Metal Finishing Guide Book

2013

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welds 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 Stainless steel tanks can be compared to plastic tanks Fig. 1. Flanged nipple outlets in tanks and covers. Welds "A" in the respect that they are should be burned into plate so welds meet from opposite solid steel, thus eliminating sides, thereby excluding air pocket. Welds must be peened the need to protect a vulnerand ground smooth. able exterior from fumes and splash. Stainless steels generally are classified as straight iron-chromium alloys and iron-chromium-nickel alloys. In the metal-finishing 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 equivalent 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 hydrofluoric acids. The vulnerability of stainless steels to halogenated acids is easy to understand when you recognize that pickling solutions for stainless steel are acids such as hydrochloric and hydrofluoric and various combinations of nitric and hydrofluoric. 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, honeycomb, form marks, etc.; freedom from contaminants and additives, i.e., form release agents, air entraining agents, etc.; and hydrostatically tight and waterproofed on the exterior if located below grade. Self-supporting plastic and stainless steel tanks must comply with similar structural manFig. 2. Flanged nipple outlets when welding neck is specified. Weld dates as those enumer1 "B" to be laid in V in beads not to exceed /8-in. deep. After "B" is ated for carbon steel built up above plate outside, the inner surface must be routed out and Portland cement sufficiently to remove all scale and slag. Weld "C" is to be built up concrete. above the surface of plate, peened, and ground flush. 760

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