The Research On Mechanism Of The Effect Of AC Stray Current On Buried Pipeline Corrosion

Nowadays,facilities of highest voltage AC power line system and oil and gas pipeline system have been closely laid together because of the limit of land utilization,which causes buried pipeline serious communication corrosion by AC interference from highest voltage AC power line.As a result,the use life of buried pipelines is shortened,which causes significal economical loss even life-threatening hazards.Not only has not united knowledge of AC corrosion mechanism formed but also has traditional and new cathodic protection criteria no longer apply under AC interference,which are verified by existing research or scene cases,so this paper deeply investigates the influence mechanism of AC interference on buried pipeline with and without cathodic protection,which is aimed at providing more accurate theoretical support and actual engineering guidance for corrosion protection work of AC interference.Firstly,the results show that AC interference cause the corrosion potential of X80 steel or zinc alloy sacrificial acquired at 1 Hz acquisition frequency to shift significantly.In case of cathodic protection,offset direction closely related to r,the ratio of polarization slope of polarization region where maximum and minimum of real potential acquired at 100 Hz acquisition frequency locate.When r >1,the corrosion potential shifts positively,otherwise shifts negatively.In case of cathodic protection,offset direction of corrosion potential of zinc alloy sacrificial anode or X80 steel is not only related to r,but also affected by coupling between them.Therefore,in the process of AC interference,the offset direction and potential fluctuation of X80 steel and zinc alloy sacrificial anode are different in different systems.Secondly,the results show that in two cases,with or without cathodic protection,in the system where X80 steel does not form a passive film,corrosion occurs when AC interference causes the maximum corrosion potential is greater than-0.775 V(vs.SCE)and it increases with the increase of AC current density.In the system where the passive film is formed,the corrosion is not intensified when the real potential is in the passivation region of X80 steel.When the passive film is destroyed and the maximum of its real potential is greater than-0.775 V(vs.SCE),corrosion occurs and the corrosion increases with the increase of AC current density.Therefore,in the process of AC interference,the corrosion of X80 steel in different systems is different.At the same time,AC interference can also lead to an increase in potential difference and an increase in galvanic current acquired at 1 Hz acquisition frequency between the sacrificial anode of X80 steel and zinc alloy,and sacrificial anode corrosion of zinc alloy accelerates.It can be concluded that the corrosion characteristics of X80 steel and zinc alloy sacrificial anode are different in different solutions,so AC interference will lead to different direction and fluctuation of corrosion potential,which will lead to different corrosion condition,so in the traditional and new cathodic protection standards respectively take average potential acquired at 1Hz acquisition frequency was lower than the-0.775 V(vs.SCE)or AC and DC current density as a criterion to protect AC stray current interference,which is defective.In the detection and protection evaluation of AC stray current,the acquisition frequency can be improved to obtain the actual potential fluctuation of buried metal pipeline,which can improve the accuracy of current cathodic protection standards for AC corrosion protection.