Corrosion of ductile iron exhaust brake housing in heavy diesel engines

Three exhaust brakes (ductile iron) were sampled and characterized; new never used (as received), working and failed. The results of optical microscopy indicated that the surface microstructure of the failed sample was different from the working and as-received samples whereas bulk microstructures were similar. Elements such as Ca, Mn, Fe, Si, S, and O were detected on the surface of the failed sample using energy-dispersive X-ray spectroscopy (EDX) elemental analysis. X-ray maps of the base metal/corrosion product interface showed that a thin layer rich in Si existed underneath the bulk product layer. The X-ray diffraction (XRD) pattern revealed that the amount of oxide formed on the shaft of the failed sample was much more than that of the working sample, which was indicative of higher temperatures experienced by the failed sample. In addition, the XRD results showed that the corrosion product that formed on the surface of the housing for the working sample was mostly Si-containing products, whereas the housing surface of the failed sample was covered with iron oxide.