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DUCTILE IRON PIPE VERSUS PVC

®



All Pipe M aterials Are Not Equal

Design engineers must consider many factors when designingand specifying potable water pipelines, including initial cost of the system, operating requirements, maintenance costs,

dependability, and long-term performance. In an effort to makethat job easier, this brochure will compare the structural andperformance attributes of Ductile Iron pipe and polyvinyl chlo-ride (pvc) pipe and provide valid current information to engi-neers who must determine a basis for selecting piping materials.

In addition to providing physical test data comparing the twopipe products, the brochure will also compare applicable AWWAdesign standards for each pipe, including ANSI/AWWAC150/A21.501 for Ductile Iron pipe, ANSI/AWWA C9002 forsmaller-diameter pvc, and ANSI/AWWA C9053 for large-diame-ter pvc pipe.

This brochure will also question why two different standardsexist for the same pvc pipe material. Whereas Ductile Iron pipestandards are conservatively consistent for all sizes, the C905standard for large-diameter pvc pipe differs substantially fromthe C900 standard. C905, for example, provides for a thinnerwall, greatly reduced safety factors, and no surge allowance.

Lastly, this brochure will compare the installation techniques andpractical aspects of utilizing the two flexibly designed conduits.

The following data are drawn from several sources, includingAWWA standards, published information from pipe manufactur-ers and associations, and physical testing performed by research

engineers from the Ductile Iron Pipe Research Association andthe Robert W. Hunt Company.4

In short, this brochure will present sound engineering informa-tion that will prove that all pipe materials, indeed, are not equal.

Why D iff erent Standards for t he Same

Piping M aterial?

Specifying engineers are asking, with good reason, why small-and large-diameter pvc pipe standards have several major dif-ferences in design and testing requirements.

AWWA C905 Standard (14- through 48-inch pvc), for example,includes a safety factor of 2.0 for internal pressure design thatis 20 percent less than the 2.5 safety factor for small-diameterpvc required by AWWA C900 (3- through 12-inch).

According to a spokesman for the pvc pipe industry, “the weak-ness of pvc pipe is its limited resistance to surging pressure.”5

And, whereas C900 pvc has an allowance for surge pressure,the C905 standard for large-diameter pvc pipe has no allowancefor surge pressure in the pressure ratings.

The total internal design pressure in the C905 standard is lessthan the total internal design pressure in the C900 standardFor C900, the Hydrostatic Design Basis (HDB)/2.5 = workingpressure + surge. For C905, the (HDB)/2.0 = working pressure. Thus, there is no surge allowance, and safety factors are

greatly reduced.

Pvc C900 and C905 Pipe Wall Thickness

Comparison

One way of realizing the inferior design of C905 compared toC900 is by comparing wall thickness. The equation for hoopstress for calculating the net thickness required for internapressure is:

in which:

t = net thickness (in)P = design internal pressure (psi)D = pipe diameter (in)S = design stress (psi)

Therefore, the net pipe wall thickness increases as the diameterincreases for constant design internal pressure. However, 100psi pressure class 12-inch diameter pvc (C900) has a wall thick-ness of 0.528-inch where 100 psi pressure rated 14-inch-diam-eter pvc (C905) has a wall thickness of only 0.373-inch (less

than the smaller 12-inch diameter pipe). This is contrary to abasic engineering reasoning.

100 psi Pressure Class/Pressure RatingC900 Standard 12-inch-diameter pvc

t = .528”C905 Standard 14-inch-diameter pvc

t = .373”

Another way of comparing the design of C900 and C905 is tocalculate the pipe wall thickness for the same diameter pipeusing both designs. For 200 psi pressure class, a 24-inch-diameter pvc pipe would require a wall thickness of 1.843 inchesbased on C900. However, based on C905, the same pipe wouldrequire a wall thickness of only 1.229 inches (33 percent lessthan C900).

200 psi Pressure Class/Pressure RatingC900 Standard 24-inch-diameter pvc

t = 1.843”C905 Standard 24-inch-diameter pvc

t = 1.229”(a 33-percent reduction in wall thickness)

DUCTILE IRON PIPE VERSUS PVC 1


PD2S

t =



Table 1 - Comparison of Ductile Iron Pipe and pvc Pipe Standards

Ducti le Iron PipeANSI/AWW A C150 /A21.50ANSI/AWW A C151/A2 1.516

Lay ing Leng ths

P ressu reC lass/Rat ings

M e t h o d o f

Des ign

In terna lP ressu reDes ign

S u rgeA ll ow ance

Externa l Load

Des ign

L ive Load

F ac to r o fSafe ty

Spec i f i edTrenchCondi t ions

Factory Tests

H yd ros ta t i c

Testing

3 ” - 6 4 ”

18 ’ , 2 0 ’

Rated up to 350 ps i .P ressu re C lass 150 , 200 , 250 , 300 , &350 . H ighe r p ressu res may be des igned .

Designed as a f lex ib le condui t . Separatedes ign fo r i n te rna l p ressu re (hoop s t r essequa t i on ) and ex te rna l l oad (bend ings t ress and de f l ec t ion ) . Cas t i ng to l e rancea n d s e r v i c e a l l o w a n c e a d d e d t o n e tth i ckness .

Rated a t 100, 150 & 20 0 psi (DRs 25 , 18, &14 , r espec t i ve ly ) a t a se r v ice temp e ra tu reo f 7 3 . 4 °F. F o r s e r v i c e t e m p e r a t u r e sgrea ter than 73 .4°F, the press ure ra t ingsmus t be ap p rop r i a te ly r educed .

Designed as a f lex ib le condui t . Separatedes ign fo r i n te rna l p ressu re (hoop s t r essequat ion) and externa l load (def lect ion) —external load is not covered by a standard.No c ons ide ra t ion fo r bend ing s t r ess .

S a m e a s C 9 0 0 .

P ressu re Ra t i ng : S t ress due to wo rk i ngp ressu re canno t exceed the HDB (4 ,000psi ) 2 .0 sa fe ty fac to r (HDS = 2 ,000 ps i ) .

P ressu re C lass : S t ress due to w o rk i ngp r e s s u r e p l u s s u r g e p r e s s u r e c a n n o texceed the HDB (4 ,000 ps i ) 2 .5 sa fe tyfacto r (HDS = 1,600 psi ) .

P ressu re C lass : S t ress due to wo rk i ngp ressu re p l us su rge p ressu re canno texceed the m in imum y ie l d s t r eng th o f42 ,000 ps i 2 .0 sa fe ty fac to r .

N o m i n a l s u r g e a l l o w a n c e i s 1 0 0 p s i( b a s e d o n a n i n s t a n t a n e o u s v e l o c i t ychange o f app rox ima te l y 2 fps ) ; how ev-e r , ac tua l an t i c i pa ted su rge p ressu resshou ld be used .

Pr ism load + t ruck load. Ring bend ing

s t ress l im i ted to 48 ,000 ps i , wh i ch i s 1

/ 2the m in imum u l t ima te bend ing s t r eng th .Def lect ion is l imi ted to 3% of the outs ided iame te r o f the p i pe , wh i ch is 1

/ 2 o f thed e f l e c t i o n t h a t m i g h t d a m a g e t h ecem en t -mo r ta r l in i ng .

AASHTO H-20, assum ing a s ing le 16,000 -l b concen t ra ted whee l l oad . Impac t fac -tor is 1 .5 for a l l depths.

P r e s s u r e D e s i g n: 2.0 ( inc lud ing surge)based on m inimum tens i le y i e ld s t r eng tho f 42 ,000 ps i .Exte rna l Load Des ign: 2 .0 fo r bend ingbased o n m inimum u l t ima te r i ng bend ings t reng th o f 9 6 ,000 ps i , o r 1.5 fo r bend ing

based on m in imum r i ng y i e l d -bend ings t reng th o f 72 ,000 ps i . 2 .0 fo r de f l ec t ionfo r cem en t -mo r ta r - li ned p i pe .N o t e : Ac tua l s a fe ty fac to rs a re g rea te r than the

nomina l s a fe ty fac to rs due to the add i t ion o f the

s e rv ic e a l lowanc e and the a l lowanc e fo r c as t ing

to le ranc e in the des ign p roc edu re .

P r e s s u r e D e s i g n : 2.5 ( inc lud ing surge)based on HDB. Exte rna l Load Des ign: N osa fe ty fac to r s can be ca l cu la ted . No ex te r -na l load cr i te r ia are def ined.Note : Sa fe ty fac to rs and s t reng th g rea t l y a f fec ted

by tempe ra tu res , s u r fac e s c ra tc hes , and ex tended

exposure to sunl ight. P ipes under cyc l ic load ingl ik e ly to hav e lowe r s a fe ty fac to rs than thos e unde r

s ta t ic load ing.

Pressure Des ign: 2 .0 ( no su rge i nc l uded )based on HDB. Sec t i on 4 .6 .2 cau t i ons tha twhen C905 p ipe s i zes a re used i n d i s t r ibu -t i on sys tems tha t the sa fe ty fac to r mayneed to be se t a t 2 .5 and an a ll owance fo rs u r g e p r e s s u re s m a y n e e d t o b e a d d e d .

Exte rna l Load Des ign: S a m e a s C 9 0 0 .Note : S a m e a s C 9 0 0 .

Five spec i f ied lay ing c ond i t ions (Types 1-5 ) . Conse rva t i ve E and so i l s t r eng thparameters l i s ted. Type 1 ( f la t bot tom,loose backf i l l ) o r Type 2 ( f la t bot tomtrench, backf i l l l igh t ly conso l idated tocen te r l ine o f p i pe ) a re adequa te fo r m os tapp l ica t ions.

Each p i pe tes ted to a m in imum o f 500

psi fo r a t least 10 seconds a t fu l l p res-su re .

Each p i pe tes ted a t 4 X des igna ted p res -

su re c l ass fo r a t l eas t 5 seconds a t fu l lp ressure. There is a provis ion (Sect ion5.1 .14) for the “purchaser and/or supp l ie r ”t o a l l o w t h e m a n u f a c t u r e r t o c o n d u c thyd ros ta t i c p roo f tes ts fo r p i pes a t tes tf r equenc ies “ o the r than the requ i r emen tss ta ted . ” In o the r wo rds , not every p ieceof pvc p ipe “m ust” be pressure tes ted .

At l eas t one samp le du r ing each c as t i ngpe r i od o f app rox ima te l y 3 hou rs sha l l besub jec ted to a tens i l e tes t ; mus t showmin imum y ie l d o f 42 ,000 ps i , m in imumu l t ima te o f 60 ,000 ps i and m in imumelongat ion o f 10%. At least one Charpyimpac t samp le sha l l be taken pe r hou r(min imum 7 f t - lb ) , w i th an add i t iona l low -tempe ra tu re impac t tes t (m in imum 3 f t -l b ) made f r om a t l eas t 10% o f the sam p lecoupons taken fo r the no rma l Cha rpyim p a c t t e s t .

Sus ta i ned p ressu re tes t ( 1 ,000 hou rs ) i srun sem i -annua l ly a t app ro x ima te l y 3 .25 -3 .5 t imes the p ressu re c l ass . Q u i ck bu rs ts t r eng th ( a t app rox ima te l y 5 t imes thep r e s s u r e c l a s s ) t e s t e d o n c e e v e r y 2 4hou rs . F l a t ten ing res i s tance tes ted onceeve ry 8 hou rs as s pec i f ied i n ASTM D24129 .E x t r u s i o n q u a l i t y t e s t e d o n c e e v e r y 8hours as speci f ied in ASTM D2152 10.

F l a t ten ing res i s tance tes ted once eve ry 8h o u r s a s s p e c i f i e d i n A S T M D 2 4 1 2 .E x t r u s i o n q u a l i t y t e s t e d o n c e e v e r y 8hours as s pec i f ied in ASTM D2 152 . Quickburs t and sus ta ined pressure tes ts a renot requi red .

Each p ipe tes ted a t 2 X des igna ted p res -

su re r a t i ng fo r a t l eas t 5 seconds a t fu l lp ressure. There is a provis ion (Sect ion5 .1 .9 ) fo r the “pu rchase r and /o r supp l i e r ”t o a l l o w t h e m a n u f a c t u r e r t o c o n d u c thyd ros ta t i c p roo f tes ts fo r p i pes a t tes t f r e -quenc ies “ o the r than the requ i r emen tss ta ted . ” In o the r wo rds , not every p ieceof pvc p ipe “m ust” be pressure tes ted .

N o t c o v e r e d i n t h e s t a n d a r d . Th eF o r e w o r d o f t h e s t a n d a r d r e f e r e n c e sA W W A M 2 3 a n d A N S I/ A W W A C 6 0 5 . C 6 0 5con ta ins f i ve t r ench co nd i t ions re fe r red toa s “ c o m m o n e m b e d m e n t t y p e s . ” T h e s et r e n c h t y p e s r e s e m b l e t h e t r e n c h t y p e sused i n the Duc t i le I r on p i pe des ign s tan -d a r d ( A W W A C 15 0 ) ; h o w e v e r , A W W AC 6 0 5 u s e s m u c h le s s c o n s e r v a t i v e t r e nc hva lues fo r the bedd ing cons tan t (K ) andso i l modu lus (E) f o r t h e c o m m o n l y u s e dp v c t r e n c h t y p e s .

S a m e a s C 9 0 0 .

Des ign not covered in the s tandard .Refe rence i s made to AWWA M23 fo rdes ign p roced u res . AASHTO H-20 , 16 ,000 -lb w heel load. Impac t factor o f 1.1 ford e p t h s o f c o v e r b e t w e e n 2 a n d 3 f e e t .Impac t fac to r o f 1.0 fo r dep ths o f c ove r o f3 fee t o r g rea te r .

S a m e a s C 9 0 0 .

No th ickness des ign s tandard for pvc

pipe. The insta l la t ion stand ard, ANSI/AWWAC 6 0 5 7, p laces a l imi t o f 5% on ver t ica lc ross - sec t i on de f l ec t i on . Re fe rence i sm a d e t o A W W A M 2 3 8 fo r des ign p roce -dures. Pr ism load + t ruck load. Ut i l i zes theModi f ied Iowa Def lect ion Equat ion; howev-er , no safe ty facto rs are def ined.

S a m e a s C 9 0 0 .

30 , 35 , o r 4 0 ps i su rge a l low ance fo r DRs25, 18, & 14, respect ive ly. Based on anins tan taneous ve loc i t y change o f app rox i -ma te l y 2 fps .

N o n e i n c l u d e d . P r e s s u r e r a t i n g s m u s tb e r e d u c e d t o a l lo w f o r p r e s s u r es u r g e s . P r e s s u r e s u r g e s b a s e d o n a ni n s t a n t a n e o u s v e l o c i t y c h a n g e o f 2 f p sw ou ld be 2 1, 23 , 26 , 29 , 30 , 32 , 35 , & 40psi ( fo r DRs 51, 41, 32.5 , 26, 25, 21, 18, &14, resp ec t ive ly) .

Rated a t 80, 100, 125, 160, 165, 200, 235,& 3 00 psi (DRs 51, 41, 32.5 , 26, 2 5, 21, 18,& 14 , r espec t i ve ly ) a t a se r v i ce tem pe ra -ture o f 73.4 °F. For serv ice tem perat uresgrea ter than 73.4 °F, the press ure ra t ingsmus t be app rop r i a te ly r educed .

2 0 ’ ± 1” 2 0 ’ ± 1”

4 ” - 12 ” 14 ” - 4 8 ”

pv c P ipeA N S I/A WWA C 9 00

pv c P ipe

A N S I/A WWA C 905

Topic

Sizes



Pvc C900 and C905 Physica l Test ing

Requirement s Comparison

Not only design requirements but also physical testing require-ments have been reduced in the C905 standard. The hydrostatictest pressure in C905 has been reduced to half of that requiredby C900. In C900, hydrostatic test pressures are four times thedesignated pressure class. In C905, on the other hand, they areonly two times the designated pressure rating. Nor does C905

require the quick burst or sustained pressure tests required byC900.

The 1997 revisions of C900 and C905 incorporated a new sec-tion titled “Additional Test Requirements.” This title is mislead-ing because the new section does not require additional testing.Rather, it gives the purchaser or supplier the option to allow themanufacturer to conduct hydrostatic proof tests of pipe (andalso couplings in C900) at frequencies less than specified in per-tinent sections of the standards. These sections, pertaining tothe proof tests, require that “each standard and random lengthof pipe” and each coupling be subjected to hydrostatic proof tests. Therefore, the purchaser or supplier (which could be a

distributor or contractor) could specify, for example, that onlyevery 10th, or every 100th, piece of pipe be tested. To precludesuch an occurrence, specifications should require certification bythe manufacturer that each piece of pipe and each coupling havebeen subjected to proof tests in accordance with the standard.

These are just a few of the reduced requirements in the C905standard for large-diameter pvc, which could result in an inferi-or product compared to C900-designed pipe. Table 1 highlightsexamples of shortcomings in the C905 standard compared toC900 and compares them to requirements of ANSI/AWWAC150/A21.50 and ANSI/AWWA C151/A21.51.

Ductile Iron Pipe Has M ore Than Eight

Times the Tensile St rength of pvc.

The pipe material’s tensile strength is a very important basicproperty because it resists the forces caused by internal hydro-static pressure and water hammer.

Figure 1 compares the tensile strengths of Ductile Iron and pvcpipe. Shown for comparison are minimum values per the appli-cable standards as well as test data from actual measurementsof specimens taken from the wall of 6-inch Pressure Class 350*Ductile Iron pipe and 6-inch DR 18 (PC 150) pvc pipe.

Typical Variat ions in Operat ing or

Installation Temperature Do Not Affect

t he Strength of Duct ile Iron Pipe.

Because Ductile Iron pipe has a moderate and dependable coefficient of thermal expansion, few problems are created bychanges in service temperatures. Also, in a typical range ofwaterworks operating temperatures (32°F to 95°F) or even aconceivable range of installation temperatures (-10°F to110°F), there is no significant difference in the tensile strengthof Ductile Iron pipe.

On the other hand, because of its high thermal expansion coef-

ficient, the performance of pvc pipe is significantly related to itsoperating temperature.11 For service at temperatures greaterthan 73.4°F, pvc loses tensile strength, pipe stiffness, anddimensional stability. Thus, the pressure capacity of the pvc pipeis reduced, and more care must be taken during installation toavoid excessive deflection.12

Conversely, at temperatures less than 73.4°F, pvc loses impactstrength and becomes less ductile, necessitating greater handling care in colder weather.13 Because the thermal expansioncoefficient of pvc is approximately five times that of Ductile Ironpipe,14 it is conceivable that, when exposed to extreme temperature changes, pvc pipe will experience undesirable structuramovements such as joint buckling or disengagement because ofexpansion or contraction.

Figure 2 shows the relationship based on the standard tensilestrength of 7,000 psi for pvc. At 110°F, the tensile strength opvc is approximately half of the tensile strength at 73.4°F.

8 0 , 0 0 0

7 0 , 0 0 0

6 0 , 0 0 0

5 0 , 0 0 0

4 0 , 0 0 0

3 0 , 0 0 0

2 0 , 0 0 0

1 0 , 0 0 00

6 0 , 0 0 0 U l t i m a t e

7 1 , 4 0 0 U l t i m a t e

5 1 , 9 0 0 Y i e l d

U l t i m a t e7 , 7 0 0

Y i e l d

5 , 8 0 0

4 2 , 0 0 0 Y i e l d

U l t i m a t e

7 , 0 0 0

Figure 1 - Tensile Strength D uc t i l e I r onp vc

Mi n i mum Va l uesper App l i c ab l e

Stand ards (AWWAC151 a nd AWW A C900)

Measured ValuesFrom

Product ion Pipe

T e

n s i l e

S t r e n g t h

i n

p s i


* Pressure Class 350 is the lowest available pressure class for 6-inch Ductile Iron pipe.



4 DUCTILE IRON PIPEVERSUS PVC

Duct ile Iron Resists Up to Four Times the

Hydrostat ic Burst Pressure of pvc Pipe.

The burst test is the most direct measurement of a pipe mater-ial’s resistance to hydrostatic pressure.

Figure 3 compares the average burst pressure of 6-inchPressure Class 350* Ductile Iron pipe and 6-inch DR 18 (PC150) pvc pipe. Note that Ductile Iron pipe is available in pres-sure ratings up to 350 psi in all sizes, 3-inch to 64-inch. No pvcpipe — C900 or C905 — is manufactured with a pressure rat-ing as great as that of Ductile Iron pipe.

Figure 4 compares the hydrostatic burst pressure of 24-inchPressure Class 200* Ductile Iron pipe and 24-inch DR 25 (PR165) pvc pipe. In laboratory tests, the average burst pressureof the 24-inch Ductile Iron pipe was 1,523 psi. For the pvcpipe, it was 527 psi — approximately one-third that of DuctileIron pipe.

The St rength of Ductile Iron Pipe Is Not Compromised By Time.

With Ductile Iron pipe, there is no measurable relationshipbetween applied tensile strength and time to failure. Thus, thestrength for hydrostatic design of Ductile Iron pipe is its mini-mum yield strength in tension, 42,000 psi.

Pvc responds to tensile stress by failing after a period of timeinversely related to the applied stress. Thus, the strength usedfor hydrostatic design of pvc pipe is less than the yield strengthof the material as established in a short time test.15 Thestrength value used is called the long-term hydrostatic strengthand is also referred to as the Hydrostatic Design Basis (HDB).

The HDB value, which is defined as the stress that results in fail-ure after 100,000 hours (11.4 years), is determined accordingto ASTM standard procedures by extrapolation from data accu-mulated from tests lasting up to 10,000 hours (1.14 years).16

For the pvc compound used in C900 and C905 pipe, the HDB is

4,000 psi.17

The HDB will be less than 4,000 psi for pvc pipeused at temperatures greater than 73.4°F.18

Since no utility wants its pipe to last only 11.4 years, a nominalfactor of safety is applied to the long-term hydrostatic strength.

The nominal factor of safety depends upon the standard underwhich the pipe is manufactured. For ANSI/AWWA C905, the fac-tor of safety is 2.0. For ANSI/AWWA C900, the factor of safetyis 2.5, which also includes a surge allowance based on two-feet-per-second instantaneous velocity change. Both of these designsare based strictly upon hydrostatic pressure and do not take intoaccount any other localized stresses that may occur duringinstallation or in operation over time, nor do they account for

possible fluctuations in pressure. Yet these factors may have agreat effect on the life expectancy of the pipe.

Figure 5 is a typical stress regression curve for pvc pressurepipe. The stress regression curve is a plot of failure points thatdemonstrates pvc’s ability to withstand stress as a function of the magnitude of the stress and the length of time that stress isapplied. Thus, the stress regression curve is a representation of the length of time until failure of the pvc at a given level of stress. And, as the curve shows, the higher the stress the short-er the expected life for pvc pipe.19

Figure 2 - Strength-Temperature Relationship for pvc

T e n s i l e

S t r e n g t h

i n

p s i

9 , 0 0 0

8 , 0 0 0

7 , 0 0 0

6 , 0 0 0

5 , 0 0 0

4 , 0 0 0

3 , 0 0 0

2 , 0 0 0

1 , 0 0 0

070 80 90 100 110

73.4Design

Temperature

Temperatu re in º F

5 , 0 0 0

4 , 0 0 0

3 , 0 0 0

2 , 0 0 0

1 , 0 0 0

0

4 1 5 0

1 0 4 0

D u c t i l e I r o n P i p e6 ” P C 3 5 0

p v c P i p e6 ” D R 1 8

P C 1 5 0

Figure 3 - Hydrostatic Burst Pressure–6-inch Ducti le Iron and pvc Pipe

Burst

Pressure

a t

Fa i lure

i n

p si

2 , 0 0 0

1 , 5 0 0

1 , 0 0 0

5 0 0

0

1 5 2 3

5 2 7

D u c t i l e I r o n P i p e2 4 ” P C 2 0 0

p v c P i p e2 4 ” D R 2 5

P R 1 6 5

Figure 4 - Hydrostatic Burst Pressure–24-inch Ductile Iron and pvc Pipe

Burst

Pressure

a t

Fa i lure

i n

p si

* Pressure Class 350 is the lowest pressure class for 6-inch Ductile Iron pipe.

* Pressure Class 200 is the lowest pressure class for 24-inch Ductile Iron pipe.



Ductile Iron Pipe Resists Up to Eight

Times the Crushing Load of pvc Pipe.

The different theories of design of buried pipelines become mostsignificant in relation to external load design. Both Ductile Ironand pvc pipe, being flexible rings, respond to external load bydeflecting.21 The interaction of the deflected ring with the sur-rounding soil is the complex question in the design theories.

The design procedure for Ductile Iron pipe is based on limitingboth the ring bending stress and deflection, while the onlyparameter used in the design of pvc pipe is ring deflection.

The standard design procedure for Ductile Iron pipe limits thering deflection due to external loads to 3 percent. This limit,

which is based on the performance limit for cement-mortar lin-ings typically specified for Ductile Iron pipe, includes an explicitsafety factor of 2. This calculation employs the same conserva-tive assumptions regarding soil parameters and earth loads usedin the bending stress calculation.

The usual design procedure for pvc limits ring deflection to 5percent22 — the only consideration given to external loading.

Both Ductile Iron and pvc pipe design procedures employ theIowa formula to predict deflection of the pipe.23 In the Iowa for-mulation, both pipe stiffness and the stiffness of the fill materi-al around the pipe contribute to limiting the deflection. Because

pvc pipe has far less stiffness than Ductile Iron, the importanceof soil stiffness is greater for pvc. This means that with pvcpipe, bedding conditions and on-the-job installation inspectionare much more critical.

The parallel plate ring crush test provides a simple comparison of the relative strengths of the two piping materials. Figure 6 com-pares pipe stiffness resulting from such tests conducted on 6-inchPressure Class 350* Ductile Iron pipe and 6-inch DR 18 pvc pipe(C900). Likewise, Figure 7 compares pipe stiffness of 24-inchPressure Class 200** Ductile Iron pipe and DR 25 pvc pipe (C905).

Duct ile Iron Has M ore than 13 Times the

Impact Strength of pvc.

Impact strength is another important characteristic of pipingmaterials. While this property relates more to conditions thepipe might encounter during handling, shipping, and installationit is nevertheless important because damage incurred duringthese activities can go undetected and later result in failures inthe operating pipeline.

Figure 8 compares the impact strength as specified and measured for Ductile Iron and pvc, which were tested by both the

IZOD (cantilevered beam) and Charpy (simple beam) methods.2

These values are representative of tests conducted at 73.4°F. Aswith tensile strength, there is no measurable relationshipbetween impact-resistance and temperature within expectedranges for Ductile Iron pipe. Pvc pipe, however, exhibits a measurable decrease in impact strength at temperatures below73.4°F.25 The impact strength of pvc is also measurablydecreased after the pipe has been overexposed to sunlight — animportant consideration in storing pvc pipe stocks.26

A pp l i ed

H oop

Stress

i n

10 3

p si

1 0

8

6

4

2

00.1 1 10 100 1K 10K 100K

Time to Fai lure in Hours

Figure 5 - Typical Stress Regression Curve for pvc Pressure Pipe 20

5 , 0 0 04 , 5 0 04 , 0 0 03 , 5 0 03 , 0 0 02 , 5 0 02 , 0 0 01 , 5 0 01 , 0 0 0

5 0 00

4 8 4 3

3 6 1

D u c t i l e I r o n P i p e6 ” P C 3 5 0

3 % D e f l e ct i o n

p v c P i p e6 ” D R 1 8


Figure 6 - Pipe Stiffness Comparison of 6-inch DIP and pvc

PipeSt i f fness

in ps i

3 0 0

2 5 0

2 0 0

1 5 0

1 0 0

5 0

0

1 4 7

D u ct i l e I r o n P i p e2 4 ” P C 2 0 0


p v c P i p e

2 4 ” D R 2 55 % D e f l e ct i o n

Figure 7 - Pipe Stiffness Comparison of 24-inch DIP and pvc

PipeSt i f fness

in ps i

* The minimum pressure class available for 6-inch Ductile Iron pipe.** The minimum pressure class available for 24-inch Ductile Iron pipe.

2 5 5


1.14 Yrs 11.4 Yrs



6 DUCTILE IRON PIPE VERSUS PVC

Direct Tapp ing Ducti le Iron is Easier, Less

Expensive, Faster — and Less Likely t o

Damage t he Pipe — Than Tapp ing pvc.

DIPRA conducted tests comparing several different parametersconcerned with the direct tapping of 5-foot lengths of 6-inchPressure Class 350 Ductile Iron pipe and 6-inch DR 14 (PC 200)pvc pipe, including leak tests, pull-out tests, and cantilever loadtests.27 Each material was tapped according to manufacturers’directions by the same machine operator. The results follow.

Leak Tests

For each material, after the tap was made at 50 psi internalpressure, pressure was increased in 25-psi increments to eachpipe’s maximum pressure rating (350 psi for Pressure Class 350Ductile Iron and 200 psi for DR 14 pvc).

Eight 3/4-inch taps were made on five pvc specimens. The cor-poration stops were torqued to 27 ft-lbs according to manufac-turers’ directions. Of the eight direct taps, five leaked prior toreaching the final 200 psi internal pressure. All leakageoccurred at the threaded connection of the pvc pipe andcorporation stop. Each of the five leaking connections wasretorqued to 35 ft-lbs and internal pressure was increased.Each of these connections continued to leak prior to the pipe’s200 psi working pressure.

According to theif a pvc pipe continues to leak after a corporation stop is torquedto 35 ft-lbs, the water main must be taken out of service, thecorporation stop removed, threads inspected and cleansed, andthe corporation stop reinstalled with 27 ft-lbs of torque andrechecked.28

Six 3/4-inch direct taps were made on Ductile Iron pipe speci-mens, which were initially torqued to 30 ft-lbs. Only one exhib-ited any leakage, which was observed at the threaded connec-tion to the pipe at an internal pressure of 175 psi. This corpo-ration stop was then retorqued for 40 ft-lbs to stop the leak.

After retorque of this single corporation, none of the connec-tions exhibited any leaks, even at 500 psi, the pressure atwhich the tests were terminated.

Retention of Corporation Stops

Another significant point of comparison is the vulnerability of damage to service connections. Figure 9 depicts the pull-outforce and moment required to break off a 3/4-inch service tapin 6-inch Ductile Iron and pvc pipe, both in tension and as a can-tilever.

The dramatic difference in values is even more significantbecause the failures of taps in the Ductile Iron pipe tests werefailures of the brass corporation stops. No damage was inflict-ed on the pipe. In each case, failures of the taps in pvc pipe werefailures of the pipe wall itself. This distinction is very importantto the relative difficulty of repair.

3 0 . 0 0

2 5 . 0 0

2 0 . 0 0

1 5 . 0 0

1 0 . 0 0

5 . 0 0

0 . 0 0

D I1 7 . 5

p v c

0 . 6 5

p v c1 . 4 2

p v c

1 . 2 5

Figure 8 - Impact Strength

Min imum*Specified Valuesper Appl icable

Standards(AWWA C151 and

AWWA C900)

Measured resul tsfrom Charpy Test

Measured resul tsfrom IZOD Test

F o o t -

P o u n d s p e r I n c h

* The minimum specified values are not directly comparable due to the different notch depths specified in the standards.

D I2 7 . 6

D I1 6 . 6

1 0 , 0 0 0

8 , 0 0 0

6 , 0 0 0

4 , 0 0 0

2 , 0 0 0

0

5 , 0 0 0

4 , 0 0 0

3 , 0 0 0

2 , 0 0 0

1 , 0 0 0

0

9 6 4 4

4 5 5 8

4 7 2 1

3 2 6 9

Figure 9 - Corporation Stop Retention

Average Load to Failure

Pull-Out Test Cantilever Test

Duct i le I ron

pvc

F o r c e

i n

P o u n d s

M

o m

e n t i n

I n c h -

P o u n

d s

Handbook of PVC Pipe-Design and Construction,



Use of Tapping Saddles

The C900 pvc pipe standard requires the use of a tapping sad-dle on certain thicknesses — and the integrity of direct tappingis questionable for all pvc thicknesses. Tapping saddles arerequired on all thicknesses in the C905 pvc pipe standard.29 Onthe other hand, the use of tapping saddles with Ductile Iron pipefor normal house services is unnecessary.

Tapp ing Advantages for Ductile Iron Pipe

When performing service taps on pvc pipe it is important to fol-low the guidelines laid out both in ANSI/AWWA C605 and themanufacturers’ installation guides.

A review of the tapping procedures outlined in the Johns-Manville (J -M) Blue Brute installation guide30 reveals many “Donots.” For example:• “Do not tap into an area of the pipe which shows discoloration(sun burning).”• “Do not tap on the outside of the curve on a pipe that has beenbent (deflected) beyond the recommended radius of curvature.”

• “Do not create ovality or otherwise distort the pipe by overtightening the tapping machine or the saddle.”• “Do not force the cutter through the pipe wall, make cutsslowly and use the follower very lightly. Do not use pipe dope orother liquid thread sealants.”

J -M also expresses additional concerns: Do not “direct tap…BlueBrute if the system is going to operate over 85ºF.” But, on theother hand, “Tapping in cold weather (below 40ºF) requiresadditional care because the pipe loses some of its resiliency andcan become more brittle and subject to damage if abused dur-ing handling. Damage done prior to tapping can show up whenthe pipe is tapped.” The J -M installation guide goes on to pro-vide explicit safety precautions for tapping pvc pipe under pres-sure: “When tapping pressurized pvc water pipe, basic safetyprecautions are advised to prevent personal injury to the work-man in the event of sudden and unexpected pipe failure. (Theyinclude:)1. Do not enter a trench or hole to perform tapping procedureswithout a second workman or supervisor present in the immediate vicinity.2. In addition to normal protective clothing, goggles or a face

shield should be worn.3. Prepare a means of simple and quick exit from the work areain the event of flooding. A sturdy ladder is recommended.4. The exposed pipe in the area of the taps should be coveredwith a heavy protective blanket. This protective blanket shouldbe approximately 4 feet x 6 feet in size and should have a holein the center to permit installation and operation of the tappingmachine.”

According to these instructions, a 4-foot x 6-foot excavation isneeded to accommodate the safety blanket and properly make atap in accordance with the manufacturer’s recommendationsUnlike Ductile Iron pipe, which has been safely tapped numerous

times in tapping contests, there are case histories of peoplebeing injured while tapping pvc pipe. If bending the pipe addsstresses that increase the likelihood of a tapping failure, onehopes that a sufficient length of pvc pipe is exposed to discernwhether the pipe to be tapped has been bent.

Research shows that the strength of Ductile Iron pipe walls exceeds the strength of the corporation stop, unlike pvc pipe walls. When stressed witheither cantilever or pull-out loads, taps in Ductile Iron pipe do not result in failure of the pipe walls. Photos of pull-out tests on pvc pipe show that leakage occurred at the threaded connection to the pipe, causing the pipe wall to break in the area of the corporation stop. During the same tests, leakage occurred inDuctile Iron pipe on the corporation stop plugs, as shown in the photo, and not the threaded connection to the pipe. Failure occurred at the threaded connec-

tion for the service line, not the threaded connection to the pipe.

The J-M installation guide provides explicit safety precautions for tapping pvcpipe under pressure. One of those precautions is to “prepare a means of simpleand quick exit from the work area in the event of flooding. A sturdy ladder isrecommended.” With pvc pipe failures such as these, such advice is worthwhile.




Flow Considerat ions

Flow Tests

DIPRA performed flow tests on in-service piping in Blackwood,New J ersey, Dothan, Alabama, and Wister, Oklahoma to estab-lish representative Hazen-Williams “C” factor values and com-pare overall flow characteristics of 12- and 18-inch Ductile Ironand pvc pipe.31

In the 12-inch-diameter Blackwood tests, the inside diameter of the cement-mortar-lined Ductile Iron pipe was 5.8 percent larg-er than that of the pvc pipe — 12 percent more flow capacity.Although the pvc pipe had a slightly larger “C” factor value (indi-cating a slightly smoother internal pipe surface), head loss wasless for Ductile Iron pipe than for pvc because of Ductile’s larg-er inside diameter.

In the 12-inch-diameter Dothan tests, Ductile Iron’s inside diam-eter was 5.4 percent larger than that of the pvc specimen — an11.1 percent larger capacity. Pvc’s smaller inside diameterresulted in a constant 11.1 percent higher velocity and a 23.5percent higher head loss than the Ductile Iron pipe althoughboth pipe sections carried the same quantity of water.

In the 18-inch-diameter Wister tests, the inside diameter of thecement-mortar-lined Ductile Iron pipe was 8.5 percent largerthan that of the pvc pipe — 17.7 percent more flow capacity.Although the pvc pipe had a slightly larger “C” factor value(140.6 versus 138.6), the pvc’s smaller inside diameter result-ed in a constant 17.7 percent higher velocity to deliver the samequantity of water with a resultant 44.9 percent higher head lossthan in the Ductile Iron pipe.

Energy Savings

Ductile Iron pipe’s larger inside diameter results in significantenergy savings, whether the savings are based on pumping costsor equivalent pipeline considerations.32

Because of Ductile Iron’s larger-than-nominal inside diameter —and resulting lower pumping costs — utilities can save appre-ciably on power costs and continue to save money every year forthe life of the pipeline.

By using equivalent pipeline theories, utilities can realize imme-diate savings with Ductile Iron pipe. Because of Ductile Iron’s

lower head loss, pvc pipelines with equivalent head loss wouldrequire larger — and, thus, more expensive — pipe diametersover portions of the pipeline. For example, a 30,000-foot-long24-inch Pressure Class 200* Ductile Iron pipeline delivering6,000 gallons per minute would have the same total head lossas 23,920 feet of 24-inch plus 6,080 feet of 30-inch PressureRated 165 pvc pipe.

Other Considerat ions

Pipe Handling

Pvc pipe manufacturers claim that pvc pipe is easier to handlethan Ductile Iron pipe because it is lighter. But this ostensibleadvantage is greatly overrated. When pipe is delivered to a jobsite, it should always be checked while still on the truck for dam-age and to ensure that the load is securely fastened and can be

unloaded in a safe manner. AWWA standards and manuals forboth pvc33 and Ductile Iron34 pipe require proper equipment andmethods for handling pipe and preclude rolling or dropping pipeinto the trench. Pvc is lighter than Ductile Iron; however, an 8-inch DR 14 pvc pipe weighs 230 pounds, not an insignificantweight for a person to handle. Twelve-inch DR 18 pvc weighsapproximately 400 pounds. Even two men should not attemptto handle a load of this magnitude. Each individual utility or con-tractor may have its own guidelines for what a safe load for oneperson is; however, 200 pounds exceeds the safe load for thevast majority of workers. Thus, the same equipment is neededto safely unload and lower both Ductile Iron and pvc pipe intothe trench.

Handling Damage

Compared to Ductile Iron pipe, pvc is a very soft material and isconsequently much more vulnerable to abrasions, scratches, andother damage during shipping and installation. In fact, both theC900 and C905 standards state that the “pipe surface shall befree from nicks and significant scratches.”35

Improper handling of pvc pipe can lead to impact damage,scratching, or gouging of the pipe wall. If such handling resultsin a scratch or gouge that is more than 10 percent of the wall

thickness, ANSI/AWWA C605 recommends rejection of the dam-aged pipe upon delivery.36 If the damage occurs during installa-tion, the damaged section should be cut from the rest of thepipe and removed. On a 12-inch DR 18 pvc pipe, a 10-percentscratch (0.05-inch) is approximately the thickness of a dime! Itis recommended that the inspector on a pvc pipe job be equippedwith the proper gauge to measure such damage as might occurwhen the pipe is handled and installed.

Ductile Iron pipe, on the other hand, is a tough material that isnot usually scratched or gouged by the type of rough handlingthat can damage pvc pipe. Furthermore, the gouge resistance of pipe materials, along with tensile/compressive strengths, is

becoming increasingly important with demanding new trench-less installation methods such as horizontal directional drilling(HDD) and pipe bursting. Because of Ductile Iron’s greatstrength and durability, there is no measurable loss of strengthdue to scratches and gouges from normal handling.

Water Hammer and Cyclic Loadings

Both Ductile Iron and pvc pipe are subjected to cyclic stressesfrom water hammer caused by velocity changes in the system.

* The minimum pressure class available for that diameter pipe.

8 DUCTILE IRON PIPEVERSUS PVC



mechanisms rely on grooved or serrated edges that dig into thepipe, they can potentially cause surface scratches to the pipingmaterial. Over time, these gouges may exceed the 10-percentwall thickness warned against in ANSI/AWWA C605. These sys-tems may also result in localized stress in the pvc material thatcan reduce the design life of the pipe. Remember that addition-al thicknesses for service and casting allowances are added toDuctile Iron pipe design, but not for pvc — despite the fact thatthe tensile strength is less for pvc than for Ductile Iron pipe.

Therefore, many utilities require that thrust blocks, rather thanrestrained joints, be applied to any point in the pvc piping sys-tem where the direction or cross sectional area of the waterwaychanges.

On the other hand, a wide variety of restrained joints are read-ily available for Ductile Iron pipe, giving the designer greaterflexibility in pipeline design and installation.

Locat ing Pipe

Because it is a non-metallic substance, buried pvc pipe cannot belocated using metal detectors. Therefore, it can be very difficult

to locate pvc pipe; however, it must be done to avoid damage.When plastic pipe is known to exist in the right of way, addi-tional time might be required to pothole excavations in order tolocate the pipe. Ductile Iron pipe, on the other hand, can be eas-ily located using conventional pipe locators commonly used bymost utilities.

It is necessary for utilities to provide field location of their exist-ing facilities to others planning excavations in the vicinity. One-call systems have been established in order to help avoid dam-age to existing underground utilities. Thus, locating piping mate-rials is an important part of the future operation and mainte-

nance of a piping system. As noted above, locating Ductile Ironpipe is easy and convenient with virtually all locating equipmentavailable on the market. Locating non-metallic pipe is difficult atbest. Very often, tracer wires and excavation tapes are installedin an effort to reduce the difficulty of locating these pipes. Whentracer wires are used, they should be tested after installation tobe sure that they are electrically continuous from one accesspoint to the next. Typically, access points would be at valveboxes, hydrants, etc. If the wires are not tested, then it is notknown whether the system is working when it is initiallyinstalled. As an alternative to an electrically continuous tracerwire, a heavy gauge wire that can be detected with conventionallocating equipment, even when conductivity is lost, can be used.

Nearby Excavation

Existing pvc pipe is substantially more vulnerable than is DuctileIron pipe to puncture or damage during excavation and con-struction of nearby pipelines.

Buoyancy

Pvc pipe is buoyant — a concern when installing the pipe mate-

rial in areas having a high water table or when trench floodingis likely to occur. To prevent loss of completed pipe embedmentthrough flotation of the pvc pipe, it must be anchored.47

Flotation is generally not a concern with Ductile Iron pipe.

Sun Exposure

Special precautions must be taken when pvc pipe is exposed tosunlight for an extended period of time, because “when subject-

ed to long-term exposure to ultraviolet (UV) radiation from sun-light, pvc pipe can suffer surface damage. This effect is com-monly termed ultraviolet (UV) degradation.”48 According toAWWA C605, if plastic pipe is stored outdoors, it may requireprotection from weathering in accordance with manufacturers’recommendations. And the covering should allow air circulationin and around the pipe.49

The J -M installation guide states that, “when pvc is exposed tothe sunlight for long periods of time, a slow discoloration of thepipe may occur. This discoloration is an indication of a possiblereduction in impact strength.”50

Although the long-term effects on pvc pipe exposed to sunlighthave not been clearly determined, changes in material propertiesobviously occur since warnings are given concerning impactstrength.

Ductile Iron pipe is not vulnerable to the effects of exposure tosunlight or weathering.

Permeation

There is also a problem where soils contaminated with hydro-carbons such as gasoline or other chemicals are encountered.

Plastic pipe walls and gasket materials are susceptible to per-meation that can damage the material and contaminate thewater. In a study conducted by the Sanitary Engineering andEnvironmental Health Research Laboratory at the University of California at Berkeley,51 pvc was reported to be involved in 15percent of the permeation incidents found in a literature searchin the United States. Other agencies have also investigatedoccurrences of this phenomenon.52 Interestingly, the Universityof California report also notes that, previously, pvc pipe had“been considered as relatively immune to permeation. . .”53

On the other hand, this study revealed only one incident wherea gasket was permeated. In Ductile Iron pipe, the only opportu-

nity for permeation is at the gasket. The standard gasket usedin push-on and mechanical joints is made from the elastomerstyrene butadiene (SBR). Even though the University of California report cites just one occurrence of a permeated gas-ket, should contaminated soils be encountered in design, gasketsmade of permeation-resistant materials such as Nitrile or fluo-rocarbon may be specified. In other words, while pvc pipe can-not be made to be resistant to soils containing permeants,Ductile Iron pipelines can.




Another Environmental Facto r

As a final observation regarding environmental considerations, itshould be noted that pvc is made from petroleum derivatives,chlorine gas, and vinyl chloride, the latter two substances beingof concern in environmental circles, while Ductile Iron pipe ismanufactured using recycled scrap iron and steel.

Performance H istory

The performance of Ductile Iron pipe extends over 45 years, andbecause of its close physical resemblance to gray Cast Iron pipe,the long-term record of Cast Iron can be used to predict the lifeof a Ductile Iron pipeline.54 This comparison has been enhancedby extensive research on the comparative corrosion ratesbetween Ductile Iron and gray Cast Iron, which has shownDuctile Iron to be at least as corrosion-resistant as gray CastIron.55

Conclusion

This brochure has presented major considerations facing designengineers when deciding what type of piping material to specifyfor any given application. Evidence has been presented provingthat all pipe materials are not equal. In every test of strength,durability, and dependability from cyclic loading and joint deflec-tion to energy savings and tapping, Ductile Iron proves superiorto pvc pipe.

The exorbitant costs associated with early replacement of underground piping make the engineer’s initial choice of the bestavailable piping material the most economical decision over thelong term.

Ductile Iron pipe is a proven performer — a product with a per-formance history dating back more than 45 years — severalcenturies if its predecessor Cast Iron pipe is considered.

Unlike pvc, Ductile Iron pipe has the same stringent design andmanufacturing standards for all sizes, not standards seeminglybased more upon manufacturing efficiencies than user depend-ability and safety.

Design engineers and owners have traditionally consideredDuctile Iron pipe the highest-quality piping material available.We believe this brochure points out some of the reasons DuctileIron pipe has earned this reputation over the decades.

References

1ANSI/AWWA C150/A21.50-02, AWWA Standard for the

Thickness Design of Ductile Iron Pipe , American WaterWorks Association, Denver, Colorado (2002).

2AWWA C900-97, AWWA Standard for Polyvinyl Chlorid e

(PVC) Pressure Pipe and Fabr icated Fittings, 4 in. through

12 in., for Water Distribution , American Water Works

Association, Denver, Colorado (1997).

3AWWA C905-97, AWWA Standard for Polyvinyl Chlorid e

(PVC) Pressure Pipe and Fabricated Fittings, 14 in.

through 4 8 in., for Water Transmission and Distribution

American Water Works Association, Denver, Colorado (1997).

4Original tests were conducted by the Robert W. Hunt Companyan independent engineering testing firm, on 2/28/80 in ChicagoAdditional tests were conducted at American Cast Iron PipeCompany in Birmingham on 3/21/90, 3/28/90, 4/4/90, and2/20/91, and witnessed by Professional Service Industries, anindependent consulting engineering firm.

5Robert T. Hucks, J r., “Design of PVC Water-Distribution Pipe,”

Civil Engineering , J une 1972, p. 73.

6ANSI/AWWA C151/A21.51-02, American National Standard

for Ductile Iron Pipe, Centrifugally Cast, for Water


7ANSI/AWWA C605-94, AWWA Standard for Underground

Insta llat ion of Polyviny l Chlor ide (PVC) Pressur e Pipe and

Fittings For Water , American Water Works AssociationDenver, Colorado (1994).

8AWWA Manual M23, PVC Pipe-Design and Installation


9ASTM D2412, “Standard Test Method for Determination ofExternal Loading Characteristics of Plastic Pipe by Parallel-PlateLoading,” American Society for Testing and Materials, WestConshohocken, Pennsylvania (2002).

10ASTM D2152, “Standard Test Method for Adequacy of Fusionof Extrusion Poly(Vinyl Chloride) (PVC) Pipe and MoldedFittings by Acetone Immersion,” American Society for Testingand Materials, West Conshohocken, Pennsylvania (1995).

11AWWA M23, p. 5.

12AWWA M23, p. 5.

13AWWA M23, p. 5.

14AWWA M23, p. 5.

15Handb ook of PVC Pipe Design and Constr uction , Uni-BelPVC Pipe Association, Dallas, Texas, 2001, p. 123.


13





16ASTM D2837 “Standard Test Method for ObtainingHydrostatic Design Basis for Thermoplastic Pipe Materials,”American Society for Testing and Materials, WestConshohocken, Pennsylvania (2001).

17AWWA M23, p. 2.

18AWWA M23, p. 5.

19

Handbook of PVC Pipe Design and Constr uction , p. 127.

20Handbook of PVC Pipe Design and Constr uction , p. 127.


22ANSI/AWWA C605-94, Section 5.3.

23Handbook of PVC Pipe Design and Construct ion , pp. 218-236.

24ASTM E23 “Standard Test Method for Notched Bar Impact Testing of Metallic Materials,” American Society for Testing andMaterials, West Conshohocken, Pennsylvania (2002).

25AWWA M23, p. 5.

26AWWA M23, p. 7.

27“Direct Tapping Comparison: Ductile Iron Pipe Versus

Polyvinyl Chloride Pipe,” Ductile Iron Pipe News , Fall/Winter1987, pp. 8-11.


29AWWA M23, p. 99.

30Blue Brute PVC Class Water Pipe Installation Guide , J ohns-Manville, Denver, Colorado, 1979.

31“Blackwood Flow Tests Prove Ductile Iron Pipe’s Lower Head

Loss,” Ductile Iron Pipe News , Fall/Winter 1986, pp. 8-9.“Flow Tests Show Lower Head Loss for Ductile Iron Pipe,”

Ductile Iron Pipe News , Spring/Summer 1986, pp. 12-13.“Flow Tests Confirm the Superiority of Ductile Iron Pipe vs

PVC,” Ductile Iron Pipe News , Fall/Winter 1999, pp. 16-18.

32“Hydraulic Analysis of Ductile Iron Pipe,” Ductile Iron Pipe

News , Fall/Winter 1997, pp. 12-17.

33ANSI/AWWA C605-94, Section 2.2.

34ANSI/AWWA C600-99, AWWA Standard for Insta llation of

Ductile-Iron Water M ains and their Appurt enances , Section4.7, American Water Works Association, Denver, Colorado(1999).

35AWWA C900-97, Section 4.3.1 and AWWA C905-97, Section4.3.1.

36ANSI/AWWA C605-94, Section 2.1.3.

37Hucks, p. 73.

38Hucks, p.72.

39AWWA M23, pp. 84-86.

40ANSI/AWWA C605-94, pp. 6-7.

41ANSI/AWWA C605-94, Figure 1.

42ANSI/AWWA C150/A21.50, Figure 1 and Table 2.

43AWWA M23, p. 34.

44AWWA M23, p. 34.

45AWWA C600-99, pp.12-13.

46Ductile Iron Pipe Subaqueous Crossings , Ductile Iron PipeResearch Association, Birmingham, Alabama, 2001.

47AWWA C605-94, p. 6.

48AWWA M23, p. 7.

49AWWA C605-94, p. 4.

50Blue Brut e PVC Class Water Pipe Installa tion Guide , p. 7.

51 T.M. Holsen, et al. “Contamination of Potable Water by

Permeation of Plastic Pipe,” Journa l AWWA, August 1991, p.56.

52“Some Town Water Supplies Threatened,” News Release,Montana Department of Environmental Quality, March 17,2000.

53 T.M. Holsen, et al, p. 56.

54Approximately 581 U.S. and Canadian utilities are members of the Cast Iron Pipe Century Club for having Cast Iron pipe in con-tinuous service for 100 years or more. At least 20 utilities havegained membership in the Cast Iron Pipe Sesquicentury Club forhaving Cast Iron pipe in continuous service for 150 years ormore.

55E.C. Sears, “Comparison of the Soil Corrosion Resistance of

Ductile Iron Pipe and Gray Cast Iron Pipe,” M ater ia ls

Protection , October 1968.



Manufactured from recycled materials.

American Cast Iron Pipe CompanyP.O. Box 2727Birmingham, Alabama 35202-2727

Atlantic States Cast Iron Pipe Company183 Sitgreaves StreetPhillipsburg, New J ersey 08865-3000

Canada Pipe Company, Ltd.1757 Burlington Street EastHamilton, Ontario L8N 3R5 Canada

Clow Water Systems CompanyP.O. Box 6001Coshocton, Ohio 43812-6001

Griffin Pipe Products Co.1400 Opus Place, Suite 700Downers Grove, Illinois 60515-5707

McWane Cast Iron Pipe Company1201 Vanderbilt RoadBirmingham, Alabama 35234

Pacific States Cast Iron Pipe CompanyP.O. Box 1219Provo, Utah 84603-1219

United States Pipe and Foundry CompanyP.O. Box 10406Birmingham, Alabama 35202-0406

An association of quality producers dedicated to highest pipe

standards through a program of continuing research.

245 Riverchase Parkway East, Suite O

Birmingham, Alabama 35244-1856

Telephone 205 402-8700 FAX 205 402-8730

http://www.dipra.org

Copyright © 2003, 1999, 1992 by Ductile Iron Pipe Research Association.

This publication, or parts thereof, may not be reproduced in

any form without permission of the publishers.

DIPRA MEMBER COMPANIES

DUCTILE IRON PIPERESEARCH ASSO C IAT IO N

DUCTILE IRON PIPE THE RIGHT

DECISION

PVC/2-03/3.5MPublished 1-92Revised 2-03

pvc vrs hierro ductil

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