Influence of the Interaction of Hydrogen with the Phase Boundary of Duplex Stainless Steel on Corrosion

Abstract

This study simulates the behavior of 2205 duplex stainless steel (DSS) in an actual service environment under hydrogen charging/releasing cycles. Electrochemical and immersion experiments are conducted to compare the pitting susceptibility and corrosion behavior of 2205 DSS under single hydrogen charging and several hydrogen charging/releasing cycles. The results reveal that under single hydrogen charging, pits preferentially initiate and propagate within the austenite phase; this finding is consistent with the results of previous studies. However, under cyclic hydrogen charging/releasing cycles, pits initiate at the phase boundary and propagate along it. Moreover, a hydrogen microprint technique is used to characterize the hydrogen enrichment sites in 2205 DSS. The results demonstrate that pits preferentially initiate at the same hydrogen enrichment sites. The study creates a schematic of hydrogen redistribution and hypothesizes that under actual service conditions, the phase boundary, rather than the austenite phase, is the primary site for pitting corrosion because of its transformation into a hydrogen enrichment site from a hydrogen trap.