Cast Iron is an iron alloy having carbon content greater than 1.5-2%. Cast irons differ from standard steels by having significantly higher carbon (C) and silicon (Si) content. The extra carbon and silicon in cast iron is added primarily to lower the melting point of the metal. There are four types of Cast Iron :
Types of Cast Iron
- Grey Iron
- White Cast Iron
- Ductile Cast Iron
- Wrought Iron
- Mondi Iron
Grey Cast Iron
Grey cast iron's grey appearance is caused by graphite particles spread throughout its mass. Grey cast iron has low tensile strength and is brittle. It has good machinability but is difficult to weld. Grey cast iron is used in applications such as construction equipment requiring vibration dampening and wear resistance.
White Cast Iron
White cast iron has no graphite particles in its mircostucture. It has much lower silicon content than gray cast iron. With less silicon, the carbon in white cast iron changes to cementite or iron carbide (Fe3C). White cast iron displays white fractured surfaces due to the presence of an iron carbide precipitate. It has poor machinability.
Ductile Cast Iron
Ductile iron is made by adding a closely controlled amount of magnesium to a molten iron of low phosphorous and low sulfur content. Addition of magnesium produces a remarkable change in the microstructure by causing the carbon in the iron to assume a spheroidal or nodular shape instead of the flake form of graphite in gray cast iron, and at the same time, producing a finer grained iron matrix in the surrounding ferrite structure. As a result of this remarkable change, a far stronger, tougher, and ductile material is obtained. Since ductile cast iron has small spherical nodules of graphite in its microstructure, this causes it to be ductile. Ductile iron is similar to Gray cast iron in machinability but has superior mechanical properties. Ductile Iron is used for pipes, valve bodies, pump and compressor casings.
Wrought Iron
Wrought Iron is pure iron low in carbon with a few percent of slag remaining in the form of iron silicate. Wrought iron finds application in water pipes.
Mondi Iron
MONDI, a special alloy of ductile iron with unique metallurgy was developed to handle 92-99% sulfuric acid at temperatures of up to 300° F (149° C). More information on Mondi piping can be found at www.acidpiping.com
Jointing of Cast Iron piping
- Mechanical Joints
- Flanged Joints
- Push-on Joints
- Bell and Spigot Joints
Applicable Codes and Standards
- ANSI/AWWA C150/A21.50 - Thickness Design of Ductile- Iron Pressure Pipe.
- ANSI/AWWA C151/A21.51 - Ductile-Iron Pipe, Centrifugally Cast, for Water.
- ANSI/AWWA C153/A21.53 - Ductile-Iron Compact Fittings For Water Service.
- ANSI/AWWA C104/A21.4 - Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water.
- ANSI/AWWA C110/A21.10 - Ductile-Iron and Gray-Iron Fittings, 3 In. Through 48 In., For Water.
- ANSI/AWWA C111/A21.11 - Rubber-Gasket Joints for Ductile-Iron Pipe and Fittings.
- ANSI/AWWA C116/A21.16 - Standard for Protective Fusion-Bonded Epoxy Coating for the Interior and Exterior Surfaces of Ductile-Iron and Gray-Iron Fittings for Water Supply Service.