<jats:sec> <jats:title>Purpose</jats:title> <jats:p>This paper aims to clarify the corrosion inhibition effects of biocides NaClO, ClO2 and C17H30ClN on carbon steel pipelines at different service stages.</jats:p> </jats:sec> <jats:sec> <jats:title>Design/methodology/approach</jats:title> <jats:p>The corrosion behavior of new service pipelines and in-service pipelines with corrosion nodulations after biocide application was compared using microbial counting, surface analysis and electrochemical tests.</jats:p> </jats:sec> <jats:sec> <jats:title>Findings</jats:title> <jats:p>The results of this study show that for the new service pipelines, the corrosion rate increases in the NaClO and ClO2 systems and decreases in the C17H30ClN system. Therefore, C17H30ClN exhibits the best corrosion inhibition efficiency for new service pipelines. For the in-service pipelines with corrosion nodulations, ClO2 and NaClO can accelerate the sample corrosion, while C17H30ClN cannot fully remove the existing corrosion nodulations. So the application of a single biocide is insufficient to reduce the risk of corrosion. The synergistic use of C17H30ClN and ClO2 is beneficial for removing the existing nodulations, thereby minimizing the risk of local corrosion during long-term service.</jats:p> </jats:sec> <jats:sec> <jats:title>Originality/value</jats:title> <jats:p>This study provides guidance for corrosion control of pipelines at different service stages.</jats:p> </jats:sec>