Corrosion Behavior Of X70 Pipeline Steel Under The Effect Of Anions And Sulfate Reducing Bacteria

In recent years,pipeline leakage accidents have occurred many times in the operation of oil and gas pipelines,posing a threat to the safe operation of pipelines,and also causing huge economic losses and environmental pollution.Most pipeline leakage accidents are caused by pipeline corrosion.Usually pipeline steel is laid on the seabed or in the soil.These environments contain a large number of microorganisms and corrosive anions.The corrosion characteristics are very complicated.In addition,dissolved oxygen,pH and temperature will also affect the corrosion behavior of pipeline steel.Corrosion is an inevitable problem in the operation of pipeline steel.According to the survey,sulfate-reducing bacteria?SRB?and anions are the most important causes of corrosion in pipeline steel.In this paper,SRB was collected from the mud of the South China Sea,and the number of SRB in the mud of the South China Sea was determined.The growth of SRB in the mud of the South China Sea was studied.The effects of Cl^-and SO₄^2-on the growth activity of SRB and the adsorption of SRB and Fe²⁺were investigated by UV-visible spectrophotometry.The results showed that with the increase of Cl^-concentration from 0g/L to 30g/L in the simulated solution,the growth activity of SRB increased first and then decreased,and the adsorption of SRB and Fe²⁺first weakened and then increased,when the concentration of Cl^-was 20g/L.When SRB activity is the strongest,the adsorption with Fe²⁺is the weakest.With the increase of SO₄^2-concentration from 0g/L to 45g/L,the growth activity of SRB is gradually enhanced,and the adsorption of SRB and Fe²⁺is gradually weakened.The effects of Cl^-,SO₄^2-and SRB synergistically on the corrosion behavior of X70 pipeline steel and its corrosion mechanism were studied by AC impedance test and polarization curve test.The results show that as the Cl^-concentration in the simulated solution increases from 0g/L to 30g/L,the corrosion rate of the steel decreases first and then accelerates;as the SO₄^2-concentration increases from 0g/L to 45g/L,the corrosion of the steel The rate gradually decreases.This is because the change of Cl^-and SO₄^2-concentration will affect the adsorption of EPS and Fe²⁺on the one hand,and thus affect the dissolution rate of the anode;on the other hand,it will affect the formation of corrosion products and the compactness of the corrosion product film.The effects of Cl^-,SO₄^2-and SRB synergistic effects on the stress corrosion cracking behavior?SCC?of X70 pipeline steel in the Nanhai sea mud environment were studied by slow strain rate tensile test?SSRT?.The results show that with the increase of Cl^-concentration in the simulated solution from 0g/L to 30g/L,the SCC sensitivity of X70 steel first weakens and then increases;with the concentration of SO₄^2-increases from 0g/L to45g/L,X70 steel The sensitivity of SCC is gradually weakened.This is because the change of Cl^-and SO₄^2-concentration will affect the adsorption of EPS and Fe²⁺on the one hand,and thus affect the dissolution rate of metal anode,on the other hand,it will affect the consumption of H atom in the cathode reaction,and the content of H atom will cause hydrogen to occur in steel.An important cause of cracking.In this way,the corrosion behavior of X70 pipeline steel in the sea mud environment of South China Sea under the synergistic action of Cl^-,SO₄^2-and SRB was proved,and the problem of unclear corrosion mechanism of X70pipeline steel when anion and SRB coexist was solved,and the occurrence of failure accident was reduced.To avoid economic losses and casualties,and to improve the protection measures of X70 pipeline steel in the South China Sea mud environment provides theoretical basis and scientific reference,which has important practical significance.