Prediction of corrosion

Other Effects Stream concentration can have important effects on corrosion rates. Unfortunately, corrosion rates are seldom linear with concentration over wide ranges. In equipment such as distillation columns, reactors, and evaporators, concentration can change continuously, makiug prediction of corrosion rates rather difficult. Concentration is important during plant shutdown presence of moisture that collects during cooling can turn innocuous chemicals into dangerous corrosives. 

Corrosion likelihood describes the expected corrosion rates or the expected extent of corrosion effects over a planned useful life [14]. Accurate predictions of corrosion rates are not possible, due to the incomplete knowledge of the parameters of the system and, most of all, to the stochastic nature of local corrosion. Figure 4-3 gives schematic information on the different states of corrosion of extended objects (e.g., buried pipelines) according to the concepts in Ref. 15. The arrows represent the current densities of the anode and cathode partial reactions at a particular instant. It must be assumed that two narrowly separated arrows interchange with each other periodically in such a way that they exist at both fracture locations for the same amount of time. The result is a continuous corrosion attack along the surface. 

The term aggressive is often used to imply some approximately quantitative estimate of the likelihood of corrosion and depends on measuring factors such as soil water (resistivity), pH, redox potential, salt concentrations and bacterial populations in order to establish criteria for the prediction of corrosion rates . Similar measurements for predicting corrosion... 

Reliable pH data and activities of ions in strong electrolytes are not readily available. For this reason calculation of corrosion rate has been made using weight-loss data (of which a great deal is available in the literature) and concentration of the chemical in solution, expressed as a percentage on a weight of chemical/volume of solution basis. Because the concentration instead of the activity has been used, the equations are empirical nevertheless useful predictions of corrosion rate may be made using the equations. 

The overall design process depends on the use of codes of practice and specifications, and to an increasing extent on computer-based techniques. The potential cost of delay is therefore a strong incentive to the use of standard solutions, compatible with the codes of practice , and to develop ways of using the computer to provide corrosion information and knowledge, or to improve prediction of corrosion behaviour. Note that both points relate to the use of existing knowledge, in the sense of an important conclusion of the Hoar Report. ... 

Criaud, A., C. Fouillac and B. Marty, 1989, Low enthalpy geothermal fluids from the Paris basin, 2 - oxidation-reduction state and consequences for the prediction of corrosion and sulfide scaling. Geothermics 18, 711-727. 

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. 

The oil analyses have shown that the TBN values of lubricating oils deplete completely while at the same time, the corrosion rate can be considerably reduced. The relationship between the solubilization of large quantities of acid, total base number (TBN), and total acid number (TAN) values with the rate of corrosion is still unresolved. TAN values are not a good prediction of corrosion, and the source of extra TBN is much more important in the neutralization of corrosive acids than the simple numerical value of TBN. The effect of hard-core RMs shows poor correlation between used oil sample TAN values and the potential for bearing corrosion (Denison, 1944 Kreuz, 1970). Where corrosion rates are reduced by treatment with hard-core reverse micelle detergent, and no significant reduction in TAN has occurred, corrosion protection must have occurred by a... 

The predicted and known classifications of skin corrosion potential are given in Table 18.7. Predictions of corrosion potential made by the QSAR in step 1 are made only for the 36 single chemicals that are organic liquids, since the domain of the QSAR excludes inorganic substances,... 

Chapter 4 describes how the electrical nature of corrosion reactions allows the interface to be modeled as an electrical circuit, as well as how this electrical circuit can be used to obtain information on corrosion rates. Chapter 5 focuses on how to characterize flow and how to include its effects in the test procedure. Chapter 6 describes the origins of the observed distributions in space and time of the reaction rate. Chapter 7 describes the applications of electrochemical measurements to predictive corrosion models, emphasizing their use in the long-term prediction of corrosion behavior of metallic packages for high-level nuclear waste. Chapter 8 outlines the electrochemical methods that have been applied to develop and test the effectiveness of surface treatments for metals and alloys. The final chapter gives experimental procedures that can be used to illustrate the principles described. 

Auscor Prediction of corrosion of austenitic stainless steels UK Savior... 

EIS data extrapolation, uses neural networks to train on electrochemical impedance spectroscopy data for extrapolation Filter debris analysis (FDA) expert system, condition monitoring of aircrafts GENERA, generic problem-solving framework for characterizing corrosion and materials problems LipuCor, prediction of corrosion in oil and gas systems... 

Predict, prediction of corrosion in oil and gas production and transmission environments Socrates, selection of materials for oil and gas production service... 

Strategy, programs for evaluation of cracking in steels used in pipelines and refineries USL Corrosion Model, program for prediction of corrosion in gas condensate wells... 

S. Srinivasan, V.R. Jangama, R.D. Kane, Prediction of Corrosivity of C02/H2S Systems , EuroCorr/97, The European Corrosion Congress, Trondheim, Norway, Sept. 22-25, 1997, Publ. by Norwegian University of Science and Technology, Trondheim, Norway, Vol. 1, 1997, pp. 33 10. 

Descriptions of individual corrosion processes can be assembled and used to predict materials degradation in macroscopic systems. However, the computations required are usually so lengthy and complex as to require access to large scale computational facilities. Expansion of this approach to the analysis and prediction of corrosion behavior on a wider scale requires the development of more efficient mathematical techniques and algorithms and of methods for simplifying the calculations without loss of significant factors. 

Prediction of Corrosion Behavior of Active-Passive Type Metals and Alloys in Specific Environments... 

Lister [1981] states that Equation 7.31 has formed the basis of some reasonable predictions of corrosion product deposits in various high temperature water systems [Brusakov 1971]. 

Depending on which model is taken, various properties of the concrete have to be known beforehand. For example Parrotf s model [15] for prediction of corrosion initiation requires knowing the air permeability of concrete, the content of calcium oxide in the hydration products of cement and a coefficient that is a function of the relative humidity. For predicting the propagation time, the corrosion rate and the maximum acceptable corrosion penetration have to be known. In order to be able to use these models, test methods have to be clearly specified and the interdependencies between variables have to be verified. 

By combination of thermodynamic stability diagrams of the salt phase to be investigated and the oxide phase under consideration, phase stability diagrams can be constructed to predict the behavior of any oxide in any molten salt. Figure 5 shows the Na-Fe-S-O-phase diagram [11,12] for prediction of corrosion of iron in a Na2S04 melt at 1200 K. This diagram is constructed from... 

Fig. 5 Na-Fe-S-O-phase diagram for prediction of corrosion of iron in a Na2S04 melt at 1200 K.

Prediction of corrosion performance can be done from published data and testing. Accelerated testing should involve the same mode of failure and reflect a known order of resistance of some alloys in service media (128). The common test objectives of SCC are high stresses, slow continuous straining, precracked specimens, higher concentration of corrosive agent than in service medium, higher temperature, and electrochemical stimulation (129). For electrochemical corrosion, the properties of the medium at the interface should be noted in accelerated tests. 

Case Study 12.1 —Prediction of Corrosion Initiation Time and Life of Rebars under Real Time (Practical) Conditions... 

Srinivasan S, Kane RD. Prediction of corrosivity of CO2/H2S Production Environments. Corrosion/96, Paper No 11, NACE, Houston, Texas, 1996. 

Nesic S, Postlethwaite J, Olsen S. An electrochemical model for prediction of corrosion of mild steel in aqueous carbon dioxide solutions. Corrosion/95, Paper No 131, NACE, Houston, Texas, 1995. 

Prediction of corrosion performance in this approach now depends greatly on the ability to identify past cases that are similar to the problem case. This identification is not merely a simple Unear proximity calculation, but rather, it requires the consideration of the weighted effect of the difference in each parameter between the similar case and the problem case. 

Another basis for thermodynamic prediction of corrosion reactions is the equation AG = —nFE, where n is the number of electrons transferred in the reaction, F is Faraday s constant (96,500 C, which is equivalent to 1 mole of electrons), and A is the cell potential. A positive cell potential will lead to a negative AG , and hence the reaction will proceed spontaneously as written in Eq. (2). As the overall cell reaction proceeds, the voltage difference between the electrodes drops as the free energies of the products and reactants approach each other. At steady state, both electrodes have the same voltage and no charge transfer occurs. 

The factors promoting corrosion of aluminium alloys are complex and interrelated. They often operate synergistically, making prediction of corrosion difficult. In wet storage of aluminium clad spent fuel, there are a number of corrosion mechanisms involved. The most important mechanisms as related to spent nuclear fuel are briefly discussed here. Other details and definitions related to aluminium corrosion can be found in the normative publications and ISO standards provided therein. 

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