Control of Corrosion

Edwards, A. M., Proc. Symp. on Developments in Methods of Prevention and Control of Corrosion in Buildings, British Iron and Steel Federation, London (1966)... 

The standard electrode trotential, Ep, 2+ Pb = —Q.126V . shows that lead is thermodynamically unstable in acid solutions but stable in neutral. solutions. The exchange current for the hydrogen evolution reaction on lead is very small (-10 - 10"" Acm ), but control of corrosion is usually due to mechanical passivation of the local anodes of the corrosion cells as the majority of lead salts are insoluble and frequently form protective films or coatings. 

The effective control of corrosion reactions must be based on an understanding of the mechanism of such reactions and on the application of this knowledge to practical problems. The work, regarded as a whole, represents an attempt, therefore, to present the subject of corrosion as a synthesis of corrosion science and corrosion engineering. Thus in the planning of the content an attempt has been made to strike a suitable balance between the primarily scientific and the primarily practical aspects, and so the nature of individual sections ranges from the fundamental and theoretical to the essentially practical. 

Recommended Practice Control of Corrosion on Offshore Steel Pipelines, RP-0675-88, NACE, Houston (1988)... 

The priming coat provides the bond between the metal and subsequent coats. It gives electrochemical control of corrosion. Adhesion is dependent largely on the nature of the binder and the cleanliness of the metal surface. 

The pigment is the principal agent in the electrochemical control of corrosion by primers (see Section 14.3). Probably the best known anticorrosive pigment is red lead. When used in conjunction with linseed oil as the binder it gives very good primers which will perform well over relatively poorly prepared (manually abraded) steel surfaces. Present-day use of red lead (and lead pigments, generally) in paints has been drastically curtailed as a result of understandable pressure from the environmentalists. 

Corrosion tests provide the basis for the practical control of corrosion and therefore deserve a more exhaustive discussion than limitations of space will permit. A detailed description of all the procedures and devices that have been employed in corrosion studies in many countries will not be attempted. Instead, attention will be directed principally to underlying principles and to comments on the significance and limitations of the results of the test methods that are considered. Further details may be obtained from the references and from the comprehensive works by Champion and Ailor ... 

Thus, the effective control of corrosion requires not only limiting the presence of oxygen but also minimizing the risks of waterside deposits. These measures in turn require good management of waterside chemistry and competent mechanical operational practice. 

The ease with which an atom gains or loses electrons is termed the electronegativity of the element. Tabulation of the elements in order of ease by which they lose electrons is called the electrochemical series and is shown in Table 6.10. Chapter 4 explains the importance of this to the formation and control of corrosion, and Chapter 6 discusses the relevance to predicting reactivity of metals towards water and their potential to become pyrophoric. 

Z. Jiashen and Z. Jingmao. Control of corrosion by inhibitors in drilling muds containing high concentration of H2S. Corrosion, 49(2) 170-174, February 1993. 

Where control of corrosion is dependent on the concentration of contaminants or moisture, the operator should demonstrate that procedures and the necessary controls are in place to maintain a safe operating condition. Similarly, where inhibitors are added or systems such as cathodic protection are used, the operator should demonstrate that these systems are inspected and adequately maintained to ensure continued protection of the process. 

Control of pH. The control of corrosion in the condensate system is generally accomplished by adding one of the following chemicals ... 

The main purposes of corrosion testing are (i) evaluation and selection of materials for a given application (ii) evaluation of new or old materials to determine the environments which are suitable (iii) control of corrosion resistance of the material or corrosivity of the environment and (iv) study of the corrosion mechanism. 

The control of corrosion in pharmaceutical product processes is largely managed through the use of stainless steel. Rust-free surfaces and cleanliness issues to prevent product contamination have been the primary corrosion concerns. Resistance to mildly aggressive cleaning solutions and saline solutions and the potential for under deposit or crevice corrosion present the most severe service conditions. The high standards of cleanliness necessary for pharmaceutical processes favor the mitigation of corrosion. 

High temperature and high pressure processing of materials often involves the use of supercritical fluids. Corrosion studies are quite essential for evaluation of the equipment in supercritical fluid operations. Previous electrochemical measurements for alloys in supercritical fluids are rare (1-1). The reported measurements (3) show that passivation of iron alloys is different at supercritical conditions compared to ambient conditions. The study of the electrochemistry of iron alloys can lead to control of corrosion of equipment utilizing the alloys. Thermodynamic analysis provides the information about stable species, i.e. corrosion products under given temperatures and pressures. 

Abstract Quality control of corrosion test results implies the validation of the corrosion test method and estimation of the uncertainty of corrosion rate measurement. The corrosion test in an artificial atmosphere of the salt spray mist needs evaluation of corrosivity of the test cabinet by reference specimens. Such calibration of corrosion environment raises very strict requirements for the method description and details of all procedures and used specimens. Reliable corrosion measurements by spray tests require validation of the experimental device together with the experimental procedure and determination of corrosivity uncertainty of the test cabinet environment. 

Thermal. Combustion techniques bum waste for the recovery of heat energy, Waterwall combustors are the most technically developed energy recovery systems and employ special grates to bum "as received urban waste and recover steam either at saturated or superheated conditions. Over 250 plants are operating worldwide seven of them in the United States. Three of the seven were originally built as incinerators. Worldwide there have been a number of technical problems, with the control of corrosion and erosion being the most serious. The most recent European designs have solved these problems but at an increased capital cost. 

The brief survey of chemical additives for the control of corrosion illustrates the many ways in which control can be achieved. The choice of method will depend on the effectiveness required, coupled with the costs involved. 

Control of the total sulfur content, hydrogen sulfide, and mercaptans ensures that the product is not corrosive or nauseating. Stipulating a satisfactory copper strip test further ensures control of corrosion. 

At the same time, systems for the direct control of corrosion have been developed, as well as systems for measuring parameters directly related to the corrosion itself (redox and corrosion potentials). 

Give four examples of the economic significance of the control of corrosion. 

Theoretical Bases of Corrosion Control. This section provides a brief review of thermodynamic and kinetic considerations In the control of corrosion. Shrelr ( 5) or one of the other general references (3-12) can be consulted for detailed discussion. 

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