Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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ground smooth. The following typical outlet and weld details are suggested when fabricating carbon steel that will be lined with various types of linings (see Figs. 1 and 2). Stainless Steel Tanks Fig. 1. Flanged nipple outlets in tanks and covers. Welds "A" should be burned into plate so welds meet from opposite sides, thereby excluding air pocket. Welds must be peened and ground smooth. Stainless steel tanks can be compared to plastic tanks in the respect that they are solid steel, thus eliminating the need to protect a vul- nerable exterior from fumes and splash. Stainless steels generally are classified as straight iron-chromium alloys and iron-chromium-nickel alloys. In the metal-fin- ishing industry, the iron-chromium-nickel alloys, i.e., the 300 series appear to be the most popular. Types 302, 304, 321, and 347 are considered to be generally equiv- alent in chemical resistance. The stainless steel alloys exhibit excellent resistance to such oxidizing acids as nitric and chromic. They have virtually no resistance to hydrochloric and hydro- fluoric acids. The vulnerability of stainless steels to halogenated acids is easy to under- stand when you recognize that pickling solutions for stainless steel are acids such as hydrochloric and hydrofluoric and various combinations of nitric and hydro- fluoric. Figs. 3-5 provide typical outlet and weld details for the fabrication of tanks. Portland Cement Concrete Tanks Concrete tanks are acceptable so long as good design engineering is practiced and includes: sufficient reinforcement to prevent buckling and cracking; minimum 3,000 psi compressive strength after 28 days; smooth, monolithic interior free of ridges, depressions, honey- comb, form marks, etc.; freedom from contam- inants and additives, i.e., form release agents, air entraining agents, etc.; and hydrostatical- ly tight and water- proofed on the exterior if located below grade. Self-supporting plastic and stainless steel tanks must com- ply with similar struc- tural mandates as Fig. 2. Flanged nipple outlets when welding neck is specified. Weld "B" to be laid in V in beads not to exceed 1 /8-in. deep. After "B" is built up above plate outside, the inner surface must be routed out sufficiently to remove all scale and slag. Weld "C" is to be built up above the surface of plate, peened, and ground flush. 623

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