Abstract
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 has been known to be the most important alloying element in weld overlay cladding for protection of boiler tubes against sulfidation, erosion-corrosion and coal-ash corrosion. For current boilers including both subcritical and supercritical units, Ni-based alloy 622 (ERNiCrMo-10) is the most widely used overlay alloy. The present paper discusses a high Cr Type 312 stainless steel as a low-cost alternate overlay alloy for protection of boiler tubes in coal-fired boiler application.
