Process for cleaning and self-passivation of surfaces fouled with Iron oxide deposit

摘要

Chemical cleaning for removing corrosion products is the most economical, rapid, and in some cases the only viable option. The earliest procedures used mineral acid or organic acids to remove iron oxide from heat exchange surfaces comprising both hot and cold water loops. These procedures are dangerous to handle, present huge problem for disposal and could dissolve bare metals. In some processes such as glass-lined reactors, acid can cause sever damage to the glass lining. After the acid cleaning, an immediate surface passivation is needed to prevent flash rust. Unfortunately, post passivation is often not performed.rnThis paper presents a new rust cleaning method, which is safe to handle and can be used to remove rust from various systems, including heating-cooling lines used in glass-line reactors. The chemical cleaning treatment described in the paper dissolves, disintegrates, and removes the deposit from the surfaces while protecting the underlying metal during cleaning. The cleaning product contains a reducing agent, a chelating agent, a polymer, and surfactants. At the optimum pH for cleaning, the chelating agent has the highest affinity for Fe (III) ions only. The optimum chemical composition and conditions were determined using experimental-design methodology and a rigorous statistical analysis. The bulk of the chemistry has no chemical reaction with the bare metal. It is believed that at the end of cleaning, due to the reducing environment of the treatment, a protective film of magnetite is created that eliminates the need for passivation step after cleaning. A number of case histories were developed, covering various applications which include field trials as well as commercial applications in hot water loops, water supply system, and machine-tool manufacturing.