Investigation On Corrosion Resistance Of Domestic825Alloy For Residue Hydrotreating High-pressure Air Cooler

With the progress of modern science and technology, chemical, aerospace, transportationand related fields have been developed rapidly. The requirements of materials and equipmentand production equipment for these industries are becoming higher and higher. For example,the petrochemical industry, a lot of equipment running at high temperature and pressure. Asthe poor quality of raw materials for processing oil, corrosion and leakage problems ofhydrogenation of high pressure air making carbon steel have become increasingly prominent.Compared to austenitic stainless steel, carbon steel materials, the nickel-based corrosionresistant alloy with high Cr content is the ideal material. Representative nickel base alloymaterial is Incoloy825alloy （referred to as825alloy）. Due to previous domesticmetallurgical technology was not mature and many other factors, this material was mostlydependent on imports. As China’s metallurgical technology was mature, the nation hadsuccessfully developed a825alloy own property, and listed in2010.Therefore, it wasnecessary to investigate corrosion resistance for domestic825alloy, its findings can provide areference for the design department of chemical containers and user using the material.1. The corrosion resistance of domestic825alloy had been studied in acidic （HCl, HNO₃and H₂SO₄） and alkaline （NaOH） and salt （NH₄Cl, Na₂S, Na₂SO₄with differentconcentrations of NaCl mixed salt） using corrosion weight loss method, and themicrostructure and elemental composition of pipe and plate for domestic825alloy had beenanalyzed. The results show that the main element of pipe and plate for domestic825alloy wasNi, Cr, Fe, Mo, and which contains a small amount of Al, Si. Moreover, both themicrostructure of single-phase austenitic.The corrosion rate of the domestic825alloyincreases with the concentration of the respective media increased in the corrosion medium ofstudy; The corrosion rate of the domestic825alloy in HCl and H₂SO₄significantly greaterthan several otherkinds of media compared to HNO₃, NaOH and the salt medium.2. The corrosion resistance of domestic825alloy had been studied in acidic （HCl, HNO₃and H₂SO₄） and alkaline （NaOH） and salt （NH₄Cl, Na₂S, Na₂SO₄with differentconcentrations of NaCl mixed salt） using corrosion electrochemical method. The results showthat the corrosion rate of the domestic825alloy increases at first then decreases with theincrease of H₂SO₄concentration in H₂SO₄solution, and the maximum at40%, while thecorrosion rate in the other test media were increased with the increase of the concentration oftheir respective media. Moreover, the results obtained by electrochemical testing was thesame as corrosion coupon method, also domestic825alloy appear obvious passivation regionin HCl and H₂SO₄media and only10%of the concentration of HNO₃and secondarypassivation phenomenon in Na₂S medium. 3. Local corrosion and high-temperature oxidation corrosion of domestic825alloy hadbeen studied using tensile test, salt spray test, intergranular corrosion test and hightemperature oxidation test. The results show that the domestic in alloy825had stresscorrosion susceptibility in10%HCl,2%of NaOH and3.5%NaCl solution medium, and thestress corrosion sensitive parameters corresponding to5.1204,2.7108and3.6144,respectively. The type of fracture of domestic825alloy was ductile fracture in the airenvironment and brittle fracture in10%HCl and2%NaOH and mixed fracture in3.5%NaClsolution. The intergranular corrosion rate of domestic825alloy was0.0106mm/a in65%boiling nitric acid, the reason for the intergranular corrosion caused by chromium depletionzone at the grain boundaries. The316L stainless steel have been contrasted to domestic825alloy at salt spray corrosion corrosion and high temperature oxidation, the results show thatcorrosion resistance of salt spray and high temperature oxidation for the825alloyare greaterthan316L stainless steel, both the salt spray corrosion rate were respectively6.7457×10^-6mm/a and9.4747×10^-6mm/a, corrosion rate were respectively1.1621g/h·m²and34.3105g/h·m²after high temperature oxidation8h at800oC, surface of domestic825alloy had alayer of tight black oxide after oxidation, which was Cr₂O₃（28.8%）, Fe3O₄（18.1%） and Fe2O₃（15.4%）.4. The corrosion resistance of domestic825alloy welded joints had been investigatedusing chemical immersion and electrochemical method in HCl and Na₂S medium, Moreover,the localized corrosion and high-temperature oxidation corrosion had been studied andmicrostructure had been analyzed. The results show that the microstructure of weld zone forwelded joints was austenite and a small amount of ferrite, and the base metal was austenitic,and the microstructure of heat-affected zone basic was consistent with the base metal andweld zone.Corrosion rate of welded joints and base metal were respectively30.4211g/h·m²,1.8546g/h·m²after soaking27.5h in10%HCl at150oC, Moreover, the weld zone occuredserious corrosion.Corrosion rate of welded joints and base metal were respectively0.0019g/h·m²,0.0018g/h·m²after soaking336h in1mol/L Na₂S at150oC. Results obtainedelectrochemical test were consistent with corrosion soak. Intergranular corrosion rate ofwelded joints were greater than the parent material and the corrosion rate were respectively0.1159mm/a,0.0106mm/a. High-temperature oxidation corrosion rate of welded joints weregreater than the parent material and the corrosion rate were respectively1.4838g/h·m²,1.1621g/h·m².