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7/24/2019 Plumbing Design Guide - Expansion
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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.
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~~
Plumbing Engineering Services Design Guide
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
Plumbing Engineering Services Design Guide
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