Removing Stains From a Steel Sheet in a Continuous Pickling Line

• Herbert Nuwagaba
• Marvin Ambrocio

This project is focused on removing surface stains that form on a pickled steel sheet that is being processed in a continuous pickling line. Pickling is a treatment that is used to remove impurities, rust, and scale from the surface of materials like steel. ArcelorMittal, the world’s largest steel mining company, is looking to improve the quality of their steel finishing products. The main issue was the presence of stains on the newly manufactured steel which caused a drop in sales due to customer dissatisfaction. In order to find a solution, the current pickle parameters including pickle acid concentration, temperature, and residence time at #3 continuous anneal line were analyzed. During the analysis, it was found that the acid from the pickle tank was being carried over into the rinsing tank. Pickling results in the formation of iron fines and carrying this over into the rinsing tank results into an accelerated re-oxidation of the steel strip surface which causes staining. Also, most staining occurs when the steel strip is allowed to dry via precipitation. When pickle liquid dries, it leaves behind precipitant that will stain the steel. The steel strip has to be wet between tanks or completely dry it through mechanical means like using wringer rolls. The proposed design solution is to use a rinsing aid that is mostly composed of citric acid in the rinsing tank. This allows the rinsing to occur at the same pH as the pickling tank, however, fresh rinsing aid will be used and not the leftover acid from the pickling tank. Also, the proposed design will have better-configured wringer rolls, spray headers, and air headers to prevent the steel strip from drying due to evaporation between tanks. This will prevent the formation of stains from the pickle acid when it dries.