51314-4126-Review of Field Experience of Weld Overlays in Coal-Fired Boilers For The Past Two Decades

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Product Number: 51314-4126-SG

ISBN: 4126 2014 CP

Author: Bingtao Li

Publication Date: 2014

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With the installation of low NOx burner technology for reducing NOx emissions in coal-fired boilers in early 1990s many boilers began experiencing drastic increases in tube wastage rates on the waterwall tubes made of carbon and low alloy steels due to sulfidation attack under low NOx combustion conditions. The early trials and adoption of weld overlays of chromia-forming alloys by the industry in mid- and late-1990s showed surprising successes in eliminating the wastage issue for the waterwalls. However with longer services under the low NOx combustion conditions some weld overlay alloys were found to be susceptible to circumferential cracking in some supercritical units. For reheater and superheater application in coal-fired boilers it is well-known that boiler tubes also experience coal-ash corrosion. The current paper reviews the field performance of various weld overlay alloys in both subcritical and supercritical units based on field inspections and metallurgical analyses of field exposed samples from various boilers for the past two decades. Materials issues related to sulfidation-induced wastages and circumferential cracking on the boiler’s waterwalls sootblower erosion erosion-corrosion and coal-ash corrosion of superheaters and reheaters for various weld overlay alloys which include stainless steels such as Types 309 and 312 and Ni alloys such as alloys 33 625 622 52 and 72 will be discussed.