某沿海火电厂贮煤仓构件腐蚀机制分析

目的研究某火电厂沿海煤仓构件的腐蚀情况,分析其腐蚀机制。方法采用扫描电子显微镜(SEM)对构件表面与内部区域的腐蚀形貌及腐蚀产物分布进行表征,借助能量色散X射线光谱仪(EDS)和X射线衍射仪(XRD)等仪器,对腐蚀产物元素组成及物相进行表征分析,结合贮煤仓构件服役环境探讨腐蚀机制。结果沿海火电厂贮煤仓构件腐蚀情况较为严重且分布极广,腐蚀类型主要为点蚀。腐蚀产物厚度约为3.82 mm,表层和内部分别为黄色物质和灰黑色疏松物质,且聚集有球状和丝状或棉团状铁锈。腐蚀产物组成元素以O、Fe为主,其中表面黄色物质的主要物相为Fe2O3,表面丝状或棉团状物质主要为α-FeOOH,内部灰黑色物质的主要物相为Fe3O4,针片状物质为γ-FeOOH,球状物质的C、Si、Al、Ca、Mg等元素含量较高且主要物相为SiO2,为煤粉颗粒。结论沿海电厂贮煤仓构件腐蚀初期为Fe的吸氧腐蚀,并发生完全氧化脱水生成Fe2O3,其良好致密性使内部发生氧浓差腐蚀生成Fe3O4,底面产物主要为Fe3O4和Fe2O3的混合物,而煤粉颗粒和燃煤产生的CO2、SO2等酸性气体为腐蚀的快速发生提供了环境。发生的点蚀极易造成穿孔,需采取更有效的防护措施。

Corrosion Mechanism Analysis of Parts of Coal Storage Bunker in a Thermal Power Plant along the Coast

This work aims to investigate the corrosion mechanism of coal storage bunker parts in a thermal power plant. The study focuses on the analysis of corrosion mechanisms and causes on the coal storage bunker of power plant situated in coastal environment. The corrosion morphologies and the extent of corrosion products distribution on the surface and internal layers of the parts were systematically characterized by scanning electron microscopy (SEM). The phases and composition of the corrosion products were analyzed by the energy dispersed X-ray spectrum (EDS) and X-ray diffraction (XRD). The corrosion mechanism of parts were extensively discussed. It was noted that the mode of corrosion was localized corrosion, which severely attacked the working parts and structural materials on the coal storage bunker. The thickness of the corrosion area was about 3.82 mm. The corrosion morphology was heterogenous in nature with surface layer appearing rust brown while the internal layers had loose gray coloration. Aggregation of spherical and filamentous or cotton like rust alternated between outer and internal layers. The O and Fe were the main ingredient elements of the corrosion products. The main phase constituents of the brown rust, filamentous or cotton-like, gray-black substances and the needle-like substance were Fe2O3, a-FeOOH, Fe3O4 and g-FeOOH, respectively. Whereas, the globular substance consisted of a relatively high content of C, Si, Al, Ca, Mg and the main component was SiO2. which was caused by the pulverized coal particles. The corrosion mechanism of the parts was a complex reaction between various factors. At the initial stage of corrosion, the oxygen-absorbing corrosion reaction happened between the anode of Fe and the cathode of O2, and the following dehydration led to the production of the Fe2O3. However, due to lack of O2 in internal and bottom of the parts the corrosion products of Fe3O4 appeared as oxygen concentration cell corrosion. Thus, the bottom products were mainly the mixture of Fe3O4 and Fe2O3. Acidic gases such as CO2 and SO2 produced by pulverized coal particles and coal combustion created the conducive environment for the rapid corrosion. In these severe corrosive environments, failures of the parts like perforation could happen due to the pitting corrosion, which needed to be minimized by effective protective measures.