SABI Magazine SABI Magazine June July 2017 | Page 20

How to ...
How
to ...
install LDPE pipe
Low density polyethylene pipe is one of the most commonly used utility pipes in the
irrigation sector. Various quality grades of pipe are available as well as a mix of
fittings and adaptors. This editorial will focus on jointing procedures for LDPE pipe
and also includes some discussion on proposed specification changes relating to
future pipe diameters - by Mike de Villiers
INTRODUCTION
Polyethylene piping is a widely used raw material for irrigation piping. It is an extremely ductile material which gives the piping flexibility and
toughness as well as excellent resistance to pressure fluctuations, such as water hammer. Polyethylene piping is supplied in its high density form,
known as HDPE, which is used for higher pressure applications up to PN 16 (16 bar) and larger diameters up to DN 1000 mm. In its low density form,
it is used extensively for small diameter low pressure distribution pipe systems in conjunction with sprinklers and micro irrigation emitters. LDPE piping
is available in sizes DN 10 to DN 80 mm and in pressure classes PN 3 and 6 (3 bar and 6 bar). Both HDPE and LDPE pipe systems have their own
dedicated jointing systems and adaptors, which have been in use in the RSA since the 1970’s.
Specifications
South African Bureau of Standards (SABS) specifications have been in
existence since the 70’s for polyethylene pipe, however the old SABS 533
( part 4) specification for HDPE was replaced by SANS ISO 4427 in
2008. (SANS is a relatively new notation and stands for a South African
National Standard). This left the old SABS 533 (part 1) specification in
place to cover the LDPE range of pipes. These specifications differ in
that the SANS ISO 4427 specification covers the full range of outside
diameter pipe sizes and the SABS 533 (part 1) specification only covers
inside diameters. This indicates why the two pipe systems have different
jointing systems, namely compression and electro-fusion fittings for
HDPE and insert fittings such as Full flow® for LDPE.
In 2008 the SANS 533 (part 1) specification for LDPE pipe was scrapped
by the SABS working committee and replaced by the SANS ISO 4427
specification. This effectively meant that all new production of SABS
certified polyethylene pipes would have to change to outside diameter
dimensions, thus creating a pipe range that cannot be used with the
current range of locally made insert fittings. Due to representations from
the irrigation component manufacturing industry, the inside diameter
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dimension tables from the SABS 533 specification were included in the
SANS ISO 8779 specification in 2013, but only for a period of 5 years.
These developments will have to be managed by the pipe and fittings
manufacturing industry in the near future, however, note that these
developments only apply to SABS accredited pipe.
The bulk of the irrigation market has been using non-certified (non-
SABS) utility pipe since its inception. This means that the quality standard
of the pipe relating to production tolerances and raw materials has been
determined by the individual manufacturer, with the pipe diameters being
based on the SABS 533 (part 1) specification. In most cases this does not
imply inferior quality, as many of the ISO 9000 accredited manufacturers
produce both SABS and non-SABS grades of pipe. However, the lack
of accreditation may result in variations in the quality of the pipe due
to the absence of quality monitoring, carried out routinely by the SABS
on their mark bearing products. Inadequate control of the quality and
quantity of recycled raw materials, used in utility pipe, leads to changes
in the ductility of the pipe and inconsistent shrinkage rates, both of which
impact on joint quality and hence the lifespan of the system