A Comparison of Cathodic Protection Parameters with High- Strength Pipeline Steels in Soil Solution

Cathodic protection is usually used to control the corrosion in service pipeline. The optimum cathodic protection potential (OCPP) becomes a vital part in order to get the best protective effect in the whole research of cathodic protection. Up to now, the OCPP is often defined between 200mV to 300mV more electronegative than the free corrosion potential under usual circumstance (neutral aqueous solution or soil). However, the phenomena of over-protection and under-protection usually occur in service pipeline. The cathodic protection parameters of pipeline steel X65, X80 and X100 pipeline steel in Dagang simulated soil solution have been investigated by using the polarization test and AC electrochemical impedance spectroscopy (EIS) measurements. The values of charge transfer resistance (Rt) by analyzing the EIS curves at various cathodic protection potentials show that the polarization resistance of the specimen has a maximum value with negative shift of the polarization potential. The value is negative to 1000 Ώ∙cm2, hydrogen evolution reaction will occurs. The potentials of hydrogen evolution of X65, X80 and X100 in Dagang simulated soil solutions increase orderly. The study on cathodic protection parameters of X65, X80 and X100 pipeline steels in simulated soil solution have greatly useful value and practical significance on the research about the application of transportation pipeline.