Characterisation of soil/pipe interface at a pipeline failure after 36 years of service under impressed current cathodic protection

摘要

Study on corrosion behaviour of buried pipeline in saline soil is presented, the pipeline is protected by coating and impressed current cathodic protection system. In this work, spectrometric and spectroscopic techniques were used to characterise the pipe/coating/soil interfaces. The results show the coating/pipe interface forms corrosion products including the following phases: magnetite, goethite, akaganeite and hematite. However, the main phases found at coating/soil interface are magnetite and ferric ion. The behavior is consistent with the corrosion of carbon steel in soil with oxygen and chloride ion. The reaction paths are proposed under the conditions of deteriorated coating, cathodic protection, saline soil and seasonal fluctuations.