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The purpose of this review is to discuss environmental effects, especially hydrogen sulfide and carbon dioxide on pitting susceptibility of low alloy steels and corrosion resistant alloys.
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Duplex stainless steel (25Cr) can suffer from corrosion in seawater at temperatures exceeding 20 deg.C. To prevent corrosion cathodic protection from attached sacrificial anodes are often used. However this can cause hydrogen stress cracking (HSC) on the alloy assuming tensile stresses above certain levels occur in the component. Some HSC failures have been observed on submerged seawater pumps assemblies made from 25Cr duplex stainless steel protected by sacrificial anodes. To avoid HSC to initiate anodes have been removed on some pumps. Despite the fact that seawater temperature are below 20 deg.C severe localised corrosion attacks have been observed after the anodes have been removed.This presentation gives an overview of the outcome from a test program examining the effect of pre-cathodic polarisation of 25Cr duplex stainless steel on critical crevice/pitting temperature and the anodic polarisation curve. Both welded samples and base metal in addition to different cathodic polarisation levels have been examined. The effect of cathodic polarisation on the oxide layer thickness and composition have been examined with SEM EDS and XRD.The test results show that there is astrong reduction in critical crevice/pitting temperature due to pre-cathodic polarisation. This effect is caused by a change in the oxide layer composition after cathodic polarisation.
Internal corrosion of pipelines associated with oil and gas production and refinery has always been a challenge for corrosion engineers. Over the past decades, corrosion engineers have made significant progress in developing mitigation approaches to protect these carbon steel pipelines by using corrosion inhibitors (CIs), corrosion resistant materials, and various cleaning techniques. Among all these mitigation strategies, corrosion inhibitors are considered as the first choice in handling the internal corrosion of pipelines.
AC corrosion of structures under cathodic protection (CP) is a major concern for pipelines. This work investigates the effect of soil constituents - earth alkali elements Ca and Mg - believed to have a large influence on the precipitation of hydroxides and carbonates in front of a coating damage.
In all nuclear power generating countries, high-activity, long-lived radioactive waste is an unavoidable by-product of the contribution of this energy to the global electricity generation. Disposal in deep, stable geological formations is, at present, the most promising option accepted at an international level for the long-term management of these wastes. Geological disposal relies on a combination of engineered (man-made) barriers and a natural barrier (the host rock), in order to prevent radionuclides and other contaminants ever reaching concentrations outside the container at which they could present an unacceptable risk for people and the environment.
Naval Nuclear Laboratory has developed Alloy 52i, a high chromium (~27 wt%) weld metal that can be welded onto Alloy 600, Alloy 625, or Alloy 690 wrought material. Alloy 52i by itself has shown to be very resistant to SCC in deaerated pure water. However, there is a concern when welding Alloy 52i onto the more SCC susceptible Alloy 82H or Alloy 600 that the first weld bead would be chromium diluted by the mixing with the lower-chromium base metal. This lower chromium level may lead to higher SCC susceptibility than the surrounding weld metal, since chromium content has shown a correlation with nickel alloy SCC susceptibility. In commercial nuclear power applications, many plant components are limited by SCC propagation in welded components within the weld metal; this test program seeks to understand which weld combinations, with respect to chromium concentration, may yield deleterious SCC properties for improved lifetime of plant components.
The strain-induced accelerated corrosion has been reported for many alloys used in structural and functional applications. . Results from electrochemical tests on specimens of carbon steel A569 with different amounts of cold-work are discussed in this paper.
Stress corrosion cracking (SCC) growth in 300-series stainless steels (SS) exposed to high temperature water is known to generally increase with increasing levels of cold work. The influence of cold work on SCC has been reported for both oxygenated boiling water reactor (BWR) normal water chemistry as well as for hydrogenated pressurized water reactor (PWR) water chemistry.
Ultra-high-performance concrete (UHPC) has been introduced for reinforced concrete structures due to its enhanced mechanical performance including high compressive strengths and tensile compacity. In certain applications such as at closure joints connections and concrete repairs reinforcing steel may be embedded in dissimilar concrete elements partially incorporating the UHPC. Superficially UHPC can be considered to provide enhanced corrosion durability in marine environments due to its low permeability which would mitigate chloride-induced corrosion of rebar in the bulk material. However the localized galvanic effects of steel in dissimilar concrete in aggressive environments can be important. For example steel embedded in the concrete perimeter of repair patches can undergo premature corrosion failure after repair due to the halo effect. This research exploring the corrosion durability of steel embedded in dissimilar concretes incorporating UHPC examines the extent to which enhanced chloride transport may occur at the cold joint. The effectiveness of the bond at the concrete interface (with various levels of moisture availability at the time of UHPC repair) to minimize chloride penetration was examined. To this effect the substrate concrete was conditioned to moisture content (5% 75% 100% RH and wet) prior to UHPC repair concrete casting. Chloride penetration was accelerated by an impressed current and chloride content was assessed by concrete sampling at the cold joint as well as in the bulk concrete and potentiometric titrations.
Carbon steel remain the most commonly used material in most oilfield applications. The susceptibility of carbon steel to various forms of corrosion is one of the major drawbacks to its remarkable economic and metallurgical advantages. Localized and/or pitting corrosion carbon steel used in oilfields is one aspect of its limitation that is very common and yet most unpredictable and difficult to mitigate against. The nature of the environment is also a key contributor to the evolution of localized and/or pitting corrosion especially in complex oilfield environment containing both H2S CO2 and other acid gases. The presence of H2S in a corrosion environment often introduces some complexities to the localized and/or pitting corrosion behaviour of exposed carbon steel materials. As a protection against uniform corrosion iron sulphide has been shown to form and has received much attention in the scientific literature. The evolution of iron sulphides (stoichiometric and non-stoichiometric) during the corrosion process of carbon steel is still not fully understood. This makes the already difficult challenge of predicting pitting/localized corrosion of carbon steel more complex and challenging especially since the electronic (and so conducting properties of iron sulphides) can mean that anodic/cathodic reactions can be supported on what are corrosion products or deposits on the corroding surface. This work focuses on understanding FeS formation evolution; dissolution and/or transformation using a combination of different electrochemical responses such as Linear and Tafel Polarization combined with post-experiment surface analysis such as XRD and SEM. It builds on and complements the large literature in this area. The study is carried out in 3.5 wt. % NaCl solution saturated with two different sour corrosion systems; H2S-CO2 and H2S-N2 at 80°C and for up to 21 days. The relationship between the processes of FeS formation evolution; dissolution and/or transformation and the evolution of localized and/pitting corrosion is also established. Pitting and/localized corrosion characterization is achieved using 3D surface profilometry which allows characterisation of discrete pit parameters such as depth diameter etc.