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What is more, ductile iron pipes have a guarantee
of hygienic and environmentally friendly
operation in the form of their linings (polyurethane
to EN 15655 [6] and mortar based on
blast furnace cement for the supply of drinking
water [7] or mortar based on high-alumina
cement for the disposal of sewage [8]).
4 Durability:
Avoidance of future expenditure
There is no other pipe material which can provide
such convincing practical proof of its
durability, and therefore of the safety which it
maintains for generations, as ductile iron. The
technical operating life of ductile iron pipes is
up to 140 years. If ductile iron pipes with their
high-grade coatings as follows
■ a cement mortar coating (ZM-U) to EN
15542 [9] and
■ polyurethane (PUR) to EN 15189 [10]
are taken as a basis, they provide a particularly
impressive and emphatic confirmation of
this long operating life. A systematic study has
been made in which the outer surfaces of pipes
which had been in operation for periods of up to
32 years were examined and samples for examination
under DIN 50929, part 3 [11] were taken
of the native soils and of the bedding materials
used in the respective cases. At all the test digs,
it was found that, after being in use for from
25 to 32 years, pipes coated with cement mortar
were in a virtually good as new state and were
not showing any damage due to corrosion [12].
Similar studies to provide practical proof of the
long-term resistance of the polyurethane coating
are going on in Switzerland. Two runs of
test pipeline, which are continuously monitored
by the SGK (Swiss Society for Corrosion
Protection), have been operating for more than
20 years in Zurich. The protective potentials of
the polyurethane coated pipes and their contact
resistances with the ground are measured in
different soils. In all the beddings studied, these
field studies show constant good performance
on the part of ductile iron pipes coated with
polyurethane [13].
From all these studies, it can be concluded
that these ductile iron pipe systems with
high-grade coatings, will undoubtedly
achieve a technical operating life of 100 to
140 years.
10
A glance at the pre-industrial era reveals
another impressive fact: In 1783, Clemens
Wenceslaus, the Archbishop-Elector of Trier,
gave instructions for a water pipeline to be
laid to supply the public wells of the town of
Koblenz. This pipeline, known as the Metternich
water pipeline, consisted of socketed cast
iron pipes of a laying length of 1.5 metres and
a diameter of 80 millimetres. When, after more
than 150 years, this pipeline was exposed in
1934, it was found that the material of the
pipes was still in excellent condition after their
long time in operation. The then Lord Mayor
of Koblenz confirmed this in an official letter
to the “Deutscher Gußrohr-Verband” [14],
today’s europäische Fachgemeinschaft Guss-
Rohr systeme (FGR®) e. V. / European Association
for Ductile Iron Pipe Systems · EADIPS®,
www. eadips.org.
Polyethylene pipes are assumed to have an
operating life of around 60 years. That is less
than half the demonstrable working life of ductile
iron pipes. This means that re-investment
and rehabilitation budgets can be set at an
appreciably lower level when ductile iron pipes
are used.
5 Trenchless installation techniques and pipelines
subject to high stresses
Trenchless installation techniques have now
become very important all over Europe. To avoid
site noise and obstacles to traffic in inner-city
areas and to allow crossings to be made under
obstructions such as roads or rivers, trenchless
installation techniques are now indispensable
when pressure pipelines have to be replaced.
They are low-cost techniques which are kind
to the environment. There was been a close
connection between their development and
the ductile iron pipe and its joints and types of
external protection. Because of their ability to
carry high mechanical loads, ductile iron pipes
with restrained joints are very much superior to
pipes of any other material for trenchless installation
(Fig. 3), a superiority which is also seen
in the allowable tractive forces which can be
used with them (Fig. 4).
FGR® / EADIPS® 46