Influence Factors Of Cathodic Disbonding Of3PE Coating On Buried Pipelines

Using electrochemical method, Three types of polythene anti-corrosion layer（3PE coating，heat shrinkable wraparound sleeve and heat shrink sleeve）were studiedin this paper by observing the changes of cathodic protection current with differentcathode polarization potentials in the cathode stripping process and cathodicdisbonding resistance performance in different conditions of the three kinds ofanti-corrosion layers. Using electrochemical impedance spectroscopy (EIS) method, bychoosing appropriate circuit to fit the impedance spectrum, we get the changingregularity of the resistance of the three kinds of polyethylene anti-corrosion layerunder different experimental conditions. The anti-electrolyte infiltration and cathodicdelamination performance of the three polyethylene anti-corrosion layer underdifferent cathodic polarization potential are studied. At the same time, using infraredspectrum,comprehensive thermal analyzer to analyze product of the cathode strippingarea of the sample.Results show that:(1) When the potential is more than-1.1V, the potential movesto negative excessively, the protection of3PE anti-corrosive coating will becomeinvalid ahead of time.(2)Polarization current of three polythene anti-corrosion layerappears to be different volatility when the potential is more than-1.1V polarization.(3)When cathodic protection current density was a sharp increase orders of magnitude,anticorrosive coating has a serious cathode detachment. Cathodic protection currentdensity up to10mA/m2,3PE anticorrosive coating began to appear cathode dissectionof the phenomenon, when the current density increases rapidly to100mA/m2,anti-corrosion layer stripping obvious cathode intensified. In the soil, the averagecurrent density of cathodic protection reached0.1mA/m2anticorrosive coating began to appear cathode dissection of the phenomenon, the average current density increasesrapidly to1mA/m2, anticorrosive coating cathode stripping increased obviously.(4)with the decreasing of cathodic potential and the increasing of time,the resistance ofthe specimen decreases obviously and even sharply reduces if the cathodic potential istoo negative. It is proved that the electrolyte is easier to infiltrate the ethyleneanti-corrosion layer if the cathodic is too negative, and make the anti-corrosion failureearlier as a result.(5)3PE anticorrosive coating the happening of the cathodestripping.(6) Products of the cathode stripping area is white. Using scanning electronmicroscopy, infrared spectrum, comprehensive thermal analyzer and X-rayfluorescence spectrometer to analyze that, we kown this products are inorganic salt andorganic compound mixing. Inorganic salt are calcium, magnesium ions in the cathodestripping alkaline environment of the formation of the sediment.organic compound are3PE anticorrosive coating layer or epoxy primer the glue in alkaline conditionsdisintegrate of the products.