Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 623 of 707

finishing plant engineering CHEMICAL-RESISTANT TANKS AND LININGS BY C. E. ZARNITZ ATLAS MINERALS & CHEMICALS INC., MERTZTOWN, PA.; The dominant and most economical construction materials used in the metal-fin- ishing industry are steel and concrete. Unfortunately, both of these materials are highly susceptible to corrosive attack from many of the chemicals used in the met- al-finishing industry. Pickling and plating chemicals are highly corrosive and, without proper protection, the life span of steel and concrete is limited. Tanks and tank linings must be capable of: 1. resisting attack from organic and inorganic, oxidizing and nonoxidizing chemicals at varying concentrations, as well as from various solvents; 2.resisting broad thermal variances including thermal shock; 3. resisting weather extremes because economics dictate that very large stor- age and waste treatment vessels be located outdoors; 4. resisting physical abuse that accompanies processing strip, heavy parts, shapes and castings; and 5.maximizing performance, value, and ease of maintenance. TANKS AND LININGS The type of tanks that have excelled in the metal-finishing industries include lined carbon steel; lined, precast, or poured-in-place concrete; precast or poured-in-place polymer concrete; self-supporting plastics, i.e., thermosets and thermoplastics; and alloys. The success of steel or concrete-lined tanks is predicated on good engineering design of the structural shell. The ultimate success of the lining, besides good engi- neering design, is predicated on the finish and structural integrity of the sub- strate, as well as on the skills and proficiency of the applicator. If the structure can- not sustain the stress imposed by the process, lining failure is imminent. Similarly, plastic or alloy tanks will fail if good design engineering has been compromised. Carbon Steel Tanks When fabricating carbon steel tanks for subsequent lining, the following are important: 1.Minimum number of pieces and sufficient reinforcement must be used to pre- vent bulging when subjected to optimum process stress. 2.Vertical reinforcing is preferred to horizontal. Ledges are eliminated, thus min- imizing potential for drag-out to hang, concentrate, and corrode the vessel from the "outside-in." 3.Welds to receive lining are to be solid and continuous. 4.All corners are to be ground to a minimum radius of in.; no sharp right angles. 5. Exterior reinforcing members may be skip welded. 6.All body seams must be butt welded true and flat with variation on alignment not to exceed 25% of plate thickness and in no case more than in. 7. All outlets to be flanged. 8. Interior of vessel must be free of weld splatter, pits, deep gouges, and all welds 622

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