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DESIGN OF POWER BOILERS 9.8 CHAPTER NINE Particular Formula For values y, C, and sa refer to Tables 7-1, 7-3, and 7-6 The thickness of a blank unstayed full-hemispherical head with the pressure on the concave side h¼ pL 1:6sa  9-11aị hẳ pL 2sa  0:2pị 9-11bị Equation (9-11b) may be used for heads exceeding 12.5 mm (0.5 in) in thickness that are to be used with shells or headers designed under Eqs (9-9) and (9-10) and that are integrally formed on seamless drums or are attached by fusion welding and not require staying The formula for the minimum thickness of head when the required thickness of the head given by Eqs (9-9) and (9-10) exceeds 35 percent of the inside radius h ẳ Ly1=3 1ị 9-12ị where yẳ 2sa  ỵ pị 2sa  p ð9-12aÞ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Cp=sa ð9-13Þ UNSTAYED FLAT HEADS AND COVERS The minimum required thickness of flat unstayed circular heads, covers and blind flanges as per ASME Power Boiler Code h¼d where C ¼ a factor depending on the method of attachment of head on the shell, pipe or header (refer to Table 8-6 for C) d ¼ diameter or short span, measured as shown in Fig 8-9 The minimum required thickness of flat unstayed circular heads, covers or blind flange which is attached by bolts causing edge moment Fig 8-9( j ) as per ASME Power Boiler Code h ¼ dẵCp=sa ỵ 1:78WhG =sa d 1=2 9-14ị where W ¼ total bolt load, kN (lbf ) hG ¼ gasket moment arm, Fig 8-13 and Table 8-22 For details of bolt load HG , bolt moments, gasket materials, and effect of gasket width on it Refer to Tables 8-20 and 8-22 and Fig 8-13 The minimum required thickness of unstayed heads, covers, or blind flanges of square, rectangular, elliptical, oblong segmental, or otherwise noncircular as per ASME Power Boiler Code t or h ¼ d pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ZCp=sa  Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website ð9-15Þ DESIGN OF POWER BOILERS DESIGN OF POWER BOILERS Particular 9.9 Formula where Z ẳ 3:4 2:4d=a 9-15aị a ẳ long span of noncircular heads or covers measured perpendicular to short span, m (in) Z need not be greater than 2.5 Equation (9-15) does not apply to noncircular heads, covers, or blind flanges attached by bolts causing bolt edge moment The minimum required thickness of unstayed noncircular heads, covers, or blind flanges which are attached by bolts causing edge moment Fig 8-9 as per ASME Power Boiler Code h ¼ dẵZCp=sa ỵ 6WhG =sa Ld 1=2 The required thickness of stayed flat plates (Figs 8-10 and 8-11) as per ASME Power Boiler Code h ẳ pt 9-16ị p ẵ p=sa c5 9-17ị where pt ẳ maximum pitch, m (in), measured between straight lines passing through the centers of the stay bolts in the different rows (Refer to Table 9-7 for pitches of stay bolts.) c5 ¼ a factor depending on the plate thickness and type of stay (Refer to Table 8-15 for values of c5 ) For sa refer to Tables 8-8, 8-23, and 8-11 h2 sa c5 p2 i The maximum allowable working pressure for stayed flat plates as per ASME Power Boiler Code p¼ For all allowable stresses in stay and stay bolts Refer to Chapter ð9-18Þ Also for detail design of different types of heads, covers, openings and reinforcements, ligaments, and bolted flanged connection COMBUSTION CHAMBER AND FURNACES Combustion chamber tube sheet The maximum allowable working pressure on tube sheet of a combustion chamber where the crown sheet is suspended from the shell of the boiler as per ASME Power Boiler Code P ¼ 27000 hðD À di Þ wD USCS ð9-19aÞ where h ¼ thickness of tube, in w ¼ distance from the tube sheet to opposite combustion chamber sheet, in Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website 100 110 120 125 130 140 150 160 170 180 190 200 225 250 300 0.67 0.76 0.83 0.86 0.90 0.96 1.03 1.10 1.17 1.24 1.31 1.38 1.55 1.72 2.07 131.25 125.000 118.750 118.750 115.625 112.500 106.250 103.125 100.000 7.8125 (5.25) (5.000) (4.75) (4.75) (4.625) (4.50) (4.25) (4.125) (4.000) (0.3125) 159.375 150.000 143.750 140.625 137.500 134.375 128.125 125.000 121.875 118.750 115.625 112.500 106.25 100.000 9.375 Source: ASME Power Boiler Code, Section I, 1983 psi MPa Pressure (6.375) (6.000) (5.75) (5.625) (5.50) (5.375) (5.125) (5.000) (4.875) (4.75) (4.625) (4.50) (4.25) (4.000) (0.375) 184.375 175.000 168.750 165.625 162.500 156.250 150.000 146.875 140.625 137.500 134.375 131.25 121.875 115.625 106.250 10.9375 (0.50) 14.0625 (7.375) (7.000) (6.75) (6.625) (6.50) (6.25) (6.000) (5.875) (5.625) (5.50) (5.375) (5.25) (4.875) (4.625) (4.25) 209.375 200.000 193.750 190.625 184.375 178.125 171.875 168.150 162.500 159.375 153.125 146.875 137.50 125.000 (8.375) (8.000) (7.75) (7.625) (7.375) (7.125) (6.875) (6.75) (6.50) (6.375) (6.125) (5.875) (5.50) (5.000) 209.375 200.00 193.750 187.500 184.375 178.125 175.000 162.500 156.250 140.625 Maximum pitch of staybolts, mm (in) 12.500 Thickness of plate, mm (in) (0.4375) TABLE 9-7 Maximum allowable pitch for screwed staybolts, ends riveted over (8.375) (8.000) (7.75) (7.500) (7.375) (7.125) (7.000) (6.50) (6.25) (5.625) (0.5625) 209.375 203.125 196.875 193.750 181.250 171.875 156.250 15.6250 (8.375) (8.125) (7.875) (7.750) (7.25) (6.875) (6.25) (0.625) 212.500 200.000 175.625 175.00 17.1875 (8.50) (8.00) (7.625) (7.000) (0.6875) DESIGN OF POWER BOILERS 9.10 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website DESIGN OF POWER BOILERS DESIGN OF POWER BOILERS Particular 9.11 Formula D ¼ least horizontal distance between tube centers on a horizontal row, in di ¼ inside diameter of tube, in P ¼ maximum allowable working pressure, psi P ¼ 186 hðD À di Þ wD SI ð9-19bÞ where p in MPa; h, D, di , and w in m The vertical distance between the center lines of tubes in adjacent rows where tubes are staggered Dva ¼ ð2di D þ di2 Þ1=2 ð9-20Þ where di and D have the same meaning as given under Eq (9-19) For minimum thickness of shell plates, dome plates, and tube plates and tube sheet for firetube boiler Refer to Table 9-8 For mechanical properties of steel plates of boiler Refer to Table 9-9 TABLE 9-8 Minimum thickness of shell plates, dome plates, and tube sheet for firetube boiler Diameter of Shell and dome plates Minithickness Tube sheet Shell and dome plates Tube sheet m in m in mm in mm in !0.9 >0.9–1.35 >1.35—1.8 >1.8 !36 >36–54 >54–72 >72 1.05 >1.05–1.35 >1.35–1.8 >1.8 42 >42–54 >54–72 >72 6.25 7.81 9.375 12.5 0.25 0.3125 0.375 0.50 9.375 10.94 12.5 14.06 0.375 0.4375 0.500 0.5625 Source: ASME Power Boiler Code, Section I, 1983 TABLE 9-9 Mechanical properties of steel plates for boilers Tensile strength Grade MPa kpsi Yield stress, percent of tensile strength 2A 2B 333.4–411.9 362.8–480.5 509.9–608.0 48.4–59.7 52.6–69.7 74.0–88.2 55 50 50 Elongation percent gauge ffiffiffiffiffi p length, 5.65 aà a 26 25 20 aà area of cross section Source: IS 2002-1, 1962 a Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website DESIGN OF POWER BOILERS 9.12 CHAPTER NINE Particular Formula Plain circular furnaces FURNACES 300 mm (12 in) TO 450 mm (18 in) OUTSIDE DIAMETER, INCLUSIVE Maximum allowable working pressure for furnaces not more than 41 diameters in length or height where the length does not exceed 120 times the thickness of the plate p¼ 0:36ð18:75T À 1:03LÞ D SI ð9-21aÞ USCS ð9-21bÞ where p in MPa; T, D, and L in m p¼ 51:5ð18:75T 1:03Lị D where p in psi D ẳ outside diameter of furnace, in L ¼ total length of furnace between centers of head rivet seams, in T ¼ thickness of furnace walls, sixteenth of an inch The maximum allowable working pressure for furnaces not more than 41 diameter in length of height where the length exceeds 120 times the thickness of the plate p¼ 29:3T LD SI ð9-22aÞ USCS ð9-22bÞ SI ð9-23aÞ USCS ð9-23bÞ SI ð9-24aÞ USCS ð9-24bÞ where p in MPa; T, L, and D in m p¼ 4250T LD where p in psi; T, L, and D in in Circular flues The maximum allowable external pressure for riveted flues over 150 mm (6 in) and not exceeding 450 mm (18 in) external diameter, constructed of iron or steel plate not less than mm (0.25 in) thick and put together in sections not less than 600 mm (24 in) in length p¼ 56h d where p in Pa; h and d in m p¼ 8100h d where p in psi; h and d in in d ¼ external diameter of flue, in The formula for maximum allowable external pressure for riveted, seamless, or lap-welded flues over 450 mm (18 in) and not exceeding 700 mm (28 in) external diameter, riveted together in sections not less than 600 mm (24 in) nor more than 31 times the flue diameter in length, and subjected to external pressure only p¼ 6:7h À 0:4l d where p in Pa; h, l, and d in m p¼ 966h À 53l d Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website DESIGN OF POWER BOILERS DESIGN OF POWER BOILERS Particular 9.13 Formula where p in psi and d in in h ¼ thickness of wall in 1.5 mm (0.06 in) l > 600 mm (24 in) and

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