Monitoring pitting‐crevice corrosion using the WBE‐noise signatures method

Abstract

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) and noise signatures analysis have been applied in novel combinations to study crevice corrosion behaviour in the presence of pits. Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps, which indicate corrosion rates distributions, corrosion patterns and the degree of pitting and crevice corrosion. Specifically, two characteristic noise patterns were observed: (i) the characteristic noise pattern of quick potential changes towards more negative direction with no recovery (termed noise signature I) was found to correspond with the initiation and stabilization of the anode inside crevice; and (ii) the characteristic noise pattern of the cyclic potential oscillation at a constant frequency (termed noise signature II) was found to correspond with the stable anodic dissolution in the occluded cavity site in WBE current distribution maps. A new parameter namely the localization parameter (LP) has been proposed to describe the degree of localization. The LP for crevice corrosion was found to be low compared to that for pitting corrosion.

The influence of nickel–aluminium bronze microstructure and crevice solution on the initiation of crevice corrosion

“…Characteristic E corr oscillations are clearly evident after about 17 days. Similar oscillatory responses have been observed for other crevice corrosion processes [32,34], which have been reported to correspond with successive anodic area formation within the crevice zone and continued propagation of crevice corrosion [32]. Similarly, previous analysis of the NAB crevice solution chemistry has shown significant changes in the period immediately after immersion [35].…”

“…However, there are localised areas at the crevice edge where the formation of relative thick Cu 2 O deposits has occurred. The initiation of crevice corrosion is often reported to produce a sharp drop in the corrosion potential [32,33], i.e. a shift in the negative direction without a recovery, as can be seen after 10 days in Fig.…”

Sensing localised corrosion by means of electrochemical noise detection and analysis

“…A recent development of the WBE method is its combined use with electrochemical noise analysis (ENA) for the purpose of increasing the sensitivity of localised corrosion detection 8,11,30,[35][36][37] . Electrochemical noise refers to random and spontaneous potential and current fluctuations observable in electrochemical processes including corrosion reactions [38][39][40][41][42][43][44][45][46][47][48][49][50][51] .…”

“…The WBE (Figure 1) has been employed during the past several years as a unique sensor for detecting electrochemical noise in various corrosion systems 8,11,30,[35][36][37] . Figure 7 shows a schematic diagram of an experimental setup used for detecting electrochemical noise from a WBE exposed to a carbon dioxide corrosion environment 8 3.1 Simultaneous detection of potential noise and WBE maps A typical experimental arrangement used for detecting potential noise over a WBE surface, and also for mapping galvanic currents flowing among coupled wires in the WBE is illustrated in Figure 8.…”

“…Obviously recognition of such noise signatures could be applied as a means of early detection and prediction of localised corrosion. In industrial corrosion systems, noise recordings could be more complex and could consist of the superimposition of the basic signatures described above37 .…”