Corrosion Behavior Commonly Used Metal In Seawater Source Heat Pump

Due to Energy saving, seawater source heat pump system is widely used incoastal areas recently years. However, the metal material selection and the corrosionprotection problems are the key issues unsolved in the seawater source heat pumpsystem. Due to the complex ion composition of seawater, NaCl solution is adopted tostudy the impact of the environmental factors to the metal corrosion by mostresearchers. The corrosion behaviors of the commonly used metal materials （TA1titanium,316L stainless steel, B30copper-nickel alloy and HAl77-2brass） inseawater were studied. The four kinds of metal corrosion electrochemical propertiesare discussed in different seawater conductivity, pH and flow rate of seawater toadapt to the performance of the comprehensive evaluation of the four metals. And anew idea is put forward about the passivation of the316L stainless steel to explore asimple passivation process which can be used in large-scale industrial production andcan improve its pitting resistance in seawater.The average corrosion rate of B30copper-nickel alloy and HAl77-2brass indifferent environmental factors seawater was studied by the weight loss test. And thecorrosion electrochemical information of four metals was collected by potentio-dynamic polarization curve test and electrochemical impedance spectroscopy （EIS）.Four metals immersed in the different conductivity of the filter-sterilizedseawater are detected. The results show that the corrosion resistance of the four metalsis reduced with the increase of seawater conductivity. The pitting sensitivity of316Lstainless steel is improved. The corrosion rate of B30copper-nickel alloys andHAl77-2brass increases. From the perspective of the film impedance analysis, thecorrosion resistance of four metals in different conductivity of seawater as follows:TA1titanium,316L stainless steel, B30copper-nickel alloy, and HAl77-2brass. Three detection methods were used to study the effect of pH on the corrosionlaws of four metals. The results showed that the membrane impedance of four metalsincreases, with pH value increasing. The corrosion potential of TA1titanium,316Lstainless steel shifts and corrosion rate of B30copper-nickel alloys and HAl77-2brassdecreases. In the same pH value of seawater, the corrosion resistance of four metalswas as follows: TA1titanium,316L stainless steel, B30copper-nickel alloy andHAl77-brass by comparing four kinds of metal film resistance.The experiment of the corrosion of four metals in still seawater and1m/sseawater shows that the flow of seawater reduces the corrosion resistance of the fourmetals. In1m/s flowing seawater, with the increasing of soaking time, the pittingpotential of316L stainless steel reduces and the corrosion rate of B30copper-nickelalloys and HAl77-brass reduces by surface oxide film thicking.Double-passivation technology was applied to improve resistance to pittingcorrosion of316L stainless steel. The result show that the stability of the passive filmand the pitting potential of316L stainless steel were improved by passivationtreatments in nitric acid（Temperature of40℃, the passivation time of1h, the nitrateconcentration of35%） and the stable treatment of H2O2. Especially the pittingpotential of316L stainless steel was highest after the stable treatment in0.3%H₂O₂stabling30min.