Metal loss and corrosion attack of FeCrAl overlay welds on evaporator tube shields of a waste-fired power plant

Three FeCrAl alloys (APMT, EF100 and EF101) from Kanthal® and the reference Ni-Cr Alloy 625 were used as weld cladding materials on tube shields in the evaporator tube bank of a waste-fired combined heat and power plant. For each alloy type, the overlay welded tube shields were placed in both roof and floor positions within the evaporator for 6 months. The metal-loss rate, the microstructure and hardness of the overlay welds before and after exposure and the corrosion products were analysed. The results showed higher metal-loss rates in the welds placed in the roof position, confirming heterogeneities in the evaporator bank environment. Alloys were ranked from higher to lower erosion–corrosion resistance as follows: APMT ≈ Alloy 625 > EF101 > EF100. The analysis of the corrosion attacks showed a significant variation among the alloys, from a primarily homogeneous corrosion attack on APMT to intergranular corrosion in EF100 and pit formation in EF101.