IS 7634 (Part 2) : 2012
(2022
reaffirm)
PLASTICS PIPES SELECTION, HANDLING, STORAGE AND INSTALLATION FOR POTABLE WATER SUPPLIES — CODE OF PRACTICE
PART 2 LAYING
AND JOINTING OF POLYETHYLENE (PE) PIPES
1 SCOPE
This standard (Part 2) gives guidance for the recommended methods of laying, jointing
and testing of polyethylene (PE) pipes for the potable water supplies
(pumping and distribution mains and service lines
buried under ground and for the conveyance of
water above ground for the both outside and inside buildings).
This standard is applicable for the
water supplies up to and including 45°C water temperatures.
This standard does not purport to give
guidelines for designing and dimensioning of pipe lines.
Local bye-laws shall be observed,
whenever used for municipal
water distribution.
2 REFERENCES
The standards given in Annex A contain provisions, which through reference in this text, constitute provisions of this standard. At the time of publication the editions indicated were valid. All standards are subject to revision and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards given in Annex A.
3 JOINTING TECHNIQUES
General
Polyethylene pipes are made by continuous extrusion process and are generally available in factory cut lengths and in form of coils. PE pipes conforming to IS 4984, as they are UV protected (due to carbon black content in the pipe), may be stored either in open or covered.
The commonly used joints are as follows:
a) Fusion welding:
1)
Butt fusion welding;
2)
Socket fusion welding;
and
3)
Electro fusion welding;
b) Insert type joints;
c) Compression fittings/push fit joints;
d) Flanged joints;
and
e) Spigot and socket joints.
Fusion Welded Joints
The principle of fusion welding is to heat the two pipe surfaces to a designated temperature and then fuse them together by application of sufficient force. This force causes the melted materials to flow and mix, there by resulting in fusion.
Fusion welding of PE pipes must be carried out with welding equipment having temperature and pressure (where applicable) display arrangements. PE pipes and PE fittings, to be joined by face-to-face (butt fusion) welding must be of the same wall thickness and the ends must be cut square. However, in some cases of fusion, where face-to-face contact is not involved the jointing pipes/fittings wall thicknesses need not be same. The integrity of the fusion joint is dependent on the cleanliness, temperature control and designated equipment that has been properly maintained.
The pipe ends shall be dry and free of dust. Mating surfaces shall be planed/scraped before fusion to remove surface material as polyethylene (PE) oxidizes on exposure to air. These prepared (scraped) surfaces should not be touched, as there is a risk of contamination of the surface, which may affect the weld efficiency. The site conditions must be protected against bad weather influences such as moisture and temperatures below 5°C.
The fusion welding procedure described here is suitable for welding polyethylene pipes and fittings falling in melt flow rate (MFR) range of 0.1–1.2 g/10 min at 190°C with nominal load of 5 kgf.
Butt Fusion
Welding (see Fig. 1)
FIG. 1 BUTT
WELDING PROCEDURE OF PE PIPES
Butt fusion equipment
Basic welding machine shall be self-supporting such as guides and clamps to suit the stability of the basic machine and with sleeves as per the size requirement along with the following accessories:
a)
Non-stick coated with poly tetra flouro ethylene (PTFE), heating plate with thermostat and temperature indicator,
b)
Chamfering ( Planing) tool — electrical/ manual as appropriate, and
c)
Electro-hydraulic power pack (for sizes greater than 125 mm) unit with pressure indicator, by- pass arrangement and accumulator.
The butt fusion equipment shall incorporate a facility for supporting the heating plate and planing tool (necessary to square cut the pipe end) when in use. The machine shall be robust enough to withstand normal field use.
Butt welding machines can be manual (for diameters up to 125 mm), hydraulic or pneumatic. However, a locking system to hold the fusion force is to be ensured in all the systems, and the equipment shall be protected against exerting over-pressure on the pipe. It shall be able to maintain the required interface force on the pipe or fittings end as long as necessary.
Butt welding procedure
(see
Fig. 1)
a)
Clamp
the pipes/fitting in the butt fusion machine.
b)
Wipe the ends to be welded, inside and
out, with a clean cloth to remove
water, dirt, mud, etc.
c)
Welding ends should be squared. In case of pipe, plane
both ends by a planer (mechanical/ electrical for pipe diameters
greater than 160 mm) until they are perfectly square. Fittings’ ends can be re-cut square, where necessary.
d)
Remove the plastic shavings from the vicinity of the ends without touching the
prepared surface as any contamination will be detrimental to the welding process.
Re-clean the surface with proper solvent.
e)
Bring together the two ends and ensure
they are aligned.
f)
Check
the hot plate (mirror) temperature (range 200-230°C) and make certain
the plate surfaces
are clean. It is good practice to make ‘dummy’
welds daily, prior to welding sessions as a means of cleaning the mirror. That is, the weld procedure should be
taken to the heat soak stage, when
the process can be aborted. The hot
plate surface must not be touched
with hand, metal implements or tools.
A damaged or dirty hot plate will result in a poor joint. Heating mirror is nothing but a metallic
plate heated up to the required temperature by electrical coil embedded inside. The word ‘mirror’ has come into vogue because
the heating plate radiates heat.
g)
Prior to heating, levelling of the pipes/fittings is essential to ensure square plane face over the heat surface
[see 3.2.1.2 (c)].
h)
Move the pipe/fitting ends into contact
with hot plate and a steady pressure
of 0.15 ±
0.01 MPa shall be applied while a uniform bead forms around the circumference of the both ends. This procedure is to ensure that the entire face of the weldable portion heats uniformly through the surface contact with the mirror.
j)
After the bead height is formed as per Table 1 relieve
the pressure but maintain contact
pressure between the plate and the ends of the heated surfaces as per pressure build up time mentioned in Table 1.
k)
Push back the pipe/fitting ends away from the mirror
after the above operation. When removing the mirror, make sure it is not brushed across the molten pipe ends.
m) Bring the molten ends together
and follow the recommended pressure as per the requirement of the pipe/fitting
wall thickness (see Table 1). This pressure
should be applied by building up
gradually to avoid squeezing out too much of the melt. Do not disturb
the joint during the required cooling time. Follow
the pressure-time diagram as given in Fig. 2.
n)
Relax the pressure and carefully remove
the clamps only after ensuring that
cooling time has elapsed.
p) Inside or outside bead removal after the weld joint cools, shall have no affect on the weld performance.
Caution
It is essential to ensure the pressure-temperature chart and the corresponding timing table is followed.
While jointing, the pressure should be maintained as mentioned in Table 1. After the pressure is relieved, the joint is allowed to cool to ambient temperature. Under no circumstance the weld should be forcibly cooled (no quenching).
Table 1 Values of the Recommended Bead Width and Timing for Butt Fusion Welding
(Clauses 3.2.1.2 and 3.2.1.3)
Sl No.
Nominal Wall Thickness
Bead Height on the Heated Tool
Heating Up
Change Over
Pressure
Build-up Time
Jointing and Cooling
Cooling Time Under Pressure
Cooling Time During Pressure Relaxation
mm mm s s s s S (1) (2) (3) (4) (5) (6) (7) (8)
i) Up to 4.5 0.5 45 5 5 6 300
ii) 4.5-7 1.0 45-70 5-6 5-6 6-10 600
iii) 7-12 1.5 70-120 6-8 6-8 10-16 900
iv) 12-19 2.0 120-190 8-10 8-11 16-24 1 200
v) 19-26 2.5 190-260 10-12 11-14 24-32 1 500
vi) 26-37 3.0 260-370 12-16 14-19 32-45 1 800
vii) 37-50 3.5 370-500 16-20 19-25 45-60 2 100
viii) 50-70 4.0 500-700 20-25 25-35 60-80 2 700
NOTE — Bend strap testing is suggested on a test sample to
verify fusion joint integrity and to qualify the welding technicians. The specimen shall be made by the cutting the
pipe longitudinally into strips of 1 or 1.5 times the wall thickness wide and
by about 300 mm or 30 times the wall
thickness in length with the fusion centred strip (see Fig. 3). The fusion sample should be bent till the ends meet
and visually inspected. The sample
should be free of cracks and breaks and shall have seamless joint surface.
Testing shall be done on the each size of the pipe being used at the site, to qualify various machines and the technicians that are likely to be employed at the site.
FIG. 3 BEND
STRAP TEST — WELDED PIPE
PORTION
CUT LONGITUDINALLY AND BENT
Socket Fusion (see Fig. 4)
This technique consists of simultaneously heating the external surface of the pipe and the internal surface of the socket fitting until the material reaches fusion temperature; inspecting the melt pattern; inserting the pipe end into the socket; and holding it in place until the joints cools.
Socket fusion procedure
a)
Prepare
the pipe — cut at right angles and trim;
b)
Chamfer
pipe end. Remove burrs and chips from inside pipe ends;
c)
Utilize
proper depth gauge to ensure correct insertion depth and pipe roundness;
d)
Clean
pipe and fitting
with cloth to remove all the contaminants;
e)
Verify
proper heater plate temperature. Temperature should be 200-230°C;
f)
Force fitting and pipe onto a heater
surface. Be sure to insert pipe
completely into female socket and
the fitting completely onto the male
socket;
g)
Apply the heat on the surface of the pipe;
h)
Remove the pipe and fitting from the
heater. Care should be taken for
not to apply torque or twist the pipe or fitting;
j)
Quickly
insert heated portion
of the pipe into the heated socket
of the fitting and ensure
co- axial alignment
of the pipe and fitting;
k)
Allow joint to cool for proper cooling
time. Be sure to maintain
pressure while cooling;
m)
Allow
joint to cool to room temperature before moving the joint; and
n)
Inspect joint for weld integrity.
Electro Fusion (see Fig. 5)
Electro fusion is a heat fusion process where a coupling or fitting containing an integral heating source (resistance wire) is used to join the pipes and fittings. The jointing areas, that meets the pipe surface and the inside the fittings are overlapped and the resistance wires inside the fitting are heated by electric current. During heating, fitting and pipe materials melt, expand and fuse together. Heating and cooling cycles are automatically controlled by the bar code arrangement on the fittings and machinery used.
FIG. 4 SOCKET FUSION
JOINTING PROCEDURE
The welding equipment or its accessory shall be able to supply the required voltage for the electro fusion joint. The device must switch off as soon as the necessary heat has been fed to the welding zone. The welding machine must be calibrated and timing adjusted to the electro fusion fitting’s bar code data (the fitting and machinery manufacturer recommend- ations shall be followed).
Electro fusion is the only heat fusion procedure that does not require longitudinal movement of the joinable surfaces. It is frequently used where both pipes lengths are constrained, such as for repairs or tie-in joints in the trench. Joints between dissimilar polyethylene grades and different wall thicknesses can also be made using electro fusion, as the procedure readily accommodates polyethylene grades with different melt flow rates and is independent of the pipe wall thickness.
FIG. 5 ELECTRO FUSION PROCESS
Electro fusion welding procedure
a)
Prepare the pipe — Cut at right angles
and trim;
b)
Remove the outer film of pipes using scraper;
c)
Clean pipe surfaces with cleaner (as recommended by the electro fusion
fittings supplier);
d)
Mark the insertion
depth on the pipe;
e)
Remove
the fittings from the packaging
without touching the fusion surface;
f)
Firmly
push-in the pipe until the centre stop or marking;
g)
Mount and fix assembly attachment;
h)
Slide in the second pipe up into the fitting to centre
stop or marking;
j)
Firmly
fasten the integrated clamp to ensure
no movement while welding;
k)
Follow operating instructions of the
machine and fitting manufacturer or read the bar code;
m) Check the fusion indicator
on the fittings and then remove cable; and
n)
Wait for cooling
to remove the assembly (follow the fusion guidelines of the
fusion fittings supplier or what is
given in the bar code data).
Insert Type Joint
(see Fig.
6)
Insert type of fittings are available in both plastic and metal for use with PE pipes. These are commonly used for the delivery pipe connections of bore/tube well pumps.
In corrosive locations plastic/stainless
steel insert fittings
are preferred. In less corrosion conditions gunmetal fittings may be used and in normal or slightly
corrosive environments, brass fittings
may be employed. The insert
moulding plastic fittings with metallic inserts
are also available. The outer serrations of PE/metal insert type fittings
— slightly over sized
— lock into the pipes to prevent their coming out under sudden pressure surge. The pipe bore is expanded by immersion in oil bath (130°C) where the heat of the oil bath would soften the pipe to enable insertion of fitting.
The insertion of these fittings into the
bore of the pipe is done with by hand
pressure only. A worm driven type clip while the surface
of the pipe is relatively warm should be tightened over
the pipe to ensure the grip. Bolting
or riveting the inserted fitting onto
the pipe wall is also recommended for carrying
heavy weight, such as submersible pump.
This type of jointing is used normally
for diameter pipes up to 110
mm and internal pressure below 0.4 MPa. Load carrying capacity
of this assembly depends on the pull force applied by the weight of the total assembly including the
weight of the hung item (say a
submersible pump) and media weight inside the pipe. The pipe manufacturers’ recommendations are to be followed for allowable total pull force on a given pipe with insert
type connection. The elongation of PE pipe is very high (over
600 percent), hence these recommendations attain significance. More so, if the load on to the assembly
is very high such as in the
case of submersible pump lowered with
PE pipe as a delivery pipe with this type of connection.
Compression
Fittings (see Fig. 7 and Fig. 8)
Compression fittings are detachable
joints and are made of metal or
plastics [polypropylene (PP)] or a
combination of both. Compression fittings form a tight seal by applying a compressive force to the pipe and pipe fitting. The fitting is compressed
against the pipe with a force sufficient to eliminate all space
remaining in the joint, thus preventing the fluid from leaking.
It is critically important to the
integrity of the fitting that excessive force
is avoided in tightening the nut.
If the fitting is over tightened, the gripper (clip ring) will deform and cause leaks. Over tightening is the most common cause of leaks in compression fittings. As a general
rule, a compression fitting should be ‘finger tight’ and then tightened one
turn with a wrench. The fitting should
then be tested, and if slight
weeping is observed, the fitting should be slowly tightened a bit more until the weeping stops.
Compression fittings are also available as metal fitting such as the type of fitting
commonly used for copper tubes. In this type of joint the dimensions of the pipe are generally not altered. The joint
is affected by an internal
liner and a compression ring or sleeve which shrinks and therefore compresses the pipe
wall on the liner, thus gripping to
the wall of the pipe. The liner and compression sleeve may also be an integral unit.
FIG. 6 TYPICAL ILLUSTRATION OF MAKING
INSERT TYPE JOINTS
FOR PE PIPES
FIG. 7 POLYPROPYLENE COMPRESSION COUPLER (SOCKET)
IS 7634 (Part 2) : 2012
Compression fittings
with collar/pipe ends and flat gaskets
Aluminum alloy or brass fitting with male and female coupling parts may also be used for jointing with metallic fittings. The male and female ends of the coupling are welded face to face on two ends with hot plate or electric coil. The two collars are brought together and the female end of the coupling is tightened on the male end. A water tight seal is made between the flanges. This is the detachable type of jointing and is practicable up to 50 mm diameter pipes (see Fig. 8).
FIG. 8 METALLIC COMPRESSION FITTING
Compression fittings do not require
fusion. They work at higher pressures
and even with toxic media.
Compression fittings are especially useful in
installations that may require occasional disassembly or partial removal for maintenance, etc,
since these joints can be detached
and re-joined without affecting the integrity
of the joint. They are also used in situations where a heat source, in
particular a heating plate, is
prohibited and inside bead formation by butt
fusion is not preferred.
For coiled polyethylene pipes, of small diameters
(<110 mm) where the working pressure do not
exceed 1.6 MPa, jointing by polypropylene (PP)
compression fittings is generally recommended over fusion jointing.
Various varieties of PP compression fittings such as couplers, bends,
tees, reducers and threaded/flanged adapters to connect to valves /tanks/
non-PE pipes are available.
Polypropylene compression fittings are easy to fit
requiring no special skills, have no possibility of infiltration (seepage) from outside or leaks from inside and therefore, are most ideal for domestic
service connections enabling
easy threaded connections to the ductile/cast iron/PVC-U/PE pipe ferrules/saddles of the
main lines.
Flanged Joints (see Fig. 9)
These
are used for jointing the PE pipes particularly
of larger size to valves and vessels and large
size metal pipes, and where non-PE pipes are to be joined with PE pipes.
It contains slip-on metallic/polyethylene flanges with
collar/stub ends. The collar/stub end is welded
by butt, socket or electro fusion, as per procedures (see
3.2.1.2, 3.2.2.1 and 3.2.3.1) to
the pipe. In case polyethylene flanges
are used a suitable metallic
backing plates shall be used to support the polyethylene flanges so that the bolt force does not
deform the plastic flange.
Injection moulded polyethylene flanges without backing
flanges conforming to IS 8008
NOTE — Dimensions and bolt tightening
torque shall be as per manufacturers’ recommendations.
FIG. 9 TYPICAL FLANGED JOINT
(Part 7) may also be used. Sealing is improved by incorporating a natural or synthetic rubber gasket between flanges.
Table 2 Allowable Bend Radius for Various SDRs
(Clause 4.1)
Spigot and Socket Joint (see Fig. 10)
Sl
No.
Pipe SDR Minimum
Bending Radius
R
Any joint that permits sliding of the free end (spigot end) inside the socket with a rubber or suitable
gasket, without
leakage is called a spigot and socket joint.
The socket (bell) could be an integral
part of the pipe at one end or a special
coupler, into which the
free ends (spigot ends) of the pipes are pushed to achieve a water tight joint. Various types of ‘O’ rings
(1) (2) (3)
i)
SDR £ 9 10 times diameter
ii)
9 < SDR £ 13.6 13 times diameter
iii)
13.6 < SDR £ 21 17 times diameter
iv)
SDR > 21 20
times diameter
NOTE
— SDR (Standard Dimension Ratio) is defined as:
Outside diameter, mm
SDR =
Minimum wall
thickness, mm
are available
in the market and the user may check with the manufacturer about the suitability of the same
These
joints are normally
weak in longitudinal pull and hence need anchoring
wherever such a tendency
of longitudinal pull is likely in the pipe line. The supports of the side connection should
ensure that excessive lateral
bending does not occur. In small diameter,
the coupler itself could be modified to have
a split, threaded, grip type gasket of hard materials in addition to ‘O’
ring to prevent loosening because of longitudinal
pull. Special type of rubber gasket (for water tightness) to prevent any slipping out of the free end of the pipe shall be used.
This type of joint is best used for non-pressure applications, such as gravity lines
and for encasing
cables or smaller diameter pipes.
FIG. 10 SPIGOT
AND SOCKET JOINT
4 BENDING
Cold Bending (see Fig. 11)
Polyethylene pipes have a degree of flexibility such that a substantial radius may be set up within a length of pipe itself without heating and causing residual stress. This enables gradual curves to be negotiated without the need for special bends or flexible couplings. However the radius of the bend shall be as per Table 2. Cold bending should only be used on pipes at ambient temperature.
FIG. 11 BEND
RADIUS
Hot Bending
Forming
of small radius bend may easily be done by the application of heat either by hot
air oven or by immersion in a suitable
liquid at an appropriate temperature. For lower density
polyethylene pipe, the temperature range is 100 to 110°C and suitable
liquids are water, glycerol
or a solution of calcium chloride. Higher
density polyethylene pipe should be heated in
an inert liquid, such as glycerol at a temperature of 130°C. Electrical heating coils or plates
may be used only by experienced technicians.
In preheating operations, the low thermal
conductivity of PE should be kept in mind. Over heating can usually be recognized
by surface discolouration and distortion. On the other hand bending
operations should not be performed
at too low a temperature.
At higher temperature, the bore of the pipe tends to collapse and therefore requires
support during the bending operation. Internal support should
be affected
before heating by packing the bore of the pipe with warm fine dry sand or by inserting rubber pressure hose, rubber rod or a flexible spring. After the pipe is uniformity heated it should be bent around a sample jig and held in the correct position until the form is cooled.
It is recommended that radius of the
bend for pipe up to 50 mm size should
not be less than three times the outside diameter
of the pipe for lower
density PE and five times the outside
diameter for higher
density PE. Pipes of large diameter will require an increase in radius. General
recommendations of the bend radius given in Table 2 are to be followed. The pressure
compatibility of the bend is to be tested before
using the same in the field.
5 PIPE LAYING
The pipe line may be laid along side of
the trench and jointed there. There after the jointed pipeline
shall be lowered
into the trench carefully without
causing undue bending. The pipeline shall be laid inside the trench with a slack of up to 2 m/100 m of pipe line.
Polyethylene pipes conforming to IS
4984, being black in colour, when
subjected to direct sunlight or warm ambient temperature
may become warmer than the ground temperature. When placed inside the trench, the pipe will contract in length
as it cools to the surrounding soil temperature. If the pipe is connected to sub-surface structures (such
as preset valve, etc) before it is
cooled sufficiently, excessive pull
forces could develop. Allow the pipe to cool to ambient temperature prior to making a connection to an anchored joint.
Polyethylene pressure piping systems
jointed by butt welding,
electro fusion and flanges do not require
external joint restraints or thrust block joint anchors.
Polyethylene pipes are non-metallic, so once buried, metal
detector type locators
are ineffective. To facilitate
locating a buried PE pipe, metallic locating
tapes or copper wires can be placed alongside the pipe. Locating
tapes/wires are placed slightly above the crown
of the above before the final back fill.
Because of high integrity of properly
made fusion joints, PE pipes can be
used with special installation techniques such as horizontal directional drilling, pipe bursting, micro tunnelling methods
of trench less technologies.
6 EARTH WORK AND PIPE SUPPORT (TRENCHING)
Trench width and depth shall be as per
Fig. 12 and Table 3.
Table 3 Trench Dimensions
(Clauses 6.1 and 6.4.1)
All dimensions in millimeters.
Sl Size of Pipe Width Initial Range of Depth No. mm Back Fill of Cover
(1) (2) (3) (4) (5)
i) 20-110 300 150 900-1 100
ii) 125 425 150 900-1 100
iii) 140 440 150 900-1 100
iv) 160 460 150 900-1 100
v) 180 480 150 900-1 100
vi) 200 500 150 900-1 100
vii) 225 525 150 900-1 100
viii) 250 550 150 900-1 100
ix) 315 615 150 900-1 100
x) 355 655 150 900-1 100
xi) 400 700 150 900-1 100
xii) 450 750 150 900-1 100
xiii) 500 800 150 900-1 100
xiv) 560 860 150 900-1 100
xv) 630 930 150 900-1 100
xvi) 710 1 010 150 900-1 100
xvii) 800 1 100 150 900-1 100
xviii) 900 1 200 150 900-1 100
xix) 1 000 1
300 150 900-1 100
NOTES
1 Width may be increased
where jointing inside the trench
becomes necessary because of site conditions.
2 Under national/state
highways, a concrete/hume pipe shall be covered
over the pipe.
3 Depth is to be measured over the crown of the pipe.
4 In case of
mole-plough technique of pushing the coils of diameters
20-100 mm in am narrow trench the width of 300
mm is not mandatory.
5 Initial back fill
material shall be as per this standard.
6 For gravity
lines SDR more than 22, manufacturers should be consulted for allowable
deformation calculations under dynamic traffic load.
Flexibility
For rigid pipes such as concrete, etc, the pipe alone has to take the main vertical forces acting on the pipe, while flexible PE pipe makes use of the horizontally acting soil support accumulating as a result of the deflection of the pipe. This aspect improves the load bearing capacity of PE pipe especially useful property in gravity pipe design where there is no internal pressure to ensure the pipe circularity.
Trench Bedding
Polyethylene pipe requires no special bed preparation for laying the pipe underground, except that there shall be no sharp objects around the pipe. However, while laying in rocky areas suitable sand bedding should be provided around the pipe and compacted.
Trench Depth
The trench depth shall be as per Table
3. The initial back fill up to 150 mm
above the crown of the pipe should be
compacted with screened excavated material
free of sharp stones or objects or with fine
sand where no such material
is available.
IS 7634 (Part 2) : 2012
12A For Soil having
no Rocks and Natural Aggregate
Comprised Primarily of Rounded Particles Created by Mechanical Erosion
12B For Soil having
Sharp Rocks and Unconsolidated Material
that are Made
Up of Rocks Fragments > 20 mm Diameter
FIG. 12 TRENCH LAYOUT
The excavated soil from the trenches
should be placed such that it shall
not interfere with stringing and jointing
of the pipes.
In all cases, 150 mm above the top of
the crown of the pipe is to be compacted either by mechanical or manual means.
Wherever road crossing with heavy traffic
is likely to be encountered — a concrete pipe
encasing is recommended.
Polyethylene pipes can be jointed inside or outside the trench, as per site conditions.
However, in case of jointing inside
the trench, the width of the trench may be suitably
increased to ensure work space.
Water in the Trench (see Fig. 13)
The pipe shall be laid on a stable foundation. Where water is present or where the trench bottom is unstable, excess water should be removed before laying the pipe. In case there is a chance of floatation because of likely flood, the pipe shall be encased with concrete weights as per the buoyancy calculations.
Under Water Installations (see Fig. 14)
Polyethylene pipes are frequently used for carrying potable water across rivers/canals/lakes. Even water filled PE pipe is lighter than water. Thus the pipe can be aligned along the recommended route over the water surface and then submerged with suitable weights (see Fig.13). Submerged installations require permanent concrete ballast rings attached around the pipe to ensure submergence and stable system once it is submerged. Concrete block design depends on type of installation, tidal flows and wave actions.
Service Connection (see Fig. 15A and Fig. 15B)
New service connections can be made on PE pipes with mechanical saddles
or electro fusion saddles. Mechanical saddles are similar to those
available for PVC-U and ductile iron.
FIG. 13 TYPICAL ANTI-BUOYANCY WEIGHT — CONCRETE BLOCK
Installation of mechanical saddle is
similar to techniques used to install
saddles on other piping materials, however care has to be taken as
excessive tightening of the side
bolts may make the pipe oval. Mechanical saddles
should have wide straps to distribute
compressive forces and must be installed as
per manufacturer’s recommendations.
Installation of electro fusion saddle
shall be as per the electro fusion jointing procedure
detailed in 3.2.3.1.
Mechanical saddles can also be used for
PE to metal connection as a transition tapping.
7 INSTALLATION
Lowering
When jointed outside of the trench the
jointed pipeline shall be lowered into the trench (for underground installations) carefully
(preferably with mechanical handling
equipment for sizes greater than 160 mm) without
causing undue bending that can cause
kinking. The pipeline shall be laid inside
the trench
FIG. 14 UNDER WATER
INSTALLATION
15A Typical
Mechanical Saddle Tappings
15B Typical
Electro Fusion Saddle
Tappings
FIG. 15 TYPICAL SADDLE
TAPINGS
with a slack of up to 2 m/100 m of the pipeline (pipe line to be laid in a sinuous alignment).
Bending
of pipe inside the trench involves excavating the trench to the desired
bend radius. Exposed
black PE pipe to ambient
temperature greater than 30°C will have very high surface
temperature that makes it difficult to handle. Proper
precautions shall be taken to ensure safety at work site.
Thermal Expansion
For exposed PE pipes, provisions shall
be made for the effects of thermal movement.
The support anchors
for exposed PE pipes should
not grip or distort the pipe (see Fig.
16), but should allow free movement of the pipe due to temperature variation.
FIG. 16 TYPICAL PIPE
CLAMP
Plastics pipe clamps may be used to
support the pipe. Standard pipe
clips may also be used but care shall be taken not to over tighten and cause the clips to bite into the pipe. Pipe clips should be correctly
aligned and should provide a
smooth flat surface for contact with pipe. Sharp edged supports should be avoided.
Painting
Plastics pipes in general need not be painted. Painting may disguise its character. Hazard might occur by mistaking this pipe for metal one in using it for load bearing support, or for electrical grounding.
Precaution — Polyethylene pipes shall not be installed near hot water pipes or near any other heat sources.
Valve Anchoring (see Fig. 17)
All types of manual controls and valves in particular should be anchored firmly so as to avoid the turning torque imparted by the operation of the hand wheel of the valve onto the pipe. In short the valve should not be ‘hung’ on the pipe, as is normally done for metallic pipes.
FIG. 17 VALVE
ANCHORS
Support Spacing
Suitable supports as agreed to between the buyer and the supplier for horizontal over ground run of PE pipe with pipe clamps/brackets should be used. At >40ºC, continuous support is recommended, if the pipe is carrying heavier liquids.
Effect of Temperature
Expansion and Contraction
The co-efficient of expansion is about fourteen times than that for expansion experienced with metal pipes. This also holds good for contraction due to fall in temperature.
In underground pipe the normal
changes in the direction
of the pipe provide an adequate means of accommodating expansion/contraction.
In the continuous straight runs of exposed pipe it
is necessary to insert units to absorb the expansion. Expansion loops, bellows or sliding gland expansion joints may be used.
Care
should be taken
in, to account for the high increase
in surface temperatures of these pipes in cases of
exposed laying or laying in the close proximity of artificial heat sources.
PE Fittings
Polyethylene pipe fittings conforming to IS 8008 (Parts 1 to 9) and IS 8360 (Parts 1 to 3) may be used for connecting the pipes and other system appurtenances. These fittings can also be used for connecting to metallic valves (sluice, scour and air), tanks, pipes and other mechanical equipment (pumps, etc). However, where there is a likely hood of vibrations and turning torques in such connections, the fitting wall thickness shall be minimum one rating higher than the corresponding pipe.
Concrete Encasement
Polyethylene pipes may be encased in concrete, wherever necessary. Compressible padding material at least 3 mm thick and at approximately 150 mm from the face of concrete shall be provided around pipes at the entry and exit points to eliminate any potential sharp edges from rubbing against the pipe wall. Pipeline shall not be filled with water until the concrete has developed sufficient strength.
8
LAYING THE PIPE IN TRENCHES
Trench Filling
On completion of the pipe laying
operations up to a length of about 1 000 m while further
laying work is still in progress, refilling of
trenches of this stretch shall be carried out up to 300 mm above pipeline.
Pipe laying shall follow closely
the progress of trench excavation. Only soft earth and gravel of good quality free from boulders, roots vegetable
matter, etc, shall be used first. If
sufficient quantity of suitable (sharp edge
stone free) excavated earth is not available, the trench shall be filled by borrowed gravel or material up to 300 mm above top of the pipe.
Care shall be taken during back filling
for not to damage the pipe or joints. Filling
has to be carried out simultaneously
on the both sides of the pipes so that unequal
pressure does not occur. Load on the buried pipeline
shall not be permitted unless the trench has
been filled to the height of at least 300 mm over the top of the pipe. Filling
shall be done in layers
of 150 mm, with the first
layer watered and compacted by stamping
or by mechanical means. The trench shall
be refilled so as to build up the original ground level,
keeping due allowance for subsequent settlement likely to take place.
9
FIELD TESTING
OF PIPELINE
The pipeline to be tested shall be filled with water slowly allowing for splurging the entrapped air. Air valves at high points should be open to allow air to escape while water is being filled. Before pressure is applied, the pipeline section under test shall be restrained against movement.
The following procedure is recommended for PE pipe testing:
a)
Polyethylene pipelines shall be pressure tested at ambient temperature. After filling with water the pipeline
shall be left to stabilize
for a period of 1 h.
b)
Fusion joints may be covered during
testing. Flanged joints shall be
kept open for visual inspection. The
pipeline shall be filled with water
and pressure tested from the lowest point.
c)
During
the test period,
make-up water is continuously added to maintain
the pressure.
d)
The test pressure shall be 1.5 times the
rated pressure of pipes or of the proposed
maximum design pressure
of the section. Apply the pressure
by continuously pumping at a constant
rate.
e)
Under
no circumstance, air is to be used instead of water for testing.
f)
Tests
should be performed
on reasonable lengths of pipelines. Long lengths more
than 2 000 m may make leak detection more difficult.
g)
Acceptance criteria — If the pressure remains steady (within 5 percent of the target
value) for 1½ h, leakage is not
indicated. Flanged connections shall be visually
inspected.
h)
If the test is not complete because of
leakage or equipment failures, the
test section shall be depressurized
and allowed to relax for at least 8 h, before starting the next testing
sequence.
j) Testing outside the trench is to be avoided, as pipe rupture may involve safety issues.
10 REPAIR AND MAINTENANCE (see Fig. 18)
A perfectly welded fusion jointed PE pipes is totally leak proof. A good compression fitting also ensures total integrity of the system. However, there may be external conditions that necessitate repairs and
maintenance of the system. Various
methods may be employed for repairing leakages
or damage to sections of PE pipes.
In general, the best way is to cut the
damaged portion and to replace
it by a new pipe or pre-fabricated flanged replacement section. The
connections of new pipe to either ends of the old pipe may also be done by insert
type of fittings (subject to their pressure
limitations) and by electro fusion fittings. Butt fusion inside the trench for repairs is not
recommended as the movement of the
pipe for attaining the required facial
pressure for good weld integrity may not be possible. When failure or damage occurs in a
welded joint, the original
weld shall be removed entirely before re-welding. No patch work is recommended.
11
GENERAL GUIDANCE
Freezing
Freezing of water inside the PE pipes does not fracture it, as the pipe expands to allow the extra volume. However, direct application of intense heat, such as a torch or open flames should not be used to de-freeze.
Pressure Check
In any application where polyethylene pipe is attached to a pressure source, which is greater than the pressure rating of the polyethylene pipe being installed, adequate pressure reduction devices shall be installed. Whenever, such devices are installed a regular check of such devices should be made to ensure their continued proper functioning as a protection to the PE pipe.
Surge Pressure
Polyethylene pipes, by their visco-elastic nature and creep properties, can withstand much higher short term loads, that is, 2.3 times the working pressures. This property enables PE pipe to be able to withstand repetitive water hammer surges of pumping mains, without any need for any extra correction factor. However, for velocities higher than 1.5 m/s a surge check is necessary.
NOTE — The saddles
shown in Fig. 15A and Fig. 15B can also be used as repair
sleeves.
FIG. 18 REPAIRING PE PIPE
Slack in Laying
When PE pipes are laid inside the trench, up to 2 percent slack is permitted.
12
SUPPLY, PACKAGING, HANDLING, STORAGE
AND TRANSPORTATION OF POLYETHYLENE PIPES
Supply
The polyethylene pipes shall be supplied
in straight lengths either independent or bundle together, or as self supporting coils as agreed to between the supplier
and the purchaser.
Their
ends shall be clearly cut square and protected
against shocks. Coils shall be protected for
the ingress of foreign bodies by appropriate end caps.
Packing
Generally, PE pipes are tough and do not require any special packing. However, where necessary (during long distance transportation) the pipes shall be bundled to eliminate scratches. Coils may be wrapped in jute cloth.
Handling
Polyethylene is a tough resilient material which may be handled easily. However, because it is softer than metals, it is prone to damage by abrasion and by objects with a cutting edge. Such practices as dragging pipes over rough ground should therefore be avoided. If handling equipment is not used, techniques, which are not likely to damage the pipe are to be chosen.
Coils
Individual coils must not be rolled off the edge of the loading platforms or trailers. These coils should be slung individually when off-loading with a crane. Uncoiling the pipe at site requires trained personnel. The manufacturer need to be consulted, as unloading of the coils may involve safety concerns of the workmen involved.
If, due to improper storage or handling, a pipe is damaged or kinked the damaged portion should be cut out completely.
Straight Pipe
Handling and storage of straight polyethylene pipes should be such so as to avoid penetration by sharp objects. When loading, unloading or handling of large outer diameter (>160 mm), it is preferable to use mechanical equipments. Safety precautions should be followed while unloading the pipes at site. Unloading
of the large outer diameter pipes from trucks and trailers shall be with the help of properly set-up platforms and the same shall be rolled smoothly and not dumped from a high ground.
Transportation
When transporting straight polyethylene
pipes, use flat bedded vehicles.
The bed shall be free from nails and
other projections. The polyethylene pipes shall rest uniformly in the vehicle
over their long length.
The vehicle shall have side supports approximately spaced 2 m apart, and the
pipes shall be secured effectively
during the transportation. All posts
shall be flat with no sharp edges. Strapping the pipe bundles during transit may be required to avoid excessive
movement in the truck.
Polyethylene pipes shall not be transported with other metallic
items in the same vehicle.
Coiled pipe with outer diameter < 63
mm may be supplied on pallets. The
coils should be firmly strapped to the pallets,
which in turn be firmly
secured to the vehicle.
Coiled pipe with outer diameter ³ 63 mm should
be supplied individually.
There should be facilities to ensure
that each coil is securely fastened
throughout transit and the un-loading process.
To save on transport cost nesting of coils/ straight lengths can be considered, if agreed to between the purchaser and the supplier.
Storing
Polyethylene pipes conforming to IS 4984 may be stored either
under cover or in the open as the pipes
are suitably protected from ageing due to sun light by the addition of the appropriate quantity and the type of carbon black. Other non-black
polyethylene pipes, however, should
be stored under cover and protected from direct sunlight (see Fig. 19).
Polyethylene pipes shall be stored in the manner
to prevent damage from elevated temperature, contact with harmful chemicals (such as
solvents). Prolonged exposure to direct
sunlight shall not alter the pipe performance,
but the pipe may bend because of the heat
during summer months. Precautions are to be taken accordingly.
Non-ventilated covering of the
polyethylene may sometimes create
excessive heat, which may be cumbersome for pipe handling.
Storage of pipes in hot areas should
be avoided.
IS 7634 (Part 2) : 2012
While storing the pipes at temperatures above 45°C continuous support may be provided by leveled sand layer or other suitable methods.
The polyethylene pipes shall be stacked
on a reasonably flat surface, free from sharp
objects, stones or projections likely to deform or damage them.
.jpeg)
No comments:
Post a Comment