Coal ash corrosion is a chronic problem in many coal fired boilers. The combination of sulfur and ash produces a corrosive molten alkali iron tri-sulfate that rapidly dissolves protective oxide scales. This can lead to corrosion rates of 50 to 250 mpy (1.27 – 6.35 mm/y), even on 18Cr-8Ni stainless steels (such as 304H). Two new materials have been tested in the laboratory to evaluate their resistance to coal ash corrosion: Alloy 33 (UNS R 20033) and Alloy 45TM (UNS N 06045). Alloy 33 can be applied as a protective weld overlay and Alloy 45TM can be used as a solid tube material. Both of these new alloys offer greatly improved corrosion resistance over the common boiler tube materials (such as T-22, 304H, and 321). In addition, Alloys 33 and 45TM are both more corrosion resistant than Type 310 stainless steel, which is known to have excellent resistance to coal ash corrosion. From these tests, it is expected that major improvements of tubing life can be expected, compared to the traditional boiler tube materials used for super-heater and re-heater tubes.

Subject
New alloys, Materials, Corrosion resistant alloys, Stainless alloys, Corrosion rate, Tubes, Tubing, Ash, Boilers, Coal, Corrosion resistance, Stainless steel, Alloys
Keywords:
Coal ash, super-heater tubes, re-heater tubes, boiler tubes, weld overlay, alloy 33, alloy 45TM, type 310 stainless steel
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2005
Association for Materials Protection and Performance (AMPP)
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