There is no single answer. There are several possible reasons that we can number as being responsible for the appearance of these cracks:
– Lining compaction inappropriate.
– Segregation of the lining.
– Loss of thin through the coil.
– Hanging of the lining from the pan.
What can happen?
Most likely metal infiltration and as a result the furnace should be demolished immediately.
What to do?
Analyse how it has been possible that it has been formed together with the supplier of the lining.