Research On Corrosion Analysis And Countermeasures Of Styrene Distillation System

The styrene distillation separation system need to run in the conditions of vacuum,adding polymerization inhibitor and lower distillation temperature.The overhead distillate composition from separation tower is complicated and hypothermal,likely to caused corrosion of the tower head and pipeline.Therefore,it is urgent to study the cause and mechanism of the corrosion in the styrene distillation system,carry out on-line monitoring of corrosion and propose corresponding anti-corrosion measures.This paper aimed at the pressing problem which the overhead pipeline corrosion leaks,seriously affect the safe and stable operation of the device,to carry out the research of styrene distillation separation system corrosion analysis and corrosion prevention measures.Thus,the operating conditions of styrene distillation system were analyzed.The composition and ingredient of distillation column were characterized and analyzed by some professional equipment and methods such as GC-MS,ICP,etc.Besides,the corrosion pieces were dissected by Metallurgical microscopy and Scanning electron microscopy.The simulation system of styrene distillation separation in Lab was set up.The electrochemical measurement of 20#carbon steel in styrene distillation system was carried out.The influencing factor were investigated as follows:temperature,time,pH,rotational speed and oxygen content.And the pipeline material corrosion test piece were simulated?The main research contents are exhibited as follows:(1)By analyzing the components,corrosion scale and corrosion characteristics in styrene distillation separation system,the water samples showed neutral weak acidity,high content of HCO3-and free CO2,the presence and concentration of carbonic acid led to solution become acidic,acidic conditions prone to dew point corrosion.The high content of Cl-and SO42-lead to serious chlorine corrosion and sulfur corrosion.The concentration of Cl-,SO42-and HCO3-is 4.21 mg/L,13.28 mg/L and 12.80 mg/L,respectively.The order of the three ions causing corrosion is Cl->SO42->HCO3-.The corrosion scale of the reflux tank is mainly composed of Fe2O3 and organic matter with loss of ignition loss,the ratio is 6:4.The elements of the scale sample analysis are consistent with the ions detected in the water sample obtained from the pipeline,including Mg2+,Na+,Ca2+,SO42+,Cl-and other corrosive ions.The pipeline with the lower ratio of oil to water has the most serious corrosion and the largest perforation because of more corrosive composition.The flow,pH,and ion concentrations are in a dynamic fluctuations in the styrene distillation system,resulted in the case of higher local ion concentrations.The perforation focused on the pipeline welding,turning and easy fluid accumulation position.(2)Through the simulation system of separation equipment,the corrosion potential,polarization curve,corrosion rate and AC impedance of 20#carbon steel which is consistent with the corrosion tower were analyzed.The main control variables are:medium temperature,corrosion time,rotating speed,acidity,oxygen concentration and so on.The severe corrosion on the surface of 20#carbon steel is due to acidity,organic matter,oxygen,chloride ions,sulfate ions and other factors,mainly caused by acid corrosion and ion-induced electrochemical corrosion.In the simulation system,the corrosion started rapidly.Along with the corrosion reaction continued,the rust layer gradually deposited on the surface,and the surface properties of the electrode gradually reached a relatively stable state.The impedance decreased with the increase of temperature at 30?95?.The initial corrosion rate increased rapidly and then stabilized when the corrosion time reached 60h.The corrosion rate is the minimum when the solution is alkaline.The greater the flow rate,the corrosion is more severe.(3)The study established the fault tree of styrene rectification plant,analyzed the corrosion reasons from the dimension of structure?composition?dynamics and material quality respectively,and put forward the corresponding anti-corrosion measures.