Study On SCC Behavior Of X70 Steel In Near-neutral Ph Solution Under The Synergistic Effect Of DC And SRB

With the rapid development of the power grid,energy and transportation industries,due to the limitation of geographical environment,the laying of buried metal pipelines and high-voltage transmission lines or electrified railways is inevitable,even in some areas.The direct current environment in these public areas interacts with microorganisms to complicate the stress corrosion behavior of pipeline steel.Therefore,the self-made experimental device was used to construct the corrosion environment under the action of direct current and SRB.The slow strain rate stretching method combined with SEM microscopic analysis method was used to study the stress corrosion of X70 pipeline steel in near-neutral pH solution by direct current and SRB.The law of influence of behavior.The main conclusions of this paper are as follows:(1)When the applied DC electric field intensity is low(less than 200V/m),the SRB growth is basically unaffected;when the electric field strength is 500 V/m,the efficiency of the material transfer inside and outside the SRB cell membrane and the metabolic activity of the bacteria are gradually enhanced;At 1000 V/m and 1500 V/m,the electric field changes the permeability of the microbial membrane,resulting in the inactivation of SRB cells and accelerating the death of SRB in NS4 solution.(2)In the aseptic NS4 solution under DC field strength,the anodic dissolution process of X70 steel accelerated under the action of electric field,accelerated metal corrosion rate,and the secondary crack on the metal surface increased gradually,which increased the stress corrosion cracking sensitivity of X70 steel.When the DC electric field strength is 1500 V/m,the SCC is more sensitive.X70 steel has the lowest SCC sensitivity when no external DC electric field is applied.(3)In the NS4 solution with DC field strength,the anodic dissolution process of X70 steel accelerated under the action of SRB,the corrosion rate of metal accelerated,and the metal surface easily formed pitting pit,which increased the stress corrosion cracking sensitivity of X70 steel.With the increase of DC electric field,the SCC sensitivity decreased first and then increased in the NS4 solution.(4)When there is no current,SRB has four growth stages in near-neutral soil,logarithmic growth phase at 1-4 d,stable growth period at 5-8 d,and decay period at 9-11d,12-14d is the death period.When the applied DC current density reaches 1 A/m~2,the decay period of SRB in near-neutral soil is advanced to 7 days.When the applied DC current density reaches 3 A/m~2,the logarithmic growth period of SRB is shortened to 1-4 d,the decay period is advanced to the 6th day,and the death period is advanced to the 10th day.When the applied current continues to increase above 5 A/m~2,the logarithmic growth phase of SRB is shortened to 1-3 d,the decay period is advanced to the 5th day,and the death period is advanced to the 9th day.With the increase of the applied DC current density,the current accelerates the growth and reproduction of the bacteria while promoting its death process,and the SRB activity is sequentially weakened.(5)In the aseptic NS4 solution under direct current,the anodic dissolution process of X70 steel is very rapid under the action of current,the metal corrosion rate is too fast,and the metal surface is easy to form a large number of pitting pits,which increases the stress corrosion cracking sensitivity of X70 steel.In the process of increasing the DC current density of X70 steel,the corrosion rate is gradually increased,and the corrosion product film is broken under the action of tensile stress,resulting in serious metal corrosion and strong SCC sensitivity.Direct current density 0 A/m~2 under sterile conditions,the corrosion in the solution is slight,SCC sensitivity is weak.(6)In the NS4 solution with direct current,the DC current has a great influence on the DC current density,which accelerates the corrosion of the metal and increases the stress corrosion cracking sensitivity of X70 steel.With the increase of DC current,the SCC sensitivity decreased first and then increased in the NS4 solution.