Comparison of Hydrogen Environment Assisted Cracking Susceptibility of Alloy 825/625 Welds to Duplex Stainless Steel 2205/2209 Welds In Reactor Effluent Air Cooler Vessels

Abstract Hydro-processing reactor effluent air cooler (REAC) systems are exposed to startup, in-service, and shutdown operating conditions that can promote sulfide stress cracking (SSC) and hydrogen environment assisted cracking (HEAC). Welds are the primary cracking location for both damage mechanisms. Typical weld consumables used in REAC systems include duplex stainless steel (DSS), carbon steel (CS), and Alloy 825/625 consumables. SSC occurs after some period of service while HEAC failures have reportedly occurred shortly after startup as well as after some period of in-service operation. This paper will focus on key factors associated with these failure mechanisms in REAC systems. In addition, the paper will discuss results from a series of slow strain rate tensile (SSRT) tests carried out on duplex stainless steel weldments extracted from operating REACs and Alloy 825/625 weldment from new REACs. The SSRT tests were performed under high pressure hydrogen gas with test temperatures, hydrogen absorption, and flux rates designed to simulate start-up vessel operation. The results will be presented, trended, and ranked to characterize susceptibility to hydrogen embrittlement with respect to strength, ductility, and failure surface morphology for each alloy and test condition. The outcome of this work provides valuable insight and guidance for optimizing the design, fabrication, maintenance and operation of REACs to minimize HEAC damage mechanisms. Preliminary results show that Alloy 825/625 weldments have lower UTS values but higher ductility when compared to DSS 2205/2209. These tests were conducted at temperatures of 10, 22, and 50 Celsius (50, 72, and 122 Fahrenheit) in a total pressure of 12.2 MPa (1770 psig) composed of 90% H2 and 10% Argon