Pipe Sizing Steam Supply andCondensateReturn Lines

1 45 pipe Sizing Steam Supply and Condensate Return LinesDefinitionsSteam mains or mains carry Steam fromthe boiler to an area in which multiplesteam-using units are branch Lines take Steam fromsteam main to Steam -heated discharge Lines move condensateand flash Steam from the trap to a return Lines receive conden-sate from many trap discharge Lines andcarry the condensate back to the : The velocity ranges shown in SteamPipe Capacity Tables 45-1 through 46-4 canbe used as a general guide in Sizing steampiping. All the Steam flows above a givencolored line are less than the velocities shownin the SizingTwo principal factors determine pipesizing in a Steam system:1.

2 The initial pressure at the boiler andthe allowable pressure drop of the totalsystem. The total pressure drop in thesystem should not exceed 20% of thetotal maximum pressure at the includes all drops line loss,elbows, valves, etc. Remember, pressuredrops are a loss of Steam velocity. Erosion and noiseincrease with velocity. Reasonablevelocities for process Steam are 6,000 to12,000 fpm, but lower pressure heatingsystems normally have lower consideration is future expan-sion. Size your Lines for the foreseeablefuture. If ever in doubt, you will have lesstrouble with oversized Lines than withones that are table below gives the color designationsas they correspond to the velocities:Table 45-3.

3 Steam pipe Capacity at 30 psig Schedule 40 PipeTable 45-2. Steam pipe Capacity at 15 psig Schedule 40 PipeTable 45-6. Steam pipe Capacity at 125 psig Schedule 40 PipeTable 45-1. Steam pipe Capacity at 5 psig Schedule 40 PipeTable 45-4. Steam pipe Capacity at 60 psig Schedule 40 PipeTable 45-5. Steam pipe Capacity at 100 psig Schedule 40 Pipe4102452811602704907301,0401,9303,160 6,59012,02019,29061531681002103506509701 ,3702,5404,1708,68015,84025,420921449715 03005009201,3701,9403,6005,91012,31022,4 6036,0501126541201803706101,1301,6802,38 04,4107,25015,09027,53044,19011330621402 104307101,3001,9402,7505,0908,36017,4003 1,76050,970111/411/2221/2331/245681012 Pressure drop per 100 ft of pipe lengthPipe Size(in)

4 1/81/41/23/41/23/4 Pressure drop per 100 ft of pipe length125571152533958001,3182,4103,6055, 1009,44015,45032,20058,90094,50023581163 3585581,1301,8603,4105,0907,22013,30021, 90045,55083,250133,2005551282585678821,7 902,9405,4008,06011,40021,10034,60072,10 0131,200210,600 pipe Size(in)82040891392824658531,2751,8003,3 205,47511,36020,80033,300122857127197282 6601,2051,8002,5504,7107,72516,10029,400 47,1001740811792795659301,6902,5503,6106 ,66010,95022,80041,50066,700214910021934 26911,1402,0903,1204,4628,15013,42027,90 051,00081,7501/23/4111/411/2221/2331/245 6810121/23/41/41/83/41/2111/411/2221/233 1/2456810125132759911803005608301,1802,1 803,5807,45013,60021,8308183883130260430 7901,1801,6603,0805,06010,53019,22030,84 01126531201803706001,1101,6602,3504,3507 ,15014,88027,15043,570143265140220450740 1,3602,0402,8805,3308,75018,22033,25053.

5 37011637761602605208601,5702,3503,3306,1 6010,12021,06038,43061,69022352110230360 7401,2102,2203,3204,7008,70014,29029,740 54,27087,100 Pressure drop per 100 ft of pipe lengthPipe Size(in)1/81/41/23/4 Pressure drop per 100 ft of pipe lengthPipe Size(in)^21501002203406901,1402,0903,120 4,4208,17013,42027,93050,97081,810 26611202704208501,4002,5603,8305,42010,0 2016,45034,25062,500100,3001307014031048 09801,6202,9604,4206,26011,58019,02039,5 8072,230115,900243992004406801,3902,2804 ,1806,2508,84016,35026,84055,870101,9001 63,6005681603206901,0802,1903,6106,6109, 87013,96025,84042,41088,280161,100258,50 0111/411/2221/2331/2456810121/23/431/212 21/234568101211945912023126301,0401,9052 ,8504,0257,45012,20025,42046,50074,50022 8641292834408921,4722,6904,0205,70010,55 017,30036,00065,750105.

6 500 Pressure drop per 100 ft of pipe lengthPipe Size(in)3/41/211/411/21/23/41/41/8716327 01102233686759901,4202,6254,3159,00016,4 0026,350102245991563165209531,4052,0203, 7206,10012,70023,20037,25014326414222044 67351,3402,0102,8505,2608,65018,00033,30 052,5001739791742705469001,6522,4703,490 6,45010,60022,00040,25064,50057517234776 41,1852,4103,9607,26010,88015,35028,4004 6,50097,100177,000284,100247109220483751 1,5202,5504,5906,8509,70017,95029,50061, 400112,000179,600133771553415321,0751,77 53,2454,8506,85012,70020,80043,40079,100 127,1003/429661342964609301,5352,8154,20 05,93011,00018,07037,55068,500110,20014, 71030.

7 65056,00089,90023541092413757601,2502,28 03,4304,8408,950 Pressure drop per 100 ft of pipe length1/23/4111/411/2221/2331/245681012 pipe Size(in)1/2 AboveVelocities Less ThanViolet6,000 fpmYellow8,000 fpmBlue10,000 fpmRed12,000 fpmGreen15,000 fpm46steam main to the new unit. The useof the tables is best described by solvinga typical problem:Assume a boiler operates at a steampressure of 15 psig and is supplying a300-ton Steam absorption machine whichrequires a minimum operating pressureof 12 psig. There is a 2 psig pressuredrop along the Steam mains and theabsorption machine is rated to condense6,000 lbs/hr.

8 The branch line is 50 feetlong and has three standard elbows plusa gate valve. Allowable pressure drop isnot to exceed 1 psi. Assuming that a 5" pipe will be needed, use Table 48-2 todetermine the equivalent length of pipe tobe added to compensate for 5" standard elbows at 11 = ft1 5" gate valve at = ftTotal for valve and fittings = ftAdding this to the 50-foot length of pipegives a total effective length of feet call it .85 hundred feet. Dividing ourmaximum allowable pressure drop of .85 gives psi per 100 feet. Referto Table 45-2 for 15 psig Steam .

9 With apressure drop of psi per 100 feet, a5" pipe will give a flow of 6,160 lbs/hr. Onthe basis of pressure drop only, a 5" pipecould be selected, however, the velocitywill be between 10,000 and 12,000 of this, it may be wise toconsider the next size pipe , 6", asvelocity will then be less than 8,000 Discharge LinesTrap discharge Lines are usually the trap is properly sized forthe job, use a trap discharge line thesame size as the trap connections. Atvery low pressure differential betweentrap and condensate return pipe , trapdischarge Lines can be increased onepipe size Return LinesFor medium and large-sized plants,the services of a consultant should beemployed to engineer the condensatereturn pipe or pipes.

10 Usually it is consid-ered good practice to select return pipeone or two sizes larger to allow for 1) in-crease in plant capacity and 2) eventualfouling of pipe with rust and and High Back PressureBack pressures excessive by normalstandards may occur due to fouling ofreturn Lines , increase in condensate loador faulty trap operation. Depending onthe operation of the particular trap, backpressure may or may not be a Recommendation Chart on GatefoldB. If a back pressure is likely to exist inthe return Lines , be certain the trapselected will work against pressure does lower the pressuredifferential and, hence, the capacity ofthe trap is decreased.