Study On Corrosion Behavior Of Oxygen Free Copper In Domestic Water In Northern Area

In recent years,oxygen free copper heat exchangers often have failure used a few months in some areas of northern China.This paper studies on the corrosion behavior of oxygen free copper in the domestic water containing C1^-,SO₄^2-and CO₃^2-through cyclic voltammetry and Tafel curve.The XRD,SEM and opticalscope were used to analysis the surface morphology and corrosion product phase of copper which have had the simulation of immersion corrosion test,to study the effect of operating conditions and the temperature of the heat exchanger on the corrosion behavior of copper.The results of the reseach are as follows:1)C1^-,SO₄^2-and CO₃^2-have a corrosive to oxygen free copper,and the erosion of C1^-and SO₄^2-are the strongest in the scope of the national standard of living water.The increase of C1^-concentration will accelerate the copper general corrosion,promote the pitting nucleation,but not be beneficial to the development of pitting corrosion.The concentration of SO₄^2-increased will not have effect on the general corrosion of copper,but that will promote nucleation and development of pitting.The increase of concentration for CO₃^2-will accelerate the copper general corrosion.When the concentration of CO₃^2-is below 0.01 mol/L,the increase of concentration will promote the nucleation and development of copper corrosion,and be easy to pitting.While the concentration of CO₃^2-is above 0.03 mol/L,the increase of the concentration can inhibit the pitting.2)In the mixture of C1^-and SO₄^2-,the concentration of C1^-plays a leading role,and increasing concentration of C1^-will promote the general corrosion of oxygen free copper.When the concentration of C1^-is below 0.01 mol/L,the increase concentration of SO₄^2-will promote nucleation and developmen of pitting,and be easy to cause the occurrence of pitting.When the concentration of C1^-is above 0.03 mol/L,the concentration of C1^-will dominate the pitting.In the mixture of C1^-and SO₄^2-or SO₄^2-and CO₃^2-,when the concentration of CO₃^2-is below 0.01 mol/L,the rising of concentration of C1^-or SO₄^2-will not only accelerate the general corrosion of copper,but also promote the occurrence of pitting.The general corrosion behavior of copper in solution is mainly controlled by the concentration of CO₃^2-,and the increase of the concentration of CO₃^2-can inhibit the occurrence of pitting corrosion when the concentration of CO₃^2-is above 0.03 mol/L.3)In the range of 20⁵0 ?,the increase of temperature will accelerate the general corrosion and pitting nucleation of oxygen free copper,but will inhibit the development of pitting.The concentration of SO₄^2-in domestic water which has reached the national standard of lving water in the northern region is easy to cause pitting for oxygen free copper.4)The corrosion of copper in dynamic water is more serious than in static.The oxygen free copper is susceptible to pitting in 30 ?.The uniform corrosion product layer formed on the oxygen free copper surface at 30 ? is weak in protection and easy to breakdown.That is easy to be the formation of large cathode small anode corrosion batter and pitting.5)Grain size has little effect on the corrosion behavior of oxygen free copper.Surface cracks can accelerate the overall corrosion and increase the pitting sensitivity of oxygen free copper.The influence of water quality on the corrosion of oxygen free copper is greater than that of surface cracks.6)Cause of failure for heat exchanger tubes is pitting.The pitting hole on heat exchanger coil is mainly distributed in the area with a temperature of 30 ?.That is consistent with the simulated corrosion immersion test which result show that the oxygen free copper is susceptible to pitting and the corrosion is more serious when the temperature is 30 ?.7)The main factors that influence the corrosion behavior of oxygen free copper are corrosion product layer formed by uniform corrosion and water quality.The pitting corrosion and uniform corrosion of oxygen free copper occur simultaneously.The formation of pitting can occur due to the inhomogeneity of the uniform corrosion product layer and the defects.At the same time,the high content of SO₄^2-in watere can greatly improve the pitting sensitivity of oxygen free copper,and futher promote pitting corrosion.