Centrifugally cast HF-modified austenitic-ferritic stainless steel piping has been used in hydroprocessing reactor circuit for about 40 years. Over the years, there have been a few reported cases of cracking incidences. One resulted in a leak upon start up, after a planned shut down. The others were non-penetrating.

Room temperature Charpy V-notch impact values of this alloy are significantly reduced once the material is subjected to service conditions. Crack tip opening displacement (CTOD) tests were performed on service exposed, as well as unused HF-modified piping to study resistance to crack propagation. Base metal, weld metal, and heat affected zone were tested. Some samples were subjected to a hydrogen charging treatment prior to testing. The flaw tolerance of HF-modified piping materials was estimated with the aid of the PREFIS(1) software. The lower bound Charpy - CTOD correlation was used to compute limiting flaw size versus Charpy V-notch energy.

Subject
Materials, Piping, Correlation, Hydroprocessing, Stress cracking, Base metals, Flaws, Stainless steel, Ferrite, Alloys, Toughness, Weld metal, Hydrogen
Keywords:
HF-modified, stainless steel, hydroprocessing, hydrocracker, fitness for service
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2004
Association for Materials Protection and Performance (AMPP)
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