Joining poly pipes for long-lasting use
olyethylene pipes are commonly used
on-farm to deliver water for stock and
irrigation but they can often split or crack,
requiring repair.
Most piping is available in 100-metre rolls
which for long runs requires the use of joiners.
After installation, these pipes are frequently
split, cracked or torn and require repair with
pipe joins.
Joining poly pipe is generally a simple task
but carrying out the following procedures will
ensure joints are effective and lasting.
There are three main methods of joining
poly pipe. The most common is using a fitting
P
or joiner. The joiner is made from a number
of pieces which lock and seal the pipe ends
together using a threaded fitting.
The second method involves electro-fusion
of the two pieces of plastic using heat.
Electro-fusion fittings are an external
fitting on the pipe which have a wire heating
coil moulded into the plastic. After being
placed on the pipes to be joined an electrical
current passed through the joint heats
both the inside of the joint and the pipe to a
molten stage, fusing the two pieces of plastic.
This method is used for 20–355-millimetre
diameter fittings. Cost is $25 per fitting.
Farmers can buy an electro-fusion joiner for
$2000–$5000 or hire a machine for $100 per day.
The third method is butt welding and also
involves electro-fusion. This uses an external
heat source to melt both faces of the pipe.
The molten ends of the pipes are then pushed
together under pressure to ensure fusion of
the two pipe faces until cooled. This method
is usually employed for larger pipes from
63–630mm in diameter. Hiring costs of the
butt welder are $75/hour with an operator or
$110/weld. A miniature version is the Hotbutt
welder that joins 19–50mm pipe.
Acknowledgement: Southwest Water Services.
Conventional poly pipe fittings
2
1
Compiled and photographed by Ben White and Richard Sulman.
To mend a damaged pipe or to join two pipe ends the tools required are a hacksaw, a small knife and
a block of wood as well as the poly pipe joiner.
For damaged pipes, cut out the damaged
section. It is important to cut the pipe squarely.
If joining two lengths of pipe, ensure the ends
are also square. Inset: Clean any plastic filings
out of the pipe using a small knife.
4
It is important the fitting is assembled in the correct order (see picture 3) as when in place the O-ring
insert is difficult to remove. Push both ends of the O-rings into the threaded joint, ensuring the
O-ring sits firmly and is not twisted as this is the crucial seal.
3
Place the threaded collar and tapered locking
ring on the pipe before pushing the O-ring
insert into place. Using a block of wood, tap the
O-ring insert to ensure it is firmly in place. These
inserts not only have a barbed profile but are
also slightly tapered to ensure a tight fit.
Repeat this procedure for the other end of the
pipe then push the locking ring to meet the
secured insert. These rings also feature barbs to
ensure the pipe will not slip out.
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5
Tighten the locking collars over the threaded joint and hand-tighten before using two pipe wrenches
(inset) to tighten the joint.
FARMING AHEAD No. 103 - July 2000
Electro-fusion joint
Butt welded joint
2
1
Select
the
required
electro-fusion joint for
the diameter pipe used.
The joint features two terminal points and
a coil inside the pipe fitting. Each joint
carries the fitting diameter, heating time and
cooling time required. Inset: The terminals
are colour-coded so the correct electrode is
placed on the corresponding terminal.
Place the pipes to be joined in the jaws of the
joiner cradle which ensures the pipe does not
move during the operation. The cradle is
hydraulically operated to provide sufficient
pressure to fuse the join after heating.
1
Cut both faces of the pipes to be joined as
squarely as possible. On most pipes this can be
carried out using a handsaw.
4
2
Insert the heating element between the two
faces and heat. Gradually apply pressure until a
bead of molten plastic appears on both faces of
the pipe near the heating element. Heating time
and temperature vary for different pipe sizes
(about five minutes at 200o Celsius for the pipe
pictured). Check the operator’s manual for full
details of heating times.
The outside surface of each pipe needs to be
roughened 50mm from the end. This ensures
there is no oxidation in the joint, which may
cause inferior fusion between the joint and
the pipe.
5
3
3
Place the pipe ends in the joint, attach the
electrodes to the terminals and heat for the
specified time. Some electro-fusion machines
such as the one pictured can sense the
heating time required and prompt the user
through the process. Allow the joint to cool
before use.
FARMING AHEAD No. 103 - July 2000
Insert the facing disc and gently apply hydraulic
pressure in the cradle until a flat, even slice of
material is cut from both faces. Curling of the
shavings indicates the surface has not been
squarely faced, in this case continue cutting
until flat shavings are produced. Clean both
faces with methylated spirits to remove any oils
or contaminants.
After the heating element has been removed,
press the two molten faces together and apply
pressure. This has to be carried out within seven
seconds of removing the heating element.
Allow the join to cool while maintaining
pressure so the joint will set properly.
Cooling times vary. For example, the 250mm
pipe pictured requires 30 minutes of cooling
time before removal from the cradle. Check the
operator’s manual for cooling times.
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