DX51D Galvanized Roof Sheet Corrugated Steel Sheet Gi Iron Roofing Sheet have excellent corrosion resistance, print-ability and workability. The De-greasing Section helps the removal of oil and dirt by a cascaded process of hot alkaline de-greasing, cold rising, hot rising and hot air drying. Then annealing is done in an electrically heated horizontal furnace operated under a protective atmosphere with a calibrated ratio of nitrogen and hydrogen generated in a state–of–the–art automated Protective Gas Plant using ammonia and air as primary raw materials.