Investigation of corrosion of 55AlZn coated roof sheets in Al smelting plant. (September 2020) - Pawar, Sachin
Highlights: 55AlZn coated sheets were used in Al smelting plant for roofing application. Heavy corrosion of these sheets was observed after 10 months of service. Two regions of corrosion were observed. First, whitish region of perforation/holes. Second, reddish brown region of uniformly distributed pits. Fumes in exhaust gas of Aluminum smelting process caused pitting of roof sheet. Deposition of particulate aggravated the effect. Abstract: 55AlZn coated sheets were used in Aluminum(Al) smelting plant for roofing application where aggressive corrosion on bottom side of sheet was observed causing premature perforation within 8 to 10 months of service affecting ~465 m 2 area. The sheets used had a total of 3 coating layers on each side. Two distinct areas of corrosion were identified on the surface of roof sheet, confirming two different corrosion rates. While a thin layer of deposits was observed on the entire sheet, this layer was thicker in area surrounding the resultant holes. This indicated the role of deposits in aggravating the corrosion. Overall analysis indicated that fumes in exhaust gas of Aluminum smelting process caused pitting of roof sheet uniformly all over the surface and deposition of this particulate aggravated the effect. Corrosion of roof sheets can be mitigated by a) Providing fumes extraction system which will minimize the exposure of roof sheet to corrosive atmosphere b) Epoxy based coating can be used.