Study On Q235 Carbon Steel Corrosion Characteristics Induced By Marine Diatoms

Marine microbiologically influenced corrosion is the main form of damage to ships and marine equipments,resulting in economic losses of trillions of dollars each year,and causing immeasurable security risks.The main microorganisms that cause marine microbiologically influenced corrosion are bacteria,fungi,and microalgae.At present,scholars from various countries have studied the marine bacteria such as sulfate-reducing bacteria,nitrate-reducing bacteria and iron bacteria,thus getting a clear understanding for the mechanism of the corrosion process.However,the influence of microalgae in the corrosion process has not been widely concerned,and the corrosion mechanism is not clear.Microalgae as autotrophic organisms,photosynthesis under light conditions,and respiration under dark conditions are two completely different life activities,which will produce different physical and chemical states on the substrate surface.Therefore,it is of great significance to deeply study the influence of different life activities of microalgae on substrate corrosion to complete the mechanism of microbiologically influenced corrosion.In this paper,the growth status,dissolved oxygen and p H values of P.tricornutum,which are widely present in the ocean,were studied under the conditions of light 24 h,no light(dark 24 h)and alternating light(light/dark:12 h/12 h).Using surface analysis technology,electrochemical test and chemical analysis of corrosion products,the adhesion and biofilm composition of P.tricornutum on the surface of carbon steel Q235 under 3 conditions were studied.The micro-morphology and chemical composition of corrosion products were detected,and the corrosion morphology and degree of corrosion on the surface of carbon steel were observed.The mechanism of different life activities under dark and light on the corrosion of carbon steel Q235 was analyzed and summarized.The results showed that P.tricornutum could adhere to the surface of carbon steel and accelerate the corrosion rate of the substrate.Q235 and caused microbiologically influenced corrosion.Under the condition of light 24 h,in the light intensity of 2000lx,3000 lx,5000 lx and 6000 lx,with the increase of the light intensity,the growth rate of P.tricornutum was accelerated,the open circuit potential of the sample was increased,and the capacitive arc radius decreased significantly,the charge transfer resistance was reduced,and the corrosion current density was significantly increased,especially when the light was 6000 lx,the corrosion current density was 2.3 times than that of in the seawater without algae(8.146x10^-6Amp·cm^-2),and it was nearly 1.8times higher at 2000 lx..Corrosion occurred in the form of pitting corrosion.With the increase of light intensity,deeper and larger pitting pits appeared.The diameter of pitting pits at 6000 lx was even as high as 78.2?m,and the depth exceeded 24.906?m.The photosynthesis of P.tricornutum significantly increased the dissolved oxygen content.The depolarization of oxygen was the main cause of the corrosion reaction,which caused the p H values to rise.The corrosion products were mainly wurtzite(?-Fe OOH)and magnetite(Fe3O4).In the dark of 24 hours,the corrosion caused by CO2 destroyed the surface of the substrate in the form of uniform corrosion.The p H values decreased,and the dissolved oxygen content was as low as half of that in the light of 24 hours.The corrosion products were composed of siderite(Fe CO3).Electrochemical results showed that the open circuit potential was negatively shifted,the radius of the capacitive arc and the charge transfer resistance were significantly reduced,and the corrosion current density was significantly increased.Weight loss experiments showed that the corrosion rate was even increased to 3.5 times compared to the control group.Alternating light(light/dark:12 h/12 h)as the natural growth condition,Q235carbon steel was corroded in the form of pitting corrosion and had the characteristics of uniform corrosion at the same time.The corrosion products contained lepidocrocite(?-Fe OOH)and magnetite(Fe3O4)and siderite(Fe CO3).The p H values and dissolved oxygen content were between light 24 h and dark 24 h.Weight loss experiments showed that although the corrosion rate was reduced,it was still about twice than that of in the seawater without algae.