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Pitting Corrosion (pitting + corrosion)
Selected AbstractsPitting corrosion on 316L pipes in terephthalic acid (TA) dryerMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2009Y. Gong Abstract Grade 316L is a type of austenitic stainless steel with ultra-low carbon content and it exhibits superior corrosion resistance. However, pitting is always observed in 316L steel when it is exposed to media containing halide ions. In the present study, we found that in the presence of acetate acid (HAc) containing chloride or bromide ions, pitting occurred on the surface of the rotary steam pipes with the matrix material of 316L steel in terephthalic acid (TA) dryer. In order to identify the causes of the failure, metallographic structures and chemical compositions of the matrix material were inspected by an optical microscope (OM) and a photoelectric direct reading spectrometer. Beside these, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) as well as ion chromatography (IC) were used to analyze the micromorphologies of the corrosion pits and the chemical compositions of the corrosion deposits within them. Analysis of the results revealed the sources of halide ions and the factors accelerating the corrosion rate. Beside these, detailed mechanisms of pitting were discussed and six out of all the seven theoretical morphologies of pitting features were obtained in practice. [source] Mechanical and corrosion properties of spot-welded high-strength austenitic stainless steel EN 1.4318MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2008M. T. Alenius Abstract Mechanical and corrosion properties of spot-welded high-strength austenitic stainless steels EN 1.4318 2H/C1150 and EN 1.4318 2H/C850 were studied. Microhardness measurements, lap shear and cross-tension tests, corrosion fatigue tests and corrosion tests were carried out. The corrosion environment was 3.5% sodium chloride solution at +50,°C in the corrosion fatigue tests and 3.5% sodium chloride solution at ambient temperature in the electrochemical pitting corrosion tests. Stainless steel EN 1.4318 2H/C850, t,=,1.92 mm, exhibited better fatigue endurance than EN 1.4318 2H/C1150, t,=,1.2 mm, and EN 1.4318 2H/C850, t,=,1.0 mm, stainless steels did. There were no significant differences between the stainless steels of different strength levels (2H/C850 vs. 2H/C1150) in the line load range analysis of the fatigue data. High hardness gradient was found in the heat-affected zone (HAZ) of EN 1.4318 2H/C1150 stainless steels. EN 1.4318 2H/C1150, t,=,1.2 mm, stainless steels seemed to have slightly higher lap shear strength with the same nugget diameter as EN 1.4318 2H/850, t,=,1.9 mm, stainless steel. In the case of EN 1.4318 2H/C1150 stainless steel increase in the nugget diameter bigger than required 5,t did not increase the cross-tension force significantly. The pitting corrosion susceptibility of the spot-welded samples and the base materials of the steels EN 1.4318 2H/C850 and EN 1.4318 2H/C1150, t,=,1.2 mm, was investigated by measuring the corrosion current for 1 h at +100 mV versus saturated calomel electrode (SCE) in 3.5% sodium chloride solution at ambient temperature. Pitting corrosion occurred in all spot-welded samples but not in the base materials. There was a difference between the investigated steels in the location of the pits. In stainless steels EN 1.4318 2H/C850 the pits appeared around the spot weld, but in the steel EN 1.4318 2H/C1150, t,=,1.2 mm, the pits are located mainly at the spot-weld area. [source] Probability modelling and statistical analysis of damage in the lower wing skins of two retired B-707 aircraftFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2001D. G. Harlow A plausible mechanistically based probability model for localized pitting corrosion and subsequent fatigue crack nucleation and growth is used to analyse tear-down inspection data from two retired B-707 aircraft that had been in commercial service for about 24 and 30 years. Sections of the left-hand lower wing skins from these aircraft had been previously disassembled and inspected optically at 20× magnification. The inspections were augmented by metallographic examinations for the lower time aircraft. The evolution of damage in the fastener holes is estimated by using reasonable values for the localized corrosion and fatigue crack growth rates, statistically estimated from laboratory data. The primary loading, assumed to be the mean design load, is considered to be from ground,air,ground wing bending cycles, augmented by ,average' gust loading, only. The encouraging agreement between the estimated probability of occurrence and the observed distribution of multiple hole,wall cracks attests to the efficacy of the approach and its relevancy to airworthiness assessment and fleet life management. [source] Application of Inhibitor-Loaded Halloysite Nanotubes in Active Anti-Corrosive CoatingsADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Dmitri Fix Abstract Halloysite particles are aluminum-silicate hollow cylinders with a length of 0.5,1,µm, an outer diameter of ca. 50,nm and a lumen of 15,nm. These nanotubes are used for loading and sustained release of corrosion inhibitors. The inhibitor is kept inside the particles infinitely long under dry conditions. Here, halloysite nanotubes filled with anticorrosive agents are embedded into a SiOx,ZrOx hybrid film. An aluminum plate is dip-coated and immersed into 0.1,M sodium chloride aqueous solution for corrosion tests. A defect in the sol,gel coating induces pitting corrosion on the metal accompanied by a strong anodic activity. The inhibitor is released within one hour from halloysite nanotubes at corrosion spots and suppresses the corrosion process. The anodic activity is successfully restrained and the protection remains for a long time period of immersion in NaCl water solution. The self-healing effect of the sol,gel coating doped with inhibitor-loaded halloysite nanotubes is demonstrated in situ via scanning vibrating electrode technique measurements. [source] Metallurgical characterization, galvanic corrosion, and ionic release of orthodontic brackets coupled with Ni-Ti archwiresJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Myrsini S. Darabara Abstract In orthodontics, a combination of metallic alloys is placed into the oral cavity during medical treatment and thus the corrosion resistance and ionic release of these appliances is of vital importance. The aim of this study is to investigate the elemental composition, microstructure, hardness, corrosion properties, and ionic release of commercially available orthodontic brackets and Copper Ni-Ti archwires. Following the assessment of the elemental composition of the orthodontic wire (Copper Ni-TiÔ) and the six different brackets (Micro Loc, Equilibrium, OptiMESHXRT, Gemini, Orthos2, and Rematitan), cyclic polarization curves were obtained for each material to estimate the susceptibility of each alloy to pitting corrosion in 1M lactic acid. Galvanic corrosion between the orthodontic wire and each bracket took place in 1M lactic acid for 28 days at 37°C and then the ionic concentration of Nickel and Chromium was studied. The orthodontic wire is made up from a Ni-Ti alloy with copper additions, while the orthodontic brackets are manufactured by different stainless steel grades or titanium alloys. All tested wires and brackets with the exception of Gemini are not susceptible to pitting corrosion. In galvanic corrosion, following exposure for 28 days, the lowest potential difference (,250 mV) appears for the orthodontic wire Copper Ni-Ti and the bracket made up from pure titanium (Rematitan) or from the stainless steel AISI 316 grade (Micro Loc). Following completion of the galvanic corrosion experiments, measurable quantities of chromium and nickel ions were found in the residual lactic acid solution. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Evaluation of different sealing methods for anodized aluminum-silicon carbide (Al/SiC) composites using EIS and SEM techniquesMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2007H. Herrera-Hernandez Electrochemical impedance spectroscopy (EIS) and the scanning electron microscope (SEM) have been used in an investigation of the effectiveness of various sealing methods that can be used to improve the corrosion resistance of an anodized aluminum-silicon carbide (Al/SiC) composite. Anodic oxide films were grown on Al7075-T6 and the Al/SiC composite by sulfuric acid anodizing and sealing in a cold saturated solution of nickel acetate. Other samples were sealed using the traditional method of boiling water or hot nickel acetate for comparison. The results revealed a uniform anodized layer on Al7075-T6 that resisted pitting corrosion for more than 2,weeks exposure to NaCl, whereas a cracked oxide film with variations in thickness was observed on the composite material. Pit initiation occurred in less than 5,days on the anodized Al/SiC that was sealed in the hot solutions. This study suggests that the traditional hot sealing methods did not provide sufficient corrosion protection for aluminum metal,matrix composites (MMCs) because the reinforcing SiC particles deteriorated the surface film structure. However, this defective film can be repaired by nickel hydrate precipitation during cold sealing or by applying a thick polyurethane coating. [source] On-line corrosion and corrosion-wear monitoring using a modified electrochemical noise techniqueMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2005P.-Q. Wu Abstract In this study, a modified electrochemical noise (EN) technique was used to monitor uniform corrosion and pitting corrosion. In the EN technique, one working electrode is coupled to a microelectrode (e.g. Pt) through a zero resistance ammeter to sense current noise. Results show that the EN technique with a properly selected microelectrode appears to be able to distinguish different corrosion processes like uniform corrosion on mild carbon steel and pitting corrosion on stainless steel. Furthermore, this EN technique was successfully implemented in on-line corrosion-wear monitoring of stainless steel. In addition, the modified EN technique can sensitively detect the interface of nitrogen ion implanted layer and the stainless steel substrate, thus determining the thickness of the implanted layer. [source] Synergistic or additive corrosion inhibition of mild steel by a mixture of HEDP and metasilicate at pH 7 and 11MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2004D. Mohammedi Abstract Electrochemical measurements (steady-state current-voltage curves and AC impedance) were coupled with mass-loss measurements, SEM examinations, and EDSX analyses to investigate the inhibition of corrosion of a carbon steel by a mixture of phosphonic acid HEDP (acid 1, hydroxyethylene, 1-1 diphosphonic) and sodium metasilicate pentahydrate Na2SiO3. 5H2O in an industrial hard water containing 3.10,3 M Ca2+ ions. At pH 7, HEDP and Ca2+ act in a synergistic manner, by formation of a HEDP and calcium containing layer. Addition of silicate at this pH value, allows to reach an efficiency of 94% due to an additive inhibition effect. At pH 11, metasilicate, HEDP, and Ca2+ ions reinforce the passive layer in a synergistic way. The mixture (1.7 · 10,5 M HEDP + 2.6 · 10 -3 M SiO2,3) in the Ca2+ containing electrolyte is shown to be able to inhibit efficaciously the corrosion of iron at room temperature, considering uniform corrosion at pH 7 or pitting corrosion at pH 11. [source] Determination of the weaker phase in the pitting corrosion of non-standard low-Ni high-Mn-N duplex stainless steelsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2004R. Merello Abstract In this paper, the use of Energy Dispersive Spectrometry (EDS) is proposed to determine the partition coefficients of the elements of a new family of duplex stainless steels that are characterized by having low contents of nickel, together with high levels of manganese and nitrogen. From the values of the partition coefficients, the chemical compositions of the constituting phases have been determined, in order subsequently to calculate the value of the Pitting Resistance Equivalent Number (PREN) of each phase. The proposition put forward in this study is that the phase having the lower PREN determines the pitting corrosion behaviour of these types of steels. Results obtained by means of optical and scanning electron microscopy have provided confirmation that the pitting corrosion behaviour of these new materials gets determined by the resistance of the weaker phase and consequently by the phase having the lower PREN value. Lastly it has been proved possible to determine the existence of an exponential relationship between the alloys pitting potential (Ep) and the weaker phase PREN; this can be utilized for the low-nickel duplex stainless steels design in which the pitting corrosion resistance is controlled. [source] Initiation and propagation of stainless steel pitting corrosion under heat fluxMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2003T. Pro nichtrostender Stahl; Lochkorrosion; Wärmeübergang; Wärmefluss Abstract An effect of heat flux on initiation and propagation of pitting corrosion of austenitic stainless steel in chloride environment has been studied using electrochemical and exposure methods. The experiments were performed at constant surface temperature of 60°C and heat flux from , 15 to + 74 kW m,2. The presence of heat flux from metal to solution shifted the breakdown potential towards noble values and lowered the pit density, whereas the pit propagation rate increased. Presence of maximum heat flux caused, in comparison with isothermal conditions, increase of the breakdown potential by approx. 100 mV, reduction of pit density by 30% and increase of the average pit depth by 40%. The positive effect of heat flux from metal to solution was given mainly by improving the protective ability of the passive film, as the amount of oxygen available at the metal surface increased. With a smaller significance, the effect of intensified mass transfer, which made accumulation of the chloride ions on the surface more difficult, occurred. Entstehung und Fortschreiten der Lochkorrosion von nichtrostendem Stahl bei Wärmefluss Der Einfluss von Wärmefluss auf die Entstehung und das Fortschreiten der Lochkorrosion bei austenitischen nichtrostenden Stählen in chloridhaltiger Umgebung wurden unter Verwendung elektrochemischer Methoden und in Auslagerungsversuchen untersucht. Die Versuche wurden bei einer konstanten Oberflächentemperatur von 60°C und einem Wärmefluss von , 15 bis 74 kWm2 durchgeführt. Ein Wärmefluss vom Metall hin zur Lösung verschob das Durchbruchspotential hin zu edleren Werten, es verringerte sich die Lochdichte, während eine Zunahme der Lochbildungsrate erfolgte. Ein Maximum des Wärmeflusses bewirkte im Vergleich mit isothermen Bedingungen eine Zunahme des Potentials um ca. 100 mV, eine Verringerung der Lochdichte um 30% und eine Zunahme des Wertes für die Lochtiefe um 40%. Der positive Einfluss des Wärmeflusses in Richtung vom Metall zur Lösung ergab im wesentlichen eine Verbesserung der Schutzwirkung des Passivfilms, da sich die verfügbare Menge Sauerstoff an der Metalloberfläche erhöhte. Weniger signifikant war der Effekt eines erhöhen Stofftransportes, der eine Akkumulation von Chlorid-Ionen an der Oberfläche erschwerte. [source] Anion effects on the stress corrosion cracking behaviour of aluminium alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2003R. Braun Spannungsrisskorrosion; Aluminiumlegierungen; Chloride; halogenfreie Anionen Abstract The stress corrosion cracking behaviour of plate material of the aluminium alloys 2024-T351, 8090-T8171, 7475-T651, and 7075-T7351 was investigated performing constant load tests. Short transverse tensile specimens were permanently immersed in aerated aqueous 0.6 M Na2Cl solutions with additions of Na2SO4, NaNO3, NaHCO3, NH4HCO3, Na2HPO4, Na2SO3 or Na2CO3. The concentration of the added salts was 0.06 M. The applied stress was 100 MPa, except with 7075-T7351 specimens, which were loaded at 300 MPa. Environment induced failure was not observed in neutral 0.6 M NaCl solution. The various salts added promoted intergranular stress corrosion cracking with the alloys 2024-T351, 8090-T8171, and 7475-T651. Threshold stresses were generally below 100 MPa. For 8090-T8171 exposed to chloride containing electrolytes with additions of sulfate, hydrogen phosphate, or sulfite, threshold stresses were approximately 100 MPa or higher. Similar results were obtained for 7475-T651 plate when immersed in chloride-hydrogen phosphate and chloride-carbonate solutions. Alloy 7075-T7351 was resistant against intergranular stress corrosion cracking. Specimens suffered pitting corrosion during immersion in the corrosive environments. Failure observed with 7075-T7351, in particular when exposed to the chloride-nitrate solution, was associated with reduction of cross-sectional area due to pitting and transgranular stress corrosion cracking. Anioneneinflüsse auf das Spannungsrisskorrosionsverhalten von Aluminiumlegierungen Das Spannungsrisskorrosionsverhalten von Plattenmaterial der Aluminiumlegierungen 2024-T351, 8090-T8171, 7475-T651 und 7075-T7351 wurde in kurzer Querrichtung untersucht. Dauertauchversuche wurden unter konstanter Belastung in wässrigen 0,6 M NaCl Lösungen mit 0,06 M Zusätzen von Na2SO4, NaNO3, NaHCO3, NH4HCO3, Na2HPO4, Na2SO3 oder Na2CO3 durchgeführt. Die aufgebrachte Spannung betrug 100 MPa, außer bei Zugproben der Legierung 7075-T7351, die mit 300 MPa belastet wurden. Während bei Auslagerung in neutraler Natriumchlorid-Lösung kein Versagen beobachtet wurde, lösten die zugegebenen Salze bei den Legierungen 2024-T351, 8090-T8171 und 7475-T651 interkristalline Spannungsrisskorrosion aus. Die kritischen Grenzspannungen lagen überwiegend unter 100 MPa. Bei Auslagerung in chloridhaltigen Elektrolyten mit beigegebenen Sulfat-, Hydrogenphosphat- oder Sulfitionen waren die kritischen Grenzspannungen für die Legierung 8090-T8171 etwas höher; sie hatten einen um 100 MPa oder darüber liegenden Wert. Gleiches galt für die Legierung 7475-T651 in chloridhaltigen Lösungen mit Hydrogenphosphat- oder Carbonatzusätzen. Plattenmaterial der Legierung 7075-T7351 war in den untersuchten Elektrolyten beständig gegen interkristalline Spannungsrisskorrosion. Die Proben wurden jedoch durch Lochkorrosion geschädigt. Querschnittsverminderung infolge Lochkorrosion und transkristalliner Spannungsrisskorrosion führten zum Versagen von Zugproben der Legierung 7075-T7351 innerhalb der maximalen Prüfdauer von 30 Tagen, insbesondere bei Auslagerung in eine chlorid-nitrathaltige Lösung. [source] Improving the properties of aluminium alloys by retrogression and reageingMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4 2003J. S. RobinsonArticle first published online: 11 APR 200 Abstract Retrogression and reageing heat treatments offer the potential of improved tensile properties in combination with greatly increased resistance to stress corrosion cracking. The potential of this technique is reviewed with respect to the current application in the European and North American Aerospace Industry. To illustrate the performance increase associated with RRA treatments, the stress corrosion cracking performance of the established aerospace plate and forging alloy 7010 has been evaluated using an alternate immersion constant load tensile type test (ECSS-Q-70-37A) Specimens were cut from a large aerospace rectilinear forging and tested in three different tempers, T652, T7452 and a retrogressed and reaged condition (RRA). In the T652 condition the material has been shown to be highly susceptible to intergranular corrosion and stress corrosion cracking. In the T7452 and RRA conditions 7010 showed much improved resistance to SCC but pitting corrosion resulted in failure of some specimens within the 30day requirement of the test standard. [source] A study of the relation between current oscillations and pittingCHINESE JOURNAL OF CHEMISTRY, Issue 10 2003Hou-Yi Ma Abstract Anodic polarization behaviors of iron in pure H2SO4 and three mixed acidic solutions, H2SO4 + NaCl, H2SO4 + NaNO3 and H2SO4+ NaCl + NaNO3, were investigated. The potentiodynamic sweep curves showed that the current densities rose and dropped irregularly in H2SO4 + NaCl solution at the more anodic potentials since the iron surface suffered pitting attack in the solution, but the pitting corrosion was inhibited effectively in the presence of nitrate ions. The surface morphological measurements indicated that pits appeared on the iron surface in H2SO4 + NaCl solution and only a few unobvious corrosion spots were observed in H2SO4 + NaCl + NaNO3 solution after the iron electrode was potentiostatically polarized at 1.3 V. The oscillatory properties of iron are associated with the susceptibility of the iron to pitting. In H2SO4 + NaCl solution, the regular potentiostatic current oscillations gradually evolved into the irregular current fluctuations due to occurrence of the pitting; whereas in H2SO4 + NaCl + NaNO3 solution, the current oscillations took place regularly, like the oscillatory behavior in the pure H2SO4 solution. Thus, when the higher the oscillatory frequency, the more irregular oscillatory process and the more sensitive to pitting iron occurred. [source] | ||||||||||