Document 3YqdazYLeDrDL4n6bopbbQba

454 CHAPTER 32 1959 Guide hn. Table 1 .... Thermal Conductivity (Jc) of Industrial and Pipe Insulations (for Mean temperature* fixiiusfed} . Expreued m Bte per (hoor) (kjuot* foot) (FafaranMf degree temperature d/fferenc* per tnj Material (Competition) Accepted ' Max. Dms)]' Temp, for Ut/Cu Ft U**F 40 Typfcat Conductivity It ot Moan Temp. Fafv. 70 too 200 300 500 700 900 BLANKETS - MINERAL WOOL (Rock, Slag, or Glass) Felt-Semi-Rigid Type VEGETABLE A ANIMAL FIBER Hair Felt or Hair Felt plus Jute 1200 450 450 6-15 0.29 0.35 0.42 0.56 0.5-3 6.23 0.25 0.26 0.34 045 2-8 0,24 0.25 0.27 0.35 0.44 180 10 0.27 0.28 0.30 BLOCKS ASBESTOS AND Molded Amosite A Binder BOARDS Laminated Asbestos Paper Corrugated A Laminated Asbestos Paper 8 ply .. . * CALCIUM SILICATE CELLULAR GLASS CORKBOARD (Without Added Binder) DIATOMACEOUS SILICA 1200 700 300 300 300 1200 800 200 1500 1900 18 0.37 0.40 0.47 0.76 30 0.40 0.45 0-50 11-13 15-17 18-20 0.54 0.57 0.68 0.80 0.49 0.51 0.59 0.69 0.47 0.49 0.57 0.65 11 9 6.5-8 22 25 ' 0.37 0.26 0.39 0.27 0.33 0.41 0.28 0.38 0.48 0.43 0.55 0 53 0.64 0.75 0.70 0.80 85% MAGNESIA Mag. Carb. A Asbestos 600 11-14 0.35 0.38 MINERAL WOOL (Roc*. Slag or Glass) Low Temp. (Asphalt or Resin Bonded) (With Inorganic Binder) . PLASTICS (Foamed) RUBBER (Foamed) 200 .600 1600 175 150 6-18 0.28 0.29 0.30 6-10 0.28 0.35 0.43 16-24 0.34 0.39 0.44 1.6. .5 0.26 0.28 0.30 0.23 0.24 0.25 0.64 PIPE IN- ASBESTOS . SULA- Molded Amosite A Binder TION Laminated Asbestos Paper Corrugated A Laminated Asbestos Paper 8 Ply per in. 1200 700 300 300 300 16 30 11-13 15-17 18-20 0.33 0.38 0.43 Q.4Q 0.45 0.50 0.54 0.57 0.62 0.80 0.49 0.51 0.59 0.69 0.47 0.49 0.57 0.65 CALCIUM SILICATE CELLULAR GLASS DIATOMACEOUS SILICA . 1200 800 200 1500 1900 11 9 7-10 22 25 0.37 0.27 0.39 0.28 0.36 0.41 0.29 0.40 0.48 0.30 0.44 0-55 0-55 0.70 0.75 0.80 85% MAGNESIA Mag. Carb. A Asbestos ' 600 MINERAL WOOL (Rock, Slag or Glass) Low Temp. (Asphalt or Resin Bonded) Low Temp. (Fine Fiber Resin Bonded) ~ - High Temp. Blanket-Type (Metal Reinforced) 200 ' 450 1200 PLASTICS (Foamed) RUBBER (Foamed) 175 150 11-14 0.39 0.42 0.45 15 0.28 0.30 0.33 0.39 3 0.22 0.23 0.24 0.27 0.31 6-15 0.29 1.6 0.26 0.28 0.31 5 0.23 0.24 0.25 VEGETABLE A ANIMAL FIBER Wool Felt Hair Felt or Hair Felt plus Jute 180 20 180 ; 10 0.29 0.31 0.33 0.27 0.28 0.30 INSULAT- 85% MAGNESIA Mag. Carb. A Asbestos 600 18 0.46 0.52 0.58 CE- MINERAL WOOL (Rock, Slag or Glass) MENT With Colloidal Clay Binder 1800 24-30 0.49 0.61 Ttmm temperatures ere geitenUty accepted e maximum. Whefi cperetinf temperature approaches tbeae limits the Manufarturer'a recorewendstions should be followed. Pipe and Industrial Insulation 455 temperature. Insulation for conservation of beat energy must, therefore, often be applied so as to permit enough heat to escape to retain mechanical strength. TEMPERATURE LIMITATIONS OF INSULATIONS Probably the greatest volume of low temperature insula tion is used for temperatures from minus 100 F to atmos pheric. The effect of temperature alone on physical integrity is not ordinarily very important for most types in the low temperature field. There are more definite limitations for materials in the high temperature field where decomposition, excessive linear shrinkage, softening, or some other effect of temperature alone will put a maximum limit on the tempera ture for which a material is suited. As extremes in tempera ture are approached, both high and low, the selection of a material for a specific service becomes more critical and must be based on experience and factual performance data. FORMS OF INSULATION The 'physical form of industrial insulations varies from powders and loose fills which might be called formless, through materials with varying degrees of compressibility and flexibility, to completely rigid shapes often referred to as preformed insulation. After deciding that a material has the necessary insulating value, physical properties, and tem perature resistance, the choice of the form desired will usually be governed by considerations of material and application cost. The application method and cost in turn will be greatly affected by the. nature of the surface to be covered. Loose fills such as powders and granules must be supported in place by retaining walls, coverings, etc. for application on vertical surfaces and on the underride of horizontal surfaces. Insulating cement is a loose material which when mixed with water to obtain plasticity and adhesion, may be trowelled on a surface and dried in place to serve as insulation. Both loose-fill and insulating cement are especially suited-for covering uneven and irregular surfaces. Flexible and nonrigid insulations are generally grouped as blanket insulation, and are available in many types and varieties, both organic and inorganic, with and without binders, and with reinforcing coverings on one or both sides. Only inherently fibrous materials are generally suited for blanket insulation. Such materials are wood, cotton, and hair in the organic field, and asbestos and mineral wool in the in organic field. Coverings and facings such as paper, aluminum, asbestos sheet, wire mesh, metal lath, may be used as re inforcing, vapor barriers, reflective surfaces, or surface fin ishes in general. Thicknesses and shapes may be of any di mension that can be handled although standard rises are generally used. Some blanket insulations are prepared in roll form for economical shipping. Rigid materials are preformed during manufacture to standard lengths, widths, and thicknesses of a size that can be handled readily. In the case of insulation for pipes and cylindrical surfaces the radius of curvature is varied to suit all standard sizes of pipe and tubing. Some materials are offered in shapes curved to fit greater radii up to several feet or more. Material in rectangular dimensions is usually called block, board, or sheets, the name varying with custom for particular uses. Most common sizes of block insulation are 36 in. long, 6 in. or 12 in. wide, and in thicknesses ranging from 1 to 4 in. Boards in the building insulation field range up to 12 ft long by 4 ft wide with the thickness usually Vi to 1 in. but ranging up to lVi in. Smaller hoards, or sheets, are used on air-conditioning ducts, equipment, and in. cold storage. BARE SURFACE HEAT LOSSES-- FLAT SURFACES AND PIPE Heat losses from or to uninsulated surfaces of pipes, ducts, vessels, or furnaces may be of considerable magnitude if the temperature of the surrounding medium differs appreciably from that of the surface. Losses are increased by motion of the surrounding air or by contact of the hot or cold surface with bodies of high conductivity. Good design, therefore, must include consideration of such heat losses and provision for adequate insulation wherever needed. The basic principles of heat loss from surfaces are discussed in Chapter 5. In that chapter radiation and convection are treated separately. Heat losses from horizontal bare steel pipes, based on tests at Mellon Institute and calculated from the fundamental radiation and convection equations (Chapter 5), are given in Table 2. This table also gives the heat losses or .surface con ductances for flat vertical and horizontal surfaces for surface temperatures up to 10S0 F with the surrounding air at 80 F. The surface per linear foot of pipe is given in the second column of Table 2. ~ Heat losses from tarnished copper pipe and tube are given in Table 3. The surface per linear foot of tube is given in Table 4. Table 3, Section A, of Chapter 9 also gives the sur face conductances for flat surfaces of different emissivities and orientations in contact with still air. Table 5 gives the area in square feet of flanges and fittings for various standard pipe sizes. These tables can be used to advantage in estimat ing the amount of insulation required. Examples 1 and t show how the annual heat loss from un covered pipe and its dollar value may be computed from the data in Table 2. Example 1: Compute the total annual heat loss from 165 ft of 2 in. bare pipe in service 4000 hr per year. The pipe is carry ing steam at 10 psi pressure and is exposed to an average air temperature of 80 F. Solution: The pipe temperature is taken as the steam tem perature, which is 239.4 F, obtained by interpolation from Steam Tables. The temperature difference between the pipe and air -- 239.4 -- 80 = 159.4 F. By interpolation in Table 2 between tem perature differences of 150 ana 200 F, the heat loss from a 2-in. pipe at a temperature difference of 159.4 F is found to be 2.615 Btu per (hr) (sq ft) (F deg). The total annual heat.loss from the entire line -- 2015 X 159.4 X 0022 (linear ft factor) X 165 (linear ft) X 4000 (hr) - 171,100 Mb. (Mb = 1000 Btu.) Example t: Coal costing $1100 per ton and having a calorific value of 13,000 Btu per pound is being burned in the furnace supplying steam to the pipe line given in the previous example. If the system is operating at an overall efficiency of 55 percent, determine the monetary value of the annual heat los from the line. Solution: The cost of heat per 1000 Mb supplied to the sys tem = 1,000,000 X 115 (dollars) -t- [13,000 (Btu) X 2000 (lb) X 055 (efficiency >] = $0504. The total cost of heat lost per year = 0504 X 1711 (thousand Mb) = $13756. CONDUCTIVITY OF INDUSTRIAL INSULATIONS The conductivities of various materials used for insulating steam and hot water systems are given in Table 1. They are given as functions of the mean temperatures or the arithmetic mean of the inner and outer surface temperatures of the in sulations. HEAT ROW . CALCULATIONS The heat losses through 1, IVt, and 2-in. thick pipe insula tion on various size pipes for various temperature differences