采用金相、EMPA、X—射线衍射和化学分析等方法对南京磷肥厂使用十个月后未经保护的12CrMoV和使用一年后经喷铝保护的12CrMov及18-8不锈钢管取样进行了分析。结果表明,二级过热器管的失效起因于管子表面的高温氧化和硫化腐蚀。 未经保护的12CrMoV管腐蚀严重,其腐蚀产物是非保护性氧化皮和铁的硫化物,而经喷铝保护的12Cr_1MoV管和18-8不锈钢管在该腐蚀条件下,由于生成能阻止O_2和S侵入金属的Al_2O_3和Cr_2O_3保护膜而表现出良好的抗腐蚀性能。 根据上述结果,提出了可能的腐蚀机制及其解决途径。
In order to find out the causes of failure of the secondary superheater tubes in waste heat boiler in the production of sulfuric acid from sulfur, samples from an uncoated 12CrMoV tube after ten months' service, an aluminium-sprayed 12CrMoV tube and an 18-8 stainless steel tube both after one year service in the Nanjing Fertilizer Plant have been examined by metallography, EMPA, X-ray diffraction and chemical analysis. Results obtained indicate that service failure of the secondary superheater tubes was mainly caused by the corrosion of tube surface, the nature of corrosion was high temperature sulfidation and oxidation.The uncoated 12CrMoV tube suffered from severe corrosion, and the corrosion products consisted of nonprotective oxide and sulfide of iron, while the aluminium-sprayed 12CrMoV tube and the 18-8 stainless steel tube had much better performance in this corrosion environment, because of the formation of protective Al_2O_3 and Cr_2O_3 scale which appeared to prevent ingress of oxygen and sulfur to the metal.On the basis of experimental results, possible mechanisms of corrosion and methods of solving the corrosion problem are proposed.
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