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How long will white walls in a fabrication shop stay white? How many welding shops exceed 99-percent x-ray acceptance of submerged-arc welds?
Because MVE. Inc. satisfies both of these criteria, the firm has become one of the most successful fabricators of cyrogenic storage and transportation tanks in the world. With six manufacturing plants including U.S., European, and Asian locations, MVE designs and manufactures vacuum-insulation products for industrial-gas users, biological-storage systems, restaurant applications, refueling and transport systems, and oxygen equipment for medical use.
At the company's 240,000-square-foot plant in New Prague, Minn., workers turn out bulk-storage tanks, portable liquid cylinders, transport tanks and trailers, helium- and hydrogenstorage tanks, railcars, insulated pipe, nitrogen-storage systems, and low-temperature-storage freezers for the artificial-insemination market and the medical-research industry.
Cryogenic storage touches everyday life: the fizz in a soft drink, medical research, microprocessor manufacturing, laser-beam cutting, an oxygen tank for breathing. Cryogenic technology converts gases into liquids, from C02 at 0 F to helium at -452 F.
99-percent xray acceptance
Fabricating pressure vessels to ASME codes requires well-thoughtout and applied procedures. MVE supports its quest for the ideal cryogenic tank with inhouse and technicalschool training, weld inspections including x-ray and ultrasound, and use of positive feedback from welders to improve procedures. Production traveler sheets for each tank show plate specs; rolling, fitup, and welding procedures; requirements of x-ray and other inspections; and a diagram of the tank with drawings and callouts of Welding Procedure Specifications (WPS) and weld symbols.
"Our ability to meet code requirements," states Ken Rezac, welding-engineering manager, "begins with every piece of metal that enters our shop. Accurate fitup is critical to welding operations, because we have reduced plate thickness 5 to 15 percent and design around standard-size plates. The design requires more seam welds per tank, a change from trying to minimize welds and the risk of defects."
Plate and tank-end caps, formed by a vendor, are cleaned in a BCP blasting machine to remove mill scale and rust that could cause weld imperfections.
Base materials processed here include aluminum alloys, Type 304 and 316L stainless steels, 9-percent SA 553 and 612 nickel-alloy plate, and SA 612 carbon-steel plate. Plates are sized and piece parts cut on a gantry plasma-arccutting machine, an Esab Avenger 2. It...