The Corrosion Characteristics And Anti-corrosion Technology Research Of Aluminum Tube In Seawater Evaporator

Seawater is a kind of corrosive electrolyte solution.Heat transfer tube could inevitable occur corrosion in the condition of seawater's scouring in seawater desalination.So the material of heat transfer tube should have good corrosion resistance.Aluminum alloy also has good corrosion resistance,well thermal conductivity and popular price.Now,the aluminum alloy tube has been applied successfully in seawater desalination as the heat transfer tube by IDE.According to statistics,the cost has decreased about 25%.It has an important theoretical significance to explore the corrosion characteristics of aluminum alloy heat transfer tube in seawater desalination.Furthermore,to find out an effective way to inhibit corrosion will decrease the price of desalinated water,increase the competitiveness of LT-MED and promote the development of seawater desalination.In this paper,a horizontal tube falling film evaporation corrosion experimental apparatus is used to test the corrosion characteristics of test tubes.The salinity of experimental seawater is 2.9%.The material of test tube is 3FL aluminum alloy.The experimental condition is quite similar to the actual condition of desalination plants.In order to research the corrosion characteristics of aluminum alloy tube applied in evaporator and evaluate the anti-corrosion technology,to carry out experiments with the saturation temperature of 60?,the spray density of 0.1 kg/(m·s)and the concentration of DO of 120 ppb.The experimental variables are the deion process,the scale inhibitor and the tube pitch.The morphology and the attachment of tube surface could be analyzed by SEM and EDS.The diameter and density of pitting are counted after experiments.The corrosion rate of 3FL aluminum alloy is researched in different seawater by using the polarization curve test.The results of this test is similar to the former.The ICP-OES is used to analyze the change rules of the cupric,ferric and calcium ions' concentration in the deion process.The results show the concentration of three ions have decreased obviously.The results of polarization curve test show,as the extension of deionized and deaerated time,the corrosion rate of the aluminum alloy working electrode decreases obviously.The deaerate process could inhibit the corrosion especially.The morphology of tubes' surface is analyzed by SEM and EDS in different pretreatment of seawater and different tube pitch.The results show the deposition of CaCO3 scale which is acicular has decreased after the deion process.The type of corrosion product has changed from compact layer to scaly layer.The pH of seawater is monitored by using pH meter.The result shows the pH increase slowly.The seawater is also a kind of alkalescent solution during the experiment.The small increase of pH could inhibit the change of corrosion type from oxygen absorption corrosion to hydrogen evolution corrosion.The pitting density and average diameter have decreased obviously after the deion process of seawater,meanwhile,the influence of tube pitch is not obvious.So the deion and deaerate pretreatment could inhibit the pitting corrosion.Shorten tube pitch could inhibit the erosion of aluminum alloy tube.