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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]

Weld overlay is one of the most critical welding processes for pressure vessels, reactors, valves and pipelines construction. Welding parameters control, influencing mechanical properties of weld metals, is obtained - as well as other welding processes - through the use of welding procedure specification (WPS), necessary to provide a welding operations plan. Production of welding procedure specification is a basic factor, but it is not enough to ensure welded joints requirements. Some defects and chemical compositions of clad metals can be evaluated by nondestructive methods while it is not possible to check metallurgical imperfections with non-destructive methods. These factors require a proper quality control, before and during overlay welding, essential for qualification of welding procedures. [ABSTRACT FROM AUTHOR]