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The present investigation involved the execution of electrochemical corrosion tests on three distinct modified 9Cr–1Mo steel alloys, each characterised by varying nitrogen and boron contents. These alloys, denoted as P91 (B=0, N=330 ppm), P91B (B=100 and N=20 ppm) and P91BN (B=60 and N=110 ppm), underwent exposure to varying concentrations of NaOH (0.1, 0.2 and 0.5 M) solutions. Additionally, the study explored the influence of chloride (0.1 M NaCl) on the occurrence of pitting corrosion within an alkali environment. The results indicated that the passive current density in all the concentrations of NaOH studied is maximum for alloy P91 followed by P91B and P91BN, respectively, indicating alloy P91 is more prone to corrosion than alloy P91B and P91BN. Electrochemical impedance spectroscopy demonstrated a higher polarisation resistance value for P91BN and the lowest for P91. Scanning electron microscopy analysis revealed that in alloy P91B and P91BN, pits are formed at the M23C6 carbide/matrix interface whereas in alloy P91 apart from carbides, pits are formed at inclusions. Energy-dispersive X-ray mapping identified the elemental composition of the inclusion in P91 which is found to be complex Al2O3–MnS inclusions enriched with Mo. P91BN demonstrated better pitting corrosion resistance compared to alloys P91 and P91B when exposed to NaOH+NaCl medium. [ABSTRACT FROM AUTHOR]

Microalloying is an effective method to improve the properties of Al–Mg alloys. The microstructure, mechanical properties and corrosion behaviours of Al–9.2Mg–0.8Mn–xCu (x = 0–1.2 wt-%) alloys are studied to promote the application of Al–Mg alloys. The addition of Cu increases the strength of the alloy, where the ultimate tensile strength of 0.6 wt-% Cu alloy is improved by 43 MPa. Moreover, the addition of Cu significantly affects the corrosion behaviours of alloys. For as-sensitised alloys, compared to the matrix, the 0.1 wt-% Cu alloy shows a 28.3% reduction in pitting corrosion mass loss, which is attributed to the Cu element can form a stable passivation film, and the 0.3 wt-% Cu alloy shows a 15% reduction in intergranular corrosion mass loss, which is attributed to the addition of Cu can restrict the β phase precipitation at grain boundaries. The study shows that Cu-alloying can improve the comprehensive properties of Al–9.2Mg–0.8Mn alloys. [ABSTRACT FROM AUTHOR]

Corrosion is a major factor that inhibits the longevity of automotive components especially in countries where significant amount of salt is sprayed on highways during winter. In this paper the effect of cosmetic, perforation and red pitting corrosion on indirect hot-stamped Ultra-High-Strength-Steel UsiborR 1500 were investigated using two different Al–Si coating weights AS80 and AS150. The experiments were conducted in a cyclic corrosion chamber over 12 weeks. The results show that AS150 and AS80 exhibited similar excellent perforation corrosion resistance compared to 22MnB5 due to highly protective corrosion products; Both AS80 and AS150 show maximum depth of corrosion attack less than 200 µm compared to 22MnB5 of 900 µm. AS150 displayed better resistance to cosmetic corrosion than AS80. AS80 coating shows higher resistance to red rust pitting corrosion than AS150. E-coat thickness of 15 µm results in higher resistance to red-pitting corrosion than lower e-coat of 8 µm. [ABSTRACT FROM AUTHOR]

This investigation focuses on the ranking of pipeline leakage susceptibility of two categories of pipeline systems. One consists of three oilfield water-handling pipeline systems and the other consists of five dry crude systems. Online corrosion monitoring (OCM) method was used for both systems, forthermore, in-line inspection (ILI) method, with Magnetic Flux leakage (MFL) tool, was also used for the dry crude systems. The OCM leakage susceptibility potential is derived from the combined severity of general corrosion, pitting corrosion, fluid corrosivity and sessile bacteria population density in the process streams. The ILI leakage susceptibility potential is derived from the average number of corrosion anomalies greater than 10% of the wall thickness and the maximum depth of the anomalies (as percentage of the wall thickness). In spite of such distinctions, the ranking of pipeline leakage susceptibility for the five dry crude pipeline segments turned out to be identical for the two methodologies. [ABSTRACT FROM AUTHOR]

This study applied a novel in situ spectral modulation interferometry (SMI) technique to quantitatively measure the spatiotemporal corrosion kinetics on the surface of low carbon steel. The 3D topography map showed an early formation of localised shallow pits on the surface subjected to a chloride-free solution. In contrast, the steel samples in chloride-enriched solution revealed early-age microcracks or intergranular defective sites. The quantitative analysis of the height profile data (acquired from SMI) verified the heterogeneity of the corrosion process of these samples susceptible to pitting corrosion and intergranular corrosion behaviour. The estimated volume loss followed a similar trend to the 3D surface topography data. Still, a distinct behaviour in the volume loss was observed when compared to the void volume obtained from the electrochemical data. [ABSTRACT FROM AUTHOR]

In the present study, laser surface melting (LSM) of 304L stainless steel (SS) was performed using 250 W pulse Nd: YAG laser which resulted in a 250 µm thick melted layer with refined microstructure on the surface. Potentiostatic polarisations at various potentials in the transpassive regime in 6 M HNO3 solution at 95°C were used to quantify the IGC rate. The transpassive dissolution rate was significantly reduced after LSM. The pitting corrosion susceptibility was assessed by potentiodynamic polarisation in 3.5 wt-% NaCl solution. LSM resulted in an increase in pitting potential. Following electrochemical tests, sample surfaces were examined using optical and scanning electron microscopes besides a 3-D optical profilometer. The depths of IGC attack and pit were significantly reduced after LSM. The improvement in resistance to pitting corrosion and transpassive dissolution was attributed to the elimination of inclusions and impurity segregation at the grain boundaries brought about by LSM. [ABSTRACT FROM AUTHOR]

The intergranular corrosion behaviour of Al-Cu-Li-Sc alloy with different microstructures was systematically investigated in this work. The SKPFM characterisation revealed that the AlCuSc (W) phase has more negative potential compared to the Al matrix and undergoes dealloying in the intergranular corrosion solution. The dealloying rate of the W phase in the corrosive solution is relatively slow, which does not lead to serious pitting characteristics. As denser anodic T1 precipitates formed on low-angle grain boundaries of the partially recrystallised sample will reduce the precipitates on the sub-grain interior, resulting in the low-angle boundary being prone to preferential corrosion and reduced intergranular corrosion resistance. The complete recrystallised sample exhibits corrosion of grain interior and propagates along corroded bands parallel to {111}Al habit planes of T1 precipitates, reducing the expansion rate of corrosion along the grain boundaries. Restraining the IGC along the low-angle grain boundary and inducing crystallographic corrosion to improve the intergranular corrosion resistance. [ABSTRACT FROM AUTHOR]

Corrosion behaviour of 2024-T6 castings produced by sand mould and metallic mould has been studied in media with different sodium chloride concentrations and pH values, using electrochemical techniques and scanning electron microscope. Corrosion rates and anodic and cathodic reaction kinetics are detailed to provide a fundamental understanding of the electrochemical behaviour of 2024-T6 at different conditions. The study shows a different corrosion mechanism depending on the pH. At pH 12, the more negative values of Ecorr confirmed that the alkalinisation of aluminium incites the dissolution of the Al substrate. The effect of chloride concentration is reflected in shifts of Ecorr towards more negative values. The research on the effect of the used mould demonstrates that the impact of the casting process in the cooling rate affects the pitting corrosion resistance. [ABSTRACT FROM AUTHOR]

The behaviour of metastable pitting and its effect on stress corrosion cracking (SCC) in 2205 duplex stainless steel (DSS) welded joints were investigated through microstructure characterisation, immersion experiments, electrochemical experiments and slow strain rate tensile (SSRT) experiments. The study revealed that the corrosion in the heat-affected zone (HAZ) and weld metal (WM) increased with longer immersion time due to the environment and welding thermal cycle. The majority of the metastable pitting occurred at inclusions in the ferrite phase and ferrite (α)/austenite (γ) interface. Metastable pitting can increase the DSS SCC susceptibility, with cracks typically initiating at the bottom of pits in the ferrite phase and propagating in the direction of slip bands as either transgranular-stress corrosion cracking (TGSCC) and intergranular-stress corrosion cracking (IGSCC). [ABSTRACT FROM AUTHOR]

Amplicon sequencing is applied to monitor microbial species residing in the biofilm that formed on steel surface submerged in surface water along the Ghent Terneuzen canal, stretching 31 kms from Belgium to the Netherlands. Temporal and spatial differences in the biofilm microbiota were revealed by 16S rRNA composition analysis. The loss-of-mass from S235 steel coupons showed uniform corrosion rates ranging from 242 to 906 g/m2 after 3 months. Notably, enhanced pitting corrosion was seen at one specific location near ‘Heide’ affecting the surface with depths up to 1210 µm after 6 months. We presume the excessive steel deterioration in micro-cavities is associated with microbial activity of iron-oxidising bacteria (IOB) and sulphur-reducing bacteria (SRB), such as Shewanella spp. and Gallionella spp., respectively, as redox-active species. Indications for microbially induced corrosion (MIC) are highlighted at sites with apt microbial composition, irrespective of physico-chemical water parameters. Coupons affected by high corrosion and assumed MIC did not stand out in terms of species richness and alpha diversity did not increase, suggesting partial take-over of the microbial community by IOB or SRB. [ABSTRACT FROM AUTHOR]

In the present paper, an investigation was carried out to understand the microstructure or secondary phase changes formed during thermal ageing at nose temperature (where Cr diffusion was faster) and its influence on the pitting corrosion behaviour of type 316LN SS with marginally lower Cr in as-received (AR) and 10% cold work (CW). X-ray diffraction studies confirmed Cr23C6 and Cr2N in AR and CW conditions. On thermal ageing, AR material from 0 to 10 h and CW from 10 to 24 h, although with lower Cr, the degree of sensitisation (DOS) and pitting potential (Epit) were insignificant due to nitrogen where as above 10 h in AR condition and below 10 h in CW condition resulted reductions in pitting potential (Epit) in different chloride mediums. These results provide new insights on the interplay between pitting, microstructures, alloying elements. [ABSTRACT FROM AUTHOR]

Corrosion was currently the most crucial factor hindering the commercial development of supercritical water oxidation (SCWO) technology. Stainless steel represented by 316L and Ni-based alloy represented by Inconel 625 were performed and compared with corrosion resistance in supercritical environment with high concentrations of oxygen and chlorides. The results shown that the duplex layer was formed on two samples. The surface of 316L SS was mainly composed of loose magnetite and haematite, resulted in pitting corrosion, microcracks, and the exfoliation of oxide. The inner layer were separately a small amount of Cr2O3 oxide and FeCr2O4 spinel, which were caused by the lower content of chromium. Compared with 316L SS, the oxide film structure of Inconel 625 was composed of the outer layer of spinel and the inner layer of Cr-rich oxide. Some nodular oxides were formed, and it can be explained by the volatilisation process of chromium. [ABSTRACT FROM AUTHOR]

In order to study the effect of high hydrostatic pressure on the corrosion of low-alloy steels in deep-sea environments. The electrochemical corrosion behavior of single-metal system and triple-metal coupled system of 907A steel, 921A steel and 1# steel under different hydrostatic pressures were studied by electrochemical, weight loss and morphology observation methods. The results show that the high hydrostatic pressure promotes the corrosion of low-alloy steel by changing the composition and morphology of corrosion products. In addition, there was also severe galvanic corrosion between the couples with a low potential difference (< 60 mV),907A steel was used as the anode of the three-metal coupled system, and 921A steel and 1# steel as the cathode. The galvanic coupling effect accelerates the pitting corrosion of 907A steel as an anode metal. When using multi-metal couplers with low potential differences, they should be protected by both coating protection and cathodic protection. [ABSTRACT FROM AUTHOR]

The effect of nitrogen on the pitting process is investigated using the electrochemical noise (EN) approach in 0.01 M FeCl3 for 24 h at a sampling frequency of 1 Hz. The EN signals were investigated using wavelet analysis on four alloys of 316L SS containing varying quantities of nitrogen (0.07, 0.12, 0.14 and 0.22 wt-% nitrogen). Using an energy distribution (ED) and standard deviation of partial signal (SDPS) plot, the primary corrosion process in various nitrogen-containing 316L SS was found. The ED plot showed that as the nitrogen percentage in the alloy increased, the energy of the low-frequency signal decreased, indicating that long-time transients were suppressed. The SDPS figure revealed a drop in pit density as nitrogen levels increased. For specimens containing 0.07, 0.11, 0.14 and 0.22 wt-% nitrogen, the pit density was determined to be 439 ± 8, 383 ± 6, 212 ± 6 and 108 ± 4 pits mm−2, respectively. [ABSTRACT FROM AUTHOR]

The passive film properties and resistance to general and different types of localised corrosion of the AISI 304L stainless steel were analysed. The properties and behaviour of two microstructural states, the as-received and sensitisation-annealed, are comparatively analysed by electrochemical methods (linear sweep voltammetry-LSV, Mott–Schottky, electrochemical impedance spectroscopy-EIS and electrochemical potentiokinetic reactivation method with double loop-DL-EPR) and surface analytical techniques (scanning electron microscope-SEM/EDS and X-ray photoelectron spectroscopy-XPS). XPS analysis showed the presence of Fe2+, Fe3+ and Cr3+ oxides and hydroxides, and a higher Cr:Fe ratio in the passive layer for the sensitised than as-received specimens. Sensitised stainless steel shows a lower defect density and higher protective stability of the passive layer, and a higher resistance to general corrosion, than the as-received one. However, during LSV measurements, at higher electrode potentials, sensitised stainless steel showed lower passive film stability, due to the metastable pits formation and transformation in the stable pits. [ABSTRACT FROM AUTHOR]

The influences of the rust layer on the passivation and corrosion of Q235b carbon steel in simulated concrete pore solution were studied. The differences between the inner and outer rust layer were characterized. Results show that the pre-rusted samples could still reach passive state at high pH condition free of chloride ions. However, the quality of the passive film formed on the pre-rusted steel were dramatically lower than that formed on the fine polished steel. The pitting corrosion resistance of the pre-rusted steel was significantly higher than that of the fine polished steel in the chloride-containing pore solution. The pitting corrosion potential would be further promoted after the elimination of the outer rust layer. The reaction between the hydrogen ions and the rust layer could inhibit the pitting initiation. Furthermore, the consumption of the corrosive agents induced by the rust layer could further retard the area expansion of the pits. [ABSTRACT FROM AUTHOR]

The susceptibility to localised corrosion of the high strength alloys, AA2050-T84 and AA7050-T7451, used in the aerospace industry, was investigated in this study by localised electrochemical techniques, specifically, scanning vibrating electrode technique (SVET) and scanning ion-selective electrode technique (SIET), in 0.005 mol L−1 NaCl solution. The study was initially carried out using both alloys individually and then, coupling the two alloys and evaluating the effect of galvanic coupling between them. The results revealed that the AA2050-T84, being nobler than the AA7050-T7451, presented higher corrosion current density values when tested in isolation and the depth of corrosion penetration was significantly deeper in the AA2050-T84 alloy than in the AA7050-T7451. However, galvanic coupling of the two alloys resulted in cathodic protection of the AA2050-T84 alloy and a reduction in corrosion current densities on both alloys. [ABSTRACT FROM AUTHOR]

This study extensively compares the corrosion behavior of austenitic 316L and Duplex 2205 stainless-steels at different partial pressures of H2S gases. The results showed that the corrosion rate of both steels at 3 bar H2S showed the highest rate among those parameter setups. 316L steel is dominated by both uniform and pitting corrosion under H2S-containing conditions due to the dissolution of Cr present on the alloy surface. According to the cross-sectional analysis, a Cr enrichment layer formed at 0 bar H2S in both steels. After depletion of the Cr compound in the passive film of both steels, Ni was enriched in the outer layer at 3 bar H2S, forming Ni oxide/sulphide compounds within the passive layer. At 15 bar H2S, Mo was enriched in 316L steel, while Fe and Cr were enriched on the 2205 steel surface. Thus, a kinetic study of the chemical composition of both steels was discussed. [ABSTRACT FROM AUTHOR]

Corrosion behaviour and intergranular corrosion (IGC) sensitivity of 6061 aluminium alloy were investigated using electrochemical polarisation. A 10% tensile stretching was carried out on as-quenched 6061 alloys to understand the effect of pre-deformation on precipitation during subsequent aging treatments. Grain boundary (GB) TEM micrographs were taken to correlate the relationship between the changes in microstructure and corrosion resistance. For artificially aged 6061 alloys, the introduction of the 10% pre-deformation reduces the corrosion rate, but is unable to change their IGC susceptible nature. Conversely, pre-deformation dramatically reduces the pitting depth and pit distribution of naturally aged 6061 alloys. Needle-like β″ precipitates were found homogeneously distributed in the matrix and the GB areas in the pre-deformed and naturally aged 6061-T3. It is suggested that strain-induced dislocations and misorientation sites cover the lack of vacancies around the as-quenched GBs, therefore promote homogeneous precipitation across the GBs which improves resistance against localised corrosion. [ABSTRACT FROM AUTHOR]

The nucleation, propagation, and rehabilitation of pitting corrosion of Al–Mg–Si Aluminium alloy (AA6063) are studied in 3%NaCl solution by using electrochemical noise measurement. It shows that the composite film composed of sequent precipitation of ceria and 1-tetradecylphosphonic acid (DPA) presents the best pitting corrosion resistance compared with the independent ceria conversion film or self-assembling DPA film. XPS and microscopic Raman spectra confirmed that Ceria film is an excellent interlayer for the self-assembling of alkyl phosphate on the intermetallic particles in Al alloy. The anti-corrosion performance of Cerium oxides and DPA composite film is totally dependent on the deposition sequence. Prior deposition of ceria and then DPA film can increase the hydrophilicity of Al matrix and AlFeSi intermetallic particles, further promoting the self-assembling of upper DPA molecules, thus dramatically improving the overall and pitting corrosion resistance of AA6063. This could be attributed to the synergistic effects between the upper DPA film and underlying Ce conversion film. On the contrary, Prior assembly of DPA and then deposition of ceria, may significantly degrade their inhibition efficiency. [ABSTRACT FROM AUTHOR]

FV520B stainless steel is an important material for compression turbine impellers. Its corrosion resistance at high temperatures is critical for the manufacturing and service reliability management of impellers. Therefore, this study investigated the electrochemical corrosion of FV520B stainless steel in an acetic acid solution bearing hydrogen bromine from 130 to 200 °C by potentiodynamic polarisation, electrochemical impedance and corrosion morphology observation. Active corrosion peaks were evident, and the corrosion current densities increased with the increase of the concentration of hydrogen bromine and temperature. However, the breakdown potential first shifted into noble value and then decreased with the further rise in temperature, where the maximum value was at 175 °C. EIS analysis and corrosion morphology revealed that the presence of pitting potential peak is possibly attributed to the competition between the attack of bromine ion and the growth of a surface oxide film under high-temperature water. [ABSTRACT FROM AUTHOR]

In this study, the corrosion behavior of X60 was investigated in the presence of a mixed culture of sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) via weight loss, electrochemical impedance spectroscopy (EIS), and Tafel polarization techniques. Moreover, field emission scanning electron microscope (FESEM) images and X-ray diffraction spectrometry (XRD) were used to study the morphological changes of the surface of X60 and the composition of corrosion products after exposing X60 to the abiotic and biotic systems. EIS result confirmed the occurrence of microbial corrosion in the presence of SRB and IRB. In the exposed coupon to the mixture of bacteria, the result illustrated that the existence of IRB promoted the SRB growth, so corrosion rate increased compared to the exposed coupon to SRB and IRB, respectively. The mixture of SRB and IRB showed a synergistic effect and enhanced the pitting corrosion on the surface of X60. [ABSTRACT FROM AUTHOR]

The serial-type deep-sea environmental test device was used to investigate the corrosion behaviour of 1060 aluminium exposed at real sea for 0.5 year and 2 years. Specimens were deployed at a depth of 1200, 2000 and 3000 m, respectively. A three-stage corrosion process was proposed after analysing the corrosion profile and the corrosion products of the specimens. The corrosion regularity was studied by employing the imaging processing technology and grey correlation analysis. The results show that the 1060 aluminium is prone to pitting and crevice corrosion. For the 0.5 year period test, the corrosion rate increases from 0.0114 to 0.0147 mm year−1 when the sea water depth increases from 1200 to 3000 m. For the 2 year period test, the corrosion rate first decreases and then increases when the sea water depth increases from 1200 to 3000 m, and the maximum corrosion rate at 3000 m depth is 0.006 mm year−1. Oxygen content and conductivity are the most important factors affecting the corrosion rate. [ABSTRACT FROM AUTHOR]

This paper reports pitting corrosion loss data of AA5005-H34 aluminium alloy immersed in natural seawater for up to 2 years. It is shown that the data for mass loss, maximum pit depth and the average value of 15 deepest pits as a function of exposure time are not closely consistent with the classical power-law function. Instead, the data show a greater affinity to the early part of a bi-modal trend. The uncertainty of the pit depth data was analysed using extreme value theory. The results are that scatter in the data sets increases with exposure time. This is considered to be the result of the pit depth data population being non-homogeneous, characterised by a mixture of deep pits with differing pitting morphologies. The results of this study suggest that longer-term data and homogeneous data population are likely to be more reliable for future corrosion loss prediction purposes. [ABSTRACT FROM AUTHOR]

Experimental investigation on the relation of grinding induced surface residual stresses (RS) with stress corrosion cracking (SCC) susceptibility and electrochemical behaviour was conducted on 316L austenitic stainless steel in 3.5% sodium chloride aqueous solution. Grinding was done with the same process parameters to lower the effect of other known parameters on SCC initiation. The corrosion behaviour was characterised by Potentiodynamic and galvanostatic tests. The latest was performed under fixed current density in metastable region. There was a strong relationship between the electrochemical results with RS magnitude. Microscopic investigation showed that the RS induced by grinding could not be the reason for SCC and the dominant defect observed was pitting for all the specimens. The time needed for the breakdown of the passive layer was exponentially related to RS level but the propagation of pits was nearly the same for all the specimens. [ABSTRACT FROM AUTHOR]

Pitting corrosion of aluminium alloy AA5005-H34 immersed in natural sea water for up to 2 years is presented, together with new interpretations of the development of the pitting process over extended exposure periods. Trenching initiated at surface-located Fe-rich intermetallic (IM) particles. It occurred more extensively in sea water compared to atmospheric exposures. With increasing exposures, the pitting morphologies became more complex. Three types, i.e. hemispherical pits (Type 1), crystallographic pits (Type 2) and characteristic 'petal'-like pits (Type 3), were observed after 12 months. It is suggested that the formation of Type 2 and Type 3 pits occurs at an advanced corrosion stage, and are associated with large Fe-rich IM particles near the metal surface. The influence of marine growth on pitting was negligible. [ABSTRACT FROM AUTHOR]

Parameters characterising the properties of soils used as backfill in immediate contact with cast iron pipes exhumed from a variety of soils after up to 129 years exposure are used together with average annual precipitation to estimate the average time of wetness. This is shown to correlate closely with pipe wall corrosion penetration. The possibility of microbiologically influenced corrosion is dismissed owing to lack of critical nutrients. The presence of chlorides in some soils most likely arises from pipe wall corrosion penetration and subsequent leakage of chlorinated drinking water. The predictions from the derived model are compared with an independent set of 16 pipe-wall corrosion penetration observations for pipes with up to 98 years exposures and found to agree well. The potential influences of soil temperature, physical damage and poor quality backfill are discussed. [ABSTRACT FROM AUTHOR]

The flagship congress of the European Federation of Corrosion (EFC), EUROCORR 2019, was held under the theme of 'New Times, New Materials, New Corrosion Challenges' at the Barcelo Sevilla Renacimiento, Seville, Spain, from 9–13 September. This major corrosion event will be reviewed in four parts over four issues, with the technical sessions on Automotive Corrosion, Corrosion and Corrosion Protection of Drinking Water Systems and Pitting Corrosion of Copper in Drinking Water Installations, Corrosion by Hot Gases and Combustion Products, Environment-sensitive Fracture, Corrosion Mechanisms, Modelling and Methods, Modelling Using Cellular Automata and Tribocorrosion being summarised in this, the third, instalment. [ABSTRACT FROM AUTHOR]

Micro-alloying is thought to improve the performance of Al–Mg alloys commonly used in transport applications. The effect of Ce addition (not higher than 0.9 wt-%) on the microstructure, corrosion behavior, and mechanical properties of the Al–9.2Mg–0.7Mn alloy was systematically investigated to assess its potential use in engineering applications. Ce addition had a significant effect on pitting corrosion resistance due to its segregation in the Mn-rich phase. In particular, the pitting corrosion rate of the alloy in the sensitization state decreased substantially with Ce addition, and was approximately 48 and 53% lower than that of the alloy matrix with 0.1 and 0.3 wt.% Ce, respectively. In addition, its strength was improved through 0.3 wt.% Ce addition (providing an increase in ultimate tensile strength of approximately 30 MPa) at no expense to intergranular corrosion resistance, indicating that Ce micro-alloying could comprehensively improve the properties of Al–Mg–Mn alloys. [ABSTRACT FROM AUTHOR]

Professor Brian Cherry was always been a firm believer in understanding first the fundamentals of any aspects of corrosion science, then the mechanisms, before embarking on the engineering of solutions to the management of materials corrosion. So it was with steel-reinforced concrete. This paper endeavours to walk a reader through the fundamental and mechanistic aspects of the excellent protection afforded to steel reinforcement by concrete (including electrochemistry), corrosion of steel reinforcement [including uniform (microcell/minicell) and pitting (macrocell) aspects, corrosion products composition and development], chloride-induced corrosion mechanisms (passive film breakdown/pit initiation, metastable pitting, pit growth/propagation, chemical conditions within propagating pits and reinforcing steel quality effects), carbonation-induced corrosion mechanisms, leaching induced corrosion of reinforcement and reinforcing steel stray current corrosion and interference. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of electrochemically induced surface annealed (EISA) 304L stainless steel was analysed using a range of electrochemical methods, such as polarisation, impedance and Mott–Schottky techniques. Secondary ion mass spectroscopy was used to examine the elemental distribution around the surface of an EISA-treated specimen. The results showed that the EISA treatment increases the resistance to pitting corrosion due to surface densification caused by the absorption of NO and/or N2, which had been reduced under cathodic polarisation during the EISA process. Owing to the limited annealing depth, however, the prolonged corrosion process (i.e. Fe dissolution) can lead to the dissolution of NO and/or N2 species, which had been absorbed on the outer surface, and only smaller portions remained with an uneven distribution at the surface. This can make the EISA-treated steel more vulnerable to corrosion. [ABSTRACT FROM AUTHOR]

Commercially pure aluminium and two model aluminium–magnesium alloys were subjected to hydrostatic extrusion (HE). The microstructure of materials was observed using optical microscopy (OM). All materials were subjected to electrochemical corrosion tests in the 3.5 wt-% water solution of sodium chloride. The potentiodynamic polarisation measurements and electrochemical impedance spectroscopy were performed after samples' immersion in open circuit potential. The surface of samples after corrosion examination was observed with the use of scanning electron microscopy. It was stated that all undeformed materials underwent pitting corrosion and further pits repassivation, while after HE pitting was also observed, but pit repassivation did not occur. This may be related to the microstructural changes caused by deformation, such as grain refinement. What is more, the pits character changed with the addition of a different amount of Mg to Al. Deterioration of corrosion resistance was also observed for all materials after HE. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to assess and dynamically update the risk of process components affected by pitting corrosion. The proposed framework considers the time-dependent growth of pits and uses the non-homogenous Markov process to model the maximum pit depth. The developed pit depth model is incorporated into a limit state function to estimate the failure probability of affected components. Economic consequences are estimated considering both business and accidental losses due to failure. The estimated risk is updated using Bayesian analysis as new inspection data become available. Different risk management strategies including prevention, control and mitigation measures are also studied. [ABSTRACT FROM AUTHOR]

An investigation into the general and pitting corrosion rates of rolled homogeneous armour (RHA) steel in immersion and salt-fog environments is presented. Although the mechanical properties of RHA steel have been studied, the corrosion effects on RHA steel have not been quantified. An immersion environment of 3.5% NaCl was used to induce corrosion for four immersion samples. A Q-fog corrosion tester was used to simulate a salt-fog/humidity/drying environment for four salt-fog samples. The different mechanisms of corrosion and their rates were quantified through mass loss, laser profilometry and scanning electron microscopy. The immersion samples show a linear rate of corrosion of 1.47 g/year (R2 = 0.994) throughout the entire testing period. The salt-fog samples had a significant mass gain for the first 500 h of corrosion, as the corrosion products are retained. Immersion samples showed no signs of pitting, while the salt-fog samples had sustained pit nucleation, growth, and coalescence. [ABSTRACT FROM AUTHOR]

In this paper, 7050-T7451 C-Ring stress-corrosion alternate immersion test in neutral 3.5% NaCl solution was conducted to investigate the mechanism of stress-corrosion cracking (SCC). The SCC sequence was proved to comprise dealloying, pitting, micro-cracks, and intergranular (IG) cracks. Besides, anodic dissolution characterised by reticular IG cracks within pitting zones and IG Dimple Rupture is suggested to be the main operative mechanism during this static stress-corrosion process. Since pitting originates from coarse constituents whose number can be reduced by optimised solution treatment, the formation of pitting can, therefore, be delayed by adopting more effective solution treatment before artificial aging to enhance the SCC resistance. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the influence of heat input and dilution on the corrosion behaviour of a weld overlay coating of Inconel 625 deposited using a plasma transferred arc process. Cyclic potentiodynamic polarisation, double-loop electrochemical potentiometric reactivation and critical pitting temperature (CPT) experiments were performed to determine sensitisation and pitting corrosion resistance of the coating, besides microstructural characterisation and microhardness testing. The overlay showed to be resistant to sensitisation in all cases. Within the scope of this study, only the CPT test was able to cause pitting in the alloy, which showed that increments of the specimen's chemical dilution and heat input induced a lower CPT. This is mainly due to different chemical compositions among the distinct phases present in the coating. [ABSTRACT FROM AUTHOR]

This study investigated the susceptibility to pitting corrosion of 316L in CO2 and N2 environments at temperatures from 30 to 80°C in 3 wt-% NaCl at pH 4. Results from cyclic polarisation technique confirm greater pitting susceptibility of 316L in the CO2 environment. Electronic properties and composition of the passive film were identified by electrochemical impedance spectroscopy, Mott-Schottky, and X-ray photoelectron spectroscopy. Increasing temperature negatively affects the passive film stability, and its influences are amplified in the presence of CO2 as compared to N2. In the CO2 environment, the passive film becomes porous with the increasing temperature leading to higher defects (donor/acceptor densities). [ABSTRACT FROM AUTHOR]

This paper evaluates the stress corrosion cracking (SCC) effect in gasohol E-10 and E-85 of X-70 experimental Ni-microalloyed steel, with different aging treatments (4-12 h at 600°C). The tension tests show that for all treatment periods, the samples tensile strength and elongation increase, with the largest increment exhibited by the samples undergoing 4 and 6 h of aging treatment. Microstructural analysis showed that the microstructure remains unchanged, the increase in tensile strength in the steel is directly related to the precipitation kinetics. The slow strain rate test (SSRT) shows that the steel under all conditions presents no susceptibility to SCC, thus reducing the area ranging from 83% to 90%, with predominantly ductile fractures. The results of the polarisation tests showed no signs of pitting corrosion, as well as a low corrosion rate for both media under study. [ABSTRACT FROM AUTHOR]

Commercially available silicon nitride (Si3N4) spherical bearing rolling elements containing TiO2, Y2O3, MgO and Al2O3 additives were evaluated for corrosion-resistance in high-temperature, high-pressure hydrothermal tests designed to simulate aero propulsion conditions. Spheres were exposed in an autoclave at 523-623 K and 5.2-16.5 MPa for 12-48 h and characterised using mass change and pH measurements, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy and inductively coupled plasma mass spectrometry. The oxidation resistance of the TiO2/Y2O3/Al2O3-sinter-aided Si3N4 ceramic closely matches the Y2O3/Al2O3-doped Si3N4 and outperforms the MgO-sinter-aided Si3N4. Additional studies on the TiO2/Y2O3/Al2O3 Si3N4 composition show pitting initiates around titanium-rich inclusions, due to a break in the protective hydroxide layer, accessible diffusion paths around inclusions and the catalytic nature of titanium. This study demonstrates that the addition of TiO2/Y2O3/Al2O3 to hot pressed Si3N4 reduces corrosion rates in high-temperature, high-pressure, hydrothermal environments. [ABSTRACT FROM AUTHOR]

Chloride-induced corrosion is very serious for steel rebar, because chloride-induced corrosion causes local disruption in the passive layer of the steel, forming surface pits. This paper proposes a novel corrosion monitoring method for steel rebars on the basis of the stress concentration in the plane stress condition caused by chloride-induced corrosion. The fundamentals of corrosion monitoring and the design concept of the proposed sensor are illustrated. The influence factors for corrosion monitoring are simulated to improve the sensitivity. Potentiostatic accelerated corrosion tests are conducted to evaluate the efficacy. The studies indicate that this indirect method for monitoring changes of physical properties caused by corrosion is effective. Influence factors in chloride-induced corrosion can be neglected, as compared with electrochemical techniques. The proposed corrosion monitoring method can provide useful information to evaluate the risk of corrosion initiation and propagation for steel rebars. [ABSTRACT FROM AUTHOR]

The growth rate of pits formed on Alloy 800 in chloride solutions containing various thiosulphate concentrations was assessed by potentiostatic polarisation, in situ corrosion image observation, and image analysis. The pitting growth rate was a function of solution chemistry: in chloride solution pits were small but numerous, in chloride + thiosulphate solution, the pits were large. Competitive adsorption on Alloy 800 of chloride and thiosulphate ions affected the pitting potential and therefore the pitting growth rate on the metal. The reduction of thiosulphate to elemental sulphur accelerated the pitting growth rate in chloride + thiosulphate solutions. [ABSTRACT FROM AUTHOR]

High-strength age-hardenable aluminium alloys are susceptible to localised corrosion. It is vital to monitor the evolution of the corrosion depth in order to prevent a critical degradation of the mechanical properties. This study presents the application of 3D optical pattern profilometry for the analysis of the pitting corrosion behaviour of the aluminium alloy EN AW-2024-T3. Therefore, measurements were conducted using a 1 M NaCl solution at different exposure times. The measurements are compared to the results of optical microscopy investigations of metallographic specimens as well as laser scanning microscopy measurements. In immersion bath tests, the 3D pattern profilometry shows a high measurement accuracy of the pitting corrosion. Regarding the pit characteristics, corroded metal sheets exhibit an increase in the pit depth, volume and area with an increasing exposure time of up to 312 h and then decrease. Moreover, a higher increase in the width in rolling direction than perpendicular to it is noticeable. [ABSTRACT FROM AUTHOR]

Three hundred and four stainless steel and 6061 aluminium alloy samples were exposed to different concentrations of smoke generated by polyvinyl chloride in high humidity. The corrosion kinetics of 304 stainless steel and 6061 aluminium alloy under smoke were found to obey the power function and a linear rule, respectively. Pitting corrosion in smoke became increasingly obvious with exposure time. Surface morphology and chemical compositions of corrosion products were analysed by scanning electron microscope, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Possible corrosion mechanisms were proposed and compared. All the analysis helps to provide basic information for the determination of smoke damage and timely rescue after fire. [ABSTRACT FROM AUTHOR]

The semiconducting properties of passive films formed on copper, in anaerobic alkaline sodium chloride solution, were studied using Mott-Schottky analysis and electrochemical impedance spectroscopy, based on the point defect model. Results showed that the corrosion resistance increased with increasing potential, which was attributed to a well crystallised, refined grain structure, and a thicker passive film at higher potential. P-type semiconducting characteristics were obtained with or without chloride. The density of copper vacancies was approximately 1020 cm−3, and increased with the increasing chloride concentration, which was attributed to faster film-formation in a higher chloride environment. The diffusion coefficient of the defects, a key dynamic parameter for passive film breakdown, was in the range of 10−16-10−15 cm2 s−1, and increased with increasing chloride concentration, thus leading to a greater probability of pitting. [ABSTRACT FROM AUTHOR]

Improved understanding of the development with time of pitting and corrosion of the external surfaces of buried cast iron water pipes is crucial for the management of water supply distribution networks. The present study reports observations of surface topography of cast iron pipes exposed between 34 and 129 years in clay soils. Pit depths, surface areas and widths associated with deeper pits are reported, including as functions of exposure period. Pitting appears to progress in a step-wise manner as also earlier reported for the corrosion of steels. While there is a relation between pit depth and lateral size of pits through the amalgamation of pits to form plateaus into which new pits tend to form, the predominant progression of material loss through corrosion and pitting is into the metal rather than laterally. The practical implications of these observations are discussed. [ABSTRACT FROM AUTHOR]

Data published in the 1957 Romanoff National Bureau of Standards report for the corrosion of steels buried in soils for up to 17 years are re-interpreted using the bi-modal model for corrosion in wet environments. The relevant soil properties are those of the backfill, not those of the undisturbed soil at the depth of the steel samples. Using estimated backfill properties shows that stiff clays, calcareous loams and gravelly loams corrosion transitioned from Mode 1 to Mode 2 after 4-8 years, following severe corrosion and deep pitting. For most other backfill soils, the transition occurred later and corrosion was less severe. These differences are attributed to the relative influence of differential aeration and localised corrosion caused by air-voids at the soil-metal interface. The declining rate of corrosion in the later part of Mode 2 is attributed to backfill consolidation decreasing the diffusion of oxygen and possibly also of moisture. [ABSTRACT FROM AUTHOR]

The resistance of stainless steels to localised corrosion can be adversely affected by environmental and metallurgical heterogeneities existed in complex industrial infrastructures such as seawater desalination plants exposed to aggressive evnironments. It is therefore critical to enhance the localised corrosion resistance and understand the corrosion behaviour of stainless steels in complex and aggressive industrial environmental conditions. In this work, the localised corrosion resistance of chromised stainless steel 316L (SS316L) in simulated seawater desalination systems has been investigated by electrochemical and surface analytical techniques. It has been found that chromising processes have improved the localised corrosion resistance of SS316L by reducing its susceptibility to pitting, crevice, and welding zone corrosion in simulated seawater desalination environments. This increased corrosion resistance has been explained by electrochemical polarisation studies and surface analysis showing that the chromising treatment at 1050°C resulted in a continuous and stable chromium-enriched layer on the SS316L surface. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of 2101 duplex stainless steel (DSS) in NaCl solution was studied and compared with that of 2205 DSS. The effects of chloride concentration and solution temperature on pitting corrosion behaviour were focused. The relative sensitivity to pitting corrosion of the constituent phases in both 2101 and 2205 DSSs was also explored. Pitting corrosion susceptibility was evaluated by conducting cyclic polarisation curve measurement. The corrosion morphology was examined by a scanning electron microscope equipped with energy dispersive spectrometer. The experimental results showed that the pitting corrosion resistance of 2101 DSS was inferior to that of 2205 DSS by exhibiting a lower threshold chloride concentration and a lower critical pitting temperature. For both 2101 and 2205 DSSs, the ferrite phase was more susceptible than austenite phase to pitting corrosion. This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17). [ABSTRACT FROM AUTHOR]

Major water supply distribution networks in many cities consist of buried cast iron pipes. Often the pipes are internally cement-lined. For these the most severe external pitting corrosion is important because this may cause leakage and eventual structural failure. Herein representative data is reported for 10 pipes, ranging in age from 34 to 129 years and from 200 to 600 mm diameter that are part of a larger data set. The pipes examined were selected by the water utilities from several critical locations. Pit depths over 1–2 m lengths of pipes were measured and examined and soil properties measured. The morphologies of pitting around the pipes were found to be very different, with often much greater pit depths and larger pit areas at the base of the pipes. There were also considerable differences along the length of individual parts of pipes. When plotted on a Gumbel plot for the maximum pit depths, the deepest pits showed a different Gumbel trend compared with the majority of pit depth maxima. Theoretically, this indicates that different pitting mechanisms are involved. This possibility is explored by reference to earlier work on the long-term pitting corrosion of steels in sea water. Comments are made also about empirical fitting with other extreme value distributions, as sometimes suggested. [ABSTRACT FROM AUTHOR]

The pitting corrosion of thermally aged Z3CN20.09M cast duplex stainless steel (CDSS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy. Both pitting potential and charge transfer resistance values of thermally aged specimens became less positive with aging time, while passive current density increased, indicating that thermal aging causes degradation in pitting corrosion resistance. The pitting potential of thermally aged specimens after annealed is higher than that of thermally aged specimens revealing that the pitting corrosion resistance of annealed specimens has been improved. The α’ phase precipitation during thermal aging in ferrite brings the Cr-enriched and Cr-depleted zone microstructures which mainly induced the degradation of pitting corrosion resistance. The microsegregation of Cr element or Cr enriched and Cr-depleted zones will be alleviated or even removed due to the Cr-rich α’ phases dissolution during the process of annealing. So, the pitting corrosion resistance of annealed specimens is improved. [ABSTRACT FROM AUTHOR]