Design And Application Of Electrochemical Probe For Hydrochloric Acid Dew Point Corrosion

The atmospheric and vacuum distillation unit is the first and most important process in the oil refining industry.When crude oil containing a large amount of acid and inorganic salts is processed through the atmospheric and vacuum unit,the cooling system at the top of the atmospheric and vacuum tower will condense and absorb the hydrochloric acid in the environment to cause hydrochloric acid dew point corrosion,which will cause the pipeline to crack and leak.At present,two measures are often adopted at home and abroad to slow down the corrosion of metal equipment caused by the hydrochloric acid dew point environment of the tower top condensation system: process corrosion protection and material upgrade.However,there is still a lack of effective measures for the monitoring and prevention of hydrochloric acid dew point corrosion.Therefore,given the particularity of hydrochloric acid dew point corrosion,a probe based on electrochemical measurement technology is designed to measure and study hydrochloric acid dew point corrosion in situ.The main work is as follows:An electrochemical impedance probe for in-situ measurement of hydrochloric acid dew point corrosion was developed.The probe is made of two identical Q235 carbon steel electrodes connected in series through a thin-film resistor.Compared with the traditional impedance threeelectrode measurement system,the error of the probe to measure the corrosion rate is only 9%,and the test time is shortened by about 20 times.At the same time,this probe is used to study the influence of the dynamic changes of the hydrochloric acid dew point corrosion environment on the material.When the dew point continues to occur,the more the acid film on the surface of the material,the greater the instantaneous corrosion rate of the material.As the condensed liquid film further forms acid droplets and drops under the influence of gravity,the corrosion rate of the material decreases instantaneously.Because the probe test time is very short,it can effectively measure this dynamic change process.Since the electrochemical probe can only measure the instantaneous corrosion rate of the material in the dew point environment,the cumulative corrosion rate of the material determines the service life of the device.In response to this shortcoming,this paper designs a probe with electrochemical impedance technology coupled with galvanic technology to achieve the simultaneous measurement of instantaneous corrosion rate and cumulative corrosion rate,and proposes a new method for monitoring and evaluating hydrochloric acid dew point corrosion in actual pipelines.First,the reliability of the galvanic technology to measure the cumulative corrosion rate was verified in the hydrochloric acid solution and the dew point environment of the hydrochloric acid.The study found that the use of graphite electrodes as the cathode of the galvanic probe can effectively reflect the true corrosion status of the anode material.The error of the corrosion rate obtained by the measurement and the measurement result of the corrosion coupon method is 13%,and the error of the measurement result of the electrochemical polarization method is 4.6%.After that,the coupling probe was used to measure the corrosion of the material in the hydrochloric acid environment.The experimental results show that the cumulative corrosion rate and the instantaneous corrosion rate obtained by the probe are consistent and the error between the two is only 2.7%,so this coupling probe can be used effectively In-situ measurement of hydrochloric acid dew point corrosion and further study of its corrosion mechanism,so as to propose effective measures for the dew point corrosion monitoring and prevention of the tower top condensation system.