Nodular cast iron is used in the construction of drain covers and grates, and requires maximum resistance. The production process of this particular alloy needs a very strict control, which already constitutes a valid guarantee of constant quality. The EN1563 standard classifies the spheroidal cast iron according to the mechanical characteristics of the material. The drain covers and grates made from ductile cast iron are designed so that the elastic limit of the material is reached long before breakage, thus ensuring a wider safety margin. Regulation EN 124 requires not only compliance with the test load in relation to the class they belong to, but also conformity regarding the value of the residual sag.

The manhole covers and grates made of ductile cast iron, in case of a possible failure?however unlikely?do not break into several parts, as it happens with those in lamellar cast iron, but only show outer damage, ensuring in any case the coverage of the hole that would otherwise remain unprotected. The spheroidal shape of the graphite produces a lower concentration of stress compared to the lamellar type; also, the spherical shape is such that the same volume presents a lower surface, and thus the iron matrix is less subject to damage, allowing a better exploitation of its mechanical characteristics.