Corrosion principles

This book is designed as a handy desk reference covering fundamental engineering principles of project planning schemes and layout, corrosion principles and materials properties of engineering importance. It is intended as a general source of typical materials property data, useful for first pass materials selection in process design problems. 

In brackish waters, the same general corrosion principles may apply as for sea water. Experience has also shown that there may be considerable variation from plant to plant in the performance of metals, even where the cooling water comes out of the same general source such as a deep bay or estuary. There are coastal sites where the salinity may show very marked seasonal fluctuation. Protective film formation is essential for long lifetime in condenser tubing. Tubes installed at the season of the year when conditions are most favorable to form protective films tend to give longer service. 

H. Kaesche, Metallic Corrosion, Principles of Physical Chemistry and Current Problems, NACE, Houston, Tex., 1985. 

M. Oki (2007), Corrosion-Principles and Practice, Nigerian Environmental Society, Port Harcourt. 

Several deterministic corrosion models have been developed, some purely theoretical while others incorporate empirical results. For a review, see for example Nyborg (2002) or Nesic (2007). Many researchers have studied the mechanisms of corrosion on carbon steel in hydrocarbon environments. The purpose of the experiments has mainly been to study the effects of different influencing factors on the corrosion rate. With a theoretical background and mathematics based on physical understanding of the corrosion principles, these models often perform well under controlled experiments. However, their vahdation is limited outside the laboratory. This limited validation for field applications is mainly due to two reasons ... 

Rowe, L. C., "Corrosion Principles Applied to Body Engineering Design, Body Engineering Journal, October 1977, p. 67. 

NACE, Corrosion Costs and Preventive Strategies in the United States, www.nace.org and especially at http //events.nace.org/library/corrosion/Principles/CostPreventive.asp... 

The principles pertaining to carbon blast furnace hearths apply as well to submerged-arc furnace hearths. In some processes, such as in d-c arc furnaces, the electrical conductance of carbon is a most important factor. The long life of carbon linings in these appHcations is attributable to carbon s exceptional resistance to corrosive slags and metals at very high temperatures. 

D. A. Jones, Principles and Prerention of Corrosions Macmillan Publishing Co., New York, 1992. 

The industrial economy depends heavily on electrochemical processes. Electrochemical systems have inherent advantages such as ambient temperature operation, easily controlled reaction rates, and minimal environmental impact (qv). Electrosynthesis is used in a number of commercial processes. Batteries and fuel cells, used for the interconversion and storage of energy, are not limited by the Carnot efficiency of thermal devices. Corrosion, another electrochemical process, is estimated to cost hundreds of millions of dollars aimuaUy in the United States alone (see Corrosion and CORROSION control). Electrochemical systems can be described using the fundamental principles of thermodynamics, kinetics, and transport phenomena. 

Transfer of Momentum Deceleration of one fluid (motivating fluid) in order to transfer its momentum to a second fluid (pumped fluid) is a principle commonly used in the handhng of corrosive materials, in pumping from inaccessible depths, or for evacuation. Jets and eductors are in this categoiy. 

The selection of materials to be used in design dictates a basic understanding of the behavior of materials and the principles that govern such behavior. If proper design of suitable materials of construction is incorporated, the eqiiipment should deteriorate at a uniform and anticipated gradual rate, which will allow scheduled maintenance or replacement at regular inteivals. If localized forms of corrosion are characteristic of the combination of materials and environment, the materials engineer should still be able to predict the probable life of equipment, or devise an appropriate inspection schedule to preclude unexpected failures. The concepts of predictive, or at least preventive, maintenance are minimum requirements to proper materials selection. This approach to maintenance is certainly intended to minimize the possibility of unscheduled production shutdowns because of corrosion failures, with their attendant possible financial losses, hazard to personnel and equipment, and resultant environmental pollution. 

Linear polarization re.slstance probe.s. LPR probes are more recent in origin, and are steadily gaining in use. These probes work on a principle outlined in an ASTM guide on making polarization resistance measurements, providing instantaneous corrosion rate measurements (G59, Standard Practice for Conducting Potentiodynamic Polarization Resistance Measurements ). 

The initial measurement of electrical resistance must be made after considerable time. Phenomenological information has been determined based on the corrosion rate expected at what period of time to initiate readings of the electrical resistance. Since these values are based on experiential fac tors rather than on fundamental (so-called first) principles, correlation tables and lists of suggested thicknesses, compositions, and response times for usage of ER-type probes have developed over time, and these have been incorporated into the values read out of monitoring systems using the ER method. 

Galvanic corrosion is location specific in the sense that it occurs at a bimetallic couple (Fig. 16.2). It is metal specific in the sense that, typically, corrosion affects the metal that has less resistance in the environment to which the couple is exposed. Hence, in principle, we would anticipate galvanic corrosion of relatively reactive metals wherever they are in physical contact with relatively noble metals in a sufficiently aggressive, common environment. Experience has shown, however, that all such couples do not necessarily result in unsatisfactory service. This is because of the interplay of various critical factors that influence galvanic corrosion. These critical factors are discussed in the next section. 

Consideration of the basic elements characteristic of the galvanic corrosion process, as discussed above, points to the principles of sound preventive techniques. Since a galvanic potential difference is the driving force for corrosion reducing the magnitude of this difference can reduce or prevent galvanic corrosion. 

Evans, U. R., Corrosion and Oxidation of Metals Scientific Principles and Practical Applications, Edward Arnold Ltd., London, 1960. 

Use less corrosive chemistry (inherently safer principles)... 

J. P. Chilton, Principles of Metallic Corrosion, 2nd edition. The Chemical Society, 1973, Chap. 2. M. G. Fontana and N. D. Greene, Corrosion Engineering, McGraw Hill, 1967, Chap. 11. 

In this chapter we look first at an important class of alloys designed to resist corrosion the stainless steels. We then examine a more complicated problem that of protecting the most advanced gas turbine blades from gas attack. The basic principle applicable to both cases is to coat the steel or the blade with a stable ceramic usually Cr203 or AI2O3. But the ways this is done differ widely. The most successful are those which produce a ceramic film which heals itself if damaged - as we shall now describe. 

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