Document KzGX951G4X9Edm0BMKpBbg3wx

American Society of Heating and Ventilating Engineers Guide, 1929 senting the given temperature difference: thence vertically to the line representing the conductivity of the given material; thence horizontally, Chapter XV--Heat Insulation for Pipes and Surfaces weather-proof the insulation and to provide a drainage system for the water which may get into the conduit. HEAT LOSSES FROM BARE FITTINGS Very often, even where pipes are thoroughly insulated, flanges and fittings are left bare due to the belief that the losses from these parts are Fig. 7. Heat Loss through 2 in. thick Covering to the left, to the line representing the given discount on that material; thence vertically to the curve representing the required per cent return on the investment; thence horizontally, to the left, to the curve repre senting the given pipe size; thence vertically to the scale at the top of the sheet where the economical thickness may be read off directly. The dotted line on the chart illustrates its use in solving a typical example. It is impossible to determine accurately the economic thickness of insulation to use for an underground installation owing to the -many variables which are present such as depth of line, conductivity of ground, moisture `conditions, etc. However, it is considered good practice to insulate undergroundjines--with_approximately in. less thickness of insulation than for above ground installations under similar operating conditions. It is necessary to keep the insulation absolutely dry if the efficiency is to be maintained, therefore,' precautions should be taken to thoroughly 256 (L. B. McMillan, Iron and Steel Engineer, July 1926.) Fig. 8. Heat Losses from Surfaces : Exposed to Various Air Velocities - not large. However, the fact that a pair of 10-in. standard flanges having, an area of 3.43 sq. ft, would lose, at 100 lb. steam pressure, an amount of heat equivalent to more than a ton of coal per year shows the necessity for insulating such surfaces. Table 3 shows the areas of both standard and extra heavy flanged fittings including the accompanying flanges bolted to the fittings. 257