In situ and ex situ investigation on the product films evolution of pipeline steel under AC interference and high cathodic protection conditions

An in situ Raman measurement set-up coupled with AC interference and CP circuits was developed to provide more intuitive detection data for combined action AC and CP corrosion processes. Combined with XPS, AFM and other ex situ surface analyses and electrochemical tests, the evolution of composition, structure and electrochemical properties of surface film is studied. Initially, a passive film is formed on specimen surface, which undergoes successive redox processes. Eventually, the passive film evolves into magnetite and rust, and hydrogen evolution produces mechanical damage to rust layer. Based on this, the model for the evolution of AC corrosion is constructed.