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Localized Corrosion of High-Grade Stainless Steels in Chlorinated Seawater

Picture for Localized Corrosion of High-Grade Stainless Steels in Chlorinated Seawater
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In natural seawater, microorganisms can fix, grow and develop on practically any surface, including stainless steels, which may cause industrial issues such as microbial induced corrosion, loss of heat transfer efficiency, or undesired colonization from macro-fouling. In particular, the presence of a biofilm on passive alloys such as stainless steels or nickel-based alloys can strongly enhance the cathodic reactions such as reduction of dissolved oxygen, and shift the open-circuit potential (OCP) to the noble direction.This results in an increase in OCP, also called cathodic depolarization or biofilm-induced ennoblement, and affects the risk of localized corrosion, since the critical pitting or crevice potential can be exceeded.

Product Number: 51323-18911-SG
Author: Nicolas Larché, Charles Leballeur, Sandra Le Manchet, Wenle He
Publication Date: 2023
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Chlorination is widely used in seawater systems to avoid fouling. Free chlorine is a strong oxidizing agent that prevents the biofilm formation on immersed surfaces, when used above a certain content. However, the presence of residual chlorine associated with the high chloride content in seawater, significantly increases the risk of localized corrosion for most stainless steels. In the present study, a module initially developed to quantify the formation of electroactive biofilms on stainless steels has been used to assess the corrosivity of chlorinated seawater. Both the electrochemical potential and the cathodic current were measured on super-duplex stainless steel as a function of residual chlorine levels and seawater temperatures. In parallel, long term localized corrosion tests have been performed in simulated environments to assess the environmental limits for safe use of high-grade stainless steels in chlorinated seawater. It includes crevice corrosion exposure tests using adapted ISO18070:2015 crevice formers and internal tube pitting corrosion exposure tests in model tube heat exchangers simulating heat flux from 35°C to 170°C. The synergetic effect of residual chlorine content and temperature on the risk of localized corrosion has been quantified. Corrosion resistance properties are correlated to the electrochemical monitoring data, and the environmental limits of selected stainless steels have been established for duplex stainless steel UNS S32205, super-duplex stainless steel UNS S32750, hyper-duplex stainless steel UNS S32707 and the high-grade austenitic stainless steel UNS S31266.

Chlorination is widely used in seawater systems to avoid fouling. Free chlorine is a strong oxidizing agent that prevents the biofilm formation on immersed surfaces, when used above a certain content. However, the presence of residual chlorine associated with the high chloride content in seawater, significantly increases the risk of localized corrosion for most stainless steels. In the present study, a module initially developed to quantify the formation of electroactive biofilms on stainless steels has been used to assess the corrosivity of chlorinated seawater. Both the electrochemical potential and the cathodic current were measured on super-duplex stainless steel as a function of residual chlorine levels and seawater temperatures. In parallel, long term localized corrosion tests have been performed in simulated environments to assess the environmental limits for safe use of high-grade stainless steels in chlorinated seawater. It includes crevice corrosion exposure tests using adapted ISO18070:2015 crevice formers and internal tube pitting corrosion exposure tests in model tube heat exchangers simulating heat flux from 35°C to 170°C. The synergetic effect of residual chlorine content and temperature on the risk of localized corrosion has been quantified. Corrosion resistance properties are correlated to the electrochemical monitoring data, and the environmental limits of selected stainless steels have been established for duplex stainless steel UNS S32205, super-duplex stainless steel UNS S32750, hyper-duplex stainless steel UNS S32707 and the high-grade austenitic stainless steel UNS S31266.

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Picture for Effect of Oxygen in Back Shielding Gas on Corrosion Resistance of Super Duplex Stainless Steel Pipe
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51318-11107-Effect of Oxygen in Back Shielding Gas on Corrosion Resistance of Super Duplex Stainless Steel Pipe

Product Number: 51318-11107-SG
Author: Takayuki Tokumine / Takanori Mimoto / Gen Ogita / Yoshiyuki Shimizu / Masanori Gokou / Fu-Gao Wei / Toshiaki Ashitani / Masayuki Tanaka
Publication Date: 2018
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The effect of back shielding gas types and contained oxygen level on the corrosion resistance of welds was investigated for gas tungsten arc welding (GTAW) of UNS S32750 super duplex stainless steel (SDSS) pipes.
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Crevice and Pitting Corrosion of Stainless-Steel and Nickel based alloys in Deep Sea Water

Product Number: 51319-13123-SG
Author: Erwan Diler
Publication Date: 2019
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The exploration and exploitation of deep seawater presents promising prospects for many industries. Hence the use of reliable materials resistant to corrosion is required.In natural seawater many parameters can influence the kinetics of corrosion such as: temperature oxygen content biofilm and fouling activity flow rates and hydrostatic pressure.For passive material such as Cr Ni Mo stainless steels and nickel-based alloys the specificity of the above parameters in deep sea environment might have an impact on both initiation and propagation phases of localized corrosion e.g. pitting and crevice corrosion. Currently there are still many uncertainties on the corrosion behavior of these materials in deep seawater; Actually the results obtained in laboratory cannot be extrapolated to deep seawater since the levels measured in deep sea of some of these influential parameters weren’t reproduced accurately in these experimental studies. In parallel field data on the corrosion behavior in deep seawater is rather scarce especially for recent materials such as Lean Duplex Stainless Steel. For example phenomena that are induced by biofilm formation and can increase the localized corrosion risk such as the so-called potential ennoblement i.e. an increase in the open circuit potential (OCP) by about + 0.350 V and the increase of the cathodic current are not yet well documented.In this study 13-Cr Stainless Steel Austenitic Lean Duplex Duplex Super Duplex Super Austenitic Hyper Duplex Stainless Steels and Nickel based alloys were exposed during 11 months at 1020 and 2020 m water depth in the Atlantic Ocean. For comparison non-resistant materials such as carbon steel and 13-Cr were also exposed. The susceptibility to pitting and to crevice corrosion were assessed. PVDF crevice gaskets at two different pressures namely 3 and 20 N/mm² were used to assess the crevice corrosion. Potential monitoring was performed in-situ in order to characterize the formation of the biofilm at the material surface. At each exposure depth the environment was characterized using environmental sensors e.g. temperature flow velocity dissolved oxygen salinity and biofilm sensors.The obtained results allow i) ranking the passive material in terms of corrosion resistance to pitting and crevice in deep water at 4°C ii) comparing biofilm activity and kinetics of corrosion at 1020 and 2020 m depth.
Picture for 01501 DEEP WATER CATHODIC PROTECTION: Laboratory
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01501 DEEP WATER CATHODIC PROTECTION: Laboratory Simulation Experiments

Product Number: 51300-01501-SG
ISBN: 01501 2001 CP
Author: William H. Hartt and Shaowei Chen
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