INCONEL FILLER METAL 72M PROVIDES CORROSION AND WEAR RESISTANCE AND LOW 'DELTA T' THROUGH WALLS OF TUBING IN FOSSIL-FIRED BOILERS

摘要

INCONEL Filler Metal 72, a 43% Cr nickel alloy welding wire, has been used in elevated temperature service to protect boiler tubing for over 20 years. Along with FM 72 overlays, INCO-CLAD 671/800H co-extruded tubing has also been used to great advantage for resisting sulfidation, oxidation, carburization and wear in boiler environments. INCONEL Filler Metal 72M is an optimized alloy that offers improved weldability and the lowest corrosion rate of any of the alloys evaluated in our simulated low NO_x boiler environment. Testing results are presented along with illustrations of applications for the above materials. New interest has been expressed in 72 and 72M for waterwall tubing overlays where the normal failure mode with other weld overlays has been circumferential cracking and corrosion fatigue. Filler Metal 72 overlays have shown outstanding resistance to abrasion and wear in soot blower lane tubing and resistance to corrosion-fatigue-cracking in severe waterwall service. 72M overlays have been chosen to replace erosion shields in the high wear "nose" areas of superheater and reheater tubing. 72M overlays provide protection against corrosive attack even under reducing conditions created by low NO_x firing, and 72M is capable of performing well at the high temperatures experienced in advanced ultra-super critical (AUSC) boilers. In addition to outstanding corrosion resistance, both 72 and 72M weld deposits increase in hardness and thermal conductivity with exposure time at service temperatures. As thermal conductivity of weld overlays increase with service time, the "delta T" (temperature difference across the tube wall) is reduced and provides substantial increases in thermal efficiency for the boiler, while providing long life due to excellent corrosion and erosion resistance and reduced tendency for thermal fatigue (corrosion fatigue). Overall cost-savings are derived from lower maintenance costs as well as higher boiler thermal efficiency. Both waterwall and upper boiler tubing overlays will be addressed with historical commentary offered on how the optimum alloy choices have been made. Failure mechanisms are discussed and the attributes of the successful alloy choices are defined.