Failure analysis of the brass tubes in a lubricating oil cooler

Failure analysis was carried out on leaked brass tubes of a lubricating oil cooler. Direct evidences of dezincification and stress corrosion cracking (SCC) were observed by scanning electron microscope (SEM) and energy dispersive spectroscopic (EDS) analysis. It is found that there are many small pits distributed on the fracture surface and EDS analysis revealed the occurrence of dezincification in the small pits. SCC was observed on the cross-sectional plane of the fracture by SEM. Ammonia test has proved the existence of residual stress in the as-received tubes. It is determined that the brass tubes have been suffered from the co-action between dezincification and SCC.

► The failure of the brass tubes is attributed to the co-action between the small pits formed by dezincification and SCC.
► SCC of the brass tubes was initiated from the small pits which formed by dezincification.
► Direct evidences for the dezincification and SCC of brass tubes were obtained by SEM observation and EDS analysis.