This duct work was fabricated with mitered elbows from SA-516 grade 70 carbon steel, and was designed for absorbing tower piping in an acid plant. It has a 72" outside diameter and measures 23"-2/4" from the centerline, elbow to elbow. This assembly was only a single portion of a duct work system that included 36", 48" and 60" diameter sections of fabricated duct work. The duct work was fabricated with roundness tolerance of +/- 1/8". A 100% dye penetrant test, soap and air test, and spot x-ray testing of all pipe circumferential and long seam welds was performed prior to shipment.