换热器T2紫铜管在潮湿状态下的腐蚀机理研究

STUDY ON THE CORROSION MECHANISM OF T2 COPPER CONDENSER TUBE UNDER THE HUMID ENVIRONMENT

研究了换热器中的T2紫铜管在为期2年的保养中因受残留H2O及挥发水蒸汽作用而出现泄漏降压的现象.利用SEM,OM和体视显微镜观察发现,在Cu管与不锈钢折流孔构成的所有缝隙部位都发生了严重的腐蚀,而且在少数位置发生了穿孔.润湿实验表明,T2紫铜管外表面与折流孔孔壁之间形成的缝隙足够小,以至于可以对Cu管外表面上结露的薄水膜产生虹吸作用,形成连接Cu管表面与折流孔孔壁的液体.因此,在Cu管外表面与缝隙部位Cu管间存在供氧差异,Cu管外表面为富氧区,而缝隙部位Cu管表面为贫氧区.电位监测结果表明:表面带有氧化皮的外部Cu管的电极电位高于缝隙部位裸Cu管的电极电位,二者之间形成电偶电池,折流孔部位的Cu管表面为阳极区,外部Cu管表面为阴极区.供氧差异和电偶的联合作用是导致Cu管折流孔部位发生严重局部腐蚀的原因.

During the maintenance of two years, T2 copper tube in a heat exchanger has leaked, it can be deduced that the residual water and volatile water vapor would play an important role in leakage. By SEM, OM, stereo microscope observation, it was found that serious corrosion happened on the surface of copper in the gaps constituted by copper tube and stainless steel baffle holes, and perforation occurred in a few locations. Wetting experiments show that the gap formed between the T2 copper tube and the baffle hole wall is small enough that it could produce siphon liquid film, which could connect the copper tube surface and baffle hole. Therefore there is a difference of oxygen supply between the copper tube outer surface and the copper tube in the gap site, the outer surface of copper tube becomes oxygen-rich zone and the copper tube in the gap site oxygen-poor zone. Potential monitoring results show that the potential of the external surface of copper tube with an oxide is higher than that of copper in the gap site leading to a galvanic cell formed between them. The surface of copper in the gap site is anode region and the external copper tube surface is cathode region. The differences of oxygen supply combined the effect of the galvanic cell leads to the severe localized corrosion of copper tube in the gap site.