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872 CHAPTER 41 4950 Guide \ Electric Radiant Heat va. Steam Convection,,by Douglas Dow (Electrical World, August 10,1940, p. 61). Infra-red vs. Convection Ovens for Drying Paint Coatings, by F. J. Gschwind (Industrial. Finishing, September 1945). . Recent Advancements in Industrial Heating Processes and Equipment, by Eugene Mittelman (Industrial Healing* September. 1944). Heating of Non-magnetic Electric Conductors by Magnetic Induction, by R. M. Baker (Electrical Engineering, June 1944). Operating Experience with- HF Heating, by-Henderson C. Gillespie (Electronic Industries, February 1944). Unusual Methods of-Applying Electronic Heat.-by E. D.Tillson (Electronics, April 1945). Dielectric Heating, by T, W. Dakin and R. W. Auxier (Industrial and Engineering Chemistry, March l945). ' Induction and Dielectric Heating, by Kennard Finder (Electrical Engineering, February 1947). High Frequency Heating in the Radio Spectrum,-by W?C.- Undd (Electrical-Engi neering, June 19A7)l Standard Handbook for Electrical.Engineers, McGraw Hill Book Co.. CHAPTER 42 CORROSION AND WATER FORMED DEPOSITS, CAUSES AND PREVENTION Definitions, Classification and Characteristics of Water, Causes and Prevention of Scales and Sludges, Causes and Prevention of Slimes, Under-Water Corrosion, Atmospheric Corrosion, Buried Pipe Lines, Handling Water Treating Chemicals, Legal Regulations THE surfaces of heating and ventilating equipment that are in in timate contact'with water sometimes are affected by the chemical' characteristics of contacting waters to such an extent that prohibitive amounts of insoluble materials are formed or corrosion ensues "at an in sufferable rate. To avoid or to correct such troubles, it is desirable that heating and ventilating engineers have a general appreciation of industrial water chemistry. The principal purpose of this chapter is to provide those criteria by which the average engineer may judge Whether a problem is one that will yield, to rather simple remedies, or will require the skill of an experienced water technologist. , DEFINITIONS ^ The following definitions for water-formed deposits, corrosion, arid closely allied terms have been proposed: Water-Formed Deposits. A water-formed deposit* iaany accumulation of insoluble material derived frpm water or formed by the reaction of water upon surfaces in contact with water. Deposits formed from or by water in all of its phases may be further classified as scale, sludge, corrosion products, or biological deposits. Scale. Scale* is a deposit formed from solution directly in place upon a confining surface. It is a deposit which will retain its physical shape when mechanical means are used to remove it from the surface on which it is deposited. Scale, which may or may not adhere to the underlying surface, is usually crystalline and dense, fre quently laminated, and occasionally columnar in structure. ' ' - Sludge. Sludge* is a water-formed sedimentary deposit. It usually does not cohere sufficiently to retain its physical shape' when mechanical means are-used,to remove it from the surface upon which it deposits. Sludge is not always found at the; place where it is formed. It may be hard and adherent, and baked to the surface on which it has been deposited. ." Biological Deposits. Biological deposits* are water-formed deposits of biological organisms or the products of their life processes. Biological deposits may be micro scopic in nature, such as slimes, or macroscopic, such as barnacles or mussels. Slimes are usually composed of deposits of a gelatinous or filamentous nature. .., : . Corrosion. Corrosion* is destruction of a metal by -chemical or electrochemical; reaction with its environment. In, the corrosion process, the reaction products formed may be soluble or insoluble in the contacting environment. Insoluble cor rosion products may deposit at or near the attacked-area, or be carried along and j deposited at a considerable distance from the attacked area. Corrosivity. Corrosivity* is the capacity of an environment to bring about de >i struction of a metal by the process of corrosion. Corrosivity is a property of the environment, but it has no significance.until the metal in question is specified, . 873 i V'-' : - ' ' '* - '