Round Industrial Duct Construction Standards (SMACNA 1520) is an American National Standard (ANSI) standard and expands the scope of the 1977 version of the publiction, updating original text to incorporate a revised theory of design, new materials and more "user friendly" tables. Offers a standardized, engineered basis for design and construction of industrial ducts of Classes 1 to 5. Includes a spiral duct chapter for Classes 1 and 2, covers design pressures ranging from 30" w.g. negative to 50" w.g. positive, plus carbon and galvanized steel tables. Changes to the manual include expanded tables for stainless steel and aluminum, expanded tables for duct sizes up to 96 inches in diameter, introduction of a new Duct Class 5 for systems handling corrosives, and spiral lockseam pipe. As alternatives to table use, the publication has a manual calculation procedure using equations and fully developed examples, and offers optional calculation software. Includes soft metrics.