Acid pickling is the primary method for removing mill scale – the oxide layer formed as steel strip cools from hot rolling. As acid pickling evolved from a batch to a continuous process, and from use of sulfuric acid to hydrochloric acid, its economics have improved. However, despite the ability to ‘regenerate’ the acid, issues with this hazardous substance – worker safety, storage and transport, disposal, special permitting and reporting – make acid pickling an environmental and safety liability. Alternatives have been researched, from chemical reduction processes to continuous dry shot blasting, but none proved economically attractive or capable of matching acid pickling’s consistency.
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