Abstract: The two submarine pipelines A and B in the South China Sea were put into operation in 2011 and 2018 respectively, and corrosion failure occurred when they did not reach the design service life. According to the historical operation data of submarine pipelines, the corrosion detection data of CO₂ and H₂S, microorganisms, chloride ions and other corrosion detection data in the pipeline were comprehensively analyzed, and internal corrosion causes of the pipeline were discussed in combination with the flow rate and water content. The results show that the CO₂ content of A and B submarine pipelines during operation was far more than the design value, and there was a risk of CO₂ corrosion. There was CO₂/H₂S synergistic corrosion in A submarine pipeline. The Cl^- contentrations in the transportation medium of the two submarine pipelines were both high, the medium flow rates were both low, there were severe microbial corrosion, and the pigging method and the selection of sterilization agent were not appropriate, which eventually led to the corrosion failure of A and B submarine pipelines without reaching the service life.