防火泥涂覆5052铝管的快速点蚀穿孔研究

Accelerated Pitting Perforation of 5052 Aluminum Tube with Fireproofing Mud Coating

目的对运行仅3 a的浙江近海某主变出线气室GIS筒体8 mm厚铝管SF6泄漏事故展开研究,以明确事故原因。方法通过光谱、金相、表面形貌(SEM)与能谱(EDS)、X射线衍射(XRD)等技术手段,从材料、结构、环境等角度探讨了该GIS筒体铝管点蚀穿孔可能的原因,并利用电化学测试技术进一步验证了模拟环境的腐蚀性,据此研究了某防火泥对5052铝管快速点蚀穿孔的影响。结果腐蚀样基材材质为5052,与腐蚀铝材紧密接触的防火泥中的总氯质量分数达24.5%,按照GB/T 12007.31989,测得其无机氯质量分数为3.3%。腐蚀导致的微裂纹密布反过来促进了腐蚀介质的传输。此外,设备所处区域临海,2012年降雨的年均pH值低至4.64,为明显的酸性雨水,同年降雨中Cl年均浓度高达1.8 mg/L,均有利于铝自催化反应的发生。结论防火泥的高氯含量是导致该GIS筒体铝管快速点蚀穿孔的主要原因,微裂纹结构、酸雨及临海大气环境具有促进作用。

The work aims to study the leakage of SF6 from GIS cylinder 8 mm-thick aluminum tube in air chamber of a main transformer in Zhejiang offshore,which has only operated for 3 a and then determine the cause of the accident.Through the technical means of optical spectrum,metallography,SEM,EDS,and XRD etc,the possible causes of the leakage of SF6 and pitting in the aluminum tube were discussed from the aspects of material,structure,environment,etc.Corrosiveness of simulated environment was validated by electrochemical testing.Then,the effect of fireproofing mud on accelerated pitting perforation of 5052 aluminum tube was revealed.The substrate material of corrosion sample was 5052 and the chlorine content of fireproofing mud in contact with the etched sample was up to 24.5wt%.According to the GB/T 12007.3—1989,the inorganic chlorine was about 3.3wt%.The dense microcracks caused by corrosion in turn promoted the transmission of corrosive medium.Furthermore,area where the GIS was located lied on the coast.Annual Cl−content of rainfall was up to 1.8 mg/L in the region in 2012.Rainfall was obviously acidic and had a pH of 4.64 at the same year.Both pH and Cl−content were beneficial to autocatalystic reaction of aluminum.The high chlorine content of fireproofing mud is the main reason for the rapid pitting and perforation of the aluminum tube of the GIS cylinder,and the microcrack structure,acid rain and the coastal atmospheric environment have a promoting effect.