We do a fair amount of pressure vessel fabrication, and rolling the shell courses is always one of the more satisfying parts of the job. This fall we rolled a set of SA-516-70 carbon steel shells for a customer building ASME Section VIII storage tanks — 36″ inside diameter, with plate thickness ranging from 3/8″ to 1/2″ depending on the course.
We rolled the shells on our 4-roll plate bender. The 4-roll design is a real time-saver compared to a 3-roll because you can pre-pinch the leading edge before starting the roll, which eliminates the flat spot problem at the beginning of the plate. For a 36″ diameter, we took two or three passes per plate to work the material into the curve gradually — trying to force it in one pass just causes the plate to ovalise.
After rolling, each shell was tacked up and run past a roundness check using a radius template. Out-of-roundness has to stay within ASME tolerances, which is 1% of the nominal diameter — on a 36″ vessel that’s about 0.36″. All shells came in under 0.2″. Longitudinal seam welding and hydro testing happened after — all passed. It’s good, honest fabrication work and we enjoy it.