Study On Corrosion Behavior Of Q235 Carbon Steel In Seawater Environment

The marine environment is very complex.The corrosive ion of the ocean will affect the corrosion behavior of the metal which makes the engineering material in ocean corroded badly.This loss is not reversible.The loss metal along with the change of mechanical properties can not play a role normal function.It is the clear point that affecting the condition of seawater corrosive ions change will take an important affect on the corrosion behavior of engineering materials in ocean.Temperature and flow velocity are two important environmental factors which affect the diffusion velocity of the ion.It will accelerate the corrosion of seawater materials.The marine microorganisms may also affect corrosion behavior of metal materials in ocean besides the temperature and flow velocity.Marine microorganisms which can formate the biofilm on the surface will be attached to the metal surface.The biofilm makes local environment changed on the surface of the metal,which finally affects the corrosion behavior of metals.So it is of great practical significance to study the influence of temperature,flow velocity and marine microorganisms on the corrosion behavior of engineering materials in seawater and to find an effective and environmentally friendly way of corrosion prevention in the face of such a prominent problem of marine corrosion.In this paper,Q235 carbon steel was selected as the experimental metal material and Bacillus sp.was used as the experimental marine microorganism.The influence of temperature,flow velocity and microbial adhesion on corrosion behavior of Q235 carbon steel was studied by means of electrochemical test and surface analysis.The results showed that both temperature and flow velocity would affect the electrochemical corrosion of the samples.The higher the ambient temperature and the higher the flow velocity,the greater the corrosion rate of the samples.The diffusion rate of corrosive ion was accelerated in seawater as the temperature went up.In addition,the corrosion products formed on the sample surface at different temperatures of the same time point were not the same.It indicated that the temperature would also affect the morphology of the corrosion products.The rise of the flow velocity made cracks appear among the corrosion products on the surface of the sample.The cracks gradually expanded and developed with the increase of time.The appearance of cracks made the sample directly exposed to seawater,which accelerated the corrosion of the sample.Compared with temperature,the change of flow velocity had more obvious effect on the corrosion rate of metal.The corrosion rate of the sample in the solution containing Bacillus sp.was lower than that in seawater at different temperature.It indicated that Bacillus sp.could play a certain role in corrosion inhibition of metal.Because the temperature had an important effect on the attachment of Bacillus sp.The temperature could affect the growth of Bacillus sp.and metabolism ability.Bacillus sp.could secrete more EPS as the temperature went up.EPS and Fe²⁺could form the complexing substance.It fused with the corrosion product which has played a protective effect better than that of single corrosion products.30°C was the optimum temperature for the growth of Bacillus sp.It could be seen from the SEM figure that the sample surface was attached more Bacillus sp.than the other temperature.The corrosion rate of sample soaked in the two systems under different temperature showed that the corrosion inhibition was best,which suggested that the corrosion inhibition of Bacillus sp.was more obvious with increase of the temperature.