Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 630 of 707

Table VIII. Chemical Resistance of Structural Plastics Polyvinyl Medium Aluminum salts Cadmium salts Chromic acid, to 10% Copper salts Gold cyanide Hydrochloric acid Hydrofluoric acid Iron salts Magnesium salts Nickel salts Nitric acid, to 20% Perchloric acid Phosphoric acid Sodium chloride Sodium cyanide Sodium hydroxide, to 30% Sodium salts Sulfuric acid, to 50% Trichloroethylene Trisodium phosphate Zinc salts Chloride R R R R R R R R R R R R R R R R R R NR R R C, conditional; R, recommended; NR, not recommended. Historically, chemical-resistant brick and tile linings go back approximately 100 years, paralleling the development of sulfuric acid, various dyestuffs, and explosives. The use of masonry construction has grown in the basic steel, metal-working, and metal-finishing industries. Chemical-resistant masonry sheathings are not to be con- strued as hydrostatically tight tank linings. They are, in fact, porous, and consequent- ly must be considered as chemical, physical, and thermal barriers for protecting mem- branes installed behind these sheathings. Brick sheathings contribute to the longevity of tank linings by offering additional chemical, thermal, and physical pro- tection. They are excellent insulating barriers and, consequently, can be considered as energy savers. PLASTIC TANKS AND LININGS There are a multitude of plastics available for solving corrosion problems in the metal-finishing industry. The more popular and cost effective are polyvinyl chloride (PVC), Type I; polypropylene (PP); linear polyethylene (PE); and fiberglass- reinforced plastics (FRP). All of these plastics have been successfully used as self-supporting tanks and "drop-in" tank liners for process and storage applications. The thermoplastics (PVC, PP, and PE) are being used for mechanical bonding to concrete for similar applications. Polyvinyl chloride is one of the oldest proven plastics for fabricating highly chemical-resistant structures. (See Table VIII for the chemical resistance of structural plastics.) Type I PVC is one of the best plastics available for resis- tance to a multitude of strong oxidizing environments up to its thermal limitation 629 Polyethylene R R R R R R R R R R R C R R R R R R NR R R Polypropylene R R R R R R R R R R R C R R R R R R NR R R

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