Document 7OrJjjNrK63XN1LyYRnYKdaKV

458 CHAPTER 31 Table 14 .. Dimensions of Socket-Welding Fitting! A. Dimenriant of Socket-Welding Efbowt, Toe*, and Crosw 1960 Guide ' Nominal Pipe Sue Depth of Socket, Min Center to Bottom of Socket Sdted 40 and 80 Sdied 160 Bore Otamater of Socket, Min Socket WafJ Thrckne**, Atta Sdted 40 Sdied 80 Sdied 160 Bore Diameter of fitting Sdwd 40 Sdted 80 Sdted 160 AB C D Xx XX X 'X XX HX 1X lX X ix X 2X 2* H 3% Ks Ks % XX XX 0.420 0.555 0.690 0.855 1.065 0.125 0.125 0.125 0.136 0.141 0.125 0.149 0.158 0.184 0.193 0.234 0.273 0.269 0.364 0.493 0.622 0.824 X 1H lKs `X IK IX 1.330 1.675 1.915 0.166 0.175 0.181 0.224 0.239 0.250 0.313 0.313 0.351 1.049 1.380 1.610 IX m m *x 2K *X 2.406 2.906 3.535 0.193 0.254 0.270 0.273 0.345 0.375 0.429 0.469 0.546 2.067 2.469 3.068 B. Dimenriont of Socket-Weidiag 4S Dag Bbowt, Coopting*, and Half Coopting* 0.215 0.302 0.423 0.546 0.742 0.957 1.278 1.500 1.939 2.323 2.900 0.466 0.614 0.815 1.160 1.338 1.689 2.125 2.626 Center to Bottom of Socket for 45 Deg Bit Nominal Pipe m Depth of Socket, Min Sdted 40 and 80 Sdted 160 CoupGngt Distance Between Boffomt of Socket* Half Coapfingt, Bottom of Socket to Opporite Face Bore Diameter of Socket, Min Socket Wad Thickniw, Min Sdted Sdted Sdted 40 80 160 Bare Diameter of fitting Sdted Sdted Sdted 40 B0 160 A E FB C D H X X, X X x, X X H X M X X X X, X X X X X M X 1 X Ms >K X ix X lXe 1X, X IX X H. 1 X 2 X1 IK 2X X ix IK 3 X ix IK X X X X X >Kg X 'Xt ix ix. ix ix l`He ix 0.420 0.555 0.690 0.855 1.065 1.330 1.675 1.915 2.406 2.906 3.535 0.125 0.125 0.125 0.136 0.141 0.125 0.149 0.158 0.184 0.193 0.234 0.273 0.269 0.364 0.493 0.622 0.824 0.215 0.302 0.423 0.546 0.742 0.466 0.614 0.166 0.224 0.313 1.049 0.957 0.815 0.175 0.239 0.313 1.380 1.278 1.160 0.181 0.250 0.351 1.610 1.500 1.338 0.193 0.273 0.429 2.076 1.939 1.689 0.254 0.345 0.469 2.469 2.323 2.125 0.270 0.375 0.546 3.068 2.900 2.626 From A merita* Standard let Sled Socid-Wddine Fittiat*. ASA BIS.U-1MS. All dimension* an in incbee. This gives Equation 3 F - aSAM. (3) Values for a and E are given in Table 21 for various pipe materials, to facilitate determination of the stress in an ac tual pipe. The following example illustrates the computation of stress. Example 1: What is the force set up by a 1-in. Schedule 40 steel pipe if the thermal expansion from a 100 deg temperature increase is fully constrained? Answer; From Table I, determine that for a 1-in. Schedule 40 steel pipe, the metal area = 0.494 sq in. Then, from Table 21, aB -- 195 psi, and from Equation 3 F = 195 X 0.494 X 100 - 9630 lb. It is interesting to note that length does not enter into the determination of the constraining force. This is so because the Pipe, fittings, Welding Table 15___ Dimensions ofMalleable 90-Deg Elbows, Tees, Crosses, and 45-Deg Sbows (Straight Sizes, 150 Lb) ELBOW TEE CROSS 45'ELBOW not Pipe Size Inride Diam Bbowt, Toes, and Center to End, 45-Oeg Bbowt length of Thread, Min Width of Band, Min eter of Fitting Min Max Metal Thick- Creme* A C Be f G Outride Diameter of Band, Min 'H X 0.69 X 0.81 X 0.95 X 1.12 0.73 0.80 0.88 0.25 0.32 0.36 0.43 0.200 0.405 0.435 0.090 0.215 3.540 0.584 0.095 0.230 0.675 m.719 0.100 0.249 0.840 0.897 0.105 0.693 0.844 1.015 1.197 X 1.31 0.98 0.50 0.273 1.050 1.107 0.120 1.458 1 1.50 1.12 0.58 0.302 1.315 1.385 0.134 1.771 IK 1.75 1.29 0.67 0.341 1.660 1.730 0.145 2.153 IK 1.94 1.43 0.70 0.368 1.900 1.970 0.155 2.427 2 2.25 2K 2.70 3 3.08 3K 3.42 1.68 1.95 2.17 2.39 0.75 0.92 0.98 1.03 0.422 2.375 2.445 0.173 0.478 2.875 2.975 0.210 0.548 3.50G 3.600 0.231 0.604 4.000 4.100 0.248 2.963 3.589 4.285 4.843 4 3.79 2.61 1.08 0.661 4.500 4.600 0.265 5.401 5 4.50 3.05. 1.18 0.780 5.563 5.663 0.300 6.583 6 5.13 3.46 1.28 0.900 6.625 6.725 0.336 7.767 From America* Standard for HolleaUe-lren Screwed PiUinft, ISO Lb. ASA BttX-1951. All dimeoooDa given in inches. stress is a unit length function and so is the expansion; there fore, they cancel each other. In other words, if a weight stretches a 10-foot wire 0.10 in., then that tame weight would stretch a 100-foot wire one inch. In both cases the elongation was 1 part in 1200. The realisation that thermal stress is in dependent of length is important, but often overlooked. Nonetheless, that concept explains the feasibility of utilizing the inherent flexibility of the pipe to take care of expansion. Regardless of the length of pipe between anchors, it is possible to take care of the expansion by putting the force of expansion into the pipe as internal stress. If the pipe is not straight, then the force of expansion will cause a bending moment. The pipe will then be under a com bined stress. The stresses will be longitudinal and transverse, and to a small extent radial. All of these stresses tend to fracture the pipe, and therefore must be added to make up what is called allowable combined stress. The Code for Pres sure Piping, ASA B31.1, published by the ASME, sets up very definite limits for the allowable combined stresses for various pipe materials. For temperatures below 400 F and for piping that is for neither district heating nor power, any standard pipe material may be used. For high-temperature or highpressure work, some text on expansion and flexibility should be consulted. It is beyond the scope of this chapter to de velop the theory of expansion caused by high temperatures. For the ampler problems encountered for temperatures 459 400 F and less, which the heating engineer is more apt to en counter, there are four methods of allowing for expansion. The first method is to use packless expansion joints. These joints include types of bellows expansion joints, rubber, cor rugated copper and other metals. Rubber-type joints are generally used in vacuum or lowpressure steam lines. Maximum temperature is generally ISO F. If oil is present in the line, rubber-type joints will be attacked. Travel of these joints is up to 1 inch. The travel to be expected can be calculated by using Equation 2. The second type of expansion joint is called a dip joint. This joint allows for expansion by a sliding of a female mem ber over a male member. The joint is kept tight by mwns of packing. The packing determines the limit- of the tempera ture to which the joint may be subjected. The main disad vantage to this joint is that it must be continually inspected for a deterioration of the packing. By using double dip joints, the travel may go to several feet, but generally a single joint allows about a foot of expansion. It is common practice to use slip joints up to 250 psi. The most common method of allowing for expansion in heating systems is to use the swivel joint. This is the third method. The swivel joint was first used with screwed fittings, but it is also used now with welded fittings. With welded el bows, the swivel introduces torsional stress in the elbow and in the swing piece. This type of joint is adequate for taking up the expansion in a header, and preventing fracture of the riser or heating element. The fourth method is to allow the flexibility of the pipe to absorb the stress of expansion. A technique used to reduce the stress in the expanded pipe is to cold spring it before hook ing it up. Cold springing can be used to absorb about onehalf the stress. The technique is to install the pipe with an opposite stress. For example, if the pipe were to have a com pression of 2000 psi, then the pipe would be installed with 1000 psi of tension. For refrigeration, the pipe would be cold sprung in compression. For conditions not requiring rigorous analysis, it is per missible to use expansion bends designed by means of Equa tion 4 t = 6.16y/D* (4) where L = length of pipe, feet. Dt -- outside diameter of pipe, inches. e " deformation, inches (see Equation 2) fiber stress g 16,000 pounds per square inch. U bend with 4 fittings U bend with 2 fittings Fig. 3 .... Measurement of L on Various Pipe Bends