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452 CHAPTER 31 1959 Guide requirement. Complete information can best be obtained from a hanger manufacturer. APPLICATION OF PIPE, TUBE, AND FITTINGS In the application of pipe, tube, and fittings it is necessary to comply with regulations contained in local codes and ordi nances. Table 23 is offered as a guide to current practice in hpftt.tTig and air conditioning. It is based on practice in a num ber of consulting engineers' offices and information extracted from Reference 7. It should be borne in mind that selection of material to be used will also be influenced by the familiar ity of local artisans with methods of using different materials. REFERENCES 1 American Standard Code for Pressure Piping (American Standards Association, ASA B-31.1, 1942). * API Specification 6L for Line Pipe (American Petroleum Institute). * Standard Manual on Pipe Welding (Heating, Piping and Air Conditioning Contractors National Association, 1951, 2nd ed.). Welding Handbook (American Welding Society, 1942). 4 ASMB Power Boiler Code (American Society of Mechanical Engineers). * Marine Engineering Regulations of the Coast Guard (Amer ican Bureau of Shipping). Welding (General Specifications for Inspection of Material, Appendix VII, U. S. Nary). General--for vessels of the U. S. Navy {.Specifications for Welding, Ap pendix 5, Part 1, Bureau of Ships, April 1940). *Sabin Crocker: Piping Handbook (McGraw-Hill Book Co., New York). E. A. Wert, S. Smith and E. T. Cope: A Manual for the Design of Piping for Flexibility by the Use of Graphs (The Detroit Edison Company). C. S. Beard: Control valves and positioners {Industry and Power, March 1953, p. 67). CHAPTER 32 PIPE AND INDUSTRIAL INSULATION Industrial Insulation: Uses, Properties, Temperature Range of Use, Temperature limitations. Forms; Bare Surface Heat Loss,Conductivities; Heat Flow Calculations; Thickness for App/icatioiv Economical Thickness,low Temperature Insulation,- Insulation to Prevent Freezing; Application; Underground Insulations THE PAST 50 years have seen an enormous increase in insulation the user should consult the manufacturer or obtain the use of thermal insulation by industry. Where once the results of unbiased tests. it was not uncommon to see hot water and steam lines, and Other properties of thermal insulations that are of more or even boiler surfaces, uninsulated, it is now rare indeed to see less importance, depending upon the use, are strength, hard any surface operating more than a little above or below am ness, density, compressibility,,specific heat, resistance to high bient temperature without insulation. Higher costs of fuel, or low temperature, and thermal coefficient of expansion. The increased efficiency of industrial operations, and the necessity final choice of an insulating material for a given purpose for close control of the temperature of industrial processes usually involves a compromise with regard to several de are among the factors that have caused this greatly increased sirable properties. For example, an insulating firebrick must usage of thermal insulation.. have considerable strength and must be resistant to the tem USES OF INDUSTRIAL INSULATioN perature to which it is to be exposed. The desirable properties of low conductivity and light, weight must be sacrificed to Thermal insulation serves five principal purposes: (1) to conserve heat or some other form of energy, for example, some extent to achieve these necessary properties of strength and temperature resistance. electrical energy to operate a refrigeration compressor; (2) to increase the comfort of living spaces; (3) to facilitate con trol of the temperature of a process; (4) to reduce the tern--- TEMPERATURE RANGE OF USE OF INDUSTRIAL INSULATION perature of the shell of a pressure vessel; and (5) to control the external temperature of the insulated space in order to avoid danger to personnel, to protect surrounding structural members from damage by high temperature, to reduce the temperature of working spaces, and, in case of equipment operating below ambient temperatures, to prevent sweating or icing at the warmer surface. Depending on the application, one or another purpose may govern the choice of insulation; usually' two or more are concurrently of importance. Since thermal insulation reduces the exchange of heat en ergy between an insulated surface and its surroundings, it can be useful at any temperature from the lowest to the highest. Actually insulation is used in industrial processes operating at temperatures from --400 F to +3000 F and higher. At the low end of the scale are processes involving liquefied' gases, usually in vessels or piping, at temperatures from the lowest up to about --40 F. From --40 to normal atmospheric PROPERTIES OF INSULATIONS temperatures large amounts of low temperature insulation are used for enclosing freezing tunnels, cold storage rooms, Low thermal conductivity is the property that distin and a great variety of food and industrial processes, requiring guishes a thermal insulation. Thermal conductivity is defined low temperatures. as the rate of heat flow through unit area of a homogeneous At normal and near-normal temperatures insulation in substance under the influence of unit temperature gradient building structures is required for economical' operation of in the direction perpendicular to the area. Many units have heating and air-conditioning systems. Insulation for heating . been used to express thermal conductivity but the most com and cooling equipment and for the distribution ducts, piping, mon engineering unit is Btu (hour) (square foot) (Fahren etc., is, however, usually considered as industrial. The range heit degree per inch of thickness). The usual symbol for of temperatures is from that of chilled water or about 32 F thermal conductivity is k. up to steam at 100-125 psig (about 350 F).. Reflective insulations, such as aluminum and steel coated Drying and hairing ovens, small and large boilers, distilla with a reflecting coating, depend not upon low thermal con tion equipment in oil refineries, and high-pressure and super ductivity for their resistance to heat flow, but upon the low heated steam piping call for insulation suitable up to *1200 F. thermal emissivity of their surfaces and subdivision of the Petroleum cracking units, heat treating furnaces, and ceramic air space. To be effective in retarding heat flow by radiation, kilns may reach 2200-2400 F. Still higher temperatures with the reflective surface must face an air space. surfaces to be insulated up to 3000 F are found on melting fur Thermal conductivity values of the most commonly used naces for glass, iron, steel, and metals of all kinds as well as industrial and pipe insulations are shown in Table 1. These furnace enclosures for combustion spaces for many kinds of values, have been selected as typical and useful for engineering heating units. calculations, and may or may not apply to a particular ma Above 3000 F the variety of materials physically suited for terial or application. For accurate values for a particular walls and structural parts decreases rapidly with increasing 453