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 inrnsome cases the only viable option. The earliest procedures used mineral acid or organicrnacids to remove iron oxide from heat exchange surfaces comprising both hot and coldrnwater loops. These procedures are dangerous to handle, present huge problem forrndisposal and could dissolve bare metals. In some processes such as glass-lined reactors,rnacid can cause sever damage to the glass lining. After the acid cleaning, an immediaternsurface passivation is needed to prevent flash rust. Unfortunately, post passivation isrnoften not performed.rnThis paper presents a new rust cleaning method, which is safe to handle and can be usedrnto remove rust from various systems, including heating-cooling lines used in glass-linernreactors. The chemical cleaning treatment described in the paper dissolves, disintegrates,rnand removes the deposit from the surfaces while protecting the underlying metal duringrncleaning. The cleaning product contains a reducing agent, a chelating agent, a polymer,rnand surfactants. At the optimum pH for cleaning, the chelating agent has the highestrnaffinity for Fe (III) ions only. The optimum chemical composition and conditions wererndetermined using experimental-design methodology and a rigorous statistical analysis.rnThe bulk of the chemistry has no chemical reaction with the bare metal. It is believed thatrnat the end of cleaning, due to the reducing environment of the treatment, a protective filmrnof magnetite is created that eliminates the need for passivation step after cleaning. Arnnumber of case histories were developed, covering various applications which includernfield trials as well as commercial applications in hot water loops, water supply system,rnand machine-tool manufacturing.