Why Ductile Iron Pipe
Why would you choose ductile iron pipe rather than other pipe
materials? The reasons are obvious for that not only ductile iron
pipe possesses the inherent strength and flexibility of ductile
iron, combined with proven corrosion protection systems, but also
the cost savings can be achieved from design to installation and
Ductile iron is produced by treating molten low-sulfur base iron
with magnesium under closed controlled conditions. In ductile iron,
the graphite exists in the form of spheroidal shape, which has
little influence on weakening the matrix and resulting in
centralizing strain, so ductile iron possesses good flexible
property. While, in grey iron, the graphite is present in flake
form, which has the effect of cutting the iron matrix and making it
become brittle and easy to crack.
Remarkable Mechanical Properties of ductile iron
The mechanical properties of ductile iron are markedly superior to
those of grey iron and approaching the properties of steel. Ductile
iron possesses the nature of iron and properties of steel. The much
improved properties were recognized to be of particular benefit in
the centrifugal pipe industry and as such most of the pipe
production now in ductile iron.
Documents relevant to earthquakes show that the damage rate per
kilometer for ductile iron pipe mains is one quarter of that for
grey iron and one thirteenth of some other materials of pipes.
Advantages of Ductile Iron Pipe
♦ Ductile iron pipe possesses excellent mechanical properties. It
has the tensile strength, yield strength and module of elasticity
that are comparable with steel pipe.
♦ Ductile iron pipe has high corrosion resistance. Ductile iron
pipes are lined with cement or resins, and coated with bitumen
paints, which solves the problems of internal and external
corrosion that grey iron pipes and steel pipes can not solve.
Therefore, the users don’t have to take any anti-corrosive
measures. It also prevents secondary pollution to the water
♦ The joints are flexible and have good adaptability. The
connections of ductile iron pipes are push-on joints or gland
mechanical joints with rubber gaskets, and have good leak tightness
and ductility. No welding is required. The designed deflection is
3~5 °, so the number of fittings required can be reduced. The
joints can absorb the stress caused by foundation settlement and
prevent pipe rupture.
♦ Easy to assembly. Ductile iron pipe installation is convenient and
not subject to weather conditions. The installation does not need
sophisticated equipments and workers do not have to be highly
♦ The pipes satisfy the highest hygienic standards. Drinking water
and ground water are protected by pipe walls which seal against
diffusion. The pipes are resistant to extremely high internal
♦ The service time is up to 50 years, with the material properties
♦ High load-bearing capacity.
♦ Ductile iron pipes are environmentally-friendly. Pipes are
sustainable and recyclable, and the materials used are inorganic.
♦ Both deep and shallow top covers are possible. The pipes are
suitable for all soils and laying methods.
No need for change of soils or additional bedding for the pipes,
and the soils excavated can be re-used.
Major savings of time and money, because the soil excavated does
not have to be taken away.
General Principle of Electrolytic Corrosion
Corrosion can occur due to differences in the electrolyte. These
differences may be in soil resistivity, oxygen concentrations,
moisture contents and various ion concentrations. The variations
produce current flow from one location, through the electrolyte, to
another portion of the same metallic structure. In the case of
electrolytic corrosion, the external man-made current generates
Anti-Electrolytic Corrosion of Ductile Iron Pipes
Due to the large electric resistance, ductile iron pipes are not
easily subject to electrolytic corrosion. The gaskets for ductile
iron pipes with mechanical joint are insulated; therefore it is no
need to worry about the electrolytic corrosion. The electric
resistance of ductile iron and steel are as follows: