STEAM BOILERS 121 



In Fig. 2 is shown a corrugated expansion joint, which is some- 

 times used on large exhaust pipes. It consists of a short 

 section of flanged corrugated 

 pipe, usually copper, which is 

 put in the steam pipe wherever 

 necessary. The elasticity of FIG. 2 



this section, due to the corrugations, permits expansion and 

 contraction. 



Expansion Bends. The best way of allowing for expan- 

 sion is by using expansion bends, or bent pipes; but the space 

 they occupy often limits their use. The forms of bends more 

 commonly used are shown in Fig. 3, the trade name being given 

 below each bend. Where a bent pipe is used, the radius r of 

 the bend should not be less than six times the diameter of the 

 pipe, for wrought iron or steel; to secure the proper spring in 

 bends used on long lines of piping, the radius should be greater 

 than this. Bends of copper pipe may be of shorter radius, 

 as copper yields more readily than iron or steel. 



Bends made from iron or steel pipe must be bent while red 

 hot. Iron and steel pipe bends generally have iron flanges 

 fastened on; copper bends either have composition flanges riv- 

 eted and brazed on, or have steel flanges, the edges of the pipe 

 being turned over. The piping is usually installed so that it is 

 under a slight tension when cold; when filled with steam, the 

 expansion of the pipes removes the tension, and there is no 

 stress on the pipe except that due to the steam pressure. 



Pipe Coverings. To prevent loss of heat by radiation, steam 

 pipes are covered with various kinds of materials that are poor 

 conductors of heat. As a rule, the covering is manufactured 

 in short sections molded in halves to fit the pipe, the valves and 

 fittings being covered with the same material in a plastic state. 

 After the covering is properly secured in place, it is frequently 

 covered with a heavy duck or canvas jacket sewed on and 

 painted, and sometimes ornamented by brass bands placed at 

 regular intervals. 



The substances used for covering steam pipes for this pur- 

 pose are very numerous and vary considerably in efficiency. 

 Among the best and most widely used non-conducting materials 

 are hair felt, cork, magnesia, asbestos, and mineral wool. 



