35 巻 (2017) 1 号 p. 1-5
The pulp industry has recently been required recovery boilers with higher steam temperature and pressure to improve plant efficiency. Given severe plant conditions, furnace water wall tubing tends to be suffered from serious smelt corrosion.
In order to prevent the corrosion problems on the furnace water wall tubes in recovery boilers, a 25%Cr ferritic SMAW overlay material, which is included of Nb 1%, Al: 0.1% and Ti: 0.1%, has been developed in behalf of the 18%Cr overlay welding materials.
On practical fabrications of the overlay welded panels in a factory, GMAW and PTAW, in addition to the SMAW welding materials, are needed to application to the automatic welding machines as one of the highly efficient welding methods. The 25%Cr GTAW welding material is also useful for a repair welding in order of good appearance of the overlay welded tubes.
This study introduces the development of three kinds of 25%Cr ferritic welding materials, such as GMAW, PTAW and GTAW welding materials for furnace water wall in recovery boilers. The weldability, bend property and corrosion resistance of these overlay weld materials were examined. From these results, an overlay welded panel was fabricated by using of the 25%Cr overlay welding materials. Good corrosion resistance of the panel has been confirmed as the result of the field test in a recovery boiler in service for about two years. 25%Cr overlay welded tubes in the field test showed a good corrosion resistance.