5,PIP!NG HANDBOOKReprinted from HYDROCARBON PROCESSTNG . Gulf Publishing Company . 01968 . $1 .25

PIPING HANDBOOKTABLE OF CONTENTSSTRESS ANALYSIS

A Simplified Computer Program For PipePiping Design Method Beats ComputerSymmetrical Piping Arrangement Solves

Expansion Loop DesignTwo-Phase

Page No.

Flow Distribution ProblemsLAYOUT

Plant Layout And Piping Design For Minimum Cost SystemsWhat lnformation ls Essential For Good Piping DesignHow To Design Yard Piping . .Locate Tower Nozzles QuicklyPiping Of Pressure Relieving Devices

MATERIALSU.S. vs British AndWhich Material For

. .139

European Piping SpecificationsProcess Plant Piping?

45

10

202425343949596667738081889496

EXPANSIONFind Best Pipe Expansion Loop QuicklyExpansion Joints: How To Select And Maintain ThemSpring Pipe Hanger Design SimplifiedPiping Tierod Design Made Simple

THERMOWELLSProcedures For The Piping Designerlnstallation And Soecifications ., . .lnstallation And Specifications ., . . .Selection Of Thermowell lnsertion Lengths

PRESSURE DROP AND VIBRATIONSimplified Utility Loop Balancing . .Piping Design Stops Pulsation FlowFind Line Pressure Drop By NomographNew Approach To Pipe Reactions

STEAM TRACING .New Guide To Steam Tracing Design

100101105111

120121125131133138

3

SS ANALYSIS

A Simplified Compufer Program forPipe Expansion Loop Design

Using a single input card withterms and measurements common toany drafting room, computercomputation and analysis has5:1 time advantage over manualmethods

W. W. Shul!, and G. N. Bogel, Jr.The Dow Chemical Co.. Ilouston

A conputnn pRoGRAM has been written that will de-sign piping expansion loops with less cost and with lesselapsed time than ,existing rnanual methods. It requires asingle input card containing measurements common toany drafting room.

Mqnuol l,lethod. A previous articlel recornurends amanual method for piping loop design except for criticallines (those with high or low operating temperatures andpressures andfor force sensitive connected equipment)and except for piping which conveys hazardous or flam-nrable materials. These exclusions eliminate applicationof the author's semi-graphical methodl from most of thepiping in a petrochemical plant and require that the pip-ing designer both understand and have access to processdata. Even if process data were available, the hours re-quired to segregate the hazardous senice and criticalpiping for solution by a stress consultant or specialist andthe queue hours for the attention of the stress consultantor specialist are additional factors which the authorsomitted.

The authors' make the claim that, for non-excludedpiping, their graphical approximations are obtained in afraction of the time it takes to prepare the data for com-puter analysis. Readers will have to guess at the engineer-ing and clock times used by the authors in arriving attheir conclusions. In our trial runs, assembling of datatook the same time and computation and analysis of re-sults from computer and hand calculations had a five toone time advantage in favor of the computer, besides hav-ing the ability to better understand the effect of the vari-ous alternates. It is probable that the computer programsavailable to the authorst did have a complicated input forsolution to simple problems; and considering only over-alltime lapse, their claim is often true for an answer to anyone single problem which happens to fit a manual methodwhich the designer uses with sufficient frequency to main-tain his speed and accuracy.

Effective use of computer programs also requires userfamiliarity with their input requirements and their outputcapability. This learning eflort is less than the eflort oflearning any equivalent manual method. Moreover. onernan can examine pipe layouts for a plant, input the loopson a computer program input form, and get answers forone to several hundred problems within 24 hours, andin some offices within the hour. Well planned piping de-sign jobs seldom need answers faster than 24 hours; but,under planned conditions, the computer results can bernade available within minutes.

Resislonce ?o Computer Use. It has been our experi-ence that people who resist using the computer as a toolfor the routine as well as the difficult tasks in design maybe described in two groups. The first group thinks thatcomputer answers are either beyond question or are notsubject to parametric study of input variables or modifi-cation based on engineering judgment. This group has

5

A SIMPLIFIED COMPUTER PROGRAM FOR . . .S AND B ENGINEERTNG SEPVICES PIPE LOOP OESIGN PROCRAX{AINLINE PIPE LOOP DESIO

-_sINGLE PLANE'2 TO 6 PIPE IEXAERSrITH I TO 5 ELAOiS OR BENOS OF SAXE BENO RADIUS

IRITTEN BY T.I.SHULL ANO G.N.AOGEL' HOUSTON TEIASI ilAY T967'PRL]GRA{ USFS FORNULAS ANO T BLES PPESilTEO IN TIPIPING OESIGN ANDENGINEERINGI' THE GRINNELL COXPANYIINC't PFOVTONCEI RHOOE ISLANDTusA. SECOND EOtTION. 196f,.ALL SUBS FILOI PROCEOUPE AS DETAILO ON PAGES 52t5f OF CRINNELL

INPUT STAFTING IITH NY XEXBER AND NDING IITH ANY f,EiAER'EACH XEXAEF HAS T'O JOINIS (TELDO) IHICH ARE ANALYZED FOR

IHE LO.EST ANO HIGHESI JOINI NUXBERS ARE CONSIDEREO IO tsE THELOCATION OF IHE TNNER{OST PAIR OF GUIDES OR THE LOCAION OFANCHORS IF IHE lNPUT LENCIH TOUISIDE OF GUIOES' I 5 ZEKO.iHE EXCEPTTON IO THIS RULE TS FOR TIO XETBEF ISINGLE ELBOI'JOINIS FOR IBICH THE PROGRAI TILL INCREIENT ONE f,EMBERS LENCTHTO PROVIOE THE NECESSARY FLEXTBILTTY'

c.rf,xoN o(6) t6(6).vl 6),x( r2 );Y( r2l.xL( r2r,r( l2l,rxl l2ltrY(12,,R(12)r.s( r2t.Rxt t2),sT( t2), AAI 20 )COTXON SIPTPI. TLA IXKTSAETAI XBARtYtsAR! XLP!YLPTPXYTP I XTPI Yt IMAX ICT'

IFX! FY t CONSIX!CONSIYTOA'THX !FST{AXTDEMT ILEN!ALTsICOHXON TLNCTXOFY.OLNGcoxf, oN tEx(5, t TRY( 5),BXl 5l.AY( 5),OXl 5l rAST (5' rBR'srtAXrKBDCOIXON KPFI TKSTI(FNDIKFSI!KLOOPt J!K'N.KXAiOOUBLE PRECISION PIPEIOt.JI = OST TO.ENTROIO X OIRECTIONY(J) = DST to CENTROID Y DIRECTIoNII IJI: LFNGIB OF SEGXENIR(J) = X DIST FROY CENTFOIO5(J) = Y OISI FROB CENTROIOPXY = PROO OF INIER I APIX = COU OF IdTERIA ABOUI XPtY = xof, oF INIERIA ARoUT YCT = ExPANSION AT TEHPXLGTYLG = t ANO Y DIST FND FOINT TO END POINTPI = P1PE IOXENI OF TNTERIASf,P = PIPF SECT TON XODULUS

CENTROIO OF STFAIGHT LtNE IN PLANE OF PROJECTION -

COLNA = LENGTH B= x OR Y DISI EoN rCOLNlarB, = A*A( CENIRDTO OF BEND XK=FLEx.FACT'R=RADIUS OF aEND!X=DI5T TO AXISE0NS

c coaNo(xKrRrxt= t.57axxrx aRC PROD. OF INIEFIA LINE PARALLEL TO AN AXIS EON6 XL=LENGTHC PLNXY(xL!x.Yr= xL t r: Y< PROO OF INTENIA AEND NEG IHEN AXIS I RADIAL OR ARC( PENON(xKrR.x!Yl= xK +.lf7rFaRrR. xKI r.57 +R +x' YC PROD OF INTERIA EEND POS iHEN AXIS

'

RADTAL AND AFC( pBNOp(XK!R,r,y)= XXr.r37*R+R*R + iKal.57tR*XrYC MOMENI OF INTERIA ST L'NE tN PLANE OF PROJ PARALLEL TO AXIS X( PLMILNIxLTY) = XL aY:YC MOU OF INI SI LTNE PERPENDICULAR TO AXTS Y( ppxtLN(iL,xl = iL*xllxL/I2.. XL+X1XC IDB OF tNT BEND FROM AItS Y< p!taN (xxrRrxt = xK +to.r49aRrR+Rl. l.s7! xK tR tx.xC PIPE SECIION NOOULUs DA = ACTUAL OTA. THK= THICXNESS IALL

s!( oA. rHKr sxx )=0. 25loarsMx*( DA+oa_2.4( DA.THK T+2.a(rHK.THKl ). LAMBAOA XLAX F = RADIUS OF PIPE AEND

iL^{l THK. R. DA)=THK+R/l ( cA_rHK I *(DA-THxl +.2s)C FLFX. FA'TDA XLA = LAMNADA

FF ( xL A l= I .65/ xL AC STRESS INIENSIFICAIION FACTORT AETAS' FOF IELDED ELBOIS OR BENDS'

EEIAs( xLA l=0. 9/xLA*t O. 6667C OIPE CROSS 5ECTION!L ICTAL AR-A

PAREAI DATIH('=3. I4 I 6IIHK:(OA_TBK Ic plpE ioH oF lNr

PMINTI OA'THK I=3. L 4I6*I DA-IHK)'+O3TIHK/4.C XBAR DISTANCEC D l5 DISI v= vAFIAELE B=tsEND RAOIUSC XPRI--A NON-ZEEN ENIPY IN CDL 7A PRINTS VALUES TN CO{{ONC LPRT--NON-ZERO ENIRY IN CI]L. 79 SHOYS LAST OF PIPE LODP5 USINGC HEADER CAFD ANO PR'GRAil TILL EXPECT A NEt HEAOER CARD'C NPPI_-PFINIS STRESS A5 PtOF IEilBER LENGTH IS VARIED FOR OESIGNC PROALEqS. ENIER IN COL. AO DIGIT 1 FOP STNESS EACB.5 FEFITC DIGIT 2 FOR STRE5S EACH I. FEEIIC DIGTT 3 FOR SIREsS EACH I.5 FEEI! ETC'C 6UIOE INOICAIES OI5IAN'E IN X OR Y DIRECTION OUISIDE THE SECIION A AOC OEFINED FY Ol-D6 . o=x l=Y DIHECTIoNS x=Ol

'D3'D5C T5I DAIA FROM GFINNELL SIJCOlO EDITION PAGE 52. 1CT FROM PAGE 9 A 72c A6 F5.O Fs.O Fs.O F5.O Fs.O Fs.O F5.O F5.O F5.O F5.O F5.O rtF4.IIF4-IlF4. JI1C tD DIA TH( ALiST CT tsND D DT D2 03 D5 06 GUIOEVARYLVARYA PRTcP.52R1O.75.50 17675 996.50, {0. 24. 12. 14.cP.5201o.75.50 17675 996.50.40. lO. 12. A. 2 lO.l4oOOCP.52RGRINNELL ANsiER5: ANCHoRS x=2795rY:lA67LB5. END HOMFNIS=24f64'-23970 FT-LBC FOR PROBLE{ P.52: MAi.HE'TD STRESS EET. JOINI 2

'

3 = 9O3OPS] t IOA'=29672C {ANUAL-GRAPHICAL: 6REATESI STRAIcHT PtPE tS AI JOINI 2 = a7l4 Pstc INEPIIA oF PIPE=212. !BAR=3a.63!YBAR=9.6oFT.C sEcTloN MOOULUS=39.43 lxY=lO4s7. lx=941s. lY=21i69'

C 'OHPUTER

RESULTS: XAX.BEND STRESS RET.JOINTS 2 A 3 = 9IA2 PSIC FOR PAOBLEM P.52: GREATEST JOINI SIREsS IS AT JOTNT 2 = A723 PSIc INERTIA OF PIPE=2\?. XBAR=34.62'YBAR=9.59 Fr.C sEaTloN HoDULUS=19.43 tXY=I0446. lX=9395. lY=2135'.c

105

c

I lottt

at2ttJtr5C

I l6c

rlt

I to

toolorto!lo:lto2zIOalI O2aI 0?5

lo2,t 0t

I O7l06

]L32a,

t20121

t22

c

23

2a26

3tJ2ll

fa

4a

5l52

55

575A

65

little knowledge of the difficulty of progran'ring a com-puter to satisfy every possible need or whim of the user.Its members reject the computer as a tool when the pro-gram's logic requires flexibility in the user's notion ofinput and output content.

The second group has some experience rvith either pro-graming or using the computer; yet, its members over-

6

tla

l4i

tro

estimate the difficulty of communication r.vith thecomputer. Both groups deter the economical emplo1'msn1of computers and thus restrain the development of theengineering sciences from the precomputer art of apply-ing empirical relationships to approximate solutions for-nvhich exact theoretical solutions exist. Fortunateln mem-bership in either of these groups need not be perrnanent!

(ONT RL:2rRITE (f,r r r5)

lor RE-aD (rtl29, aA5J

to2 icITE (r, r30l NPACETAADO tOr J=rt 132

oo tor J=r53r2lllOa AlJl=0.0

READ I tr lf I I PIPEIO,DA!IHKTALIST.CT tAFAOtD!kFSr!FSTMAx.

TPf,OBLE X I D El,lTlF lC AT lOil

.?a,aat+.cnt, ,tF ,1/tC, ,4 , t , , tLOOP

lDEl'lTlFlCA-ilot

I 6

ACTITAL0wsl0E

PIPE

PIPErlU_

ALLOY-IELEsTncss(PSt,

fr 2

cFACIOff

ATOEB. E

D ,t

Itotu3OF PIPE

BEilD

FIBSTLOOP

sE00ilDr.ooP

TAINDLOP

SEEIETTLEXGrllITEEI)

g, at

FOUNilLOOP

FIFTIILUn

strTltLooP

.=

i=Era-*Et

ltax.LDE

lBuI ax-

IETL.

IETGTIIIFEET}

ara

LEUOTNIFEETI

P al

IErt6TE(FEETI

t 5

LEXGTH(FEEN

o tt

LEI'IGIHIFEEN

o A

BF/0|'lDiIJIDE

DITUETERlrilcHEsl

7

Ir[cr{Esl

2 1

ltnurEJ,llIERs-01

t7 !i e

TYPICAL LOOP LAYOUTSTART AT ANY MEMBER,AND STOPAT ANY MEMBER TO DEFINE LOOPGEOMETRY - EETWEEN ANCHORSOR GUIOES

Fig. 2-lnput card with data for problem shown on Fig. 5.

The Progrom. A computer Program in FORTRAN IVwas written (Fig. 1), just to see if it could be done, tosolve expansion Ioop design based on a published manualmethod.2 The program does not require manual inter-

'-'i1"allowsolveupon consultants. If the loop as input has too great ananchor force or too great a stress, the program providesthe required flexibitity by increasing the length of a desig-nated member of the loop within user input limits. TheIocations of guides normally are not altered becauseguides usually are mounted on supports whose locationsare subject to controls other than piping flexibility.

Input Data. The entries for an individual piping loopr"qri." a single card (Fig. 2-80 letters or digits maxi-mum) containing the following information:

. PiPe loop identification name or number.o Outside diameter of the pipe and the wall thickness

l;:n"r) . There are no limitations on diameter or thick-

o An allowable stress range at bend and terminal jointsbased upon code or connected equipment limitation(pounds/square inch).

o A value of C obtained from the following equation:

^ Expansion, in.,/100 ft. (E")r-@or from Literature Cited 2, page 9. This value combinesthe lineal therrnal expansion in inches from 70o F to theoperating temperature with the tensile modrrlus of elas-ticity at 70o F (pounds/inch).

o Radii of bends (inches)-a single bend radius isapplied to all bends.

o Lengths between corners of the loop members withinthe innermost pair of guides (feet). A "corner" is de-fined as the intersection of the center line extensions ofstraight pipe members (however short) which connect toa 90" bend or square elbow. The input length must be

not less than the sum of bend radii (expressed in feet)incorporated in the particular member.

o The number of a member whose length the programalleltheex-

etohold anchors and move guides.

o The maximum permitted anchor force (pounds) andthe X or Y direction of this limitation.

o The piping length (most pair of guides andaxis of this additionalcontributes force because of thermal expansion.

An additional header card precedes a grouP of pipeloop entries. This card contains any desired alphabetic ornumeric descriptive data desired in the output printout(job title, user's name, accounting information, etc.).

Whol The Progrom Solves. The program is capableof expansion to handle many possibilities of piping loopdesign but implemented for PurPoses of this documelta-tion for the following frequently used single-plane looptypes which have no external loads or restraints betweenanchors except guides:

o U-shaped loop with unequal or equal legs plus upto trrzo tangent members of unequal or equal length.(Terms correspond with Literature Cited 2 terms forU-shaped examples.)

o U-bend expansion loops similar to above. IJse ourterm "legs" instead of the Literature Cited 2 term "tan-gents" for the expansion U-bend examples in LiteratureCited 2.

o Simple two member loop with one elbow.o Z-shaped expansion loop.o Hooked Z-shaped with up to one tangent rnember.

Progrom Tesis. The program has been tested with bookproblems' (Fig. 3) and with the examples from the

7

A + C = ENTRY IN NET LENGTH

PIPE LDOP FlPE IALL ALLOI FACTOR C RADIUS LENGTHS OF ME{AERS (TO CENTER OF CORNERSI D- IHICH ANCHOR FORCE LIXIT,

rnFNt- n D THtak- qTRFsS a nFG-F oF FFNn Dl n2 Df nd n< nA xaY vAeV .=Nn- I -Y ,=v nlorNcHEs l-lellEs

-_e5!_ --__---

!!!tsES- -EEEI- -EEEI- -EEqf- -EEEI- -EEEI- -EEE.M: EEE! qlqE PouNDs FoRcE

75O-......_o

SE qI_rnrNT . )> --E- 6330. A020. 63A0, 962- 7426.

JOINT 2 HAS GREATEST STRESS ANcHoR F0RCE IN X-DIREcTION = 2a03. ANcHoR FoRCF IN Y-DIRFCTION= 147O.

LENGTH OF sUM DF MEABERS

--

F' rrrn qtrH--Dl=D6 LENG.IHS -

FEET FEFT FEET AX I S

COORDINATE OFFSET FEET MAXIMUM STRESS IS IN BEND LENGTH OUTSIOE AXIS DISTANCE.ll-uI_1,f.-_THRU .r I AErEF{ rpiHiB

' ^Hp r I O,|I

X_AXIS Y-AXIS IN POUNDS/SO. INCH

MOMENT AT JOINT I = DIAGRAM OF PTPE LOOP MO{ENT AT JoINT a =L4LOz.-

_J5_{EXBEF "I_J6_rl

J7

ll-

--L-Lq-ottrrrr -.+

| o-ooo ffELMFMBER D2 MEMEER O4

| _J9__MEMRER D5__J r o_ |

LOOP O. K. FROM STRESS STANDPOINT

Fig. 3-Test problem based on book2 input data.

PIPE LOOP PIPE TALL I|.OI FACTOK C PAOIUS LENGTHS OF MEMBERS (TO CFNTER OF CORNERS) D- IHICH ANCHOR FORCE LIf,ITlrlclEs rNe,BES __PS!_ !NS!ES-

-EEE!- -EEEI- -EEEI- -EEEI- -EEEI- -EEE! !S! EEEI qgOE eQ!.Nqs FoRcE

j.o9B lm lMo-a-@lo4Lp4

7t96. l6la7. l30aa. 2154f,. 24642. I tq6. o- o.

JOINT 5 HA5 GREAIEST STRESS ANCHOR FORCE IN X_DIRECTI ON - I2N6. ANCHOR FORCE IN Y-DIRECTION=

LENGTH OF SUM OF MEMBERS COORDINATE OFFSET FEET MAXTMUM STRESS TS IN EEND LENGTH OUISIOE AXIS OISTANCEFtLF PATH.

-D.!=s. LENGTHS -JONI

J+-THPU J IFEET X_AXIS Y_AXT5

1NO 7 !@IN POUNDS/SO.INCH FEET AX I S

MOMENT AT JOINI. DtaGRAM 0F PIPE LotP MOMENT AT JOINT IO =

+ leooo rEL l. ro.o@ ErMEMtsER D2 VEMEEi D4

/ l2.ooo FEET J3 I-

- - -- -AG-INNIN5-:]Jl---::4EUBER-oJ:=:-:r+=l-

--

. . l--cuIDE = |

J'

I o.o FEETEtBU N-E

I

I

F#T- --

JrL=-I J9____MEMBER D5___JrO_l

L_-

THIS I OIIP OVERSTRESSEO

Fig. 4-1"r, problem based on Haque/Starczewskil input data.

8

PIPE LOOP PIPE TALL ALLOI FACTOR C RAOIUS LENGTHS OF MEMBERS (TO CENTER OF CoRNERSI D- THICH ANcHoR FoRcE LIHTTJ!-C!ES I-NCHE5

--eS.!.- ------- !!g!ES- -E-EE.L- -ECtrI- -EEEI- LEEEI- -EEEJ- -EEEL lsi EEEI ggqE EgUNgS-FoRcEt!Pu' OgL6.6fs O.'r0 -'5Oo. 35s.0 d.ooa r2.OO A.^0 a.OO a.OO 12.^O O.O 2 4.5O t e2OO.ertrH w^ovrNc xFMqFa I Fil.TH

= a-6 FFEY. eToFss I< r.:Ao- I aq/ea IU

- aM.Hno FnorFc y-6ro

= ,^A9.. w-DIp

- -OIITH VARYING HE{BER LENGTH = a.s FEET' STRESS IS 30O79. LBS/SO.IN.r ANCHOR FORCES X-DIR.= la3l.. y-DlR.= -O.YIT{ vAqvINA {EMBS I ENGrts = o O FFFr- STREq( rq

'a^^1- LA

Piping Design Method Beats Computer

Symmetrical, U-type PiPing looPscan be analyzed for flexibilitYusing this new graPhical method.lt can be done faster than thetime required to prePare the datafor computer analysis

M. S. Hoque, Engineering Consultant, EMMCON,London and J. Storczewski, Woodall Duckham, Ltd',Crawley, England

ple easy to follow method is used and no extr'aordinarymathematical knowledge is required.

In structural design, the imposed force on the systemis specified and the deflection pipingdesign, the deflection is given by theimposed deflection is determi rigor-ous methods available which accu-racy, but their involved computational intricacies demandthe attention of an engineering mathematician or an ex-perienced pipe stress analYst.

A less time consuming, easy to use method is the onlyanswer. One that would even win over the total time in-volved to solve a problem on a comPuter, and at the sariretime produce acceptable results and also satisfy the re-quirements of the Code for Pressure Piping ASA 831.1or British Standard Specification 3351-1961.

The authors present a method which can be used for

to

the solution'of 'lJ' type symmetrical expansion loops. Itprocluces results reasonably accurate in almost a fractionof the time it takes to Prepare the data for computeranalysis.

The total deflection in a piping system is usually known'For example, if the pipe length of a symmetrical loop is50 ft., i.e. 'U' length betrveen anchor points, the thermalexpansion 4 inch per 100 ft. of lincar length, then thetotal deflection : 50/100(4) : 2 inches. The height andwidth of the loop are generally detennined by the spaceavailable. Oncc the shape of the loop is decided by thelayout engineer, forces, moments, and stresses can easilybe found using the graphs presented in this article.

It is suggested that the use of precise and analyticalmethods and also comPuter analysis shor.rld be limited toonly critical and hazardous lines. Critical lines are thoseinvolved with high or low operating temperatures andpressures and/or the type of equiprnent to which they areConnected. Hazardous lines are those concerned l'r'ith thenature of fluid being conveyed, highlf inflammable etc.Therefore, designers should segregate all critical and haz-ardous lines rvhich demand the attention of a pipingstress consultant or specialist. For simpler, noncriticallines an approxirnate calculation method is permitted bythe Code for Pressure Piping ASA B31'1. The Starczew-ski/Haque stored energl'method is an approrimate solu-tion and the analvsis produces safe results.

Allowqble Stress. It is recommended that the stressobtained bv this method should be compared by the codeallor,r'able stress range S.1; rvhere

S,r : I ( 1.25 ,Sc + 0.25 Sr, )S" : allorvable stress (S value ) in cold conditionS,, : allorvable stress (S value) in the hot conditionS" and S,, are to be taken from tables in the applicable sec-

tions of the codef : stress-range reduction factor for cyclic conditions. IJse

a value of 1.0 for one cycle pcr day or less. ConsultASA 831.1.

2.0 1.8 r.6 1.4 t.2 r.0 0.8 0.6 0.4 0.2SCALE P

Weight and other sustained external loadings shall notexceed Sa.

Pipe supports qnd restrqints are not considered in theflexibility calculation. It is assumed that the supportswhich have not been considered in the analysis shouldbe located and designed so as not to interfere with theflexibility of the system. The reactions computed by thismethod shall not exceed the limits which the attachedequipment can safely sustain. Equipment such as. pumps,hrrbines and similar strain sensitive machines should re-ceive the manufacturer's approval; and the piping systemshould be designed flexible enough to comply with theirrecommendations.

SAMPLE PROBTE'VISThe following data apply to all sample problems, un-

less otherwise stated.PipeSize:3in.Schedule : 40Operating Temperature : 8600 FE : Young's Modulus (cold) : 27.9 (10") psi.Thermal Expansion : 7.37 in. per 100 ft.1 : Moment of Inertia : 3.02 ina.Z : Section Modulus : 1.724 trf .i : Stress intensification factor : 1.78Material : Carbon SteelCode : Power PipingSe : Allowable Stress : 16,800 psi.Solution: Use Figures L and 2.

Fig. l-Force graph (above) and moment graph (right) forU-typ" pipe expansion loops.

Somple Problem l. For a simple 'IJ' type expansionloop as shown in Fig. 3, check maximum stress in theloop, and if the calculated stress is much less than theallowable, suggest a loop which will produce a maximumstress equal to or near Sa. Space does not permit the mod-ification of 11, but G can be modified.

Given: 3 inch carbon steel line, Sch. 40, thermal ex-pansion 2 in. per 100 ft., temp. 325oF.

Data:, I : 3.02 h.n; Z : 1.724 in.3; i : 1.78. Allow-able Stress Sr : 18,000 psi (Power Piping).

Solution:w10B- :_:1

'H10

?o304050

t00

200300400500 a

5rp00

2p003p004,0005p00

rop00

ll

2.0 t.8 t.6 1.2 r.0 0.8 0.6 0.4 0.2SCALE B

G10o:7.-ro-1 z.T50.u00 d,)=

too,ooo Eut=o=

6o -

Total thermal expansion:+ (100) :2 inches.

Note: B and a and other nomenclature have no con-nections with similar symbols used in piping design books.These are used in this article just as symbols.

Step 1. Determine Force Fe using Fig. 1 (Force graph).Entei scale p with F : t then move vertically upwardsto the curye a : 1, and now move horizontally to theright to the line 8o : 2 and then vertically move downtJthe line FI : 10 ft. and horizontally from this pointto scale Fal I and read the value Faf I : 38-

The Force Fa : 38(I) : 38(3.02) : 114.76.SaY Fa : 115 lb.Step 2. Determine maximum moment in the bend using

Fig. 1 (Moment graph).Enter B scale with 13 : l. Move to curve d : 1 and

then horizontally on right to H : 70 ft. and verticallydown to line F1 : 115 lb. From this point go horizon-tally to the moment scale to rcad BM, (Bending Mo-ment) : 6,300 lb.-in.

Step 3. Calculate the maximum stress in the bend.

.S, : Expansion stress : U{ ,,: 63oo ,r.rr)

-

6.52opsi.r.72+',

,S, : 8,000 psi. S, ( S.

500,000

The system is acceptable. The calculated Stress is lessthan the allowable stress.

Step 4. Determine the flexible loop, rvhich will pro-duce a stress of 8,000 psi. Use Fig. 2.

.s. 18.000Stress ratio 1_l_- _-2.i'6sE b,5zuFind, y : 0.475 from Fig. 2 when a : 1 and F : 1'New y :0.475 (stress ratio) :0.475 (2.76) :1.312.Enter Fig. 2 with new y : 1.312, move to 13 : l,

then travel vertically dorrnrvards to read ne\v d : 0.25.G

Since a : i:0.25, G: 0.25 (11) : 0.25 ( 10) - 2.5/ft.

I

PIPING DESIGN METHOD BEATS COMPUTER

l'-n

t23456789a=G/H

Fig. 2-Variation of bending mometrt and stress with beta andalpha.

p:Y: t,b/ -

lo, tr -

to..H

The suggested loop will have the following dimensions:H

-

l0 f.t.,W -

10ft., G -

2.5 ft.,and U- 100 ft.This new loop will produce a stress : 18,000 psi.Check stress:

Calculated BM: 6300 lb.-in.Stress ratio

-

2.76BM (Stress ratio)

-

6,300 (2.76) -

17,400 lb.-in.

New stress -

BM ,,

17'4ooZ ,): ,12a (1'78):lB,000Psi.

Somple Problem 2. Calculation of forces at the nozzles,see Fig. 4.

,:(+) -4/to_ 0.4

/c \a:l_ I :8,/10-0.8\H/t-al

U, : 100 (55) :4.05 in. (Thermal expansion of 'U')

From Fig. I find FalI : l2O."'

Fe -

120(I) : 120(3.02) : 362lbs.Computer result : 252 lbs.Kellogg graphical : 368 lbs.Fa : Force of pipe on anchor or nozzle, caused by

thermal expansion.

Somple Problem 3. See Fig. 5.:0.4

:07.37

uo : 100 (55) : 4.05 in.

From Fig. 1, by interpolation, FalI :270.:. F.q. : 270 (I) : 270 (3.02) : 815 tbs.By computer Fe:6421bs.

Somple Problem 4. See Fig .6.

-

0.4

:0l-itoo: 100 (4) :0.295 in.

Find force from Fig. l, FalI : 20.:' Fe

- 20 (I) :20 (3.02) : 60.40lbs.

By computet Ft : 46.0 lbs.From the above three cases, it is obvious that the result

by this method compared with computer analysis indicatesafe and reasonably accurate values; and for these shapes,this method wins over computer analysis including datapreparation time.

Somple Problem 5. See Fig. 7.

G10a:- - --:1H 10

7 .313: -r55,-4.05in.u - loo

Find from Fig. 1, F^lI : 78.F.E : 78 (I) : 7A (3.02) : 236 ]bs.M 1 - 12,000 lbs, in.

Stress in the bend. So- M;!- qil -- ':::?z '' 7.12+

(t.78) : 12,400 psi.S,i : 16,800 psi. Sr ( S,rThe reactions and stresses are within the allou,able

Iimits. The svstem is therefore adequately flexible.

Economic Loop Design. If the anchor forces are not thefactors which dictate the design, then the loop can bequickly determined by the use of this method which willproduce maximum moments and stresses equal to its al-lowable limits. No trial and error method is needed. Byusing Fig. 2 a great deal of labor can be saved. This alsoeliminates a large amount of mathematical computationsand reduces the chances of errors to a negligible degree.The graph is self-explanatory and results are sufficientlyaccurate for most engineering purposes. The followingexample illustrates how Fig. 2 can be used efficiently.

oW4' H 10

GOA:-: -

H10

THI

oW4p:-: -

'_H10GOH10

O: G/HB=w/tt

t.00.9E 0.8P 0.7

s06u) 0.5at)H 0.4F-

w106:_: : IH r0

0.090.080.070.060.05

t3

If the calculation, based on either the Starczewski/Haquemethod or an analytical method, indicates that themoments and stresses exceed the allowable limits, thenFig. 2 can be used to predict the guide distance "G"which would enable the shape to become flexible enoughand to yield moments and stresses equal to the allowablelimits.

Sompte Probtem 6. A loop which has the ratio a :GIH :3 and p : IrylH: 5, and the solution indicatesthe Bending Moment : 50,000 lbs. in. and ExpansionStress : 30,000 psi. This exceeds allowable limits.

Allowable BM :25,000Ibs. in.Allowable Sr : 15,000 psi'Determine, U-tyP" symmetrical expansion loop to yield

the maximum moment and stress equal to the allowablelimits.

Solution, Step 1. Determine from Fig. 2 when a : 3and p : 5. FolLw the arrows and read value of 1 : O.l7which is the moment and stress factor on the left handvertical scale.

Since the allowable stress Sr : 15,000 psi. and thecalculated expansion stress SB : 30,000 psi' then theratio : 15,000/30,000 : 0.5.

Therefore, corrected y : 0.17 (0.S; : g.g8t.It is assumed that F : W lu : 5 remains unchanged'

Step 2. Determine new d.Enter in Fig. 2 the corrected y : 0.085 on the vertical

scale from the left hand side of the graph, and movehorizontally to the right to the curve F : 5 then movevertically down to the e scale and read the new ot : 5.7.

Now summarize the new values as follows:

a: 5.7B:5Expansion stress Sa : 15,000 Psi.Bending Moment BM :50,000 (0.5) : 25,000, equals

the allowable moment.

Step 3. Determine the distance of the guide 'G'.New a :5.7 : GIH when 11 remains as before.Therefore, the distance of the guide G : 5.7 (H) . II

the 'G' is increased to 5.7 (H) then the new shape willyield a stress of 15,000 psi. which is equal to allowablestress.

Bosis For Method. This method assumes that the energyis stored in a system because of bending, which is causedby the deflection due to the thermal condition of thepiping material.

Energy stored : tY! (1)J2Again: It is accepted that when a piping system-is

subjected to deflection it stores energy, and that thestored energy must be equal to the work done upon thepiPe'

The work done by a force upon a piping system : y?

(2)t4

Fig. 3-Simple U-type expansion loop for Example l.

Fig. 4-Calculation of forces on nozzle, Sample Problem 2'

G:0

oo'U

Fig.'A-Figure for Sample Problem 3.

Fig. 6-Figure for Sample Problem 4.

.rc'J l*-u=,0'U=55i

Fig. 7-Figure for Sample Problem 5.

where, F : Force and X : Distance travelled by theforce in the direction of the force 'F'.

Also: Interndl energl' stored by the system is causedby'e Compressive stresseso Tensile stresseso Bending moment.

PIPING DESIGN METHOD BEATS COMPUTER .

Fig. &-Basis for the method starts with this piping layout.

'i-1

Fig. 9-The loop deforms from the cold to the hot position.

l.--G6-------*j l.-Gf ---i

Fig. 10-The forces and moments acting on the Fig. I loopare shown.

If the energy stored by compressive and tensile stressesare neglected then the total energy stored will be due tobending moment only.

See Figs. B, 9 and 10.

Energy due to Bending Moment : BM : I+ (3)MBut d0 : EI d* (4)

Therefore, the equation will be transformed as follows:

ur,:l*!ru:l+W)fMzdx:Jzn (s)

Deflection taken by the shape between (a) and (Gr) i.equal to 8o/2

Fa6o/2 f U, a* I G"2 :l-Znr)n (5A)Thermal stresses in symmetrical expansion loops are

derived as follows:

E,f-its-Lq

lzl

---tR1

Deflections 81, 82 and 8s are produced by elementsLab, Rae and. cd respectively.

The system is confined between 2 anchor points.Le: Teft hand side anchorRa : right hand side anchor.

The following conditions apply in derivation:o That the whole system lies in one plane.

That the system is treated with square corners inter-sections.

That the system is composed of straight elements ofpipe of uniform size and thickness.

o That the thermal expansion of a given element is ab-sorbed by the elements orientated perpendicular to thedirection of the deflection.

o That the effect of dead weight, wind etc. are neglected.o That the clearance between guides and pipe is nil.o That the compressive stresses within the element are

neglected.o That the flLxibility of the elbow caused by an oval

shape is neglected.

The three deflections in the horizontal plane are:81 + 8, * 8, : 8o: total deflectionThe total deflection 66 must be absorbed by the system

contained between the points a and fo which is tJle flexibleportion of the system, see Fig. 9.

The loop will deform from a cold condition to a hotcondition, when the system is subjected to the operatingtemperature, as shown in Fig. 9.

Fr : thrust acting on the loop at the point ,a,, seeFig. 10.

Mo: bend'ng moment acting on the loop at the point'a', see Figure 10.

From Fig. 9 it is evident that the slope at the point Gomust be horizontal.

IIence the change in the slope between point a andpoint Gs is equal to zero.

i.e ll o'1"":oF o: Fo and Go- G1

Fr+

(6)

Mo: M6Bending moment, BM at point X

-

X -

Me- FEU) e)Slope and Bending Moment. The general relationship

between slope and BM, is as follows:

dt: M,!: (8)EITherefore the total slope change between point a and

point Go is:

ll+l'"X : Pipe Iength in general,

(s)

Go

I

q.I

-lI

[,--1

f--0.------!

r5

.:llr#):". llr-#, *,), * ll*+* *)*,"But the change in slope between a and. Go: Q

*{*"*o) +M,(H) -L#L * Y* - elnw)l:of w1 fu, r+twtl

*"1. +H+ T):r"l;*-)f H,+H(wt I T H2+H(w\ IM,:Fo Lzrdffit ):'"tdc +TiTT)

M-- F,'" H *W"2(G+H)+w

Now refer Equation 1 to 5a,Further,

(10)

(II)

oruo:4

EI 3o2Fo

EI 3o2 FoH2

Er 60w

: r, {,, + w),\,I' WI-'2H3

HW-3-2 4(G+H)+2tr I (13)t +2 p + p,+al4l2P

H2 tl/1 -L2 _ -L-)-Hl

c- rlH

(#)':"[-f, * Force, Moment, and Stress. The follou'ing units applyin the formula below:

Modulus of elasticity : E (psi.)Resisting force : F, : F" (lbs.)Moment of inertia of the pipe : 1 (in.n)Total thermal expansion between anchor points is in

inches.Height of the loop : Il (ft.)Width of the loop : W (ft.)Distance of first grride : G (ft.)Section modulus of pipe : Z (in.')Stress intensification factor for the bend : i : 0.9 lh

where h : tRlr'See code for pressure piping ASA 831.1.Then the force is

, +2 + ' (#)'

-(+) WLLL,)'t-H

I

r+28+p'--

I3 , 2 4aa4l29where F

-

I,Y/H and, a : G/H. I ,,-,2B+++2p414B2

'oouo : ;*{ll -; o""f:' +ll w.- rot) *7'"*ll ,*"-'outo'f*""|

# {rr ", (r-ffi *r)' ("" * " *[) - FoH r#T, (FoH, + FaHW)* r,, (F * L)\

I c+H+w/z l l, H, zz\ttr@+h+wF - T(G+h +w-l - 3 - Tl

: ,o * rr'{ 212(G+H)+w) 2(G+H)+W(H + 14/)2

t1/H+

+) . r*'(+wH

t6

(12)

PIPING DESIGN METHOD BEATS COMPUTER The maimum stress can therefore be in a system eitherat bend b or at the bend c.

It is suggested that the moment at point b and pointc be calculated, then take the largest moment of the twoto calculate the expansion stress SE in the loop.

Ms,,

-

_ (i)

Fig. l2-Loop designations for round corners.

Fig. ll-For round corners, ttewidth, height, and guide distancesmust be modified.

Fig. l3-Symmetrical loopwith guide G distance frombend.

Fig. l4-Symmetrical loopwith guide very near to thebend.

( 1e)

Loop Restroinls qnd Supporls. Design engineers shouldmake certain that the loop between the two guides ismade to function without any environmental obstructionsor restraints. Also that the system is fully supPorted andno branch connections are made within the flexible por-tion of the loop. It is not recommended to induce anyexternal loading upon the loop. The designers shouldavoid locating rigid sections, such as large valves etc.,within the loop. A good practice is to locate valves andother rigid sections near the guide or between the anchorand the guide.

Line Size Limits. This method provides engineers withreactions and stresses that are reasonably accurate forpipe up to 6 inches in diameter. Lines above 6 inchesin diameter can be safely analyzed by this method. How-ever, the authqrs would like to point out that the resultsthus obtained will be on the conservative side. Therefore,where the system is dictated by the space, reactions andstresses or economic limitations, a precise analysis shouldbe made.

Round Corners. Solutions to loops having round cornerscan be solved as follows:o If the square corner solution gives reactions and

stresses, which exceed acceptable limits,o If the radius of the bend is more than 1.5 pipe diam-

eters,

o If the line is above six inches in diameter,. Refer Figr,rres 11 and 12. Use Equations 20, 21,22, and

23, to modify the width (W) , height (I1), and guidedistance (G) respectively.Use Figs. I and 2 to determine forces and moments.Assumption:R : radius of all the bends whichI{: height of the loop which must

sides.G : distance of the guides which

both sides.

must be the same.be equal on both

must be equal on

Fig. l5-A two-plane loop configuration.

Er s^ l-n'- " t_^ 3456H3 I 1

IIs lis

p L+2tt+t2, Z 4a*4*2Fthe following forroula

(lbs. )(15)

derived.

( 16)

(17)

( 1B)

From equation (10)

Mo: FoH H+W2(G+H) +W

W:u+1.57R(K/3)H-h+t.s7R(K/3)H-h+1.57R(K/6)C:e*1.57R(K/6)

K:1.65/h -flexibility factor, K) 1,

rf R)rvhere h

-

' ..' ; i: thickness of pipe; r: mean

r2pipe: R: radius of the bend,

1-rB' Fo It T; )-, +-O (lbs.-ft. t

Note that Fo : F^

(20)(21)(22)I 2q\

(24)

radius ol

M": Mo- Fr(H) (lbs.-ft.)Note: For force calculation use modified Height (H) of

loop. For moment calculation use original Height (II) ofioop'.

thetheln general:

Stress : M /Zt7

For Figs. 13, t4, and 15, u: W -

2R; h: H -

2R;g:G_R.

Symmetrical Loop. Refer to Figs. 12 and 13. ModifyW, H, and G as follows:

For W, use Equation 20.Eor H, use Equation 21.For G, use Equation 23.

Symmetrical Loop. Refer to Fig. 14. Note that theguide is very near the bend.

For W, use Equation 20.For H, use Equation 21.Since the guide is at or near the bend, G:0.Two-Plane Loop. Refer to Fig. 15.For W, use Equation 20.For H, use Equation 21.For G, use Equation 23.

U-Loop With Equal Legs. Refer to Fig' 16.u:W-2R.h:H-R.For W, use Equation 20.For 11, use Equation 22.G :0.Two-Pliane Loo,p With Y-Leg Longer Than Fitting

to Fitting.w:W-2Rhr: Ht

-

2Rhr: H,

-

2Rg:G_RFor W, use Equation 20.H:.: Ht * Hz.For G, use Equation 23.

Two-Plane Loop With Equal Legs.u: IU

-

2R.hr: H,

-

R.Hr: H,

-

2R.For W, use Equation 20.For IIr, use Equation 22.For H2, use Equation 21.H: Hr]- Hr.G :0.U-Loop with Equal Legs and Single Tangent. Refer

to Fig. 19 and solve the same as Fig. 16.

Grophicol vs. Computer Solufions. The following ex-amples are given to illustrate the results obtained by thismethod and by the computer.

Example. Given: 4 in. pipe, schedule 40; radius ofbend : 0.5 ft.; operating temperature : 3500 F.; mate-rial : ASTM 106 GR. B; thermal expansion : 2.26in./100 ft.; allowable stress : 22,500 psi.; code : PowerPiping; moment of inertia : I : 7.23 (in.a); sectionmodulus : Z' : 3.22 (n.3); stress intensification tac-tor:i:1.95.t8

Fig. 17-A twb-plane loop configuration with the Y leg longerthan fitting to fitting.

Fig. lLA U.loop configurationwith equal legs.

Fig. 18-A two-plane loop with equal legs.

Fig. 19-A UJoop corfiguration with equal legs and singletangent.

a:GfH : 12110 : 1.2;B : WIH : B/10 : 0.8;8o : (2.261100) (180) : 4.06 in.

From Fig. 1, Force Graph, FII : r : 86Force : r(I) :86(7.23) : 620From Fig. 1, Moment Graph, BM : 27,100 lb.lin.

stress : +# (1.95) : 16,450 psi.

Fwi

PIPING DESIGN METHOD BEATS COMPUTER . . ized staff members to spend their valuable time only onthe analysis of critical and hazardous lines. Alsq it willhelp site engineers design and incorporate a loop in a rackpiping system, or in a long transmission line, without seek-ing help from the design office.

Furthe4 the method will help project engineers esti-mate piping flexibility in the proposal stage of the project.

Symbols used:

Allowable Stress (psi.)Modulus of Elasticity (psi.)Moment of Inertia (in.u)Section Modulus (in.3)Force (lbs.)Force component in the direction of axis.Moment (lb./ft.)Stress intensification factor.

,s/EIZF

FxM

i

Fig. 20-An example configuration calculated by the graphicaland computer methods.

Fig. 21-A square corner configuration calculated by graphicaland computer methods.

MethodForce,

lbs.

Moment Max. stressat guide at bi:nd, RemarksIb./in. psi.

About the quthorsM. S. HIQUB is an engineering consul-tant as s o ciated.with E M M C O N, L ondon.He specializes in pipe stress analysi,s,piping lo,gout, and fleribilitg analgsi,si,n th,e lal1out stage. Mr. Haque receiueda diploma in mechanical and electricalengineet"ing from Dehri Technical In-stitute of India. He is an o,ssociatenzember of ASME, Institute of Engi-neering Designers, Institute of PlantEngineers, Associate Fellou; of the In-

stitute of Petroleum, and Associate of the Institute of Fuel.He has had 16 gears enperience as a senior designer andpiping analyst usith such, firms as Wellman Smith Ou;enEng. Co., Mattheu Hall & Co., Ltd., McKee Head Wright-son, Ltd., and Constructors Joh.n Brou.tn, Ltd., all in London.He also has fi,ae years fi,eld eupet'ience on construction jobsin Ind:ia.

J. St-q.nczowsKr 'is an engineet'wi,thWoodall-Duckham, Ltd,, Crawley, Eng-land. He o,ttended the Polislt TechruicalCollege in England and completed aB.Sc, mecltanical course at London Urvi-oersity. He has done graduate work influid dgnamics, mathematics, andnuclear energA. Mr. Starczeu.tski hashad, enperience in heat enchanger de-sign, pressure aessel design, u-teldingequipment dea elopment, special pu,t'posemachine design and, other process equi,pment design. He h,asuorked, u.titlt, such firms as Constructors John Brown, Ltd.,and, Caird & Raynet", Ltd,. both in London,

Graphical 620 27,100 16,450 square cornersolution

Computer 2 7,000 t6,47s .t;?.?;,:to"*

Example. Given: 6 in. pipe, schedule 40.All other data as in example above.8o : 4.06 in., I : 28.1, Z : 8.50, i : 2.27From Fig. 1, Force Graph, r : 86, r(I) : 86(28.1) :

2,410 lbs.From Fig. 1, Moment Graph BM : 90,200 lb. in.Stress : 90,200 18.5(2.27) : 24,550

Force, Moment Stress,lbs. lb./in. psi.

Graphical 2,4tO 90,200 21,550 sq. corner soln.Computer 2,179 90,500 20,122 sq. corner soln

In conclusion, the authors feel that the introduction ofthis time saving piping flexibility analysis method will helppiping design engineers solve most of the simpler config-urations. This will allow consultants and highly special-

6t7

Method Remarks

T9

Symmetrical Piping Arrangement SolvesTwo-Phase Flow Distribution Problems

The secret to two-phase distributionin branched piping systems is strictadherence to symmetrical piping and anevenly dispersed liquid flow pattern

John L. GreeneThe Fluor Corp., Ltd., Houston

A rnequrNT ENcrNEEnrNc problem is designingbranched piping systems for flow distribution, mist ordispersed flow, and an over-all low pressure drop. Con-trolling flow patterns, liquid distribution, flow distribu-tion, and optimizing pressure drop need to be considered.Recognizing flow polterns in two-phase flow is thefirst part of the problem.1,3 In a two-phase system, whengas flows at various rates, demonstrative types of flowpatterns are developed. In general, these flows are de-scribed as bubble, plug, stratified, wavy, slug, annular,and spray, mist, or dispersed. Slug formation, plug flow,wavy flow, and stratified flow are shown in Figures l, 2,3. and 4, respectively. For this discussion, slug flow isdefined as a mixture of liquid and gas that has a varyingdensity with respect to time. Therefore, the term slug flowwill also include plug flow and will border on annularand bubble flow.

fn engineering design the flow pattern must be deter-mined in every two-phase application. fn a service wherepressure fluctuations cannot be tolerated, there can be noslug formation. For example, slug flow downstream of adistillation column will cause pressure fluctuations andunstable operation, or downstream of catalytic reactorsit can cause catalyst attrition.Liquid Distribution. When two phases flow through thesame pipe, the gas flows faster than the liquid. In a20

Fig. l-Shows slug flow; G:0.0085 lblsec; L: 0.38 lb,/sec.*

Fig. 2-Shows plug flow; G:0.00421 lb,/sec; L:0.38 lblsec.*

Fig. 4-Shows stratffied flow; G : 0.0081 lblsec; L :0.38 lb/sec.'

* Water and air at atmospheric conditions and in a 2-inchOD horizontal pipe.'

Fig. 3-Shows wave florv; G : 0.0083 tblsec; L : 0.38 lb,/sec.*

ll ,'=T,'(I) ELBOW PERPENDICULAR (2) ELBOW PARALLEL (3) TEE 8 CAP

TO HEADER TO HEADER TO HEADER(GOOD) (POOR) (ACoEPTABLE)Fig. S-Shows liquid distribution into a header: (1) elbowperpendicular to header (good); (2) elbow parallel to header(poor); (3) tee and cap to header (acceptable).

The problem of two-phase flow distribution in manifoldpiping arrangements is frequently encountered in largeplants, particularly around air coolers, parallel exchang-ers, etc.

The simplest solution to flow distribution is to providea block valve in each branch line. From the standpointsof valve and of pressure drop costs this is often unattrac-tive. Therefore, the pressure drops through the systemmust be depended upon to distribute the flow. As is shownin Figure 6, if valves are not provided in each branch lineof two-phase flow, then the layout should be symmetrical.

For comparison the preferred layouts for single-phaseflow are shown in Figure 7. The selection depends uponthe importance and duty of each service. Friction loss inthe fittings was determined by using Bernoulli's Theorem(Velocity head method) and velocity head coefficientsfrom the literature.5,6 To determine the pressure drop intwo-phase flow when there is less gas by weight thanIiquid, two-phase flow correlations should be used.2

Applicotions. Savings can be realized in optimum over-design of heaters, heat exchangers, etc. In large systemshorsepower usage from pumps and compressors can bereduced.

With this knowledge of how to minimize pressure lossesin manifolds, plot plans can be laid out more efficiently.The preferred piping layout creates fewer plot planchanges and shorter pipe runs.

Slug flow causes pressure fluctuations in the system.Elimination of slug flow helps stabilize the unit. Slug flowcan also cause major problems such as catalyst attrition.Therefore, catalyst life can be increased. Minimizing pres-sure drops and equalizing liquid and flow distributionwill increase yields and decrease capital and operating cost.

Exomple Problem. Distribution into and out of a 16-section air cooler with 5.3 pounds per square inch pres-sure drop (16-6' nozzles) and with the following flow:

LIQUIDFlow lb/hr.Specific Gravity @ Tem-

perature & PressureTemperature oFViscositl, Cp.

VAPOR

Fis.pass

&-Shows symmetrical pipingand (2) two pass.

(2) TWO PASSin two-phase flow: (1) three

(I) GOOD DISTRIBUTION (2) FAIR DISTRIEUTION (3) POOR DISTRIBUTIONFiS. Iayouts for single-pass flow intwo d distribution, (2) fair distri-buti

smooth turn the iiquid has a tendency to follow the out-side wall. The elbow or turn should be perpendicular tothe manifold, as is shown in Figure 5. If thii is not possi-ble, a tee and cap or a mixing length after the turn maybe used.

The liquid must be distributed into heat exchangers,air coolers and other types of equiprnent. Often it isnecessary to rotate an elbow to the shell of an exchangerin order to distribute the liquid on the baffling ,.r.a.rg"-ment. Tees and caps or mixing'lengths are also used onthe inlets to heat exchangers. On the outlet, liquid dis-tribution is not usually important.

The severity of the operation and the duty (size ofheat release) of the service as selected to provide liquiddistribution are determined by an economic balance.Therefore, each case must be looked at individually.

Flow distribution in monifold piping systems is afunction of pressure losses through each lateral system.

IN484,000

0.670277

0.310

IN

OUT652,000

0.678150

0.412

OUTFlow lb/hr.Molecular weightViscosity Cp.

533,0008.49

0.01132

365.0005.99

0.0099

Three cases r,vill be considered to determine the bestpiping layout. Economics prevents putting valves in eachof the 16 sections.

Cqse. l. One header with 16 ]aterals on the inlet andoutlet is shorvn in Figure B.

(I) THBEE PASS

2t

ST RATI FI ED

Flow Pattern. From Baker's1,2 two-phase flow corre-lations the type of flow is determined aIter each lateraltake-ofl and is shown in Figure 8. The flow patterns gofrom mist to annular to slug to stratified flow. This flowpattern change is not acceptable.

Pressure Drop. The pressure drop calculations are atrial and error procedure to determine the exact distribu-tion. Using Bernoulli's Theorem and velocity head coeffi-cients from the literature5,6,7 the initial pressure and flowdistributions (assuming equal distribution) are as followsfor the first and sixteenth pass:

o First Branch System: AP1 : 10.46 psi includingcooler loss

o Sixteenth Branch System. APro : 8.24 psi includingcooler loss

.'. Percent flow not distributed : 4.89 percent

On a service with a large duty this 4.89 percent of mal-distribution of flow is not acceptable. Case I is not agood system.

Cose ll. One tapered header with 16 laterals on the inletand outlet is shown in Figure 9.

Flow Pattern. From Baker's1'2 two-phase flow correla-tions the type of flow is determined to be in mist flow thetotal length of the header on both the inlet and the outlet.

Pressure Drop. The pressure losses were calculated thesame way as Case I only the expansion and contractionlosses were considered.

' First Branch System: aP,:1i.86 psi includingcooler loss

o Sixteenth Branch System: APre : 9.55 psi includingcooler loss

.'. Percent flow not distributed : 4.64 percentOn a service with a large duty this 4.64 percent of mal-distribution of flow is not acceptable. There is 8.73 per-cent rnore pressure drop than in Case I and the taperedheader is expensive. Case II is not a good system.

16-6.. LATERALS SPACED AT 8 SECTIONSFig. 8-Shows single 24-irch headers with 6-inch laterals(example problem-Case I).

Fig. 9-Shows tapered (24 x 8-inch) headers with 6-inchlaterals (example problem-Case II).

Fig. l0-Shows semi-symmetrical manifold piping layout(example problem-Case III).

Cose lil. A semi-symmetrical manifold piping system isshown in Figure 10.

Flow Patterns: AII of the piping is designed so thatonly mist flow is encountered. All turns into headers haveto be rotated corectly so that the liquid is evenly dis-tributed.

Pressure Drop. The pressure losses were calculated asin Case I.

o First Branch System: AP, : 9.34 psi includingcooler loss

o Fourth Branch System: APr:9.97 psi includingcooler lossPercent flow not distributed : 1.96 percent

In Case III the florv is in the dispersed legion throughoutthe system. The flou, distribution is the best that can beeconomically justified. This is good piping la.vout.

LITERATURE CITED

Indqirrg Tere: Ctrmputations-l0, Design-4,8, Distribution-7, Fluid Flow-4,7,Layout-4,6. Liquid Phase-5, Piping-9, Vapor Phase-5.

22

NOTES

23

LAYOUT

Plont Loyout qnd Piping Designfor i,tinimum Cost Systems

Afier process ond equipment ronditionsore sel, plont loyout con be the lorgestsingle cost sover in HPI plonts. Line sizesond pressure drops depend on pipe lengrhond configurotion. Use these guides iomoximum plping system economy

Robert Kern, The M. W. Kellogg Co., New York

PrprNc EcoNoMy is closely related to three areas ofplant design:o Equipment layouto Piping design

a. Line sizing and flow slntemsb. Piping layout, and

o Piping detailsThese areas are interdependent; without an economical

Plonl Loyout qnd Piping Economy. Plant layout canbe the biggest single cost saver in refinery and petrochem-ical plant design, after process and equipment designposibilities have been exhausted. Savings can be rcalizednot only in piping but also in the cost of pumping com-pression and utility cost. Often a layout can eliminateequipment (for example, pumps with well arrangedstandbys).

The most important document issued to the layout

engineer is the process flow diagram (PFD). This hasto be evaluated for an economical plant arrangement.From a layout standpoint, three types of lines can bedistinguished.

Main Process Flow Lines. First, lines which representthe main process flow. Such streams pass throughfurnaces, reactors and dryers, then they continue astower bottom and feed inlet to the next tower, oftenwith exchangers and pumps between them. These lineswill be the shortest if towers are arranged in processflow sequence as close to each other as equipment sizesand access space permits. With smaller interconnectinglines, towers can be located further apart without muchincrease in piping cost il other economies can thus berealized. For example: the grouping of condensers be-tween two towers can result in a shortening of coolingwater lines; a conrmon steam line can be designed forgrouped reboilers. Grouped condensers and reflux drumswill permit a common supporting structure. Figure 1shows an example of alternative tower arrangements.Many configurations are possible and justified if shorten-ing of these process lines is the ultimate result.

Process flow is not always a simple straight throughflow but can split into two or three streams, as is oftLdone with a number of distillation columns. Subsidiarycircuits to process flow must also be considered such asthe refrigeration circuits in ammonia or ethylene units.

are generally large diameter lines and should have pref-erence over the first group which are wually smallerprocess lines.

Feed and Product Lines. The third group of lines are25

PLANT LAYOUT AND PIPING DESIGN

tower arrangements can shorten main

an optirnum location for minimum Prp-"--ttlt' For ex--

changer, drum, and pump locations the following general-'., classifications can be n ade:

Exchongers.o Exchangers which are next to towers use short piperuns. These are thermosyphon reboilers and condensers'Short reboiler and overhead lines are essential for botheconomy and reliable oPeration'

o Exchangers which should be close to other processequipment. For example, exchangers in closed pump cir-crits srch as some reflux circuits. In the case of a bot-tom-draw-off-exchanger-pump, flow exchangers shouldbe close to the tower or drum to give short suction lines'

runs.

o Exchangers located between Process equipment -and

the unit li-it .ut be located at one end of the plant'Such exchangers are, for example, product coolers'

Drums.. Drum location when it must be next to a tower or ex-changer. For example, when a tower bottom flows bygrarriiy into a collecii.rig d.rrm, the drum should be underor next to the tower. A reflux drum should be next tothe condenser. Compressor suction drums and knock-outdrums should be close to the comPressor'

. Most process and utility drums serve as seParators,,..rrg" trrd reflux drums and should be arranged inprocess flow sequence.o Storage drums or tanks, Iocated within a unit usuaHyare given secondary consideration and are located asspace permits mostly at the peripheries of the unit'

Pumps.o Pumps have one general rule: put them close to andbelow their point of suction.

So far, our discussion has dealt w'ith the bases ofeconomical process unit piping, rvithout mentioning speci-fications, site information and project design data' con-struction, oPeration, and maintenance.

Specifications describe the client's requirements or con'tlactor companies standards for all sections of plant de-

y concern econofil)" maln-and sPecial requirements.

ign should read them. De-tailed discussion here is unnecessary.

Site and Project Desrgn Data. The unit has to be

Fig. 1-Alternativeprocess flow lines.

MAII{TEMI'CEROAI)

Fig. 2-Exchanger location for minimum pipe runs'

the feed. lines and the usually small diameter productIines. These lines can be minimized if they start at equip-ment close to that battery limit where feed and pro'ductlines terminate.

ments.

Location For Minimum Pipe Runs. For plant layout,in addition to tower sequence, every equipment item has

26

located on a given site. Soil conditions, existing accessroads, pipe lines, connections to the unit, even prevailingwind can have its affect on the economy of the plantand piping layout.

Construction. A plant arrangement should also be dis-cussed with the Construction Department. They knowavailable crane and construction clearances, access widthand location requirements, and difficult constructionpoints. Expense can rise rapidly with poor access toequipment or difficult-to-erect piping. In some cases, in-creased structural and piping cost to facilitate construc-tion is more than oflset by the saving in construction cost.

Operation and Maintenance. An engineering com-pany's reputation can be enhanced or injured after aplant has been built and operated. Beside performanceand production costs, the plant layout and piping designcan influence maintenance and, operating costs.

It is essential to have road access to exchanger'bundleremoval, tower tray removal, to pumps, catalyst loadingand removal, crane access to compressors, etc. It is ad-visable to study plant and piping layout from this stand-point.

Also, it is essential to have convenient and adequateaccess to points of operations and instrument adjustment.Grouped, lined up manifolds and functional locations ofcontrol valves help to maintain economy of operation. Itis here where all details of piping design gains muchimportance.

In short, economical design is provided by good accessto the unit as a whole and to points of operation andmaintenance. Beside this, it should be rgmembered thatroads and access space spread the unit apart and addsto the length and cost of piping.

The Plot Plon. Figure 3 shows an estimate plan of thefeed gas compressor area of a 200,000 long tons per yearethylene unit. Main pipe runs are also shown. This area(and the whole plot plan) has been developed with theprinciples outlined so far. It is an "In-Line-Layout" withequipment in process flow sequence. The large diametergas lines directly interconnect process equipment. On thecomplete plot plan, equipment (including compressors)are arranged on both sides of a central yard in processflow sequence. Pumps are located at their point of suc-tion and are lined up under the yard. To every line ofequipment, a parallel road is arranged for convenient con-struction and maintenance access.

For economical plot arrangements, many equipmentgroupings can be adopted. Two obvious groupings are:furnaces and reactors. Small furnaces, however, are oftenplaced in several locations as process flow dictates. Forsafety and economy, these furnaces should be located atthe periphery of the process unit.

Another often employed equipment grouping is housedcompressors. Economy is achieved here by the commonbuilding and maintenance facilities; also, by the opera-tion of the grouped compressors.

On Figure 3, the feed gas compressor has been sepa-rated from the refrigeration compressors. Saving inpiping and construction cost justified two compressorhouses. Also, centrifugal compressors require less atten-tion from operating personnel.

Some layout systems use similar equipment groupings

more extensively. Several towers car, be lined up fairlyclose to each other on one side of the yard providingcommon interconnecting platforms. Piping economy isusually sacrificed for convenient access to manholes, valv-ing and instmments on the towers. F.xchangers can a.lsobe grouped on the other side of the yard and a commongantry crane provided for convenient maintenance. Insuch cases, tower overhead and other process lines to ex-changers cross the yard, increasing pipe length and thenumber of fittings.

In the case of piled foundations, the plot arrangementshould also be discussed with a structural expert. Oftenby regrouping equipment, a number of piles can besaved, which can often more than pay for increased pip-ing cost.Economy-of Ycrrd Piping. The main arterial system ofa plant is the yard piping. It is here where long,processlines are located interconnecting distant equiprnent, andlines entering and leaving the unit. Also, utility headersare located in the yard supplying steam, air, gas, andwater to process equipment. Here are located all reliefand blow down headers. Often instrument lines and elec-trical supply conduits are also supported on the yardsteel.

Figure 4, shows those critical dimensions which willinfluence piping cost from a yard piping layout stand-point. These dimensions depend on the over-all plantlayout and should be carefully considered when the plotis arranged.

Dimension A is the total length of the yard and isgoverened by the amount and size of equipment, struc-tures and buildings arranged along both sides of the yard.If, with good layout practices, the same amount and sizeof equipment can be arranged on a shorter yard length,yard piping cost can be considerably reduced. Equip-ment in pairs, stacked exchangers, exchangers under ele-vated drums, drums or exchangers supported on towers,two vessels combined into one, closely located towers withcommon platforms, drums supported on exchangers,process equipment located under the yard are only afew examples which help shorten the yard length. Thesearrangements, of course, shorten not only process linesinterconnecting equipment directly or in the yard, butalso shorten those lines which pass through this area andutility headers serving this area.

Equipment not associated with but arranged along theyard increase yard piping cost unnecessarily. A controlhouse located along the yard, for example, will increaseyard piping cost because all lines must pass by withoutreally being associated with the relatively long controlhouse.

The careful selection of dimension B and C (Figure 4)can minimize pipe length between the yard and processequipment and pipe length interconnecting equipmenton opposite sides of the yard. Not more than necessaryyard height (Dimension D and E) will minimize verticalpipe runs.

When changing direction, change elevation is an oldrule in piping design. This happens with all lines con-necting to yard piping. Ilowever, some large diameterIines can make a flat turn when entering at the edge ofthe yard.

So far, process plant layout has been developed. Inthe following a classification is presented for the most

27

FROMFURNACE

LII{ES WITH ONE EI{DEELOW AIIID OTHEREiID ABOVE YARD CAIIBE LOCATED ON EITHERYARD ELEVATIOiI

CONTROL,VALVES ALTERNATE PUiTP SUCTIOil

LIiIES WITH BOTH E]IDS HIGHERTHATI TOP YARO EANK I-OCATEDO}I THE HIGHER LEVEI.

ACCESS 10PUMPS

G PSOCESS LI}'IES Y'ITH BOTH ENDS LOWEF THAN -

rOU YINO AANT lgg 1-oCATEO ON THE LOWER LEVEL

i

ETOPIPI}IG

P0ssrELE

EL. lO0'

VALVES

PROCESS EQUI PMENT

___-______==_

-l>'-- I

---

I

Fig. 3-Part of ethylene utrit Plot plan showing direct routing of piping'

FLAT.BE}ID AT ED6E OFYARD.FOR LARGE LI}IES

28

Fig. +-1r,"al cross'scction of yard piping showing geueral pipe runs'

common equipment elevations, also highlighting the com-parative cost involved.

Cost ond Equipment Elevqlions. Towers, drums andexchangers can be elevated for the following reasons:

Withchoose adenser isfloor canand construction, maintenance and operation access im-proved. Vertical pumps usually give a minimum heightfrom grade to equipment because their suction inlet noz-zle is below grade.

If for some reason equipment is elevated higher thanthe required NPSH, a reduction in line size and pumpdifferential is often possible.o Thermosyphon Reboiler Circuits. The driving force ina reboiler circuit is the static head difference betweenthe head of the liquid draw-off line, and that of theliquid-vapor mixture in the return Iine minus frictionloss. For horizontal reboilers at grade, an increase in driv-ing force requires greater elevation of the tower or drum.Line sizes can be reduced because higher friction losscan be allowed. By decreasing the vertical legs of reboilerqipil-S the driving force will also decrease, consequently,the line size of the system will have to be increised ioprovide lower friction losses.o Liquid FIow Measurement. The requirement of accu-rate liquid flow measurement can also elevate processequipment (see Figure 5). If liquid is near the boilingpoint, a static head is required in the front of.the conltrol valve to overcome pipe friction losses and avoidflushing in the line. Minimum equipment elevation, ori-fice range and minimum line size will result if the orificeis as close_ to the equipment as possible, and up to thecontrol valve the piping has only one elbow.

LIOUID NEAfi-EotLtNG po[{T

ORSEELEOY

EQUIPITEiIIELEVAITOT

r D VYITH 2rD flTH I'60)

-(l-}1ffiSTRAIGHT RUII

Fig. LPut control valve close to process equipment for econ.omy and reliability of operation.

o Gravity FIow. Requirements often elevate processequipment. The-size and elevation of associated equip-ment; size and arrangement of interconnecting piping;clearances for structural membersl headroom and accessto valves and instruments will influence the final eleva-tion of process equipment.. Grade Location. The most economical and commonlocation of process equipment is at grade. Supportingstructures and platforms are not required. Constructionis easy. Most valves and instruments can be made acces-sible from grade. Operation and maintenance is conven-ient.

-

Elevated equipment with associated structures, plat-forms, handling beams etc., means cost increase. irr-.e*r-eral design areas.

In layout and design, the first attempt should be toeliminate structures, extra supporting columns and extraplatforms. Smaller equipment can be supported on tow-ers, on yard columns, or structures for larger equipment.

The second attempt can be to combine two or threeqrripment. Some equip-le over-all plant layout,be more than a possible

Piping Design for Leqst CostA pRocr.ss lrxrl should he cbsignecl for a milrirnurn

of or.er-all (ost, \\.hic[r is not neccssarily a nrinimrutr ofPiPing cost (or a nrininrurn cost in other r:quiprnentgrorr;rs) . This can be achievcd [rr, a t.losel), coorclinateclover-lrll clesign and accurate cost conrl;arisoir betrveen ol_ternatir.e soltrtions.

Economy of Piping Design. Line sizes give a readilyavailable basis for comparison. Ifowever, accurate costdepends on weight, type of material, insuiation and con-struction. Consequently, pipe lines for economical com-parison are better represented with an in-place dollarfigure per unit length, than with line size, schedule andmaterial alone. Special attention should be given to alloy

lines, high pressure piping, and large diameter of carbonsteel piping. For rough comparison, irr-placc piping costis about double carbon steel piping ruatt:rial ..rri., "At an early stage of plant layorrt. line sizes at.e notavailable. Two items of process data from the processFIow Diagram (PFD) S for rough linesize cornllarison: flou,inC Irressurc differ_ences betrveen t\{'o vessels lr.r florv quanti_ties or higher available ces for fiictionlosses will result in smaller diameter lines. For suction anddischarge to pumps, only quantities should be comparedfor the feel of line size.

For line size calculations, The M. W. Kellogg Co. useseconomical pressure drops. This is a most direct approach

29

PLANT TAYOUT AND PIPING DESIGN stlaiglrt luns oI piping. thatthere is a rnuch highel rificethan ivith a pitot tube. orterstraight ru., of pipe wit Pitottube.

Reboiler Piping. Two types of thermosyphon reboilersare used: vertical ar-rd horizontal'

A vertical reboiler has very little piping and its lengthdetermines the height of the torver skirt. Supports atgrade are sa.r'ed but supPorts on the tou'er have to beadded.

Many tolvers have a bottorn drau'-ofl pump, andNPSH r-equirements usually elevate the torver higherthan that

"f tt," reboiler's miuirnum. This increases the

static hcacls in the vertical legs, also the driving force inthe circuit. With the increasecl torver lieight, it is rtorth-rvhile to check the reboiler circuit for reducing the liquidand the return line size.

Symmetrical piping arrangement betu'cen the drarv-ofland reboiler inlef nozzlcs, similarly betrveen the reboileroutlet and return connection on the tower, is preferredfor equal flow in the reboiler circuit' Nonsymmetricalarrangements may also be accepted for a rnore economicalor mole flexible PiPing design.

Overheqd Lines. Scveral variations exist for overheadreflux circuits. A condenser can be eievated above thereflux drum. The reflux drum can be elevated but thecondenscr is at grade' Thcse arlangenlents can be ad-jaccnt or so-eruhat remote from ttre torver' The sin-iplestoverhead line is shorvn on Fig' 2, sketch A'

Littlc pressure drop is usually ar''ailable in these linesand longer overhcacl fnes rvith more elborvs quicklr' resultin increised line size (see sketch B)'

Fig. l-The hydraulic slide rule is used for fast florv calcula-tions.

flow conditions exist.It is helpful to know a few general rules rvhen esti-

rnating or ialculating line sizes and associated fittings'

Valves and check valves are generally line size' Maxi-murn control valve size is line size' In most cascs, controlvalves are one size smaller than line size' When a largerpressure clrop is available, control l'alves can be trvo orihree sizes snraller than line size'

Sometin'res it is feasible to coDrPaIe piping cost and

valve assembly.Orifice Runs. Because of metering accuracl'' olifice

straigl-rt runs.can be madcstraight runs

cs and .shorter

About the outhor

gineer.

30

CONDEN SER

REFLUXDRUI,4

SKETCi] A

THE SIIIPLES'iOVERHEAD tINi

as much as possible for a direct gas flowg and equipmentin the circuit should be in process flow sequence.

Because of the ever present vibration problems atreciprocating compressors, pipe supports have a very im-portant role in piping design. Supports independent ofany other foundation or structure is almost mandatory.Pipe systems "nailed down" close to grade is a muchpreferred arrangement. If badly desighed compressorpiping has to be corrected after startup of the plant itcan become very expensive.

Compressors are used in process plants for transportinggases. With constant gas inlet and outlet conditions, thecompressor size and cost on one hand and the cost ofdriving force on the other depends on the volume of gascompressed; the compression ratio between inlet andoutlet pressure; (and temperatures: and material ofconstruction).

Pressure differential is composed of friction loases inequipment (furnace, exchangers, and reactors), controldevices, and piping. Consequently, plant Iayout andpiping design has an effect on the compressor's drivingcost; and sometimes on its size.

The selection of an optimum pipe size is also moreinvolved. With increased line sizes, the cost of pipingincreases but pressure drop and utility cost decreases.

SKETCH 8 SKETCH C SKETCH D

REI\4OTE CONDENSER LOCATION INCREASES LINE PIPING CONFIGURATION AFFECTS PRESSURE DROP ANDLENGTH,NUIIBER 0F FITTINGS AND PIPE DIAMETER. STATIC HEAD BACK PRESSURE (Dll\ilENSlON X).

Fig, 2-Typical overhead piping arrangements.

The yearly utility cost per unit pressure drop can becalculated. Multiplied by the time of amortization (num-ber of years) gives the cost of utilities for the period ofcapital payout. Pipe cost plus utility cost gives the totalcost of compression for the calculated period and processconditions.

The example on Table 1 is a tabulation for comparingline sizes, pressure drops, alloy piping cost and utilitycost for a portion of a centrifugal compressor circuit. Thisexample shows that for a two-year payout time, a l2-inclrline is the most economical. For five years, any line'from12 to 16 inches is economical, and a 16-inch line shouldbe selected. For 10 years, a 16-inch line will be the mosteconomical.

For maintaining these calculated economies, line sizesshould be calculated, at least, with a good preliminarylayout.

Optimum pressure drops and sizes can be establishedfor all equipment groups in the compressor circuit.2

Table 1 assumed that the compressor works well withinits capacity and pressure range. fn border line cases, thecost difference between the price of smaller or largercompressor will also enter an over-all cost comparison.Pump Gircuits. Centrifugal pumps are used in process

TABLE I -Alloy Pipe Size Selection for Vqrious

poyout Times

Total Costcol. 3 & ,1

$Uttltty Cost

$Total Costcol.3&6

$Uttltty Cost

s

PAYOUT TIME WITH YEARLY UTILITY COST OF I pst ap : gS50l0 YearE

Llne Slzeappsl

10"

9.75

PTANT LAYOUT AND PIPING DESIGN

TABLE 2-Economico! Unit Pressure Drops for Pump DischorgeLine Sizing

Fig. LPiping and valving between reactor and furnaces'

units for transporting liquid. Sizes are established as forcompressors. Piping and over-all economy for very large-u"hir,"t can be sinrilarll' evaluated as notecl for com-pressors. Time consuming calculations might not be justi-fied with smaller than average pumPs.

Very small pumPs, in-line or vertical Pumps, are usuallyadjacent to thiir suction vessel. With many PumPs takingsrction from the same vessel (crude Iractionator, for ex-ample) adjacen ible with onlY fouro, si* prr-pr. T dium or large sizedp.r*p., .oud u. It is advantageousand Lconomical d to all tlre PumPsin the plant for convenient operation and maintenance'This is achieved r'r'ith an "In-Line" plot layout' Toomany dead ended access roads between process equipmentwill lengthen the Yard bank'

Suction piping should be designed without loops orpockets. Tho sultion line is generally one or two sizes

larger than the gives unitpreisure drops will giveiconomical pr-rn ds to theheader are otle than thepump nozzle.3

Reqcfor Piping. In connection with reactor-furnacepiping it should be remembered that it is usually themost expensive alloy piping in a process unit (because ofhigh temperatures and pressure) and it is olten part of acompressor circuit.

and reactor design. IJnder such circumstances, piping lav-out economy depends on the ingenuity of the designer,who can scrutinize his layout and eliminate every unneces-sary fitting, flange, and field weld, establish optimumequipmeni locations and interconnect a piping system witha minimum of pipe length and fittings.

Fig. 3 shows some extensive valving in reactor pipingand gives an idea how much piping and valving costcan be saved. with line size reduction. It pays to recalcu-late and check line pressure drops with an exact pipinglayout. It also pays to investigate the pressure drop dis-tribution in the entire compressor circuit' Decreasedpressure drop in other equipment groups (exchangers,lrlr.r""r, reactors) can help in decreasing alloy line andassociated valve sizes and still hold the over-all pressuredifferential constant.

With large expensive piping, the smallest detail canrun into thousands of dollars. Here is where care indetailed design pays large dividends. Details of pipingdesign have been discussed in several articles of Hvoxo-cARBoN Pnocrssrwc eNo Pernor-EUM RETINT:n.a-10

A last remark to the reader. Piping economy is ex-tremely complex. About each paragraph heading in thisarticle an entirely separate report could be written. IIow-ever, for writing technical reasons, ideas in this report havebeen simplified, classified, itemized and organized whatis believed in a logical sequence. In their application,these principles are not so orderly and cannot be sep-arated. Many factors influence an optimum solution anddesign ideas have to be related simultaneously. The morepenetrating an analysis becomes, the more likely it willlead to a most economical piping design solution'

ACKNO\\'I.EDGMENTThe author expresses his thanks to \t'. J. H' Baker and Mr' O' H' Hoeg-

U".g lo" the suigestions and hclp rcceivcd -during- the prcp:ration^ of the

-uir,..ipt a.d to* M.- J. Lundgrcn for the design shown on Figurc 3'LITERATURE CITED

l Mendel, O. Chemical Etgiteeritg' Vol. 68, \{ay 15, 1961' P' 190', i.t.i*ir, F. W. HydrccZrbon iocessing l Petroletm Refircr, YoL 43'

No. 6, June 1964, P. 153.";'g.l;", n. u. g Happel, J. Chemical Etgiteeritg, Vol' 60, No' 1, Jan1953. P.180.'"; S"rd], V. L. and Romain, D- H1'drocarbon Processitg I Petroleum Re'finer,Yol.43, No.6, June 1964, P. 116''"iil"l.k"it, L. R. i"irnl"r* Ii"fit"t, Yol' 39, No' 7,.Julv 1960' P'

-127' -."ih;;;: 7. w. Hvdrn"otbot Processing I Pettoleun Reftet' Yol' 44'No. 2. Febrorv 1965. P. 153.

";'xi." n- l'lriiltuu [cIaer, Vol. 37' No. 3, March 1958, P' 136'"ii;;;; R. Pctrnlcu,r Il,f,ner, Vot. 39. No' 2, Februarv.1960' P' 137'"-K;;;: R:

'fttriltuu n.6n.'. vot.39. No' 12, Dcc. 1960, P' 139'-

--

.-f "rri,

-i. Hldrocatbotr !'rtressing I Peuoleum Refiter' YoL '10' DIo' 5'May 1961, P, 195.

PI.AIFOR',I

E LE VAT ION

oRooor[J o5

Ap pst Per 100 Ft.

Optimum FrictionLosses ForExtended Payout Tiine

25,7

32

NOTES

33

ANALYT|CALscTtoN

PPOJECTDESlONDITA

Fig. l-Piping Division organization and flow of information.

Whot lnformqtion ls Essentiqlfor Good piping Design?

Three moior source documentsore essenriol for good piping design:Engineering Flow Diogroms,Nomenclolure, Equipment Elevotions

R. W. Judson, The M. W. Kellogg Co., New York

Trre PrprNa ANar-vrrcer, ENoTNBBn is the key infor-mation center for the piping designer. He produces threemajor piping source documents (Engineering Flow Dia-grarns, Nomenclature and Equipment Elevations). There-fore he must realize that when he puts down a symbolor writes a note on his flow sheets, he gives specific in-structions to the piping designer. These instructions mustbe clear, logical, concise and necessary. A.y extraneousinformation which does not pertain to the operability ofthe design itself does not belong on the flow sheet, be-cause it limits the designer's concePt of the arrangementho is able to provide. Essentially tfie Engineering FIowDiagrams must contain a schematic representation of thelines themselves. They must incorporate all arrangementscritical to the operability of the hydraulic design. Further,

34

each and every piece of control or indicating hardwaremust be incorporated.

Some information essential to layout and productiondesign does not appear on the flow diagrams. In essence,this information consists of equipment elevations, pipewall thicknesses, and insulation specifications which arerequired for the individual line. This information is pro-vided to the designer in the equipment elevation sum-mary and on the nomenclature. Every line incorporatedon the engineering flow diagram is identified and anyemergency or special conditions which relate to this lineare tagged with the same identification number andspelled out in the nomenclature or in the elevation in-formation. Basically this co-ordination between the threesource documents results in a detailed identification ofevery line on the Engineering Flow Diagrams. Without ita chaotic arrangement of information would exist withno logical system available for finding the informationrequired.

To fully understand the requirements imposed on thedetailed design, it is necessary to understand what infor-mation is required of the Piping Division, the scope of theinformation they receive, and how much information theyactually place on tho flow diagrams themselves. Thepiping designer must have enough information to designaccurately and yet not be hampered by too much infor-

P/P/N6D/V/S/ON

,2QODUC7/ONSECTlON

/IlZTEQ/ALCEQU/S/7/OM/NG

PLOT i LA4OUTSTUD/ES

Fr'BP/CAT/ON

CONSTzUCT/ON

to4-C

Fig. 2-Portion of typical Process Flow Diagram.

mation, which would restrict his optimization of thepiping arrangements.

Flow of lnformqtion. To understand any major break-

vision itself.Engineer on each ncru project

ic docunrents rvhich pror.ide hirnturn out his three rnajor piping

equipment erevations). diagranls' r'tolllenclatures and

Process data sheets supplement the PFD ancl givephysical data related to process equiprnent; (vapo. li-quid proportions of tower trays, physical data, safetyfactors for pumps, detailed furnace florv conditions, etc.).

From the fnstrument Division: The process ControlDiagram (PCD) shows the instrumentation of the plant.See Fig. 3.

From the Specification Group; Specifications which

Fig. L-Portion of typical Process Control Diagram.

give detailed design requirements concerning piping de-sign, valving, safety, operation and maintenance.

o Specifications which give minimum wall thickness,schedule and insulation requirements.

o Specifications which glve a clearly marked print of

35

ESSENTIALS FOR GOOD PIPING DESIGN . . .

PFD showing special piping materials (glass linedpiping alloy piping, high pressure piping, corrosionallowances, etc.)

From Project Engineering: Engineering design datawhich gives specific requirements for all utility and auxil-iary syslems which are normally not shown on the PFD'

Applicorion. With this information in his possession, thePiping Analytical Engineer analyzes the entire processdesign and expands this design on his Engineering FlowDiagrams. In addition he designs the necessary utility andauxiliary systems which are required to support theprocess flow.

In fulfilling this responsibility, the engineer decides onthe necessary valving to fulfill the specifications and proc-ess requirements, includes all instruments dictated by thePCD, sizes all lines, and insures realistic pressure drops.He further indicates on evefy line the material specifica-tion and the specification break points. To suit thesespecifications he determines wall thickness, and schema-tically represents an accurate picture of the number oIlines required which may have been a single flow lineon the process flow sheet. Fig. 4 is an example of a de-veloped engineering flow diagram for the same area thatwas depicted on the process flow diagranr in Fig' 2 andprocess control diagram in Fig. 3.

Loyoui. All the information designed and specified bythe Piping Analytical Engineer is contained in the threebasic source documents. These are then transmitted with-in the Piping Division to the Layout Section and theProduction Section. The Plant Layout Section analyzesits arrangement of equipment on the plot with the engi-neer's design as a basic guideline and further performslayout studies of the critical areas as indicated on theflow sheets. The Production Section receives the plotplan, layout studies and the source documents from thePiping Analytical Section, and proceeds to design theindividual key plans of areas and isometrics of individuallines. Once this has been completed, eve4r piece of ma-terial is taken off the isometrics and transmitted to theMaterial Control Section which writes the material requi-sitions, issues the isometrics to the shop (where job fabri-cation is necessary) and arranges with procurement forthe shipment of material to the construction site. Herethe isometrics, flow sheets and nomenclature are used asa road map in the fabrication and erection of the pipingsystem.

Flow Diogrom Symbols. Since the engineering flowdiagrams are the source document for all productionwork to be done at later stages of the job, the symbolswhich are contained in these flow diagrams must conveya distinct, accurate, and concise description of the re-quirements established by the engineer. The EngineeringFlow Diagram sl,rnbols are the key working tool for thepiping design function. Since every firm engaged inthe process industry operates through a flow sheet asa base document, each has adopted a different methodof maintaining their own piping symbols. Thus, 'we willnot go into any extensive listing of symbols. (Fig. 5 is36

a list of some of the r.najol t1'pical symbols as used in theillustrations) .

It can be noted from an investigation of the sampleengineering flow diagrams that the major symbols in-cluded are those for piping and valves. The only fittingsymbols which generally appear on an engineering flowdiagram are the symbols for reducers, which indicate achange in line size, and the symbol of a cap, which in-dicates a header where the Engineer has decided a dead-end is allowable.

Instrumentation, being an essential part of the chem-ical process, is fairly well defined in basic sgnbol lan-guage. The reader is referred to the "Basic Instrumen-tation S),rnbols RP5" of the Instrument Society ofAmerica. The syrnbols recommended in this publicationare generally accepted for notation on the engineeringflow diagrams. These instrumentation spnbols must showif the instrument would actually control an automaticcontrol valve in the process stream. Thus, we can seethe need for showing the location of the instrumentation'The critical locations are indicated on the engineeringflow diagrams as required. The board mounting instru-ments are generally so indicated that key operating in-formation can be readily available to the personnel inthe control house.

flardware and Instrumentation. In essence, flow sheetsyrnbols fall into two major categories' The first beingtLe symbols for the hardware iterns such as regular valves(gate, globe, check, plug, lubricated plug, etc-) andspecial valves (control valves or relief valves). The sec-ond classification, the instrumentation sr'mbols, falls intothree categories: temperature, pressure, and flow indi-cators. Properly used and properly indicated on the flowsheets, these symbols can tell the entire control and hard-ware arrangement requirements for the plant.Engineering Flow Diograms. From the information en-tering his section, the Piping Analytical Engineer putstogether a set of Engineering Flow Diagrams- In com-piling these diagrams he duplicates the flow requirementsof the process as indicated on the PFD and converts asingle process flow diagram into from 5 to 10 engineeringflow diagrams which are Process-oriented. The process-oriented engineering flow diagrams are separated fron.rthe auxiliary and utility systems by both a numberedsequence of drarvings and by mantler of presentation. f'heprocess diagrams are in schematic form showing actualarrangenlents and denoting special considerations suchas gravity flow wherever necessary. Whereas, the auxiliaryand utility flow diagrarrs are laid out acconding to plotplan arrangement.

In addition to the information found on the processflow sheet, these process-oriented engineering flow dia-grams contain the start-up conditions required by theunit, the normal operating conditions and considerationsfor shutdown. They further specify the valving and pip-ing necessary for the pump sparing arrangements. Theexchanger arrangement, i.e., number of shells, number ofshell and tube inlet and outlet connections, is also shownschematically on the flow sheets. Any critical arrange-ments of piping where the Engineer has to specify theexact arrangement in order to obtain proper operationshould also be shown.

The auxiliary and utility flow diagrams on the other

hand have no preliminary design butare designed completely by the PipingAnalytical Engineer. His basis of de-sign is simply supporting the processflow stream itself and his auxiliary andutility sptems must meet this require-ment. Ilere tho engineer must be moreconscious of physical layout as hisauxiliary and utility header sizes are adirect function of flow quantity as thevarious pieces of equipment are fed.The entire set of process, auxiliary andutility flow diagrams, constitute majorsource documents from which the pip-ing designer details his design of theover-all plant.

Nomenclqiure. As previously stated,some of the design data presented onthe engineering flow diagrams must berecorded in the nomenclature. Eachand every line tagged with a numberon the flow sheet must be Iisted innumerical order in the nomenclature.On the average size job there areapproximately 1500 lines under con-sideration. This presents a tedious taskfor the Piping Analytical Engineer,