Corrosion Potential Measurements

In-vitro fretting corrosion experiments have been performed using weight loss , polarisation and corrosion potential measurements. Thull and Schaldach have performed corrosion potential versus time measurements in-vitro in a joint simulator with different values of applied load. Brown and Simpson have performed similar studies with screw/plate fretting. Both studies found larger shifts towards active potentials with larger loads . 

Corrosion potential measurement is increasing as a plant monitoring device. It has the very big advantage that the plant itself is monitored rather than any introduced material. Some examples of its uses are ... 

In 1979, Leidheiser ( reviewed the use of corrosion potential measurements with regards to the prediction of corrosion at metal-organic coating interfaces. Wolstenholme had last reviewed this literature in 1970 (10). Work in the 1930-1940 s focused on the magnitude of the corrosion potential and how it changed with time (11-14). Negative potentials with respect to uncoated substrates were indicative of corrosion beneath the coating. Positive potentials with respect to uncoated substrates were indicative of the absence of corrosion. 

An epoxy paint for temporary protection of high zinc content 88.3 % relative to dry mass of the coating was investigated on mild steel wire electrodes of 5 mm diameter. The coatings of 27 2 jtim in thickness were studied. The measurements were carried out in 3 % non -- deaerated NaCl solution at room temperature in the frequency range from 1 Hz to 60 kHz using a sine signal of 10 mV amplitude. The measurements were i>erformed in a three-electrode system with the corrosion potential measured vs. the saturated calomel electrode. 

In low pH oxidizing solutions, copper is not expected to form a surface film. The copper corrosion potential measured in 1 vol% HNO3 is 100 mVsHE- At a pH of 1 and a potential of 100... 

M. Ullberg, On Corrosion Potential Measurements in BWRs, in Proc. 4th Int. Symp. Environ. Degrad. Mat. Nucl. Power Systs. - Water Reactors, Jekyll Island, August 6-10, 1989, NACE, Houston, TX (1990). 

Figure 8 Pourbaix diagram for iron in an environment with 10 2M carbonate, and 2 X 10 4M dissolved iron at a temperature of 10°C, generated by the software HSC chemistry 5.0 from Outokumpu. The thermodynamic data for the different corrosion products are compiled by the French Agency for Nuclear Waste Management (ANDRA). Flatched area shows the pFl values and corrosion potentials measured in situ at Nydam. Dotted line shows the stability limit for water...

In the case of a metal substrate covered with an electrolyte, it has been shown by Stratmann et al. [16, 20] that a simple linear relation exists between the Volta potential difference Af lef (where El denotes the outer surface of the electrolyte) and the corrosion potential Ecorr As the corrosion potential, measured versus a standard hydrogen electrode (SHE), is given by Eq. (8)... 

Fig. 9 In situ monitoring of phosphating reactions quartz crystal microbalance and corrosion potential measurements. (From Ref [17].)...

The activity of the substrates was determined by means of corrosion potential measurements and potentiostatic data. 

The potential of the corroding surface can be monitored periodically by means of a reference electrode. One such example is the corrosion potential measurement of reinforced steel rebar in concrete structures. Corrosion of the steel in reinforced concrete is a major factor in the deterioration of highway and bridge infrastructure. A survey of the condition ofa reinforced concrete structure is the first step toward its rehabilitation. A rapid, cost-effective, and nondestructive condition survey offers key information to evaluate the corrosion, aids in quality assurance of concrete repair and rehabilitation. 

Fig. 2.12 Corrosion potential measurement of reinforced steel rebar in concrete.

Applications of Linear Polarization Technique—Estimation of Corrosion Rates Corrosion Potential Measurements as a Function of Time (OCP vs. Time)... 

CORROSION POTENTIAL MEASUREMENTS AS A FUNCTION OF TIME (OCP VS. TIME)... 

Concrete Bridge Protection and Rehabilitation Chemical and Physical Techniques—field Validation. Covers the field application and short-term corrosion performance of six trial installations of two inhibitor-modified concrete systems. The installations were applied to both deck and substructure components in a range of environments. Both pre- and posttreatment corrosion assessments v/ere performed to estimate the corrosion performance of inhibitor mcdified concrete systems, including visual inspections, delamination surveys, cover depth sur eys, chloride contamination levels, corrosion potential measurements, and corrosion current measurements. 67 pages. SHRP-S-658... 

Chiu SL, Selman JR (1992) Determination of electrode kinetics by corrosion potential measurements zinc corrosion by bromine. J Appl Electrochem 22 28—37. doi 10.1007/ BFO1093008... 

Figure 11.8 Simplified schematic to illustrate possible sources of fluctuations in corrosion current, /(-orr or corrosion potential measured at a distant reference electrode, for general corrosion with a diffusion-limited cathodic reaction such as oxygen reduction. Fluctuations leading to fluctuations in can be in (1), the transport rate of the cathodic reagent, leading to changes in diffusion-limited current (2) and (3), the relative areas of the anodic and cathodic processes, caused for example by detachment of surface scales or by changes in the electrode kinetics of these processes caused for example by the addition of corrosion inhibitors or change in surface concentration of such inhibitors (4), in the solution resistance between cathodic and anodic areas, if these are spatially separated, caused for example by fluctuations in local electrolyte composition itself linked to the occurrence of the corrosion reaction.

Due to its simplicity, open circuit corrosion potential measurements (see Chapter 20 of this manual) have been used in MIC studies for many years. Corrosion potential measurements as a function of time have been used to obtain information on MIC of steel, aluminum alloys, stainless steels, and other passive alloys. By itself, the corrosion potential of plain carbon and low alloy steels indicates very little because these steels can corrode at a wide range of potentials. Rapid changes in the corrosion potential, however, can be used to indicate cathodic depolarization, or an enhancement of the anodic reaction, or to the formation of a semi-protective film. 

A recent pubheation [23] presents a summaty of the systems that have been investigated to date. However, the influence of potential distribution is not considered in this model [9,20]. As with corrosion potential measurements, an independent calibration method demonstrates that with the appropriate electrolyte the polarization resistance is proportional to the exposed substrate area. For tin-coated steel tested in thiot -anate solution, favorable agreement is found between polarization resistance and corrosion potential measurements (Fig. 8). 

Figure 7-61. Transient of the corrosion potential measured within the delaminated zone after a sudden change from air to Ar (left) and from Ar to oxygen (right) (Leng et al., 1999c).

Damborenea (1995) also studied the behavior of coated steels in aqueous media (NaCl 0.6 M and HCl 2 M) through voltametry experiments. It is observed that the values for the corrosion potential measured as a function of time range between 220 and 140 mV in the case of coated steels, and between -200 and -50 mV on uncoated steel. However, the kinetic measurements using complex impedance and polarization resistance showed that the resistance to corrosion diminished notably over time, with the R.p values reaching the same levels as those of naked steel after 24 h (Fig. 19-11). This downturn revealed the presence of defects or pores in the coating, which permitted the movement of ions and, consequently, the contact of the environment with the metal substrate. 

In the 2XXX system, corrosion potential measurements were conducted on high-purity aluminum and various binary Al-Cu alloys up to and beyond the limit of solid solubility of 5.65% copper. Also, it was possible to produce large particles of the stoichiometric precipitates CuAla and CuMgAla so that their corrosion potentials could be measured. Figure 19.2 is a plot of the corrosion potential of the various materials as a function of copper content, showing that significant potential differences of as much as... 

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