1 SCOPE 1.1 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).
1.2 This standard is applicable for the water supplies up to and including 45°C water temperatures.
1.3 This standard does not purport to give guidelines for designing and dimensioning of pipe lines.
1.4 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
3.1 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.
3.1.1 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.
3.2 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.
3.2.1.1 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, bypass 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. 3.2.1.2 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.
3.2.1.3 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).
3.2.2 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. 3.2.2.1 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 coaxial 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.
3.2.3 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.
3.2.3.1 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
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