Electrochemical Evaluation of the Effect of Different NaCl Concentrations on Low Alloy- and Stainless Steels under Corrosion and Erosion-Corrosion Conditions

Abstract

The main objective of this study was to assess the influence of salt concentration on the corrosion behaviour, including the role of hydrodynamic conditions, of two broad classes of ferrous engineering materials. These are comprised of alloys, typified by a low-alloy steel (UNS G43400) that corrodes actively in aqueous conditions and a range of passive-film-forming stainless steels (UNS S31600, UNS S15500 and UNS S32760). Corrosion monitoring employed electrochemical (potentiodynamic polarisation) techniques. Three concentrations of aerated sodium chloride were utilised: 0.05 wt% NaCl, 3.5 wt% NaCl and 10 wt% NaCl. In quiescent, liquid impingement and solid/liquid impingement conditions, the corrosion rate of the low-alloy steel was observed to peak at 3.5 wt% NaCl, followed by a reduction in 10 wt% NaCl solution. These findings expand the range of previously reported trends, focused on static conditions. Such corrosion rate/salinity trends were observed to be dictated by the progress of the anodic reaction rather than influence on the cathodic reaction. Detailed studies were undertaken using segmented specimens to facilitate comparisons of the influence of hydrodynamic variations on corrosion behavior; these revealed that such variations influence the corrosion rates of low-alloy steel to a much lesser extent than the effect of changes in salinity. For the stainless steels, in quiescent and flowing conditions, when surface passive films are stable, there was a constant increase in corrosion rate with salinity. In solid-liquid conditions, however, the periodic film-destruction/repassivation events resulted in a similar corrosion rate/salinity trend to that displayed by the low-alloy steel, but with a much larger effect of hydrodynamic conditions. Additonally, the study revealed an underlying influence of stainless steel composition that mirrored, to an extent, the corrosion behaviour in pitting/re-passivation situations

Use of Attapulgite as a Corrosion Inhibitor for Industrial Metals and Alloys: Case of Aluminum, Zinc and Aluzinc in a 0.5 M Hydrochloric Acid Solution

“…We believe that at 2 g/L, the protective layer has broken down under the action of chloride ions. The Clion is known to be destructive to passive films that can be formed at the metal/electrolyte interface [21,22]. The chloride ion causes a localized corrosion phenomenon, such as pitting and stress corrosion cracking [23 -25].…”

Development of an In Situ Micro-Corrosion Cell for the Investigation of Pitting Corrosion on Austenitic and Ferritic Stainless Steels

“…Under specific service conditions, the existence of media containing halides can impair the corrosion-inhibiting properties. In this case, halogen ions, such as chloride ions (Cl − ), attack the passive layer and thereby weaken it, which leads to pitting corrosion [7][8][9]. If the stainless steel contains precipitates reaching up to the top surface of the material, it is possible that the passive chromium oxide layer cannot be built up homogeneously to cover the entire surface.…”