Linear Polarization Techniques Research Articles

Effects of Stress on Cracking Velocity and Critical pH Value inside Stress Corrosion Cracks

Abstract The effects of stress on corrosion velocity and stress corrosion crack growth rate for the system 18-8 austenitic stainless steel (SS) (sensitized)/Cl− were studied by using linear polarization and slow strain rate techniques in simulated occluded cell solutions of different crack propagation stages with different pH values at 90°C. The stress—elongation curves, crack length—time curves, and corrosion rate—pH curves all showed a critical pH value (≥1.8), which is higher than that found previously (≅1.3) for unstressed specimens. The actual stress corrosion cracking (SCC) velocity was several orders of magnitude higher than the corrosion rates of stressed specimens, indicating that mechanical failure induced by hydrogen embrittlement is the dominating factor for SCC velocity.

MODIFICATION OF THE COMPOSITION OF LASER WELDS IN ELECTROGALVANIZED STEEL AND THE EFFECT ON CORROSION PROPERTIES

Abstract Compositional modification of the weld metal during laser welding of electrogalvanized steel sheet was achieved by the injection of metal powder or by a technique in which zinc that had been volatilized as a result of the welding operation was redeposited on the weld bead. Corrosion testing by means of the linear polarization technique showed that the coating corrosion rate in the case of laser welds containing redeposited zinc was substantially lower for an initial period than for normal laser welds. Only a small decrease in corrosion rate was achieved by the injection of tool steel powder during laser welding while an increase in coating corrosion rate was produced by the injection of nickel powder or stainless steel powder

An electrochemical investigation of the behaviour of aluminum alloys in different electrolytes

The anodic behaviour of aluminum alloys, mainly Al 5083-H321 and Al 6061-T651, in aqueous chloride solution in the presence of sulphate ions has been investigated at room temperature by the linear sweep polarization technique and potential step method. For both electrodes the i- E curves were characterized by a minor peak prior to the major dissolution region, but with the high current density for Al 5083-H321 due probably to a monolayer(s) formation of Al 2O 3 and/or MgO. The detection of Mg was shown by SIMS analyses. Significant pitting was observed for Al 5083-H321, as a result of the combined effects of the electrochemically active Mg in the matrix of the electrode, its subsequent influence on hydrogen evolution, and the chloride attack on the aluminum electrode surface.

Electrochemical Corrosion Probe for High Resistivity Hydrocarbon/Water Mixtures

Abstract Laboratory electrochemical corrosion rate measurements have been made in highly resistive mixtures of water in hydrocarbon liquids (e.g., crude oil) using a probe with flush-mounted measuring electrodes in a coplanar configuration. The effect of the high solution resistance between the reference and working electrodes is eliminated by chemically modifying the dielectric surface between the electrodes to make it ionically conductive. This allows corrosion rates to be measured using linear polarization techniques in hydrocarbon-continuous environments of water dispersed in the liquid hydrocarbon within a heated, pressurized autoclave. Good correspondence is found between electrochemical and coupon weight loss corrosion rates. Other electrochemical corrosion tests, such as potentiodynamic polarization, have also been successfully conducted in the hydrocarbon/water mixtures.

The Effects of Short‐Term Changes in Water Quality on Copper and Zinc Corrosion Rates

In this study, the linear polarization technique was used to evaluate changes in the corrosion rates of copper and zinc surfaces in response to short‐term changes in water quality. This analytical technique can be applied wherever uniform corrosion, as opposed to pitting, is occurring. The parameters investigated included temperature, pH, dissolved oxygen, chlorine residual, flow, and conductivity. All the parameters except flow rate affected copper corrosion rates. Conductivity, dissolved oxygen, chlorine residual, and temperature affected zinc corrosion rates. Reproducible corrosion rates were obtained within a few minutes of the changes in water quality.

Electrochemical Reactions in Molten Na2 SO 4 at 900°C

The chemical/electrochemical behavior of pure molten was studied upon polarization of a Pt working electrode. The linear polarization technique was used together with cyclic voltammetry. A doped zirconia electrode served as an oxygen sensor and a Ag/Ag+/mullite electrode as a sodium sensor. A chemical/electrochemical autocatalytic reaction involving is proposed from the interpretation of the polarization path on a Na‐S‐O phase stability diagram. The roles of the two specific ion reference electrodes are discussed and clarified.

Electrochemical determination of erosive wear of high carbon steel grinding balls

A jet slurry apparatus has been constructed to test corrosive/erosive wear properties of grinding ball metal Plain high carbon steel heat treated to a hardness of about 60 Rc was used. Slurries of quartz and chalcopyrite ore concentrate were used as the jetting media. Weight loss due to pure corrosion was determined by the linear polarization technique. Weight loss due to pure erosion was determined by jetting while cathodically protecting the sample. By comparing the total weight loss with the sum of the weight losses from pure corrosion and pure erosion, it was found that there was a synergistic effect between corrosion and erosive wear. Corrosion rate, erosion rate, and total erosion/corrosion rate are given as a function of pH and mineral type.

The effect of heat treatment and carbon content on the corrosion behaviour of iron—chromium steels in sulphuric acid solutions

In this study the corrosion behaviour of iron—chromium steels was investigated. The samples were subjected to heat treatment. The current density—potential curves were obtained in 1 N H2SO4 by electrochemical, potentiodynamic (1 mV min−1), potentiostatic and galvanostatic methods. Corrosion rates were obtained from the extrapolation of anodic and cathodic Tafel lines and using potentiodynamic, potentiostatic and galvanostatic linear polarization techniques with the Stern—Geary equation. It was seen that the effect of chromium on the rate of corrosion varies with the heat treatment method applied and the amount of carbon content.

Electrochemical Polarization and Passivation of Tin in neutral solutions of chloride, bromide and iodide ions

AbstractPassivation of commercial grade tin (99.5%) was studied in 0.1 M KCl, KBr and KI solutions using the potentiodynamic technique involving cathodic and anodic polarization at various scan rates. While low scan rates (0.1 mV/sec) lead to the complete deterioration of the anode in chloride solutions, higher scan rates of 1 and 5 mV/sec lead to the appearance of two anodic peaks. These peaks disappear at still higher rates (10 mV/sec). In bromide solutions, two anodic peaks appear with scan rates of 1 and 5 mV/sec, and only one peak is observed with 50 mV/sec. A white precipitate is formed in both chloride and bromide solutions during anodic scanning. No gas evolution (O2, Cl2 or Br2) could be detected up to anode potentials of 3–4 V (SCE). At scan rates of 1 mV/sec and higher values, pitting does not occur, and thick anode films are formed. The film is gray in chloride solutions, and yellowish gray in bromide solutions. Values of the corrosion potential Ecor are recorded for the forward and reverse scanning. The corrosion cd Icor is calculated both by the Tafel extrapolation procedure and by the linear polarization technique. The latter gives more accurate results. In Cl− and Br− solutions, the first anodic peak associated with passivation is more anodic than the equilibrium potentials for the tin/tin oxides or hydroxides. Passivation is explained as a result of the formation of the sparingly soluble salts Sn(OH)Cl, Sn(OH)Br which appear both in the precipitate and in the anode film. The passivating films are constituted at least partially of these basic salts, and contain a proportion of the oxides and hydroxides of Sn. From the effect of scan rates on the characteristics of the anodic peaks, it appears that the formation of thick anode films is governed by the diffusion kinetics for porous films. Of the three possibilities considered as explanations for the second anodic peak (oxidation of impurities, oxidation of halides to oxyacids, and structural changes in the film) the latter appears to be the most probable one.Thick anodic films are not formed in iodide solutions (scan rates 1, 5, 10 mV/sec), and the anode surface remains very bright. Dense evolution of I2 occurs during anodic polarization, and apart from I2 which dissolves in solution, the latter remains clear. Only one peak is observed in the forward anodic scanning. The polarization resistance technique gives Icor = 0. Thermodynamic calculations show that I3−, HIO, IO−, HIO3, IO3−, HIO4, and IO4− occur in 0.1 M KI solutions at potentials less anodic than the potential of the anodic peak (1.32 to 1.37 V, vs SCE). This peak potential is more anodic than the quilibrium potential for I2 evolution.

On-line Application of Corrosion Rate Monitoring in Industrial Plants

Abstract Corrosion rate monitoring based on electrochemical methods is shown to provide an adequate tool for the fast and accurate determination of on-line corrosion rate in industrial electrolytic environments. Case histories, concerned with desalination plants and cooling tower water circuits, show that instantaneous corrosion rate measurements by the linear polarisation technique, combined with exposure of coupons, provide an efficient tool for optimising the technical-economic operation of the plant, and for determining the influence of the operating parameters on corrosion, thereby contributing to improved plant performance and efficiency.

Assessment of corrosion rate of steel in sea water by polarization resistance technique

Linear polarization techniques have been applied to a corrosion system, plain carbon and low-alloy steels in sea water, featured by time-dependent phenomena. Polarization resistance measurements have been interpreted according to equivalent circuits representative of the steel surface behaviour in sea water, in order to avoid misleading contributions arising from the presence of solid corrosion products. Electrochemical data are in good agreement with weight loss measurements throughout four years of immersion in natural sea water and give information about the corrosion mechanisms, mainly based on the settling of localized macro-cathodic and anodic areas.

Monitoring of Varying Corrosion Rate Systems: Fe–Cr Alloy in H3PO4Solutions

AbstractThe corrosion of iron–chromium alloys in phosphoric acid varies with time as protective and non-protective films are formed. This is difficult to study by traditional weight-loss methods and misleading results can be obtained By means of the linear polarisation technique it has been shown that this variation can easily be monitored. The method has been carefully checked against weight-loss methods taking care of the variation with time. By measurement of corrosion rate as a funciion of potential it has been possible to reconstruct potential-log current density data and compare these with short term polarisation tests. The corrosion of iron–chromium alloys containing up to 7%Cr takes place because the free corrosion potential cannot exceed the Flade potentialfor this alloy in phosphoric acid at any concentration.

The Validity of Electrochemical Methods for Measuring Corrosion Rates of Copper-Nickel Alloys in Sea Water

Abstract This work was stimulated by reports that electrochemical methods for measuring the polarization resistance of copper, nickel, or copper-nickel alloys in aqueous systems may lead to appreciable errors in the estimates of the corrosion rate. In the present work, the polarization resistance (Rp) of two copper-nickel alloys (90:10 Cu:Ni and 70:30 Cu:Ni) was monitored as a function of time in flowing sea water that contained 0.045, 0.85, 6.6, or 26.3 mg/dm3 dissolved oxygen. Rp values were obtained using the linear polarization, potential step, and AC impedance techniques. The total weight loss during the test period was calculated from the area under the 1/Rp versus time curve and compared with the measured weight loss. The experimental data support the validity of electrochemical methods for measuring corrosion rates of copper-nickel alloys in sea water, provided that a sufficient number of Rp measurements are made during the first 24 hours, and provided that proper consideration is given to the capacitive elements of the metal/solution interfacial impedance. Previous reports that electrochemical measurements may lead to underestimates of the corrosion rates are thought to have resulted primarily from undetected (and very high) corrosion rates at short exposure times. Reported overestimates of the corrosion rates are thought to have resulted from the use of a potential sweep rate that was too high (linear polarization technique), a time for current decay that was too short (potential step technique), or excitation frequencies that were insufficiently low (AC impedance technique).

Corrosion of Copper-Nickel Alloys in Sea Water Polluted with Sulfide and Sulfide Oxidation Products

Abstract The corrosion rates of copper alloys 706 (90:10 Cu:Ni) and 715 (70:30 Cu:Ni) were measured, using rotating cylinder specimens in sea water that contained oxygen, sulfide, sulfur, and polysulfide, either singly or in combination. In addition a control test was performed using unpolluted deaerated sea water. Corrosion rates were monitored for over 24 hours, using linear polarization and potential step techniques. The work has shown that copper-nickel alloys can corrode quite rapidly in deaerated sea water if these normally “passive” alloys are made active by the presence of sulfide, or if sulfur is available as an oxidant.

The problem of corrosion and tarnish of dental restorative and implant metals.

The linear polarization technique has been used to measure polarization resistances and corrosion currents directly in the mouths of baboons and in vitro for a wide range of dental and implant alloys. Good correlations were found to exist between these two conditions, indicating that this test is accurate and valid as well as being simple to perform. Intraoral corrosion proceeded faster, probably due to abrasion by foodstuffs. Tarnish has also been measured using an intraoral tristimulus colorimeter and results were compared with the corrosion determinations. The tarnish of pure metals (Au, Ag, and Cu) was inversely proportional to corrosion. Gold alloys tarnished little but varied in corrosion current. Dental amalgams corroded the most but the tarnish experience depended more on their chemistry than their precious metal composition.

Practical Experiences with Linear Polarization Measurements

Abstract The linear polarization technique in principle is a convenient and rapid way for determining corrosion rates. In practice, one finds that it is often applied under conditions alien to the assumptions on the basis of which it was derived. This paper will present a series of comparative observations between linear polarization, resistance probe, and weight loss measurements in different systems. The systems studied were: (1) Hydrochloric acid containing acetylenic inhibitors, (2) a two phase system containing hydrocarbon and water saturated with H2S, and (3) tap water containing various inhibitors. An equation will be derived showing the effect of ohmic resistance due to corrosion product buildup. The effect of polarization on the properties of a corrosion product layer will be discussed qualitatively.

The Röschenbleck equation

Several authors have proposed the use of the Röschenbleck equation δ E corr 2.3 δ pH = B as an alternative method for the determination of B. This latter value must be known when the linear polarization technique for the evaluation of the corrosion current density is used. This equation has however to be corrected, because it doesn't take the pH dependence of the partial metal dissolution reaction into account. The following equation is proposed: δ E corr 2.3 (p+q) δ pH = B with p and q respectively the reaction order of the partial current densities with respect to the hydroxyl and hydrogen ions.

High-Temperature Corrosion in Gas Turbines and Steam Boilers by Fuel Impurities—Part V: Lead Containing Slags

The effect of lead on the corrosivity and friability of slags containing various ratios of sodium, vanadium, magnesium, and silicon has been evaluated. The application of the linear polarization technique was demonstrated. Lead produces very corrosive melts and tenacious slags. Magnesium will inhibit corrosion to acceptable levels and produce friable slags at 800 °C with a 4 to 1 ratio of additive to vanadium plus lead and a sodium to vanadium plus lead ratio no greater than 0.1. To produce friable slags at 900°, sodium must first be reduced to a sodium to vanadium plus lead ratio of 0.01. Second, a magnesium-silicon additive must be used at a 6 to 1 ratio of additive to vanadium plus lead. The corrosion rates of lead containing melts increases rapidly with sodium level.

Hardened Portland blast-furnace slag cement pastes II. The corrosion behavior of steel reinforcement

The corrosion behavior of reinforcing steel embedded in various slag cement pastes was studied using the galvanostatic polarization technique. The corrosion resistance is appreciably affected by the degree of fineness of the dry slag cement. In pastes produced from high Blaine area cement, the behavior of embedded steel was very close to that in normal or type I portland cement paste, and is much better than a low Blaine area cement. W/C ratios of 0.25 and 0.40 provided a better passivating medium as compared with W/C ratios of 0.18 and 0.70. Effects of lime or gypsum addition were also investigated and comparatively studied for their action on the corrosion of embedded steel. The results obtained were supported by corrosion rates obtained using the linear polarization technique.

Use of Charge Curve Analysis Technique for In Vivo Determination of Corrosion Rates

Abstract Type 316L stainless steel, commercially pure Ti (75A, TCA), and Ti-0.2Pd bone plates were attached to the femurs of adult New Zealand white rabbits using nylon screws. Corrosion rate-time determinations were conducted using linear polarization (LP) and charge curve analysis (CCA) techniques during 2160 hours following surgery. Of the materials tested, Ti-0.2Pd seems to be the most corrosion resistant and Type 316L stainless steel the least. At the end of the test period (90 days), corrosion rates (in mpy) were in the order of 0.02 for 316L SS, 0.005 for Ti and 0.001 for Ti-0.2Pd. Very good correlation was obtained between determinations made with LP and MCCA. Histopathologic examination of the bone plates and surrounding tissues were conducted. All plates were surrounded by a fibrous tissue capsule. Adverse tissue reaction was minimal.