Although Duplex Stainless Steel (DSS) Reactor Effluent Air Coolers (REACs) have in some cases been successfully in service for more than 30 years, several cracking failures of DSS REACs and associated piping have occurred, with many cases reported starting in about 2000. Most failures reported have been due to SSC that initiated at high ferrite regions associated with welds. A method for assessing the risk of SSC in DSS REACs has been presented in this paper. It requires consideration of the effectiveness of ferrite control during fabrication, operating environmental severity and in-service crack detection inspection results.

More recently, header box ruptures during tightness testing with high pressure hydrogen during unit commissioning have occurred. These appear to be dependent on weld quality and are associated with high hydrogen test pressure.

Materials selection for REACs has evolved. Due to the uncertainty with the performance of DSS in REACs and associated piping, existing DSS REACs are often being replaced with Alloy 825 or Alloy 625 to avoid in-service cracking risk. When alloy is needed, Alloy 825/Alloy 625 is typically being specified for new REACs and piping rather than DSS.

Subject
Embrittlement, Test methods, Piping, Welding, Inspection, Repair, Reactor effluent air coolers, Cracking, Sulfide stress cracking, Ferrite, Alloys, Cracks, Hydrogen
Keywords:
Duplex SS, SSC, Alloy 825, Alloy 625, Ferrite, HEE, REAC
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2023
Association for Materials Protection and Performance (AMPP)
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