ABSTRACT

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.

INTRODUCTION

2205 Duplex Stainless Steel (DSS) UNS S31803 has been used in refinery hydroprocessing unit reactor effluent air coolers (REACs) since the mid 1980's (1). 2205 was selected due to its good resistance to ammonium bisulfide (NH4HS) corrosion and perceived resistance to chloride stress corrosion cracking because it was an economical choice when compared to higher nickel alloy alternatives such as Alloy 825 or Alloy 625.

Many of these DSS REACs have remained in service successfully, with some in service for more than 30 years. However, several incidences of cracking failures of both REACs and associated piping have occurred in industry. Some failures have resulted in major plant damage and long outage time. Some refiners have been replacing DSS REACs with Alloy 825 to avoid in-service cracking risk. Others have made risk assessments and continue to operate with DSS REACs, often with periodic in-service crack detection inspections.

Keywords:
h2s management, drilling fluids and materials, upstream oil & gas, production chemistry, canada government, weld, geologist, united states government, dss reac, fabrication
Subjects:
Drilling Fluids and Materials, Production Chemistry, Metallurgy and Biology, Corrosion inhibition and management (including H2S and CO2)
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