Evaluation of Corrosion Inhibitors

In order to determine the effect of chemical additives on corrosion, an actual corrosion process must be taking place, so that the inhibitor test and the corrosion test are inseparable. The fact that many variables affect a corrosion process means that numerous different inhibitor tests are available. Although additive concentration is generally low, the type of system, whether once-through or recirculating, or the method of treatment, continuous or batch-wise, will determine, not only the test method, but also the inhibitor concentration required. 

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Martinez-Palou, R. J. Rivera L.G. Zepeda A.N. Rodriguez M.A. Hernandez J. Marin-Cruz A. Estrada. Evaluation of corrosion inhibitors synthesized from fatty acids and fatty alcohols isolated from sugar cane wax. Corrosion 2004, 60, 465-470. 

Commercial inhibitors are frequently blends of several compounds, thus the mechanistic action can be multiple and difficult to identify. This will lead to major difficulties in the independent evaluation of corrosion inhibitors that are proposed in commercially available concrete repair systems. 

A systematic evaluation of corrosion inhibitors is now underway at the UK Building Research Establishment preliminary results may be available in 1997-8, SHRP undertook field trials of two inhibitor applications on bridge decks and substructures in the USA, These will be monitored from 1994 to 1999, Other trials are underway in Europe on. i pecLfic materiaLs. 

Tafel line extrapolation for the determination of corrosion rates is used mainly for laboratory testing conducted in acid electrolytes, a typical example being the evaluation of corrosion inhibitors. 

The evaluation of corrosion inhibitor effectiveness is significantly different in many respects from corrosion testing for the purpose of evaluating material performance. The addition of a chemical to a corroding system requires compatibility, chemical and thermal stability, and in some cases physical stability as well. Transport properties become important where localized or gasphase corrosion (dew point) are an issue. Finally, no corrosion inhibitor, no matter how effective in preventing corrosion, can be considered successful if it causes process upsets. This latter aspect is usually summarized under secondary properties testing [7] (cf. also Chapter 1 in this book). 

T.H. Muster, A.E. Hughes et al, A rapid screening multi-electrode method for the evaluation of corrosion inhibitors , Electrochimi. Acta, 54,3402 (2009). 

Rosero-Navarro N.C., Curioni M., Bingham R., Duran A., Aparicio M., et al. (2010), Electrochemical techniques for practical evaluation of corrosion inhibitor effectiveness. Performance of cerium nitrate as corrosion inhibitor for AA2024T3 alloy , Corros. Set, 52, 3356-66. 

However, poor reproducibility at intermediate concentrations and efficiencies limits the ability to differentiate between the cost-effectiveness of alternative additives. Similar difficulties have been reported with respect to the evaluation of corrosion inhibitors in refinery processes and other applications and in testing the effect of surfactants employed as corrosion inhibitors and/or anti-foulants on the water tolerance of jet fuels (WSIM test). The limitations of screening tests emphasize the inadvisability of undue reliance on them and the need for following such tests with careful plant studies to obtain reliable technical and economic data on anti-foulant applications. 

C.C. Nathan, C.L. Dulaney 1971. Statistical concepts facilitate evaluation of corrosion inhibitors. Materials Protection 10, 21-25. 

Finally it deals with monitoring internal corrosion. It provides guidance for on-line monitoring of internal corrosion in plants associated with the oil, gas and chemical industries, and guidance on laboratory monitoring and evaluation of corrosion inhibitors. The book also covers experiments on the corrosion behaviour of high-alloy tubular materials iu inhibited acidizing conditions. 

Monitoring can also be used to optimize the chemistry and level of corrosion inhibitors used. If too little inhibitor is used, enhanced corrosion can result and failure may follow. If too much is used, costs will increase without providing any additional protection. Optimization of the addition of inhibitor in terms of time, location in the process, and method of addition can also be evaluated through the use of carefully placed probes. 

Britton, C. F., The Selection, Evaluation and Testing of Oil Field Corrosion Inhibitors , Seminar The Development and Use of Corrosion Inhibitors , Oyez Scientific and Technical Services Ltd., London (1983)... 

A fully automated instrumental procedure has been developed for analyzing residual corrosion inhibitors in production waters in the field. The method uses ultraviolet (UV) and fluorescence spectrophotometric techniques to characterize different types of corrosion inhibitors. Laboratory evaluations showed that fluorescence is more suitable for field application because errors from high salinity, contamination, and matrix effect are minimized in fluorescence analysis. Comparison of the automated fluorescence technique with the classic extraction-dye transfer technique showed definite advantages of the former with respect to ease, speed, accuracy, and precision [1658],... 

Kendig, M. et al. "The application of impedance spectroscopy to the evaluation of corrosion protection by inhibitors and polymer coatings", CORROSION 85. 1985, NACE, Houston, Texas, Paper 74. 

The principal application of the two codes, a version of which for IBM compatible computers is under development, concerns especially the study of the behaviour of ferrous materials in acid environments with or without corrosion inhibitors. In particular, the use of the frequency interval [0.08, 20 X 10 ] Hz in the SOFTCOR-AC-GS code permits a more accurate characterization to be made of the properties of corrosion inhibitors by evaluating some electrochemical parameters under the assumption that the experimental curve Zi = f Zr) is satisfactorily represented by a circle equation. 

S. Papavinasam, Evaluation and selection of corrosion inhibitors, in Uhlig s Corrosion Handbook, 2nd edition, R. W. Revie, editor, Wiley, New York, 2000, pp. 1169-1178. 

Concrete Bridge Protection and Rehabilitation Chemical and Physical Techniques—Feasibility Studies of New Rehabilitation Techniques. Examines chemical methods for corrosion protection of reinforcing steel in concrete bridges. A broad spectrum ot chemicals w ere evaluated including corrosion inhibitors, chloride scavengers, and polyaphrons. 170 pages. SHRP-S-665... 

The evaluation of the associated matrix effects on the iodometric determination of KHI involved the following A) Effect of brine composition, B) Effect of condensate, C) Effect of sulfide (S ), D) Effect of the presence of corrosion inhibitor (Cl), and E) Iodine reagent eontribution to backgroimd. 

In order to keep conditions as constant as possible the constant pH "Kettle Test was used to evaluate a large series of corrosion inhibitors of which a few results are shown in Fig. 1, represented according to Eq 3. The inhibitors were intended for use in oil field systems and were, therefore, tested in fluids containing brine and a hydrocarbon phase saturated with 1 bar CO2. The results show the following ... 

In summary, EIS may have its place in mechanistic studies of corrosion inhibitors and should be used to elucidate some of the mysteries of corrosion inhibition from a chemical point of view. For routine evaluations of inhibited systems EIS has no specific advantages over LPR and is afflicted with the same uncertainties discussed above. 

Hausler, R. H. and Stegmann, D. W., "Studies Relating to the Predictiveness of Corrosion Inhibitor Evaluations in Laboratory and Field Environments, SPE Production Engineering, August 1990, p. 286. 

Suppliers usually provide the laboratory evaluation (using conventional test methods) of corrosion inhibitors, scale inhibitors, bactericides, and oxygen scavengers. User companies generally provide evaluation by field monitoring with corrosion specimens. Crevices may be incorporated in specimens to evaluate the possibility of localized corrosion, such as that related to oxygen contamination. 

Rust problems during usage of certain refined products, such as steam turbine oils, are controlled by addition of corrosion inhibitors. Evaluation of the performance of these inhibitors is done using ASTM D 665 or ASTM D 3603, Test Method for Rust-Preventing Characteristics of Steam Turbine Oil in the Presence of Water (Horizontal Disk Method). 

Corrosion inhibition can thus be evaluated conveniently by sequential pulse experiments with surfaces in contact with or in the absence of corrosion inhibitors. Similar work can be carried out with gaseous corrosive agents and metal surfaces treated with corrosion inhibitor vapours such as butylamine. 

Considering the electrochemical nature of corrosion processes, the potentiostatic technique was successfully applied in the evaluation of corrosion processes. Polarization curves were recorded for stainless steel in aqueous model solutions with or without inhibitors (Fig. 9-11). The results of these experiments are summarized in Table 9-5. The polarization resistance (/ p) values are representative for general corrosion (Teleg-... 

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