Research On Corrosion Behavior Of Sacrificial Anode Of Magnesium Alloy In Buried Pipeline Under Stray Current

Stray current refers to the current flowing outside the specified circuit.The main source is the urban subway with DC electric traction.The generation of stray current will have a huge impact on the safety of buried gas pipelines,especially the sacrificial anodes of gas pipelines.The actual engineering experience in Shenzhen shows that after the opening of the subway,the service life of the anode protection system of some gas pipelines is shortened by 70-80% before the opening of the subway line.This shows that the stray current generated by the rail transit system in Shenzhen has been very disturbing to the buried pipeline.In this paper,based on the measured bipolar characteristics of the sacrificial signal on the sacrificial anode side of the buried pipeline magnesium alloy,it is different from the traditional AC electric stray current method,and the self-designed stray current laboratory simulation device was used to realize the same as the measured signal.Equivalent analog of frequency and bipolar.Based on the experimental device,the magnesium alloy sacrificial anode excavated in the field was studied,and conducted the corrosion weight loss under the condition of stray operation,equivalent DC working condition,no stray natural protection condition and natural corrosion condition.After the experiment was completed,the corrosion mechanism of magnesium alloy sacrificial anode under stray current was proposed by means of macroscopic morphology observation,3D morphology observation,X-ray diffraction and other methods.The effects of different service conditions on the electrochemical behavior of the sacrificial anode magnesium alloy were described by means of linear polarization curves,electrochemical impedance spectroscopy and potentiodynamic scanning of electrochemical workstations.The results show that when there was no current interference or under the condition of equivalent DC signal,a stable passivation film will be formed on the surface of the magnesium alloy,but the existence of stray current will accelerate the destruction of the passivation film,making the magnesium alloy substrate exposed to corrosion,and the corrosion rate of the magnesium alloy was increased.In order to further analyze the influence of stray current on the service life of magnesium alloy,the weight loss experiment of magnesium alloy under different stray current densities was carried out.Based on the principle of corrosion electrochemistry,the stray corrosion mechanism of magnesium alloy was discussed.The results show that with the increase of stray current density,the blunt current density of magnesium alloy increases continuously,and the resistance of the film layer decreases continuously.The combined effects of the two alloys make the magnesium alloy more susceptible to corrosion.At the same time,combining the corrosion time and the stray current density with the weight loss curve of magnesium alloy,the life prediction method of magnesium alloy sacrificial anode under the spurious signal interference in Shenzhen was established.