Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones

Material

As

buried pipes

are

supported

by the

trench bottom,

there

are

more possibilities

for

selecting piping mate-

rials

and

joints.

As

force mains

are

much longer than

the

pipe within

a

pumping station, substantial savings

are

possible

by

choosing

the

most economical pipe.

Recommended materials

are

compared

in

Table

4-11.

Plastics other than

PVC are

used

for

acids

and

chemi-

cals.

For

sewage service, both

acrylonitrile

butadiene

styrene (ABS)

and PVC are

commonly used,

but PVC

pipe

is the

only plastic commonly used

for

potable

water

service.

Reinforced

concrete pressure pipe, generically

described

in

Table

4-11,

is

divided into

four

types

described

in

Table 4-12.

Practical

Selection

Considering experience with,

and

characteristics

of,

the

various pipe materials available

for

sewage force

mains,

the

following materials

are

recommended.

Use

HDPE

or PVC up to a

diameter

of 600 mm (24

in.)

for

wastewater force mains. Note, however, that

if the

pressure

is 75% or

more

of the

working pressure

of

Pipe

Ductile

iron pipe (DIP)

Steel pipe

Polyvinyl

chloride

(PVC)

pipe

High-density

Polyethylene (HDPE) pipe

Asbestos cement (AC)

pipe (ACP)

Reinforced

concrete

pressure pipe (RCPP)

Advantages

See

Table

4-1;

high strength

for

supporting

earth loads, long

life

See

Table

4-1;

high strength

for

supporting

earth loads

Tensile strength (hydrostatic design basis)

=

26,400

kPa

(4000

lb/in.

2

);

E =

2,600,000

kPa

(400,000

lb/in.

2

);

light

in

weight,

very

durable, very smooth, liners

and

wrapping

not

required, good variety

of

fittings

available

or can use

ductile

or

cast-iron

fittings

with adapters,

can be

sol

vent-

welded;

diameters

from

100

to

375 mm (4 to 36

in.)

Tensile strength (hydrostatic design basis)

=

(8600

to

1

1,000

kPa

(1250

to

1600

lb/in.

2

);

light weight, very durable, very smooth,

liners

and

wrapping

not

required

for

corrosion protection; usually jointing

method

is

thermal butt

fusion,

which

develops

the

full

strength

of the

pipe;

flanges can be

provided; diameters

from

100

through 1575

mm (4

through

63

in.);

low

installed cost

Yield

strength:

not

applicable; design based

on

crushing strength,

see

ASTM

C 296

and

C

500;

E =

23,500,000

kPa

(3,400,000

lb/in.

2

);

rigid,

light weight

in

long lengths,

low

cost; diameters

from

100 to

1050

mm (4 to 42

in.),

compatible

with

cast-iron

fittings,

pressure ratings

from

1600

to

3100

kPa

(225

to 450

lb/in.

2

)

for

large pipe

450 mm

(18

in.)

or

more

Several types available

to

suit

different

conditions (see Table 4-12); high strength

for

supporting earth loads, wide variety

of

sizes

and

pressure ratings,

low

cost, sizes

from

600 to

3660

mm (24 to 144

in.)

Disadvantages/limitations

See

Table

4-

1

;

may

require wrapping

or

cathodic protection

in

corrosive soils

See

Table

4-1;

poor corrosion resistance

unless both lined

and

coated

or

wrapped,

may

require

cathodic

protection

in

corrosive soils

Maximum

pressure

=

2400

kPa

(350

lb/in.

2

);

little reserve

of

strength

for

water hammer

if

ASTM

D

2241

is

followed,

AWWA

C900

includes allowances

for

water

hammer; limited resistance

to

cyclic

loading

as the

fatigue

limit

is

very low;

unsuited

for

outdoor

use

above ground

Subject

(as are

many plastics, including

PVC)

to

permeation

by low

molecular

weight organic solvents

and

petroleum

products, unsuited

for

manifold piping

for

pumping

stations; scratches

on the

pipe

wall

can

significantly

reduce service

life;

requires

careful

bedding

and

compaction

beneath

the

springline;

cannot

be

solvent

welded

nor

threaded

Attacked

by

soft

water, acids, sulfates;

requires thrust blocks

at

elbows, tees,

and

dead ends; maximum pressure

=

1380

kPa

(200

lb/in.

2

)

for

pipe

up to 400 mm

(16

in.);

brittle

and

requires care

to

install

Attacked

by

soft

water, acids,

sulfides,

sulfates,

and

chlorides,

often

requires protective

coatings; water hammer

can

crack outer

shell, exposing reinforcement

to

corrosion

and

destroying

its

strength with time;

maximum

pressure

=1380

kPa

(200

lb/in.

2

)

Table 4-11.

Comparison

of

Pipe

for

Buried

Service

the

pipe

or if

there

are

repetitive pressure cycles,

as

with

cycling constant speed pumps

off and on,

experi-

ence

has

shown that

the

material

may

fail.

For

larger

pipe,

use

polyurethane

or

fusion-bonded, epoxy-

coated ductile iron

or

steel pipe. Consider RCPP with

a PVC

lining above

a

diameter

of 900 or

1050

mm (36

or

42

in.).

If

there

is a

possibility

of air

entering

the

force

main, line

the top of the

RCPP with

PVC to

guard

against

the

potential

for

acid corrosion.

Careful

evaluation

with regard

to

internal pressures, external

loads,

corrosiveness

of the

wastewater,

and

corrosive-

ness

of the

soil

is

required

in

selecting

the

pipe mate-

rial

for a

given project

or

application.

Joints

Because buried piping, such

as a

force main

or

water

line,

is

fully

laterally supported,

the

joints should

be

flexible

to

accommodate minor settlement; hence,

less expensive joints, better suited

for

burial than

bolted

flanged

joints,

can be

used (see Figures

4-7

and

4-8).

Many

kinds

of

joints

are

available (see Figures

4-7

through

4-13),

and

several common ones

are

listed

in

Table

4-13.

The

check marks

(v)

show

the

type

of

pipe

for

which

they

are

suited.

For

buried service, sliding cou-

plings (such

as

Dresser®)

need

not be

harnessed

if

thrust

blocks

are

installed

at

bends

or if

there

is a

sufficient

length

of

pipe

on

both sides

for

soil

friction

to

resist

the

thrust

(see DIPRA

[U]).

Grooved-end couplings (see

Figure 4-4) allow

for

slight changes

in

alignment (about

5°

per

coupling),

but do not

deliberately make

use of

this

flexibility;

use

bends

or

ball joints instead.

For

ductile iron pipe, push-on

and

mechanical

joints

are the

most commonly used

for

buried service.

These joints allow

for

some pipe deflection (about

2 to

5°

depending

on

pipe size) without

sacrificing

water-

tightness. Except

in

certain unstable soils, buried joints

are not

required

to

support

the

weight

of the

pipe.

Gaskets

for

various joints

are

described

in

Sections

4-3

to

4-5.

Table

4-12.

Reinforced

Concrete

Pressure

Pipe

(RCPP)

Type

Specification Description

Steel

cylinder AWWA

C300

Steel

cylinder within

a

reinforcing

cage;

walled

inside

and out

with

dense

concrete,

steel

joint

rings

welded

to

cylinder, rubber gasket joint

Prestressed,

steel

cylinder AWWA C301

Cement-mortar-lined

steel

cylinder,

wire wrapped

and

coated

with

mortar

or

concrete;

two

types

differ

slightly

Noncylinder AWWA

C302

Circumferentially

reinforced

concrete

pipe

without

a

steel

cylinder

and not

prestressed

Pretensioned,

steel

cylinder AWWA

C303

Cement-mortar-lined

steel

cylinder

helically

wrapped with continuous

pretensioned

steel

bare

and

coated

with

mortar

Figure 4-7.

Couplings

and

joints

for

ductile

iron

pipe

for

buried

service,

(a)

Sleeve

(Dresser®)

coupling

(also

for

asbestos

cement

pipe);

(b)

mechanical

joint;

(c)

push-on

joint;

(d)

ball

joint

(also

for

exposed service).

Courtesy

of

Wilson

&

Company,

Engineers

&

Architects.

Thickness

The

thickness

of

buried pipe must

be

sufficient

to

resist

the

external soil

and

overburden loads

as

well

as

internal

pressure.

If

there

is no

traffic

loading

and the

burial

is

shallow (say,

2 m or 6

ft), ductile iron pipe

Class

50 can

often

be

specified

where internal pres-

sure

is

less than

the

pipe pressure rating.

The

stresses

in

(and

deflection

of)

pipe walls

due to

soil

and

overburden loads

are

complex

functions

of

(1)

pipe material, diameter,

and

thickness;

(2)

bedding

conditions;

(3)

soil properties;

(4)

trench width

and

depth;

(5)

frost;

and (6) the

overburden load

and its

distribution.

Although

not

difficult,

the

calculations

are too

involved

to be

included here.

Refer

to

•

AWWA

Ml 1 [9] for

steel pipe

•

DIPRA

[11]

for DIP

•

ASTM

D

2774

and

Uni-Bell

Handbook [12]

for

PVC

pipe

•

AWWA

C401

and

C403

for AC

pipe

•

AWWA

M9[

13] for

RCPP

•

Spangler [14,

15] for the

most extensive discussion

Linings,

Coatings,

and

Cathodic

Protection

The

discussion

of

lining

for

exposed service applies

to

buried service

as

well. Buried glass-lined pipe should

be

DIP,

but if

steel

is

used,

it

should

be

plain-end pipe

joined

by

mechanical couplings.

Steel

and

sometimes ductile iron pipe corrode

on

contact with some soils. Asbestos cement

and

con-

crete

are

attacked

by

acidic waters

or by

high

sulfate

soils.

In

aggressive environments

the

pipe

can be

coated (see Section

4-3 for

details).

Figure

4-8.

Rubber-gasketed

push-on

joints

for

steel

pipe

in

buried

service,

(a)

Fabricated

joint;

(b)

rolled-groove

joint;

(c)

tied

joint;

(d)

Carnegie-shaped

joint

with

weld-on

bell

ring.

After

AWWA

M11

[9].

Figure

4-9.

Welded

joints

for

steel

pipe

in

buried

or

exposed

service,

(a) Vee

butt

weld;

(b) vee

butt

weld

with

weld

ring;

(c)

double

butt

weld;

(d)

cup-type

weld;

(e)

sleeve

or

butt

strap

weld.

Courtesy

of

Wilson

&

Company,

Engineers

&

Architects.

Figure

4-10.

Couplings

and

joints

for

polyvinyl

chloride

(PVC)

pipe

in

buried

service,

(a)

Twin-gasketed

coupling

(also

for

asbestos

cement);

(b)

bell

and

spigot

joint.

Courtesy

of

Wilson

&

Company,

Engineers

&

Architects.

In

addition

to the

protective coatings, cathodic pro-

tection

may

also

be

required. Corrosion

of

iron

and

steel pipe

is an

electrochemical reaction. Cathodic

protection consists

of

introducing

a

controlled

dc

cur-

rent

to

oppose

the

natural destructive current.

An

alternative method

is to

bury

sacrificial

anodes that

also reverse

the

current. Cathodic protection

of

iron

and

steel pipes

is

commonly used

in

aggressive soils

or

where there

are

stray electrolytic currents. Stray

electrolytic currents

can

occur near buried power

transmission lines

and

near other pipelines equipped

with

cathodic protection systems. Most petroleum

and

gas

transmission lines have

impressed-current

cathodic protection.

Any

ferrous

metal

in the

vicinity

becomes

an

anode, loses metal,

and

eventually

fails

unless

it,

too,

is

protected.

If in

doubt, consult

a

corro-

sion specialist. Minimum voltage requirements

are

determined

by

experience

and field

studies

of

ambient

conditions such

as

moisture, chemical content,

and

resistivity

of the

soil.

A

more detailed discussion

of

cathodic protection

is

included

in

AWWA

Mil

[9]

and

NACE Standards

RP-01-69

and RP

05-72.

Figure

4-11.

Push-on joints

for

concrete

pipe

in

buried

service,

(a)

Reinforced

pressure

pipe

with

rubber

and

con-

rete

joint;

(b)

reinforced

cylinder

pipe

with

rubber

and

steel

joint;

(c)

reinforced

pressure

pipe

with

rubber

and

steel

joint;

(d)

prestressed

embedded

cylinder

pipe

with

rubber

and

steel

joint.

Courtesy

of

Wilson

&

Company,

Engi-

neers

&

Architects.

Figure

4-12. Restrained

rigid

joints

for

concrete

pipe

in

exposed,

buried,

or

subaqueous

service,

(a)

Reinforced pres-

sure

pipe

with

rubber

and

steel

joint;

(b)

reinforced

cylinder

pipe

with

rubber

and

steel

joint.

Courtesy

of

Wilson

&

Company,

Engineers

&

Architects.

Asbestos cement pipe

is

usually

used without inte-

rior

or

exterior coatings.

If

corrosion

can

occur, con-

sider other materials.

Reinforced

concrete pressure pipe carrying corro-

sive

water

can be

lined

with

coal-tar enamel

or

coal-

tar

epoxy. (Coal-tar enamels

and

epoxies

are not

used

in

potable water service.) These linings require main-

tenance,

however,

and

should

be

used only where

the

pipeline

can be

removed

from

service periodically

for

inspection

and

where

the

pipeline

is

large enough

in

diameter

to

permit painting

in

place. Alternatively,

the

pipe

can be

lined

by

securing

plastic

sheets

with

T-shaped ribs

to the

pipe

forms.

The

ribs lock

the

liner securely into

the

finished

pipe. Field joints

in

the

liner

are

made

by

heat-

welding

plastic strips

after

each joint

of

pipe

has

been installed

in the

trench.

The

pipe could also

be

encased

in

plastic

to

protect

it

from

corrosive (high

sulfate

or

acidic) soils.

Figure

4-13.

Adapters

for

connecting

concrete

pipe

to

ductile

iron

or

steel

pipe,

(a)

Flanged

adapter;

(b)

mechanical

joint

adapter;

(c)

sleeve

(Dresser®)

coupling

adapter.

After

Millcon

Corp.

Table

4-13.

Common

Types

of

Joints

for

Buried

Pipe

Type

of

pipe

Type

of

Ductile

Joint

Figure

joint

3

iron

Steel

PVC AC

RCPP

Flanged joint

4-1,2

R

J J

Lugged sleeve coupling

(Dresser®),

harnessed 4-3a,

b F

77

Sleeve coupling

(Dresser®),

unharnessed 4-7a

S V

7

Mechanical joint 4-7b

F J

Push-on joint 4-7c

F

J

Push-on joint

4-8 F

7

Ball (also

for

exposed service) 4-7d

F

J

Twin-gasketed coupling

4-1Oa

F

>/

Bell

and

spigot

4-1Ob

F, S

)

Grooved-end coupling (Victaulic®) 4-4a

F

J

Welded

joint

4-9 R J

RCPP

Push-on

4-11

S

7

Lugged, rigid 4-12

R

)

RCPP

to

iron

or

steel

Flanged

4-13a

R

J

Mechanical

or

sliding 4-13

b, c S

)

3

R

=

rigid;

S =

sliding

or

slip;

F = flexible.

Fittings

The

ductile

and

gray

cast-iron

fittings

shown

in

Table

4-9

are

also available

with

mechanical joints. Fittings

for

other

kinds

of

pipe

are

given

in

Table

4-13.

Ductile iron

fittings

are

used

for

asbestos cement pipe

and PVC

(AWWA

C900).

Fabricated steel

fittings can

also

be

used.

Economics

The

cost

of the

pipe

at the job

site

is

only

one

factor

of

many.

Others include

•

Size

•

Weight

and

length

of

sections,

difficulty

of

han-

dling,

and

machinery required

•

Bedding. Flexible pipe, such

as

plastic sewer

pipe,

requires special bedding conditions (see

Uni-Bell

Handbook

[12])

•

Type

of

joint

and

amount

of field

labor

•

Maintenance

(frequency

and

difficulty

of

repair)

•

Water hammer control

(different

for

different

mate-

rials)

•

Friction

coefficient

•

Shoring requirement

for

laborers

to

enter trenches

deeper (depending

on

soil stability) than

1.2 or

1

.5

m

(4 or 5

ft)

—

especially

severe

for

trenches

deeper than

3 m (10

ft). Consult OSHA regulations

for

shoring requirements.

Selection

is

further

complicated

by

local condi-

tions that significantly

affect

the

cost

of one

material

versus

another,

and

these conditions

may

change radi-

cally

with

time.

Carefully

investigate

the

cost

and

availability

of all

types

of

suitable piping.

For

exam-

ple,

API

steel pipe

is

made

in

great quantity

and is

fre-

quently

readily available

and

cheaper than other steel

pipe. Coatings

and

linings

can be

applied

to API

pipe

in

the

same manner

as

applied

to any

other steel pipe.

4-3.

Ductile

Iron

Pipe

(DIP)

Detailed descriptions

of

DIP,

fittings,

joints, installa-

tion,

thrust restraint,

and

other factors relating

to

design

as

well

as

several important

ANSI/AWWA

specifications

are

contained

in the

DIPRA handbook

[11]

(see also Section

4-1 and

Tables

4-1 and

4-11).

Materials

Cast-iron pipe

is

manufactured

of an

iron alloy cen-

trifugally

cast

in

sand

or

metal molds. Prior

to the

early

1970s,

most cast-iron pipe

and fittings

were gray

iron,

a

brittle material that

is

weak

in

tension.

But now

all

cast-iron pipe except

soil

pipe (which

is

used

for

plumbing)

is

made

of

ductile iron

in

which

the

graph-

ite is

formed into spheroids

by the

addition

of

magne-

sium

and

heat treatment, which makes

it

about

as

strong

as

steel.

Cast-iron

fittings are

still available

in

gray

iron

as

well

as

ductile iron.

Tolerances, strength, coatings

and

linings,

and

resistance

to

burial loads

are

given

in

ANSI/AWWA

C151/A21.51.

A

special abrasion-resistant ductile iron pipe

for

conveying

slurry

and

grit

is

available

from

several

manufacturers.

Regular ductile iron pipe

(AWWA

C151)

has a

Brinell

hardness (BNH)

of

about 165.

By

comparison, abrasion-resistant ductile iron

has a BNH

of

about 280.

The

sizes available

are

150

through

600

mm

(6

through

24

in.)

per

AWWA

C

151

in the

stan-

dard

AWWA

wall thickness classes.

Available

Sizes

and

Thicknesses

As

shown

in

Tables

B-I

and

B-2,

the

available sizes

range

from

100 to

1350

mm (4 to 54

in.).

The

standard

length

is 5.5 m (18 ft) in

pressure ratings

from

1380

to

2400

kPa

(200

to 350

lb/in.

2

).

Thickness

is

specified

by

class, which varies

from

Class

50 to

Class

56

(see

the

DIPRA handbook

[1

1]

or

ANSI/AWWA

C150/A21.50).

Thicker pipe

can be

obtained

by

special order.

loints

Buried joints should

be of the

mechanical joint

or

rub-

ber

gasket push-on type. Various types

of

restrained

joints

for

buried service

are

also available.

Exposed joints should

be flanged

(AWWA

Cl 15 or

ANSI

B

16.1)

or

grooved

end

(AWWA

C606)

(refer

to

"Joints"

in

Section 4-1).

Gaskets

for

ductile iron

or

cast-iron

flanges

should

be

rubber,

3.2 mm

(Vg

in.) thick.

Gaskets

for

grooved-end joints

are

available

in

eth-

ylene

propylene diene monomer (EPDM),

nitrile

(Buna

N),

halogenated butyl rubber,

Neoprene™,

sili-

cone,

and fluorelastomers.

EPDM

is

commonly used

in

water

service

and

Buna

N in

sewage

or

sludge service.

Gaskets

for

ductile

iron push-on

and

mechanical

joints described

in

AWWA

ClIl

are

vulcanized natu-

ral

or

vulcanized synthetic rubber. Natural rubber

is

suitable

for

water pipelines

but

deteriorates when

exposed

to

sewage

or

sludge.

Fittings

Dimensions

of

cast-iron

and

ductile iron

flanged fit-

tings

are

covered

by

ANSI B16.1

and

AWWA

CIlO,

and

fittings for

abrasion-resistant pipe

are

generally

furnished

in one of the

following categories:

•

Type

1

:

Low

alloy

fittings

with

a

minimum hardness

of

about

260

BNH, with

flanged,

grooved-end,

or

mechanical joints.

•

Type

2:

Special ductile iron

fittings

with

a

minimum

hardness

of

about

400 BNH and flanged or

mechan-

ical joints.

•

Type

3:

Ni-Hard®

fittings

with

a

minimum hard-

ness

of

about

550

BNH, with plain

end or

mechani-

cal

joints.

Linings

and

Coatings

For a

discussion

of

linings, refer

to

Section

4-1.

Although

ductile iron

is

relatively resistant

to

corro-

sion, some soils (and peat, slag, cinders, muck, mine

waste,

or

stray electric current)

may

attack

the

pipe.

In

these applications, ductile iron manufacturers recom-

mend that

the

pipe

be

encased

in

loose-fitting,

flexible

polyethylene

tubes

0.2 mm

(0.008

in.) thick (see

ANSI/AWWA

C105/A21.5).

In

some especially corro-

sive

applications,

a

coating such

as

adhesive, hot-

applied

extruded polyethylene wrap

may be

required.

An

asphaltic coating

(on the

outside) approxi-

mately

0.025

mm

(0.001

in.) thick

is a

common coat-

ing

for DIP in

noncorrosive

soils.

In

corrosive soils,

consider

the

following coatings

for

protecting

the

pipe:

•

Adhesive, extruded polyethylene wrap

•

Plastic wrapping

(AWWA

C

105)

•

Hot-applied coal-tar enamel

(AWWA

C203)

•

Hot-applied coal-tar tape

(AWWA

C203)

•

Hot-applied extruded polyethylene [ASTM

D

1248

(material

only)]

•

Coal-tar epoxy

•

Cold-applied tape

(AWWA

C209)

•

Fusion-bonded epoxy

(AWWA

C2

13).

Each

of the

coatings

is

discussed

in

detail

in the

AWWA

specifications. Because each

has

certain lim-

ited uses, consider each specific installation

and

con-

sult

the

NACE standards

for the

particular service.

4-4. Steel

Pipe

The

principal advantages

of

steel pipe include high

strength,

the

ability

to

deflect

without breaking, ease

of

installation, shock resistance, lighter weight than

ductile iron pipe, ease

of

fabrication

of

large pipe,

the

availability

of

special configurations

by

welding,

the

variety

of

strengths available,

and

ease

of field

modifi-

cation (see Section

4-1 and

Tables

4-1

and

4-11).

Material

Conventional

nomenclature refers

to two

types

of

steel pipe:

(1)

mill pipe

and (2)

fabricated pipe.

Mill pipe includes steel pipe

of any

size produced

at a

steel pipe mill

to

meet

finished

pipe specifications. Mill

pipe

can be

seamless,

furnace

butt

welded, electric resis-

tance

welded,

or

fusion

welded using either

a

straight

or

spiral seam. Mill pipe

of a

given size

is

manufactured

with

a

constant outside diameter

and an

internal diameter

that

depends

on the

required wall thickness.

Fabricated pipe

is

steel pipe made

from

plates

or

sheets.

It can be

either straight-

or

spiral-seam

fusion-

welded pipe,

and it can be

specified

in

either internal

or

external diameters. Note that spiral-seam,

fusion-

welded pipe

may be

either mill pipe

or

fabricated

pipe.

Steel pipe

may be

manufactured

from

a

number

of

steel alloys with varying yield

and

ultimate tensile

strengths. Internal working pressure ratings vary

from

690 to

17,000

kPa

(100

to

2500

lb/in.

2

)

depending

on

alloy,

diameter,

and

wall thickness. Specify steel pip-

ing

in

transmission mains

to

conform

to

AWWA

C200,

in

which there

are

many ASTM standards

for

materials

(see ANSI

B

3

1.1

for the

manufacturing

processes).

Available

Sizes

and

Thicknesses

The

available diameters range

from

3 to

6000

mm

(V

8

to 240

in.),

although only sizes

up to 750 mm (30

in.)

are

given

in

Tables

B-3 and

B-4. Sizes, thicknesses,

and

working pressures

for

pipe used

in

transmission

mains range

from

100 mm to

3600

mm (4 to 144

in.)

and

are

given

in

Table

4-2 of

AWWA

Ml 1

[9].

Manufacturers

should

be

consulted

for the

avail-

ability

of

sizes

and

thicknesses

of

steel pipe (see also

Table

4-2 in

AWWA

Mil,

which shows

a

great variety

of

sizes

and

thicknesses).

According

to

ANSI

B36.10,

•

Standard weight (STD)

and

Schedule

40 are

identi-

cal for

pipes

up to 250 mm (10

in.).

All

larger sizes

of

standard weight pipe have walls

9.5 mm

(

3

/

8

in.)

thick [see Tables

B

-3

and

B

-4

for

standard weight

pipe

from

3 to 750 mm

(V

8

to 30

in.)].

For

300-mm

(12-in.)

pipe

and

smaller,

the ID

approximately

equals

the

nominal diameter.

For

larger pipe,

the

OD

equals

the

nominal diameter.

•

Extra strong (XS)

and

Schedule

80 are

identical

for

pipes

up to 200 mm (8

in.).

All

larger sizes

of

extra-

strong-weight

pipe have walls 12.7

mm

(

1

I

2

in.) thick.

•

Double extra strong (XXS) applies only

to

steel

pipe

300 mm

(12

in.)

and

smaller. There

is no

corre-

lation between

XXS and

schedule numbers.

For

wall

thickness

of

XXS, which

(in

most sizes)

is

twice

that

of XS, see

ANSI

B36.10.

For

sizes

350 mm (14

in.)

and

larger, most pipe

manufacturers

use

spiral welding machines and,

in

theory,

can

fabricate pipe

to

virtually

any

desired size.

But

in

practice most steel pipe manufacturers have

selected

and

built equipment

to

produce given

OD

sizes.

For

example,

one

major U.S. manufacturer uses

a

578.6-mm

(22

25

I

32

in.)

OD

cylinder

for a

nominal

525-mm

(21

-in.)

pipe.

Any

deviation

from

manufac-

turers' standards

is

expensive.

To

avoid confusion,

either show

a

detail

of

pipe size

on the

plans

or

tabu-

late

the

diameters

in the

specifications.

For

cement-

mortar-lined transmission mains,

AWWA

C200,

C205, C207,

and

C208 apply.

Manifold

piping

in

pumping stations should

be

considered

a

large special

fitting or a

series

of fittings

connected together. Dependence

on

AWWA

C200

alone

is

inadequate

for

designing such headers

or

manifolds

because

it

does

not

address

the

following:

•

Reinforcement

at

openings (tees, laterals, branches)

(see

"Pipe

Wall Thickness"

in

Section 4-8)

•

Wall thickness

for

grooved-end couplings (see

Table 4-5)

•

Thrust harness lugs

for

flexible

pipe couplings (see

Example

4-1)

•

Additional wall thickness required

at

elbows

and

other

fittings

because

of

stress intensification

factor

(see

the

following subsection

on fittings).

Thus,

the

design

of

steel manifolds depends

on a

com-

bination

of a

number

of

factors.

Steel pipe must sometimes either

be

reinforced

at

nozzles

and

openings (tees,

wye

branches)

or a

greater

wall

thickness must

be

specified.

A

detailed procedure

for

determining whether additional reinforcing

is

required

is

described

in

Chapter

II and

Appendix

H of

ANSI

B31.3.

If

additional reinforcement

is

necessary,

it

can

be

accomplished

by a

collar

or pad

around

the

noz-

zle

or

branch,

a

wrapper plate,

or

crotch plates.

These

reinforcements

are

shown

in

Figure

4-14,

and the

calcu-

lations

for

design

are

given

in

AWWA

Ml

1

[9].

Steel manifold piping

500 mm (20

in.)

and

smaller

must

inevitably

be

made

in

accordance with ANSI

B36.10.

Material would usually conform

to

ASTM

A

53, A

135,

or API 5L. For

pipe

600 mm (24

in.)

and

larger,

a

fabricator might

elect

to use

pipe

conforming

to

ASTM

A 134 or A 139 as

well.

As

shown

in

Tables

B

-3

and

B

-4,

the

size

of the

pipe (nominal diameter)

approximates

the ID for

300-mm (12-in.) pipe

and

smaller,

but

size equals

the OD for

350-mm

(14-in.)

pipe

and

larger.

For

pipe larger than

500 mm (20

in.),

steel pipe size

can be

specially fabricated

to any

size.

The ID of

steel pipe should match

the ID of

iron

valves,

particularly

butterfly

valves.

One way is to

select pipe

one

size larger than

the

nominal pipe size

and

line

it

with cement mortar

so

that

the ID of a

mor-

tar-lined pipe matches

the

nominal pipe size. Consider,

for

example,

a

requirement

for a

steel header with

a

nominal 400-mm

(16-in.)

ID. A

pipe fabricator could

use an

ANSI

B

3

6.

10

standard weight pipe with

a

true

OD of 457 mm (18

in.).

The

wall thickness

of the

steel

cylinder

is 9.5 mm

(0.375

in.),

which gives

an ID of

438 mm

(17.25

in.).

A

13-mm

(V

2

-m.)

mortar lining

provides

a net ID of 413 mm

(16.25

in.),

which

is

close

to the

desired size,

and if the

mortar lining were

16-mm

(

5

/

8

-in.)

thick,

the ID

would

be

exactly

406 mm

(16

in.).

As

shown

in

Table 4-6,

the

minimum thickness

of

the

cement-mortar lining

is 7.9 mm

(

5

I

16

in.).

Figure

4-14.

Reinforcement

for

steel

pipe

openings.

(a)

Collar

plate;

(b)

wrapper

plate;

(c)

crotch

plates.

Obtaining internal diameters

in

even sizes

for

steel

pipe smaller than

350 mm (14

in.)

can be

done

by

using

plastic linings.

For

example,

a

250-mm

(10-in.)

standard weight pipe

has an OD of 273 mm

(10.75

in.)

and

a

wall thickness

of

9.27

mm

(0.365

in.);

for a

minimum

cement-mortar thickness

of 6.4 mm

(

l

/

4

in.),

the ID is

only

242 mm

(9.5

in.).

A

practical alternative

is to use a

plastic lining, such

as

fusion

bonded epoxy,

that

makes

the ID

equal

to the

nominal 250-mm

(10-in.)

diameter.

Some

benefits

of

using standard weight ANSI

B36.10 pipe

are

that

(1) the

pipe

is

readily available,

and

(2) the

wall thickness

is

•

often

sufficient,

so

that reinforcements

at

openings

(wrappers, collars,

or

crotch plates)

are

unnecessary;

•

often

sufficient

in

pumping stations

for use

with

thrust

harnesses

on

flexible

pipe couplings,

so

that

additional wall thickness

is

unnecessary;

and

•

sufficient

for use

with

AWWA

C606

grooved-end

couplings

without

additional reinforcement

at the

pipe ends.

Joints

for

steel pipe

are

listed

in

Table

4-13.

For

buried

service, bell

and

spigot joints with rubber gaskets

or

mechanical couplings

(with

or

without thrust har-

nesses)

are

preferred. Welded joints

are

common

for

pipe

600 mm (24

in.)

and

larger. Linings

are

locally

destroyed

by the

heat

of

welding,

so the

ends

of the

pipe must

be

bare

and the

linings

field

applied

at the

joints.

The

reliability

of field

welds

is

questionable

without

careful

inspection,

but

when properly made

they

are

stronger than other joints.

Fittings

Specifications

for

steel

fittings can

generally

be

divided

into three classes, depending

on the

joints

used

and the

pipe size:

•

Threaded

(ANSI

B

1

6.3

or

B

1

6.

1

)

but

only

for

pipe

75 mm (3

in.)

and

smaller

•

Flanged, welded (ANSI

B

16.9)

•

Fabricated

(AWWA

C208).

Fittings larger than

75 mm (3

in.) should conform

to

ANSI

B

16.9

("smooth"

or

wrought)

or

AWWA

C208 (mitered); avoid threaded

fittings

larger than

75

mm

(3

in.).

The

ANSI

B

16.9

fittings are

readily avail-

able

up to 300 to 400 mm (12 to

16

in.)

in

diameter.

Mitered

fittings are

more readily available

and

cheaper

for

larger

fittings.

The

radius

of a

mitered elbow

can

range

from

1 to

4

pipe diameters.

The

hoop tension concentration

on

the

inside

of

elbows with

a

radius

less

than

2.5

pipe

diameters

may

exceed

the

safe

working stress. This

tension concentration

can be

reduced

to

safe

levels

by

increasing

the

wall thickness,

as

described

in

ANSI

B31.1,

AWWA

C208,

and

Piping

Engineering

[16].

Design procedures

for

mitered bends

are

described

in

ANSI

B3

1.

1

and

B3

1.3.

Caskets

Gaskets

for

steel

flanges are

usually made

of

cloth

inserted rubber either

1.6 mm

(

1

J

16

in.)

or 3.2 mm

(Vg

in.)

thick

and are of two

types:

• ring

(extending

from

the

inside diameter

of the

flange

to

the

inside edge

of the

bolt holes);

•

full

face (extending

from

the

inside diameter

of the

flange to the

outside diameter).

For

mechanical

and

push-on joints, refer

to

"Gas-

kets"

in

Section 4-4.

Linings

and

Coatings

Cement mortar

is an

excellent lining

for

steel pipe (see

Table

4-6 and

AWWA

C205

for the

thickness required;

refer

to

"Linings

and

Coatings"

in

Section

4-1 and to

"Linings"

in

Section

3-3 for

further

discussion).

Steel pipe

can

also

be

protected with mortar,

but

soil conditions

affect

the

necessary thickness

of the

mortar coating. Corrosive soils

may

require mortar

coatings

of 25 mm (1

in.)

or

more regardless

of

pipe

size. Alternatively,

a

hot-

applied

extruded polyethyl-

ene

coating with heat-shrink jackets

for

joints that

complies with ASTM

D

1248

is an

excellent coating

for

both steel

and

ductile iron pipe.

As

another alternative,

epoxy-lined

and

-coated

steel pipe could

be

used. Because this lining

is

only

0.3-

to

0.6-mm

(0.012-

to

0.020-in.)

thick,

the ID of

bare pipe

is

only slightly reduced

by

such linings (see

Tables

B-I

and

B-2). Epoxy-lined steel pipe

is

cov-

ered

by

AWWA

C203, C210,

and

C213 standards.

The

supplier must

be

consulted

to

determine

the

limitations

of

sizes

and

lengths

of

pipe that

can be

lined with epoxy.

Flange

faces should

not be

coated

with

epoxy

if flanges

with

serrated

finish per

AWWA

C207

are

specified.

4-5.

Plastic

Pipe

In

the

United States, where

it is

used

in

both water

and

sewage service, poly

vinyl

chloride (PVC)

is the

most

commonly

used plastic pipe.

It is a

polymer extruded

under

heat

and

pressure into

a

thermoplastic that

is

nearly

inert when exposed

to

most acids, alkalies,

fuels,

and

corrosives,

but it is

attacked

by

ketones

(and

other solvents) sometimes

found

in

industrial waste-

waters.

It has a

high

strength-to-

weight

ratio

and is

durable

and

resilient,

but it

lacks

the

stiffness

neces-

sary

for

exposed service

and is

susceptible

to flotation

in

groundwater conditions. Most types

of PVC

pipe

should

not be

exposed

to

direct sunlight (see ANSI/

AWWA

C900). Some designers have

had

poor experi-

ences

with

solvent-welded

flanges and no

longer

use

them

on

buried

PVC

pressure pipe

in any

size.

PVC

pipe conforming

to

AWWA

C900

or

C905

with duc-

tile iron

fittings

can be

used

for

buried service

in

sizes

1000

mm (24

in.)

or

smaller.

For

larger pipe,

AWWA

C905

may not be

sufficiently

conservative

in

some

applications.

A

proper analysis

of

static

and

transient

internal

and

external pressures

is

required. Note that

the

fatigue

limit

for PVC is

very low,

and the

pipe

could

be

vulnerable

to

rupture

from

excessive pres-

sure

cycles. HDPE pipe

is

better

for

cyclic loading.

High-density

polyethylene (HDPE) pipe

and

poly-

vinyl

chloride (PVC)

are

both suitable

for use in

pota-

ble

water service

and raw

sewage service. HDPE,

in

general,

is

much

less

sensitive

to

surge pressures than

PVC

because

of the

long molecular chains

in the

plas-

tic

material.

See

AWWA

C906

for the

method

of

cal-

culating

the

required pressure class.

The

heat

fused

butt

joint system

for

HDPE pipe

is a

satisfactory joint

that

is

easy

to

install

in the field.

A

key

consideration

in

specifying

either

PVC or

HDPE

is

their susceptibility

to

scratches

in the

pipe

wall

that

can be

caused

by

dragging

the

joined

sec-

tions

of

pipe

for

long distances over

the

ground.

Rocks usually cause scratches about

3-mm

(Vg-ni.)

deep

and

sometimes much deeper.

In

HDPE, scratches

0.19-T

(T is the

pipe wall thickness) deep reduce

the

cyclic loading

life

span

by

90%, whereas scratches

0.04

T

deep have little

influence

on

fatigue

strength.

Specifying

that pipe must

be

dragged over smooth

surfaces,

such

as

railroad ties,

is one way to

avoid

deep scratches.

In

addition,

careful

attention must

be

paid

in

speci-

fications

and

construction inspection

to

ensure that

the

pipe

is

fully

bedded, with

no

voids

or

poorly com-

pacted areas beneath

the

springline. Because

of its

permeability

to

organic solvents with

low

molecular

weight

(gasoline,

for

example) HDPE should

not be

used

for

potable water beside roads where gasoline

could penetrate into

the

ground. Other than

the

above

considerations, HDPE

is

ideal

for

systems with mod-

erate pressures. Although

the

cost

of the

pipe itself

is

about

the

same

as it is for

steel,

its

installed cost

is

likely

to be

less

than that

of

steel because

of the

ease

and

speed

of

handling.

Many

designers

refuse

to

specify

PVC

pipe

for the

small

(75

-mm

or

3

-in.

and

smaller)

piping

that,

for

example, conveys seal water inside pumping stations.

The

primary reason

is due to the

difficulty

of

getting

the PVC

pipe

installers

to do a

proper job. Specific

problems that occur include:

•

Inadequate

or

excessive amounts

of

solvent cement

applied

to the

joints.

See

ASTM

D

2855.

•

Inadequate curing time allowed before moving pipe

with

solvent-cemented joints.

It is

wise

to

specify

eight hours

of

curing time before pipe

can be

moved

(in

spite

of

manufacturers'

claims that

two

hours

is

adequate).

•

Forcing

and

springing

the

pipe into position

to

make

up

for

errors

in

initially installing

the

pipe.

The

overstress

in the

pipe

can

result

in

breakage

after

a

time lapse

of

less

than

a

year. Adequate inspection

during

installation could prevent

the

overstress,

but

inspection

after

installation

is

useless.

Because

of

these problems, copper, steel,

or

stain-

less steel

for the

small-size service piping

is a

better

choice where applicable. These metallic piping sys-

tems

are far

more

resistant

to

poor

installation

prac-

tices than

is

plastic piping. Furthermore,

it is

preferable

to

avoid exposed plastic pipe

in any

pump-

ing

station because

of the

hazard

of

melting

(or

even

supporting combustion)

in fires

(see NFPA 820). Plas-

tic

pipe may, however,

be the

only practical selection

for

chlorine solution

or

other chemical

services.

Other plastic piping materials include

•

Aery

lonitrile-butadiene-

sty

rene

(ABS)

•

Chlorinated polyvinyl chloride (CPVC)

•

Polypropylene (PP)

•

Polyethylene (PE)

•

Polyvinylidene

fluoride

(KYNAR™

or

PVDF)

•

Fiberglass-reinforced plastic (FRP).

Most

of

these materials

are

used

for

corrosive chemi-

cals,

but

some

may

have special uses

for

water, sewage,

or

sludge. Consult manufacturers

for

properties, joints,

and

fittings.

Investigate installations before

specifying

such

materials.

The

impact strength

of

most plastics

decreases when exposed

to

sunlight. Consequently,

be

wary

of

using plastic pipe

in

exposed outdoor service

unless

it is

coated with

an

ultraviolet-resistant paint

such

as a

polyurethane.

However,

FRP

should

be

installed only where

it is

exposed

and

easily inspected;

Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones

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