Failure Analysis of Skid Beam in Walking Beam Reheating Furnace of Hot Strip Mill

Walking beam reheating furnaces in hot strip mills use water-cooled skid beams for moving the slabs inside the furnace. These skids were found to fail frequently with water leaks. Failure of these skids results in process interruption and production loss. Detailed failure analysis was carried out to investigate the mechanism and reasons for such failure. The scale deposits were collected from the inside of the skid pipes and analyzed by XRF. The XRF results inferred the oxidized layer to be primarily of iron oxide with some percentage of water-based deposits (oxides of Ca, Mg, and Si). The skid beam samples were collected at the affected and unaffected regions and were analyzed using optical microscopy and hardness testing. The microstructures of the unaffected skid samples revealed a ferritic-lamellar pearlitic structure, whereas at the affected region the microstructure showed spheroidization of carbide particles and degenerated pearlite. This change in microstructure indicated that failure resulted from prolonged high-temperature exposure of the skid beams. The poor strength of the skid pipe refractory insulation system has led to the exposure of the skids to high temperatures and resulted in the early rupture of the skid pipe.