The roller screen is a key piece of equipment in the pelletizing process, responsible for separating the raw pellets based on their size. One of the most significant causes of shutdowns in the pelletizing unit is related to the roller screens, which encounter issues such as a reduction in the rollers' outer diameter, bending, the adhesion of concentrate on the roller surfaces, and other mechanical problems. Given the importance of this equipment in the pelletizing process, the diagnostic study of roller screens is of great significance. In this research, a comprehensive failure analysis was initially conducted on the rollers of roller screens made of 304 stainless steel, 1.4313 steel, and St52 steel with a hard chrome coating. To accurately investigate the causes of the failure, visual inspection and macroscopic examination were performed in the first stage, followed by the use of scanning electron microscopy (SEM) to examine the samples and their defects. The corrosion resistance of the samples was also eva‎luated using the PREN index. Despite its high corrosion resistance, 304 stainless steel exhibited microcracks due to its low yield strength, which could lead to necking under high mechanical stress. 1.4313 steel faced pitting corrosion, primarily due to inclusions and manufacturing defects, as well as chromium segregation in certain areas. For St52 steel with a hard chrome coating, issues such as coating delamination and the formation of surface microcracks were observed, mainly due to improper bonding between the substrate and the coating, inappropriate coating thickness, and inadequate surface preparation of the substrate. To address these issues, the use of steels with more suitable properties, stricter monitoring of the pipe manufacturing process, and improvements in surface preparation and coating thickness control are recommended.

مريم كرباسي

الهه اميرخاني

مهدي احمديان , مهدي علي زاده