Showing papers in "Corrosion in 1990"

Basic Aspects of Electrochemical Impedance Application for the Life Prediction of Organic Coatings on Metals

Abstract: Electrochemical impedance spectroscopy (EIS) applies well to surfaces having a high electrical or electrochemical impedance. The method is, therefore, particularly suitable for the early d...

The Effect of Temperature on the Acidic Dissolution of Steel in the Presence of Inhibitors

Abstract: The corrosion of mild steel in sulfuric acid containing 4 × 10−4 M of either D-galactose thiosemicarbazone, 1-phenyl thiosemicarbazide, or 4-phenyl thiosemicarbazide, has been studied over...

Statistical Modeling of Pitting Corrosion and Pipeline Reliability

Abstract: Pitting corrosion is treated as a time-dependent stochastic damage process characterized by an exponential or logarithmic pit growth. Data from water injection pipeline systems and from th...

Localized Corrosion Behavior of Alloy 2090—The Role of Microstructural Heterogeneity

Abstract: The pitting and intergranular corrosion behavior of alloy AA 2090 (Al-2Li-3Cu, UNS A92090) in a 3.5 wt% NaCl solution was investigated. Techniques used included potentiodynamic polarization, galvanic couples, and pH measurements in simulated crevices. Polarization scans were performed on under-aged and peak-aged material to obtain the standard polarization parameters. Corroded specimens were examined with optical microscopy, scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDAX) to distinguish various local corrosion morphologies. Ingots were cast to approximate the subgrain boundary, T1 (Al2CuLi) phase, and Al-Cu-Fe constituent phases inherent in the alloy. These were then galvanically coupled to solution heat treated (SHT) 2090 to identify their role in local corrosion processes. Simulated crevices were produced by inserting pH micro-electrodes into crevices machined in 2090 blocks to measure pH versus time response in occluded environments. Based on the experiments...

Pit Morphology of Aluminum Alloy and Silicon Carbide/Aluminum Alloy Metal Matrix Composites

Abstract: Pit morphology of Al 5456 (UNS A95456), Al 6061 (UNS A96061), SiCw/Al 5456, and SiCw/Al 6061 is studied in order to compare pitting processes of SiCw/Al metal matrix composites with that of corresponding unreinforced alloys. Work on anodized samples of Al 6061 and SiCw/Al 6061 is also included. Pits on the composites are significantly more numerous, shallow, and widespread than on the monolithic materials. Studies of pit structure suggest there are two stages in pit development. The first involves the initial dissolution of metal atoms and opening of the pit, and the second involves pit enlargement or growth. For both materials, pits initiate at secondary particles within the metal matrix. In the case of Al 5456 and SiCw/Al 5456, it is shown that these particles are intermetallic phases composed of alloying elements Mg, Cr, Mn, and Al, as well as, Fe, which is an impurity of the metal. Under equivalent conditions of preparation and processing, a greater number of intermetallic phases form in the ...

Galvanic effects on the active dissolution of duplex stainless steels.

Abstract: This investigation has concerned the active dissolution of a duplex stainless steel in two different acidic solutions together with a comparison of the active dissolution of the correspond...

A review of the probabilistic aspects of localized corrosion

Abstract: Localized corrosion has a stochastic character by nature. This character leads to an observed random behavior: fluctuations of the free potential, fluctuations of the current when a constant potential is maintained. This random signal, which is similar to an electric noise, can be analyzed either in the time domain by counting the events or in the frequency domain by measuring the power spectral density of the electrochemical noise. The experimental techniques developed for investigating the localized corrosion on the probabilistic point of view, i.e., statistical counting and power spectral density measurements, are briefly recalled. Then the experimental results reported in the literature are reviewed in order to see what kind of parameters are accessible and how they can be related to the localized corrosion processes.

Characterization of Organic Coatings on Metal Substrates by Electrochemical Impedance Spectroscopy

Abstract: Organic coatings on phosphated and bare mild steel exposed to aqueous sodium chloride solutions were investigated by electrochemical impedance spectroscopy (EIS). The corrosion protection ...

Stress Corrosion Crack Coalescence

Abstract: The stress corrosion cracking of a pipeline steel exposed to a carbonate—bicarbonate solution has been studied under various loading conditions, particularly those involving a relatively s...

1990 Plenary Lecture: Strain Rate Effects in Stress Corrosion Cracking

Abstract: Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals and environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependences of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Nevertheless, laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crac...

Some Advantages and Pitfalls of Electrochemical Impedance Spectroscopy

Abstract: The use of electrochemical impedance spectroscopy (EIS) in corrosion research is briefly reviewed with particular emphasis on the advantages offered by this technique over other electroche...

Corrosion of iron in gaseous environments and in gas-saturated aqueous environments

Abstract: The corrosion of alloy 4130 (UNS G41300) steel has been investigated at temperatures up to 400°F in gaseous environments containing varying amounts of H2S and CO2 and in gas-saturated aqueous environments having dissolved chlorides. Thermogravimetric techniques have been used for establishing the kinetics of corrosion in the gaseous medium whereas electrochemical techniques have been applied in the case of the aqueous medium. Studies in the aqueous medium have been extended to pressures as high as 2000 psi. In gaseous environments, the major corrosion product has been identified to be pyrrhotite, Fe1−xS, which is found to grow by the predominant outward migration of ferrous ions through the sulfide scale. The rate-limiting step, however, is found to be the dissociation of H2S at the outer surface of the sulfide scale. Additions of carbon dioxide to H2S have the effect of accelerating sulfide scale growth rate, presumably by increasing the dissociation rate of H2S on the iron sulfide scale. In the...

Technical Note: Mackinawite Formation During Microbial Corrosion

Abstract: Mackinawite, a tetragonal iron sulfide mineral, is generally a major corrosion product when iron alloys are corroded by sulfate-reducing bacteria (SRB). The experimental database for the m...

Numerical simulation of crevice corrosion of stainless steels and nickel alloys in chloride solutions

Abstract: This paper describes the development of a new mathematical model of the incubation period of crevice corrosion. The model uses a new treatment of the transport processes, which includes both ionic migration and diffusion. An explicit finite-difference technique was applied to a uni-dimensional crevice along the crevice depth, with appropriate boundary conditions at both the crevice tip and bulk solution. Transient concentration results demonstrate that the major reason for the pH decrease in crevice solution is the production of soluble metal hydroxides, particularly CrOH2+. No solid monomer metal hydroxides (ex. Cr(OH)3 〈s〉) were formed in any of the simulations, which suggests that metal oligomeric complexes will be formed in the crevice solution. In addition, a comparison of the simulation results and experimental literature data (for alloys 304 [UNS S30400], 316L [UNS S31600], 904L [UNS N08904], and Inconel 625 [UNS N06625]) are discussed. The numerical simulation results, using Inconel 625, ...

Hydrogen Sulfide Effect on Hydrogen Entry into Iron—A Mechanistic Study

Abstract: The recently developed I-P-Z model is modified in order to analyze the observed enhanced permeation of hydrogen that occurs in the presence of hydrogen sulfide during cathodic hydrogen charging of iron. The modification accounts for the fact that the energy of adsorption becomes coverage dependent at the higher coverages and affects the hydrogen evolution reaction (HER) in the presence of H2S. Charging experiments were performed on Ferrovac E-iron membranes 0.5 mm thick using a Devanathan-Stachurski cell in deaerated, pre-electrolyzed solutions made from 0.1 M HClO4 and 0.1 M NaClO4 with pH values of 1 and 2. The transfer coefficient, α, exchange current density, i0, thickness-dependent absorption-adsorption rate constant, k″, recombination rate constant, k3, surface hydrogen coverage, θH, and discharge rate constant, k1o, were obtained by application of the model to the experimental results. As a result, the role of H2S has been clarified. While θH is increased in the presence of H2S, the overpo...

Interaction of Molybdate Anions with the Passive Film on Aluminum

Abstract: Using x-ray photoelectron spectroscopy (XPS), the interaction of sodium molybdate with Al was studied under a number of different conditions, including variations on molybdate concentration, pH, and applied potential. By comparison with a database of Mo binding energies, the results show several different oxidation states present in the film. Mechanisms were developed to describe how changes in passive film chemistry lead to improved resistance to pitting in chloride solutions. In contrast to earlier investigations, it was found that the formation of Mo+4 did not improve passivity. Improvements in pitting resistance were associated with a molybdate-rich region on the film surface that inhibited the ingress of Cl− anions to the metal/film interface.

Technical Note: The Effect of Heat Treatment on the Pitting Behavior of SiCw/AA2124

Abstract: A study was initiated at this laboratory to better understand the role of heat treatment on the pitting behavior of SiC/AA2124

Relationship Between the Structure of Disturbed Flow and Erosion—Corrosion

Abstract: Flow-dependent erosion—corrosion often occurs under disturbed flow conditions at geometrical irregularities such as fittings, valves, and weld beads. Flow separation and reattachment produces high turbulence intensity and particle—wall interactions that can lead to high erosion—corrosion rates. This paper presents the predictions of 2-D turbulent, single and two-phase liquid/particle flow with recirculation, after a sudden constriction and expansion. The model is based on a two-phase flow version of a standard k-e model of turbulence and a stochastic simulation of particle—fluid turbulence interactions. It is capable of successfully predicting local values of time-averaged fluid velocities and turbulence intensities, as well as predicting particle dispersion, and particle—wall interaction. The numerical predictions of the flow structure are used to explain the results of an experimental erosion—corrosion study of water and water/sand mixture flowing in a pipe with a sudden constriction and expans...

The effect of dissolved co2 and o2 on the corrosion of iron

Abstract: Reports concerning the effects of dissolved carbon dioxide on the corrosion of iron have ranged from “no effect” to a catalytic mechanism for the observed corrosion processes. Pedagogical references indicate that dissolved carbon dioxide is benign towards iron corrosion. Contrary to this, our results suggest that carbon dioxide does indeed play an active role in the corrosion of iron much as chloride and other aggressive ions. Visual, spectral, and electrochemical results all support the significance of the effect of dissolved carbon dioxide on the corrosion of iron.

Electrochemical Noise Generation during SCC of a High-Strength Carbon Steel

Abstract: Stress-corrosion cracking experiments have been performed on a high-strength carbon steel exposed to acidified sodium chloride solution poisoned with sodium sulfide. The electrochemical potential of the specimen was monitored during the experiment, and this paper reports the observed electrochemical noise. The analysis was performed using both the maximum entropy method and the discrete Fourier transform. A consistent noise behavior was observed throughout the experiment, with the only perturbation of any significance being associated with major transients that occurred when the specimen actually failed. The average noise power measured over a period of the same order as the duration of the transients has been found to be an effective method of detecting them, but it is expected that this will be much more difficult in service conditions.

The Relation Between the Resistance of IGA and IGSCC and the Chromium Depletion of Alloy 690

Abstract: The influence of heat treatments on the intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) resistance of lnconel 690 (UNS N06690) were studied. The chromium profiles adjacent to the grain boundary were predicted by thermodynamic and kinetic modeling and benchmarked with experimental results. The relative susceptibilities of alloy 690 with various heat treatments to stress corrosion cracking (SCC) in 0.001 M Na2S2O3 and low pH at room temperature were evaluated. The results of slow strain rate tensile (SSRT) testing showed good IGSCC resistance of alloy 690. The results of the Huey test showed very little weight loss for various heat treatments. The good resistance of IGA and IGSCC for alloy 690 are considered to be attributed to the higher equilibrium chromium concentration at the intergranular carbide–matrix interface.

Chloride Diffusion in a Porous Concrete Slab

Abstract: Chloride ion diffusion in porous concrete is one of the two major factors that cause corrosion to the reinforcing steel bars. A physical model is given in the present paper for describing ...

Thin-layer mixed-potential model for the corrosion of high-level nuclear waste canisters

Abstract: A thin-layer mixed-potential model (TLMPM) is described for calculating redox and corrosion potentials for high-level nuclear waste (HLNV) canisters in a tuff repository. The model assumes that the canister surface covered by a thin liquid (water) layer, which is irradiated by {gamma}-photons from the decay of radionuclides in the waste. The dose rate and the temperature at the surface are assumed to decay exponentially with time. Redox and corrosion potentials are calculated by equating the sum of partial currents for charge-transfer reactions involving various electroactive radiolysis products and the metal substrate to zero.

Quantitative Modeling of Sensitization Development in Austenitic Stainless Steel

Abstract: Existing capabilities to quantitatively model carbide precipitation and sensitization development in austenitic stainless steels are assessed and critically analyzed. A theoretically based, empirically modified model is described that predicts carbide nucleation kinetics, chromium depletion characteristics, and material degree of sensitization (DOS) as measured by the electrochemical potentiokinetic reactivation (EPR) test. Individual model components are validated by correlation to the available database including direct comparisons to grain-boundary chromium depletion. The model is shown to quantitatively predict isothermal sensitization development in a large number of commercial type 304 (UNS S30400) and 316 (UNS S31600) stainless steel (SS) heats. This work represents a first step to evolve methods that realistically assess microstructural characteristics and structural reliability in stainless steel components and weldments.

Mixed Oxidation of Iron–Chromium Alloys in Gases Containing Oxygen and Chlorine at 900 to 1200°K

Abstract: The mixed oxidation of three binary Fe-Cr alloys containing 1, 5, and 20 wt% Cr in Ar-50%O2−1%Cl2 and in Ar-50%O2−025%Cl2 at temperatures between 900 and 1200 K has been investigated using thermogravimetric analysis and examination of the corrosion products by scanning electron microscopy At 1000 K and above, the alloys experience accelerated corrosion associated with the formation of a porous two-layered oxide scale Iron oxide is concentrated in the outer layer and chromium oxide in the inner layer Iron chloride deposits are detected near the scale-metal interface at 1000 K, but not at higher temperatures Although the 20% Cr alloy is much more resistant to oxidation than the other alloys in uncontaminated O2, the rates of corrosion of all three alloys are very similar in the chlorine-containing environments at 1000 K A mechanism proposed for the accelerated oxidation in these environments is based on the formation, diffusion, and reoxidation of volatile iron chlorides

Effects of MnS inclusion dissolution on environmentally assisted cracking in low-alloy and carbon steels

Abstract: In fatigue both monotonic and cyclic plastic zones are formed ahead of the crack tip, inside which the strain history can be studied on the basis of stable hysteresis loops and structure anticipated in the crack-tip process zone and in the area of the maximum tensile stress (MTS) ahead of the crack tip. With these materials, slow strain rate tests (SSRT) were performed both in bulk pressurized water reactor (PWR) environments and in the simulated crack tip environments (MnS-contaminated PWR water). Environment-sensitive cracking occurred in the simulated crack tip environment at low corrosion potentials, −550 to −700 mV (vs a standard hydrogen reference electrode [SHE]), and in pure PWR water after anodic polarization to 0.0 mVSHE.

Relationships Between Pitting, Stress, and Stress Corrosion Cracking of Line Pipe Steels

Abstract: This paper presents observations about the results of an investigation into the relationships between pitting, stress, and stress corrosion cracking of line pipe steels. This work showed that the number of stress corrosion cracks varied exponentially with specimen stress. The cracks generally nucleated from pits, whose depths followed a lognormal distribution. A mathematical analysis of the crack number and pit depth data supports the hypothesis that a crack nucleates from the bottom of a pit when the stress concentration at the bottom of the pit reaches a critical value. The increase in crack number with stress results from the corresponding decrease in the critical pit depth, and hence an increase in the number of critically sized pits. The number of critically sized pits was found to increase exponentially with stress.

The Prevention of IGSCC in Sensitized Stainless Steel by Laser Surface Melting

Abstract: The use of a laser to melt a thin surface layer of sensitized stainless steel is shown to be an effective method for the prevention of intergranular stress corrosion cracking (IGSCC). The ...

Rapid Corrosion Screening in Poorly Defined Systems by Electrochemical Impedance Technique

Abstract: One strength of the electrochemical impedance technique is its usefulness for rapidly screening the corrosion resistance of alloys or corrosivity as a function of process conditions. Curve...

Cathodic Protection of Aluminum in Seawater

Abstract: Cathodic protection of aluminum generally requires small current densities, e.g., roughly 10 times less than the current requirement for steel in seawater. Potentiostatic tests carried out...