Fluidised Catalytic Cracking Unit (FCCU) in a petroleum refinery produces valuable middle distillates from the heavier fraction of refined Crude oil. The heavier fraction contains higher amounts of Sulphur and the process requires high temperatures of operation to produce the desired distillates. Hence, most of the components are made of Stainless Steel or high Chromium high Nickel alloys. The basic components are Reactors, Regenerators Orifice chambers and CO duct. The most damaging mechanisms in these components are microstructural deterioration in the form of Sensitization and Embrittlement due to sigma phase precipitation. External Stress Corrosion Cracking (ESCC) due to chloride leaching from thermal insulation and internal stress corrosion cracking due to polythionic acid are the other modes of damages in the structure. Microstructural damages are time dependent phenomenon and require periodic microstructural assessment. In- situ replication technique has been proved to be the best non- destructive technique for such periodic assessment. These components have been monitored over a period of time and an early detection of Crack initiation in a sensitised Stainless Steel structure has been made possible using in-situ metallography technique, thus avoiding a catastrophic failure.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 2, pages 1105 - 1108 Publisher:Ashgate Publishing Company
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