Cost Effective Weld Overlay Alloys for Waste-to-Energy Systems

Alloy 625 (UNS N06625) has successfully been used as a weld overlay for many years in waste-to-energy systems to combat corrosion.  UNS N06625 will likely remain the preferred alloy for the most aggressive regions of the boiler; however there are other regions in the system where leaner and less costly weld overlay materials are more than sufficient.  Alloy 31 (UNS N08031), with 31%Ni-28%Cr-6.5%Mo, has been tested in both the laboratory and in the field with corrosion resistance approaching that of UNS N06625 in many cases and is significantly less expensive than UNS N06625.   A comparison of the corrosion resistance of UNS N08031against other alloys is presented.  In addition, field data is presented from various field tests and is shown to support a laboratory corrosion based empirical model previously suggested by other researchers.  This model is used to project the corrosion response of UNS N08031 in the field, which is further supported by 2 year field exposures in one boiler.  Lastly an economic analysis is used help select the best material for various locations in the waste-to-energy boiler.