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

Abstract

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.