Aluminum-based sacrificial anodes were installed to reinforced concrete to stop ongoing corrosion in cooling water tunnels in a Swedish nuclear power plant. The steel rebars were also unintentionally connected to stainless steel water pumps. Therefore, the consumption rate of the sacrificial anodes was higher than predicted. An experimental and a field study were performed to assess if the steel rebar suffer from galvanic corrosion and if the stainless steel pumps are responsible alone for the high consumption rate. It was found from the experimental study that there is an increased risk of galvanic corrosion for steel rebar when the corrosion potential is raised to -200mV (SCE) for samples with 1% CL- by mass of cement and -500mV (SCE) for samples with 2% Cl- by mass of cement. The experimental results were compared with the corrosion potential measured in the cooling water tunnel where sacri ficial anodes were in use and not mounted at all. The cooling water tunnel without sacrificial anodes had generally more anodic corrosion potentials compared to the tunnel with anodes. The tunnel with anodes had also more anodic potentials closer to the stainless steel pumps than further away which means that the rebar is affected by the stainless steel pumps. However, the measured corrosion potentials in the tunnels were not as anodic as the potentials needed for high galvanic current measured in the experimental study.
Reinforced mortar samples were exposed in humidity chambers with different relative humidity or exposed in cyclic moisture conditions. The rebars were in an “as received” condition meaning that the preexisting oxide scale were intact. The lowest chloride concentration that initiated corrosion was 1% Cl− by mass of cement, corrosion was then observed for samples exposed at 97% relative humidity. It is suggested that the corrosion rate decreases when samples are exposed to a relative humidity lower than 97%. The results indicate that threshold levels should be evaluated at rather humid conditions (97%) despite the fact that the maximum corrosion rate at higher chloride levels is observed in the interval 91–94%. For samples exposed to cyclic moisture conditions, a lower chloride concentration was needed to initiate corrosion compared to samples exposed in static moisture conditions.
A global transition towards more sustainable, affordable and reliable energy systems is being stimulated by the Paris Agreement and the United Nation's 2030 Agenda for Sustainable Development. This poses a challenge for the corrosion industry, as building climate-resilient energy systems and infrastructures brings with it a long-term direction, so as a result the long-term behaviour of structural materials (mainly metals and alloys) becomes a major prospect. With this in mind “Corrosion Challenges Towards a Sustainable Society” presents a series of cases showing the importance of corrosion protection of metals and alloys in the development of energy production to further understand the science of corrosion, and bring the need for research and the consequences of corrosion into public and political focus. This includes emphasis on the limitation of greenhouse gas emissions, on the lifetime of infrastructures, implants, cultural heritage artefacts, and a variety of other topics. © 2022 The Authors.
Since 2014, the concept developed for the disposal of high-level radioactive waste in the French deep geological repository project Cigéo includes a cement-based grout material. This cement-based grout material will be injected between the casing and the claystone to neutralize the potential acidity resulting from the claystone oxidation induced by the drilling process of the disposal cell. In these conditions of pH (around 10.5) and temperature (90°C, maximum expected during the disposal), the metallic materials could be sensitive to stress corrosion cracking (SCC). In this project, different environments (aerated or deaerated, at room temperature or at 90°C) and synthetic solutions are considered to reproduce the different periods expected during the long life repository. The project is based on electrochemical measurements (polarization curves to define the SCC critical domain of potentials), slow strain rate tensile tests, and long-term immersion for crack initiation and propagation tests.
In France, deep geological disposal is considered for the storage of high and intermediate-level long-lived radioactive wastes. For aluminium, the possibility to encapsulate the wastes in a cement-based matrix is studied. However, cement being an alkaline environment, aluminium can lose its passivity, starts to corrode leading to hydrogen evolution in the infrastructures and generate a possible explosive hazard after decades of storage if hydrogen can accumulate somewhere in the facility. It is therefore necessary to study the corrosion behaviour of aluminium in the different cements considered for the encapsulation to estimate the possible amount of hydrogen that could be generated through corrosion and design the cement capsules accordingly. This work mainly focused on the reaction occurring at the aluminium-cement interface. Raman spectroscopy did not highlight significant differences in the nature of the corrosion products forming at the cement/aluminium interface, leading to the conclusion that it is not the chemistry of the cement that is the key factor controlling the corrosion rate but rather the physical properties of the cement matrix.
In the context of the high-level radioactive waste disposal CIGEO, the corrosion rate due to microbially influenced corrosion (MIC) has to be evaluated. In France, it is envisaged to dispose of high- and intermediate-level long-lived radioactive waste at a depth of 500 m in a deep geological disposal, drilled in the Callovo-Oxfordian claystone (Cox) formation. To do so, a carbon steel casing will be inserted inside disposal cells, which are horizontal tunnels drilled in the Cox. A specific cement grout will be injected between the carbon steel casing and the claystone. A study was conducted to evaluate the possibility of MIC on carbon steel in the foreseeable high radioactive waste disposal. The corrosiveness of various environments was investigated at 50°C and 80°C with or without microorganisms enriched from samples of Andra's underground research laboratory. The monitoring of corrosion during the experiments was ensured using gravimetric method and real-time corrosion monitoring using sensors based on the measurements of the electrical resistance. The corrosion data were completed with microbiological analyses including cultural and molecular characterizations.
In this study, experiments were carried out to assess the microbially influenced corrosion (MIC) risk in the context of the French high-level radioactive waste disposal. The exposures were carried out at 80°C in different repository relevant conditions, including the presence of different cement-grout mixtures as filling material. Biotic conditions with nutrient and nonsterile conditions with indigenous microbes added from Callovo Oxfordian clayey rock and without nutrients were considered. For biotic conditions, specific preparations of microbial inoculum were carried out from samples collected at Andra's Underground Research Laboratory and microorganisms from microbial culture collection centers. Corrosion kinetics were determined using traditional coupons and completed with real-time corrosion sensors. Microbiological characterizations consisted of cultural approach, quantitative polymerase chain reaction, and next-generation sequencing. The obtained results show no significant MIC and a reduced risk with the use of more alkaline filling material. © 2023 The Authors.
In this study, short-term experiments were carried out to assess the microbially influenced corrosion (MIC) risk in the context of the French high-level radioactive waste disposal CIGEO (Centre Industriel de Stockage Géologique). The exposures were carried out in different representative media, including the presence of different cement-grout mixtures as filling material. Nonsterile and biotic conditions with nutrients were considered. For biotic conditions, specific preparations of microbial inoculum were carried out from samples collected at ANDRA's Underground Research Laboratory and microorganisms from the library. Corrosion kinetics were determined using both traditional coupons and completed with real-time electrical resistance sensors. Microbiological characterizations consisted of cultural approach, quantitative polymerase chain reaction, and next-generation sequencing. The obtained results show no significant MIC, but a reduced risk was observed using more alkaline filling materials. © 2023 The Authors.
The development of new metallic coatings to protect steel, as well as the optimization of maintenance operations on site requires obtaining relevant corrosion data as function of the exposure conditions. In atmospheric and aggressive environments such as under accelerated corrosion tests or in coastal zones, electrical resistance (ER) sensors have demonstrated their ability to provide relevant real-time corrosion data. Among the sensors commercially available, only single material such as steel, zinc, copper are proposed. However, even if this allows obtaining interesting corrosion data for such reference materials, these data are not representative of industrial systems, such as galvanized steel. Indeed, zinc-based coatings can contain different alloying elements, e.g., aluminum and magnesium, which impact drastically their resistance to corrosion. In addition, with single material sensors, the influence of the galvanic coupling between the coating and the substrate, in the presence of a defect or a cut edge is not considered. In this study, hot dip galvanized, electrogalvanized, and painted steel ER sensors are exposed in accelerated corrosion tests. The results show that this method is very promising to (i) detect the red rust apparition; (ii) assess the corrosion resistance of industrial zinc and organic coatings; and (iii) obtain relevant data in real-time along the exposure time.
In this study, the use of electrical resistance (ER) sensors to monitor the corrosion of Al94Cu6 alloy is assessed and compared with 2024-T3 coupons. Under uniform corrosion, a good correlation was found between the ER sensors and mass loss on coupons. Three different chloride depositions are studied: (i) pre-contamination with dry/wet cycles, (ii) Volvo standard accelerated corrosion test and (iii) neutral salt spray test. The obtained results show good reproducibility of the ER sensors under all tested conditions. This suggests that ER sensors more levelled the effect of localised corrosion through a large surface evaluation compared with cross-sections. The corrosion thickness obtained with the ER sensors does not correspond to the mean depth obtained by cross-sections. This can be explained by the distribution and size of the localised corrosion events according to a finite element model proposed. The ER method allows obtaining useful real-time corrosion data for the understanding of the corrosion mechanisms and the development of accelerated tests. The chloride concentration, the frequency of salt application and wet/dry cycles have a strong influence on the corrosion rate of aluminium alloys. © 2021 The Authors.
An austenitic alumina forming stainless steel was exposed in a nitriding atmosphere comprising 5 vol% H2/N2 for 100 and 1000 h. After 100 h, the sample displayed aluminium nitrides down to 450 μm and chromium nitrides down to 200 μm. Thermodynamic equilibrium calculations and kinetic modelling of the system to simulate 100 h of exposure time were performed using the software ThermoCalc 4.1 including DICTRA. The order of appearance of nitrides in the sample starting from the surface can be understood from the thermodynamic equilibria as well as from results of kinetic modelling. However, the nitridation depth predicted by the kinetic modelling, was larger than experimentally observed, and the cubic chromium nitride predicted to be present on the surface was not detected in the exposed sample. One difference between model and experiment was a thin oxide layer present on the surface of the sample. As this oxide layer can decrease the inwards flux of nitrogen, attempts were made to describe the effects of this layer in the model. The model was also used for qualitative comparison of varying alloy compositions, temperatures and initial nitrogen contents of the matrix.
In this work, three different stainless steels (304L (CrNi-18-8), 253 MA®(CrNiSi-21-11), Kanthal® A-1 (FeCrAl)) and a reference low-alloyed ferritic steel (16Mo3 (Fe0.3Mo)) were exposed in a commercial biomass gasifier for three periods of 9 min, 580 and 1054 h in the temperature range 350–500 °C. Biomass is a fuel with generally higher amounts of chlorine and lower amounts of sulphur compared to coal and there is a current lack of data on materials performance in such environments. A high level of zinc sulphide was observed on the surfaces of all materials after exposure. It is argued that zinc plays a key role in capturing sulphur in this environment, thus preventing iron from sulphidation. Some incorporation of sulphur in the oxide scale was observed for Fe0.3Mo and CrNi-18-8. CrNiSi-21-11 showed some internal oxidation and pitting was observed for the FeCrAl material. All four materials showed acceptable performance with low total metal loss.
The effect of heat tints on the corrosion resistance of a 2507 duplex stainless steel tungsten inert gas (TIG) welded joint was assessed. The scanning vibrating electrode technique (SVET) was used to study oxide dissolution, initiation and propagation of corrosion on the weld. Small spot X-ray photoelectron spectroscopy (XPS) was used to investigate the composition and thickness of the heat tints. Both heat tinted and post-weld cleaned conditions were tested. Post-weld cleaning methods investigated were brushing, brushing plus polishing and brushing plus pickling paste. It was seen that heat tints dissolve by electrochemical reactions that can be mapped with the SVET and correlated with the level of discolouration of the oxides, with the purple–brown oxide being the most active. The mechanical post-weld cleaning methods proved to be insufficient to remove the anodic activity in the heat tint. The most efficient process was brushing followed by pickling which resulted in a totally passive surface measured with SVET and a higher critical pitting temperature.
Zinc release data from 5 years of unsheltered exposures in a marine and an urban site is compiled for different zinc material types. The thin surface treatment on zinc materials is gradually detached after approximately 2 years at both sites, revealing the pre-weathered zinc surface unprotected. This consequently increased the release rates of zinc from this surface, whereas the zinc runoff rate from the bare zinc sheet remained relatively stable. Raman studies on bare zinc sheet exposed for 5 years at the marine site revealed zinc oxide of varying crystalline nature and hydrozincite to appear localized and separated from each other.
This study investigated the corrosion behavior of AISI 316L produced by direct energy deposition (DED). Microstructural and chemical analysis showed a homogeneous distribution of Si and Si–Mn inclusions of 0.5–1 µm and the Cr and Mo enrichment within interdendritic areas. Scanning Kelvin probe analysis of additively manufactured stainless steel highlighted a regular “striped-like” surface potential feature with a potential gradient of 30 mV for a mean value of 0.320 ± 0.017 V versus standard hydrogen electrode. It can be related to the presence of the residual stress in the oxide film and the complex thermal history due to the fabrication process. A cyclic corrosion test simulating atmospheric conditions revealed the same corrosion properties for stainless steel fabricated by DED compared to cold rolled one. Various surface preparations of 316L were also exposed for corrosion tests. It was found that the “as-received” and “brushed” surfaces exhibited poorer corrosion resistance due to the presence of an as-build defective layer. However, prior passivation of brushed surface, machining, or mechanical grinding down to P1200 improve significantly the corrosion resistance. © 2022 French Corrosion Institute part of RISE Research Institutes of Sweden. Materials and Corrosion published by Wiley-VCH GmbH.
The use of infrared (IR) cameras has in recent years gained interest as a non-destructive testing (NDT) technique in a number of different research fields. All objects with a temperature above absolute zero emits IR radiation, and the amount of radiation increases with temperature. Infrared thermography is a non-contact technique with high speed which allows inspection of large areas in a relatively short time. In the present work different aspects of IR thermography are described and discussed. Further, corrosion panels with defects, i.e. blisters and filiform corrosion, have been investigated with pulsed thermography. The area of the blisters and filaments, measured with pulsed thermography, have been evaluated, the result obtained have been compared with results from surface profile measurements of the same area. The differences between the results and the limitations of the pulsed thermography are discussed. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred.
With lower alloying costs and higher mechanical properties, lean duplex stainless steels can be a good alternative to the more commonly used austenitic stainless steels. A study was initiated to define the limits of the use of lean duplex stainless steels for urban wastewater treatment (WWT) units. This paper gives and discusses the corrosion results in an aerated wet atmosphere containing H2S at different levels. Exposures were performed both at laboratory scale and in the field WWT plant for 1 year. A specific probe was also designed to study the corrosion process below water condensate film contaminated with H2S. Under such conditions, the properties of stainless steel were strongly modified with an enhanced risk of localized corrosion. The results obtained on lean duplex materials (UNS S32101, S32202, and S32304) are compared with austenitic UNS S30403 and UNS S31603 and with the more standard duplexes UNS S82441 and UNS S32205. The results show that lean duplexes can be used in aerated wet atmospheres in case of moderate contamination of H2S (<10 ppm) and chloride (<200 ppm). For higher contaminations (e.g., H2S around 100 ppm/chloride around 1000 ppm) the duplex S32205 should be preferred.
Several studies sponsored by the French Naval Authorities have been conducted during the last 10 years aiming to develop more reliable testing conditions than the conventional neutral salt spray test that should not be used for prediction of material performance. A satisfying correlation to atmospheric field exposure on a ship in service was observed using a 6 months cyclic test from the automotive industry (e.g., Volvo STD23-0014) with a deviation inferior to 25% and an acceleration factor of 4. The possibility to shorten the test duration with a target of 3 months without losing correlation to field exposures is investigated in the present study. A design of experiment is used to study key parameters such as NaCl concentration, the mode of salt application and its frequency as well as the temperature. Ten different marine paint systems used for shipbuilding have been selected. The results indicate an enhancement of the aggressiveness of the test when doubling the salt concentration from 1 to 2 wt%, increasing the number of salt spray per week (from 2 to 3), and the temperature from 35 to 45 °C. The data are compared to marine field exposures in tropical and temperate climates. The most reliable testing conditions to field exposure in marine sites of severity from low C5M to CX on steel include cyclic corrosion tests using 2 wt% of NaCl.
Electron backscatter diffraction and confocal laser microscopy have been used to quantify the degree of crystallographic anisotropy during corrosion of AISI 316L in two test solutions. Corrosion in 30 vol% H2SO4 sulphuric acid shows pronounced crystallographic anisotropy in which the corrosion rate increases in the order {111} < {110} â‰2; {100}. The ratio between the slowest corroding {111} and the fasting corroding {100} surfaces is about 3. Pitting corrosion in a solution of FeCl3 and AlCl3 in ethanol/glycerol agrees with other reported observations that high-atomic density surfaces {111} and {100} are less prone to pit nucleation, however the effect was relative small.
Depending on the lifetime and level of radioactivity of radioactive wastes, different disposal facilities are considered. Though low- and intermediate-level short-lived waste can be disposed in surface disposal facilities, deep geological disposal is considered for high- and intermediate-level long-lived waste. In France and Belgium, long-term disposal is studied in clay host rock media. For aluminum, the disposal concept is based on encapsulation of the waste in a cement-based matrix. It is also well-known that aluminum is prone to severe corrosion in sufficiently alkaline environments leading to possible hydrogen production. To ensure the safety of the disposal facilities and the integrity of the cement capsules, the amount of aluminum that is disposed in each waste package must be specified and is limited to mitigate the level of hydrogen production by aluminum corrosion. In the present study, the corrosion resistance of an aluminum alloy (grade EN-AW-5754/H111) in two different cement matrices was studied in different configurations at room temperature. In each case, the evolution of hydrogen production was monitored to address the corrosion rate variation versus time.
Cr-free paints applied on different aluminum alloys were exposed for 5 years at different atmospheric weathering sites worldwide. By image analysis, the extent, and the type of corrosion (filiform or blistering) were determined after 1, 2, and 5 years. In that way, it was possible to rank the different systems as a function of their resistance to corrosion. The kinetics of degradation of each system at all sites was also determined. From the results, it is shown that the kinetics of degradation is system dependent. It is also shown that it is the combination of several climatic parameters which contributes to the corrosivity of the site and not only one single parameter such as chloride deposition, relative humidity, and so on.
The corrosion process during the drying out of zinc surfaces confined in crevices was studied using real time photograpy and in situ FTIR microspectroscopy. A pH-indicator was used to visualise differences in the pH during the drying process. The distribution and the composition of the corrosion products after several wetting and drying cycles were studied with FTIR microspectroscopy and SEMEDS. An area with high pH formed during the drying process at the border of the electrolyte, with a zone of white corrosion products that contained zinc hydroxycarbonate in the electrolyte inside this area. A differential aeration cell is present at the border of the electrolyte, and the cathodic oxygen reduction reaction takes place close to the border of the electrolyte during the drying process. The corrosion attack and the distribution and composition of the corrosion products on the surface depend strongly on the drying process of the surface. The corrosion attack of confined surfaces was localised, with a significantly higher corrosion attack in some areas. Outside the drying front a thin layer of electrolyte formed as a result of surface tension driven flow of electrolyte from the electrolyte border. This effect was attributed to the alkaline pH of the electrolyte due to the oxygen reduction reaction at the border. A galvanic element was formed between the local cathodes in the area outside the drying front and the anode in the area with bulk electrolyte. The main corrosion products detected after several wet dry cycles were ZnO, Zn5(OH)6(CO3)2, and Zn5(OH)8Cl2 · H2O, but Na2CO3 · 10H2O was also detected. The corrosion products were non-homogeneously distributed on the surface and the distribution was related to the anodic and cathodic processes that took place in different regions on the surface during the corrosion process.
Panels coated by hot dipping with zinc (HDG), Zn-5Al (Galfan) and Zn-1.5Al- 1.5Mg coatings at different thicknesses were phosphated and painted on an industrial line. Crevice panels with non-painted bare parts modelling conditions in hem flanges, reference panels with open surfaces and formed non-painted panels were exposed to a cyclic accelerated automotive test. Zn-Al-Mg coatings with the thickness of 10 μ rovided similar or even better protection than HDG and Galfan at 20 mmin both confined and open configurations. In comparison to 10-μm HDG, the Zn-Al-Mg coating delayed red rust appearance in crevices by a factor of 2 and the maximal depth of corrosion in the steel substrate was by 42% lower. Confined areas were more corroded than open surfaces. For HDG, the time to red rust appearance dropped by 50-75%, corrosion attack in steel was from 3.5 to 7 times deeper and mass gain was about 2.3 times higher in crevices than on open surfaces. Corrosion of Zn-Al-Mg may be more affected by local environmental conditions created by the crevice configuration than for HDG. Red rust appearance on formed panels of 20-mm Galfan, 7-, 10- and 14-mm Zn- Al-Mg was delayed to 10-μm HDG by a factor of 2.8, 3.5, 3.8 and >4.5, respectively. No adverse effect of forming was noticed. The results indicate that 2- to 3-fold reduction of the coating thickness for Zn-Al-Mg alloy coatings in comparison to traditional HDG may be possible without compromising the corrosion performance.
In this study, the local electrochemical activity of untreated and passivated (natural or chemical passivation) zinc specimens was observed during immersion in a 0.1-M NaCl solution. The localized anodic activity during the exposure, measured with the scanning vibrating electrode technique, was linked to zinc dissolution by the pitting corrosion mechanism. It was correlated to specific corrosion products characterized by Fourier transmission infrared (FTIR) microscopy. FTIR molecule maps were produced from individual pitting corrosion sites (100–200 µm in width). With argon ion beam milling and latest energy-dispersive X-ray spectroscopy (EDS) technology, element maps with a high spatial resolution (≪100 nm) were recorded from abrasion- and beam-sensitive corrosion products, showing a residual layer structure. This study demonstrates the capability of FTIR mapping, cross-section polishing, and state-of-the-art scanning electron microscopy imaging, and EDS element mapping to produce high-resolution elemental, molecular, and visual information about pitting corrosion mechanisms on a hot-dip galvanized steel sample.
Scanning Kelvin probe force microscopy and magnetic force microscopy have been used in combination with SEM/EDS and immersion tests to study a 317L electroslag strip weld which contains austenite and interdendritic ferrite and sigma phase. The individual phases can easily be recognized from the compositional contrast, magnetic pattern and Volta potential variation. Austenite, which is paramagnetic, exhibits the highest Volta potential followed by non-magnetic sigma phase and ferromagnetic ferrite, respectively. Corrosion testing in acidic chloride solutions indicates that the Volta potential measured in air can be related to the tendency to uniform corrosion, while pitting corrosion shows different dependence. In both cases ferrite and sigma phase behaved in a similar manner, indicating that there was no specific detrimental effect of sigma phase on corrosion properties in this material. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
To be able to give safe recommendations concerning the choice of suitable stainless steel grades for pipelines to be buried in various soil environments, a large research programme, including field exposures of test specimens buried in soil in Sweden and in France, has been performed. Resistance against external corrosion of austenitic, super austenitic, lean duplex, duplex and super duplex steel grades in soil has been investigated by laboratory tests and field exposures. The grades included have been screened according to their critical pitting-corrosion temperature and according to their time-to-re-passivation after the passive layer has been destroyed locally by scratching. The field exposures programme, being the core of the investigation, uses large specimens: 2 m pipes and plates, of different grades. The exposure has been performed to reveal effects of aeration cells, deposits or confined areas, welds and burial depth. Additionally, investigations of the tendency of stainless steel to corrode under the influence of alternating current (AC) have been performed, both in the laboratory and in the field. Recommendations for use of stainless steels under different soil conditions are given based on experimental results and on operating experiences of existing stainless steel pipelines in soil. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The electrochemical properties of corrosion products formed under sodium chloride deposits on zinc coatings alloyed with aluminium and magnesium have been studied using impedance spectroscopy (EIS), scanning Kelvin probe (SKP) and photoluminescence (PL) techniques. The low-energy band gap identified in corrosion products on hot-dip galvanized steel was associated with their higher electric conductivity and efficiency of the rate-controlling oxygen reduction reaction. It was attributed to the presence of ZnO, zincite. The formation of ZnO was hindered by the alloying. The alloyed coatings were covered by more compact layers of corrosion products with lower electric conductivity and better barrier properties.
The main aim of the present study has been to investigate the electrochemical behavior of, and oxide film formation on, the bulk amorphous Zr55Cu30Ni5Al10 alloy and the crystalline counterpart in simulated body fluid. Different analytical methods, e.g., polarization and electrochemical impedance measurements, were used to compare the results of the samples when exposed to, phosphate buffered saline (PBS), with or without the addition of protein (albumin). Moreover, the influence of pH on the corrosion behavior of the materials was also investigated. Pitting corrosion was observed to exist on both amorphous and crystalline samples after exposure to the PBS solution, but the passivity region was much smaller for the crystalline material. The addition of protein to the PBS solution improved passive behavior and led to higher pitting potential in the case of the crystalline samples, while the pitting corrosion potential decreased slightly in the case of the amorphous samples. Furthermore, a decrease in the pH level accelerates the dissolution rate of both materials when exposed to the PBS environment, however, in the presence of albumin the pitting corrosion potential increased in the case of both materials.
Electrochemical behavior of, and metal ion release from the bulk amorphous (glassy) Zr55Cu30Ni5Al10 alloy (Zr-MG) was evaluated in simulated body fluid (phosphate buffer saline [PBS]), with and without additions of protein (albumin Fraction V) at pH 7.4 and 5.2 and at body temperature 310 K (37 °C). The passivation behavior and susceptibility to pitting of the Zr-MG was compared with conventional load bearing implant materials, that is, the medical grade ASTM F75 cast CoCrMo alloy (CoCrMo) and AISI 316 LVM low carbon vacuum re-melted stainless steel alloy (SS). Furthermore, the metal ion release from the main constituent elements of each alloy was measured and compared. All materials showed passive behavior in the PBS solution with and without presence of albumin, though the passive region was smaller for the Zr-MG compared to the CoCrMo and SS. Moreover, all materials experienced pitting corrosion in the PBS solution while the Zr-MG was the most susceptible and the CoCrMo was the least one. Protein additions to the CoCrMo and SS prevented the formation of stable pits at pH 7.4 and 5.2. A decrease in passive region and pitting potential was seen in the case of albumin additions for the Zr-MG at pH 7.4, while the opposite was seen at pH 5.2. Furthermore, the total metal ion release from the Zr-MG was less than for the CoCrMo.
With an expanding use of low quality bio fuels, corrosion problems on water wall tubes are increasing. In this study, the possible corrosion reducing effect when adding digested sewage sludge to the fuel in a used wood (also known as waste or recycled wood) fired furnace has been evaluated. The low alloyed steel 16Mo3 and the stainless steel 310S were exposed for 14.25 h at the furnace wall position when firing only used wood and used wood with sewage sludge additions. The exposures were performed in a bubbling fluidized bed boiler and the metal temperature of the test samples was controlled to 350 °C. Chemical analysis of the deposits and microscopic evaluation of the metallic samples showed reduced amount of alkali metals and chlorine in the deposit together with reduced initial corrosion for both materials when co-firing with digested sewage sludge. In the corrosion process, metal chlorides were formed for both materials when firing only used wood, iron chlorides for the low alloyed steel, and chromium chlorides for the stainless steel. When co-firing with sewage sludge, this behavior was suppressed.
High amounts of lead in waste/recycled wood fuel are known to be a contributing factor to the increased corrosion often related to this type of fuel. In combination with potassium, usually present in the fuel, low-melting point salt mixtures between lead chloride (PbCl 2) and potassium chloride (KCl) are expected to form. The purpose of this study is to investigate reactions in the mixed salt of PbCl 2 and KCl and its interactions with carbon steel P265GH and its oxide. Laboratory exposures were performed in an isothermal tube furnace with a salt mixture of PbCl 2/KCl (50/50 mol%) put on steel samples. The test duration was 24 hr at either 300°C or 340°C in an atmosphere of 100 ppm HCl and 20 vol% H 2O in synthetic air. After exposure, the salt mixture consists of distinct areas of KCl and PbCl 2 but also the compounds K 2PbCl 4 and KPb 2Cl 5. A general observation is that the oxide thickness increases with temperature and that areas with Pb/K-mixed salt are frequently found in close connection to more corroded areas. Often the more lead-rich phase KPb 2Cl 5 is located closest to the corrosion product indicating its importance for the corrosion.
Due to the corrosion of steel in reinforced concrete structures, the concrete with low water-cement ratio (w/c), high cement content, and large cover thickness is conventionally used for prolonging the passivation period of steel. Obviously, this conventional approach to durable concrete structures is at the sacrifice of more CO2 emission and natural resources through consuming higher amount of cement and more constituent materials, which is against sustainability. By placing an economically affordable conductive mesh made of carbon fiber or conductive polymer fiber in the near surface zone of concrete acting as anode we can build up a cathodic prevention system with intermittent low current density supplied by, e.g., the solar cells. In such a way, the aggressive negative ions such as Cl-, CO3 2-, and SO4 2- can be stopped near the cathodic (steel) zone. Thus the reinforcement steel is prevented from corrosion even in the concrete with relatively high w/c and small cover thickness. This conductive mesh functions not only as electrode, but also as surface reinforcement to prevent concrete surface from cracking. Therefore, this new type of covercrete has hybrid functions. This paper presents the theoretical analysis of feasibility of this approach and discusses the potential durability problems and possible solutions to the potential problems.
Copper is the intended canister material for the disposal of spent nuclear fuel in Sweden. At repository depth the groundwater may contain dissolved sulfide. The main goal for this work is to study the tendency for stress corrosion of copper in sulfide solutions and examine the influence of various experimental parameters on stress corrosion. Slow strain rate testing was performed on copper test rods in solutions with 1.0 mM sulfide. The pH was kept near neutral with phosphate or borate buffer. The test matrix included variations in temperature, strain rate, and duration of the tests as well as salt and buffer concentrations. Cross-sections of the specimens after testing were investigated using scanning electron microscope/energy dispersive X-ray spectroscopy detector. Stress–strain curves do not reveal any signs of stress corrosion. However, intergranular corrosion in the shape of crack and pit-like features developed in all tests with 1.0 mM sulfide. The length of the deepest features in all these tests was of the same order of magnitude (10–20 µm). The suggested mechanism proposes that crack-like features originate at the surface of the copper metal from the oxidation of grain boundaries that behave as slightly less noble. © 2023 The Authors.
There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments.
Zn coated steel (Z) and ZnAlMg coated steel (ZM3.7/3 = Zn–Al (3.7 wt.%)-Mg (3.0 wt.%)) have been exposed for 6 years at twelve different weathering sites world wide. The mass loss of the coatings have been measured after 1, 2, 4, and 6 years exposure. From the results, it is shown that ZM3.7/3 had always a better corrosion performance compared to Z. The ratio of performance after 6 years of exposure varied from about 1.4 to 4.4 with a mean value of 2.8. At temperate marine sites (e.g., temperature between 9–20°C) with low to moderate SO 2 pollution a good relationship was observed between the relative performance of ZM3.7/3 and the corrosion rate of Z. It was thus concluded that ZM3.7/3 has a better relative performance in harsh environments. The corrosion performance of ZM3.7/3 was shown to be connected to the formation of protective corrosion products.
Hot-dip Zn55Al-coated steel samples have been exposed for up to 6 years at 11 different weathering sites, including marine, marine-industrial, acid-rain and dry atmospheres. From the mass loss measurements, Zn55Al metallic coating showed globally long-term good corrosion resistance in all weathering conditions compared with hot-dip Zn-0.2Al-coated steel (Z). Yet, weaker performance was observed on Zn55Al in high SO2 polluted atmosphere, particularly when combined with seawater aerosols. This is explained by a more acidic surface condition linked to high SO2. Although the extent of corrosion in this phase was different at the different sites, the final corrosion products formed after 6 years were rather similar at all sites. This consists of hydrous aluminium sulphate or hydrous aluminium hydroxy sulphate and, probably also a smaller amount of sulphate-containing zinc corrosion products or Al/Zn products.
Carbon steel, zinc and limestone samples were exposed in Kathmandu for one year. Their corrosion was measured at ten locations and related to SO2, NO2, O3, HNO3 and PM concentrations and climatic factors. Corrosion rates vary considerably and are correlated mainly with the SO2 concentration. Estimated policy targets for SO2 are most stringent for limestone, in the range 3 to 6μgm-3. The Kathmandu carbon steel and limestone samples matched a general pattern from exposures at more than twenty sites in Asia and Africa. At these Asian/African sites corrosion of copper is generally higher than corrosion of zinc. This is in contrast to experiences from European conditions where corrosion of zinc is higher than corrosion of copper.
Corrosion of superheater tubes is a serious problem during combustion of fuels with a high content of chlorine, such as waste and certain biomasses. The alkali chlorides are released to the flue gas and may condense on the heat exchanger tubes forming corrosive, chloride-rich deposits. In this work the effect of ammonium sulphate ((NH4)2SO4) injection on gaseous alkali chlorides, deposit chemistry and initial corrosion attack of superheater tubes during biomass combustion have been investigated. The investigation was carried out at three different sulphate injection rates (reference, low and high) and at three air excess ratios (λ = 1.1, 1.2 and 1.4). Short-term exposures of Sanicro 28 specimens, using temperature controlled probes, were used for deposit collection and to study the initial corrosion attack. The results showed reduced concentrations of potassium chloride in the flue gas when injecting ammonium sulphate and in particular in combination with high air excess ratios. A decrease of chlorine was also observed in the deposit, but the concentrations did not always correlate to the flue gas measurements. In particular, it was evident that a subsequent sulphation occurred on the tube surface at low air excess ratios. Metallography revealed that sulphation reactions on the tube surface, rather than in the flue gas, had a detrimental effect on the initial corrosion attack. As a consequence, the corrosion attack correlated more clearly to the KCl(g) concentration in the flue gas than the chlorine content in the deposit.
Gas turbines operating under fuel-rich conditions may suffer from material degradation and metal dusting.To evaluate this cyclic exposures have been done at 700 °C during 5000 h in two synthetic environments having a carbon activity of 0.26 and above unity. It was found that the common stainless steel 304L is incapable of withstanding either of the environments, while the stainless steel 253MA performs well because a protective silica layer is formed. The ferritic alumina formers Kanthal APM and Kanthal APMT perform well, together with several commercial chromia forming Ni-base alloys. As a general trend the material degradation is slower in the environment with the higher carbon activity, but pre-oxidised samples of chromia forming alloys did experience sudden and rapid carburisation after scale failure. Also a TBC system failed earlier in this environment, because graphite formation at the top coat/bond coat interface caused spalling of the top coat. Further the MCrAlY bond coat cracked and caused carburisation of the underlying Ni-based substrate. A silicon modified aluminide coating showed good degradation resistance, but stimulated excessive carbon deposition in the environment of high carbon activity. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The aim of this study is to evaluate fatigue performance of joined assemblies (spot weld and/or adhesive bonding) in corrosive environment. Various assemblies have been tested in alternated and simultaneous fatigue-corrosion modes. Adhesive joints are strongly affected by simultaneous fatigue-corrosion with a large drop of the fatigue life compared to results in air. By alternating fatigue and corrosion, the reduction of fatigue life is important. For spot welding, fatigue life is decreased at higher load amplitudes and increased at lower amplitudes. These results are strongly linked to the opening of the gap near the spot weld at high load amplitudes. At low amplitudes, corrosion might limit the local stress at the notch root of the weld.