In blast furnace ,pool type runner is used to reduce the frequent patch up of runner while furnace is in running condition.Whether any instrument is available to measure the runner wall thickness in online(metal holding will be in runner always)
Install under runner an electromagnetic source and above runner an electromagnetic detector. By measuring an electromagnetic flux which pass through the runner you can determine the wall thickness which remains on the runner
In practice that is done by installing thermocouples in runner refractory outer layer. Knowing thickness and conductivity of all unner refractory layers and assuming heat flux from hat metal/slag we calculate remaining refractory thickness.