This paper summarizes the development and use of a non-intrusive, field/plant patch-type probe for use in monitoring hydrogen flux in wet H2S piping, vessels and pipelines. It utilizes a Devanathan cell with a Ni layer on the external surface of the equipment. The use of the Ni-layer was found to be less expensive and easier to implement on-site than conventional Pd systems. Laboratory tests were conducted with the flux monitoring system in several wet H2S environments, including the standard NACE TM 0177 and TM 0284, to determine its response and to correlate its current output with the susceptibility of conventional A516-70 steels to hydrogen induced cracking. This paper also describes the successful use of the probe in a PETROBRAS refinery for a two years period. During that period critical flux readings, above which wet H2S cracking would be expected to occur in service, were made and were
correlated with process variables. Keywords: hydrogen permeation, hydrogen sulfide, petroleum refining, hydrogen flux monitoring