Dynamic Experimental Study On Corrosion Rules Of Chlorine Dioxide On Typical Pipe Fittings For Reclaimed Water

The metal pipeline of reclaimed water appears severe corrosion problem during the water-transfer process,especially at the special location where the flow mutates in the pipe network,since it is more prone to erosion,causing damages such as thinning of the tube wall,leakage and burst accident.The corrosion products of the special pipe fittings will be washed off and drop into the water body,which will seriously affect the quality of the reclaimed water.Simultaneously,the selection of the reclaimed water's disinfection technology also serves as a key factor which affects the erosion of reclaimed water pipe network.Because of the complexity of water-quality constituents,a corrosion products layer with special construction will be generated by the combination and reaction between the corrosion products and the impurity ions in the water.At the location of pipe network where the flow state mutates,such layer is more easy to come off,leaving the pipe matrix directly exposed in the water,and the corrosion will speed up due to the strong oxidizing property of the disinfectants.This paper used Computational Fluid Dynamics,electrochemical corrosion and microanalysis,and built an experimental network of reclaimed water to conduct a dynamic experimental study of the corrosion rules that chlorine dioxide had on typical pipe fittings of the reclaimed water pipe network.First,this paper adopted the methods of Computational Fluid Dynamics to simulate the velocity,pressure and shearing force distribution of the reclaimed water pipe network.Selecting the elbow as the typical fitting to research the corrosion rules.And then building the pipelines which combines the dynamic electrochemical test platform in the laboratory and arranging corrosion electrochemical monitoring points on the elbow and the straight pipe section.By testing the open circuit potential and electrochemical corrosion rate of the different positions in the pipe fittings,the points that were easily to corrode at the elbow were determined after comprehensive analysis;the dynamic experiments of the pipe network were conducted under three entrance velocity conditions-0.7 m/s,1.0 m/s and 1.3 m/s respectively and then performing electrochemical tests on the elbow and the straight pipe;exploring the flow velocity's influence on corrosion rate and corrosion products layer,and conducting structural analysis of the corrosion products layer by adopting micro-analysis technology at the same time.The study showed that the easiest positions to corrode were at the central place of interior elbow and the downstream position outboard.The corrosion process occurred at the fastest rate when the entrance velocity was at 1.3 m/s,but during the stationary phase of the corrosion,the corrosion rate decreased as the current velocity increased.Based on the study above,this paper also conducted a relevant experiment of chlorine dioxide corrosion at the most corrosive conditions(under the entrance velocity of 1.3 m/s)of the experimental pipe network to discuss the influences what the disinfectant had on the positions of severe dynamic corrosion.First,using the ANSYS software to simulate the distribution of chlorine dioxide's spatial components in the reclaimed water network,then measuring the corrosion rate with the methods of electrochemistry and loss-weight to study how the corrosion rate,whether at the elbow or the whole network,was affected by the inflow of chlorine dioxide;Second,analyzing the influences the chlorine dioxide would have on the structure of the corrosion products layer and its related corrosion mechanism by employing the tests of polarization curves and electrochemical impedance spectroscopy;At last,using microanalysis technology to analyse the influences of chlorine dioxide conditions on the structure of the corrosion products.The results showed that at the initial period when chlorine dioxide was dosed into the water,the initial corrosion of the experimental fittings delayed because the disinfectant inhibited the growth of microorganisms,but during the stable period of corrosion,the corrosion products at the positions where a sudden change of flow state happened were more likely to be washed off and thus formed a serious corrosion state,mainly caused by the oxidability of chlorine dioxide and the loose structure of the corrosion products which contained chlorine element.