Interactive effect of ant nest corrosion and stress corrosion on the failure of copper tubes

•Failure copper tubes were studied by XRD analysis, SEM/EDS and Optical microscopy.•The interactive effect of ant nest corrosion and stress corrosion on the failure of copper tubes was revealed.•The morphology of interactive corrosion is thinner than single ant nest corrosion.•The sample “in service” exhibits intergranular fracture while the sample “in simulate” exhibits transgranular fracture.

Premature failure of copper tubes used in air-conditioning units is a serious problem for air conditioning manufacturers and customers. Several failure theories were put forward, such as ant nest corrosion and inter-granular stress corrosion. A new opinion is raised in this article that the interaction of ant nest corrosion and stress corrosion cause the failure of copper tubes. This article analyzes the interactive effect through comparing the morphologies of the failure copper tubes in practical application with the samples which were exposed to the concentration of 1 vol% formic acid vapor in airtight glass vessels for different days. The experiment results show that most of copper failures result from the interactive corrosion due to the morphology of interactive corrosion tunnels is thinner than single ant nest corrosion and the corrosion starting points of interactive corrosion tend to distribute at the bottom of internal groove where the tensile stress was concentrated.