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The oil and gas industry regularly uses Type 25Cr super duplex stainless steels (SDSS) for components exposed to seawater and hydrocarbon environments in topside facilities, downhole, and subsea equipment. Much debate still exists concerning the effect of tungsten on pitting and crevice corrosion resistance, particularly in standardization committees.Whereas some researchers claim that tungsten has a strong synergistic effect with molybdenum when added above a certain threshold value, others argue that tungsten additions at the expense of molybdenum could lower corrosion resistance. The objective of this investigation was to examine the effect of tungsten on localized corrosion of two super duplex stainless steels: a low-W (modified UNS S32750) and a high-W (UNS S39274) grade. Both crevice-free and creviced samples were studied. Tests were conducted in 3.5 wt% NaCl or natural seawater with temperatures ranging from 20°C to 95°C. Various independent methodologies including cyclic potentiodynamic polarization, electrochemical critical pitting temperature testing per ASTM G150, and long-term open-circuit potential exposure in natural seawater were used. Results showed that, in the solution annealed condition, tungsten additions to super duplex stainless steels had a marked positive effect on pitting and crevice corrosion resistance, increasing critical crevice temperatures by as much as 30°C. These findings suggested that tungsten-containing SDSS had a corrosion resistance on par with super austenitic stainless steel grades containing 6 wt% molybdenum. A new parametric definition of the pitting resistant equivalent is proposed to reflect the alloy's localized corrosion resistance and to support standardization efforts in the materials oil and gas community.

ElsevierIgual Muñoz, AN.; Espallargas Álvarez, N.; Johnsen, R.; Torres, C. (2013). A new experimental technique for quantifying the galvanic coupling effects on stainless steel during tribocorrosion under equilibrium conditions. Wear. 307(1-2): 190-197. doi:10.1016/j.wear.2013 generates a wear accelerated corrosion process within the depassivated area (worn surface) that is electrically in contact with the still passive one. The galvanic coupling effect at OCP was recently modelled using an electrochemical approach allowing for the theoretical quantification of the wearaccelerated corrosion under equilibrium conditions. Despite the usefulness of this model that mathematically determines the electrochemical conditions inside the wear track in terms of anode potential via the approximation of the net anodic current density, an experimental technique allowing for their experimental determination is essential in the effort to verify the galvanic coupling models and further understand the tribocorrosion mechanisms at OCP. In the present work, a new experimental technique based on galvanic current and potential measurements through a ZeroResistance Ammeter (ZRA) for quantifying the electrode potential and anodic current inside the wear track during rubbing at OCP has been assessed. This experimental set-up has allowed for the first time to determine the prevailing electrochemical conditions (electrode potential and anodic current) inside the wear track by solely exposing the wear track to the electrolyte and physically separating the cathode from the anode (wear track). The effects of sliding wear at open circuit potential have been investigated for a super duplex stainless steel (UNS S32750) in 3.4 wt.% NaCl. The new experimental set-up proposed in this work, separates the cathode from the anode and exposes solely the wear track to the electrolyte. Using well-established electrochemical theories, the effect of the extent of the galvanic coupling on wear at the open circuit potential conditions has been quantified. WEAR Confirmation of AuthorshipPlease save a copy of this MS Word file, complete and upload as the "Confirmation of Authorship" file.As corresponding author, I Nuria Espallargas hereby confirm on behalf of all authors that:1) The authors have obtained the necessary authority for publication.2) The paper has not been published previously, that it is not under consideration for publication elsewhere, and that if accepted it will not be published elsewhere in the same form, in English or in any other language, without the written consent of the publisher. 3) The paper does not contain material which has been published previously, by the current authors or by others, of which the source is not explicitly cited in the paper.Upon acceptance of an article by the journal, the author(s) will be asked to transfer the copyright of the article to the publisher. This transfer will ensure the widest possible dissemination of information. This manuscript deals with the development of a new experimental technique to measu...

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