Document eQzjQXk8MxOrOxn9pqqXYdqe

644 CHAPTER 27 1955 'Guide the line before it can be transferred; to, such equipment as boilers or pumps. By means of solid anchors, the anchors can be used to divide the piping into .isolated sections that cannot transmit the stresses to other.sections. .Hangers are used to. support the piping, and. to take out the bending stresses. They are of the spring, roller, or rod type. Such types gen erally allow the free movement of the pipe and yet maintain full support. The Code for Pressure Piping, A SA B31.1, has strict requirements for the materials used in hangers and supports. The structural properties have a safety factor of five, and consequently there is little'chance of failure due to a sudden change of load. ... .There is a type of, support foralmost every conceivable requirement. Complete information can best be obtained from a hanger manufacturer. REFERENCES 1 American Standard Code for Pressure Piping, ASA B-31.1--1942, American Standards Association1, -i .' -* See API' Specification 5L for Line Pipe, American Pelroleurh Institute. Standard Manual on Pipe Welding {Heating, Piping and Air Conditioning Con tractors National Association, Second Edition, 1951)1 Welding Handbook'(American Welding Society, 1942). ASME Power Boiler Code, American'Society of Mechanical Engineers. 1 Marine Engineering Regulations of the Coast Guard, American Bureau of Shipping. General Specifications for Inspection of Material, Appendix VII, Welding, U. S. Navy. Specifications for Welding, Appendix 5, Part 1--^General--for Vessels of the V. S. Navy, Bureau of Ships, April, 1940. See (1) Piping Handbook, by Sabin Crocker (McGraw-Hill Co.); (2) A Man ual for The Design of Piping for Flexibility by the Use of Graphs, by E. A. Wert, S. Smith, E. T. Cope (The Detroit Edison Company). CHAPTER 28 PIPE AND INDUSTRIAL INSULATION Heat Losses from Bare and Insulated Surfaces and Pipes, Thermal Conductivities of Various Insulations, Low Temperature Pipe Insulation, Insulation of Pipes to Prevent Freezing, Economical Thickness of Pipe Insulation, Underground Pipe Insulation 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 thermal conductivity. Good, design, therefore, must include careful consideration of such heat losses and provision for adequate insulation wherever indicated. HEAT LOSSES FROM BARE SURFACES The basic principles of heat loss from surfaces are discussed in Chapter 5. In that chapter radiation and convection , are treated separately. Table 1, Section A, of Chapter 9 gives the surface conductance of flat surfaces of different emissivities arid orientations in contact with still air, the values given including the effects of both radiation and convection. HEAT LOSSES FROM BARE PIPES 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 1. Heat losses from horizontal copper tubes and pipes with tarnished surfaces, are given in Table 2.1 Heat losses from bare pipe of materials having lower emissivities may be calculated from data appearing in Chapter 5. The area in square feet per linear foot of pipe is given in Table 3 for various standard pipe sizes, and Table 4 for copper tubing, while 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 estimating the amount of insulation required. Very often, when pipes are insulated, flanges and fittings are left bare, so as to allow for easy access to the fittings in case of repairs. The fact that a pair of 8-in. standard flanges having an area of 2.41 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. Examples 1 and 2 show how the annual heat loss from uncovered pipe and its dollar value may be computed from the data in Table 1. serv'Can?^e 1 Compute the total annual heatloss from 165 ft of 2 in. bare pipe in rvice 4000 hr per year. The pipe is carrying steam at 10 lb pressure and is exposed 0 811 average air temperature of 70 F. Solution. The pipe temperature is taken as the steam temperature, which is 239.4 .obtained by interpolation from Steam Tables. The temperature difference be`"e PIP an<l air = 239.4 -- 70 = 169.4 F. By interpolation of Table 1 between perature differences of 157.1 and 227.7 F, the heat loss from a 2-in. pipe at a tern- 645