Abstract
The reactor effluent air cooler system includes the equipment and piping subject to ammonium salting, NH4HS corrosion, and associated fouling. The system typically includes air coolers. Duplex stainless steel (DSS) is one material choice to fabricate the reactor effluent air cooler (REAC) of hydrotreater units. Unfortunately, several failures from around the world have been reported in REAC units constructed of DSS, some within five years of service and others just during initial startup. Based on failure analysis reports, the failures were generally associated with welded joints. Given the condition of hydrogen-rich environment, high-pressure process fluid, and service temperature, this type of cracking is most likely a form of hydrogen assisted cracking (HAC) i.e., in-service sulfide stress cracking (SSC) at weldments or hydrogen environment assisted cracking (HEAC) occurring during tightness testing in high-pressure hydrogen. The failures are highly influenced by phase balance (ferrite/austenite) after welding, with high levels of ferrite in the weld metal or HAZ increasing the susceptibility to cracking. In this paper, a summary of considerations to weight in the design, material selection, operations and inspection approach are proposed. Focus is on material selection, inspection access, hydrogen embrittlement, full penetration welds and operation scenarios. The paper also refers to recently published technical report API 932-C. This technical report covers results of a survey of the petroleum refining industry concerning the use of duplex stainless steel (DSS) in Hydroprocessing reactor effluent air cooler (REAC) systems.
