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June 1, 2011

Ductile cast iron is stronger and more elastic to give the material steely properties. Certain materials used to be prescribed for pressure-bearing parts (casing) in the water engineering and power plant construction industries.

Laminated cast iron (GG) was permissible for pressure ratings of up to PN 25. For greater pressure ratings steel or cast steel were generally used. The reason for this rule was that normal cast iron is much more brittle than cast steel. In order to compensate for this disadvantage, high safety standards were specified for the use of GG (safety factor 7), in contrast to cast steel, for which a safety factor of 2 was sufficient. This is why it was only effective and permissible to use GG up to PN25, since it was only possible to produce safe, castable, pressure-bearing parts up to this pressure rating.

The range of applications of cast iron changed with the development of GGG materials. The new material, "ductile cast iron GGG" had similar tough properties as cast steel and is hence used in Germany and Europe for higher pressure ratings as well. This is not only happening in water engineering, but also in extremely demanding areas such as the chemical industry and power plant construction. The GGG-40 (EN-GJS-400-15) GGG material used by VAG is permissible for a nominal pressure rating of up to 100 bars according to AD technical information sheet W3/2, provided that a certain pressure content factor is not exceeded.

The fact that GGG-40 may be used for higher pressure ratings has now been taken into account in the new European norm and flange norms for ductile cast iron of up to a pressure rating of PN 63 have been specified. Another advantage of GGG materials over steel or cast steel is that they have better anti-corrosive properties.

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