of the Christmas tree hydraulic valve and detecting the physical and chemical properties of the material (chemical composition, mechanical properties and metallographic structure),It is found that the main reason for the corrosion of the inner cavity of Yidong fan is that in the production process, due to improper heat treatment process, Cr element is accumulated in the metallographic structure of the hydraulic valve matrix, forming a grid like high Cr region, and the grid becomes a low Cr region, under the action of formation water containing CO2, the low Cr area is corroded, and large and deep corrosion pits are formed in the internal cavity of the hydraulic valve.
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