51313-02184-High Chromium Stainless Steel for High-Temperature Corrosion Protection in Coal-Fired Boilers

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Product Number: 51313-02184-SG

ISBN: 02184 2013 CP

Author: Bingtao Li

Publication Date: 2013

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It is well-known that the installation of low NOx burner system and staged combustion techniques can cause unacceptably high wastage rates for carbon and Cr-Mo steels due to sulfidation attack in coal-fired boiler waterwall area. The current preferred approach for protecting these carbon or Cr-Mo steel waterwall tubes is the application of sulfidation-resistant weld overlay claddings. For some supercritical units corrosion attack can take the form of preferential sulfidation penetration which could lead to circumferential cracking in waterwall tubes. Superheaters and reheaters which are typically made of Cr-Mo steels or austenitic stainless steels also rely on weld overlay claddings to provide protection against sulfidation erosion-corrosion and coal-ash corrosion. Chromium is found to be the most important alloying element to resist sulfidation attack. In addition the material cost is an important factor for overlay alloy selection because of the large amount of filler metal demands in coal-fired boiler overlay applications. In the present paper long-term field performance after services for times varying from couples of years to 10 years for several major weld overlay alloys including stainless steels such as Type 309SS and Type 312SS and Ni-base alloys such as Alloys 625 622 52 and 72 are discussed. The discussion includes the resistance of these alloys to general wastage and circumferential cracking in the protection of waterwalls and also the resistance of these weld overlay alloys to high-temperature corrosion and coal-ash corrosion in superheaters and reheaters. Some results of laboratory simulation tests are also presented. The present studies indicate that the high chromium Type 312SS could provide a cost-effective weld overlay alternative to higher cost Ni-base alloys such as alloys 33 and 622 etc.