plumbing design guide - expansion

7/24/2019 Plumbing Design Guide - Expansion

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Consideration for design and in stallation

Calculation of expansion and contraction

Controlled pipework movement

92

92

92

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Pipework exp nsion

Plumbing Engineering Services Design Guide

ABS

Aluminium

Brass

Bronze

Cast iron

Chromium

Copper

Duralumin

Lead

Mild

Steel

Nylon

Polyethylene

High

Density

Polyethylene

Low

Density

PVC unplasticised

Tin

Zinc

Consideration

6 o 110.2

25.6

19

18

12

7

16.9

23

29

11.3

80

140.2

225

60

to 100

21

30

for

design and

installation

All

pipework will expand and contract

longitudinally and around the

circumference when subjected to

temperature variations.

The temperature variations can occur as

a resu lt of fluids within the p ipework

being heated or cooled, or from the

effects of e xternal heat sources, such as

the surrounding air temperatures, solar

heat, etc.

The temperature variations can range

from gradual, such as the increase and

decrease in room air temperatures,

to

almost instantaneous, such as when hot

water is discharged from a sanitary

fitting, or when heated water is suddenly

circulated through the pipework.

Genera lly the chang e in diam eter of

pipework used for Building Services

Engineering will not require detailed

consideration, other than to ensure that

adequate clearances are maintained

between pipes, pipe supports, joists,

building structures, etc, to allow free

movement of the pipework.

The expansion and contraction along the

length of pipework can how ever be very

significant, particularly for steam ,

condensate, heating, domestic hot water

and certain waste pipework installations.

Expansion and contraction within cold

water pipework systems is m inimal and

generally does not require any special

consideration.

It should be no ted that the rate of

expansion and contraction varies as a

result of the type of m aterial, as well as

the temperature variation. PVC pipework,

for instance, will expand at over three

times that of copper, for the sam e

temperature rise.

Damage and failure from stress and

strain can occur to pipework systems,

pipework support systems and building

structures unless careful considera tion is

given to the change in pipework length

due to temperature change and the

direction in which the expansion and

contraction will take place.

Calculation of

expansion and

contraction

The change in length of pipework, for

both expansion and contraction, due to

temperature variation can be calculated

using the following formula:

Formula

AI = I x a x A t

where:

I = The chan ge in length of the pipe

due to temperature change.

I = The original length of the pipe.

=

The co efficient of linear expansion

t

= The change in temperature to

NOTE

K

denotes deg rees Kelvin. This is the same

as a temperature rise measured in Celsius.

I can b e any m etric unit of mea surement.

AI will be calculated n the same unit of

measurement as that used for

4:

Generally

units of either metres m) or millimetres mm )

will be used.

(mm/K) .

which the pipe is subjected (K).

Table

Typical coefficients o f linear

exoansion for various materials

Material

C o e f f i c i e n t

fmmK

x

1W61

NOTE

P6

ndicates that the decimal point of the

value being considered should be moved six

places to the left, eg:

10 2

x U6

quates to

0 0000

102

Example

What would be the increase in length and

the final length of a straight copper pipe 15

metres long when subjected

to

a

temperature increase from 20C

to

80C.

From Table 1 the coefficient of linear

expansion for copper is 16.9

x

10-6rnm/K.

From Formula 1

AI

= I x a x A t

= 15 x 16.9 ~ 1 0 . ~80 20)

=

0.0152m (15.2mm)

Therefore the pipe would expand 0.0152m

and the final length of the pipe would be:

=15m

+

0.01 52m

=

15.0152m.

Upon cooling down the pipe will return

to

its

original length, unless it has been heated

excessively to such a point where

a

loss

in

form hasoccurred.

Controlled

pipework

movement

Freedom of movement

Consideration must be given during the

design and installation of all pipework

systems to ensure that they are free to

expand an d contract. The following

important points should be considered:

a. Pipework passing through structures

should be provided with sleeves or

installed through neatly formed holes,

to enable unrestricted movement.

This includes walls, floors, ceilings,

floorboards, floor joists, etc. It must

be ensured that the pipework will not

come into contact with the sleeve or

wall of the ho le. Any m astic or other

material used to fill the gap must

permit m oveme nt of the pipe.

b. Felt pads, or similar, should be

provided between pipework and

notched joists, and between adjacent

pipes which may come into close

contact with each other.

c. Pipe clips, supports and guides must

not restrict the m oveme nt of the pipe,

particularly on long pipe runs.

d. Whe re it is necessary

to

bury the

pipework in the screed, provision

must be incorporated

to

prevent

damage to the pipework and screed.

This could take the form of a

proprietary plastic coated pipe

wrapped in fibreglass and the whole

surrounded with expanded m etal or

similar.

192


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~~


Dotted line indicates h ow the

pipework will expand away

from anchors

Anchor)(Anchor

-L

e. Ensure that any branches conn ected

to

expanding pipework (eg:

connections

to

radiators), are of

adequate length to provide natural

flexibility to pre vent the co nnec tion

shearing.

f. Ensu re that expa nding pipework will

not clash with structures.

g. The direction of pipework expansion

must always be controlled using

suitable anchors, guides and clips.

Standard pipework clips may be

adequate for short pipework lengths

of sma ll bore copper and plastic.

h. Open type pipe clips must not be

used wh ere there is a possibility of

the p ipe springing away from the clip.

The above requirements are also

essential

to

ensure that excessive

frictional noises do not occur as a result

of expansion and contraction.

Anchors

Where expansion is excessive, pipe

movement must be controlled by

installing anchors. Anchors restrain the

pipework ensuring that any m ovement

due

to

expansion occurs in a direction

away from the anchor.

Anchors a re usua lly fixed to the m iddle of

the pipe

to

enable the pipe to move in

two d irections, therefore effectively

halving the maximum cha nge of

pipework length in any given direction.

Som etimes however, it

is

desirable to

provide an anchor at one end of a p ipe

run, for instance, to prevent a pipe from

coming into contact with an adjacent

wall.

When a nchors are installed to control

expansion, forces will be exerted on the

anchor. It is therefore essential to ensure

that:

a. The anchor is adequately secured to

the pipe

b. The anchor itself is structurally

adequate

Short length

of

pipe, taken

rom original of carryin

iipe (the length split

solder

Pipework prov ided with additional bends

to

accommodate expansion shown in solid line,

with 4 anchor positions.

J

/

Originally intended pipework

route

shown dotted.

.;,

Figure 2 Typical anchor for copper pipework

Figure 5 Providing additional bends to

accommodate pipework expansion

Plastic coated

Socket saddle strap

channel ~

I / \ I

Socket

A n c h o r A

nchor

Figure

3

Typical anchor for steel pipework

Figure

6

Expansion loop/horseshoe section

light load)

Heavy mild steel strap

welded to pipe; bolt

to suppor t dependent on

Angle or channel

support

Locking

channel/an

not require

for lightly

loaded

anchors

This anchor may be used

for

copper pipes

using brass strap.

Figure 4 Typical light to medium load anchor

c. The anchor fixings

to

the building

structure are adequate

d. The building structure itself,

to

which

the anchor is fixed, is adequate

to

accept the forces.

Whe re necessary, the advice of a

structural engineer should be obtained

to

ensure the anchor and support

arrangements are adequate for the

anticipated forces which may b e exerted.

Pipework expansion

devices

If expansion and contra ction of pipew ork

cannot be contro lled with the u se of

anchors alone, then consideration must

be given to providing additional devices

to enable movement to take p lace. These

include:

a. Rou ting pipework with additiona l

b. Providing purpo se design ed

bends or offsets

loop/horseshoe sections in the

pipework

c. Installing expansion bellows or

comDensators

d. Providing expansion coup lings for soil

and w aste pipework systems.

The provision of additional bends, offsets

or loop/horseshoe pipework systems

must pro vide adequ ate natura l flexibility

to

accommodate the pipework

expansion.

Expansion bellows or compen sators are

proprieta ry manufactured devices,

designed to accommodate or absorb

expansion and contraction.Various

different types of these d evices are

available. It is es sential that the

manu facturer be con sulted for their

particular recommendations regarding

the m ost suitable type for the situation

and for their requirements or anchors

and guides.

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Pipework expansion


Be

w

s

15-20

pipe

diameters

The following points should be noted

when using expansion bellows or

compensators:

a. Axial type bellows must not be used

where the pipe is hung or suspended

freely. The pipe sup ports m ust guide

the pipe and allow only axial

movement along the entire length of

the pipe.

b. It is essential to ensure that the pipe

is guided carefully on ea ch side of

the be llows. The guides m ust allow

only axial movem ent onto the

bellows.

c. It is essential to ensure that the pipe

is guided carefully at the necessary

intervals along the whole pipe run.

d. Only the bellows unit shou ld be

installed between two pipe anchors.

e. The line between two anchors should

be straight, in plan and in elevation,

with no sets or bends.

f. Pipe anchors must be of adequate

strength.

g. Bellows must be stretched by half the

total expansion movement (cold-

draw). This does not apply to spec ial

applications or pre-c old drawn units.

h. Screwe d end units must be held firm

when installing to prevent twisting of

the bellows.

The most common method of providing

the facility for expansion and contrac tion

in plastic soil and wa ste pipe systems is

the use of prop rietary expansion

couplings incorporating socket and spigot

joints having rubber sealing rings. The

couplings should be of the same

manufacture as the pipework system.

The expansion couplings should be

introduced at 1.8 metre intervals or as

recomm ended by the manufacturer, to

connect pipes together.

Plastic pipework should be an chored and

supported in a ccordance with the

manu facturers recomm endations. This

will depend on the system employed.

Supports and pipe guides

The purpo se of a sup port is to transfer

the load of the pipe and the conten ts

within the pipe safely to a structure. The

pipe support sh ould redu ce deflection of

bending of the pipe.

The pu rpose of a p ipe guide is to con trol

the direction in which a pipe will move

when it expands. A pipe guide is any

form of constraint which allows the pipe

true axial m ovement along its length but

prevents offset movement whether

horizon tal or vertical. Pipe guides can,

however, be designed to also pro vide a

supp ort facility. Som e typical pipe guides

are indicated in Figures 7 to

11.

Figure 7

Strap type guide

c,

Figure

8

Strap type guide with tube roller

Figure

9

Strap type guide with roller and chair

figure

1

Tube type Guide

Figure

11

Slip on Flange Type Guide

Clearance

For guides nea rest the bellows, the

clearances between the outside pipe and

inside guide walls should not be greater

than 1 .6mm for pipe diameter up to

IOOmm and n ot greater than 3.2mm for

larger pipes. For the guides alon g the

pipe run, maximum clearances of 3.2mm

and 6.4mm respectively shou ld be used.

Guides nearest

the bellows

The fu nction of guides closest to the

bellows is to ensure true axial movement

on to the be llows. This can be achieved

by using a tubular type guide (as Figure

10)

of such length that the neces sary

clearances to permit axial movement do

not allow appreciable offset m ovement.

Gene rally a tubular guide having a length

to diameter ratio of 6 :l will be adequate.

Tubular guides are gen erally only fitted to

small pipes. For larger sizes (50m m and

over), proprietary straps and roller guides

are normally employed. Straps and roller

guides are sho rt and ind ividually cannot

contro l angular m ovem ent of the pipe. To

ensure alignment of the pipe onto the

bellows, an add itional set of gu ides is

require d as follows.

I - I Yz pipe

r

iameters

l-----I

lllllllt

Tubular guides 5-6 pipe

diameters

Figure

2

Guide near bellows

I

I

Guides as

necessary

I I ~ipe

iameters

Figure 3

Installation

of

additional strap and

roller guides

Figure 4

Pipework failure may occur without

pipe guides

I

Bowing force

Anchor

Correct guides

No

ghdes

Andhor

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Plumbing Engineering Services Design

Guide

Pipework expansion

It is essential to ensure that the complete

pipe run is adequately guided and not

just

local to the bellows. If this is not

carried out, the pipework may bow

outwards as a result of the compressive

forces imposed on it.

It is essential that all support

arrangements, except for purpose

designed anchors, enable controlled

pipework movement. If the pipework is

incorrectly restrained, damage to the

pipe supports or structure may result,

due to excessive friction or forces.

Cold draw of bellows

It

is normal for bellows to be cold drawn

eg. stretched) by half the total calculated

expansion when installed into a pipe. The

bellows will then absorb the total

expansion, half in tension and half in

compression from the neutral position.

This keeps the stress in the bellows

material to a minimum for a given

expansion and provides maximum

bellows life.

In steam and high temperature heating

applications, it is not necessary to allow

for ambient temperature variation

dayhight, summer/winter) when

installing the bellows, since this variation

is very small compared with the working

temperature range. However, on low

temperature applications, allowances

must be made when calculating cold

draw. Where very small movements,

vibration or subsidence are

to

be

absorbed, the bellows manufacturers

often recommend that cold draw is not

used.

, I

,

I I I I I Bellows - neutral

Bellows - cold draw

Bellows- hot

Total expansion

Cold draw movement

Figure

5 Cold draw in expansion bellows

~~

Figure

8a Point contact

Ci =

0.25

Figure 8c Line contact

Cold draw can be achieved by:

a. for flanged bellows:

Leaving a gap internally between the

bellows and pipe flange at one end of

the unit and then tightening up the

flange using over-sized lange bolts.

Under-cutting he length of an

adjacent pipe section and allowing

the thread of a connecting union

to

expand the bellows. Care must be

taken that the bellow is not twisted

during the tightening process.

Installing a pair of flanges in the

pipework adjacent to the bellows with

a gap initially between the flange

faces and then tightening up the

flange using over-sized flange bolts.

By purchasing pre-cold drawn

bellows.

b. for screwed bellows:

c.

for welded end bellows:

d. for all bellows:

Figure 6 Taking up cold draw on flanged bellows

Figure

9

i

=

0 3

Figure 86 Line contact

C i

=

0.4

Figure

18d Face-to-face contact

Calculating forces

on anchors

The following main factors have to be

taken into consideration when

determining forces on anchors:

a. The effect of test pressure on the

cross-sectional area of any bellows

installed within the pipework system.

b. The elasticity force

to

stretch and

compress bellows installed through

the working movement.

c. Frictional orces between the pipe

and pipe supports, acting against the

direction of movement.

d. The slope of the pipe, affecting the

lower anchor vitally important

f

the

pipe is vertical).

e. Fluid pulsation and flow effects in the

pipe.

f.

Differential orces due to changes in

pipe diameter.

Quoted friction coefficients between

pipework and supports vary considerably

but the values shown in Figures 18 a),

b), c), and d) may be used as a

general guide for steel on steel.

The frictional resistance kg)

=

dead load

at point of support kg)

x

coefficient of

friction.

Figure 7 Taking up cold draw on welded end bellows

Anchor Be

I

ws

Anchor

Guide at necessary

intervals

~~

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Pipework expansion

Plumbing

Engineering

Services Design Guide

This resistance acts against the direction

of movement e.g. it can act either way,

depending on whether the pipe is

warming up

or

cooling down.

Should the above figures give

unacceptably high forces consideration

could be given to using special PTFE

support pads which gives figures as low

as 0.02.

Example

2

The following example illustrates the

calculation to determine the force imposed

on an anchor under normal working and

test conditions on a pipework installation

indicated in Figure 19, which incorporates

axial type bellows.

The designer must obtain the relevant data

from the bellows manufacturer.

Pipe weight

=

22kg/m

Water weight = 19.5kgh

Lagging weight = 6kgh

Effective area of bellows = 0.023m2

Thrust to compress or extend bellows

through full movement = 6700N

from manufacturers data Newtons)

Coefficient of friction between

System working pressure

=

550kPa

System test pressure

=

830kPa

pipe and supports

=

0.3

550 x 1 0 3 ~ 4

Length of pipe

=

42.5

Pipework sys tem under

normal work ing condi t ions

Thrust due to internal pressure on bellows

=

working pressurex effective area

= 550

x

103

x

0.023N

= 12650N pushing outwards on anchors

Force due to bellows stiffness bellows

compressed n working platform)

=

6700N pushing outwards on anchors.

Frictional resistance to pipe movement over

its supports:

=

coefficient of friction

x

total weight of

=

0.3

x

[ 22

x

42.5) 19.5

x

42.5)

= Converted to Newtons 1kg = 9.807N)

pipe + water lagging)

6 x 42.5)Ikg

=

0.3

x

[ 22

x

42.5

+

19.5

x

42.5)

+ 6 x 42.5)] x 9.807N

direction of movement, eg. pushing

outwards on anchors.

=

approximately 6000N against the

Total Thrust on Anchor

=

12650 6700 6000

=

25350N Newtons) pushing outwards

on anchors.

Pipework sys tem under tes t condi t ions

Thrust due to internal pressure on bellow

=

test pressure

x

effective area

=

830

x

1O3

x

0.023N

=

190909 pushing outwards on anchors

Force due to bellows stiffness bellows

stretched in cold-draw position)

Frictional resistance

=

6700N pulling inwards on anchors

=

NIL as pipe only moves under

temperature effect

Total thrust on anchor

=19090-6700

=

12390N pushing outwards on

It can be seen in this instance that the

greatest force acting on the anchor is under

normal working conditions, this however is

not always the case.

anchors.

The following important points should be

considered when installing bellows:

I

ii

iii,

i

v.

V.

When a fitting such as a bend, valve

or distance piece is installed into

a

pipe and subjected

to

internal

pressure. The fitting will act just like a

pipe itself, holding the internal

pressure, but not pushing or pulling

on the pipe.

When an axial bellows is fitted into a

pipe and subjected to internal

pressure, it reacts

to

the internal

pressure by trying

to

open out

lengthways. An outward pressure is

therefore exerted by the bellows.

When a pipe restrained by an anchor

at one end, but otherwise free to

move longitudinally, is subjected

to

heat, it will expand away from the

anchor position, exerting an outward

force away from the anchor.

When a pipe anchored at two points

and provided with a bellows between

the anchor points is subjected

to

heat, pressure is exerted by both

pipework sections towards the

bellows. Meanwhile the pressurised

bellows is exerting pressure outwards

towards the two anchor points.

When the pipe gets hot, it expands

towards the bellows and tries

to

compress it. Meanwhile, the

pressurised bellows is trying to open

out lengthways. The expanding pipe

therefore has to overcome this

pressure force as well as the stiffness

of the bellows and the friction of the

pipe supports. Hence the need for

firm anchors

at

each end of the pipe

run, and careful guiding not only on

each side of the bellows but also

along the pipe run.

vi. The pipe between bellows and

anchors is frequently in compression

and unless the pipe is guided

carefully, and runs accurately in a

straight line from anchor

to

anchor,

the pipe may bow out sideways. This

will pull the bellows with it and may

cause failure.

vii. Never use axial bellows in pipework

systems incorporating suspended

hanger supports or any other support

systems which can readily swing.

viii. Confirmation should always be

obtained from the bellows

manufacturer regarding any special

requirements they may have

regarding the position of anchors and

guides.

196

plumbing design guide - expansion

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