Abstract

The refractory lining in a smelting furnace is crucial to providing structural integrity to the furnace and protecting the furnace exterior from the molten metal inside. Refractory bricks used in smelting furnaces are designed to withstand extreme mechanical, chemical and thermal stresses; however, soon after the start-up of a furnace, the lining inevitably suffers from wear and deterioration.  Usually, critical loss of refractory is the main reason for the repair or reline of furnaces, which results in expensive maintenance costs and loss of production.  Due to the nature of smelting furnaces it is nearly impossible to drill into the lining while the furnace is in operation and directly determine the remaining lining thickness and evaluate the refractory condition.  Due to this need, several non-destructive testing (NDT) or indirect methods were developed.  These select NDT techniques can measure refractory lining thickness and can evaluate refractory quality by determining if any chemical changes, hydrations, cracking, oxidation or metal impregnation have occurred within the refractory. The accuracy of these indirect NDT methods relies largely on the quality and homogeneity of the refractory bricks in the lining. Experience and knowledge of smelting furnaces in addition to understanding refractories as a composite ceramic is required to understand the variation in the mechanical properties of the refractory bricks in the lining and, as a result, accurately analyze the NDT measurements. In this paper, the available furnace refractory lining NDT and monitoring techniques will be reviewed and discussed. The advantages and disadvantages of the various techniques will be shown through examples and case studies. Finally, this paper will demonstrate how monitoring refractory lining can help extend the campaign life of a smelting furnace and save furnace management millions of dollars in production loss and maintenance costs.