Abstract
The influence of a direct current (DC) stray current on the corrosion and cathodic disbondment of X80 steel coated with a polyethylene (3PE) coating in 3.5% NaCl solution was studied by immersion experiments, electrochemical tests, three-dimensional microscopy, and a surface analysis. The results showed that the potential of the X80 steel sample shifts under the direct current. After 100A/m2 DC interference was applied, the potential of the sample in the anode region positively shifted from –0.68 to –0.43 V. At the same time, the sample in the cathode region negatively shifted to –1.45 V. Under the DC anode action, the X80 steel corrosion exhibited no passivation and followed Faraday’s law of electrolysis, in which the corrosion rate is proportional to the current density. Three-dimensional (3D) digital microscopy showed that, as the DC current increased, the depth of the corrosion pit also increased (gradually), indicating a higher corrosion degree. The sample in the cathode region only underwent a hydrogen evolution reaction, which caused cathodic disbondment of the coating. The stray current had a critical current density for the coating disbonding: the coating delamination area reached its maximum and then remained unchanged.
Highlights
Due to the complexity of the coating process and mechanical damage during construction, pipeline coatings will inevitably be damaged and/or destroyed
Microscopy, and a surface analysis to study the cathodic disbondment of a polyethylene (3PE) coating caused by the inflow of a direct current (DC) stray current and the corrosion behavior of the pipeline steel caused by the outflow of a DC stray current in 3.5% NaCl solution
When the DC passed through the X80 steel, the balanced electrode reactions became disturbed, When the DC passed
Summary
Due to the complexity of the coating process and mechanical damage during construction, pipeline coatings will inevitably be damaged and/or destroyed These coatings are severely affected by various long-term corrosion factors in the soil during the life of the pipe and its service, and these factors often cause coating disbonding. When a DC current passes through the damaged portion of the coating of buried long-distance pipelines, an anode region forms that causes electrolytic corrosion of the metal pipeline, resulting in a corrosion piercing [14,15]. While studying a DC stray current’s influence on buried metal pipelines, it is necessary to consider both corrosion of the pipeline and cathodic disbondment of the coating to improve the anticorrosion performance of the organic coatings that protect metal pipelines. Microscopy, and a surface analysis to study the cathodic disbondment of a polyethylene (3PE) coating caused by the inflow of a DC stray current and the corrosion behavior of the pipeline steel caused by the outflow of a DC stray current in 3.5% NaCl solution
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