Document b5kvJYdm56BXZMZRO5YqvX64O

HEATINC VENTILATING AIR CONDITIONING GUIDE 1941 Swivel joints are used extensively in low-pressure steam and hot water heating systems and in hot water supply lines. The swivel joints absorb the expansive movement of the pipe by the turning of threaded joints. In many cases the straight pipe in the offset of a swivel joint is sufficiently flexible to take up the expansion without developing enough thrust to produce swiveling in the threaded joint. This is preferable since con tinued turning in the threaded joint may in time result in a leak, par ticularly when the pressure is high. The amount of elongation which a swivel joint can take up is controlled by the length of the swing piece employed and by the lateral displacement which is permissible in the long pipe runs. Probably the most economical method of providing for expansion of piping in a long run is to take advantage of the directional changes which must necessarily occur in the piping and proportion the offsets so that sufficient flexibility is secured. Ninety-degree bends with long, straight tangents in either a horizontal or a vertical plane are an excellent means for securing adequate flexibility with larger sizes of pipe. When flexi- Offset U bend Fig. 1. Measurement of L on Various Pipe Bends bility cannot be obtained in this manner, it is necessary to make use of some type of expansion bend. The exact calculation of the size of ex pansion bends required to take up a given amount of thermal expansion is relatively complicated1. The following approximate method, however, has been found to give reasonably good results and is deemed to be sufficiently accurate for most heating work. Fig. 1 shows several types of expansion bends commonly used for taking up thermal expansion. The amount of pipe, L, required in each of these bends may be computed from the following formula: L = 6.16 A (2) where L -- length of pipe, feet. D = outside diameter of the pipe used, inches. A = the amount of expansion to be taken up, inches. This formula, based on the use of mild-steel pipe with wall thicknesses not heavier than extra-strong, assumes a maximum safe value of fiber stress of 16,000 lb per square inch. When square type bends are used, the width of the bend should not exceed about two times the height. It is 'Piping Handbook, by Walker and Crocker, and A Manual for the Design of Piping for Flexibility by the Use of Graphs, by E. A. Wert. S. Smith, and E. T. Cope, published by The Detroit Edison Company. 330 CHAPTER 17. PIPE. FITTINGS. WELDING further assumed that the corners 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 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 light-weight radiators, to allow for freedom of expansion in order that no pipe strain Table 6. Thermal Expansion of Pipe in Inches per 100 Ft (For superheated steam and other fluids refer to temperature column) - SATtmATBD Steam Elongation in Inches pee 100 FT FROM --20 F UP Saturate!) Steam Elongation at Inches per 100 ft from --20 F up Vacuum Pressure Pounds Tem perature Inches of Hg. aP Square loch Gage Degrees Fahren heit CastIron Pipe Steel Pipe Wrought Iron Pipe Copper Pipe Pressure Pounds _Per Square Inch Gage Tem perature Degrees Fahren heit CastIron Pipe Steel Pipe Wrought Iron Pipe Copper Pipe 29.39 28.89 27.99 26.48 24.04 20.27 14.63 6.45 ____ ____ ____ 2.5 10.3 20.7 34.5 52.3 74.9 103.3 138.3 180.9 232.4 293.7 366.1 451.3 550.3 -20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 000 0.127 0.145 0.152 0.255 0.293 0.306 0.390 0.430 0.465 0.518 0.593 0.620 0.649 0.725 0.780 0.787 0.898 0.939 0.926 1.055 1.110 1.051 1.209 1.265 1.200 1.368 1.427 1.345 1.528 1.597 1.495 1.691 1.778 1.634 1.852 1.936 .1.780 2.020 2.110 1.931 2.183 2.279 2.085 2.350 2.465 2.233 2.519 2.630 2.395 2.690 2.800 2.543 2.862 2.988 2.700 3.029 3.175 2.859 3.211 3.350 3.008 3.375 3.521 3.182 3.566 3.720 3.345 3.740 3.900 3.511 3.929 4.096 3.683 4.100 4.280 0 664.3 0.204 795.3 0.442 945.3 0.655 1115.3 0.888 1308.3 1.100 1525.3 1.338 1768.3 1.570 2041.3 1.794 2346.3 2.008 2705 2.255 3080 2.500 2.720 2.960 3.189 3.422 3.665 3.900 4.145 4.380 4.628 4.870 5.118 5.358 5.612 5.855 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 820 840 860 880 900 920 940 960 980 1000 3.847 4.296 4.477 6.110 4.020 4.487 4.677 6.352 4.190 4.670 4.866 6.614 4.365 4.860 5.057 6.850 4.541 5.051 5.268 7.123 4.725 5.247 5.455 7.388 4.896 5.437 5.660 7.636 5.082 5.627 5.850 7.893 5.260 5.831 6.067 8.153 5.442 6.020 6.260 8.400 5.629 6.229 6.481 8.676 5.808 6.425 6.673 8.912 6.006 6.635 6.899 9.203 6.200 6.833 7.100 9.460 6.389 7.046 7.314 9.736 6.587 7.250 7.508 9.992 6.779 7.464 7.757 10.272 6.970 7.662 7.952 10.512 7.176 7.888 8.195 10.814 7.375 8.098 8.400 11.175 7.579 8.313 8.639 11.360 7.795 8.545 8.867 11.625 7.989 8.7S5 9.089 11.911 8.200 8.975 9.300 12.180 8.406 9.196 9.547 12.473 8.617 9.421 9.776 12.747 "From Piping Handbook, by Walker and Crocker. This table gives the expansion from -- 20 F to the temperature in Question. To obtain the amount of- expansion between any two temperatures take the difference between the figures in the table for those temperatures. For example, if a steel pipe is installed at a temperature of 60 F and is to operate at 300 F, the expansion would be 2.519 -- 0.593 -- 1.926 in. will distort the radiators. When expansion strains from the pipes are permitted to reach these light metal heaters they usually emit sounds of distress which are exceedingly troublesome. PIPE THREADS All threaded pipe for heating and ventilating installations uses the American Standard taper pipe thread which is made with a taper of 1 in 331