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612 CHAPTER 27 1954 Guide not heavier than extra-strong, assumes a maximum safe value of fiber stress of 16,000 psi. When square type bends are used, the width B of the bend should not, exceed about twice the height, since for a given total length of pipe in the bend, the height A of the bend becomes progressively less with increase in width until the height approaches zero and no flexi bility exists. Actually, wide bends utilize to best advantage the inherent flexibility of the line, but such bends cannot be proportioned on the basis of Equation 1. For such applications, more' accurate' methods1 should be employed. It is further assumed that the comers are made with screwed or flanged elbows or with arcs of circles having radii five to six times the pipe diameter. Use of welding elbows with radii of 1^ times the pipe diameter will decrease the end thrusts somewhat,- but will raise the fiber stress correspondingly. All risers must be anchored and safeguarded so that the difference in' length when hot, from the length when cold, shall not disarrange the normal and orderly provisions for drainage of the branches. Proper anchoring of piping is especially necessary with fight-weight radiators, to allow for freedom of expansion in order that no pipe strain Fig. 1. Measurement op L on Various Pipe Bends will distort the radiators. When expansion strains from the pipes are permitted to reach these fight metal heaters, they usually emit disturbipg sounds. - HANGERS AND SUPPORTS Heating system piping requires careful and substantial support. Where changes in temperature of the fine are not large, such simple methods of support may be utilized as hanging the fine by means of rods or perforated strip from the building structure, or supporting it by brackets or on piers: When fluids are conveyed at temperatures of 150 F or above, however,, hangers or supporting equipment must be fabricated and assembled to- permit free expansion or contraction of the piping. This can be accom plished by the use of long rod hangers, spring hangers, chains, hangers or supports fitted with rollers, machined blocks, elliptical or circular rings or larger diameter than the pipe giving contact only at the bottom, or trolley hangers. In all cases, allowance should be made for rod clearance to permit swinging without setting up severe bending action in the rods. For pipes of small size, perforated metal strip is often used. For hori zontal mains, the rod or strip usually is attached to the joists or steel wore of the floor above. For long runs of vertical pipe subject to considerable thermal expansion, either the hangers should be designed to prevent ex- Pipe, Fittings, Welding 613 cessive load on the bottom support due to expansion, or the bottom support: should be designed to withstand the entire load. THREADING PRACTICE In all threaded pipe for heating and ventilating installations the American Standard taper pipe thread, ASA B2.1-1942 is used. This thread is cut with a taper of 1 in 16 measured on the diameter of the pipe so as to secure a tight joint. The number of threads per inch varies with the pipe size. Threads for fittings are the same, except that it is regular practice to furnish straight tapped couplings for Schedule 40 pipe 2 in. and smaller. For steam pressures in excess of 25 psi, it is recommended that taper-tapped couplings be used to obtain a tight joint. These may be secured by order ing line pipe2 which is used for oil piping, the couplings of which are provided with taper-tapped threads and may be used with regular mill-threaded standard weight pipe. Thread lengths should be in accordance with ASA B2.1. Right-hand threads are used unless otherwise ordered. To facilitate drainage, some elbows have the thread tapped at an angle to provide a pitch of the connecting pipe of Y in. to the foot. These elbows are known to the trade as pitch elbows and are commercially available. All threaded pipe joints should be made up with a thread paste suitable for the service for which the pipe is to be used. Table 5 contains pertinent threading data for standard weight, extra strong and double extra strong steel, and wrought-iron pipe. TYPES OF FITTINGS Fittings for joining the separate lengths of pipe together are made in a variety of forms, and are either screwed or flanged, the former being generally used for the smaller sizes of pipe up to and including V/i in., and the latter for the larger sizes, 4 in. and above. Screwed fittings of large size, as well as flanged fittings of small size, are also made and are used for certain classes of work at the proper pressure. The material used for fittings is generally cast-iron, but in addition to this, malleable-iron, steel and steel alloys are also used, as well as various grades of brass or bronze. The material to be used depends on the char acter of the service and the pressure. Malleable iron fittings, like brass fittings, are cast with a round instead of a flat band or bead, or with no bead at all. Fittings are designated as male or female, depending on whether the threads are on the outside or inside, respectively. Screwed galvanized fittings are made according to the 150 lb American Standard. As in the case of pipe, several weights of fittings are manufactured, recognized American Standards for the various weights are as follows: ,,PSH1011 Pi? flanges and flanged fittings for 25 lb (sizes 4 in. and larger), 125 lb, nd 250 lb maximum saturated steam pressure, ASA B16b2, B16a, and B16b, reBPectively. Malleab]e iron screwed fittings for 150 lb maximum saturated Bteam pressure, Aod Bl6c. 4S?Bl6dD screwe<* brings for 125 and 250 lb maximum saturated steam pressure Blfo^66* Ranged fittings for 150 and 300 lb maximum steam service pressure,.ASA fni^k6 aflwable cold water working pressures for these standards vary from 43 lb the 25 lb standard, to 500 lb for the 300 lb steel standard.