Pitting Of Stainless Steel Research Articles

Technical Note:Use of Potentiodynamic Polarization to Assess Pitting of Stainless Steels by Sulfate-Reducing Bacteria

The electronic properties of passive films on Fe-Cr alloys were determined by the photoelectrochemical technique. Measurement of the flat band potential for the passive films on the different alloys indicated that the film is doped in- creasingly n-type as the Cr concentration in the base alloy is increased. This doping is due to a Cr oxide with Cr in the 4+ or 6+ valence state. The concentration of this doping species increases as the concentration of Cr in the Fe-Cr alloy is increased. The n-type doping has the effect of de- creasing the number of oxygen vacancies in the Fe-Cr passive film. Since oxygen vacancies are the mobile point defect species in the Fe-Cr passive film, decreasing this species decreases the oxygen vacancy flux and ultimately the passive film growth kinetics. The contribution of film dis- solution and cation transmission through the passive film was also analyzed. Film dissolution was shown to be the major contribution to the passive current density.

Susceptibility to Crevice Corrosion and Metastable Pitting of Stainless Steels

Susceptibility to Crevice Corrosion and Metastable Pitting of Stainless Steels

Effect of the Nickel Content in the Pitting of Stainless Steels in Low Chloride and Thiosulfate Solutions

Abstract The effect of the nickel content on the pitting resistance of AISI 304 stainless steel (SS) and Alloys 800 and 600 in chloride-thiosulfate solutions was investigated using two techniques, ...

Die Schweißverbindung im chemischen Apparatebau und ihr Korrosionsverhalten im Betrieb

AbstractWelded joints in the construction of chemical equipment and their corrosion behaviour in operation. This contribution surveys the possible kinds of corrosion damage to fully austenitic welded stainless steels in the presence of heat cracks. Such cracks can be avoided by the presence of ß‐ferrite. However, under certain conditions of attack ß‐ferrite can cause selective corrosion. That is especially so on decomposition of ß‐ferrite. Intercrystalline susceptibility in the zone of thermal influence can be avoided by use of stabilized or low‐carbon steels. The tendency to undergo granular disintegration increases with increasing nickel content. The resistance to pitting of stainless steels is reduced at places bearing tempering colour layers. Such layers should therefore be avoided in welding or they should be removed if they persist in formation.

Electrochemical Behavior of AISI 304 Stainless Steel: Corrosion, Passivity, and Pitting in Alcohols + H2SO4Mixtures

Abstract The electrochemical behavior of austenitic AISI 304 stainless steel (SS) in alcoholic solutions (ethanol, iso-propanol, and t-butanol) containing different concentrations of sulfuric acid (0.001 to 1.0 M) has been investigated using potentiostatic and potentiodynamic techniques. Frequent active-passive transitions are observed and the critical current density (CD) for passivity is found to be dependent on the concentration of acid in ethanol, iso-propanol, and t-butanol solutions. Scanning electron microscopy (SEM) examination of electrode surfaces after the polarization studies showed severe pitting of SS in high concentrations of acid in ethanol, while etch type pitting is found in the case of iso-propanol and t-butanol containing respective concentrations of acid. The different corrosion parameters and pitting potentials have been evaluated. Repassivation has also been observed. The protection potential tended to shift in the noble direction as the scanning rate decreased.

Metastable Pitting of Stainless Steel

Abstract Current transients resulting from metastabie pitting events on stainless steel at potentials below the pitting potential are studied. Metastable pits are covered during growth and exhibit a constant current density. Rupture of the cover during metastable growth leads to repassivation of the pit. If a salt film precipitates on the pit surface before the cover ruptures, pit growth is stabilized. The kinetic factors hindering the replacement of a passive film by a salt film are discussed.

ChemInform Abstract: A Micro‐Electrode Study of the Nitrate Effect on Pitting of Stainless Steels.

AbstractNO3‐ causes abrupt passivation during diffusion‐controlled dissolution across a salt film formed on the 50 μm stainless steel micro‐electrode at higher potentials, whereas no passivation of salt‐free surfaces is observed.

Ineffective Cleaning of Polysulfone Ultrafiltration Membrane Systems and Corrosion by Bisulfite Used as a Sanitizer

Bisulfite solution was used to sanitize polysulphone ultrafiltration membranes. The ultrafiltration system consisted of a 380-L jacketed vat with agitator, prefilter, centrifugal pump, and two polysulphone ultrafiltration membranes in parallel with valves and pressure gauges before and after the membranes. The system was soiled by recycling 380L of sweet whey (40°C) for 2.0h followed by concentrating (by diverting permeate steam to drain) whey for .5h. The cleaning cycle consisted of acid cleaner (.5h, 40°C) followed by enzyme cleaner (10.0h, 40°C) and rinsing (2.0h, 40°C). A .2% sodium metabisulfite solution was circulated for 5min and the ultrafiltration unit left idle overnight. Swabs and rinse water samples were taken immediately after soiling, after cleaning, and the next morning to check sanitizing. Samples were plated on plate count agar and potato glucose agar (acidified with tartaric acid to pH 3.5) to determine numbers of bacteria, yeasts, and molds. Effectiveness of bisulfite was pH dependent. At pH 4.7, bisulfite solution was ineffective in controlling microorganisms and at pH 3.5, bisulfite was microstatic. Compared with trials with Antibac B (30ppm Cl), bisulfite (pH 3.5) was similar for controlling bacteria, yeasts, and molds. Extensive corrosion of stainless steel housings was apparent following long-term contact (2 wk) with bisulfite solution. Laboratory trials using stainless steel fittings, plates, and rubber gaskets found that extensive corrosion and pitting of stainless steel and leaching of gaskets by bisulfite solution required several conditions: low pH, exposure to bisulfite vapors, use of 304 type stainless steel, and oxygen. Intermittent or continuous exposure to acidic bisulfite vapors resulted in corrosion. Antibac B (30ppm Cl) did not show similar corrosion or leaching effects.

A micro-electrode study of the nitrate effect on pitting of stainless steels

Stainless steel micro-electrodes have been used to measure the effect of nitrate on pitting dissolution in sodium chloride solutions. No inhibiting effect of nitrate on active (film-free) dissolution is observed, even when the metal salt solution in the pit is supersaturated. However, nitrate causes abrupt passivation during diffusion-controlled dissolution across a salt film formed at higher potentials. The passivation potential of the salt-covered surface is highly reproducible and decreases with increasing ( (NO 3 − (Cl −) ratio. This behaviour is probably related to redox reactions or electrochemical reduction of nitrate within the salt film, coupled with an increase in the pH of the salt environment with potential; a related observation in pure NaCl solutions is that local passivation-reactivation events occur under the salt film above a critical potential.

Growth and Repassivation of Single Corrosion Pits in Stainless Steel

Abstract Single pits were produced in AISI 304 stainless steel using a neutral 1M sodium chloride solution with 0.04M sodium thiosulfate. The dependence of pit growth kinetics on potential was meas...

Protection potentials for pitting of stainless steel in neutral chloride solutions

Protection potentials for pitting of stainless steel in neutral chloride solutions

The pitting of stainless steel in water-containing methanol

The behavior of an austenitic 18Cr11Ni0.5Ti stainless steel during anodic polarization in methanol and in mixtures of methanol with water was studied. In nearly all anhydrous methanol (0.04 wt% H 2O) anodically polarized steel underwent pitting. Generally, increased water contents shifted the pitting into more positive values. At high contents of water (above 8 M) pitting did not occur. For the same experiments performed in the same environment the pitting potential is not a constant value. The pitting probability vs potential in methanolic-water solutions was evaluated.

Airborne contaminants and the pitting of stainless steels in the atmosphere

The present work was undertaken with the aim of determining the factors that lead to pitting of stainless steels in the atmosphere. Specimens of Types 430, 304 and 316 stainless steels were inoculated with the solid contaminants alumina, carbon, sodium chloride, ammonium sulphate and ferrous sulphate and exposed to humid atmospheres containing high (100–3000 ppm) and low (0–0.15 ppm) levels of sulphur dioxide. A synergistic effect was found with sulphur dioxide and sodium chloride; in the absence of sulphur dioxide little pitting was found with any of the contaminants investigated, including sodium chloride.

Role of Inclusions in the Atmospheric Pitting of Stainless Steel

The fate of non-metallic inclusions in stainless steels during various periods of exposure to an industrial atmosphere was determined photographically. In addition, the rate of pit propagation was also followed. The results showed that whilst many inclusions are lost from Type 430 steel the holes left by them do not necessarily propagate as pits. It was also found that pits grow to their maximum size in a relatively short time and that increasing exposure time leads to an increase in the number of pits formed. No pitting was observed on Types 304 and 316 steel during the same exposure period of 27 months.

Role of Inclusions in the Atmospheric Pitting of Stainless Steel

Role of Inclusions in the Atmospheric Pitting of Stainless Steel

The effect of microstructure on pitting of stainless steel

Using temperature as a pitting criterion, a critical pitting temperature has been defined for molybdenum-bearing austenitic stainless steels containing nominally 18% Cr which provides a quantitative measure of their pitting resistance. Single phase alloys had increasing resistance to pit initiation with increasing Mo content while the performance of duplex alloys was limited by the presence of Mo-rich second phase. The effects of heat-treatment and alloy additions on microstructure and pitting resistance are discussed Résumé Une température critique de piqûre a été définie pour des aciers austénitiques au molybdène contenant 18% de chrome. Ceci fournit une mesure quantitative de leur résistance à la piqûre.La teneur en molybdène augmente la résistance au début de piqûre alors que la performance des alliages duplex est limitée par la présence d'une deuxième phase riche en molybdène.

The effect of microstructure on pitting of stainless steel

Using temperature as a pitting criterion, a critical pitting temperature has been defined for molybdenum-bearing austenitic stainless steels containing nominally 18% Cr which provides a quantitative measure of their pitting resistance. Single phase alloys had increasing resistance to pit initiation with increasing Mo content while the performance of duplex alloys was limited by the presence of Mo-rich second phase. The effects of heat-treatment and alloy additions on microstructure and pitting resistance are discussed Résumé Une température critique de piqûre a été définie pour des aciers austénitiques au molybdène contenant 18% de chrome. Ceci fournit une mesure quantitative de leur résistance à la piqûre.La teneur en molybdène augmente la résistance au début de piqûre alors que la performance des alliages duplex est limitée par la présence d'une deuxième phase riche en molybdène.

On the Nature of Films over Corrosion Pits in Stainless Steel

not Available.

Effect of temperature on the kinetics of development of pits in stainless steel in 0·5n NaCl + 0· in H 2SO 4 solution

The kinetics of pitting of Cr18-Nil2-Mo2-Ti stainless steel in 0·5N NaCl + O·1N H 2SO 4 solution was studied by the potentiostatic method using two series of measurements. In the first series the pits were growing at 860 mV at 20, 35 and 50°, and in the second series at the same temperatures but at potentials close to the nucleation potentials (860, 660 and 440 mV respectively). In both series of measurements the exponential coefficients of increase of the current b, pitdiameter b d and pit depth b λ, were decreasing with increasing temperature, which was due to the accelerating effect of temperature on the decrease of current density in the pits during their development. In the first series of measurements the decrease of the exponential coefficients was greater as aresult of a large number of pits that are formed at elevated temperatures in these conditions.

The role of K shell ionization in the formation of F centers in alkali halides at 78° K I. KBr

Stainless steels generally have extremely good corrosion resistance, but are still susceptible to pitting corrosion. As a result, corrosion scales can form on the surface of stainless steel after extended exposure to aggressive aqueous environments. Corrosion scales play an important role in affecting water quality. These research results showed that interior regions of stainless steel corrosion scales have a high percentage of chromium phases. We reveal the morphology, micro-structure and physicochemical characteristics of stainless steel corrosion scales. Stainless steel corrosion scale is identified as a podiform chromite deposit according to these characteristics, which is unlike deposit formed during iron corrosion. A conceptual model to explain the formation and growth of stainless steel corrosion scale is proposed based on its composition and structure. The scale growth process involves pitting corrosion on the stainless steel surface and the consecutive generation and homogeneous deposition of corrosion products, which is governed by a series of chemical and electrochemical reactions. This model shows the role of corrosion scales in the mechanism of iron and chromium release from pitting corroded stainless steel materials. The formation of corrosion scale is strongly related to water quality parameters. The presence of HClO results in higher ferric content inside the scales. Cl− and SO42 − ions in reclaimed water play an important role in corrosion pitting of stainless steel and promote the formation of scales.