Acid cleaning of stainless steels and nickel alloys for FGD applications

Flue gas desulfurization (FGD) systems are typically constructed of stainless steel and nickel alloy materials In order to achieve the maximum corrosion resistance from these costly alloy materials, it is necessary to remove iron contamination, heat tint, etc. prior to placing the materials into operation. Various methods have been utilized for final surface cleanup including grinding, abrasive blasting, and acid cleaning. This paper will focus on the use of acid cleaning to prepare alloy materials for FGD installations. Alloy materials are cleaned most effectively by the use of nitric-hydrofluoric acid solutions. These acid solutions can be applied to localized areas using a pickle paste, whereas shop fabrications can be dipped in an acid tank. For field erected vessels, a nitric-hydrofluoric acid solution can be applied by spraying. This paper will address the advantages of acid cleaning, how to perform acid cleaning, and which companies can supply the solutions and perform the acid cleaning. Also, several case studies from recent FGD projects will be presented.