Causes of Internal Corrosion and Corrosion Mechanism for Gathering and Transportation Pipes in An Oil Production Plant of Changqing Oilfield

Optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used to analyze the causes of corrosion failure of pipes in six typical blocks in Changqing Oilfield, and the corrosion mechanism was also investigated. The results show that the microstructure of failed pipes in 6 typical blocks was ferrite and a little pearlite, and the element distribution was uniform. The chemical composition of the failed pipes was in accord with the standard requirements of 20^# steel. The main components of corrosion products on the perforated corrosion pipe sections in typical blocks No. 1, No. 3, No. 4, No. 5 and No. 6 were iron oxides (Fe₂O₃, Fe₃O₄). The main components of corrosion products on the perforated corrosion pipe sections in typical blocks No. 2 were iron oxides (Fe₂O₃, Fe₃O₄) and iron sulfide (FeS). Carbon dioxide corrosion occurred on pipes in typical blocks No. 1, No. 4, No. 5 and No. 6. Carbon dioxide and hydrogen sulfide corrosion occurred on pipes in typical block No. 2. Carbon dioxide and oxygen corrosion occurred on pipes in typical block No. 3.