Abstract <p>This paper presents practical experience in studying the causes of corrosion damage on the inner surface of gas pipelines made of 09Mn2Si steel after their use in gas fields. The influence of the features of the microstructure of samples of this pipe steel on the development of local defects on their surface is studied. According to metallographic studies, an uneven distribution of phases inside the steel and the presence of nonmetallic inclusions are recorded, which leads to the occurrence of heterogeneity on the inner surface of the pipe. The tests carried out under conditions of moisture condensation and alternating wetting of the steel surface with water in the presence of CO₂ showed that the pronounced banding of steel and the presence of corrosion-active nonmetallic inclusions are the main causes of corrosion initiation and can lead to the development of deep local damage on the surface of gas pipelines made of 09Mn2Si steel.</p>