Electrochemical Characterization Of Local Corrosion Under Q345R Insulation Layer In Marine Atmosphere

In order to save energy,the insulation layer is often applied to the surface of pipelines,containers and equipment under high temperature/low temperature service conditions.When the equipment is exposed to the marine atmosphere environment,corrosion under the insulation layer is very likely to occur.In order to study the electrochemical characteristics of local corrosion under the Q345 R insulation layer in the marine atmosphere environment,the corrosion behavior of thin liquid films with different thicknesses and thin liquid films under different salt concentrations was tested by potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS).,and use electrochemical impedance spectroscopy(EIS)to perform 13-day corrosion monitoring of the Q345 R under the gap.Array electrode(EA)was used to study the local corrosion evolution of the Q345 R container steel under the crevice.The COMSOL software was used to simulate the local corrosion behavior in the gap under the insulation layer.The results show:(1)The liquid film thickness is different,and the corrosion rate is different.The relationship between the corrosion rate of different liquid film thickness is 100>200>500>80>45>25>60?m.(2)Q345R in 1.75%,3.5%,7%,14% and other different concentrations of NaCl solution,in the thin 50?m and 100?m thin film,the corrosion rate decreases with the increase of NaCl concentration.In 200?m and 500?m thick liquid films,the corrosion rate first increases and then decreases with the increase of NaCl concentration,and the corrosion rate is the largest in 3.5% NaCl solution.(3)The speed of electrode erosion will be different from the position of the slit.In the electrochemical tests of the first,third,fifth,seventh,and nineteen electrolytic wires measured.It can be seen that the middle of the gap represented by the seventh root has the most serious corrosion.(4)The potential current distribution under the gap is not uniform,and the entire state of the large cathode anode is present.At the beginning of the soaking,the positive anode current and the negative electrode potential are mostly present near the gap opening.With the increase of time,the positive anode current and the negative electrode potential gradually transferred into the seam,indicating that the easily corroded electrode gradually transferred into the seam.(5)Through COMSOL simulation,the location of local corrosion under the crevice and the ease of corrosion are displayed more intuitively,and the result of the easy corrosion in the middle of the gap is obtained.