| Ni-base stainless steel is widely used in heating element, seawater cooling exchanger, evaporator, pipeline exposed in acid gas and so on because of their perfect performance of resistance to abrasion, creeping, high temperature, corrosion. Incoloy800 and Incoloy840 Ni-base stainless steel has become the first choice for heating tube. Heating tube was subjected to corrosion because they were cyclically exposed to high and low temperature condition, so corrosion happened frequently. Corrosion of the heating-element tube would affect its service life, even result in serious consequence.The thesis was aimed at study Incoloy800, Incoloy840 Ni-base stainless steel and their manufctured tubes, looking for their corrosion mechanism and influencing factors. Pitting corrosion performance of Ni-base stainless steel Incoloy800 and Incoloy840 was studied by electrochemical measurement in 3.5% NaCl solution. The result showed that during the producing process from Ni-base stainless steel to heating tube, pitting potential of Incoloy840 decreased significantly and Incoloy800 almost showed no change in pitting potential. Compared the SEM image between Incoloy800 heating tube and Incoloy840 heating tube, the result showed that pitting corrosion resistance performance of Incoloy800 was better than that of Incoloy840.Intercrystalline corrosion performance of Ni-base stainless steel Incoloy800, Incoloy840 and their manufctured tube was studied by oxalic acid etch test and double electrochemical potentiodynamic reactivation test. The result showed that Incoloy800 heating tube had better intercrystalline corrosion resistance than Incoloy840 heating tube. The producing process didn't change the intercrystalline corrosion resistance characterization of Incoloy800, while promoted that of Incoloy840.The widely used antiseptic methods such as corrosion inhibitor, medium treatment would affect water quality and heat transfer, so they were not applicable to heating tube. In the text Mg sacrificial anode, passivation, coating SiO2 film was used as the main anticorrosion measures. The curves of galvanic current density vs. time under different area ratio of cathode and anode, different temperature and different NaCl concentration were studied in the text. Protective effect of Mg on heating tube was analyzed in the text.Polarization curves of Incoloy800 and Incoloy840 heating tube after passivation and coating SiO2 film were tested by electrochemical measurement, the result showed that these two surface treatment increased corrosion resistance characterization of the two heating tubes. SEM image of the SiO2 film showed the film was homogeneous and compact, without bubble. |
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