Rat holes are caused by condensation corrosion in loose joints of silica crowns. Regardless of the improved quality of the silica bricks, they are still a problem for the glass industry worldwide. The experience of Bulgarian-based Lubisol, shows that the early detection of hot spots in the crown may help in the early detection of rat holes enabling an easy early hot repair. Condensation corrosion in the silica crown is a very slow process, taking at least 6012 months before the hot spot is converted into a rat hole. The regular inspection of the crown by measuring the cold face temperatures in different areas of the crown may help for early detection. The recommended inspection period is once a month. The cold face temperatures of silica crowns with standard light silica insulation are usually between 180-220 deg C. In cases when this temperature becomes 250-300 deg C, this may be an early indication for a hot spot formation. By removing the thermal insulation in this area one can make a hot repair by patching the crown with Lubisol's "S-Seal" and this will stop the corrosion process. The action is easy and simple and this may reduce to a great extent, the formation and further enlargement of the rat hole. Lubisol has promoted this simple method among its clients with great success. In all cases the regular monthly inspections and reports have contributed for achieving a long service life of the silica crowns where such inspections have been regularly applied.
