Surface treatments, such as weld overlays, thermal sprays, laser claddings and fused coatings have been used for many years to protect boiler tubes operating in corrosive and erosive conditions. Several variables are typically identified that influence the choice of the technology selected, and the materials used to upgrade the boiler elements. Specifically, operating conditions such as corrosive species present, tube and gas temperatures, and the presence of erosive processes such as fly ash impingement and soot blowing significantly influence the severity of the wastage mechanisms. Given the many options available, and the uncertainty in determining reliable operating data, most selections need to be based on a “fit for all” solution. Case studies for applications of protective coatings in severe applications are useful to indicate relative performance of each system. From such results, limitations and some indication of performance can be established. As an example, AmStar cladding was field applied for EfW boiler water walls protection at 4 EfW plants. A number of superheater tube samples, cladded in the AmStar shop, were installed at another 4 EfW plants. The AmStar 888® cladding material is a development specifically geared to environments that may see erosion, corrosion, or a combination of both mechanisms. The material is a Nickel Chrome alloy, with carbide and boride additions. The coating is applied (field or shop) using a high velocity spray system, and requires no post treatment. The material is also easily repaired if defects occur in the future. The presented field trials at EfW plants have brought very positive results for all carbon steel water wall applications and have shown some good potential for salvaging old poor quality Inconel weld overlay by spraying AmStar 888® cladding over it. The superheater tube trials are more complex due to the variety of boiler designs which may significantly affect environmental variables. Not surprisingly, these trials have shown a range of results so far: from very good at one plant to not satisfactory at another. Testing is ongoing, so more results will be coming. Although such field tests do not provide quantitative results, they do provide comparative performance guidelines for generally aggressive boiler environments. This data is very useful to both design and maintenance engineers, who are often faced with limited options.

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