Corrosion of defective molybdenum insert in liquid glass as the main reason of accident at glass-melting furnace

The main reason of an accident at the Piskivka glass plant (Kyiv region, Ukraine) was in failure and degradation of a molybdenum insert in refractory REFEL 1240 FVMo block in the throat of glass-melting furnace. Using the analysis of literature data and the available data obtained at the plant, it was shown that this should be preceded by active degradation and blurring of the refractory AZS. Failure analysis of the fractured molybdenum insert was carried out experimentally by light microscopy, scanning electron microscopy and X-ray diffraction. It was suggested that the degradation was caused by the intergranular corrosion that took place at high temperature due to the formation of MoNi and MoNiFe liquid eutectics along grain boundaries. The piece of molybdenum was most probably contaminated by Ni and Fe from the tools used during the processing of molybdenum insert by hot deformation. As a result, liquid glass had been penetrated through the weakened grain boundaries and initially “washed out” some grains from the surface and then crushed the inside boundaries.