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The unique properties of cast iron

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Why cast iron pipes without replacing serve for centuries?

 

It would seem that we know about cast iron everything, or almost everything. All known cast iron radiator, pans, pots, grates, ornamental castings. This metal is perceived to be ordinary and not associated with the term advanced or high technology.

However, as studies of modern scientists, the cast iron is not as simple as it seems. This is the case when the outer “gray” hiding truly unique properties. The potential of cast iron or, rather, its modifications are endless, and allows us to solve a variety of technological challenges.

So why is cast iron pipe can serve for centuries? It turns out that the reason lies in the high corrosion resistance.

This quality material is extremely important when it comes to cast-iron pipes for water supply. In fact, we are dealing with a product that is unsurpassed in durability, reliability and environmental friendliness.

Generally, cast iron is a metal with a millennial history. The appearance of cast iron referred to the VI century BC, when China began to cast various products of cast iron. European countries learned about the cast only in the XIV-XVI centuries, and at the end of the SEVENTEENTH century it was widely used.

The famous system luxurious Versailles fountains provided the water flowing through iron pipes. These pipes were cast by special order in Normandy in 1672 and regularly operated for more than 330 years.

And to the fountains of St. Petersburg water up to the present time is served by the preserved parts of the pipeline of cast iron pipes, cast another in 1755.

Historically, over a long period of its existence, is a cast-iron pipe has shown itself to be the most reliable to use. And the secret of this reliability in the high corrosion resistance of cast iron and cast iron pipes.

The study and description of the aging mechanism corrosion of cast iron introduced Australian scientists Robert Melchers – Professor, Department of civil engineering in Newcastle and Robert Peterson – research fellow, Center for the study of the efficiency and reliability of infrastructure materials, University of Newcastle (the article “Corrosion of aging cast iron pipes” in the journal “Corrosion&Prevention”, 2012). Without going into scientific details, the findings of scientists were as follows. In the process of exploitation the cast iron pipes after installation of the pipeline on the surface of the tube wall is the substitution of iron on graphite component, a so-called “layer graphitization”, which do not corrode. The result is actually retains the original thickness of the pipe, and gradually increases the graphitization layer protects the pipe surface from further corrosion.

Based on these data, it is safe to conclude that the life of cast iron pipes, even without additional corrosion protection can really reach 100-150 years.

Theoretical insights about the life span of cast iron pipes in 100 years and more, of course, respect to this material. But the really amazing what you can see with your own eyes. In the city of Saint Petersburg were found convincing confirmation of the theory of Australian scientists.

During excavations on St. Isaac’s square in St. Petersburg in 2016, was discovered the plot of iron pipe with a diameter of 250 mm 1890 styling, which operated trouble-free to this day!

The pipe had obvious mechanical damage due to external impact. It was decided to conduct a study of a sample of pipe that had lain under St Isaac’s Cathedral about 126 years.

When viewed from the outside on the outer and inner surfaces of samples of trace corrosion was found.

The study of the microstructure showed that the material from which was cast pipe is gray cast iron with carbon content of 3.25 %. But, interestingly, the external and internal surfaces of the sample had a zone with a distinct “zone graphitization”, which appeared in the corrosion process of aging.

Thus, on the basis of the conducted laboratory researches of the Petersburg trumpet the theory that during operation cast iron pipes over time, their surface area, graphitization, which protects the pipe from corrosion have received practical confirmation.

This finding scientifically confirms the durability of pipes of cast iron, which in the modern world is not too positive. As it turns out, it is in vain.

Still, in view of the disadvantages of mechanical properties, such as brittleness, manufacturing of pipes made of grey cast iron for drinking water supply today in the whole world almost stopped.

To change to gray cast iron pipe came from high-strength cast iron with nodular graphite (ductile iron), which is devoid of almost all the shortcomings of its predecessor and boasts the highest strength and corrosion resistance, plasticity, and flexibility. The history of production of pipes made of ductile cast iron has more than 60 years. Ductile iron confidently gaining a leading position in global industrial production.

Modern ductile iron pipe are manufactured with a protective coating. This provides additional corrosion protection and for a long time protects the walls of the pipelines from external influences.

According to research carried out by the Union for gas and water (DVGW) in Germany, the duration of operation of cast iron pipes of ductile cast iron is also being evaluated in a period of 100 years or more and significantly exceed the term of operation of pipelines of other materials.

Such a long service life, low failure rate of ductile iron pipes saves operating costs of pipeline systems of water supply.

If we turn to the experience of laying pipelines in a densely populated Metropolitan areas, the pipe of ductile cast iron are the clear leaders, we can say, no alternative leaders.

A large portion of the pipelines in the networks of large cities in the world constructed of ductile iron, Tokyo (97% in Singapore, 95 %, Venice — 90 %, Hong Kong — 90 %, Istanbul — 90 %, new York- 85 %, Paris — 85 %, Damascus — 80 %, London — 80 %, Vilnius — 80 %, Prague — 80 %, Algeria — 75 %, Toronto — 75 %, Budapest — 75 %, Shanghai, 75% for Berlin — 70 %).

When selecting tubing material is progressive in all the world are guided by the principles of “price-quality” and, considering all the aspects and benefits of each material, the decisive argument remains service life, reliability and sustainability of the pipeline.

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