Since in industrial facilities, as defined above, structures made of refractory materials, which are generally siliceous in nature and made of silica, must always be kept at a temperature above 300.degree. C. in order to prevent their weakening by polymorphic transformation, repair methods at high temperature have long been suggested for their repair. These methods may also be used for partial constructions of such facilities, in particular to modify an existing structure by adding a wall or a burned gas discharge pipe, for example.
Thus, bricks made of vitreous silica, which are characterized by a very low expansion coefficient, have been developed and employed conventionally in order to perform such repairs at high temperature. However, it was found that these repairs were not gas-tight, particularly in the case of batteries of coke ovens.
French patent FR 2541440-Bl (Glaverbel), corresponding to U.S. Pat. No. 4,542,888 (Robyn et al), describes a method of repair at high temperatures using vitreous silica bricks of this kind and a ceramic welding method for producing the new masonry joints and also full recharging of the structure (GB 1.330.894 and GB 2.110.200 A by Glaverbel). With this method, the vitreous silica is bricks preferably comprise a chamfer to facilitate making of the joints.
In another patent using the same ceramic welding method (DE 3643420 A1, Fosbel Europe), the full-thickness repair bricks are paired and then brought to the service temperature prior to filling the space between the old and the new masonry by ceramic welding without, however, fully recharging the zone repaired by ceramic welding.
Generally speaking, although vitreous silica bricks, when they are brought to a high temperature, start upon a slow process of crystallization (into cristobalite and tridymite), they nonetheless keep their sensitivity to creep when they are subjected to a high-temperature charge.
This effect is observed in coke ovens where repairs of this type in the vicinity of the flues show well-known sagging after being in the service for some time.