Chemical aspects of sealant products and their corrosion effects on copper

摘要

Serious damage to copper tubing brought about by the phenomenon of "ant nest corrosion" (ANC) continues to occur in the heating, ventilation and air conditioning (HVAC) industry. One specific example, reported in a paper to this Conference in 2000, was found on chilled water copper tube protected by thermal insulation in a large air conditioned building. Work since then has identified that the problem appears to occur when defects in the insulation vapour barrier exist. This leads to moisture ingress and subsequent reaction at the copper surface with a sealant material that is widely used by the building industry for the purpose described above. In this paper, we report on free fatty acids in the sealant that were found to react with copper, the most predominant one being 2 ethyl hexanoic acid. Though not formally established, these acids (or their triglycerides) appear to breakdown in the presence of water to yield formic and acetic acids, the two acids implicated in ANC on copper. We also report on methods to combat this effect, firstly by incorporating small amounts of magnesium oxide to neutralize the original acids and secondly by using more inert sealants such as those of a petrolatum base.