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EST Plant (Eni Slurry Technology) consists of about 300 pressure vessels in the following principal units and section: * EST unit (unit 90); * Hydrogen production plant (Unit 95); * SWS sulphur recovery and tail gas treatment (Unit 92 and 94). More than 100 "critical" equipments exist in the EST complex, divided in units and sections on the basis of their type of service. In detail, the considered critical items include: carbon steel and low alloy steels heavy wall pressure vessels for high temperature, high-pressure hydrogen service; carbon steel pressure vessels in sour (wet H^S service) and amine service. For fabrication of such "critical" items special base materials and filler metals were adopted according to specific material requirement, special welding processes and fabrication sequences (including advanced automatic systems for non destrucutive testing) were used. This paper shows an overview on some critical aspects and experience of fabrication of main "critical" equipments of EST Plant. [ABSTRACT FROM AUTHOR]

Modern superaustenitic stainless steels are quaternary alloys extensively used to resist severe aqueous corrosive service, with large contents of Cr, Ni, Mo and PREn index generally higher than 45. Fusion welding is the major joining method for fabricating components and vessels using these grades. In this paper, the behavior of these alloys and the consequence of their use infusion welded structures are illustrated. The typical microstructures of the base materials, the transformations followed during welding or heat treatment and their influence on the mechanical properties and corrosive resistance of the joints are presented. Fabrication practices, filler materials and the aspects common to the nickel alloys welding are discussed, as well. During the welded fabrication, the major difficult is to retain the fully austenitic microstructure with sufficient homogeneity throughout all the high temperature manufacturing operations, and to limit the tendency to the hot solidification cracking. The recent understanding of the segregation mechanisms during the solidification and the associated kinetic will allow a more effective control of the micro structural evolution, also by using high energy welding methods and newly formulated filler materials with non-austenitic primary solidification mode. [ABSTRACT FROM AUTHOR]