Investigation On Micro-Area Corrosion Behaviors And Mechanism Of The Under-Deposit For Heat Transfer Metal In Desalination

Because low temperature multiple effect desalination evaporator run in actual working condition of high temperature and high salinity water for a long time,the surface of aluminium brass?HAl77-2?and 316L stainless steel?316L SS?are easy to scale,and under-deposit corrosion happens occasionally.Meanwhile,under-deposit corrosion belongs to the corrosion under sediments.Due to corrosion and fouling influenced each other,the under-deposit corrosion is complex on the structure and special in its system.Therefore,focus on under-deposit-corrosion of the key material for low temperature multiple effect desalination evaporator has certain practical significance and research value.This paper mainly studied the behavior and mechanism of under-deposit corrosion for HAl77-2,316L SS under the simulated actual conditions of seawater desalination adopting the linear polarization?LP?,electrochemical impedance spectroscopy?EIS?,full immersion experiment,wire beam electrode technique?WBE?,scanning electron microscopy?SEM?and energy spectrum analysis?EDS?.And on this basis,a good corrosion and scale inhibitor as the control method of corrosion and scale in this system has been selected.This experiment was carried out by potentiodynamic polarization curves?PD?,electrochemical impedance spectroscopy?EIS?and static scale inhibition experiment.The results showed that:?1?The composition of the dirt on the surface of HAl77-2 and 316L SS is CaCO₃ which looks like needle or rod and has uneven,porous distribution.But the dirt of the former is more obvious.The presence of dirt promotes corrosion of both HAl77-2 and 316LSS.Dezincification corrosion existed in the process of aluminum brass corrosion.And passivation phenomena emerged in the process of 316L SS corrosion.As temperature rising,HA177-2 corrosion gradually intensifies and local corrosion is serious under the dirt.But after 60?,with the temperature further increasing,the frequency of corrosion rate increase gradually slow down.In the same time,the passivation film stability of 316L SS gradually reduce,corrosion rate is accelerated and local corrosion is also serious with the increasing of temperature.The corrosion rate of HAl77-2 under the scale increases to maximum when Cl^-concentration is near 2.3 wt.%.Due to the concentration increasing,the stability of 316L SS passivation film gradually weakens and gradually presents the local feature.All of these cause active pitting area,surface roughness and dispersion effect increase.?2?In the screening test of corrosion and scale inhibitor,this paper selected LCY,SGR,VC as the as the single corrosion inhibitor and polyaspartic acid as scale inhibitor.All the three corrosion inhibitors belong to chemical adsorption inhibitor and follow the Langmuir adsorption isotherm.LCY,SGR,VC respectively belong to the type of cathodic corrosion inhibitor,mixed corrosion inhibitor and mixed corrosion inhibitor which is given priority to inhibit cathodic.And when the adding concentration achieves their premium concentration100mg/L,70mg/L,70mg/L,the corrosion efficiency is highest.Eventually,this paper developed a matched corrosion and scale inhibitor.The main composition of this corrosion and scale inhibitor includes LCY,SGR,VC and PA.The weight ratio of their components is 60:20:20:7.It has more obvious inhibitory effect on HAl77-2 corrosion and fouling under simulated actual working condition of seawater evaporator.And its corrosion efficiency has reached 96.01%,scale efficiency has achieved 88.99%.