Corrosion Behavior Of Stainless Steel Research Articles

The Use of Polarization Curves to Evaluate Stainless Steels in Highly Oxidizing Solutions

The corrosion behaviour of stainless steels in very oxidizing solution with redox-potential + 1200 mV vs. SCE was studied by corrosion potential and anodic polarization measurements. Some weight loss immersion tests were also carried out in order to verify the results of the electrochemical tests. Because the polarization curves and corrosion potentials for stainless steels give only a rough estimate of the corrosion behaviour, polarization curves and corrosion potentials were also measured for pure chromium, molybdenum, nickel and platinum as well as carbon steel in order to estimate the effect of alloying elements and the possibility of other chemical reactions in the transpassive region. It was found that this combination of measurements is a reliable method to evaluate the corrosion behaviour of stainless steels in dissolved ozone-containing solutions. .

Corrosion Behavior of Stainless Steel in Nitric Acid Solution under Gamma-ray Irradiation

Influence of the irradiation on the corrosion behavior of stainless steel (type 304ULC) in boiling nitric acid solution was examined by using 60Co γ-ray source. It was found from the experimental results that radiolysis products of nitric acid (NOx, HNO2) resulted from the γ-ray irradiation made the environment in the bulk solution more reducing one. On the other hand, corrosion rate of 304ULC was slightly enhanced by the irradiation, which being trivial from the engineering viewpoint. From the result of an AC impedance measurement, this corrosion enhancement was inferred as caused by an enhancement in the current across the passive film by the γ-ray irradiation on the stainless steel surfaces.

The ennoblement of stainless steels in seawater: a likely explanation coming from the field

The corrosion behaviour of stainless steel in marine environments is heavily affected by the biofilm settlement on its surfaces. Cathodic reaction kinetics is modified by the biological layer through a depolarization effect of unknown origin. Many possible mechanisms have been proposed in literature to explain this phenomenum but none of them has ever received exhaustive experimental validation. This paper focuses attention on one of the proposed mechanisms which attributes biofilm action to catalytic effects coming from enzymes entrapped in the Extracellular Polymeric Sustances of biofilms. The mechanism is discussed, on the basis of the latest knowledge of the structure and composition of marine biofilms, and strongly validated by new experimental results, coming from field tests carried out at ICMM’s marine station in Genoa. The electrochemical consequences of biofilms treatment with sodium azide and glutaraldehyde (GA) are discussed and explained in conformity with the enzyme theory above mentioned.

Effects of Cold Work, Sensitization Treatment, and the Combination on Corrosion Behavior of Stainless Steels in Nitric Acid

Abstract Corrosion behavior of two stainless steels (SS) was investigated in nitric acid (HNO3) for the effect of cold work (CW), sensitization heat treatment (Sens.), and a combination (CW + Sens.). The corrosion rate of the solution-treated type 304 SS (UNS S30400) with extra-low carbon (type 304ELC SS [UNS S30403]) increased with time and reached constant values after 1,000 h of immersion. However, constant corrosion rates were obtained for 25% Cr-20% Ni-Nb (type 310Nb SS [UNS S31040]) from the initial stage of immersion. CW mitigated corrosion of the solution-treated SS. The effect of CW was different on the two types of SS, with the sensitization heat-treated type 304ELC SS showing higher corrosion rates and type 310Nb SS lower corrosion rates by CW. Corrosion resistance of type 310Nb SS was superior to type 304ELC SS after all treatments. Chromium concentration of the sensitization-treated type 304ELC SS was lower in the grain-boundary region than of the solution-treated one, although no chromium ca...

Corrosion Behavior of Stainless Steel in Nitric Acid Solution under Gamma-ray Irradiation.

Influence of the irradiation on the corrosion behavior of stainless steel (type 304ULC) in boiling nitric acid solution was examined by using 60Co γ-ray source. It was found from the experimental results that radiolysis products of nitric acid (NOx, HNO2) resulted from the γ-ray irradiation made the environment in the bulk solution more reducing one. On the other hand, corrosion rate of 304ULC was slightly enhanced by the irradiation, which being trivial from the engineering viewpoint. From the result of an AC impedance measurement, this corrosion enhancement was inferred as caused by an enhancement in the current across the passive film by the γ-ray irradiation on the stainless steel surfaces.

低pH<sub>-</sub>高Cl<sup>-</sup>濃度溶液中におけるステンレス鋼の腐食挙動に及ぼす窒素の影響

低pH<sub>-</sub>高Cl<sup>-</sup>濃度溶液中におけるステンレス鋼の腐食挙動に及ぼす窒素の影響

Manganese biofouling and the corrosion behavior of stainless steel

Manganese- and iron-oxidizing bacteria (MFOB) are widely implicated in microbially influenced corrosion, often in association with sulfate-reducing bacteria (SRB). Traditionally MFOB have been assigned a passive role in the corrosion process, promoting differential aeration cells, and providing oxygen depleted conditions conducive to the growth and corrosive attack of SRB. Recent work, summarized in this article, demonstrates that manganese biofouling alters the electrochemical behavior of stainless steel (SS), and suggests that MFOB are more active in localized corrosion than traditionally held. The paper discusses the chemistry and potentially corrosive impact of manganese and iron oxides on SS, explores the possible relationship between MFOB and SRB, and proposes a model to describe the synergistic influence these organisms may exert in the corrosion process.

An assessment of the corrosion behaviour of high-grade alloys in seawater at elevated temperature and under a high velocity impinging flow

Laboratory experiments were carried out to investigate the effect of elevated temperature (up to 60 °C) and a high velocity impinging flow on the corrosion behaviour of stainless steels and related Ni-base and Co-base alloys. DC-electrochemical techniques were employed in conjunction with microscopy to determine the extent and mechanisms of attack under the severe imposed conditions. Experiments demonstrated the clear effect of increased temperature in facilitating premature breakdown of passivity on all materials and the effect of the high velocity impinging flow was to further shift the passivity breakdown potential to more active values but not necessarily to result in greater depth of attack. In addition, the study has indicated that the relative resistances of the different materials to attack under static, ambient temperature conditions is altered significantly when they are subjected to elevated temperatures and/or high velocity seawater impingement.

Influence of nitrogen and manganese on localized Corrosion behaviour of stainless steels in chloride environments

AbstractElectrochemical localized corrosion tests in substitute ocean water at 40°C and 70°C and ASTM G48 tests in 6% FeCl3 solution were performed on three classes of stainless steels: Ni‐austenitic (both traditional and with high nitrogen content ones), high nitrogen Mn‐austenitic nickel free and duplex (both traditional and with high nitrogen content ones).The Pitting Resistance Equivalent formula, PREMn = % Cr + 3.3% Mo + 30% N – 1% Mn, proposed to consider the presence of noticeable amount of manganese in some of the new high nitrogen stainless steels yields good linear correlation with experimental results. The existence of a threshold value of PREMn (≥ 45) to attain excellent localized corrosion resistance has been recognized. According to this observation the high nitrogen Ni‐austenitic 21Cr24Ni6MoO.24N, 24Crl8Ni4MoO.48N, 24Cr22Ni7MoO.52N and the duplex 25Cr8Ni4MoO.26N “super” stainless steels are immune to localized attack also in the most severe electrochemical test conditions. This superiority is maintained also in ASTM G48 tests. Due to their values of Critical Crevice Temperature (CCTASTM G48 ≥ 35°C) these steels seem suitable for practical service in seawater environments up to about 30 °C.

Corrosion Behavior of Stainless Steel and Nickel‐Base Alloys in Molten Carbonate

The corrosion behavior of five commercially available alloys (AISI 316L, AISI 310S, Inconel 601, Thermax 4762, and Kanthal A1) in molten carbonate under reducing gas atmospheres was investigated with cyclic voltammetry and quasi‐stationary polarization curve measurements. The reactions that proceed on these materials at distinct potentials could be deduced by comparison of the cyclic voltammograms and polarization curves with those of pure metals and model alloys. The shape of the polarization curves of all materials strongly depends on the preceding electrochemical treatment. A polarization curve recorded immediately after immersion of a sample resulted in a high anodic current. This implies that the passivation of the materials is poor. When a specimen was conditioned at −1060 mV for 10 h before recording the polarization curve, the anodic current diminished, which indicates passivation. This occurred for all materials except AISI 316L. A ranking of the corrosion properties was determined from polarization curves of samples that had been conditioned assuming the current densities to be representative. The resistance against corrosion of the alloys increases in the order:. Because the current densities were recorded at molten carbonate fuel cell (MCFC) anode potentials, this order may also apply for real MCFC operation conditions. The order determined from electrochemical experiments is in agreement with the results of exposure tests which are more time‐consuming. This study confirms that the presence of large amounts of chromium and significant additions of aluminium have a beneficial effect on the corrosion resistance of stainless steel and nickel‐base alloys.

Influence of chromium on the corrosion behaviour of stainless steels in sulphuric acid containing halide ions

Introduction The passivation of iron in aqueous media has been investigated over a number of years. Bartlett and Stephenson and Froment et al. have given a deep insight into the processes of anodic depositon of FeSO4 on iron in H2SO4 solutions. Krstulonic et al. investigated the anodic passivation of Armco iron in a wide range of concentrations of suphuric avid. Alloy elements (Cr, Ni, Mo) are sometimes added to carbon steels to improve their mechanical properties and/or the effects of heat treatment. These metals can increase or decrease corrision resistance depending on the harshness of the environment. The most important alloy of stainless steel is chromium, which induces the formation of a good protective oxide film. According to the literature the alloy must contain at least 1.3 per cent chromium to form a stable passive film. The influence of chromium on the anodic dissolution of Fe‐Cr in sulphuric acid solutions has been the object of several investigations.

Abstract of the PhD thesis “Corrosion behaviour of stainless steels and nickel alloys in hot concentrated static and flowing sulphuric acid and flowing sulphuric acid”

Abstract of the PhD thesis “Corrosion behaviour of stainless steels and nickel alloys in hot concentrated static and flowing sulphuric acid and flowing sulphuric acid”

Corrosion Behavior of Stainless Steel in Phosphoric Acid Polluted by Sulfide Ions

Abstract The effect of sulfide (S2−) ions on the corrosion behavior of an austenitic steel (Uranus B6) in phosphoric acid (H3PO4) solutions was examined. The critical concentration at which the effect of S2− ions became perceptible was determined. Aggressive effects of the ions increased with increases in temperature and oxygen content. Results showed S2− ions modified the cathodic and anodic processes.

腐食防食小特集 リン酸系におけるオーステナイト系ステンレス鋼の腐食問題

Although pure phosphoric acid is generally known to be mild to austenitic stainless steel, it is corrosive to austenitic stainless steel in some cases. This paper shows the corrosion behavior of stainless steel (mainly 316L) in a low concentration (about 1% H3PO4) phosphoric acid solution at high temperature (about 200°C), and a high concentration (about 33% P2O5) phosphoric acid solution at low temperature (about 70°C).The polarization tests of stainless steels were carried out mainly in 220°C 1% H3PO4 solution with or without dissoluted oxygen. The corrosion rate decreased when Cr or Ni contents in the test specimens increased, but even Hastelloy C-22, Ni-based alloy, did not passivate by itself. Dissoluted oxygen also reduced the corrosion rate of 316L, but no self-passivation occurred.The corrosion behavior of 316L stainless steel in the solution of a phosphoric acid plant was also tested. This solution contained phosphoric acid (33% P2O5), surfuric acid (1.5%), plaster (25%), fluorine ion (2.5%) and so on. It was found that corrosion in the plaster slurry settled from the solution was severer than that in the mixed acid solution without slurry, and the quantity of fluorine ions was higher in the slurry. Thus, it is suggested that CaF2 in the plaster increases the amount of fluoric ions and accelerates corrosion. It is also suggested that ferric ions prevent 316L from corrosion in this environment.

Structure and Intergranular Corrosion Behaviour of Stainless Steel Enriched in Mo by Electron Beam Processing

Structure and Intergranular Corrosion Behaviour of Stainless Steel Enriched in Mo by Electron Beam Processing

海浜環境におけるステンレス鋼の孔食進展挙動と耐穴あき性評価法

海浜環境におけるステンレス鋼の孔食進展挙動と耐穴あき性評価法

Corrosion behavior of stainless steels in aqueous salt blanket option solutions for ITER

Corrosion experiments were performed on 316 stainless steel in solutions relevant to the aqueous blanket concept for the ITER program. Those solutions included 2.1M and 4.2M and saturated LiOH, as well as 2.1M LiNo 3 at 25°C, 60°C and 90°C. Experiments conducted were immersion tests, SCC screening, linear polarization, and potentiodynamic polarization. Experiments were performed under laboratory conditions for reference purposes, as well as in a radiation field utilizing a linear electron accelerator. General corrosion rates were in the range of 0.2–16 μm/yr for deaerated 2.1M LiOH. 2–30 μm/yr for non-deaerated 2.1M LiOH and 0.13–2 μm/yr in 2.1M LiNO 3 at 25°C. Corrosion rates increased with solution concentration and temperature. Pitting and crevice corrosion were observed in LiNO 3 solutions as well as mixtures of LiNO 3 and LiOH. No indication of SCC was observed. Radiolysis products shifted corrosion potentials in the noble direction, but had no effect on corrosion products or on corrosion rates.

硝酸塩系溶融塩中におけるステンレス鋼の溶出挙動

硝酸塩系溶融塩中におけるステンレス鋼の溶出挙動

酸化性イオンを含む硝酸中におけるステンレス鋼の腐食挙動に及ぼすCrおよびPの影響

酸化性イオンを含む硝酸中におけるステンレス鋼の腐食挙動に及ぼすCrおよびPの影響

The corrosion behavior of stainless steels and copper alloys exposed to natural seawater

AbstractThe corrosion behavior of stainless steels, titanium and copper alloys exposed to flowing Pacific Ocean water was characterized using surface analytical and electrochemical techniques. Biofilm formation on stainless steels and titanium resulted in thin films of bacteria and diatoms that did not cause significant changes of the corrosion potential (Ecorr) or surface properties. Rotating cylinder experiments indicated that both Ecorr and corrosion rates for stainless steels and titanium were independent of mass transport. Four surface layers were identified on copper‐containing materials: substratum metal; an inorganic chloride corrosion layer that contained alloying elements; a biofilm; and crystalline, spherical phosphate‐rich deposits. All copper surfaces were colonized by bacteria independent of alloy composition. The complexity of the impedance spectra for copper‐containing materials was attributed to formation of surface layers and contributions of charge transfer and mass transport controlled reactions mediated by the layers. Both anodic and cathodic reactions for copper‐based materials were affected by mass transport.