13th International Conference on Fracture June 16–21, 2013, Beijing, China include iron oxides (magnetite and hematite), sulfides, alkaline earth carbonates, sulfates, and silicates [5]. Hydrochloric acid is widely used for the chemical cleaning of structural steel from which heat transfer and piping systems are fabricated. Hydrochloric acid forms soluble products which serve to dissolve calcium or magnesium carbonates [6]. Hydrochloric acid, does not, however, dissolve sulfates or silicates. Therefore, other chemicals must be mixed or incorporated with the hydrochloric acid. It is also well known that hydrochloric acid is highly corrosive [7]. In addition, if copper salts are present in the scale, they will dissolve and reprecipitate on iron surfaces causing severe localized corrosion [8]. It is an object of the present invention to provide a nontoxic, industrial descaling and cleaning composition which is effective in removing scales and oxides from the surfaces of the process equipment used in various industries while avoiding corrosion to the equipment. 2. Detailed description of the descaling and corrosion inhibiting Solution The composition of the present invention includes as the non-toxic inhibitor from 40 to 200 parts per million, preferably from 60 to 100 parts per million (and most preferably 80 parts per million) of acridine orange. The chemical formula for acridine orange is: N,N,N'N'-tetramethyl-3,6 acridinediamine monohydrochloride. The use of this compound has been found to inhibit or block the anodic and cathodic sites in structural steel of the type that is commonly used in the fabrication of a variety of pieces of process equipment [9]. The benefits of using acridine orange (AO) are multifaceted and are as follows [10]: 1. AO has fast and direct protonation when added to acidic solutions. The protonation process is a charge transfer process, viz., flow independent. 2. The AO inhibitor molecules bind strongly to metal surfaces. 3. The free flat aromatic rings having a surface area of 38 A, are bound in a plane which is parallel to the metal surface, such that the position of the positively charged hydrogen ring in AO is close to the predominant negatively charged electric layer on the metal surface. The composition includes from about 5% to about 15%, by weight, hydrochloric acid, preferably from 5% to 10%, and most preferably 8% acid, which serves to remove most calcium, magnesium and iron oxides. The composition also preferably includes 1% to 5%, by weight, preferably 1.5% of hydrofluoric acid, which aids in the removal of silicate containing scales [11]. The conjoint use of hydrochloric acid and hydrofluoric acid serves to accelerate the dissolution of many very hard and complex scale formations. While various chelating agents can be employed in the composition and process of the present invention, such as EDTA, citric acid, HEDTA, etc., it has been found that a mixture of 2% citric acid and 2% EDTA is preferred since it is extremely effective in dissolving iron oxide deposits and also deposits containing copper oxides [12]. In point of fact, even sulfate-containing deposits will be dissolved when this mixture of chelating agents is employed.
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