Localized Corrosion Resistance Research Articles

Evaluation of the localized corrosion resistance of 316 L austenitic and 430Ti ferritic stainless steel in aqueous chloride/sulphate media for application in petrochemical crude distillation units

Corrosion problems are frequently encountered in petrochemical crude distillation units due to increased levels of chlorides and sulfur anions from the constituents of crude oil. Potentiodynamic polarization test, potentiostatic measurement, open circuit potential measurement and optical microscopy characterization was performed on 316 L austenitic and 430Ti ferritic stainless steel in 3.5 M H2SO4 solution at 0%–6% NaCl concentration to study and compared their general and localized corrosion resistance for application in industrial operating conditions simulating petrochemical crude distillation unit. Results obtained showed 316 L is significantly more corrosion resistant than 430Ti with comparable corrosion rates of 0.222 mm y−1 and 3.174 mm y−1 (316 L), and 24.218 mm y−1 and 12.238 mm y−1 at 0% and 6% NaCl concentration. Corrosion potentials of 316 L showed dominant cathodic reaction mechanisms, shifting from −0.211 VAg/AgCl to −0.290 VAg/AgCl due to higher resistance to localized corrosion reactions. Values obtained for 430Ti showed active-passive behavior resulting from general surface deterioration coupled with localized corrosion reactions. Polarization plots of 316 L displayed extensive passivation behavior during potential scanning from 0%–5% NaCl concentration. Passivation was completely absent on 430Ti plots due to accelerated destruction of the protective oxide. The morphology of 430Ti severely deteriorated with visible corrosion pits due to depassivation of specific sites on the steel surface by SO42− and Cl- anions compared to the morphology of 316 L, which starkly contrasts due to higher resistance to surface oxidation. The extent of degradation on 316 L was superficial. The open circuit potential plots of 316 L were significantly electropositive compared to 430Ti which was electronegative.

On the pitting resistance of friction stir welded UNS S82441 lean duplex stainless steel

Friction stir welding has been considered as an alternative to fusion welding processes of stainless steels. A lean duplex stainless steel, grade UNS S82441, has been recently developed and is prone to localized corrosion, such as pitting when exposed to harsh conditions during use. However, pitting resistance of UNS S82441 has not been previously investigated. In this study, UNS S82441 lean duplex stainless steel was friction stir welded, and its microstructure and localized corrosion resistance were investigated by phase volumetric fraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests. The pitting resistance of each zone was investigated by polarization tests and by determining the critical pitting temperature. The results indicated that microstructural changes promoted by friction stir welding affected the pitting resistance of the lean duplex stainless steel.

Effectiveness of an intercritical heat-treatment on localized corrosion resistance at the microstructural boundaries of medium-carbon steels

The localized corrosion resistance at the microstructural boundaries of AISI 1045 carbon steels was accessed. Under KFM measurements, regions with low corrosion potentials were found at the pearlite colony boundary in the ferrite-pearlite structure and the prior austenite grain boundary in the martensite structure, and phosphorus was segregated in these regions. The localized corrosion resistance at these boundaries was improved via intercritical heat-treatment at 1023 K (the two-phase region of austenite and ferrite) after austenitizing, which may be attributable to the apparently homogenous dissolution of ferrite forming elements, such as phosphorus, in the ferrite phase during the treatment.

Understanding the general and localized corrosion mechanisms of Cr-containing steels in supercritical CO2-saturated aqueous environments

Effect of Cr content on corrosion of steel in static and dynamic supercritical CO2-saturated aqueous environments was investigated. The results showed that adding 3 wt% Cr aggravated general corrosion of the steel under static condition while inhibited the localized corrosion under dynamic condition, and 6.5Cr steel possessed the best general and localized corrosion resistance. The scale formation process on 3Cr steel contained two stages: the in-situ formation of initial amorphous Cr-rich layer consisted of Cr(OH)3 and FeCO3; the formation of outer FeCO3 crystalline layer as well as the transformation of initial amorphous layer to inner mixed layer, which consisted of amorphous FeCO3, Cr(OH)3 and a small number of crystalline FeCO3. The well localized corrosion resistance of Cr-containing steel attributed to the in-situ formation of initial amorphous Cr-rich layer.

Evaluación ultrasónica de las fases formadas de un acero inoxidable dúplex 2205 tratado térmicamente a 750 °C y su comportamiento frente a la corrosión

El presente estudio evalúa el comportamiento de las variables ultrasónicas en probetas de acero inoxidable dúplex 2205 (UNS31803/ EN1.4462), tratadas térmicamente a 750 °C durante distintos tiempos, con el objetivo de promover la precipitación de fases secundarias, chi (χ) y sigma (σ). Se estudió la evolución microestructural mediante microscopía óptica y electrónica de barrido, y utilizando la técnica ultrasónica pulso eco de contacto. Finalmente, se realizaron ensayos electroquímicos con el objetivo de evaluar la resistencia a la corrosión. Los resultados revelaron que a medida que aumenta el tiempo de tratamiento térmico se produce un incremento de las cantidades relativas de fases χ y σ a lo largo de las interfases ferrita/ferrita y ferrita/austenita, especialmente hacia el interior del grano ferrítico. La velocidad de onda longitudinal y el coeficiente de atenuación presentaron una tendencia que coincide con los cambios microestructurales generados por efecto del tratamiento térmico. La evaluación electroquímica reveló una alta resistencia a la corrosión uniforme. No obstante, se observó una correlación entre el aumento del tiempo de tratamiento térmico con la pérdida de la resistencia a la corrosión localizada.

Local corrosion of austenitic steels and alloys for heat exchanger tubes of nuclear power stations steam generators

Elaboration of modern domestic structural materials with increased corrosion resistance in contact with advanced heatcarriers of future reactor plants is an important problem at development of innovation projects of nuclear power engineering. Heatexchanging tubes are the critical components, which influence on the safety and reliability of steam generators operation. Corrosion properties of non-stabilized nitrogen-containing corrosion resistant steels of austenite class after cold deformation, thermal treatment and long-term thermal aging studied. It was shown, that silicon introducing into chrome-nickel steel, alloyed by nitrogen and molybdenum, results in increasing of its resistance against local kinds of corrosion and equated it on resistance against intercrystallite and pitting corrosion with particularly low-carbon steels and alloys. But the experimental 03Х18Н13С2АМ2ВФБР-Ш low carbon micro-alloyed steel, proposed for operation at a heat-carrier temperature of 450–500 о С, in the first version had a tendency to a decrease of resistance against local corrosion and impact resistance after long-term thermal aging at temperatures of 360 о С and higher. At present specifying of technological parameters of production and balanced alloying element content takes place, which prevents heat exchanging tubes properties degradation. Steel 03Х17Н13С2АМ2 which has higher resistance against local corrosion and strength comparing with 316LN and 08Х18Н10Т grades, can be taken as a candidate material for production of heat-exchanging tubes of steam generators of nuclear power stations having power reactors of water-water type. The new 03Х17Н9АС2 steel, resistant against inter-crystallite corrosion in high-oxidizing media, was proposed for tests of its operation under conditions of contact with lead heat-carriers instead of 10Х15Н9С3Б1-Ш (ЭП 302-Ш) steel.

Multi-level self-healing ability of shape memory polyurethane coating with microcapsules by induction heating

A shape-memory polyurethane (SMPU) was designed and used in the field of self-healing coating due to the capability to recover to its permanent shape in a predefined way. This technique could be modified by two different kinds of microcapsules to improve the localized corrosion resistance of healed coating by induction heating. For this purpose, the SMPU was synthesized by solvent polymerization using isophorone diisocyanate (IPDI) as hard segments and polycaprolactone (PCL) as soft segments. The results obtained from dynamic mechanical thermal analysis (DMTA) displayed a phase-separation structure, which is consistent with the results of 1H NMR characterization. The repeatable shape-memory measurements further demonstrated that the shape recovery of SMPU is above 75%. Appending some microcapsules embedding Alodine 5200 and a heat-generating agent into SMPU, adhesion of aluminum substrate with healed coatings could be greatly improved, as well as corrosion resistance. In addition, the heat released from the exothermic reaction between the heat-generating agent and oxygen are supplied to the shape-memory recovery of polyurethane. It was clear that the corrosion resistance evaluations (by electrochemical impedance spectroscopy and scanning Kelvin probe measurements) confirm that the modified shape memory polyurethane have comparable healing efficiencies (η = 77.3%) and excellent self-healing performances.

Effect of surface treatments on the localized corrosion resistance of the AA2198‐T8 aluminum lithium alloy welded by FSW process

In this work, the effect of eight types of surface treatments on the corrosion resistance of friction stir welded samples of an AA2198‐T8 Al‐Cu‐Li alloy were tested and compared in an attempt to find suitable alternatives to toxic and carcinogenic hexavalent chromium treatments. All the samples were anodized and subjected to different post‐anodizing treatments. The post‐anodizing treatments were (1) hydrothermal treatment in Ce (NO3)3 6H2O solution; (2) hydrothermal treatment in Ce (NO3)3 6H2O solution with H2O2; (3) hydrothermal treatment in boiling water; (4) hexavalent chromium conversion coating; and (5) immersion in BTSE (bis‐1,2‐(triethoxysilyl) ethane. The corrosion resistance of the treated samples was evaluated by immersion tests in sodium chloride solution (0.1 mol L−1 NaCl) and electrochemical impedance spectroscopy (EIS) of the friction stir weldment. The results showed that among the alternative treatments, the Ce‐containing solutions presented the best corrosion resistance, especially when used without peroxide.

Monitoring localized corrosion of Inconel 82 weld overlay on 304L SS weld by electrochemical noise

The manuscript presents the results from the electrochemical noise (EN) monitoring of Inconel 82 weld overlay on Type 304L stainless steel (SS) weld in 0.01M FeCl3. The microstructure of the weld overlay obtained from optical and scanning electron microscopy (SEM) showed an austenite structure, containing equiaxed dendrites and secondary phases at the interdendritic region. Energy dispersive spectroscopy (EDS) attached to SEM revealed the secondary phases to be Nb rich Laves phase. The electrochemical potential noise was monitored using a three identical electrode configuration. The acquired signals were detrended, and wavelet analysis was employed to encode useful information from the noise transients. Visual examination of the potential noise-time record contained distinct high amplitude transients typical of localized corrosion attack. The energy distribution plots (EDP) of the potential noise derived from wavelet analysis depicted maximum relative energy on D6-D8 crystals, which represent large time scale events such as those occurring from localized attacks. Also, repassivation events too could be divulged from the potential EDP. The micrographs of the post electrochemical noise experimented specimens revealed the occurrence of localized attacks along the interdendritic region and none inside the dendritic cores. The presence of secondary phases along the interdendritic regions was found to be detrimental in chloride medium, imparting inferior localized corrosion resistance to the weld overlay.

Enhancement of corrosion resistance to sterilization stages of a biomedical grade AISI 316L stainless steel by means of low-temperature machining

Austenitic stainless steels are currently used for the manufacture of reusable medical instruments, thanks to their combination of elevated strength, corrosion resistance, biocompatibility and low cost. However, during their service life, they are subjected to repeated sterilization cycles, which lead to the loosening of the surface oxide stability and, as a consequence, the decrease of their durability.In the present study, the in-service corrosion behaviour of the AISI 316L stainless steel was investigated after being machined using two low-temperature coolants, namely Liquid Nitrogen (LN2) and gaseous Nitrogen (N2) cooled by LN2 to -100°C, as well as using a conventional cutting fluid.Results showed that the AISI 316L microstructure near the machined surface was significantly affected by the machining cooling strategies with the generation of a hardened and more compressed layer when low-temperature coolants were used. Such surface integrity enhancements contributed to improve both the general and localized corrosion resistance to sterilization stages. From this basis, machining using low temperature coolants can be considered a suitable technique to manufacture medical devices of increased durability.

Evaluation of Corrosion Resistance of Alloy 625 Obtained by Laser Powder Bed Fusion

The aim of this work is to compare the corrosion resistance of nickel-base Alloy 625 (UNS N06625) produced by laser powder bed fusion with that obtained via conventional casting and hot working. Cyclic potentiodynamic polarization and potentiostatic tests were performed in order to evaluate the corrosion resistance of the differently manufactured alloys according to ASTM G5, and in NaCl 0.6 M solution at pH 7 and pH 3, at 40°C. The electrochemical characterization was carried out on the as-produced alloy and after annealing at 980°C for 32 minutes (according to ASTM B446). This heat treatment was also performed on the commercial hot worked alloy. Two surface conditions, namely as-built and polished surfaces, were investigated on the additive manufactured specimens. The alloy produced by laser powder bed fusion was not susceptible to pitting in the considered environments and had a good localized corrosion resistance, slightly higher than that of traditional wrought material. However, as predicted, the corrosion resistance of the as-built surfaces increased after mechanical polishing. The correlation between the corrosion performance and microstructure is also discussed.

Corrosion of Platinum Nanocoatings Thin Films Deposited by Sputtering Deposition Method for Medical Applications

Platinum (Pt.) thin films have been deposited by Magnetron Sputtering Deposition method with 25 nm and 50 nm thickness by used power RF for deposited 5 nm Titanium (Ti) firstly then used DC for deposited Platinum (Pt) on Ni-Cr alloy substrate. SEM/EDX and Ellipsometry Spectroscopy have been used to investigate the morphology, element analysis, nanothickness and roughness of the thin films respectively. Electrochemical corrosion tests have been used to analyze the localized corrosion resistance by used cyclic polarization, Tafel extrapolation and open circuit potential (o.c.p) methods on artificial saliva solution at 37 ±1 oC. The results show the ability to deposit 5 nm of Ti before deposited of Pt. film to improve the adhesive of the films, nanostructure morphology of the Pt. film without defect or microcracks, nanocoatings thickness of Pt. film, and high localized corrosion resistance in artificial saliva corrosive media.

Use of composition profiles near sigma phase for assessment of localized corrosion resistance in a duplex stainless steel

Pitting corrosion potential of a UNS S31803 duplex stainless steel (DSS) heat treated between 750 °C and 850 °C at different aging times was related to the extent of the Cr- and Mo-depleted areas at sigma-ferrite and sigma-austenite interfaces, estimated using DICTRA® simulations. It is possible to describe the sigma formation kinetics using a model that assumes a spherical region of austenite, with radius equivalent to the mean intercept of austenite islands, surrounded by ferrite. Composition profiles at sigma-ferrite and sigma-austenite interfaces were calculated, allowing the evaluation of the degree of depletion in Cr and Mo at sigma interfaces. There is a reduction of pitting potential with increase of the degree of depletion, characterized as the weighted sum of depleted areas in Cr and Mo composition profiles, making possible the assessment of the localized corrosion resistance of aged DSS through simulation of sigma phase formation.

Effect of SO42− and Cl− anionic attack on the localized corrosion resistance and morphology of 409 ferritic stainless steel

Abstract The corrosion polarization behaviour and optical characterization of 409 ferritic stainless steel (SS409) in 0.25 M H2SO4 (at specific NaCl concentration), 0.375 M H2SO4 and 0.5 M H2SO4 was evaluated with potentiodynamic polarization technique, open circuit potential measurement and optical microscopy characterization. Results showed the SS409 corrosion rate is proportional to the concentration of SO42− and Cl− anions in the electrolyte. At 0.25 M H2SO4, SS409 corroded at a rate of 7.29 mm/y; addition of 0.125% NaCl accelerated the corrosion rate to 16.75 mm/y coupled with a corresponding increase in corrosion current density from 6.71 × 10−4 Acm2 to 3.08 × 10−3 Acm2. Further increase in Cl− anion concentration to 0.75% NaCl increased the corrosion rate to 19.49 mm/y. At 0.25 M H2SO4 the pitting current value is 1 × 10−4 A, this value increased to 1.03 × 10−4 A at 0.25 M H2SO4 (0.125% NaCl) and 8.40 × 10−4 A at 0.25 M H2SO4 (0.5% NaCl). Beyond 0.5% NaCl, passivation behavior was completely absent. Intergranular cracks, large macro-pits and numerous micro-pits were observed for SS409 from 0.25 M H2SO4 (0.75% NaCl) due to Cr depletion and dissolution of inclusions. SS409 from 0.5 M H2SO4 showed the presence of deepened intergranular cracks, shallow pits and a deteriorated surface due to the action of SO42− anions. The morphology of SS409 in 0.25 M H2SO4 + 0.125% NaCl showed slight deterioration in addition to enlarged micro-pits.

Electrochemical analysis of the pitting corrosion inhibition performance of essential oil extracts on P4 low alloy steel in H2SO4 solution

The inhibition effect of the synergistic combination of essential oil extract (jojoba and lavender oil) on the localized corrosion resistance of P4 low grade alloy steel in 1.5 M H2SO4 solution was studied with potentiodynamic polarization, ATF-FTIR spectroscopy, optical microscopy and open circuit potential measurement. The oil extracts significantly influenced the mechanism of corrosion reaction on the steel with highest and lowest inhibition efficiency values of 90.28% and 77.76%. Anodic potential shift with respect to the blank steel dominated the redox mechanism due to surface coverage of the inhibitor molecules. Passivation range and pitting potential of the steel significantly increased during potential scanning from 1.096 VAg/AgCl and 0.766 VAg/AgCl at 1% inhibitor concentration to 1.118 VAg/AgCl and 1.035 VAg/AgCl at 5% concentration. Identified (ATF-FTIR spectroscopy) functional groups within oil extracts compound completely adsorbed onto the steel according to Langmuir adsorption isotherm (correlation coefficient of 0.9642). Thermodynamic derivations confirmed physisorption adsorption mechanism. Severe surface deterioration and enlarged corrosion pits were visible on the morphology of the uninhibited steelwhich significantly contrasts the morphology of the inhibited steel.

Influence of dynamic recrystallization and shear banding on the localized corrosion of severely deformed Al–Mg–Si alloy

The low intergranular corrosion resistance of extruded aluminum alloys is a limiting criteria for several applications. In this work, we investigated the effects of shear deformation, dynamic recrystallization and peak aging on the corrosion susceptibility of an AA6061 alloy up to seven ECAP passes following route Bc. We assessed intergranular corrosion susceptibility using the standard ISO test 11846 (Method B). Our results show that dynamic recrystallization improves the localized corrosion resistance of severely deformed AA6061 by reducing the fraction of shear bands in the material. We found a clear difference in surface reactivity between the recrystallized grains inside and outside the shear bands, suggesting that in this material grain-stored energy influences corrosion more than grain boundary precipitation. In parallel, we characterized the degradation of conventionally extruded AA6061-T6. The results reveal that shear deformation is a promising process for extruded aluminum alloys with improved strength and intergranular corrosion resistance.

Effect of heat treatment processes on the localized corrosion resistance of austenitic stainless steel type 301 in chloride/sulphate solution

Abstract The effect of quenching and annealing heat treatment on the localized corrosion resistance of 301 austenitic steel in 2 M H2SO4/0.75%–2.25% NaCl was studied by potentiodynamic polarization, open circuit potential measurement and optical microscopy analysis. The corrosion rate of the quenched, annealed and untreated steel increased with increase in NaCl concentration. The quenched steel had the lowest corrosion rate values, followed by the annealed steel. Variation in Cl− ion concentration had no significant effect on the pitting corrosion resistance and passivation behavior of the quenched steel, though increase in current density at breakdown potential was observed at higher Cl− ion concentration. The untreated steel experienced significant reduction and collapse of it passive film after 1.5% NaCl. Delayed passivation occurred on the annealed steel following metastable pitting lead to short passivation range. Open circuit potential measurement showed large cathodic shift of the corrosion potential for the quenched steel, compared to the anodic shift for the untreated steel. Optical microscopic images showed a deteriorated morphology and the presence of different phases for the untreated 301SS. Intergranular cracks were observed on the annealed and quenched 301SS while corrosion pits was observed on the annealed 301SS.

The Effect of Liquid Nitriding on the Corrosion Resistance of AISI 304 Austenitic Stainless Steel in H2S Environments

AISI 304 austenitic stainless steel was low-temperature liquid nitrided in a molten salt bath at 703 K for 8 hours, which produced a 3-layered structure consisting of a top oxide layer, an intermediate nitrogen-rich layer and a bottom carbon-rich layer. The effect of nitriding on its corrosion resistance was investigated in a H2S environment. The corrosion rate of the untreated sample is about 3.3 times that of the nitrided sample after H2S corrosion. Corrosion pits can be clearly observed on the surface of the untreated sample, while the nitrided sample surface remained relatively intact. Both the oxide layer and the nitrogen-rich layer can help reduce the hydrogen permeation, which is beneficial for combating hydrogen embrittlement. The corrosion products mainly consisted of oxides, hydroxides, and sulfates. The nitrided layers can serve as a barrier to corrosion, thus preventing the corrosion of the substrate material. Active nitrogen in the nitrided layer reacts with H ions to form NH4+, which effectively prevents further acidification of the local area and inhibits the occurrence of pitting corrosion and the dissolution rate of the metal in the etching hole, thus improving the local corrosion resistance of the stainless steel.

Enhanced Corrosion Resistance of SiC<sub>p</sub>/ 2009 Al by Cerium and Lanthanum Conversion Treatment

The present study investigates the effect of lanthanide chlorides conversion coatings on the corrosion response of the 2009 Al alloy and SiCp reinforced 2009 Al MMCs. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies showed that the localized corrosion resistance increased after treatments with solutions having various combinations of CeCl3.7H2O and LaCl3.7H2O, with maximum increase noticed for 5000ppm CeCl3.7H2O. It was found that the protection degree effect obtained under similar coating conditions for 25 vol.% SiCp/2009 Al was relatively higher than 15vol.% SiCp/ 2009 Al MMC, but both of them were less than that of the unreinforced alloy. Scanning electron microscopy (SEM) accompanied with energy dispersive spectroscopy (EDS) analysis revealed the deposition of Ce and/ or La oxides/ hydroxides on cathodic intermetallics/ SiCp and the existence of crevices at the SiCp/ matrix interfaces. X-ray photoelectron spectroscopy (XPS) results indicated that Ce was incorporated as Ce3+ and Ce4+ species in the coatings.

Corrosion Characterization of AISI 304 Stainless Steel Filter

Pre-sintering for removal of lubricants is one of the most important steps in processing of powder metallurgy materials to achieve corrosion resistance. This is often the most neglected step in the sintering process. Incomplete removal of these organic compounds may result in sensitization of sintered parts. The aim of this study is to investigate the effect of lubricant removal process on the corrosion resistance of sintered AISI 304 L stainless steel filters. Pre-sintering was carried out at 450° C and sintering at 1150° C. As lubricant, 1% wax was used. The corrosion resistance of sintered samples was evaluated by polarization and tests, optical and scanning electron microscopy. The results showed that lubricant removal was not complete and during sintering sensitization of the stainless steel occurred decreasing the localized corrosion resistance of the stainless steel.