Document 5kb2dYzB6aBQ17bK1vQELRjdN

466 CHAPTER 32 1960 Guide Table 1 .... Thermal Conductivity (Jr) of Industrial and Pipe Insulations (For Moan Tenperafore* fadicotad) fxpcvxwd m 8tv par (tour) (tquare foot) (Fahrenheit degroa tempeiotuie difference per inj Dendty leap, tor lb/Co Ft Urn*F 40 Typical Condodrrrty 1 nf Moan Temp. Fahr. 70 TOO 200 300 500 700 900 BLANKETS MINERAL WOOL (Rock, Slay, or Glass} Metal Reinforced Felt-Flexible Type Felt-Scrw-Rigia Type 1200 450 460 6-15 0.29 0.35 0.42 0.56 0.5-3 0.23 0.25 0.26 0-34 0.45 2-8 0.24 0.25 0.27 0.35 0.44 VEGETABLE 4 ANIMAL FIBER Hair Felt or Hair Felt plus Jute BLOCKS AND BOARDS ASBESTOS Molded Amosite 4 Binder Laminated Asbestos Paper Corrugated 4 Laminated Asbestos Paper 4 ply. 6 ply 8 ply ISO 10 0.27 0.28 0.30 1200 700 300 300 300 18 30 11-13 15-17 18-20 0.37 0.40 0.56 0.66 0.40 0.45 0.50 0.60 0.54 0.57 0.68 0.80 0.49 0.51 0.59 0.69 0.47 0.49. 0,57 0.65 CALCIUM SILICATE CELLULAR GLASS CORKBOARD (Without Added Binder) D1ATOMACEOUS SILICA 85% MAGNESIA Mag. Carb- 4 Asbestos MINERAL WOOL (Rock, Slag or Glass) Low Temp. (Asphalt or Resin Bonded) High Temp. (Resm Bonded) (with Inorganic Binder) PLASTICS (Foamed) RUBBER (Foamed) PIPE IN- ASBESTOS SC7LA- Molded Amosite 4 Binder TION Laminated Asbestos Paper Corrugated 4 Laminated Asbestos Paper 4 Ply per in. 6 Ply per in. 8 Ply per in. CALCIUM SILICATE Calc. Sll. 4 Asbestos CELLULAR GLASS CORK (Without Added Binder) DIATOMACEOUS SILICA 85% MAGNESIA Mag. Carb. 4 Asbestos MINERAL WOOL (Bock, Slag or Glass) Low Temp. (Asphalt or Resin Bonded) Low Temp. (Fine Fiber Resin Bonded) High Temp. Blanket-Type (Metal Reinforced) PLASTICS (Foamed) RUBBER (Foamed) 1200 800 200 1500 1900 600 200 600 1600 175 150 1200 700 300 300 300 1200 800 200 1500 1900 600 200 450 1200 175 150 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 0.60 0.70 0.64 0.64 0-75 0.68 0.80 11-14 0.35 0.38 0.42 0.46 6-18 0.28 0.29 0.30 8-10 0.2S 0.35 0.43 16-24 0.34 0.39 0.44 0.54 0.64 1.6 0.28 0.28 0.30 5 0.23 0.24 0.25 16 30 11-13 15-17 18-20 0.33 0.38 0.53 0.40 0.45 0.50 0.60 0.54 0.57 0.62 0.80 0.49 0.51 0.59 0.69 0.47 0.49 0.57 0.65 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 0.64 0.70 0.66 0.75 0.71 0.80 11-14 0.39 0.42 0.45 0.51 15 0.28 0.30 0.33 0.39 3 0.22 0.23 0.24 0.27 0.31 6-15 0.29 0.36 0.42 0.56 1.6 0.26 0 2ft 0.31 5 0.23 0.24 0.25 VEGETABLE 4 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. 4 Asbestos 600 18 0.46 0.52 0.58 CE- MINERAL WOOL (Rock. Slag or Glass) 1MENT With Colloidal Clay Binder 1800 24-30 0.49 0.61 0.73 0.83 * Tfaeaa temperature* ore geaenUy raepted m rnuimm Wbeo orwetis* temperature tpprotebet these limit* tbe Mmufactorer'* reeommeadaUoB* should be Industrial Insulation 467 material for a specific service becomes more critical and must be based on experience and factual performance data (see Table 1). 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, tbe 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 under side 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. Such materials include hair, plastics, and rubber in the or ganic field, and asbestos and mineral wool in the inorganic field. Coverings and facings such as paper, aluminum, asbestos sheet, wire mesh, metal lath, may be used as reinforcing, vapor barriers, reflective surfaces, or surface finishes in gen eral. Thicknesses and shapes may be of any dimension that can be handled although standard sizes are generally used. Some blanket insulations are prepared in roll form for eco nomical 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 rises 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. 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 beat 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 1080 F with the surrounding air at 80 F. The surface per linear foot of pipe is given in tbe second column of Table 2. Heat losses from tarnished copper pipe and tube1 are given in Table 3. The surface per linear foot of tube is gives in Table 4. Table 3, Section A, of Chapter 9 also gives the sur face conductances for fiat surfaces of different emisrivities 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 2 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 beat loss from 165 ft of 2 in. bare pipe in service 4000 hr per year. The pipe is carry ing steam at 10 psi presure 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 and 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 = 2.615 X 159.4 X 0.622 (linear ft factor) X 165 (linear ft) X 4000 (hr) = 171,100 Mb. (Mb = 1000 Btu.) Example S: Octal costing $1150 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 loss from the line. Solution: The cost of heat per 1000 Mb supplied to the sys tem = 1 flOO^00 x 115 (dollars) -r [13,000 (Btu) X 2000 (lb) X 055 (efficiency)] = $0804. The total cost of heat lost per year = 0804 X 171.1 (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 FLOW CALCULATIONS The heat losses through 1, Wt, and 2-in. thick pipe insula tion on various size pipes for various temperature differences between the pipe and the surrounding atmosphere up to 525 F, are shown in Figs. 1,2, and 3. The actual thic.lmpsB of many molded pipe coverings is not exactly 1 in. However, the loss through any given thick ness of insulation can be obtained by interpolation. The heat losses through 1, tyi, and 2-in. thick block, blanket, or cement insulation when applied to a flat vertical surface is given in Fig. 4. The losses through any of the insulations given in Table 1 can be obtained by multiplying the losses obtained from Figs. 1,2,3, or 4 by the factors given in Table 6. Pipes operating at high temperatures are frequently in sulated to the best advantage by combining a high tempera ture insulation near the pipe with a moderate or low tem perature insulation around it as an outer layer. By this method an efficient material may be used for each of the two temperature ranges encountered. In calculating the heat loss through such a combination the mean temperature of each