Laboratory testing electrochemical

Evidence of localized corrosion can be obtained from polarization methods such as potentiodynamic polarization, EIS, and electrochemical noise measurements, which are particularly well suited to providing data on localized corrosion. When evidence of localized attack is obtained, the engineer needs to perform a careful analysis of the conditions that may lead to such attack. Correlation with process conditions can provide additional data about the susceptibility of the equipment to locaHzed attack and can potentially help prevent failures due to pitting or crevice corrosion. Since pitting may have a delayed initiation phase, careful consideration of the cause of the localized attack is critical. Laboratory testing and involvement of an... 

Although important contributions in the use of electrical measurements in testing have been made by numerous workers it is appropriate here to refer to the work of Stern and his co-workerswho have developed the important concept of linear polarisation, which led to a rapid electrochemical method for determining corrosion rates, both in the laboratory and in plant. Pourbaix and his co-workers on the basis of a purely thermodynamic approach to corrosion constructed potential-pH diagrams for the majority of metal-HjO systems, and by means of a combined thermodynamic and kinetic approach developed a method of predicting the conditions under which a metal will (a) corrode uniformly, (b) pit, (c) passivate or (d) remain immune. Laboratory tests for crevice corrosion and pitting, in which electrochemical measurements are used, are discussed later. 

Specifics on the types and rates of microbiological attack. These must be determined by using other methods such as chemical and microbiological analysis of the solution and materials from the corrosion sites. Consideration must be given to limitations of electrochemical techniques for MIC studies, noted previously under Corrosion Testing Laboratory Tests and subsequent subsections. 

Andco Environmental Processes, Inc., "Laboratory Test Results on Electrochemical Metal Removal."... 

It is preferable to carry out laboratory corrosion tests and to validate the data with service tests for the selection of materials. It is needless to note that the chosen test method be reliable and cost effective. Some of the test methods in use in industry are service tests, field tests, laboratory tests, and rapid electrochemical methods such as potentiodynamic polarization, linear polarization, electrochemical impedance and electrochemical noise. 

The preferred order of corrosion testing and its reliability is service tests > field tests > laboratory tests. It is not always possible to carry out service tests and hence it is recommended that coordinated corrosion testing involving a combination of (i) laboratory test and field test or (ii) rapid electrochemical tests and weight loss, or any other combination that is suitable be carried out. 

Durability. Electrochemical realkalisation has been appUed for over ten years, mainly to structures made with Portland cement concrete. Although well-documented case studies are rare, those available show that the corrosion protection obtained is durable [93]. Laboratory tests followed over several years support the dur-abiUty of the effect on reinforcement corrosion, as long as sufficient electrical charge has been applied [89,90]. As noted above, the amount of charge needed may depend on the cement type. 

Electrical breakdown is associated with the growth of trees., named after the structures that grow from charged metal needles in laboratory tests. Bow tie shaped trees grow in both directions from voids in the XLPE of high voltage DC cables (Fig. 12.7). The void acts as an electrical stress concentration, which initiates the electrical or electrochemical breakdown process. 

Even though the exposure test in practical sites is stiU very important and useful, we StiU need laboratory tests. It would be very useful to accelerate the corrosion characteristics and to evaluate the results in a relatively short time. This category has some laboratory tests filling the gap between the exposure test and very fundamental electrochemical tests. To name a few, we can mention the salt spray test, a CASS (Copper accelerated acetic acid salt spray) test, and a combined cycle test [4],... 

On the other hand, electrochemical laboratory tests are closer to the basic fundamental theory. As described already, corrosion is basically the electrochemical... 

While outside the scope of this chapter, we would like to complete this review by pointing out that real, rather than electrochemical, testing of the OER-modified catalyst was also carried out. Some formulations of the practical catalyst were extensively evaluated by a major stack developer [3, 46]. The evaluation was done in subscale as well in a full-sized architecture. The extremely favorable outcome of the protective properties of the Ir-Ru on Pt-NSTF for both CR and SU/SD tests confirmed the laboratory testing results. 

Standards and recommended practices covering different aspects of corrosion have been developed by a number of professional organizations as ASTM, NACE International, ISO and many national bodies. Useful information on the corrosion resistance of materials for a given application can often be obtained from suppliers and from the scientific and technical literature. A number of tables and databases published in the open htcrature [1- 4] present the intrinsic corrosion resistance of materials in different environments. We must keep in mind, however, that such data are not sufficient, because they do not include electrochemical interactions that can lead to localized corrosion or effects due to stress or wear. Engineers confronted with materials selection therefore need to have a basic understanding of corrosion mechanisms. Experience gained with similar equipment or installations is also a useful source of information to avoid corrosion problems. As a last resort, one may turn to laboratory testing. 

From the cost point of view, precious metals (such as Au and Pt) are surely out of contention for practical coatings on SS substrates, although they might be used for short laboratory tests. In fact, electrochemical corrosion cells will be generated from the possible pinholes in the coatings due to the electrochemical dissimilarity of the precious metals and SSs in a PEMFC environment. Difficulties encountered with the carbon-based and conductive polymer-based coatings are application at intermediate temperatures, the cold-start issue, and the differences in thermal expansion coefficients between the coating itself and the substrate SS. The risk of... 

Section HI covers Types of Tests (H. Hack, Section Editor) includirrg laboratory-accelerated tests, field tests, and service tests. The chapters in this section provide basic principles, describe test techniques and specific considerations such as specimen preparation, test duration and acceleration factors, and cite pertinent standards. Chapters included under laboratory tests are electrochemical, cabinet, immersion, high temperature, and high pressure. Field Tests chapters include atmospheric exposure, seawater, fresh water, and soil. Under service tests are industrial applications and high temperature environments. 

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